Studies on Lightweight High-Strength Shotcrete
With small deadweight, light-weight shotcrete can avoid the shotcrete lining from falling off, which benefits the bolt-shotcrete support of the roadway better under same bond strength. Light-weight shotcrete can be made by using clay ceramsite, polystyrene particles and fly-ash ceramsite to replace some gravel and sand. The experiments show that the characteristic of fly-ash ceramsite shotcrete is superior to that of clay shotcrete, while by replacing part of gravel and sand with polystyrene particles and fly-ash ceramsite, light-weight high strength shotcrete will have excellent combination properties.
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 be reduced by changing density, residual load and bond strength. A factorial experimental design was carried 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 residual loads up to 2.93 MPa, 70% of LWA reduced density below 1,600 kg/m3 with structural compressive strength above 22.5 MPa. The safest mixtures had fibers to withhold the unbonded shotcrete piece and LWA to reduce the detachment and impact energy involved.
Strength and Durability of Lightweight and Normal Weight Concrete
A research project has been undertaken in Kuwait University to investigate the long-term strength development and durability of lightweight aggregate concretes (LWAC's) and a normal weight concrete (NWC) under hot dry and hot humid coastal exposure conditions. This paper reports the strength development and durability characteristics of 35- and 50-MPa NWC specimens exposed to the seaside up to an age of 9 months. The water penetrability of LWACs seems to be more sensitive to the extent of initial curing than it is for NWC. The water penetrability of LWC50 after 7 days of initial curing and subsequent exposure to the seaside was about 1/3 more than that of the NWC50 in the same exposure condition. The depth of carbonation, sulfate, and chloride penetration, and concentration in LWC50 were somewhat higher than that in NWC50 under similar exposure regimes.