Setting of mortars in Freezing Temperature
Three mortars proportioned Cement : Sand : Water : HRWR = 1 : 2 : 0.36 : 0.007 were tested in freezing conditions.
Mortar 1 - hand-mixed
Mortar 2 - hand mixed with addition of accelerator Rapid-1 (25 oz/cwt).
Mortar 3 - High-Energy mixed for 5 minutes with the specific power 165 watt/kg.
Mortars 1 and 2 were immersed in freezing camera 2 hours after mixing. They showed 70 psi and 50 psi of penetration resistance respectively.
Mortar 3 was immersed in freezing camera right after mixing with 0 psi of penetration resistance. The subsequent tests of samples removed from the camera were carried out after thawing for 1.5 hours.
The temperature in freezing camera was suspended constant at about 8.6 oF (-13oC). The test results are shown below.
The accelerator does not work properly at such low temperature during freezing (Mortar 2). Some increase in penetration resistance of Mortar 1 (without accelerator) was evident at the beginning of cement hydration, as some water was adsorbed by cement particles.
Conclusion.
High-Energy mixing causes massive adsorption of water molecules. The freezing point of adsorbed water is much lower than the one of free water. Therefore, the initial process of cement hydration in freezing conditions, 8.6oF (-13oC), for High-Energy-mixed Mortar 3 is much more intensive. How this phenomenon develops in terms of the strength of concrete, hardening in freezing conditions, will be the subject of further investigation.
Setting of mortars in Freezing Temperature
Three mortars proportioned Cement : Sand : Water : HRWR = 1 : 2 : 0.36 : 0.007 were tested in freezing conditions.
Mortar 1 - hand-mixed
Mortar 2 - hand mixed with addition of accelerator Rapid-1 (25 oz/cwt).
Mortar 3 - High-Energy mixed for 5 minutes with the specific power 165 watt/kg.
Mortars 1 and 2 were immersed in freezing camera 2 hours after mixing. They showed 70 psi and 50 psi of penetration resistance respectively.
Mortar 3 was immersed in freezing camera right after mixing with 0 psi of penetration resistance. The subsequent tests of samples removed from the camera were carried out after thawing for 1.5 hours.
The temperature in freezing camera was suspended constant at about 8.6 oF (-13oC). The test results are shown below.
The accelerator does not work properly at such low temperature during freezing (Mortar 2). Some increase in penetration resistance of Mortar 1 (without accelerator) was evident at the beginning of cement hydration, as some water was adsorbed by cement particles.
Conclusion.
High-Energy mixing causes massive adsorption of water molecules. The freezing point of adsorbed water is much lower than the one of free water. Therefore, the initial process of cement hydration in freezing conditions, 8.6oF (-13oC), for High-Energy-mixed Mortar 3 is much more intensive. How this phenomenon develops in terms of the strength of concrete, hardening in freezing conditions, will be the subject of further investigation.
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