Volume Changes of the Plastic Paste

The reaction of cement with water causes the general reduction of this mixture volume. It can be calcirlated based on the specific density of substrates and cement hydration products. These volume changes are called the chemical shrinkage or contraction and are linked with the lower water volume in the hydrated phases as compared to its volirme in the liquid phase. On the base of contraction of cement mixture with water the progress of hydration reaction can be determined and even the strength of concrete [108]. 

Contraction depends on the phase composition of cement. CjA has the highest contraction and C2S— the lowest one. Contraction can be calculated from the molecirlar mass and densities of the substrates and of hydration products of cement corrstituents reactions with water. At simplified assumption that the tobermorite C3S2H3, with derrsity 2.44 g/cm is the product of C3S and C2S reaction with water we have  

Cement Reduction of volume in relation to initial volume, %  

The contraction is linked with the hydration rate, therefore the rate of contraction increases with the CjA and CjS share, fineness of cement and w/c ratio. Typical data for Portland cement and calcium aluminate cement are listed in Table 5.5 [38]. 

The plasticizers decreasing the intensity of bleeding influence simultaneously on the reduction of settlement of solid paste components, which leads to the decrease of shrinkage [109]. 

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