Utilization of crumb rubber and FBC-based ternary binder in shotcrete lining

Abstract

This paper describes the early-age properties of shotcrete modified by i) up to 12.5% by volume crumb rubber as a replacement for aggregates and ii) substitution of ordinary Portland cement (OPC) by a fluidized bed combustion-based ternary binder (FBC-TB) up to 80% of mass. For the tests conducted, an increase in the crumb rubber volumetric fraction of the mixture always led to a decrease in uniaxial compressive strength. Replacing OPC with FBC-TB up to 20% enhanced the development of the early-age compressive strengths; however, a larger substitution resulted in the reduction in the concrete’s final compressive strength. In a full-size experimental mock-up test, the highest-performing mixture—in terms of acceptable mechanical properties and a reasonable amount of reused by-products—was subjected to full deployment in a concrete batching plant. Two batches (6 m3 in total) of concrete with crumb rubber and FBC-TB replacement were sprayed onto a full-scale model of a tunnel for the mock-up test. Evaluation of shotcrete performance included an analysis of the development of compressive strength and a comparison of results with criteria from the relevant code of practice, the New Austrian Tunnelling Method. Based on laboratory experiments, optimization, and in-situ measurements, the mock-up tests proved shotcrete containing crumb rubber and FBC-TC is applicable for full-scale use. Keywords: Shotcrete, Lining, Crumb rubber, Calcium sulfoaluminate, Mock-up experiment, Early-age strength