The concrete structure has a vertical structure, such as a foam layer shear wall or column, and a mortar layer or a foam layer appears on the upper surface, and there is no coarse aggregate. Reasons: polycarboxylate superplasticizer content is high and contains a lot of gas; polycarboxylate reacts with cement grinding aids to produce air bubbles; concrete is excessively vibrated, slurry floats, aggregate sinks, and concrete appears to be separated and stratified. The surface layer has a lot of slurry, accompanied by a large number of air bubbles, and forms a non-strength foam layer after hardening.
Suggestion: Polycarboxylate superplasticizer will entrain some air in the matrix during the production process. The procedure of “eliminate first and then introduce” should be adopted. Before using the polycarboxylate superplasticizer, the gas content of the concrete should be determined according to the actual situation, the state of the concrete should be observed, the mix ratio of the concrete should be adjusted or the performance of the admixture should be adjusted.
When using polycarboxylate superplasticizer, the control of water consumption and dosage should be strengthened to prevent segregation and delamination of concrete mixture. Changes in concrete slump When the amount of polycarboxylate high-efficiency superplasticizer remains unchanged during the concrete production process, the state of the concrete mixture will change greatly, suddenly fluidity or segregation. Or the slump is too small.
Reason: Polycarboxylate superplasticizers are sensitive to changes in sand thickness and mud content. The quality of the sand suddenly becomes better (for example, the amount of mud is reduced, and the fineness modulus of the sand becomes larger), or a sudden increase in the water content causes a sudden increase in the fluidity of the concrete, or even isolation. Instead, the quality of the used sandstone suddenly deteriorated. If the slurry content or fineness modulus becomes smaller, the fluidity of the concrete becomes smaller.