Development of modified cement composites with enhanced crack resistance for the manufacture of precast building products

Abstract

After Amendment № 1 to GOST 13015-2012 came into force, the regulation of precast concrete products shifted from a marked crack-resistance category to a design verification of the section, while the deformation model of SP 63.13330.2018 contains no term for the bridging stresses of dispersed reinforcement across the faces of a normal crack. The gap between the gain in matrix strength and the gain in resistance to crack propagation remains quantitatively undefined. The purpose of the work is a separate assessment of the contribution made by matrix modification with condensed silica fume and by dispersed reinforcement to the force, energy and service indicators of crack resistance. An author's design model links the parameters of fibre reinforcement with the critical stress intensity factor, the specific fracture energy according to GOST 29167-2021 and the design crack width in the section of a model floor slab spanning 7,2 m. Replacing 10% of the cement with silica fume increases the matrix strength by 12,4%, raises the critical stress intensity factor by only 3,9% and leaves the design crack width unchanged at 0.305 mm, while adding 1,0% of hooked-end steel fibre increases this factor 2,45 times and reduces the crack opening to 0,090 mm. The divergence of the elasticities of the two indicators with respect to fibre volume content, 0,40 against minus 1,39, indicates that they are governed by different mechanisms, while matrix strength remains neutral towards both.