The role of defoamer in cement-based materials

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A large number of poorly structured bubbles are the most important factors that reduce the working performance, mechanical properties and durability of cement-based materials, which are mainly reflected in the following three aspects.

(1) When the cement paste is seriously foamed, the foam gathers at the pump output to form an air cushion, causing the pump to run idling and the construction to be blocked;
(2) A large number of bubbles increase the volume of cement paste, but these bubbles are easy to burst, causing volume shrinkage and deformation;
(3) A large number of bubbles will lead to a decrease in the density of the cement paste, which will reduce the mechanical properties and durability of the hardened cement paste.

Gas bubbles are generally present in the cement paste in two forms. One is that when the buoyancy of the bubble is greater than the blocking force of the cement paste to the gas phase, the bubble floats up and gathers on the liquid surface to form a continuous visible bubble. Such bubbles are prone to produce honeycomb pockmarked surfaces, resulting in defects in the apparent quality of cement-based materials. The other is that when the cement paste produces a sufficient blocking effect on the gas phase escape, the bubbles are discontinuously dispersed in the cement paste. Such bubbles can significantly reduce the density of cement-based materials, and have a negative impact on the mechanical properties and durability of the materials.

Defoamer is an admixture that can help reduce the large bubbles entrained or generated during the mixing and construction of concrete and mortar. The defoaming agent is composed of a substance capable of reducing the surface tension of the liquid phase, and functions by suppressing the formation of bubbles and breaking the bubble film. Defoamer is the most direct and effective means to eliminate harmful bubbles in cement-based materials. The defoaming agent is used to eliminate harmful large bubbles and optimize the pore structure, so that the hardened cement-based material can meet the requirements of smooth surface, no honeycomb pitting surface, good homogeneity, good mechanical properties and durability.

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