What is the effect of cement particle size on the strength and shrinkage of hardened concrete? Tell me why.

★ First of all, the particle size of cement is called fineness in professional terms.

Fineness refers to the overall thickness of cement particles. The finer the cement particles, the larger the surface area that reacts with water, so the hydration reaction is faster and more complete, and the early strength is higher, but it hardens and shrinks in the air.

Simply put, the finer the fineness of cement, the greater the specific surface area, the greater the water demand of cement, which makes the hardened cement paste increase porosity, decrease strength and increase shrinkage due to excessive water. (Usually, what we call shrinkage mainly refers to dry shrinkage. When the porosity of the material is larger, the water absorption will increase and the drying shrinkage will be larger. )

(★ Let me help you popularize some common sense about cement: Generally speaking, cement is composed of many graded cement particles. The gradation structure of cement particles has great influence on the hydration and hardening speed, water demand, workability, heat release speed and especially the strength of cement. Under normal circumstances, the hydration of cement particles is the fastest when it is 0 ~ 10 micron, and the cement activity is the largest when it is 3 ~ 30 micron. When it is larger than 60 microns, the activity is small and the hydration is slow. When it is greater than 90 microns, it can only hydrate on the surface and only play the role of micro-aggregate. Therefore, under general conditions, in order to give full play to the cementitious properties of cement and improve the early strength of cement, it is necessary to improve the fineness of cement and increase the gradation ratio of 3 ~ 30 microns. However, it must be noted that the cement is too fine, the specific surface area is too large, there are too many particles smaller than 3 microns, and the water demand of cement is too large, which will increase the porosity and reduce the strength of hardened cement paste. At the same time, the fineness of cement will also affect other properties of cement, such as the rapid decline of cement activity during storage, the large water demand of cement, the increase of shrinkage of cement products and the decrease of frost resistance. In addition, too fine cement will significantly affect the performance of cement mill, reduce output and increase power consumption. Therefore, the fineness of cement must be controlled reasonably in production, so that cement has a reasonable particle gradation. )