Influence of stone powder in machine-made sand on concrete quality

The impact of excessive amount of stone powder in machine-made sand on the strength of concrete, and the reasonable amount of stone powder.
The main factors affecting the strength of concrete by stone powder are:
① The fineness of stone powder is small, and it has a certain micro-aggregate filling effect on concrete;
②Stone powder has an acceleration effect. Limestone powder particles act as nucleation sites, which increases the probability that the dissolved C-S-H gel encounters solid phase particles and then precipitates on them, but this effect is more obvious in the early stage, while Later stages can often be ignored;
③ Limestone powder is not completely inert. It can react with C3A and C4AF in cement during the hydration process to form calcium aluminate hydrate, which can overlap with other hydration products to make The cement stone structure is denser, which increases the strength of the cement stone.

The above are the positive effects of stone powder on the strength of concrete, but when the content of stone powder increases to a certain limit, due to the large amount of stone powder, the denser packing structure in the concrete is destroyed, or the glue-bone ratio of the concrete deviates from the better value, leading to a decrease in concrete strength.

For C30 concrete, the content of stone powder is 10%~15%, the workability and strength are better; for C60 concrete, the content of stone powder is 7%~10%, the workability and strength are better; for C80 concrete, the increase of stone powder content, the concrete workability The change is not obvious, but when the content of stone powder reaches 7%, the workability will decrease obviously, and the strength of concrete will gradually decrease with the increase of stone powder content, and the content of stone powder is 0~3% is better.

In C30 low-strength concrete, stone powder can improve the chloride ion impermeability of machine-made sand concrete, and the best value of stone powder content is between 10% and 15%; stone powder has no obvious effect on the chloride ion impermeability of C60 high-strength machine-made sand concrete; For C80 ultra-high-strength concrete, the anti-chloride ion permeability coefficient of concrete is very small, and with the increase of stone powder content, the anti-permeability coefficient gradually increases. For C30 low-strength concrete, there is a good correlation between hydraulic pressure resistance and chloride ion resistance. When the stone powder content is 10% to 15%, the hydraulic pressure resistance coefficient of concrete is lower.