Effect of MB-value of Manufactured Sand on Durability of Concretes

摘要

The MB-value is one of the most important parameters for evaluating the property of manufactured sand (MS). The relation between the methylene blue (MB) value of MS and its limestone powder content and clay content was investigated. The effects of MB value ranging from 0.35 to 2.5 on the workability of fresh concrete, and the mechanical properties, the resistance to freezing as well as the resistance to chlorine ion permeation of the harden concrete were investigated. Results showed that, the MB value had no correlation with the limestone powder content of MS, while it was directly related to the clay content. With an increase of the MB value, the concrete workability decreased, and so were the flexural and 7-day compressive strengths, however the 28-day compressive strength was not affected. Furthermore, the influence of the MB value on concretes with different levels of strengths was different. For low strength concretes, an increase of the MB value could improve its impermeability, but this was not the case for high-strength concretes. Instead, its resistance to chloride ion permeability decreased slightly. However, even a slight increase in the MB value remarkably accelerated freeze-thaw damage of the MS concrete. So it was concluded that the critical MB value of 1.4 would not cause significant deterioration to the performance of MS concretes.