The Effect of Silica Fume on Critical Aggregate Fraction in Mortar

This paper studies the transport through mortar with variable volumetric aggregate fraction (AF) and OPC + SF binder, and compares it with tests on OPC mortars carried out in the previous work where a critical aggregate fraction (CAF) was discovered at which the porosity, or transport through mortar, has a positive jump, beyond which the decreasing pattern resumes. This phase is designed to investigate if the replacement of cement with SF would eliminate the above-mentioned CAF. Different transport tests are carried out on mortars with 20 % volumetric cement replacement with SF and gradually increasing AF. Inclusion of SF not only fails to eliminate the CAF, but it also exacerbates it. This finding rules out the involvement of the interfacial transition zone (ITZ) in this phenomenon, and instead the theory of sudden establishment of a 3D space frame made with cement particles supported by the internal friction between the particles and the external friction between the particles and the surrounding aggregates is proposed. Although the decreasing trend of the transport after this CAF resumes, but it is suspected that these space frames in the paste keep on existing after the onset of CAF, but decreasing effect of the reduction of paste fraction as AF increases, overwhelms the increasing effect of the existence of the space frame.