Potential use of fibrous grass silage press-cake to minimise shrinkage cracking in low-strength building materials

The fibre-rich press-cake fraction produced by ‘green biorefineries’ may provide a sustainable solution for the control of restrained drying shrinkage cracking in stabilised soil blocks and cementitious mortars. Following determination of the tensile strength of selected grass species at different harvest dates, the effect of press-cake inclusion was assessed in controlling the shrinkage of clay and mortar specimens. The press-cake was found to be effective in controlling the onset of early-restrained drying shrinkage cracking in both clay and cementitious specimens. The addition of press-cake fraction to terracotta pottery clay had a pronounced beneficial effect on early-restrained shrinkage, increasing the time to first crack by over 5 h and reducing the crack width by 4.9 mm relative to the control. Inclusion of the press-cake fraction in mortar specimens (at a rate of 2.2 kg m−3) eliminated crack formation completely, compared with the unreinforced mortar specimens which cracked after 3 h. This positive influence on the consequences of restrained shrinkage occurred despite the fact that early-age free shrinkage rates were found to increase in proportion to press-cake inclusion rate. Furthermore, in cementitious specimens the performance of the press-cake compared well with polypropylene fibres in respect of mitigating the risk of cracking due to early-age restrained shrinkage in cementitious specimens.