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Expected increase in the volume of C-S-H gel with High-Energy Mixing (HEM)

“For C-S-H it is widely accepted that the nano scale structure controls many engineering properties such as the

elastic module, creep and drying shrinkage” (Hamlin M. Jennings, Jeffrey W. Bullard “From electrons to

infrastructure: Engineering concrete from the bottom up,” Cement and Concrete Research, 2011)

The HEM technology (see the invention US2013-0305963A1) is an effective way to increase and/or establish a

required quantity of C-S-H gel starting from the volume observed in conventional mixing technology. The HEM

technology begins and ends during the process of mixing. The main idea of HEM is to provide the most favorable

conditions for absorption of the mechanical energy by the mixture. With increased energy absorption, cement particles

attract more water, resulting in deeper and faster hydration of cement accompanied by an increased volume of nano-

structured C-S-H gel.

Thus, it is necessary to evaluate the effectiveness of different HEM processes and compare them with conventional

mixing.

According to R.A. Olson et al. “Interpretation of the impedance spectroscopy of cement paste via computer

modeling” in Journal of Material Science 30, 1995, page 5081, the process of cement hydration continues at the

temperature below 0oC, where the freezing of bulk water in the macro-pores ends at -8

oC because of the high ionic

strength of the pore solution.

The supersaturated solution filling smaller capillary pores of the C-S-H gel freezes between -23oC and -40

oC.

Therefore, the reactions of cement hydration are able to continue there at the range of temperature from - 8oC to -23

oC

where the aforementioned solution doesn’t freeze.

How penetration resistance (ASTM C403) develops characterizes setting and hardening of cement paste or mortar.

One indicator of the cement hydrations in capillary pores of C-S-H gel is the continuing increase in penetration

resistance at the range of temperature shown above.

To compare the process of C-S-H gel formation in the mixtures activated with HEM with conventionally mixed, the

author placed samples of both mixes in a freezing camera at temperature -15oC during 96 hours, determining

penetration resistance after every 24 hours. These tests were done after thawing frozen samples during approximately

one hour with the increase of temperature of mixes from -15oC to +15

oC. See results Fig 1, 2.

Fig 1. Penetration Resistance development at temperature below -8oC for cement-water mixture.

Conditions: W/C = 0.297, Superplasticizer SiKa 6100-1ml/kg of activated and control mix,

Time of activation 3.5 min,

Average speed N = 2464 rpm,

Average Absorbed Power = 407 wt/Kg, Efficiency coefficient = 0.63,

Average Re number = 161,

Average Power number = 1.48.

Increase of graph area (Fig 1) for activated mix in comparing with regular one is 96%. Thus the expected increase of

C-S-H gel volume is almost 2 times as a result of High-Energy Mixing.

0

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7000

8000

9000

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0 20 40 60 80 100

Pe

ne

trat

iion

Re

sist

ance

, psi

Hours

Penetration Resistance at -15oC

Act. Psi

Contr. Psi

Fig 2. Penetration Resistance development at temperature below -8oC for cement-sand-water mixture.

Conditions: C/W/S = 1.0/0.376/2.0, Superplasticizer ADVA-190 4 ml/kg of activated mix, 1.8 ml/kg of control mix.

Time of activation 4 min,

Average speed N = 1695 rpm,

Average Absorbed Power = 132 wt/Kg, Efficiency coefficient = 0.39,

Average Re number = 141,

Average Power number = 0.73.

Increase of graph area (Fig 2) for activated mix in comparing with regular one is 213%. Thus the expected increase of

C-S-H gel volume as a result of High-Energy Mixing is more than 3 times.

CONCLUSION: An increase in the volume of the nanostructured C-S-H gel is the basic result of The High-Energy

Mixing of cement based mixtures under the conditions of quasi laminar flow when the Re number less than 800

according the invention US 2013-0305963A1.

0

1000

2000

3000

4000

5000

6000

7000

0 20 40 60 80 100 120

Pe

ne

trat

ion

Re

sist

ance

, psi

Hours

Penetration Resistance at -15oC

Act.psi

Contr. Psi