Journal of Environmental Science and Engineering A 1 (2012) 121-127 Formerly part of Journal of Environmental Science and Engineering, ISSN 1934-8932

Feasibility of Using Sea Shells Ash as Admixtures for

Concrete

Benjamin R. Etuk1, Idongesit F. Etuk1 and Linus O. Asuquo2

1. Department of Chemical and Petroleum Engineering, University of Uyo, Uyo 52001, Nigeria

2. Department of Mechanical Engineering, University of Uyo, Uyo 52001, Nigeria

Received: June 24, 2011 / Accepted: August 2, 2011 / Published: January 20, 2012. Abstract: This research aims at producing pozzolanic admixtures from waste shells of periwinkle, oyster and snail. The clean shells were ashed at 800 °C and analysed for chemical composition. The results show that they are pozzolanic in nature. The effect of using the shells ash as admixtures on the setting time and compressive strength of cement paste and mortar were investigated using varying percentages of 0%, 5%, 10%, 15%, 20%, 25% and 30% by weight of each of the shell ashes. The results show that the water consistency, initial, and final setting times of each of the cement blends were increasing with increase in percentage replacement of cement with each of the shell ashes. The optimum compressive strength with percentage replacement level of 10% for periwinkle shell ash (PSA), 15% for oyster shell ash (OSA), and 20% for snail shell ash (SSA) were obtained with ashes produced. Key words: Sea shell ash, concrete, admixtures, waste utilization.

1. Introduction

Housing delivery in Nigeria in the rural, semi-urban

and urban areas is still a serious problem due partly to

the high cost of some essential materials, especially

cement (a major material in the construction industry)

whose cost has increased over the years and may soon

be out of reach of the ordinary citizens. Recently, to

arrest the escalating cost of cement, the Federal

government directed local manufacturers to evolve

strategies to bring down the price of the commodity to

avoid a review of the existing policy on cement which

gave 2013 as the deadline for the country to be

self-sufficient in cement production [1].

Concrete is an essential construction material

composed of cement, aggregate (gravel or granite and

sand) and water. In order to reduce the construction,

researchers have been exploring the possibility of

using pozzolanic admixtures produced from locally

Corresponding author: Benjamin R. Etuk, associate

professor, Ph.D., main research fields: separation processes, particulate systems, food processing, waste control and utilization. E-mail: bretuk2001@yahoo.com.

available and/or waste materials to partially or fully

replace the costly conventional materials.

An admixture is a material other than cement, water

and aggregates that is used as an ingredient of

concrete and is added to the batch immediately before

or during mixing [2]. According to Michael [3],

admixtures in concrete can improve its workability,

hardening, or strength characteristics and generally

result in a reduction in the cost of concrete

construction [4]. For instance, activated kaolin clay,

fly ash, silica fume, baryte powder and oil shale ash

had been used as components of blended binders for

mortars with good results in terms of their pozzalinic

activity [5]. The use of cassava starch [6], rice husk

ash [7-10], rice straw ash [11], and wood waste ash

[12] to partially replace different types of cement in

concrete had also been reported. The use of these

agricultural materials helped to reduce waste as well

as improve the strength properties of the concrete.

However, the strength reduced with time due to

microbial activity.

In Nigeria, the intensity of fishing activities in the

DAVID PUBLISHING

D

Feasibility of Using Sea Shells Ash as Admixtures for Concrete

122

riverine areas has resulted in the production and

accumulation of large quantities of sea shells as

wastes along the coastal regions, market areas and

dump sites. Usually, the fleshes of the species are

processed for consumption while the inedible hard

shells are dumped at open sites thereby causing

environmental pollution.

Periwinkle, snail, oyster and all marine animals

belonging to phylum mollusca and class gastropoda

[13]. They belong to the group of exoskeleton animals.

The exoskeletons contain rigid and resistant

components that fulfill a set of functional roles

including protection, excretion, support, feeding,

acting, etc.. They contain chitin and when calcium

carbonate is added, the exoskeleton grows in strength

and hardness [14].

An exploratory study on the suitability of sea shells,

such as periwinkle shells, as partial or full

replacement for granite in concrete work had been

reported with satisfactory compressive test results at

appropriate concrete mix ratios [15]. Using the ash of

the sea shell, investigation had shown that up to 50%

replacement of cement in sandcrete blocks and 5%

replacement in laterite blocks were possible with good

results in terms of compressive strength [16, 17].

In this paper, the utilization of the ash of waste

shells of periwinkle (PSA), snail (SSA) and oyster

(OSA) as partial replacement for cement in the

construction industry is reported. The concentrations

of the ash from the different shells in finely divided

form are evaluated to determine the optimum needed

that will not compromise the workability, hardening

and strength properties of the concrete produced. The

effective utilization of these sea shell wastes which are

available almost free of cost and in abundance will not

only reduce their pollution tendency but will help in

reducing the amount of cement used in concrete work.

2. Materials and Methods

The materials used in carrying out the research were

periwinkle, snail and oyster shells. Other materials

used were UNICEM® Ordinary Portland Cement

(OPCEM), water and sand.

The periwinkle, snail and oyster shells were

obtained from Akpan Andem market in Uyo, a dump

site at Okpoedu, Itu, and Issiet in Itu and Uruan Local

Government Areas respectively, all in Akwa Ibom

State, Nigeria.

2.1 Production of Pozzolanic Admixture

The three different shell samples were each washed

thoroughly to remove dirt and mud and then sun-dried

for three days. The samples were then placed in a

furnace and ashed at temperatures of 800 °C for a

period of four hours. The ash samples were then

ground into a powdered form using metallic mortar

and pestle, sieved through a sieve mesh size of 63

microns, and kept in tight containers for analyses.

2.2 Chemical Analyses

The shell ashes were analysed to determine their

composition at the Quality Control Laboratory of

Ashakacem, Gombe, State, in accordance with

Nigerian Industrial Standard (NIS) method [18]. In the

method, stearic acid (0.4 g) and 20.0 g of each of the

three different shell ashes obtained at temperatures of

800 °C were measured and were put in a grinding pot

and ground for 60 seconds using the Herzog grinding

machine. The aluminum cup was filled half way with

stearic acid and then filled up with the samples. The

cup was carefully inserted into the pellet making

machine (Herzog pressing machine). The pellet

produced was then placed in the cement X-ray

spectrophotometer and the programme to which the

samples were analysed was selected, that is, the

program OPCEM (ordinary Portland cement), and the

start key was clicked so that within 2-3 minutes the

results were obtained [19].

2.3 Determination of Specific Gravity

The specific gravity of the ash samples was

determined in accordance with BS method [20]. The

Feasibility of Using Sea Shells Ash as Admixtures for Concrete

123

empty density bottle with stopper was weighed as W1

and then filled with shell ash to about three quarter of

the bottle. This was measured as W2. The bottle

containing the shell ash was then filled up with water

and a stopper used to cover it. This was measured as

W3. The content of the density bottle were then poured

out and the bottle rinsed with water. The bottle was

thereafter filled with water and the stopper inserted.

This was measured as W4. The specific gravity for

each of the shell ashes was determined, using the

formula: W2 – W1

Sp gr = (1) (W2 – W1) – (W3 – W4)

2.4 Determination of Consistency of Cement Pastes

Four hundred and ninety grams of the OPCEM was

weighed and placed on a non-absorbent metallic tray.

By trial mixtures, the required water content which

produced the cement paste of desired standard

consistency of between 26 and 33 (expressed as a

percentage by mass of the dry cement) was chosen.

The measured water was then added to the weighed

cement, thoroughly mixed and finely ground together

with a hand-trowel for four to five minutes to form a

neat cement paste. The neat cement paste was then

placed in a special metallic mould and the consistency

of the neat cement paste was then determined by

lowering the plunger which is attached to the Vicat®

apparatus and allowed to make contact with the top

surface of the paste before it was finally released.

Under the action of its weight, the plunger was

allowed to penetrate the paste and the depth of

penetration for a standard and consistent cement

paste was to a point 5 mm to 7 mm from the bottom of

the mould. This test meets the requirement stated in

BS [21].

2.5 Determination of Initial and Final Setting Times

The plunger used for consistency test was replaced

with a round needle with a cross-sectional area of 1

mm2 used as the initial set needle. The process of

making the needle penetrate the paste of standard

consistency was repeated at intervals of 5 minutes,

until the paste was stiffed enough for the initial set

needle to penetrate only to a point 10 mm to 20 mm

from the bottom of the mould. The initial setting time

was recorded as the time that elapsed from when the

paste was made to when it set [21].

The initial set needle was then replaced with the

final set needle with a 1 mm square needle having a

circular cutting edge of 5mm in diameter. The final set

needle was made to penetrate the paste in the mould,

so that it left a circular cutting edge of 5 mm in

diameter and set 0.5 mm behind the tip of the needle.

The process of allowing the needle penetrate the paste

was repeated at intervals of 5 minutes, and the final

set was said to have taken place when the needle

which was gently lowered to the surface of the paste

made an impression on it but the circular cutting edge

failed to penetrate [6].

2.6 Production of the Mortar Cubes

The moulds of size 50 × 50 × 50 mm were used for

all the casting of the mortar cubes. The moulds were

cleaned and oiled to enhance easy removal of the

cubes after setting and prevent damage of the test

cubes. A mixture of 0.27 kg of cement, 0.81 kg of

sand, and 0.135 kg of water, all in a mix ratio of

(1:3:0.5) was measured. The mixture was mixed

thoroughly by means of a trowel on a non-absorbent

metallic tray to obtain a homogenous mixture. This

was used as a reference sample (i.e 0% replacement).

The mix was then transferred into the mould of 50 ×

50 × 50 mm and filled in three equal layers. Each of

the layers was compacted 25 times using a rod of three

quarter diameter and allowed for twenty four (24)

hours before removing it and then cured in water for

7 days.

This process was repeated with cement replaced by

each of the shell ashes by weight at varied

concentrations of 5, 10, 15, 20, 25 and 30 percent.

The cubes were put into a curing tank containing

Feasibility of Using Sea Shells Ash as Admixtures for Concrete

124

water. This was done to maintain satisfactory moisture

content as that hydration of the cementious material

continues long enough to achieve the required strength,

durability and reduce shrinkage induced cracking in

the cube [22].

2.7 Compressive Strength Test

This test was done in accordance with BS EN

method [23] and used by Oymael [24]. The cubes were

removed from the curing tank at the end of the curing

period (7 days) and then weighed, before compressive

strength was conducted. Three cubes each for the

different replacement levels were crushed at 7 days

using a manual compressive machine, with capacity of

1000 kN. The test was carried out in the Building

Department Laboratory, University of Uyo, Uyo.

3. Results and Discussion

3.1 Chemical Analyses

The chemical composition of the OPCEM used and

the shell ashes are shown in Table 1. The results show

the cement to have the four major compounds, namely,

CaO, SiO2, Al2O3, and Fe2O3, with high percentages

of CaO and SiO2 which accounts for its strength.

Also the results for each of the shell ashes show that

they contain the main chemical compounds of cement

namely, CaO, SiO2, Al2O3, and Fe2O3, and the

similarity in most of the chemical composition in the

OPCEM and the latter make the partial replacement of

cement by each of the shell ashes to be feasible. From

the data presented, the amount of sulphur trioxide

(SO3) present in each of the shell ashes lies within the

optimum range of not more than 3.0% recommended

by ASTM [25]. However, the results show that PSA

contains more SO3 followed by OSA and SSA.

3.2 Specific Gravity Test

Table 2 shows the results of the specific gravity for

cement, periwinkle shell ash, snail shell ash and oyster

shell ash obtained. From the data, it is clear that the

specific gravity of the ashes are all lower than that of

cement used. Nevertheless, they are in accordance

with BS [20].

3.3 Consistency/Setting Time Test

Fig. 1 shows the results of water consistency of

cement paste blended with PSA, OSA and SSA

produced at temperature of 800 °C. The water

consistency of the blended cement paste increases

with increase in percentage replacement in the

following trend of PSA > OSA > SSA. The reason for

this trend may be attributed to the high silica contents

in PSA compared to OSA and SSA. For SSA the

lowest water consistency could also be as a result of

high lime content.

The results of initial and final setting times of

cement paste blended with PSA, OSA and SSA

obtained at 800 oC are presented in Figs. 2 and 3. The

results show that the initial and final setting times

increase with increase in the percentage replacement

of each of the shell ash. This may be due to the

increase in the required mix water, as well as retarded

hydration caused by having more of the shell ashes

than cement in the mix.

Table 1 Chemical composition of OPCEM and the sea shells ash obtained at 800 °C.

Component Composition (wt %)

OPCEM PSA SSA OSA

SiO2 20.06 26.26 10.20 13.41

Al2O3 5.85 8.79 4.81 4.95

Fe2O3 3.05 4.82 3.15 3.80

CaO 61.44 55.53 61.95 57.95

MgO 0.93 0.4 0.18 0.19

SO3 2.71 0.18 0.03 0.12

K2O 0.97 0.20 0.05 0.02

Na2O 0.14 0.25 0.04 0.22

P2O5 0.17 0.05 0.01 0.01

MnO3 0.20 0.07 0.01 0.01

TiO2 0.28 0.05 0.01 0.01

Table 2 Specific gravity.

Material Specific gravity

Cement 3.10

Periwinkle shell ash 2.50

Oyster shell ash 2.33

Snail shell ash 2.44

Feasibility of Using Sea Shells Ash as Admixtures for Concrete

125

Fig. 1 Water consistency with percentage replacement of cement with sea shell ash in concrete.

Fig. 2 Initial setting time with percentage replacement of cement with sea shell ash.

Fig. 3 Final setting time with percentage replacement of cement with sea shell ash.

Feasibility of Using Sea Shells Ash as Admixtures for Concrete

126

Fig. 4 Compressive strength with varying percentage replacement of cement with sea shell ash.

3.4 Compressive Strength

The results of the compressive strength of the

mortar cubes produced from cement blended with

each of the shell ashes are shown in Fig. 4. The figure

shows the plots of the 7 days compressive strength

against percentage replacement of PSA, OSA and

SSA obtained at temperatures of 800 °C. The results

show that at first the compressive strength of each of

the mixes is low compared to that of the control mix.

This is so, because the pozzolanic activity is slow as it

allows for the hydration of cement, but later increases

with increases in percentage replacement up to 10%

by weight of PSA, 15% for OSA and 20% for SSA,

and then decreases as the percentage for each of the

shell ash increases.

4. Conclusions

Based on the results of this study, the following

conclusions are drawn:

(1) Periwinkle shell ash (PSA), oyster shell ash

(OSA) and snail shell ash (SSA) are pozzolanic in

nature and satisfies the requirements of ASTM [25].

Therefore, it can be used as a cement replacement

material;

(2) The water consistency increases with increase in

the percentage replacement of each of the shell ashes;

(3) The initial and final setting times of the blended

cement pastes were found to increase with increasing

percentage replacement of each of the shell ashes;

(4) The compressive strength of the mortar cubes

decreases with increase in the amount of the shell ash

in the cement paste;

(5) The cement can be replaced partially by up to

10% by weight of periwinkle shell ash (PSA), 15% by

weight of oyster shell ash (OSA), and 20% by weight

of snail shell ash (SSA) in making of mortar cubes

without the strength being affected.

Acknowledgments

The authors are deeply thankful to Ashaka Cement

Company, Gombe State for their help in the chemical

analyses of the ash samples.

References

[1] R. Badmus, Cement: Manufacturers fine-tune strategies to meet ultimatum, The Punch Newspaper (Nigeria), May 20, 2011, p. 32.

[2] M.S. Shetty, Concrete Technology, Theory and Practice, revised ed., S. Chand and Company Ltd., Ram Nagar, New Delhi, 2005, pp. 124-217.

[3] R.L. Michael, Civil Engineering Reference Manual, 6th ed., Professional Publications, Inc., Belmont, CA, USA, 1992, pp. 142-144.

[4] C. Piper, Why Use an Admixture with Concrete? [Online],

Feasibility of Using Sea Shells Ash as Admixtures for Concrete

127

http://www.ehow.com/info_8761265_use-admixture-concrete.html.

[5] A. Shvarzman, K. Kovler, I. Schamban, G. Grader, G. Shter, Influence of chemical and phase composition of mineral admixtures on their pozzolanic activity, Advances in Cement Research 13 (2001) 1-7.

[6] O.E. Alutu, T.O. Ehondor, The setting time of portland cement pastes dosed with cassava starch admixtures, Nigerian Journal of Industrial & Systems Studies 4 (2005) 24-31.

[7] D.C. Okpala, Rice husk ash (rha) as partial replacement of cement in concrete, in: Proceeding of the Annual Conference of the Nigerian Society of Engineers, Port Harcourt, Nigeria, 1987, pp. 20-25.

[8] J.I.C. Mbachu, J.O. Kolawole, Shrinkage and elastic moduli of ordinary portland cement (opc) and rice husk ash (rha) concrete made with different coarse aggregate types, J. Envir. Sci. 1 (1998) 35-40.

[9] K. Sakr, Effects of silica fume and rice husk ash on the properties of heavy weight concrete, J. Mater. Civ. Eng. 18 (2006) 367-376.

[10] E.B. Oyetola, M. Abdullahi, The use of rice husk ash in low-cost sandcrete block production, Leornardo Electronic Journal of Practices and Technologies 5 (2006) 58-70.

[11] M.A. El-Sayed, T.M. El-Samni, Physical and chemical properties of rice straw ash and its effect on the cement paste produced from different cement types, J. King Saud. Univ. Eng. Sci. 19 (2006) 21-30.

[12] F.F. Udoeyo, H. Inyang, D.T. Young, E.E. Paradu, Potential of wood waste ash as an additive in concrete, J. Mater. Civ. Eng. 18 (2004) 605-611.

[13] C. Peter, E. Michael, Marine Biology, 15th ed., Mc Graw-Hill Companies, New York, 2005, pp. 167-225.

[14] B. Nicholas, Exceptional fossil preservation and the combian explosion, Integrative and Comparative Biology

43 (2003) 166-177. [15] A.P. Adewuyi, T. Adegoke, Exploratory study of

periwinkle shells as coarse aggregates in concrete works, Journal of Applied Sciences Research 4 (2008) 1678-1681.

[16] A.A. Umoh, I.A. Odesola, The effects of periwinkle shell filler on the compressive strength developments of lateritic blocks, Intern. J. Eng. 2 (2008) 1-11.

[17] O.F. Job, A.A. Umoh, S.C. Nsikak, Engineering properties of sandcrete blocks containing periwinkle shell ash and ordinary Portland cement, Inter. J. Envir. Sci. 1 (2009) 18-24.

[18] Nigeria Industrial Standard, NIS 412, Standards for Cement, Standard Organization of Nigeria, Abuja, Nigeria, 2009, pp. 9-15.

[19] M. Abdulfattah, Determination of chemical analysis using pellets, in: A laboratory Manual of Quality Control, Ashakacem Plc., Gombe State, 2001, pp. 1-12.

[20] Methods for Sampling and Testing of Mineral Aggregates, Sands and Fillers, British Standard Institution, London, 1975.

[21] Specification for Ordinary and Rapid Hardening of Portland Cement, British Standard Institution, London, 2000.

[22] A.M. Neville, Properties of Concrete, 5th eds., Ritman Limited, New York, 2000, p. 900.

[23] Cement, Composition, Specifications and Conformity criteria for Common Cements, British Standards Institution, London, 1997.

[24] S. Oymael, Suitability of oil shale ash as a constituent of cement, Oil Shale Journal 24 (2007) 45-58.

[25] Specification for Fly Ash and Raw or Calcined Natural Pozzolanas for Use as Mineral Admixture in Portland Cement Concrete, American Society for Testing and Materials Standards, Philadelphia, USA, 2008.