4. Results4.1 Effect of stone powde

4. Results4.1 Effect of stone powder content on shrinkage of hydraulic concreteFigure1 and 2 show the effect of stone powder content on the shrinkage of hydraulic concrete when the water-to-binder ratio is 0.37 and 0.45, respectively. It can be seen from the figure that the shrinkage rate of concrete increases first and then decreases with the increase of stone powder content. With the stone powder content of 22%, the shrinkage rate of concrete is the largest. For this, the reason is that when the stone powder content is lower than 22%, on the one hand, due to the active effect of the stone powder, it can participate in the hydration reaction to a certain extent, react with C3A to form a carbon aluminate; on the other hand, the stone powder not involving in the hydration reaction, was used as the micro-aggregate to fill the internal structure of the concrete, reducing the average pore diameter of the concrete, and increasing the capillary force inside the concrete, thereby increasing the dry shrinkage rate of the concrete. When the stone powder content is 22% or more, excessive stone powder reduces the compactness of the concrete solid particle system, and increases the average internal pore diameter of the concrete. So, the dry and water-loss concrete shall lower the capillary force, and then reduce the concrete shrinkage rate. In addition, in the concrete groups at the same water-to-binder ratio, the total amount of cement slurry increases with the increase of the stone powder content, and the total amount of cement slurry is an important factor affecting the shrinkage.