The causes and solutions for the problems of bleeding and segregation in concrete

1. Causes of occurrence

(1) When the fineness of cement is high, it is prone to bleeding. When the content of C3A in cement is low, it is also prone to bleeding. When the water requirement for the standard consistency of cement is small, it is also prone to bleeding.

(2) Small amounts of cement are prone to bleeding.

(3) Concrete with low-grade cement is more prone to bleeding than that with high-grade cement (at the same dosage).

(4) For concrete of the same grade, concrete with high-grade cement is more prone to bleeding than that with low-grade cement.

Concrete with a relatively large unit water consumption is prone to bleeding and segregation.

(6) The temperature of the concrete mixture is too high, especially in summer when the temperature is high, the hydration reaction is fast and the slump loss is large.

Concrete with a low strength grade is prone to bleeding.

Concrete with a low sand ratio is prone to bleeding and segregation.

(9) The concrete bleeding caused by continuous particle size crushed stone is less than that caused by single particle size crushed stone.

Concrete with poor water retention, thickening and air-entraining properties of admixtures is prone to bleeding.

Concrete with excessive admixtures is prone to bleeding and segregation.

(12) Some models of mixer trucks have poor mixing performance. After a certain distance of transportation, when the concrete mixture is initially discharged, there is a significant phenomenon of coarse aggregates floating up.

(13) There is accumulated water in the mixing drum of the concrete mixer truck, which is not drained completely before loading materials or water is added to the mixing drum at will during transportation.

2. Solutions

The fundamental approach is to reduce the water consumption per unit.

(2) Increase the sand ratio and select a reasonable sand ratio.

(3) In hot summer, measures should be taken to lower the temperature of the concrete mixture.

(4) Increase the amount of cement or add an appropriate amount of Grade I and II fly ash.

(5) Continuous graded crushed stones are adopted, and the content of needle and flake particles is small.

(6) Improve the performance of concrete admixtures to make them have better water retention and thickening properties, or appropriately reduce the dosage of concrete admixtures (on-site only). If the mixing plant reduces the dosage of concrete admixtures, new problems such as rapid loss of concrete slump may arise.

(7) Before unloading, the concrete mixer truck should rotate the mixing drum at medium and high speeds to ensure the concrete mixture is uniform before unloading.

(8) Strengthen management. For the mixing drum of the transport vehicle after cleaning, all the accumulated water must be drained before loading materials. After loading the materials, it is strictly prohibited to add water to the mixing drum at will.

3. Summarize experiences

In response to the problems of bleeding and segregation that are prone to occur in concrete. Through learning, exploration and experimentation, a set of solutions to problems that are in line with the actual situation has been summarized. Such as optimizing the mix ratio, strengthening the on-site inspection of raw materials, and enhancing on-site management. Eliminate the phenomenon of arbitrarily increasing water consumption due to poor on-site management of the mixing plant.