Workability, Strength, and Durability of Wet-Mix Shotcrete Incorporating a Viscosity-Enhancing and Early-Strength Agent

This study investigates viscosity-enhancing and early-strength wet-mix shotcrete (VE-ESWS) incorporating a self-developed viscosity-enhancing and early-strength agent (VE-ES). Indoor tests combined with on-site spraying were performed to quantify the effects of the water/cement ratio (W/C) and VE-ES dosage on workability, strength, and durability. VE-ES had little influence on pumpability but substantially enhanced sprayability, reducing rebound rate to below 8%. Compressive and splitting tensile strengths peaked at W/C = 0.43–0.44 and a sand rate of 55%, whereas sand rates of 50% or 60% caused noticeable reductions. Durability (water permeability, freeze–thaw resistance, wet–dry sulfate attack, and carbonation resistance) of VE-ESWS was superior to that of the reference wet-mix shotcrete. Water penetration height could be controlled to about 5 cm when W/C was 0.42–0.43. During freeze–thaw cycling, mass loss rate increased initially and then decreased; slight apparent mass gains at later cycles were attributed to moisture uptake. VE-ES effectively reduced the compressive strength loss of VE-ESWS after sulfate attack, although the mass loss rate increased rather than decreased after 100 wet–dry sulfate attack cycles. The carbonation rate of VE-ESWS decreased with increasing VE-ES dosage. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results corroborated accelerated hydration and pore-structure refinement. Based on combined indices, the recommended values are W/C = 0.42–0.44, and the VE-ES dosage = 7.5 kg/m3 within the studied ranges. This study could provide theoretical and technical support for the application of VE-ESWS in engineering practices.