When the stone has a high water absorption rate, the initial slump of the concrete will not be affected, but the fluidity of the concrete will be lost within a few minutes after being discharged from the mixer. There are many mortar particles on the surface of the stone, and there is still no fluidity after adding water. The intensity has dropped significantly.
The reason for this phenomenon is mainly caused by the water absorption of the stone. After the concrete material enters the mixer in proportion, it rotates faster in the mixer, and the mortar is transported tangentially in the mixer, so that water cannot enter the stone and has good fluidity. Once the concrete mixture is mixed in a static state, the water will quickly penetrate into the pores of the stone, resulting in a faster reduction of the cementing material of the mixing water, which is much lower than the design mixing ratio determined by the amount of water, resulting in concrete The fluidity of the mixture deteriorates quickly, and the slump loss is large.
At the same time, because the concrete water-reducing agent is dissolved in water before entering the mixer, how much water is absorbed by the stone, and the water-reducing agent is also absorbed by the stone in an equal proportion, and the concentration of the water-reducing agent in the cementitious material decreases quickly. The actual amount of water reducing agent in the cementitious material is less than the actual amount of cement paste. In particular, the proportion of retarding components in the cementitious material is significantly reduced. The final performance is that the mixture has better fluidity during the mixing process. The slump is very large. After stopping the mixing, the concrete mixture loses its fluidity as a whole within a few minutes.
When the content of sand, mud or stone powder increases, the total amount of powder increases, and the actual amount of sand is less than the design value of the mix ratio. Therefore, the sand rate is unreasonable, the initial slump of the concrete becomes smaller, and the slump loss becomes larger.
The gradation of stone grains and the content of needles and flakes have a significant impact on the concrete water-reducing agent. Under the same proportion, the increase of the content of needles and flakes will reduce the fluidity and expansibility of concrete and easily cause bleeding, segregation and other problems.
