Abstract
This paper investigates the plastic viscosity of cement mortar with manufactured sand (MS) concerning the influences of geometric features and particle size of MS. The geometric features, including overall shape, angularity and roughness, of MS with various particle sizes were evaluated by aspect ratio, convexity area ratio, convexity perimeter ratio and circularity. The plastic viscosity of cement mortar was calculated based on the Bingham model. Results show that the combined effects of overall shape, angularity and roughness provide coarser MS particles with lower circularity. In terms of relative plastic viscosity, Robinson model shows optimal fittings for all mixtures and is thus used to determine the packing fraction of MS under shearing. From the particle packing viewpoint, shear-induced orientation increases the packing fraction of non-spherical MS particles from the random loose packing fraction and the influence is increasingly prominent with the decrease of circularity. The relative volume fraction is an important parameter influencing the relative plastic viscosity of mixtures with MS while the relative paste film thickness (R_PFT), calculated from the real packing fraction and specific surface area (SSA), is found as the dominating factor. The dependence of plastic viscosity of cement mortar on geometric features and particle size of MS can be attributed to their influences on the packing fraction and SSA of particles.
Highlights
There has been increasing interest in using manufactured sand (MS) as fine aggregate for mortar or concrete to overcome the increasing deficiency in river sand and alleviate the environmental problems caused by overexploitation of river sand
Westerholm et al measured the rheology of mortar mixtures with various MS and found that the plastic viscosity of mortar increased almost three times as MS became increasingly elongated, which was attributed to the increased particle interference between non-spherical particles [11]
For the super imposed points in zone 1, they share the identical ηr of 8.4 while they have the same relative paste film thickness (R_PFT), manifested by the normalized variation of 0. Their corresponding relative volume fractions vary a lot with the 7.5% normalized variation
Summary
There has been increasing interest in using manufactured sand (MS) as fine aggregate for mortar or concrete to overcome the increasing deficiency in river sand and alleviate the environmental problems caused by overexploitation of river sand. The influence of MS on plastic viscosity of cement mortar was demonstrated as a particle shape effect [11,12]. This pro posal was supported by similar results showing that any deviation from a spherical particle shape results in an increased viscosity if the mea surement is done at the same phase volume [4,13]. By increasing the paste volume, negative effects due to decreased packing fraction of poorly shaped aggregates can be eliminated or significantly reduced [11]. It can be summarized that particle shape may influence the rheology of mortar in various ways, including the particle shape itself and its influences on the packing fraction and paste film thickness. The essential roles of geometric features and particle size of MS are analyzed
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