About the segregation of concrete! ! ! ! ! ! ! ! ! ! ! !

Concrete segregation refers to the phenomenon that the cohesion between the components of concrete mixture is not enough to resist the sinking of coarse aggregate, and the components of concrete mixture are separated from each other, resulting in uneven internal composition and structure. Usually, coarse aggregate and mortar are separated from each other, such as dense particles deposited at the bottom of the mixture, or coarse aggregate is separated from the mixture as a whole.

Reason: The causes of segregation may be improper pouring and vibrating, the maximum particle size of aggregate is too large, the proportion of coarse aggregate is too high, the content of cementing material and fine aggregate is low, the density of coarse aggregate is too high relative to fine aggregate, or the mixture is too dry or too thin. Using mineral admixture or air entraining agent can reduce segregation tendency.

Harm: it affects the pumping performance of concrete, causing tank sticking and pipe plugging, affecting the construction period, etc. , reduce economic benefits. It affects the appearance effect of concrete structure, such as sand grains, aggregate exposure and steel bar exposure on the concrete surface. The strength of concrete is greatly reduced, which seriously affects the bearing capacity of concrete structure, destroys the safety performance of the structure, and seriously causes rework and huge economic losses. The poor homogeneity of concrete leads to different shrinkage in different parts of concrete, which is easy to produce concrete shrinkage cracks. Especially in the construction of concrete floor slab, due to concrete segregation, the surface cement slurry layer thickens, the shrinkage increases sharply, and serious cracks appear. The durability of concrete such as impermeability and frost resistance is greatly reduced.

Causes and countermeasures of concrete segregation: As we all know, ordinary concrete is mainly composed of cement, water, coarse and fine aggregate, admixture and other materials; Pumping concrete is made of ordinary concrete by adjusting aggregate gradation, sand ratio and adding a certain amount of fly ash. In addition to the mixing method and mixing time, concrete segregation is generally more closely related to the cementing material quality of concrete mixture, excessive water consumption, poor gravel grading and excessive water reducing agent content.