The failure of glass-fIbre-reinforced notched beams in flexure

Abstract

Synopsis The resistance to crack propagation in glass-fibre-reinforced cement paste has been assessed by using a technique developed for measuring the fracture toughness of unreinforced cement pastes and mortars. The values measured with the fibrous material are not true toughness values but can be treated as such for small crack growths or used for relative assessment of the resistance to cracking over a larger range of growth. The material tested was an OPC/pfa matrix with chopped glass-fibre distributed at random. Three different mixes were used (0, 1·1% and 2·3% glassfibre volume fractions) tested 14, 28 and 84 days from casting. The pseudo-toughness of the fihre-reinforced material was no higher than that of the unreinforced matrix at the initiation of crack growth, but thereafter increased linearly with crack growth at a rate proportional to the fibre content. The change of toughness for crack growths up to 12 mm could be measured; at this point, the 2·3% fibre content gave about 5 and the 1·1% content ahout 3 times the toughness of the matrix material, and the toughness was still increasing with crack growth. The psuedo-toughness was not affected by age up to 84 days from mixing.