Concrete bleeding and segregation is mainly due to insufficient cohesion of the cement paste in the concrete, and the concrete has poor segregation resistance and stability. The mix ratio, raw material properties, production and construction technology of concrete are closely related to the bleeding and segregation resistance of concrete.
Usually, when the concrete porosity is large, it not only has poor strength, but also increases bleeding. For example, when the concrete gradation is unreasonable, the sand rate of the concrete is low. Or the amount of cementitious material is too low and the slurry cannot fully wrap the aggregate. Another example is the small specific surface area of cementitious materials. This undoubtedly provides a convenient channel for free water floating in the concrete. This makes the concrete more prone to bleeding and segregation. At the same time, the increase in porosity will also lead to a decrease in the cohesion of concrete.
Usually in commercial concrete, when the concrete bleeds, adding a certain amount of air-entraining agent will solve the problem, because a good air-entraining agent will add water to the concrete. High-quality small bubbles are introduced into the concrete, and the bubbles can wrap the free water moving upward in the concrete and stabilize it around the bubbles. Moreover, as the air content increases, the concrete will become denser, and the air bubbles will fill the voids in the concrete, blocking the floating channels of some free water.
When the amount of free water in concrete increases and the water-cement ratio is too large, the fluidity of the cement slurry increases but the cohesiveness, water retention, and resistance will become worse. Unable to withstand the sinking force of coarse aggregate in concrete, leading to bleeding and segregation.
The longer the setting time of concrete, the longer it takes for the aggregate to settle, and the easier it is for bleeding to occur. If cement takes a long time to set, the C3A content is too low. Excessive retarder in the pumping agent will have a great impact on the bleeding of concrete.
The compatibility between admixtures and raw materials is mainly reflected in the adsorption and dispersion effects of cement particles and admixtures. If the adsorption effect is too strong, the slump loss of concrete will be rapid. If the dispersion effect is too great, bleeding and hardening will occur, such as over-doping of water-reducing agent.
When there is insufficient vibration, honeycombs and holes will appear in the concrete, which will affect the strength of the concrete. However, excessive vibration will aggravate the settling water of the aggregate in the concrete and lead to the phenomenon of bleeding and segregation of the concrete. Bleeding of concrete caused by excessive vibration.
<img src="/upfile/202304/2023041334528065.jpg"/
微信扫一扫打赏
Chinese