1

HIGH-ENERGY MECHANICAL ACTIVATION

OF CONCRETE MIXTURE

Vladlen Fridman

vfrid38@gmail.com

© Copyright 2010 by V.Fridman

ABSTRACT

The main principles of mechanical activation of mortars or mortar component of concrete using

the method of high-energy mixing (HEM) are presented. Among them are: the use of impeller

with minimal turbulence to achieve the highest level energy absorption by the mixture; the use of

sand to provide dissipation of energy and high shear conditions on the surface of cement

particles; the optimal combination of the following factors such as the rotor’s velocity, the

amount of specific energy, and geometrical parameters of the mixer. HEM increases the surface

activity of solid particles, which results in a higher volume of the water interacting with cement

to form the C-S-H gel. Thus, the initial process of cement hydration in films of the water layer 1-

2 nanometer thick spreads out over the entire volume of the cement - water matrix. HEM is an

effective way for industrial application nanotechnology of concrete. Among the achievements

are: accelerated final setting and an increase in early strength, even at low temperatures and less

than 0oC, as well as the possibility of a 50% reduction in cement quantity with substitution by fly

ash, significantly decreasing energy consumption.

Keywords: acceleration hydration, early strength, syneresis, C-S-H gel, nanotechnology, energy

consumption, fly ash, penetration resistance, setting time, activation.

INTRODUCTION

The use of high levels of mechanical energy both before and during mixing is intended to

intensify cement hydration, thus increasing strength within the required period of time. Excess of

strength would enable to reduce cement quantity and to replace it by a finely dispersed material

that is less energy consuming, such as fly ash, well known to be a pozzolanic admixture.

The present study is not the first one to address this issue. Lindström and Westerberg [1] achieve

excess strength by means of dry- and wet-grinding cement in the so-called Sala Agitated Mill,

thereby significantly reducing the size of particles. They point to a linear correlation between

the amount of absorbed energy per 1 ton of cement and the increase in strength of concrete, the

latter reaching 18% in 3 days and 7.5% in 28 days (data calculations based on Fig. 2 of their

study). This noticeable effect weakens in the later periods of cement hydration.

K.-B. Park et al. [2] achieved a 10% increase in strength as a result of preliminary activation of

dry mixes in a spout-fluid bed lab-scale mixer. This process leads to the destruction of the

floccules formed by particles due to the turbulent flow into the inclined pipe and the impacts of

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particles on the plate, located at the output from the pipe. The dry mixes consisted of cement and

sand with ratios of 1: 2 and 1: 3.2; an alternate method combined the same ratios with a ternary

blend binder containing cement, fly ash, and micro silica proportioned 74:20:6. The authors

underline an increase in flexural strength and note an improvement in rheological properties in

mortars prepared with the above-mentioned dry mixes. However, the level of energy impact here

is lower than that presented by L & W [1], where the activation was not only accompanied by the

destruction of cement floccules, but also caused a significant diminution of the actual cement

particles.

R. Kumar et al. [3] used mechanical activation of class F fly ash by means of vibratory and

attrition milling, as well as a “jet-milled classified method”. A typical median particle size was

reduced from 36.0 to 5, 4.3 and 2.8 m respectively. This allowed for an increase in fly ash

quantity in Pozzolanic Portland Cement (PPC) production from 20% to 50 and 60 %.

Zivko Zekulic, Svetlana Popov et al. [4] mechanically activated the mixture of Portland cement

and 20% fly ash in a vibrating lab mill, equipped with rings for 3 min. They obtained a 57.9%

increase in strength in comparison with the non-activated mix. The strength reached was close to

the strength of cement without fly ash.

All of these methods propose a mechanical action prior to mixing the ingredients with water.

In contrast, H. Hodne et al. [5] carried out activation while cement was being mixed with water,

by means of increasing the rate of shear mixing. They employed three types of propeller blades

of various sizes and raised the speed to up to 12,000 rpm. The energy absorption was determined

to be 5.6 – 7.6 kJ/kg (2.54-3.44 kJ/lb) with a 2oC (3.6

oF) increase in temperature. The authors

point to a more intense air entrainment into the slurry.

Marshal L. Brown et al. carried out a considerably more powerful process [6]. By utilizing high-

speed shear mixing of cement-water paste (w/c=0.24) pre-liquefied with a superplasticizer (SP),

the authors achieved a 17oC (30.6

oF) increase in temperature and a boost in viscosity. An

analogous experiment was carried out simultaneously with the use of preliminary ground silica

flour and led to similar results in temperature and viscosity. They have shown that increased

viscosity and heating are caused primarily by friction between solid particles, as well as between

the paste and the walls and blades, and not by cement hydration.

Gary R. Mass [7] proposed a method of premixing the cement-water suspension in a high-speed

mixer before mixing it with fine and coarse aggregates in an ordinary mixer. Given the optimal

combination of speed and mixing time (unspecified in the article), he achieved a 20% strength

increase in 28 days. The author of the present article obtained the same result in a similar in-field

experiment conducted around the same time (in 1989) with the following parameters: w/c = 0.36,

impeller speed = 500 rpm (20 m/sec. or 65.6 ft/s at the end of the blade). Unfortunately, the

indicated strength increase required at least 15 minutes of premix time, which is undesirable.

The above methods represent the few existing examples that partly relate to the process of

activation outlined below. HEM method proposed for the same purpose of an increase in strength

is based on the mechanical activation of mortar, or mortar component of concrete, without

additional grinding.

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RESEARCH SIGNIFICANCE

In developing a more environmentally friendly concrete, the consumption of

Portland cement should be reduced. Manufacturing Portland cement is not only energy

consuming, but is also responsible for large emissions of CO2 [8]. Fly ash is recommended as a

partial substitute for cement. Class F fly ash is not hydraulically active, i.e. it does not have

binding properties, only pozzolanic ones. It will be demonstrated below how an impulse of

energy applied during a relatively short period of mixing time (2-4 min.) could successfully

activate cement or a two-component binder. The HEM technology makes it possible to reduce

the quantity of cement by up to 50% in the widely used concrete while maintaining the strength

of 35 MPa (5000 psi).

THE ESSENCE OF HIGH-ENERGY MIXING

The previous experiments carried out by the author showed a 20-30% increase in concrete

strength. They involved additional grinding of cement in the ball mill, with increased index of

specific surface from 350 to 550 m2/kg, (or Blaine fineness from 3500 cm

2/g to 5500 cm

2/g).

This is in accordance with data given by Geoffrey Frohnsdorff [9]. These experiments showed

that flowability was reduced by more than half in the mortars prepared with additionally grinded

cement in ordinary mixers. A tendency for an increase in viscosity was also observed in regular

cement mortars when HEM was used. This is because flowability depends on the amount of

unbound water. To achieve the same level of reduction in flowability, one needs to consider the

following as mixing parameters:

1. The relative volumes of the bowl, rotated blades and the mixture.

2. The amount of consumed energy and velocity of rotation.

3. Turbulence reduction to prevent scattering of mixture.

4. The use of fine aggregate as a dissipater of energy in the mixture. Introducing of sand

may cut the activation time by 60-80% compared to the activation time of a cement-water

suspension with no sand. In fact, the solid particles of sand in high velocity conditions

increase shear stresses on the surface of cement grains, thus promoting their physical and

chemical activity.

The author established the rate of reduction in flowability of activated cement-sand

mortars as the first indicator of the activation level [10]. The frictional heating of the mixture is

the second parameter in HEM to be used to control the process.

Figure 1 depicts a schematic diagram of the lab mixer-activator (2.7 liters / 0.71 gal) in which the

first experiments were conducted. The results that were obtained using this lab mixer provided

the basis for manufacturing industrial mixer–activators capable of producing activated mixture of

up to 350 liters (0.46 cu. Y.). One of them is also shown in Figure 1.

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It was observed that, when applying the same activation time to mixtures of same proportions

and same materials (cement, sand), the specific consumed power and the temperature increase in

the mixture are volume independent.

In this process, the mixture moves horizontally and vertically (Fig.1). The horizontal motion

leads to activation of mixture, while the vertical one provides its circulation. In the prescribed

mixer-activator the velocity of activation was significantly higher than the velocity of

circulation. Therefore, the blades must be sufficiently thick to withstand abrasion, and should be

replaced when necessary.

CIRCULATION

ACTIVATION

Fig. 1 - Schematic diagram of the mixer-activator, and the industrial mixer-activator for

producing activated mortars 140 liters (32 gal.) of the volume.

The temperature increase is usually in the range of 20oC (36

oF) - 30

oC (54

oF) after mixing for 2-

4 minutes. This is due to turbulence reduction and the presence of an energy dissipater (sand),

which causes friction to give off heat. In hard mortars with zero initial flowability, the

temperature increase during activation is a more effective indicator. This is why the temperature

of activated mixture is chosen as the basic technological parameter in [11] and [12]. The process

of activation is conducted until temperature reaches 45-50oC (113F-122

oF) due to frictional

heating [10], at which point an SP (or for expanded mortars, – SP with a gas-forming admixture)

is introduced into the mixture. The gas-forming admixture actively interacts with alkalis of

cement paste leading to the release of hydrogen and heat, consequently provoking an expansion

of the mixture. The mixture sets within a few minutes after expansion as a result of frictional and

exothermic heating.

The consumption of specific net energy in HEM (without accounting for lost energy in the

engine and transmission) depends on mix proportions and physical properties of materials. It

ranged from 22 to 45 kWh/ton of cement, which is significantly lower than in the case of

additional grinding: 60 – 120 kWh/ton of cement [1].

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Plasticizing HEM mortar

The increased viscosity of mortars prepared with additionally grinded cement is caused by

increase in total surface moistening of solid particles. Conversely, in the case of HEM, the same

effect can be explained as follows: the activated surface of solid particles of cement and sand

adsorbs more molecules of water than the non-activated one. The fact of adsorption makes this

process effective; although one should not exclude the possibility of deterioration of weak

substances and abrasion of solid particles. Both of the above processes (additional grinding and

HEM) result in a reduced quantity of unbounded water, which leads to higher viscosity of the

mixture.

Using SP to plasticize activated mortars of high viscosity is a necessary step in HEM technology.

HEM mortars require more SP to achieve the same level of flowability as non-activated ones. At

the same time, the stability of mortars is improved after activation. This useful feature, observed

in activated cement-sand mortars, makes it possible to cast small products such as roofing,

facing, and decorative tiles of any shapes and color, successfully replacing ceramics, which

require enormous expenditure of energy.

Thus, HEM creates favorable conditions for high degree of energy absorption by the mixture of

cement, sand, and water, leading to an increase in viscosity and temperature and requiring the

introduction of a SP. HEM is a type of mechano-chemical process based on an extensive surface

treatment of chemically active ingredients, which accelerates reactions of cement hydration.

EXPERIMENTAL INVESTIGATION

The primary goal of this research was to assess the effect of mechanical activation on the kinetics

of setting and strength increase of concrete and mortars in normal and low temperature

conditions. The experiment was conducted both on mixes that had only cement as a binder and

on those with cement and Class F fly ash.

Materials, mix proportions, and test methods

Materials

White Portland cement Type I, Lehigh Co, PA. Compound composition: C3S-72%, C2S-17%,

C3A-5%, C4AF-1%, Na2O+K2O-0.7%. Chemical composition: CaO-68.14%, SiO2-24.88%,

Al2O3-2.13%, Fe2O3-0.23%, K2O-0.42%, Na2O-0.28%, MgO-1.62%, LOI-1.70%, free Lime-

0.6%. Specific gravity is 3.15 g/cu cm, Blane Fineness 3670 cm2/g.

Class F Fly Ash – Cayuga AES. Chemical composition: SiO2 – 49.9%, Al2O3 – 25.97%, Fe2O3 –

10.38%, CaO – 2.53%, MgO – 1.01%, TiO2 – 1.28%, Na2O – 1.02%, K2O – 2.54%, LOI –

3.06%; specific gravity – 2.5 g/cu cm, Blane fineness – 3800 cm2/g.

Neither in conventional mixing nor in HEM did this type of fly ash demonstrate binding

properties, as studies have shown.

Dried fine and coarse aggregate were used. They were stored in room conditions.

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The control tests showed the moisture level of 0.15-0.5% for coarse and 0.20% for fine

aggregate.

“Sand for all purpose” (Quikrete) – Sand 1 and “Windham Sand” (CT) – Sand 2 were used with

Fineness Modulus respectively 2.02 and 2.57, specific Gravity SSD 2.71 g/cm3 (169.18 lbs/ft

3)

and 2.69 g/cm3 (167.93 lbs/ft

3). Specific surface of sands: 49 cm

2/g, and 36.3 cm

2/g

respectively.

Granit from Cherenzia, RI - 9.5-19mm (3/8”-3/4”), specific gravity SSD 2.642 g/cm3 (164.93

lbs/f3), 1.12 soundness, and limestone from New England Silica, Inc - 5-25mm (1/4”-1”),

specific gravity SSD 2.9 g/cm3 or 181 lbs/ft

3, 4.0 soundness were used as a coarse aggregate for

concrete.

Admixtures:

1. SPECCO W-30, Melamine-formaldehyde-sodium bisulfite copolymer “Melment”, in powder,

meets the requirements of ASTM C-494, Type F.

2. Polycarboxylic Ether “SiKa ViscoCrete 3010”, 50% aqueous solution, density 1.12, high

range water reducer that meets the requirements of ASTM C-494 Type A, F.

3. Polycarboxilate polymer ‘SiKa ViscoCrete 6100, liquid, density 1.02 meets the requirements

of ASTM C-494, Type F.

4. “ADVA-100”, High Range water Reducer, ASTM C-494 Type F. Produced Grace W.R,

5. Non-chloride hardening accelerator – SiKa Rapid-1 meets the requirements of ASTM C 494

Type C.

Admixture quantities are given in percents of cement (or cement plus fly ash) mass, as well as in

kg/m3 and lbs/Y

3 for concrete mixture.

Mix proportioning, properties of mixtures

The typical proportions of ingredients, in percents of mass for mortars and mortar component of

concrete in this experiment, are: Cement / Sand / Water = 1:2:0.37-0.38.

With fly ash as a supplemental cementitious material, the proportions were as follows:

Cement / Fly Ash / Sand / Water = 1:1:2:0.37- 0.38.

The quantity of HRWR admixture was higher in HEM mortars in comparison with the

conventional ones (as specified above). The data of concrete mixtures are given in Table 1. All

concrete mixtures were repeated twice: mixtures signed “A” included limestone aggregate, Sand

1 and SP “SiKa WiscoCrete 3010”, mixtures signed “B” had granit aggregate, Sand 2, and SP

“SiKa WiscoCrete 6100”.

Conditions of mixing

The conditions of premixing in the lab process were consistent for all variants: mixing dry

ingredients for 2 min., adding water and wet hand-mixing for about 1-1.5 min. Admixture was

introduced at the end of mixing into the control variant, and at the end of activation for the HEM

variant.

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Energy consumption: for HEM mortar with fly ash: 14.25 - 34.2 Кj / kg (6.5 - 15.5 Kj/lb) of

mixture (mixing time 2.5 – 6.0 min), for HEM mortar without fly ash: 11.5 - 26.7 Kj / kg (5.2 -

12.1 Kj/lb) of mixture (mixing time 2.0 - 4.0 min).

Using a lab mixer-activator, both mortar and mortar component of concrete were produced; the

latter was subsequently mixed manually with the coarse aggregate. In the process of activation,

temperature fluctuation and gross (net) energy consumption were continuously measured.

The experiments were conducted at ambient temperature 20-24oC (68-75.2F), 50 - 55% relative

humidity; the temperature of the control mixture was 21-23oC (70-74

oF), and the initial

temperature of HEM mixtures was 35-45oC (95-113

oF).

Test Methods

Cylinders of 76.2mm (3") in diameter and 152.4 mm (6") in height were cast from the concrete

mixture, and cubes of 50x50x50mm (2”x2”x2”) were cast from mortars. The control specimens

were prepared in the same fashion, only without activation. Curing of specimens was maintained

according to ASTM C-192/C192M-05 “Practice for making and Curing Concrete Test

Specimens in the Laboratory.” To determine the kinetics of initial and final setting for activated

and non-activated mortars, the method of penetration resistance was used according to ASTM C

403/C403M-05 “Time of setting of concrete mixtures by penetration resistance.” Compressive

strength of mortar samples was tested in accordance with “Standard Test Method for

Compressive Strength of Hydraulic Cement Mortars using 50-mm (2-inch) Specimens” ASTM C

109/C 109M-05; concrete samples: ASTM C39/C39M-05 “Standard Test Method for

Compressive Strength of Cylindrical Concrete Specimens”.

Flowability of mortars was determined according to the modified “Standard Test Method for

Flow Consistency of Controlled Low Strength Material (CLSM), ASTM D 6103-04”with a

reduced size of plastic tube - 100 mm (4”) length of 50 mm (2”) in interior diameter.

EXPERIMENTAL RESULTS AND DISCUSSION

Flowability of mortars

The results in flowability of activated and control mortars are shown in Table 2.

In the tests specified below, the quantity of SP was determined so as not to exceed the level at

which signs of bleeding begins to occur. In the activated mixture, that level is much higher than

in the non-activated and depends on the properties of the admixture (Table 2, variants 3, 4, 7, 10,

15). Some of the HEM mortars, prepared with the dosage of SP equal to the control ones,

showed a lower level of flowability (Table 2, variants 2, 6, 9, and 14). The mortars 11, 12, 13

were prepared by gradually reducing the quantity of admixture ADVA-100 (Grace W.R.). These

results illustrate how non-bleeding mixtures were achieved.

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Table 2- Flowability of mortars

Mortar

variant

Variant

of SP

Proportions of

Ingredients

W/C, or

W/(PC+FA)

SP/PC, or

SP/(PC+FA),

%

Flowability

cm/(in)

Notes

1.Control

2. HEM

3. HEM

4. HEM

SiKa

WiscoCrete

3010

PC/SAND

1 : 2

0.37 0.57

0.57

1.4

1.52

9.4 (3 ¾”)

6.0 (2 ¼”)

10cm(4”)

15.5cm(6 ¼”)

No

bleeding

5.Control

6. HEM

7. HEM

SiKa

WiscoCrete

6100

PC/FA/SAND

1 : 1 : 4

0.38 0.60

0.60

0.79

22.8 cm (9”)

9 cm (3 ¾”)

25.4 cm (10”)

No

Bleeding

8. Control

9. HEM

10.HEM

SPECCO

Melment

W-30

PC/SAND

1 : 2

0.38 0.55

0.55

1.4

15.5 cm (6 ¼”)

6 cm (2 ¼”)

22.5cm (8 ½”)

No

Bleeding

11.Control

12.Control

13.Control

14. HEM

15. HEM

GRACE.

ADVA-100

PC/SAND

1 : 2

0.38 0.86

0.75

0.65

0.75

1.02

21.5cm (8 ½”)

20.5 cm (8”)

17.5 cm (6¾”)

5.5 cm (2 ¼”)

21 cm (8 ¼”)

Bleeding

Bleeding

No bleeding

No bleeding

No bleeding

Activated mortars require more SP to achieve the same or higher level of flowability. There were

no signs of bleeding in the HEM mortars with SP quantity increased by 30% and more, as

compared to the control mortars. This was typical in mixtures prepared with all considered SPs,

which have distinct formulas. Therefore, HEM aids stability, which is very important in

flowable mortars.

Setting in normal conditions

Figure 2 shows HEM to be responsible for an extraordinary acceleration of initial and final

setting in cement mortars. According to ASTM standard C 403/C403M-05, the time of initial

setting should be determined when the penetration resistance is 3.5 MPa (500psi). Using this

criterion, the initial setting time for activated mortars was between 2.5 –6.5 hours (mortars 3,4),

depending on the quantity of SP. Starting from this point, the penetration resistance of activated

mortars with SP develops much faster, similar to the mortars without SP (1, 2). The time of final

setting in activated mortars was determined at the penetration resistance of 27.6 MPa (4000psi),

as per the ASTM standard, and took place at 4 and 8 hours in mortar with SP=0.67% and in

mortar with SP=1.25% respectively. On the other hand, for conventionally mixed mortar, the

time of initial setting was between 9-10 hours; and final setting was reached after 21-22 hours

(mortar 5, Fig. 2). The activated mortar without SP (mortar 1, Fig.2), having 0.5 hour of initial

setting ends the setting period within 1 hour after the activation is complete.

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2- Hand Mixing (SP=0.0%)

1- High-Energy mixing (SP=0.0%)

5- Hand Mixing (SP=0.67%)

4- High-Energy mixing (SP= 1.25%)

3- High-Energy mixing (SP= 0.67%)

Pen

etra

tio

n R

esis

tan

ce,

MP

a

210

20

10

40

30

53

Hours

10

80

60

50

70

90

6000

Pen

etra

tio

n R

esis

tan

ce,

psi

15 20

1000

23500

4000

2000

12000

8000

10000

14000

Fig.2 - Setting of mortars by method of penetration resistance (SP shown in percents of cement

quantity).

The initial setting time of the non-activated mortar without SP (mortar 2, Fig.2) was 1 hour,

final setting – 3 hours. Mortars 1 and 2, prepared without SP were tough, non-workable

mixtures, which were tamped during manufacturing of samples.

Setting of mortars with fly ash

Fig. 3 shows the penetration resistance of mortars with 50 % of the cement content replaced by

fly ash. The difference between mortars with SP (3, 4) and without SP (1, 2) is apparent. The

retardation activity of SP (SiKa ViscoCrete 3010) develops here similar to mortars without fly

ash (Fig 2). But initial setting of activated mortar occurs in about 14 hours, i.e. 7-7.5 hours later

because the quantity of active binder - cement is half as much. The time of initial setting for both

activated and non-activated mortars is almost the same. The crucial difference is observed after

14-15 hours, when penetration resistance of the activated mortar increases much faster (similar to

mortar without SP) than the non-activated mortar. The final setting occurs in the former after 16

hours; in the latter after 33 hours.

10

20

10

Pen

etra

tio

n R

esis

tan

ce,

MP

a

1

0

1032

40

20

30

50

2000

Pen

etra

tio

n R

esis

tan

ce,

psi

500

40

1000

30

0

7000

6000

5000

4000

3000

1- High-Energy Mixing (SP=0.0%)

2- Hand Mixing (SP=0.0%)

3- High-Energy Mixing (SP=1.0%)

4- Hand Mixing (SP=0.75%)

Fig.3 - Setting of mortars with cement and fly ash (SP shown in percents of cement + fly ash

quantity).

Analysis of results in penetration resistance of mortars with and without fly ash has shown that

the hydration reactions in activated mortar were temporarily slowed down by SP. Growing

crystals of hydration products may overcome the resistance of SP films at the time of initial

setting because of mechanical activation. The further increase of penetration resistance continues

almost parallel to curves 1 and 2 (Fig. 2, 3), i.e. similar to hard mortars without SP. Non-

activated mortars with SP develop penetration resistance more slowly and achieve final setting

significantly later than activated ones.

HEM actively accelerates setting of mortars. When working with HEM in hot weather

conditions, adding fly ash instead of a part of cement may slow the time of initial setting. A

comparison of setting development of activated mortars with and without SP shows the

important role of this admixture, and not only in the increase of flowability. SP “SiKa

ViskoCrete 3010”, for instance, works in activated mortars as a retarding admixture as well, and

may be used to control setting time.

Syneresis in activated mortars

During this study, the surface of fresh mortar samples taken from activated and non-activated

mixtures were scrutinized in relative humidity (RH) of 40-50% and 95%. Figures 4 a-d show the

exterior appearance of specimens magnified x 100.

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a) Control, just after b) Control 8 hours after c) HEM, just after d) HEM, 3hours

mixing mixing (50% R.H.) mixing after mixing.

Beginning of

setting, syneresis.

Fig.4 - Views of samples surface magnified x 100, taken during the test of penetration

resistance.

There were no immediately apparent differences between activated and non-activated mortars,

except in color: the former was paler in contrast to the yellowish tone of the latter. The white

(pale) color of fresh HEM mortar, visible under microscope, belongs to the thick layer of gel of

white Portland cement covering yellow grains of sand. The fresh control mortars show a

yellowish hue, because the color of sand grains prevails. Within 2.5-3 hours, the water drops

began to appear on the surface of the HEM mortar with 0.67% of SP (Fig. 4 d) nearly matching

the initial setting time. After 4- 4.5 hours (final setting) the drops of water were apparent even

without magnification (Fig. 5). Such discharge of water, known as syneresis, is typical in gels.

Fig. 5 - Specimens in box, 95% ambient RH, syneresis of HEM mortar - right.

Syneresis is much more noticeable in the HEM mortar, since most of the free space between hard

particles is filled with C-S-H gel. In contrast, the surface of non-activated samples appeared dry

with RH levels of both 50% or less and 90% or more.

12

According to T.C. Powers [13], when cement and water interact the thickness of the film of

water adsorbed by the surface of cement does not exceed 1.8 nm, approximately 10-13 diameters

of water molecules attracted to cement granules by the Van-der-Waals forces. T.C. Powers refer

to B.V. Deryagin, who asserts that water in this layer has properties different from the free water,

occupying the remaining volume. These ideas are substantiated by Bö Johnson’s study [14] of

the interaction between C3S particles and water, which shows the surface charge of the particles

at the distance of over 2 nm dropping almost to neutral.

Bozhenov U.M. states that the water layer potentially a 150 nm (0.15 m) thick and consisting of

molecules oriented in chains may be attracted by the surface of solid particles [15]. Considering

these data and knowing the specific surface of cement and sand, the calculated total volume of

the attracted water in 1 kg of conventionally mixed mortar (Portland cement – 296.4 g, sand –

592.9 g, water – 110.7 g) will be 17.5 cu cm, i.e. no more than 20% of water incorporated into

the mixture. Thus, 80% of free water remain incapable of producing C-S-H gel and may

potentially evaporate; resulting in micro-cracks on the surface of non-activated specimens under

50% RH within 8 hours after mixing. That is due to evaporating water and drying shrinkage (Fig.

4b). The conditions of 95% RH prevented water from evaporating and therefore cracks on the

surface. These results are consistent with the study of T.C. Powers and many other authors.

The syneresis observed on the surface of activated samples starting at 3 (Fig. 2, mortar 3) and 5-

6 hours (Fig.2, mortar 4) points to the formation gel and active growth of crystals in the cement

matrix. The modern theory of cement gel aging, as outlined in J. Thomas and Hamlin Jennings’

research [16], attributes this process to an increase in the degree of polymerization

(polycondensation) of the silicate network that frees water molecules. Using the conventional

method of mixing as their basis, the authors experienced difficulties observing syneresis, as it is

hindered by the presence of significant amounts of non-gel phases. Thus, the quantity of expelled

water may be considered as an indicator of C-S-H gel quantity in mortars. The water discharge in

HEM mortar remains unaffected by the fluctuations in ambient RH (from 48% to 95%), unlike

the conventional mixture, where water migration is influenced primarily by the changes in

relative humidity. Thus, the initial process of cement hydration in films of the water layer 1-2

nanometer thick spreads out over the entire volume of the cement - water matrix. Therefore

HEM can be considered as an effective way for industrial application nanotechnology of

concrete.

Setting of mortars in temperatures below freezing

Three cement mortars identically proportioned (Portland cement/Sand/Water = 1/2/0.37) were

tested in freezing conditions. Mortar 1 was hand-mixed with HRWR “SiKa ViscoCrete 3010”

(0.7% of PC).Mortar 2 was super plasticized, hand mixed, similarly to mortar 1, and with the

accelerator ‘Rapid-1’ varied from 25 oz/cwt to 90 oz/cwt (1.5-5.6% of cement mass). Mortar 3

was with same HRWR in the quantity 1.2% of PC, HEM for 5 minutes, with net energy

consumption of 49.5 Kj/kg (22.4 Kj/lb). After mixing, mortars 1 and 2 were stored in normal

temperature for 2 hours, before being immersed in a freezing chamber. They showed 0.5MPa (73

13

psi) and 0.35MPa (50 psi) of initial penetration resistance, respectively. Mortar 3 has shown no

penetration resistance immediately after mixing prior to being stored in a freezing chamber. In

this case, the influence of frictional heating of activated mixture on subsequent cement hydration

was ruled out. Penetration resistance tests were carried out on the specimens after they were

removed from the freezing chamber and left to thaw for 1.5 hours (melting time of ice). The

temperature in the freezing chamber was kept constant at about -13oC (8

oF). The test results are

shown below in Figure 6. The average results for mortar 2 with accelerator ‘Rapid-1’, based on

the data of 5 mortars with the dosages of this admixture indicated above, are presented.

In comparison to the hand-mixed mortars (with and without accelerator ‘Rapid-1’), the

penetration resistance of activated mortar develops much faster after 8 hours of freezing, i.e. the

liquid phase remains active and does not freeze. This is likely due to the fact that the liquid phase

in HEM mortar is mainly represented by the C-S-H gel with its the smallest capillary pores filled

with a supersaturated solution, and water bound by the solid particles. Under the same

conditions, all unbound (bulk) water contained in pores and capillaries of the ordinary mixture

will freeze, its freezing point being no lower than -8oC (17.6

oF) according to Olson et al [17].

According to this author’s data, the water freezes in the smaller capillary pores at –23oC (-9.4F);

the freezing of supersaturated solution in gel pores occurs at –40oC (-40

oF). This will

conceivably apply to the entire liquid phase in the HEM mortar. Therefore, the initial process of

cement hydration in freezing conditions of -13oC (8.6

oF) for HEM mortar is much more

intensive (Fig. 6, mortar 3).

50

30

20

10

0

Pen

etra

tion

Res

ista

nce

, ps

i

3Hand Mixing

(mortar 1)

21

15 20

High-Energy Mixing

(mortar 3)

Hand Mixing

w/Rapid 1

(mortar 2)

5000

40

7000

8000

6000

4000

10

Hours

50

1000

3000

2000

Pen

etra

tion

Res

ista

nce

, M

Pa

Fig. 6 - Penetration resistance in freezing conditions -13oC (8.6F)

Aside from penetration resistance, a strength increase in concrete under freezing conditions was

also observed. Activated and non-activated mortars without accelerator were used as the mortar

14

part for preparing two variants of concrete by adding coarse aggregate into ready mortars. Final

mixtures: Portland cement – 415 kg/m3 (704 lbs/Y

3), sand – 830 kg/m

3 (1400 lbs/Y

3), limestone

aggregate – 1106 kg/m3 (1865 lbs/Y

3), water -153 kg/m

3 (257 lbs/Y

3) were used to prepare

samples of concrete. HRWR SiKa 3010(50%) was added in quantity of 7.43 kg/m3 (12.52

lbs/Y3) into control mixture, and 14.1 kg/m

3 (23.8 lbs/Y

3) into activated mixture. All samples

were placed in freezing chamber at -13oC (8.6

oF) for curing. The compressive strength tests were

completed after removing samples and thawing them at room temperature for 1.5 hours (melting

time of appropriate quantity of ice). Even after 28 days, it was impossible to remove the

specimens of hand-mixed concrete intact from the molds, due to their lack of strength. The

activated concrete specimens were removed from the plastic molds after 3 days of storage in the

freezing chamber and showed 141 psi (1.0 MPa) of average strength. Those kept for 28 days

showed 429 psi (3.0 MPa).

Thus, the process of cement hydration took place in the temperature much lower than 0oC. It is

consistent with Deryagin’s data on the significant change in the properties of water in boundary

layers, including freezing temperature. In [18] he states that the Van-der-Waals forces,

electrostatic forces, and hydrogen bonds of water molecules to atoms of solid substrate are

responsible for these phenomena. It is likely that mechanical activation by HEM favorably

amplifies these factors. Further investigation is required to estimate their role in HEM

technology.

Strength increase at low temperatures

To assess the kinetics of concrete strength increase at temperatures between 0 and 5oC (32-41

oF),

the specimens of concrete, proportioned as mentioned above, were stored at +3о С (37

oF).

Figure 7 shows data on compressive strength after 3 and 28 days in low temperature conditions.

The Manual for Highway Construction of AASHTO («Cold Weather Concreting») recommends

discontinuing the placing of concrete at temperatures below +4.4

Co (40

oF). By contrast, HEM

makes concreting at low temperatures possible.

15

Com

pres

sive

Stre

ngth

, MPa

5

10

15

20

25

45

35

30

40

Com

pres

sive

Stre

ngth

, psi

28 days3 days

1000

2000

3000

Hand Mixing

High-Energy Mixing

5000

4000

6000

7000

Fig. 6 - Development of strength in activated and non-activated concrete

at +3oC (37.4F).

Strength of concrete and mortars with High Volume Fly Ash (HVFA)

It is well known that the principal disadvantage of using fly ash in concrete is its impact on early

strength [3]. In connection with this, experiments were conducted to determine a way to speed up

the HVFA binder hydration. In these mortars, 50% of total cementitious materials were replaced

by class F fly ash.

The following variants were compared:

- Mortar without fly ash (100% Portland cement type 1), conventional mixing

- Same mortar, aсtivated by HEM

- Mortar with 50% fly ash, conventional mixing

- Same mortar, activated by HEM

With conventional mixing, no improvement in workability was observed with fly ash, in contrast

to the mortar without fly ash. This fact made it impossible to lower the water quantity. The ratios

of water to cementitious materials (0.38:1) and of cementitious materials to sand (0.5:1)

remained the same in all the variants.

16

Cement 50%,FA 50%, conv.mixing

Cement 50%, FA 50%, HEM

Cement 100%, conv.mixingC

om

pre

ssiv

e s

trength

, M

Pa

30

10

0

20

70

50

40

60

80

Cement 100%, HEM

Com

pre

ssiv

e s

trength

, psi

4000

2000

0

10000

8000

6000

12000

1 3 28 60 90 days

Fig. 8 - Compressive strength of activated and non-activated mortars.

Table 1- Mix Proportions and properties of concrete

Variant

of concrete

Ingrédients

Quantity,

kg/cu.m.*

A B

Plastic

Density

kg/cu.m*

A B

Air, %

Slump, in

Vebe, sec.

A B

1.Cement 100%,

Conventional

mixing

Cement

Sand, QuiKrete

Water

Aggr: Limestone

Granit

SiKa 3010

SiKa 6100

408 410

815 821

155 157

1094

1046

7.8

2.77

2427 2490

1.8 2.54

0.0

25 - 30

17

2.Cement 70%,

Fly Ash 30%

Conv. mixing

Cement

Fly Ash

Sand, Windham

Aggr: Granit

Water

SiKa 6100

268

134

803

1031

150

2.73

2389

2.41

0.0

25 - 30

3.Cement 70%,

Fly Ash 30%

HEM

Cement

Fly Ash

Sand, Windham

Aggr: Granit

Water

SiKa 6100

272

136

815

1046

152

4.16

2425

0.74

0.0

15 - 20

4. Cement 50%

Fly Ash 50%,

HEM

Cement

Fly Ash

Sand, Quikrete

Water

Aggr: Limestone

Granit

SiKa 3010

SiKa 6100

202 205.3

202 205.3

808 821

151 156

1095

1038

10.9

4.81

2406 2494

0.98 0.65

0.0

10 - 15

5. Cement. 50%

Fly Ash 50%,

Conv. Mixing

Cement

Fly Ash

Sand, Quikrete

Water

Aggr: Limestone

Granit

SiKa 3010

SiKa 6100

199.5 200

199.5 200

798 802

149 152

1069

1025

7.6

2.71

2373 2431

3.3 2.49

0.0

20 - 25

*)Lbs/Y3 = 1.683kg/m

3

Figure 8 shows a significant increase in strength after the first 24 hours and over the next 3, 28,

60 and 90 days, when activation by HEM was used. This increase occurs in both mortars with

50% fly ash in the binder, and in those completely without fly ash.

The accelerating effect was attained not only in mortars, but also in concrete where the mortar

component was high energy-mixed (Fig. 9). The main difference between proportions of HEM

and hand-mixed concrete is the increased quantity of HRWR admixture that results from a higher

stability of mechanically activated mixtures (Table 1). In activated mixtures, there is evidence of

a higher specific gravity and a lower entrained air quantity, as compared to non-activated

mixtures. All concrete mixtures were characterized by similar consistency – zero slump in all,

and workability by the Vebe method, of 10-20 sec. for HEM mixtures, and 20-30 sec. for control

mixtures. Each variant was repeated at least 6 times (3 times with granite coarse aggregate and 3

18

times with limestone one), except the mixes with 30% of Portland cement replaced by fly ash,

which were repeated 3 times with granite coarse aggregate.

The results in strength of concrete (Fig. 9) are shown in form similar to the results of PPC

strength tests given in [3; page 169; Fig. 7], prepared with vibratory milled fly ash, in order to

easily compare the effectiveness of HEM vs. High-Energy milling.

H

C

Com

pre

ssiv

e S

tren

gth

, psi

C

50%

H

30% 0%

28 days

1000

0

2000

4000

3000

5000

6000

H

C

50%

H

30% 0%

15

10

20

30

25

35

40

0

5

3 days

C

Com

pre

ssiv

e S

tren

gth

, M

Pa

C - conventional mixing, H - HEM

C

C

- mixes A with granit and SiKa-6100

- mixes B with limestone and SiKa-3010

Quantity of fly ash, class F

Fig. 9 - Compressive strength of activated and non-activated concrete.

According to the data on strength (Fig. 9), concrete with an activated mortar component

containing 30% and 50% of Class F fly ash showed 5000 psi (30-35 MPa) 28 days compressive

strength, which is no lower than the control concrete without fly ash. This is true in both kinds of

coarse and fine aggregates as well as HRWR admixtures most often used in concrete.

The consumption of energy during activation was about 18.5 kWh per cu. m of concrete or 45

kWh per 1 ton of cementitious materials (not accounting the energy loss in motor and

transmission). These data were compared with the method of additional cement grinding

characterized by the same level of energy consumption (Table 3), calculated from formulas of

concrete strength gain given in [1].

Table 3-Strength increase with the different methods of activation (* data are taken

from L. Lindström and B. Westerberg [1])

19

VARIANT

Effect of Strength increase, %

24 hours 3 days 28 days

1.Fine Ground

Cement *

22.5

13.9

5.6

2.Cement 100%,

HEM

68

33

25

3.Cement 50%, FA-

50%, HEM

132

56

37.6

The above data shows that activation by HEM is more effective than the method of additional

grinding, in terms of the relative increase in strength.

Taking into consideration the results in strength of samples that contained HVFA (Fig.9), we

conclude that, when activation by HEM is used, up to 50% of cement (202 kg per cubic meter or

341 lbs/Y3.) could be replaced with class F fly ash without losing strength. The energy consumed

in manufacturing this quantity of cement would total 314 kWh (calculated using data from [8]).

Given the 12.6 kWh of gross energy consumed during activation of this quantity of cement by

HEM (expected energy losses of 40% included), the actual amount of saved energy is

approximately 300 kWh per 1 cubic meter (230 kWh per 1 Y3) of concrete.

FURTHER RESEARCH

An increased volume of gel content in mechanically activated mortar component might reduce

capillarity in concrete. This phenomenon will help avoid penetration by the chlorine ion, as well

as reduce cracks forming in concrete under high and dynamic loads. These two points require

further investigation. The study of relevant mechanical properties such as static modulus of

elasticity, Poisson’s ratio in compression, as well as creep and shrinkage should be carried out.

There are some preliminary results after conducting freezing/thawing tests of HEM concrete with

and without fly ash. These tests should be continued with the aim of obtaining reliable data on

the durability of HEM concrete. HEM technology and High-Energy milling of fly ash [3], both

result in lower Portland cement consumption and should be investigated in combination to see if

this effect will amplify.

Another area worth investigating is the benefit that the increase in volume of the C-S-H gel

might bring to the field of Portland cement solidification and stabilization of hazardous waste

consisting of heavy metals as was shown in [19].

CONCLUSION

1. Based on the abovementioned experiments, it was suggested that the indices of

flowability reduction, temperature increase, and specific energy consumption should be used to

monitor the process of HEM.

2. HEM can potentially increase volume of bound water to form the C-S-H gel. Therefore, the

classical nano-process of initial cement hydration in conventional technology is spreading in the

20

entire volume of the cement-water suspension in concrete. HEM can be considered as an

effective way for industrial application nanotechnology of concrete.

3. HEM is effective for High Volume Fly Ash concrete. Though lacking in binding properties,

Class F Fly Ash could be used for partial (up to 50%) replacement of cement.

4. The proposed method successfully accelerates the process of cement hydration, even in

low temperatures and also under freezing conditions.

5. After in-plant approbation, HEM is recommended for casting cement-sand roof and siding

tiles, paving stones (to substitute ceramic materials), as well as HVFA expanded mortar to

replace lightweight aggregate concrete.

6. High-energy mixing of mortar or mortar component of concrete during several minutes in

specially designed mixer-activator may be considered as a more energy-effective method,

alternative to additional grinding of Portland cement.

REFERENCES

[1] L. Lindström and B. Westerberg, “Fine Ground Cement in Concrete-Properties and

Prospects,” ACI Materials Journal 100 (5) (2003), pp. 398-406.

[2] K. -B. Park, J.L. Plawsky, H. Littman, J.D. Paccione, “Mortar properties obtained by dry

premixing of cementitious materials and sand in a spout-fluid bed mixer,” Cement, Concrete

Research. 36 (4) (2006), pp. 728-734.

[3] Rakesh Kumar, Sanjay Kumar, S.P. Mehrotra, “Towards sustainable solutions for fly ash

through mechanical activation. Review,” Resources Conservation & Recycling 52 (2007).

pp.157-179.

[4] Zivko Sekulic, Svetlana Popov, Mirjana Duricic, Aleksandra Rosic, “Mechanical activation

of cement with addition of fly ash,” Materials Letters 39 (1999), pp. 115-121, Elsevier.

[5] H. Hodne, A. Saasen, A.B. O’Hagan, S.O. Wick, “Effects of time and shear energy on the

rheological behavior of oil well cement slurries,” Cement Concrete Research 30 (2000), pp.

1759-1766.

[6] M.L. Brown, H.M. Jennings, W.B. Ledbetter, “On the generation of heat during the mixing

of cement pastes,” Cement Concrete Research 20 (1990), pp. 471-474.

[7] Gary R. Mass, “Premixed Cement Paste,” Concrete International 11 (1989), pp. 82-85.

[8] N. Martin, E. Worrell, L. Price, “Energy Efficiency and Carbon Dioxide Emissions

Reduction Opportunities in the U.S. Cement Industry,” Ernest Orlando Lawrence Berkeley

National Laboratory, 9 (1999), p.3

[9] G. Frohnsdorff, “Blended cements,” ASTM International (1986), p.19.

[10] V.V. Fridman, K.M. Katz, “Method of producing of agitated mineral binder,” Certificate of

Invention, USSR #1668344 8/1991.

[11] V.V. Fridman, F.M. Krantov, I.M. Reznikov, “Metod V.V. Fridman dlia proizvodstva

aktivirovannoi stroitel’noi smesi,” Patent #2017701, Russian Federation, 8/1994.

[12] V.V. Fridman, “Method for producing construction mixture for concrete,” Patent USA

#5,443,313 8/1995

21

[13] T.C. Powers, “Nature of Concrete,” Concrete and concrete – making materials, 1966, pp.

61 – 72.

[14] Bo Jösson, “Cement – The real Nanotechnology,” Abstract,

http://www.fos.su.se/%7Egunnar/seminarier/Abstract.pdf

[15] Bazhenov U.M.” Technology of Concrete,” Moscow, “Vysshaja shkola”, 1978, pp.51-52

[16] Jeffrey J. Thomas, Hamlin M. Jennings, “A colloidal interpretation of chemical aging of the

C-S-H gel and its effects on the properties of cement paste,” Cement and Concrete Research 36

(2006), pp. 30-38.

[17] R.A. Olson, B.J. Christensen, R.T. Coverdale, S.J. Ford, G.M. Moss, H.M. Jennings, T.O.

Mason, E.J.Garboczi, “Interpretation of the impedance spectroscopy of cement paste via

computer modeling III: Micro structural analysis of frozen cement paste,” Journal of Material

Science 30, (1995), pp. 5078-5086

[18] Deryagin B.V., Churaev N.V., Zorin Z.M., “Structure and properties of boundary layers of

water,” Izvestiya Akademii Nauk SSSR, Physical Chemistry, No. 8 (1982), pp.1698-1710

[19] W.A. Klemm “Ettringite and Oxyanion-Substituted Ettringites – Their Characterization and

Applications in the Fixation of Heavy Metals…” Portland Cement Association 1998, pp. 2, 7, 42