Concrete Two-speed Mixing Process Studied

Intensity destroy of concrete often occurs on the interface between gravel and mortar. The main reason is that there exist original wee crannies between the two materials and the thin layer of water that forms on the surface of gravel decrease their joint strength. Comparing with the traditional mixing method, the two-step mixing technique shows remarkable advantages in concrete performance, environment protecting, cost reducing, etc. The new technique could be further classified into five categories: primary mixing of mortar, primary mixing of grout, sand envelope with cement (S.E.C.) , gravel envelope with cement, gravel envelope with grout. The first two are more complex and costly than the latter three because they need an extra high speed mixer. The latter three can be applied with single mixer but has the disadvantage of longer mixing period. To overcome the disadvantages of two-step mixing technique mentioned above, experiments on the two-step mixing technique are carried out with a newly designed double-speed mixer. And the way of doing two-step mixing with a double-speed mixer is named as double-speed mixing art here.Based on the theoretical analysis of double-speed mixing, the best parameters of mixer are determined. The drive power is calculated and carefully chosen. A new idea is proposed to improve mixing performance, which activates grout in high speed, controls W/C ratio on gravel interface, and uses orthogonal test design to optimize all the operating parameters of the new art. Experiment results indicate that comparing with the traditional method, primary mixing of mortar can increase the average intensity of 28d concrete by 26.5% , the S.E.C. can increase the average intensity by 27.8%. In general, the concrete prepared by double-speed mixing art is better than that prepared by traditional technique.