Comparative Evaluation of Transport Properties of Shotcrete Compared to Cast-in-Place Concrete

The question is sometimes asked: "How does the durability of shotcrete compare to that of cast-in-place concrete?" The durability of shotcrete and concrete structures is strongly influenced by their transport properties. While considerable data are available regarding the transport properties of cast-in-place concrete, little has been published concerning shotcrete transport properties. This study is directed at addressing this deficiency so that factual data are made available regarding the comparative transport properties of both wet, and dry-mix shotcretes and comparable cast-in-place concretes. In this study, a comparative evaluation was conducted on cast-in-place concrete; cast wet-mix shotcrete; sprayed wet-mix shotcrete; and sprayed dry-mix shotcrete in mixtures with and without fly ash, silica fume, and accelerators. Plastic concrete and wet-mix shotcrete tests conducted included slump, air content, and setting time. Hardened concrete and shotcrete tests conducted included compressive strength at 7 and 28 days; ASTM C642 boiled absorption and volume of permeable voids; ASTM C1202 rapid chloride permeability (RCP); ASTM C1792 rate of water absorption; and U.S. Navy specification UFGS 03 31 29-3 (chloride permeability test). Calculated transport property values compared included boiled absorption (BA) and volume of permeable voids (VPV), Coulomb values in RCP test, coefficient of diffusion (Diff[OH-]), effective coefficient of diffusion (Diff[OH-] x VPV), permeability (k) and tortuosity, in U.S. Navy specification UFGS 03 31 29-3 tests. This study demonstrates that properly applied wet-mix and dry-mix shotcretes can provide equivalent or superior transport properties (for example, ionic diffusion and permeability), and hence durability, to cast-in-place concrete.