The shrinkage, cracking and water absorption of foam concrete are three closely related problems. The factors affecting shrinkage, cracking and water absorption of foam concrete mainly include the following aspects: the influence of cement dosage; the influence of cement type; the influence of aggregate.
(1) Impact of cement consumption
The volume of solid phase of ordinary Portland cement increases during hydration hardening, while the cement + water system shrinks. Secondly, the cement hydration process is accompanied by a thermal effect, causing the initial volume to expand and shrink when cooled, resulting in an increase in apparent shrinkage.
In addition, there is self-shrinkage caused by self-water absorption during cement hydration. Therefore, under normal circumstances, if other conditions are basically the same, the amount of cement increases, the shrinkage of foam concrete will increase accordingly, and cement is also one of the important factors to ensure strength, so there is a suitable range of cement dosage.
(2) Impact of cement types
Not all the volume of the cement before and after hardening is shrinking. The volume of the expanded cement does not shrink but expands before and after hardening. Therefore, if an appropriate amount of expanded cement is used, the shrinkage of the foamed concrete as a whole can be compensated for or alleviated to some extent.
(3) The influence of aggregates
Actual statistics of experiments and engineering show that the shrinkage rate of ordinary cement concrete is small, the shrinkage rate of cement paste is large, and the shrinkage rate of foam concrete is large. This is because ordinary concrete is mixed with a large amount of coarse aggregate, and the total volume of the cement paste without aggregate is reduced before and after hardening.