What is slump loss? How to reduce slump loss?
A: Slump loss means that the consistency of fresh concrete will gradually decrease with time. Slump loss is a normal phenomenon of all fresh concrete, and is the result of the gradual thickening and coagulation of the Portland cement hydration slurry while forming hydration products such as ettringite and hydrated calcium silicate.
Under normal circumstances, within the first half hour of fresh concrete, the volume of cement hydration products is very small, and the slump loss is not very large, but after that, the slump of concrete begins to decrease at a certain rate. It depends on the type of cement, hydration time, ambient temperature, initial slump and admixtures and admixtures.
The slump loss of concrete can be reduced in the following ways:
①Cement with low C3A and alkali content is selected. Due to the low content of C3A in cement, the hydration reaction of cement is relatively slow, and the initial hydration products are reduced, so the slump loss can be reduced.
②Admixture of retarder admixtures in concrete. Such admixtures can reduce the rate of cement hydration reaction and delay the peak hydration heat, thereby reducing slump loss.
③ Mix high-quality fly ash in the concrete. The slump loss can be reduced because the ball lubrication of the spherical particles in the high-quality fly ash can be maintained for a long time in the fresh concrete.
④ In the case of meeting the construction requirements, the mix ratio with the lowest slump should be selected as much as possible, because the size of the slump loss is generally proportional to the initial slump, and the greater the initial slump, the greater the slump loss. .
⑤Lower the temperature of fresh concrete as much as possible, because too high temperature will also accelerate the slump loss. By using cement with a low heat of hydration, lowering the temperature of the aggregate, and adding ice to the concrete, the temperature of the fresh concrete can be lowered, thereby reducing the slump loss.
⑥The time required for concrete mixing, conveying, pou