Assessment of freeze-thaw resistance of cement based concrete with ground glass – pozzolan through X-ray microtomography

Abstract

Over the last few years, the United States has experienced a shortage of fly ash and slag that consequently created a need for an alternative material that is locally available, sustainable, and provides desirable concrete properties. Recent studies have shown that Ground Glass Pozzolan (GGP) offers favorable attributes as a supplementary cementitious material (SCM) for concrete. However, there are limited studies demonstrating freeze-thaw (FT) resistance of concrete with GGP, as well as assessing the FT resistance in relation with the air-void system of GGP mixtures. In response, this study aimed to evaluate both macro- and micro-level behavior of GGP on FT resistance, and characterize mixtures with different contents of GGP. Six concrete mixtures were evaluated: three mixtures with 20, 30, and 40% GGP as cement replacements and three other reference mixtures with 30% fly ash and 40% slag and 100% Ordinary Portland cement (OPC). Following ASTM standards, concrete beam samples were tested for accelerated FT resistance and dynamic modulus of elasticity up to 1000 cycles. All concretes showed high FT resistance with a durability factor over 90% and, consequently, minimal deterioration and scaling. Core samples extracted from the FT conditioned beams were scanned with the X-ray micro-tomography (CTscan) to identify air-void parameters. Through image analysis a quantification of air-void parameters was obtained, and their relationship to FT resistance was established. Using CT scan analysis, we demonstrated that concretes with the highest cement replacement with GGP and slag developed the most desirable spacing factor and specific surface for FT resistance.