(1) Aggregate quality fluctuates. In the process of concrete production, often encounter sand aggregate quality fluctuation, such as mud content becomes larger or smaller, water content fluctuation, aggregate gradation change, sand fineness modulus change and so on are likely to increase the possibility of concrete bleeding.
(2) Polycarboxylic superplasticizer is sensitive to ambient temperature and has a slow release. Compared with other water - reducing agents, the water - reducing and slump - preserving properties of polycarboxylic acid water - reducing agent are greatly affected by temperature. When the temperature is high in summer, the slump of polycarboxylic acid superplasticizer with good slump protection performance may occur when the temperature suddenly drops.
(3) Add water reducer to adjust the slump. The use of polycarboxylic acid two add adjustment, sometimes can not be reasonable to grasp the amount of use, more than the theoretical requirements of admixture, excessive jianshuiji still play a role in the concrete pouring, the part of the water in the concrete precipitation.
(4) When polycarboxylic acid superplasticizer is mixed, the retarder is used improperly. In order to make concrete get good slump protection performance, a certain amount of retarding component is often added when polycarboxylic acid superplasticizer is mixed. Slow coagulate component dosage is too large, perhaps the polycarboxylic acid of compound when temperature is better reduces water agent encounters temperature suddenly when, excessive slow coagulate component can make cement hydration slow down, cause concrete to bleed water.
(5) the compatibility of cement and polycarboxylate superplasticizer. Concrete components are complex between the components of the incongruous chemical changes, especially cement and polycarboxylic acid superplasticizer compatibility, performance is particularly prominent. If cement and poly carboxylic acid compatibility is poor, will increase the saturated mixing amount of admixture, excess water reducer will extend concrete initial set time, at the same time, the free water in concrete precipitation. In addition, when the soluble alkali in cement is low, the hydration rate of cement becomes slow, and the phenomenon of lagged bleeding often occurs.
Above is the polycarboxylic acid cause concrete bleed water reason, want to know the polycarboxylic acid effect on concrete bleed water is very limited, and the influence of concrete durability is very important. From the mechanism of bleeding, it can be known that after the water from the inside of the concrete to the surface, the concrete forms a channel from the inside to the outside. These passages can reduce the resistance of concrete to osmosis.
