Cement particle flocculation and breakage monitoring under Couette flow

• The particle size and viscosity of cement paste are simultaneously monitored.
• At low rate of shear strain, the cement particle size increases over time.
• At high rate of shear strain, the cement particle size decreases over time.
• Nevertheless the viscosity on both cases decreases.
• The increase of the packing density supports the decrease of viscosity.

Freshly mixed concrete is a suspension of cement and aggregate particles dispersed in water. To secure the desired quality of freshly mixed concrete, understanding its rheological behavior, which depends on its flow rate, is necessary. A number of chemical and physical factors influence the rheology of freshly mixed concrete, and the flocculation of cement particles is thought to cause thixotropy and shear thinning. This study proposes a rheometer coupled with a laser backscattering device, which allows us to simultaneously measure the viscosity and the size distribution of cement clusters in cement paste suspension. The laser backscattering instrument measures the cluster size distribution and monitors its growth or breakdown, while the parallel-plate rheometer measures its rheological properties. As a result, the change of cement grains was continuously observed with the change of shear stress under specific strain rates of 1 s− 1, 10 s− 1, and 100 s− 1.