Stress dependence of the flowability and compressibility of building industry powders

In this study, the stress dependence of the flowability and the bulk density of various building industry powders like cements, tile cements, plaster, hydrated lime, etc. were studied using a ring shear tester. The measurements showed that the flow behavior of the various powders investigated is quite similar. The flowability strongly depends on the consolidation stress. At low stress (1-2 kPa) the flowability (ffc) is in the range of 1-2 (very cohesive) while at higher stress (approximately 40 kPa) the flowability is significantly improved (cohesive to easy flowing). The stress dependence of the bulk density for these powders can be approximated very well by a simple equation. The correlation coefficients were >0.993 for all 15 powders investigated. The constant in the approximation function, the bulk density at 1.0 kPa, correlates very well with the bulk density measured according to EN ISO 60. For the exponent c in the approximation function, a tendency is evident that for coarser powders the value of c is lower and for fine powders it is higher. However, this correlation is not very clear.