Influence of coarse coal gangue aggregates on elastic modulus and drying shrinkage behaviour of concrete

The elastic modulus and drying shrinkage are the fundamental mechanical behaviour of concrete in structural design. To date, no model has been proposed for predicting the mechanical properties of concrete using coal gangue aggregates (CGAs), including rock coal gangue aggregate (RCGA) and spontaneous-combustion coal gangue aggregate (SCGA). The aim of this study is to investigate the influence of CGAs on the mechanical properties of concrete and to theoretically propose elastic modulus and drying shrinkage prediction models for coarse CGA concrete based on composite models. For this purpose, four groups of replacement ratios were selected to prepare concrete with coarse RCGA and coarse SCGA, and their elastic modulus at different curing days and time-dependent drying shrinkages were recorded. The secant modulus of the bulk aggregates was proposed and evaluated to estimate the corresponding elastic modulus. Elastic modulus and drying shrinkage models were theoretically derived based on two-phase composite models, accounting for the elastic modulus difference between the coarse CGAs (RCGA and SCGA) and coarse natural aggregate (NA) via the tested secant modulus difference. The results show that compared to the reference NA concrete, the coarse CGA concrete exhibited decreases of up to 23% and 32% in the 28-day elastic modulus and increases of 62%–92% in the 360-day drying shrinkage due to the lower modulus of the selected CGAs; additionally, the RCGA concrete exhibited a more favourable mechanical behaviour than that of the SCGA concrete. The models proposed in this study could accurately estimate the elastic behaviour of coarse CGA concrete, but further validation work could still be conducted.