The influence of fine materials in sand o the rheology of fresh mortar

摘要

Rheology is a key characteristic for the user of fresh mortar but, because sands from around the UK are of very different fineness, ready mixed mortar producers need to be aware of the effect of sand on rheology. The objective of this work was to investigate the influence of fineness on the rheology of fresh mortar. 30 sands were selected from a much larger sampling survey (over 150) of building sands in the UK. Criteria for selection were (i) overall grading expressed as percentage passing a 300 umm sieve, (ii) degree of fine particle contamination expressed as percentage passing a 63 umm sieve and (iii) type and activity of clay present expressed as the Methylene Blue Value. Each sand was used in a single mortar mix and the effect of water content on rheology of each mortar tested in the Viskomat. The rheology of the mortar conforms to the Bingham model and the yield stress and plastic viscosity can be determined from the data. All three fineness parameters affect the water required to acheive a given level of workability and the water demand of the sands varied over a two fold range. The effects of fineness interact in a complex way with overall grading and MBV being dominant.