UNIVERSITY OF OF NAIROBI - Department of Civil...

UNIVERSITY OF

OF

NAIROBI

DEPARTMENT OF CIVIL, CONSTRUCTION AND ENVIRONMENTAL

ENGINEERING.

TITLE: INVESTIGATING THE EFFECTS OF WATER ADMIXTURES IN

CONCRETE CONTAINING LOCAL CEMENT.

STUDENT NAME: MUCHENDU GIDEON KAMANDE

REG NO: F16/28963/2009

Project supervisor: DR. S. O. ABUODHA

APRIL 2014

THIS PROJECT HAS BEEN SUBMITTED IN PARTIAL FULFILLMENT FOR THE AWARD OF A

UNIVERSITY BACHELORS DEGREE IN CIVIL ENGINEERIMG.

Investigating the effects of water admixtures in concrete containing local cement

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ABSTRACT

Due to current levels of major construction in Kenya, there is an ever increasing use for

admixtures. The demand and government encouragement to invest in cement manufacturing has

led to introduction of various brands of admixtures into the market. The lack of database on the

effects of the various water admixtures is a major drawback that faces the construction sector.

The research seeks to determine the properties of the concrete made from local cement and the

effects of the admixtures. An experimental approach has been taken to study the effect of the

constant water cement ratio and the effect of the using water admixture. This has been done by

using a designed mix ratio of 1:1:2 (C25/30) concrete for the four brands of cement. Two brands

of water admixture (Rheobuild 2000M and Pozzolith Standard) have been adopted. The

properties of these concrete mixes have been assessed by measuring both the fresh and hardened

state properties of the concrete mix.

The research has indicated that different mixes with and without water admixtures have varying

workability and compressive strengths. This may suggest various applications of water

admixtures. The use of admixtures showed that the used of admixtures can be used to achieve

high strength concrete with high workability hence reducing the costs of placing.


iii

DECLARATION

I, Muchendu Gideon Kamande, do declare that this report is my original work and to the best of

my knowledge, it has not been submitted for any degree award in any University or Institution.

Signed_______________ Date ____________

CERTIFICATION

I have read this report and approve it for examination.

Signed_______________ Date_____________


iv

Table of Contents

ABSTRACT .................................................................................................................................... II

DECLARATION .......................................................................................................................... III

TABLE OF CONTENTS .............................................................................................................. IV

LIST OF FIGURES ...................................................................................................................... VI

LIST OF ABBREVIATIONS ...................................................................................................... VII

DEDICATION ........................................................................................................................... VIII

ACKNOWLEDGEMENTS .......................................................................................................... IX

CHAPTER 1: INTRODUCTION ................................................................................................ 1

1.1 BACKGROUND ............................................................................................................................ 1

1.2 PROBLEM JUSTIFICATION ........................................................................................................... 2

1.3 PROBLEM STATEMENT ................................................................................................................ 3

1.4 OBJECTIVES ............................................................................................................................... 3

1.5 RESEARCH HYPOTHESIS ............................................................................................................. 3

1.6 SCOPE AND LIMITATIONS OF THE RESEARCH .............................................................................. 3

CHAPTER 2; LITERATURE REVIEW ................................................................................... 5

2.1 CEMENT AND CONCRETE ........................................................................................................... 5

2.1.1 BASIC CHEMISTRY OF CEMENT ................................................................................................ 5

2.2 ADMIXTURES....................................................................................................................... 14

2.2.1 Water reducing (plasticizer .................................................................................................. 15

2.2.2 Accelerating admixture ........................................................................................................ 17

CHAPTER 3; MATERIALS AND METHODOLOGY .......................................................... 20

3.1 PREPARATION OF AGGREGATES ................................................................................. 20

3.2. MATERIAL TESTING AND SPECIFICATION ................................................................ 23

3.3 BATCHING OF MATERIALS ........................................................................................... 24

3.4 MIX DESIGN ...................................................................................................................... 24

3.5 TESTING THE PROPERTIES OF FRESH CONCRETE. .................................................. 27

3.6 SAMPLING OF THE MATERIALS ................................................................................... 33

CHAPTER 4; ANALYSIS ........................................................................................................ 35

4.1 AGGREGATE ANALYSIS .................................................................................................... 34

4.2 CONCRETE ANALYSIS ....................................................................................................... 36

CHAPTER 5; DISCUSSION ........................................................................................................ 57


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5.1 SETTING TIME........................................................................................................................... 57

5.2 STRENGTH AND WORKABILITY ................................................................................................. 57

CHAPTER 6; CONCLUSIONS ................................................................................................ 60

CHAPTER 7; RECOMMENDATION ..................................................................................... 62

REFERENCES; ............................................................................................................................ 63

APPENDICES .............................................................................................................................. 64

APPENDIX TABLES AND FIGURES ....................................................................................... 64


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List of figures and tables

Figure 3.1 Chart showing the various cement manufacturing companies in Kenya ....................... 2

Table 2.1: Main compounds in Portland cement .......................................................................... 7

Table 2.2: Approximate composition limits of Portland cement ....................................................... 8

Figure 2.1 Development of strength of pure compounds (From: R. H. BOGUE, Chemistry of

Portland Cement (New York, Reinhold, 1955).) ............................................................................ 11

Figure 4.15; non workable mix for control at w/c ratio of 0.35 .................................................... 50

Table 4.7; shows the compressive strength of cylinders and the percentage strength increase due

do admixtures. ............................................................................................................................... 51

Figure 4.16; comparison of the compressive strength for cylinders of different mixes ................ 52

Figure 4.20; comparison of the tensile strength for cylinders of different mixes ......................... 55

Figure 4.21; comparison of the % tensile strength increase for cylinders due to water admixtures55

Figure 5.1; effect of plasticizer or superplasticiser addition on cement dispersion. ..................... 58

Table 1: Strength classes of cements to European Standard BS EN 197-1: 2000. ....................... 64

Table 2: Approximate Compressive Strength (N/mm2) of Concrete Mixes Made with a Free-

Water / Cement Ratio 0.5 .............................................................................................................. 65

Table 4.4 (c) Approximate free-water contents (kg/m3) required to give various levels of

workability ..................................................................................................................................... 67

Figure 5 Estimated wet density of fully compacted concrete ....................................................... 68

Figure 6 (continued).Recommended proportions of fine aggregate according to percentage

passing a 600 μm (0.6mm) sieve. .................................................................................................. 68


vii

List of abbreviations

% Percentage

OPC Ordinary pozzolanic cement

PPC Portland pozzolanic cement

W/C Water cement ratio


viii

DEDICATION

I dedicate this piece of work to my family, especially to my loving parents for their great

sacrifice to make me who I am today.


ix

ACKNOWLEDGEMENTS

I am indebted to a number of the personalities without whom my final year project would have

been a success. First and foremost Almighty God for the abundant grace and care. Secondly, My

Supervisor Dr. Abuodha for his expert guidance and assistance. Thirdly, to the department of

civil engineering for the chance to do this project.

Further appreciation goes to the laboratory team; Mr. Muchina and Mr. Wasinda among other

very able laboratory staff for their guidance and assistance during the testing phase of this

project.

I cannot forget my family and friends for their support and motivation throughout this project.


1

CHAPTER 1: INTRODUCTION

1.1 Background

Cement is an essential ingredient in most forms of building construction. Cement in general is a

binder, a substance which sets and hardens independently, and can bind other materials together.

It‟s the core constituent material in concrete, mortars and renders whose properties are crucial for

the construction of good structures.

In line with the government of Kenya‟s Vision 2030 that emphasizes on the infrastructure

development and the provision of affordable housing units, the demand of cement for

construction has increased rapidly thus high supply needed. Kenya‟s biggest producer Bamburi

Cement projects that cement consumption in the region will grow by 12 per cent since the

regional governments unveiled budgets which focused on spending on infrastructure projects

such as road. For instance, in 2003 cement consumption in Kenya was estimated at about 1.2

million metric tonnes. The level of consumption has almost doubled to over 2 million metric

tonnes in 2007. Given the rapid increase in the demand for cement, the government of Kenya has

encouraged private investors to build more cement factories in order to serve the needs and for

export to the neighboring countries at an affordable price. This has led to the expansion and

entrance of new manufacturing companies such as National Cement Company, Mombasa

cement, Pokot cement and Tororo cement, besides the already existing companies such as; East

Africa Portland cement, Bamburi cement and Athi River mining.

The shift from the OPC type of Portland cement to PPC in the modern construction works has

been a challenge due to the slower rate of strength development, even though the environmental

sustainability is enhanced. This requires closer monitoring of the project undertaken as a result of

reduced tolerances. This has led to the need for use of the admixtures.


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With the entrance of many cement brands and different concrete admixtures in the Kenyan

market there is need to carry out a study on effects of water admixtures on cement. Admixtures,

chemical and mineral, are added to concrete in very small amount mainly for entrainment of air,

reduction of water or cement content, plasticization of fresh concrete mixtures and control of

setting time. It is very difficult to ensure that an admixture that produces all the desired effects

with cement. Users, who are unaware of different effects, often suffer when admixture is

changed midway through a project. Problems arising out of different effects are often mistaken

for problems with concrete mixture design, because of the lack of information about the subject.

For a more comprehensive approach, a thorough understanding of the causes and remedies of

different effects is necessary.

By carrying out the tests on fresh and hardened concrete using various types of admixtures, the

properties will be identified and compared. This will also pose a challenge to the admixture

manufacturing industries to improve even more in their admixtures quality hence minimizing the

costs of construction. Also contractors will be able to save on time and energy.

1.2 Problem justification

The use of admixtures has been adapted in construction industry so as to modify properties of

concrete which cannot be obtained economically by changes in the composition of normal

concrete mix. However, the adoption of the admixtures has resulted in an increase of the costs, as

they are expensive and not readily available. Comparative analysis will determine the effects and

CEMENTS IN

THE LOCAL

MARKET

BAMBURI

CEMENT

EAST AFRICAN

PORTLAND

CEMENT

ATHI RIVER MINING

LTD

MOMBASA

CEMENT

NATIONAL

CEMENT

COMPANY

Figure 3.1 Chart showing the various cement manufacturing companies in Kenya


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appropriate admixture brand that is workable, hence reducing the unawareness of admixtures to

be used.

1.3 Problem statement

Despite the increase in cement manufacturing industries to meet the cement demand and the

adoption of the admixtures in the construction industry, selecting the best brand that is readily

compatible with admixtures producing concrete of improved workability and strength at a

reduced cost remains a challenge to the consumers.

1.4 Objectives

Overall objective:

To determine the properties of concrete using local cement and the effects of the water

admixtures in a concrete mix.

The objectives of the study are as listed below;

Determine the overall strength, as well as the rate of strength gain for concrete varying

water admixture type, with and without admixtures.

Determine the workability for concrete varying water admixture type, with and without

admixtures.

To determine the setting time of concrete of plain and with the water admixtures

1.5 Research hypothesis

The addition of water admixtures to concrete has varying degree of effects depending on the type

of admixture.

1.6 Scope and limitations of the research

The research will be limited to Portland Pozzolanic cement (PPC 42.5), because of the general

shift in modern construction to PPC. This shift is because PPC is more advantageous compared

to Ordinary Portland Cement;


4

Advantages of ppc over opc

Low heat of hydration

Has a slower rate of strength gain, but the ultimate strength and durability of concrete

with PPC are better that for OPC.

The research will focus on the comparative analysis of workability, setting time and strength

between the plain mix (without admixtures) and special mixes.

Water admixtures will be used in the research.


5

CHAPTER 2; LITERATURE REVIEW

2.1 Cement and Concrete

Ancient Romans were probably the first to use concrete - a word of Latin origin - based on

hydraulic cement, that is a material which hardens under water. This property and the related

property of not undergoing chemical change by water in later life are most important and have

contributed to the widespread use of concrete as a building material.

Later, Roman cement fell into disuse, and it was only in 1824 that the modern cement, known as

Portland cement, was patented by Joseph Aspdin, a Leeds builder. Portland cement is the name

given to a cement obtained by intimately mixing together calcareous and argillaceous, or other

silica-, alumina-, and iron oxide-bearing materials, burning them at a clinkering temperature, and

grinding the resulting clinker.

2.1.1 Basic chemistry of cement

The raw materials used in the manufacture of Portland cement consist mainly of lime, silica,

alumina and iron oxide. These compounds interact with one another in the kiln to form a series

of more complex products, and, apart from a small residue of uncombined lime which has not

had sufficient time to react, a state of chemical equilibrium is reached. However, equilibrium is

not maintained during cooling, and the rate of cooling will affect the degree of crystallization and

the amount of amorphous material present in the cooled clinker. The properties of this

amorphous material, known as glass, differ considerably from those of crystalline compounds of

a nominally similar chemical composition. Another complication arises from the interaction of

the liquid part of the clinker with the crystalline compounds already present.

Nevertheless, cement can be considered as being in frozen equilibrium, i.e. the cooled products

are assumed to reproduce the equilibrium existing at the clinkering temperature. This assumption

is, in fact, made in the calculation of the compound composition of commercial cements: the

'potential' composition is calculated from the measured quantities of oxides present in the clinker

as if full crystallization of equilibrium products had taken place.


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BIS Classification of cement

According to the concrete portal, although the general pattern of classification in BIS is similar

to the one in ASTM, the names for the cements are different. BIS classifies cements into the

following major categories:

Ordinary Portland Cement – IS:269-1989 (further classified into 33, 43, and 53 grade; the

grade implies the strength achieved by the cement mortar at 28 days)

Portland Cement, Low Heat – IS:12600-1989

Rapid Hardening Portland Cement – IS:8041-1978

Portland-Pozzolana Cement (PPC) – IS:1489-1976

Portland-Slag Cement (PSC) – IS 455-1976

Compared to OPC, the low heat cement has higher proportion of C2S, while the rapid hardening

cement has higher C3S and fineness. BIS classifies OPC into three different strength grades,

which are primarily achieved by differences in C3S contents, fineness. And only the strength gain

rate of concrete is faster for the higher grade cements.

Nowadays, OPC is not readily available in most areas, and the construction industry has slowly

but surely made a shift towards PPC. This is a positive development, as PPC results in a more

durable concrete in the long run. While a slower rate of strength gain is inevitable, the ultimate

strength and durability of concrete with PPC are better that for OPC.

The normal consistency and setting time are determined using the Vicat apparatus. Normal

consistency is an empirical measure that indicates the minimum water required to produce a

certain level of fluidity in the cement paste. It also enables the design of the paste for the setting

time and compressive strength experiments. The initial setting time is important to assess the

time available for concreting operations (transportation, placement, consolidation, and finishing),

while the final setting time indicates the attainment of a specific form (i.e. concrete beyond this

point cannot be remoulded). (www.theconcreteportal.com)

These project will focus on Portland Pozzolana cement.

http://www.theconcreteportal.com/


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Portland Pozzolana cement

Portland Pozzolana cement is manufactured by blending 10-30 percent by weight of pozzolanic

material with Portland cement; either by simple mixing or by inter grinding with cement clinker.

The calcium hydroxide liberated during the process of hydration of the cement combines slowly

with the pozzolana to give it cementitious properties, thereby contributing to water tightness and

long, continued gain in strength of the concrete. Portland pozzolana cement is particularly

suitable for use in mass concrete structures (such as in dams and bridge piers), where low heat of

hydration is desired; hydraulic structures of all kinds where water tightness is important;

structures subject to attack from ground water.

Four compounds are regarded as the major constituents of cement: they are listed in Table 2.1

together with their abbreviated symbols. This shortened notation, used by cement chemists,

describes each oxide by one letter, viz.: CaO = C; Si02 = S; A1203 = A; and Fe203 = F. Likewise,

H20 in hydrated cement is denoted by H.

Table 2.1: Main compounds in Portland cement

Name of compound Oxide composition Abbreviation

Tricalcium silicate 3CaO.Si02 C3S

Dicalcium silicate 2CaO.Si02 C2S

Tricalcium aluminate 3CaO.Al203 C3A

Tetracalcium

Aluminoferrite

4CaO.Al203.Fe203 C3AF

The silicates, C3S and C2S, are the most important compounds, which are responsible for the

strength of hydrated cement paste. In reality, the silicates in cement are not pure compounds, but

contain minor oxides in solid solution. These oxides have significant effects on the atomic

arrangements, crystal form, and hydraulic properties of the silicates.


8

The presence of C3A in cement is undesirable: it contributes little or nothing to the strength of

cement except at early ages, and when hardened cement paste is attacked by sulfates, the

formation of calcium sulfoaluminate (ettringite) may cause disruption. However, C3A is

beneficial in the manufacture of cement in that it facilitates the combination of lime and silica.

C4AF is also present in cement in small quantities, and, compared with the other three

compounds, it does not affect the behavior significantly; however, it reacts with gypsum to form

calcium sulfoferrite and its presence may accelerate the hydration of the silicates.

A general idea of the composition of cement can be obtained from Table 2.2, which

gives the oxide composition limits of Portland cements.

Table 2.2: Approximate composition limits of Portland cement

Oxide Content, per cent

CaO 60-67

SiO, 17-25

A1,03 3-8

Fe203 0.5-6.0

MgO 0.1-4.0

Alkalis 0.2-1.3

S03 1-3

Hydration of cement

So far, we have discussed cement in powder form but the material of interest in practice is the set

cement paste. This is the product of reaction of cement with water. What happens is that, in the

presence of water, the silicates and aluminates (Table 2.1) of Portland cement form products of

hydration or hydrates, which in time produce a firm and hard mass - the hardened cement paste.

As stated earlier, the two calcium silicates (C3S and C2S) are the main cementitious compounds


9

in cement. In commercial cements, the calcium silicates contain small impurities from some of

the oxides present in the clinker. These impurities have a strong effect on the properties of the

hydrated silicates. The 'impure' C3S is known as alite and the 'impure' C2S as belite.

Hydration involves many different reactions, often occurring at the same time. As the reactions

proceed, the products of the cement hydration process gradually bond together the individual

sand and gravel particles, and other components of the concrete, to form a solid mass.

Reactions:

Cement chemist notation: C3S + H2O → CSH (gel) + CaOH

Standard notation: Ca3SiO5 + H2O → (CaO) • (SiO2) • (H2O) (gel) + Ca (OH) 2

Balanced: 2Ca3SiO5 + 7H2O → 3(CaO) •2(SiO2) •4(H2O) (gel) + 3Ca (OH) 2

Heat of hydration and strength compounds contributors

The temperature at which hydration occurs greatly affects the rate of heat development,

which for practical purposes is more important than the total heat of hydration; the same

total heat produced over a longer period can be dissipated to a greater degree with a

consequent smaller rise in temperature.

For the usual range of Portland cements, about one-half of the total heat is liberated

between 1 and 3 days, about three-quarters in 7 days, and nearly 90 per cent in 6 months. In

fact, the heat of hydration depends on the chemical composition of the cement, and is

approximately equal to the sum of the heats of hydration of the individual pure compounds

when their respective proportions by mass are hydrated separately; typical values are given

in Table 2.3.


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Table2.3: Heat of hydration of pure compounds.

Compounds Heat of hydration (J/g)

C3S 502

C2S 260

C3A 867

C3AF 419

It may be noted that there is no relation between the heat of hydration and the cementing

properties of the individual compounds. As seen below, the two compounds primarily

responsible for the strength of hydrated cement are C3S and C2S, and a convenient rule assumes

that C3S contributes most to the strength development during the first four weeks and C2S

influences the later gain in strength. At the age of about one year, the two compounds, mass for

mass, contribute approximately equally to the strength of hydrated cement. Figure 2.1 shows the

development of strength of the four pure compounds of cement. However, in contrast to the pre¬

diction of heat of hydration of cement from its constituent compounds, it has not been found

possible to predict the strength of hydrated cement on the basis of compound composition.


11

Figure 2.1 Development of strength of pure compounds (From: R. H. BOGUE, Chemistry

of Portland Cement (New York, Reinhold, 1955).)

Setting time

This is the term used to describe the stiffening of the cement paste. Broadly speaking, setting

refers to a change from a liquid to a rigid state. Setting is mainly caused by a selective

hydration of C3A and C3S and is accompanied by temperature rises in the cement paste;

initial set corresponds to a rapid rise and final set corresponds to the peak temperature.

Initial and final sets should be distinguished from false set which sometimes occurs within a

few minutes of mixing with water (ASTM C 451-05). No heat is evolved in a false set and

the concrete can be re-mixed without adding water.

Strength of concrete

Strength of concrete is commonly considered to be its most valuable property, although in many

practical cases other characteristics, such as durability, impermeability and volume stability, may

in fact be more important. Nevertheless, strength usually gives an overall picture of the quality of

concrete because it is directly related to the structure of cement paste.


12

Strength, as well as durability and volume changes of hardened cement paste, appears to depend

not so much on the chemical composition as on the physical structure of the products of

hydration of cement and on their relative volumetric proportions. In particular, it is the presence

of flaws, discontinuities and pores which is of significance, and to understand their influence on

strength it is pertinent to consider the mechanics of fracture of concrete under stress.

However, since our knowledge of this fundamental approach is inadequate, for this project it will

be necessary to relate strength of fresh concrete to concrete containing water admixtures.

Workability of concrete

Cement is the core constituent material in concrete, mortars and renders whose properties are

crucial for the construction of good structures. For any construction, the ease with which

Portland-cement concrete is mixed, transported, placed, and compacted is extremely important in

executing successful concrete construction. (U.S Army Engineer Research and Development

center, 2001)

In order to achieve this, an analysis of the concrete workability in the Kenyan market is

important. American Concrete Institute (ACI) Standard 116R-90 (ACI 1990b) defines

workability as “that property of freshly mixed concrete which determines the ease and

homogeneity with which it can be mixed, placed, consolidated, and finished.” For this study,

workability is considered to increase or improve as the ease of placement, consolidation, and

finishing of a concrete increase. It can be simplified using the following chart

Workability

Stability Compactabililty Mobility

Bleeding

Separation of materials

Relative density

Internal friction angle

Bonding force

viscosity

Figure 1.2 Schematic representation of workability


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The U.S Department of Transportation states various factors that may affect workability of

concrete as; the properties and the amount of the cement; grading, shape, angularity and surface

texture of fine and coarse aggregates; proportion of aggregates; amount of air entrained; type and

amount of pozzolan; types and amounts of chemical admixtures; temperature of the concrete;

mixing time and method; and time since water and cement made contact.

These factors interact so that changing the proportion of one component to produce a specific

characteristic requires that other factors be adjusted to maintain workability. In most mixture-

proportioning procedures, the water content is assumed to be a factor directly related to the

consistency of the concrete for a given maximum size of coarse aggregate (Falade 1994, Hobbs

1993, and Popovics 1962).

The project will entail an analysis of the different workability of various water admixture and

their levels of effects. The workability of concrete mixtures commonly is improved by using air-

entraining and water-reducing admixtures (Malek and Roy 1992, Cordon 1955). Air entrainment

typically increases paste volume and improves the consistency of the concrete while reducing

bleeding and segregation. Water-reducing admixtures disperse cement particles and improve

workability, increasing the consistency and reducing segregation (Scanlon 1994, Mehta 1986).

Freshly mixed concrete looses workability with time. The reduction in workability is generally

attributed to loss of water absorbed into aggregate or by evaporation, or from chemical reaction

with the cementitious materials in early hydration reactions. Elevated temperatures increase the

rate of water loss in all of the modes mentioned above. The workability of air-entrained

concretes is reported to be more easily reduced by elevated temperature than workability in

similarly proportioned non-air-entrained concretes (U.S. Department of the Interior 1981).


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2.2 ADMIXTURES

ACI 116R [2000] defines the term admixture as „a material other than water, aggregates,

hydraulic cement, and fiber reinforcement, used as an ingredient of concrete or mortar, and

added to the batch immediately before or during its mixing‟.

Admixtures are chemicals which are added to concrete at the mixing stage to modify some of the

properties of the mix. Admixtures should never be regarded as a substitute for good mix design,

good workmanship, or use of good materials. (www.bamburi-homebuilding,com, last accessed

on 10th October 2009)

The specific effects of some admixtures may be significantly modified by factors such as type of

cement, mix proportions (e.g. water content, cement content), aggregate type and grading,

concrete temperature, and by type and duration of mixing. (www.concrete.org, 17/10/2009)

Uses of admixtures

The most common reasons for using admixtures in concrete are:

To increase workability without changing water content, reduce water content without changing

workability, adjust setting time, reduce segregation and/or bleeding, improve pump-ability,

accelerate the rate of strength development at early ages, increase strength, improve potential

durability and reduce permeability, reduce the total cost of the materials used in the concrete and

to compensate for poor aggregate properties.

Types of admixtures

Admixtures are normally categorized according to their effect:

Plasticizers (water-reducing agents),

Superplasticizers,

Air entrainers,

Accelerators and Retarders

http://www.bamburi-homebuilding,com/


15

According to ASTM C 494-92 the classification is as follows;

Type A Water reducing

Type B Retarding

Type C Accelerating

Type D Water reducing and retarding

Type E Water reducing and accelerating

Type F High-range water reducing or superpasticizing

Type G High-range water reducing and retarding, or

superpasticizing and retarding

2.2.1 Water reducing (plasticizer

According to ASTM C 494-92, water reducing are called Type A, but if the water reducing

properties are associated with retardation, the admixture is classified as Type D.

Also there exist water reducing and accelerating admixture which is classified as Type E but

these are of little interest.

The water reducing admixtures are used for three purposes:

(a) To achieve a higher strength by decreasing the water/cement ratio at the same workability as an

admixture-free mix.

(b) To achieve the same workability by decreasing the cement content so as to reduce the heat of

hydration in mass concrete.

(c)To increase the workability so as to ease placing in inaccessible locations.

The principal active components of water-reducing admixtures are surface-active agents which

are concentrated at the interface between two immiscible phases and which alter the physico-

chemical forces at this interface. The surface-active agents are absorbed on the cement particles,

giving them a negative charge, which leads to repulsion between the particles and results in

stabilizing their dispersion; air bubbles are also repelled and cannot attach to the cement

particles. In addition, the negative charge causes the development of a sheath of oriented water

molecules around each particle, thus separating the particles. Hence, there is a greater particle


16

mobility, and water, freed from the restraining influence of the flocculated system, becomes

available to lubricate the mix so that workability is increased.

The reduction in the quantity of mixing water which is possible owing to the use of admixtures

varies between 5 and 15 per cent. A part of this is, in many cases, due to the entrained air

introduced by the admixture. The actual decrease in mixing water depends on the cement

content, aggregate type, pozzolans and air-entraining agent if present. Trial mixes are therefore

essential to achieve optimum properties, as well as to ascertain any possible undesirable side

effects: segregation, bleeding and loss of workability with time (or slump loss).

The dispersing ability of water-reducing admixtures results in a greater surface area of cement

exposed to hydration, and for this reason there is an increase in strength at early ages compared

with an admixture-free mix of the same water/cement ratio. Long-term strength may also be

improved because of a more uniform distribution of the dispersed cement throughout the

concrete. In general terms, these admixtures are effective with all types of cement, although their

influence on strength is greater with cements which have a low C3A or low alkali content. There

are no detrimental effects on other long-term properties of concrete, and, when the admixture is

used correctly, the durability can be improved.

Rixom and Maivaganam, 2003 documents that they originate from plant extracts. A wide range

of plants have lignin within the xylem from where lignin can be extracted and then modified to

lignosulfonic acid using sulphuric acid. The most commonly used commercial admixture with

the plasticizing properties is POZZOLITH LD 10. Messazza and Tostolin cited that flow

properties increases with the increase in C3A content. The research cited out that water reducing

admixtures are more effective when used with mixes containing pozzolanas than in the Portland

cement-only mixes. The admixture has detergent like property which is referred to as a surface

active agent. These substances carry an unbalanced charge of electricity and when put into water

will migrate towards the surface of the water with the electrically charged end sticking into the

water whilst the tale is out of the water. Therefore they act as particle dispersants.

The Cement and Admixtures Association, (1977) reported that two things will happen when a

surface active agent is placed into a suspension of cement particles.


17

The surface active agents „tail‟ is absorbed on the surface of the cement particle with the

negative charge protruding into the water. As a result the cement particles do not collect together

and therefore more surface area is available for reaction with the water. At the same time water

that may be trapped inside a cement particle floc is released. The combined effects improve the

workability of the cement mix; this can be seen graphically in figure 2.2

Entrapped air is also more readily removed since orientation of the surface active agents prevents

the air bubble from attaching to cement particles, seen in figure below.

Figure 2.2 Effects of surface active agent on cement particle floc, source: cement admixture

association

2.2.2 Accelerating admixture

These ASTM Type C are also referred as accelerators. Their primary function is to accelerate the

early strength development of concrete, although they may also coincidentally accelerate the

setting of concrete. Accelerators may be used when concrete is to be placed at low temperatures

say 2 to 40

C.

Other benefits of using an accelerator are that it allows earlier finishing of concrete surface and

application of insulation for protection, and also putting the structure into service earlier.


18

2.2.3 Retarding admixture

A delay in the setting of the cement paste can be achieved by the addition to the mix of a

retarding admixture (ASTM Type B), also referred as retarder. Retarder generally slows down

also the hardening of the paste although some salts may speed up the setting but inhibit the

development of strength. Retarder do not alter the composition or identity of products of

hydration.

Retarder are useful in concreting in hot weather, when the normal setting time is shortened by

the higher temperature and in preventing the formation of cold joints. In general they prolong the

time during which concrete can be transported, placed, and compacted.

2.2.4 Super plasticizers

The main purpose of using super plasticizers is to produce flowing concrete with very high

slump in the range of 7-9 inches (175-225 mm) to be used in heavily reinforced structures and in

placements where adequate consolidation by vibration cannot be readily achieved. The other

major application is the production of high-strength concrete at w/c's ranging from 0.3 to 0.4

(Ramachandran and Malhotra 1984).

The ability of superplasticizers to increase the slump of concrete depends on such factors as the

type, dosage, and time of addition of superplasticizer; w/c; and the nature or amount of cement.

It has been found that for most types of cement, superplasticizer improves the workability of

concrete. The capability of superplasticizers to reduce water requirements 12-25% without

affecting the workability leads to production of high-strength concrete and lower permeability.

One problem associated with using a high range water reducer in concrete is slump loss. In a

study of the behavior of fresh concrete containing conventional water reducers and high range

water reducer, Whiting and Dziedzic (1989) found that slump loss with time is very rapid in spite

of the fact that second-generation high range water reducer are claimed not to suffer as much

from the slump loss phenomenon as the first-generation conventional water reducers do.


19

However, slump loss of flowing concrete was found to be less severe, especially for newly

developed admixtures based on copolymeric formulations.

The slump loss problem can be overcome by adding the admixture to the concrete just before the

concrete is placed. However, there are disadvantages to such a procedure. The dosage control,

for example, might not be adequate, and it requires ancillary equipment such as truck-mounted

admixture tanks and dispensers. Adding admixtures at the batch plant, beside dosage control

improvement, reduces wear of truck mixers and reduces the tendency to add water onsite

(Wallace 1985).

The research will use the namely brands of admixtures:

Rheobuild 2000M

Pozzolith Standard

Figure 2.4 Showing Rheobuild 2000M and Pozzolith Standard water admixtures


20

CHAPTER 3; MATERIALS AND METHODOLOGY

3.1 PREPARATION OF AGGREGATES

The term aggregates is used to describe the gravel, crushed stones and other materials which are

mixed with cement to make concrete.

Essential requirements of aggregates

a) Durability

Aggregate should be hard and should not contain materials that are likely to decompose or

change in volume when exposed to weather or to affect the reinforcement.

b) Cleanliness

Aggregates should be clean and free from any organic impurities.

The particles should be free from coatings of dust or clay, as they prevent proper bonding of the

particles.

Gravel and sand should therefore be washed to remove clay, silt and other impurities which if

present in excessive amounts, results into poor quality concrete.

Size of the aggregates

In reinforced and pre-stressed concrete construction, nominal maximum sizes of the coarse

aggregates are usually 40, 20, 14 and 10.

Aggregates should be small enough to allow concrete to flow around reinforced bars so that it

can be adequately compacted.

On the other hand, it is advantageous to use the higher maximum sizes because in general, as the

maximum size of aggregate increases, a lower water/cement ratio can be used for a given

workability to obtain a higher strength.


21

However, above 40mm, the gain of strength due to the reduced water/cement ratio is offset by

the adverse effects of the lower bond area between the cement paste and the aggregate and by the

discontinuity caused by the large particles.

Shape and the surface texture of the aggregates.

The shape of an aggregate may generally be classified as:

Rounded

Angular

Elongated/ flaky.

Similarly, terms such as smooth or rough are used to describe surface textures.

The particle shape affects the strength of concrete mainly by affecting cement paste content

required for a given workability. If the cement content is the same, then angular aggregates

would require higher water/ cement ratio than rounded one.

The surface texture affects the bond between the cement paste and the aggregate particle and also

the cement paste required to achieve a given workability.

Grading of the aggregates

For concrete to be durable, it has to be dense and when fresh, it should be sufficiently workable

for it to be properly compacted.

The mortar should be sufficiently enough to fill the void in the coarse aggregates. In turn the

cement paste should be slightly more than sufficient to fill the void in the fine aggregates.

In essence, the voids in the aggregates depend on its particle size distribution. The grading of the

aggregates affects the strength of the concrete mainly indirectly, though it has an important effect

on water/cement ratio required for specified workability.


22

Badly graded aggregates requires a higher water/cement ratio and hence results in the weaker

concrete.

Figure 3.1; Showing different sieve sizes used for grading test

Functions of the aggregates in a mix

Aggregates serve the following purposes;

They reduce the cost of the concrete. Natural aggregates require only extraction, washing

and grading prior to transportation to the site.

Correctly graded aggregates produce workable, yet cohesive concrete.

They reduce the heat of the hydration of the concrete since they are normally chemically

inert and act as heat sink for hydrating cement.


23

3.2 MATERIAL TESTING AND SPECIFICATION

Sieve analysis

Aggregate is said to be graded when it contains different sizes of particles in suitable

proportions.

The main advantage of the graded aggregate is that it provides minimum voids created by the

larger particles. It also improves workability considerably.

Sieve analysis therefore enables us to determine the proportion of different particle in an

aggregate sample. The results of sieve analysis are given in terms of % of the total aggregate

passing through each of the sieve size.

To have a visual grasp of the grading, the results can be plotted on a graph, whose ordinates

indicate % passing and abscissa indicates sieve sizes on the logarithm scale. The finer the

grading, the greater is the water requirement resulting into poor concrete. And the coarse

grading, the greater the tendency of segregation

The most suitable grading is that which gives minimum number of fines sufficient to give the

mix necessary cohesiveness.

The procedure involved, bringing the sample to an air dry condition before weighing and sieving

by drying to a temperature of 105-110C, and the dried sample weighed.The weighed sample was

then placed on the sieve and sieved successively on the appropriate sieves starting with the

largest. The sieve sizes used according to according to BS 882:1992and arranged as;

Coarse aggregates; 20, 15, 10, 5

Fine aggregates; 2.38, 1.20, 0.6, 0.3, 0.15, 0.074,

Each sieve was shaken separately over a clean tray until not more than a trace passes. On

completion of sieving, the material cleaned from the mesh, was weighed.


24

3.3 BATCHING OF MATERIALS

In every project, it is a pre-requisite that the material for use is prepared in advance to allow the

project to run as scheduled. The initial material preparation under this project involved the

acquisition of the sample from the yard. Batching was then done using the weight method. A mix

design was done and obtained weights used. The chemical admixtures adopted included;

Pozzolith standardand the Rheobuild 2000M admixtures.

3.4 MIX DESIGN

Characteristic strength of concrete = 30 N/mm2

Expected slump = 30 - 60mm

Uncrushed aggregate = 20mm

Cement type: Ordinary Portland Cement (OPC)

Age of loading = 7 and 28 days

PROCEDURE

1. Determine the target mean strength

Fm = Fc +Ks where: s is the standard deviation (figure 3 in the appendix)

Fm – target mean strength

Fc – characteristic strength (as specified)

K – Constant depending on the defective level

associated the specified strength (1.64 in this case)

Therefore: Fm = Fc +1.64s

Adopted standard deviation = 4 (more than 20 test samples)

Fm = 30 + (1.64 x 8) = 43.12 N/mm2

2. Determination of water-cement ratio


25

= 0.5 (figure 4 in the appendix)

3. Determination of free water content

Specific gravity of aggregates = 2.63

Wet density of normal concrete = 2400kg/m3

Free water-content = 210 kg/m3

4. Determination of cement content

W/c ratio = 0.5

Water content = 210 kg/m3

0.5 = 210/cement content

Therefore: cement content = 210/0.5

= 420 kg/m3

5. Determination of total aggregate content

Total agg. content = wet concrete mix density – (free water content + cement

content)

= 2400kg/m3 – (210 + 420 )kg/m3

= 1770 kg/m3

6. Determination of coarse and fine aggregate content

Slump = 30-60 mm

Free water/cement ratio = 0.5

Proportion of fine aggregates = 33% (from chart 2 in the appendix)


26

= 33/100 x 1910

= 584.1 kg/m3 (approx 585)

Coarse aggregate = (1770 – 585) kg/m3

= 1185 kg/m3

QUANTITY OF CONSTITUENTS

No of cubes to be cast = 6

Volume of cube (each) = 150mm x 150mm x150mm = 3,375,000mm3

Total volume = 3,375,000 x 6

= 20,250,000mm3(equal to 0.02025 m

3)

No of cylinders to be cast = 3

Volume of cylinder (each) = π x 1502 x 300 /4 (mm

3) = 5,301,438 (mm

3)

Total volume = 5,301,438 x 3

= 15,904,313 mm3 (equal to 0.015904 m3)

Total batch volume = 0.02025 m3 + 0.015904 m

3

=0.036154 m3

TOTAL REQUIRED CONSTITUENTS

Including wastage (10%) = 1.1 x 0.036154 m3

= 0.0397694(approx 0.04m3)

Volume of constituents = Calculated amount (kg/m3) x 0.04 m

3

Required volume of constituents


27

Calculated amount

(kg/m3)

Total required for expt.

(kg)

Fine agg 585 23.4

Coarse agg 1115 44.6

Cement 420 16.8

Water 210 8.4

3.4 TESTING THE PROPERTIES OF FRESH CONCRETE.

Slump test

This is a suitable test for normal cohesive mixes of medium to high workability and is the

workability test that is most commonly used. A workable concrete is defined as a concrete

suitable for placing and compacting under the site conditions. The slump test was carried on the

control mix and mixes with admixures. The standard slump cone with a base plate was used. A

change in the value of slump indicated changes in material water content or in the proportion of

the mix, so was useful in controlling the quality of the concrete produced. The apparatus

consisted of a truncated conical mould 100mm diameter at the top, 200mm at the bottom and

300mm high with a steel tamping rod 16mm diameter and 600mm long with both ends

hemispherical. The inside of the mould was cleaned and oiled before the test and the mould

made to stand on a smooth hard surface. The mould held down using the feet rested on the foot

rests, was filled in three layers of approximately equal depth. Each layer will be tamped with 25

strokes of tamping rod and the strokes being uniformly distributed over the cross-section of the

layer. The top surface was then smoothened using the rod as the straight edge, and the surface of

the cone and base plate wiped clean. The cone was then lifted vertically upright and the slump

measured.


28

3.5 COMPACTION FACTOR TEST (TO BS BRITISH STANDARD 1881-103.)

The compaction factor test measures the degree of compaction resulting from the application of a

standard amount of work.

The apparatus consist of a rigid frame that supports two conical hoppers vertically aligned above

each other and mounted above a cylinder. The top hopper is slightly larger than the bottom

hopper, while the cylinder is smaller in volume than both hoppers. To perform the test, the top

hopper was filled with concrete but not compacted. The door on the bottom of the top hopper

then opened and the concrete allowed dropping into the lower hopper. Once all of the concrete

had fallen from the top hopper, the door on the lower hopper was opened to allow the concrete to

fall to the bottom cylinder. A tamping rod was used to force especially cohesive concretes

through the hoppers. The excess concrete was carefully struck off the top of the cylinder and the

mass of the concrete in the cylinder recorded. This mass was compared to the mass of fully

compacted concrete in the same cylinder achieved with vibration. The compaction factor is

defined as the ratio of the mass of the concrete compacted in the compaction factor apparatus to

the mass of the fully compacted concrete.

3.6 SETTING TIME OF CEMENT PASTE

Preparation of cement paste of standard consistency

Determination of initial and final setting times

Apparatus

Vicat apparatus

Moulds 1mm2 needle

Annular attachment

Preparation of cement paste

Cement paste.

It was prepared by weighing 450g of cement and placing it in a mixing plate. Water/cement ratio

was varied between 26%-33%, added and mixed to produce a fairly stiff paste. The water was

then replaced by liquid containing water and admixture. It was prepared as follows;


29

1. Pozzolith- The admixture water was mixed in a ratio to ensure that the dosage of the

admixture was within the 400-600 ml of admixture per 100kg bag of cement recommended by

the manufacturer to avoid the overdose. The solution was then applied to all types of cements.

2. Rheobuild- The admixture water was mixed in a the ratio to ensure that the dosage of the

admixture was within the 1-1.5 l of admixture per 100kg bag of cement recommended by the

manufacturer to avoid the overdose. The solution was then applied to all types of cements.

Procedure

Cement of standard consistency was prepared. The cement paste was then filled into the mould

resting on the non-porous plate in one layer and smoothened off level the surface of the plate

using a trowel. The mould was then placed under the rod bearing the plunger, and the plunger

lowered gently into contact with the surface of the paste and then released to sink in. The depth

of penetration was then recorded and the percentage of water adjusted until a settlement of 5mm

to 7mm was achieved and the percentage of water used recorded.

The plunger on the vicat rod was then replaced by 1mm2 needle, and then lowered gently into the

contact with the surface of the paste and released to sink in. The procedure was repeated at

intervals, with the needle at different points of the surface until the penetration was about 5mm

from the bottom of the mould.

The period of elapsing between the time when the water was added to the cement and the time at

which the needle reaches the above penetration was then recorded as the initial setting time.

The needle was then changed in the vicat apparatus for that with the annular attachment. The

needle was applied on the surface until the point when upon applying; the needle makes an

impression while the attachment failed to do so. The time for this to occur was then recorded

(from the time water was added)


30

Figure 3.2; Showing Vicat apparatus

3.7 TESTING THE PROPERTIES OF HARDENED CONCRETE.

Compressive Strength

The compressive strength test was done in accordance with BS 1881-108:1983. Cylinders

moulds150 mm in diameter and 300 mm high and 150*150*150 cubes were used.

The moulds were assembled, placed on a rigid horizontal surface and filled with concrete and

then compacted to remove the entrapped air, with no segregation. The concrete was then placed

in layers of 50mm and then vibrated. Concrete paste, mixed with additional cement was then

used as capping material. The idea was to increase the strength of the cap to reduce weak point

hence allowing distribution of the load. The surface was smoothened and left for 24hrs before

dismantling the moulds and then cured by immersing in water according to BS 1881-111:1983.

The specimens were removed from water, weighed, measured to determine the area of the

cylinder and the density of the concrete. Tests were carried out on the concrete at ages 7and 28

days to determine the rate of strength gain of the concrete. Before testing the concrete, all

cylinders and cubes were inspected for defects in the concrete to ensure consistent results and

then loaded in the testing apparatus at the concrete laboratory. At each age three specimens were

tested to ensure accurate results were obtained.


31

The compressive strength of the cylinders and cubesconcrete is determined from the following

formula;

Fc = P/Ac

Where:

Fc Is the compressive strength of the concrete;

P Is the maximum force measured during testing;

Ac is the area of the cylinder or cube being tested.

Figure 3.3; Compressive Test for cubes

Splitting Tensile strength

This test is of considerable importance in resisting cracking due to changes in moisture content

or temperature. A split test is carried out on a cylinder to determine the horizontal tensile stress.

The cylinder is placed with its axis horizontal between the patens of a universal testing

machine with the load being increased gradually until failure. A vibrator is used to thoroughly

mix the mortar after which the cylinders are demoulded after 24 hours and further cured in

water until tested in a wet surface condition. Cylinders measuring 300mm height and 150mm

diameter were used.


32

Procedure

Oil was applied in the interior surfaces of the moulds to prevent the mortar from sticking to the

surfaces. The specimens were then cast in cylindrical moulds. The moulds were filled to

overflowing and after filling excess mortar was removed by a sawing motion using a trowel.

The surface was then finished smooth by means of trowel. Each sample of mortar was fully

compacted using the vibrator.

The moulds were then stored undisturbed for 24hrs in the laboratory.The moulds were then

stripped and the cylinders further cured. Each of the standard moulds was placed under the

universal testing machine, and tested for strength at7 and 28days.

Splitting tensile strength of the specimens has been calculated using the following

Formula: Ft = 2P/π·LD

where

Ft = splitting tensile strength or stress, psi (MPa)

P = maximum applied load indicated by the testing machine, kN

L = length of cylindrical specimen, in. (mm)

D = diameter of cylindrical specimen, in. (mm)

Figure 3.4; Cylinders and cubes in water for curing and Rheobuild admixture cubes after

removing moulds

Effects of water admixtures in concrete containing local cement

3.8 SAMPLING OF THE MATERIALS

The objects of the sampling was to produce a truly a representative quantity of the

consignment being sampled and of sufficient quantity for the tests required. Aggregates

concrete are heterogeneous materials and therefore greater care is needed to ensure that

the sample is truly representative if reliable test results are to be obtained. Materials being

delivered on site in relatively small lots relatively best sampled during delivery to

stockpiles. The producer needs samples for testing in quality control programs.

Purchasers of aggregate, test samples to determine if they meet specifications, or will be

suitable for the intended purpose.

Cement

The cement to be used for the project was obtained locally so as to ensure the cement

used represented the really quality of the cement used by the consumer.

Aggregates

Details for sampling aggregates are given in the BS 812:102

The bulk sample of each type or size of aggregates to be tested was obtained by

collecting increments (scoopfuls) to provide the quantity required for all the tests to be

made.

The bulk sample was reduced to smaller quantity, depending on the amounts required for

the particular test. A sample divider (riffle box) was the most convenient method used.

This is designed so that material poured at the top and divided approximately equal and

diverted to the two sides: material on one side of the box was discarded and the

remainder tested. Coarse aggregates used were surface dry.


34

CHAPTER 4; RESULTS AND ANALYSIS

4.1 AGGREGATE ANALYSIS

4.1.1 Sieve analysis

Sieve analysis for fine and the coarse aggregates was to BS 882:1992. The weight of the

aggregate percentage passing the sieves was then measured and the percentages

determined. The values the weight of the aggregates passing the sieves expressed in

percentage were recorded in the table shown. A plot of the cumulative percentage passing

against the sieve sizes done on a graph containing the sieve envelop, showed that the

natural fine aggregates particle distribution is reasonably uniform and it is in agreement

with BS grading requirement as they lie within the limits. This meant that the aggregates

were good for use and no blending of the different sizes was needed.

Fine aggregates

Original weight of the sample used=200 g

Sieve sizes

(mm)

Weight

retained (g)

% retained Cumulative

% retained

Weight

passing (g)

% passing

5.00 6.3 3 3 193.7 97

2.36 10.5 5 8 183.2 92

1.18 25.2 13 21 158.0 79

0.60 56.7 28 49 101.3 51

0.30 67.8 34 83 33.5 17

0.15 28.0 14 97 5.5 3

0.075 5.5 3 100 0 0

Table 4.1; Grading of fine aggregates


35

Figure 4.1; fine aggregate curve.

Figure 4.2; fine aggregate grading test in progress.


36

4.2 CONCRETE ANALYSIS

4.2.1 Fresh Concrete Properties

The results of the slump test gave a clear indication of the workability of the concrete

made using fresh concrete and containing water admixtures available in the local Kenyan

market. It clearly distinguished workability of the under the same conditions. A summary

of the fresh concrete tests can be seen in table.

Designed mix of class 30 was used.

Mix (with and

without water

admixtures)

w/c ratio +

admixture

Slump

(mm)

Compacting

Factor

Control 0.35

0.4 23 0.83

0.45 30 0.90

0.5 38 0.94

0.55 42 0.98

Rheobuild 2000M 0.35 23 0.86

0.4 68 0.9

0.45 84 0.92

0.5 Collapse 0.96

0.55 Collapse 0.98

Pozzolith Standard 0.35 15 0.88

0.4 45 0.9

0.45 70 0.92

0.5 96 0.95

0.55 Collapse 0.96

Table 1.2; Summary of Fresh Concrete Properties


37

As expected, the results obtained from the slump tests showed that as the water cement

ratio increased the slump of the concrete also increased and also with same water content

additional of water admixtures increased the slump also. The slump measured varied with

different mix indicating that different mixes have different levels of workability.

However, the slump test is limited in its applications especially in determination of

workability. This is because; mixes with high slump need not show good workability. For

example, a wet mix with a low proportion of fines will show high slump, but would be

harsh to handle.

The results can be seen graphically in the Figure 4.2 below;

Figure 4.3; Effect of Water Cement Ratio and admixtures on Slump


38

From the graphs it is clear that mixes with Rheobuild 2000M has high workability and

with more w/c it collapses followed by Pozzolith admixture. Also at low w/c ratio of 0.35

the admixtures are able to produce a workable mix unlike the control mix. This implies

that mix made using Rheobuild 2000M is easy to place and consolidate hence reducing

the cost of handling followed by Pozzolith then control.

Figure 4.4; Showing slump test in progress

Setting time of cement paste

The cements gave different setting time that shows an indication of the extent to which it

can be workable. The cement paste setting time at standard consistency was carried out.

The variation in the setting time was clearly observed, in a table and represented in the

following bar charts.


39

Admixture w/c ratio

+

admixture

(%)

Initial

setting time

(Min)

Final

Setting time

(Min)

Control 27 95 165

29 135 180

31 165 215

33 180 240

Rheobuild

2000M

27 135 225

29 160 280

31 180 300

33 260 360

Pozzolith

Standard

27 60 140

29 95 165

31 115 190

33 135 210

Table 4.3; setting time of cement paste

It can be observed that all mixes have initial and final setting times. This implies that the

concrete made of this mixes, have available time for concreting operation (transportation,

placement, consolidation, and finishing). The use of the admixtures had the varying

effects on the cement pastes.

As the pozzolith standard reduced the setting times of the cement pastes. This meant that

the concrete once placed hence making remoulding not possible. This is a function which

is important to areas where the concrete is required to set once placed to allow other

operations to go on.

Rheobuild had the retardation effects on the setting times of the cement pastes. The

results show that the addition of rheobuild ensured prolonged workability of concrete,

allowing it to be worked on. However, the concrete remains in that state for a long time.

Meaning that, operations cannot resume on the worked sections within a short time.


40

Figure 4.5; comparison of initial setting time of cement paste.

Figure 4.6; comparison of final setting time of cement paste.

Also, the addition of the Rheobuild admixture resulted in longer setting times and

bleeding of the cement grout. Therefore the mix was observed to be incompatible with

the admixture. The effect was as captured below for the same w/c ratio.

Effects of water admixtures in concrete containing local cement

Rheobuild cement paste (excessive bleeding) Control cement paste (no bleeding)

Figure 4.7 ; Moulds resting on the non-porous plate containing cement paste

Interaction problems are caused by the effect of the admixtures on the hydration reaction

of cement and due to adsorption of the admixture to the cement particles. This may be

due to the cement composition that results into repulsion of the water as it interacts with

the admixtures.

Figure 4.8 ; Showing needle marks

and setting time test in progress


42

4.2.2 Hardened Properties

The rate of the strength development was determined by measuring the strength at age of 7 and 28

days. The compression tests results are summarized in the tables below for 150mm cubes.

Mixes w/c ratio +

admixture

7 days strength 28 days

Compression

strength

Control 0.35

0.4 25.8 35

0.45 24 32

0.5 21.11 31

0.55 19 28.55

Rheobuild

2000M

0.35 32 47

0.4 29.2 41.8

0.45 28 39

0.5 25.33 38.4

0.55 23.6 35.8

Pozzolith

Standard

0.35 29.5 41.4

0.4 28 38.2

0.45 26.44 35.3


43

0.5 24.12 34.5

0.55 22.2 32.12

Table 4.5; Summary of Compression Tests at different w/c ratio

The mixes showed the strength development of the concrete under different water cement ratio with

and without admixtures. The results from the compression tests showed that the strength varied. The

values of strength of control mix were lower compared to other mixes.

15

17

19

21

23

25

27

29

31

33

0.3 0.35 0.4 0.45 0.5 0.55 0.6

Stre

ngt

h (

N/m

m2

)

Water content

7 days compressive strength

Control

Rheobuild 2000M

Pozzolith Standard

Figure 4.9; curves showing 7 days cube strength for different mixes


44

Figure 4.10; curves showing 28 days cube strength for different mixes

It was clearly obserrved that for all w/c ratios Rheobuild produced higher strength followed by

Pozzolith standard then control.

Further analysis was carried out to show the percentage increase of compressive strength for all w/c

ratios with respective admixture mixes.


45

Admixture w/c ratio +

admixture

7 days

strength

28

days

Rheobuild

2000M

0.35

0.4 13 19.43

0.45 16.67 21.88

0.5 19.99 23.87

0.55 24.21 25.39

Pozzolith

Standard

0.35

0.4 8.36 9.14

0.45 10.17 10.31

0.5 14.26 11.29

0.55 16.84 12.5

Table 4.5; percentage increase of Compressive strength for cubes by admixtures

Figure 4.11; curves showing 7 days percentage strength increase in compression for the

admixture mixes


46

Figure 4.12; curves showing 28 days percentage strength increase in compression for the

admixture mixes

For both 7 and 28 days Rheobuild had a higher percentage strength increase compared to pozzolith

standard.

Curves of strength development were drawn showing that admixtures mixes provided higher strengh

than the control mix.This was clearly illustrated by the graph below where values of w/c ratio of 0.5

was used as a typical.


47

Figure 4.13; comparison of the rate of strength development under constant w/c ratio of 0.5.

Figure 4.14; Bar chart showing the rate of strength development under constant w/c ratio of

0.5.

From the above graphs is clear that Rheobuild mix yielded higher strength compared to other two.

Control mix gave the lowest values under the same conditions of constant water cement ratio 0.5.


48

This is also the same analysis for the other w/c ratios as seen in the table 4.5. The concrete portal

records, the addition of the super plasticizer on concrete will result in an increase of the strength

development within the first 7 days before the development resembling the normal curve. This was

clearly demonstrated from the plotted curves. It can be ascertained that workability of the concrete

can actually be obtained using admixtures and attaining large values of the compressive strength.

However, there is need for more analysis and compare strength at different w/c ratio. To clearly

determine the effects of water admixtures, the table below contains the mix proportions according to

the designed mix.


49

Mix proportions

Admixture w/c Amount of

water

(litres)

Amount

of

admixture

(litres)

Weight of

cement

(kgs)

Weight of

fine

aggregates

(kgs)

Weight of

coarse

aggregates

(kgs)

Control 0.35 5.88 0 16.8 23.4 44.6

0.4 6.72 0 16.8 23.4 44.6

0.45 7.56 0 16.8 23.4 44.6

0.5 8.4 0 16.8 23.4 44.6

0.55 9.24 0 16.8 23.4 44.6

Rheobuild

2000M

0.35 5.63 0.25 16.8 23.4 44.6

0.4 6.47 0.25 16.8 23.4 44.6

0.45 7.31 0.25 16.8 23.4 44.6

0.5 8.15 0.25 16.8 23.4 44.6

0.55 8.99 0.25 16.8 23.4 44.6

Pozzolith

Standard

0.35 5.78 0.1 16.8 23.4 44.6

0.4 6.62 0.1 16.8 23.4 44.6

0.45 7.46 0.1 16.8 23.4 44.6

0.5 8.3 0.1 16.8 23.4 44.6

0.55 9.14 0.1 16.8 23.4 44.6

Table 4.6; Summary of mix proportions for the designed mix class 30


50

With use of admixtures a workable mix for w/c ratio of 0.35 unlike for the control, which water

content was not enough. This is shown by the below figure.

Figure 4.15; non workable mix for control at w/c ratio of 0.35

It was observed that the water admixtures used reduced the water content by 5% for Rheobuild

2000M and by 2% for Pozzolith standard without overdosing. It was also observed that the addition

of the concrete admixtures at lower water cement ratio enhances the strengths of concrete.

Compressive strength for cylinders


days. The compression tests results are summarized in the tables below for 150mm diameter and

300mm height.


51

Table 4.7; shows the compressive strength of cylinders and the percentage strength increase

due do admixtures.

Admixture w/c ratio +

admixture

28 days

Compression

strength

% compressive strength increase by the

admixtures

Control 0.35

0.4 28.3

0.45 24

0.5 20.7

0.55 18.4

Rheobuild

2000M

0.35 35

0.4 32.1 19.43

0.45 28.5 21.88

0.5 25 23.87

0.55 22.5 25.39

Pozzolith

Standard

0.35 32.9

0.4 30 9.14

0.45 26 10.31

0.5 23 11.29

0.55 21 12.5


52

Figure 4.16; comparison of the compressive strength for cylinders of different mixes

5

10

15

20

25

30

0.2 0.3 0.4 0.5 0.6

% s

tre

ngt

h in

cre

ase

Water content

% strength increase for28 days compressive strength cylinder

Rheobuild 2000M

Pozzolith Standard

Figure 4.17; comparison of the % compressive strength increase for cylinders due to water

admixtures


53

From above results it was observed that Rheobuild 2000M had high compressive strength for the

cylinders and also its increase in strength was also high than Pozzolith Standard.

Comparison of the percentage increase in compression strength in cubes and cylinders

050

0.4 0.45 0.5 0.55Rheobuild 2000M for cubes 19.43 21.88 23.87 25.39

Pozzolith Standard for cubes 9.14 10.31 11.29 12.5

Rheobuild 2000M for cylinder 13.95 16.67 19.35 22.22

Pozzolith Standard for cylinder

6.98 8.33 10.32 12.96

Stre

ngt

h (

N/m

m2

)

comparison of the % increase in compression strength in cubes and cylinders


admixtures


admixtures


54

Neville reported that the cylinder to cube strength ratio was 0.87 for concrete strength up to 50 MPa.

For materials and testing conditions adapted in these study the strength ratio was found to be 0.81 for

Rheobuild 2000m on average and which is slightly lower than that reported by Neville. For

Pozzolith on average was 0.87 which is okay.

Tensile strength


days. The tensile tests results are summarized in the tables below for 150mm diameter and 300mm

height.

Admixture w/c ratio + admixture 28 days

% tensile strength

increase by the

admixtures

Control 0.35

0.4 4.3

0.45 3.6

0.5 3.1

0.55 2.7

Rheobuild 2000M 0.35 6.1

0.4 4.9 13.95

0.45 4.2 16.67

0.5 3.7 19.35

0.55 3.3 22.22

Pozzolith Standard 0.35 5.1

0.4 4.6 6.98

0.45 3.9 8.33

0.5 3.42 10.32

0.55 3.05 12.96


55

Figure 4.20; comparison of the tensile strength for cylinders of different mixes

Figure 4.21; comparison of the % tensile strength increase for cylinders due to water

admixtures

From above results it was observed that Rheobuild 2000M had high tensile strength followed by

pozzolith standard then control for the cylinders. Also Rheobuild 2000M percentage increase in

tensile strength was also high than Pozzolith Standard.


56

Figure 22; Tensile Test for cylinders in progress


57

CHAPTER 5; DISCUSSION

5.1 Setting time

Set modifying admixtures affect the hydration of the cement, causing it to set faster (accelerating) or

more slowly (retarding). Most work by adsorption onto or absorption into the hydrating cement

surface, either having a blocking effect or a peptising effect on specific cement phases but some

admixtures also affect the solution chemistry of the soluble phases. According to the results obtained

Pozzolith Standard accelerates the setting time for the cement paste while Rheobuild 2000M retards

the mix.

Therefore Rheobuild 2000M was regarded as a retarder and it caused retardation by some of the

following mechanisms:

1) Adsorption of the retarding compound on the surface of cement particles, forming a

protective skin which slows down hydration;

2) Adsorption of the retarding compound on to nuclei of calcium hydroxide, poisoning their

growth, which is essential for continued hydration of cement after the end of induction

period;

3) Formation of complexes with calcium ions in solution, increasing their solubility and

discouraging the formation of the nuclei of calcium hydroxide referred to in (2) above; and

4) Precipitation around cement particles of insoluble derivatives of the retarding compounds

formed by reaction with the highly alkaline aqueous solution, forming a protective skin

5.2 Strength and workability

Usually, the chemical admixtures used are high-range water reducers (superplasticizers) and

viscosity-modifying agents, which change the rheological properties of concrete.

Admixtures are used as an extra fine material, besides cement, and in some cases, they replace

cement.


58

In this study, the admixtures were added to the mixes adding mineral constituents like fly-ash, slag

cement, silica fume, and capabilities that improved the flowing and strengthening characteristics of

the concrete

Admixture constituents enhances better bonds than normal concrete, between aggregate and cement.

This explains the increase in tensile and compressive strength for the concrete with admixtures

compared to the normal concrete.

The water admixtures adsorbs onto the surface of the cement causing the individual particles to

deflocculate and disperse (see in the following figure).

cement flocs cement is uniformly dispersed reduce fluidity increasing fluidity

Figure 5.1; effect of plasticizer or superplasticiser addition on cement dispersion.

This dispersion increases the effectiveness of the water, causing the mix to become much more fluid

for any given water content thus increasing the workability. The effect is called plasticizing or

superplasticising, depending on the degree of fluidity obtained. If the increased fluidity is not

required, the water content of the mix can be decreased, giving a lower water/cement ratio and hence

increased strength and durability. This is called water reduction or high range water reduction, the

demarcation being at around 12 to 14% water reduction for equal consistence.

Addition of plasticizing

admixture


59

Another option is to reduce both water and cement content to maintain strength but improve the cost

and environmental profile of the mix. The other option is to use an admixture dosage that will allow

two or more of these effects to be obtained at the same time, e.g. lower water/cement ratio and some

increase in fluidity.

It was found that the Pozzolith Standard increased slump compared to the normal concrete thus it

had plasticizing effect. For the Rheobuild 2000M it produced higher slump than normal concrete and

Pozzolith standard mix, therefore it caused superplasticising effect.


60

CHAPTER 6; CONCLUSIONS

At the beginning of this project a number of goals were set out to achieve, these goals were to:

Determine the overall strength, as well as the rate of strength gain for concrete varying water

admixture type, with and without admixtures.

Determine the workability for concrete varying water admixture type, with and without

admixtures.

To determine the setting time of concrete of plain and with the water admixtures

After the completion of testing and analyzing, there are a number of conclusions which are able to be

made;

1. With proper dosage of the admixtures, concrete can be produced at low w/c ratio, placed

efficiently and economically. This is due to the enhanced workability and high strengths. It

was seen that Rheobuild 2000M reduced w/c ratio by 5% and the highest obtained percentage

increase in compressive strength was 25% while Pozzolith Standard reduced w/c ratio by 2%

and increased increase in compressive strength by 12.5%.

2. Both of water admixtures used increased workability of the concrete at respective workable

mixes compared to plain mix without admixtures. It was observed that at w/c ratio of 0.45

slump for control mix was 30 mm compared to Rheobuild 2000M mix was 84mm and that of

Pozzolith was 70mm. This proves the admixtures increased the workability.

3. Pozzolith Standard is very cheap compared to Rheobuild therefore, it can be used to produce

economical concrete as admixtures to enhance workability and improve the strengths.

However, the levels of efficiency are lower than the Rheobuild 2000M admixtures. The

market price for 5 litres for Pozzolith standard was Kshs. 500 and Rheobuild was Kshs 2500.

Also for all mixes Pozzolith standard used was 0.1 litres amd Rheobuild 2000M used was

0.25 litres according to manufacturers instructions. Therefore, Pozzolith can be considered

cheap and economical because as seen in the various results, they did not differe much.

4. Pozzolith Standard admixture can be used to reduce the setting time of concrete while

Rheobuild 2000M admixture increases the setting time.This conclusion can be drawn

fromresults in various mixes:


61

Pozzolith standard for various mixes produced initial setting time ranging 60-135

minutes and final setting time ranging 140-210 minutes.

Rheobuild 2000M produced initial setting time ranging 135-260 minutes and final

setting time ranging 225-360 minutes.

For the control mix produced initial setting time ranging 95-180 minutes and final

setting time ranging 165-240 minutes.

Also Rheobuild caused bleeding and segregation of the particles in concrete when used at

high dosage or with high w/c ratio. Rheobuild 2000M has high rate of strength gain effect

and yields higher strength as compared to Pozzolith Standard. Therefore Rheobuild can be

termed as superplasticizing and retarding admixture while Pozzolith standard as water

reducing and accelerating admixture.


62

CHAPTER 7; RECOMMENDATION

Since this research covered only two brands of water admixtures, I recommend that further detailed

research should be carried out to come up with enhanced database on the concrete admixtures effects

and compatibility with the cements. Other mixes should also be adopted. This may help in

classifying different cement according to their compatibility, hence enabling concrete users to make

appropriate decisions.

Plant extract admixtures should be also researched on to determine the dosage, effects and

concentration to be applied on the concrete mix


63

REFERENCES;

1. Neville, A.M 1986, Properties of concrete, Longman scientific and technical

2. Taylor, W.H 1977, Concrete Technology and practice: proportioning and workability,

McGraw-Hill Book Company, New York

3. British standards

4. Wong, G.S, Alexander, A. M, Haskins, R, Toy, S. P, Malone, G. P, & Wakeley, L 2001,

Portland-cement Concrete rheology and workability, U.S Department of transportation,

Georgetown, USA

5. Cho-Liang, T, Yun, D & Yi-Shuin T 2003, Experimental study of the Rheological behavior

of fresh concrete, mortar, and clay grout, Journal of Marine Science and Technology, Vol.

11, No. 3 pp.121-129

6. Mindess, S & Young, J.F 1981, Concrete, prentice-Hall, Englewood cliffs

7. (www.bamburi-homebuilding,com, last accessed on 10th October 2009 IK

8. R. Rixom and N. Mailvaganam, Chemical Admixtures for concrete, E & FN Spon, London

(1999)

9. Ramachandran, V. S., and V. M. Malhotra. 1984. Superplasticizers. In Concrete admixtures

handbook: Properties, science, and technology, ed. V. S. Ramachandran, 211-68. Park

Ridge, N.J.: Noyes Publications.

10. Whiting, D., and W. Dziedzic. 1989. Behavior of cement-reduced and flowing fresh

concretes containing conventional water-reducing and second generation high-range water-

reducing admixtures. Cement, Concrete, and Aggregates 11 (1):30-39.

11. Wallace, M. 1985. Flowing concrete produced at the batch plant. Concrete Construction 30

(4):337-43

http://www.bamburi-homebuilding,com/


64

APPENDICES

Appendix tables and figures

Table 1: Strength classes of cements to European Standard BS EN 197-1: 2000.

Strength Class Compressive Strength (N/mm2)

Early Strength Standard Strength

2 day minimum 7 day minimum 28 day minimum 28 day maximum

32.5N 16.0 32.5 52.5

32.5R 10 32.5 52.5

42.5N 10 42.5 62.5

42.5R 20 42.5 62.5

52.5N 20 52.5

52.5R 30 52.5

The code letters in the Standards are: N- Ordinary early strength development. R- High early

strength development.


65

Table 2: Approximate Compressive Strength (N/mm2) of Concrete Mixes Made with a Free-

Water / Cement Ratio 0.5

Type of Cement Type of Coarse

Aggregate

Compressive strength (N/mm2)

Age (days)

3 7 14 28

Ordinary Portland (OPC) or Sulphate

Resisting Portland (SRPC)

Uncrushed 22 30 42 49

Crushed 27 36 49 56

Rapid Hardening Portland (RHPC) Uncrushed 29 37 48 54

Crushed 34 43 55 61

Portland Pozzolana Cement (PPC)

1 N/ mm2 = 1 MN/ m = 1 MPa SSD = based on a saturated surface-dry basis

The statistical constant k is derived from the mathematics of thenormal distribution specified in BS

5328 and increases as the proportion ofdefectives is decreased, thus:

k for 10% defectives = 1.28


k for 2.5% defectives = 1.96



66

Figure 3 Relationship between

standard deviation and

characteristic strength

Figure 4 Relationship

between compressive

strength and free-

water/cement ratio


67

Table 4.4 (c) Approximate free-water contents (kg/m3) required to give various levels of

workability

Slump (mm) 0-10 10-30 30-60 60-180

Maximum size of aggregate (mm) Type of aggregate

10 Uncrushed 150 180 205 225

Crushed 180 205 230 260

20

Uncrushed 135 160 180 195

Crushed 170 190 210 225

40 Uncrushed 115 140 160 175

Crushed 155 175 190 205

When coarse and fine aggregates of different types are used, the free-water content is estimated by the

expression: 2⁄3 Wf+ 1⁄3 Wc. Where Wf = free-water content appropriate to type of fine aggregate and Wc =

free-water content appropriate to type of coarse aggregate.


68

Figure 5 Estimated wet density of fully compacted concrete

Figure 6 Recommended proportions of fine aggregate according to percentage passing a

600 μm (0.6mm) sieve


69

Figure 6 (continued)

Figure 6 (continued).Recommended proportions of fine aggregate according to

percentage passing a 600 μm (0.6mm) sieve.


70

SUMMARY TABLE OF CUBES RESULTS FOR 7 DAYS

Mix Type w/c ratio Slump,mm Cubes Dimensions

(mm)

Average

Weight

(kg)

Volume (m3)

Density

(kg/m3) 7 days Loads (KN)

7 days

Average

Load (KN)

Avg.

Compressive

Strength

(N/mm2)

Control

0.35

150 x 150 x 150 8.2 0.003375 2439 0 0 0

0.4 23 150 x 150 x 150 8.1 0.003375 2400 580, 583, 5580 581 25.84

0.45 30 150 x 150 x 150 8.0 0.003375 2370 540, 540, 540 540 24

0.5 38 150 x 150 x 150 8.0 0.003375 2361 460, 505, 460 475 21.11

0.55 42 150 x 150 x 150 8.0 0.003375 2356 420, 443, 420 428 19

Rheobuild 2000M

0.35 23 150 x 150 x 150 8.1 0.003375 2400 740, 715, 700 720 32

0.4 68 150 x 150 x 150 8.1 0.003375 2400 650,650, 670 657 29.2

0.45 84 150 x 150 x 150 8.0 0.003375 2370 630 ,630, 630 630 28

0.5 Collapse 150 x 150 x 150 8.0 0.003375 2370 580, 565, 565 570 25.33

0.55 Collapse 150 x 150 x 150 8.0 0.003375 2370 543, 515, 535 531 23.6

Pozzolith

Standard

0.35 15 150 x 150 x 150 8.0 0.003375 2370 662, 670, 660 664 29.5

0.4 45 150 x 150 x 150 8.0 0.003375 2370 630, 640, 620 630 28

0.45 70 150 x 150 x 150 8.0 0.003375 2356 595, 590, 600 595 26.44

0.5 96 150 x 150 x 150 8.0 0.003375 2356 544, 560, 525 543 24.12

0.55 Collapse 150 x 150 x 150 8.0 0.003375 2356 485,505, 510 500 22.2


71

SUMMARY TABLE OF CUBES RESULTS FOR 28 DAYS

Mix Type w/c ratio Slump,mm Cubes Dimensions

(mm)

Average

Weight

(kg)

Volume (m3) Density

(kg/m3)

28 days Loads

(KN)

28 days

Average

Load (KN)

Avg.

Compressive

Strength

(N/mm2)

Control

0.35

150 x 150 x 150 8.3 0.003375 2447 0 0 0

0.4 23 150 x 150 x 150 8.2 0.003375 2433 775, 800, 790 788 35

0.45 30 150 x 150 x 150 8.1 0.003375 2400 720, 720, 720 720 32

0.5 38 150 x 150 x 150 8.0 0.003375 2367 700, 705, 690 698 31

0.55 42 150 x 150 x 150 8.0 0.003375 2367 635, 640, 650 642 28.55

Rheobuild 2000M

0.35 23 150 x 150 x 150 8.2 0.003375 2430 1050, 1065, 1065 1058 47

0.4 68 150 x 150 x 150 8.1 0.003375 2400 973, 930, 920 941 41.8

0.45 84 150 x 150 x 150 8.0 0.003375 2379 880, 880, 875 878 39

0.5 Collapse 150 x 150 x 150 8.0 0.003375 2376 865, 865, 863 864 38.4

0.55 Collapse 150 x 150 x 150 8.0 0.003375 2370 818, 790, 810 806 35.8

Pozzolith

Standard

0.35 15 150 x 150 x 150 8.1 0.003375 2388 930, 935, 930 932 41.4

0.4 45 150 x 150 x 150 8.0 0.003375 2370 860, 870, 850 860 38.2

0.45 70 150 x 150 x 150 8.0 0.003375 2361 792, 800, 790 794 35.3

0.5 96 150 x 150 x 150 8.0 0.003375 2364 775,775, 778 776 34.5

0.55 Collapse 150 x 150 x 150 8.0 0.003375 2359 720,730, 720 723 32.12


72

SUMMARY TABLE OF CYLINDERS RESULTS FOR 28 DAYS

Mix Type w/c ratio Slump,mm Cylinder Dimensions

(mm)

Average

Weight (kg) Volume (m

3)

Density

(kg/m3)

28 days Loads

(KN)

28 days

Average Load

(KN)

Avg.

Compressive

Strength

(N/mm2)

Control

0.35

dia=150, H=300 12.9 0.005302125 2440 0 0 0

0.4 23 dia=150, H=301 12.9 0.005302125 2430 642, 630, 640 637 28.3

0.45 30 dia=150, H=302 12.7 0.005302125 2400 540, 545, 535 540 24

0.5 38 dia=150, H=303 12.6 0.005302125 2375 478, 460, 460 466 20.7

0.55 42 dia=150, H=304 12.6 0.005302125 2375 422, 420, 400 414 18.4

Rheobuild 2000M

0.35 23 dia=150, H=305 12.8 0.005302125 2420 784, 790, 790 788 35

0.4 68 dia=150, H=306 12.8 0.005302125 2405 706,720, 740 722 32.1

0.45 84 dia=150, H=307 12.6 0.005302125 2375 643 ,640, 640 641 28.5

0.5 Collapse dia=150, H=308 12.6 0.005302125 2370 570, 565, 555 563 25

0.55 Collapse dia=150, H=309 12.6 0.005302125 2370 493,510, 515 506 22.5

Pozzolith

Standard

0.35 15 dia=150, H=310 12.7 0.005302125 2390 740, 740, 740 740 32.9

0.4 45 dia=150, H=311 12.6 0.005302125 2370 680, 675, 670 675 30

0.45 70 dia=150, H=312 12.5 0.005302125 2355 615, 560, 580 585 26

0.5 96 dia=150, H=313 12.5 0.005302125 2355 500, 530, 525 518 23

0.55 Collapse dia=150, H=314 12.5 0.005302125 2355 476, 470, 470 473 21


73

SUMMARY TABLE OF CYLINDERS RESULTS FOR 28 DAYS

Mix Type w/c ratio Slump,mm Cylinder Dimensions

(mm)

Average

Weight (kg) Volume (m

3)

Density

(kg/m3)

28 days Loads

(KN)

28 days

Average

Load (KN)

Avg. Tensile

Strength

(Kg/cm2)

Control

0.35

dia=150, H=300 12.9 0.005302125 2440 0 0 0

0.4 23 dia=150, H=301 12.9 0.005302125 2430

304 4.3

0.45 30 dia=150, H=302 12.7 0.005302125 2400

255 3.6

0.5 38 dia=150, H=303 12.6 0.005302125 2375

219 3.1

0.55 42 dia=150, H=304 12.6 0.005302125 2375

191 2.7

Rheobuild 2000M

0.35 23 dia=150, H=305 12.8 0.005302125 2420

431 6.1

0.4 68 dia=150, H=306 12.8 0.005302125 2405

346 4.9

0.45 84 dia=150, H=307 12.6 0.005302125 2375

297 4.2

0.5 Collapse dia=150, H=308 12.6 0.005302125 2370

262 3.7

0.55 Collapse dia=150, H=309 12.6 0.005302125 2370

233 3.3

Pozzolith

Standard

0.35 15 dia=150, H=310 12.7 0.005302125 2390

361 5.1

0.4 45 dia=150, H=311 12.6 0.005302125 2370

325 4.6

0.45 70 dia=150, H=312 12.5 0.005302125 2355

276 3.9

0.5 96 dia=150, H=313 12.5 0.005302125 2355

242 3.42

0.55 Collapse dia=150, H=314 12.5 0.005302125 2355

216 3.05

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