A lightweight fiber-based approach to reduce the risk of concrete detachment in shotcrete fortified tunnels

Abstract

Concrete detachments in shotcrete-fortified tunnels are a hazard to workers and users that can bereduced by changing density, residual load and bond strength. A factorial experimental design was car-ried out in the laboratory to assess the influence of lightweight aggregates (LWAs), polypropylene fibers(PF) and nano silica (NS) in the mixture performance. Results indicate that 6 kg/m3 of PF increase residualloads up to 2.93 MPa, 70% of LWA reduced density below 1,600 kg/m3 with structural compressivestrength above 22.5 MPa. The safest mixtures had fibers to withhold the unbonded shotcrete piece andLWA to reduce the detachment and impact energy involved.