Basic mechanical properties of ultra-fine iron tailings sand concrete

With the expansion of construction and mining development, the massive exploitation of natural river sand has seriously affected the ecological environment. Seeking the substitute of natural river sand for concrete preparation is one of the current research hotspots in the field of engineering. The basic mechanical properties of ultra-fine iron tailings sand (UITS) concrete are intensively investigated and several parameters, such as iron tailings sand content, sand ratio and water cement ratio are considered. The UITS concrete proportion tests are designed considering the effect of different iron tailings sand contents (i.e., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90%), sand ratios (i.e., 35%, 40%, 45% and 50%), and water cement ratios (i.e., 0.5, 0.55 and 0.6). Test results indicate that the failure mode of UITS concrete prisms is brittle fracture caused by penetrating diagonal cracks. The peak stress and elastic modulus of UITS concrete increase and then decrease as increase of iron tailings sand content or sand ratio, while the peak strain decreases and then increases. The peak stress and elastic modulus of UITS concrete are maximized when iron tailings sand content is 50% and sand ratio is 45%. The longitudinal and horizontal peak strains of UITS concrete are minimized when iron tailings sand content is 60% and 40%, respectively. The longitudinal and horizontal peak strains of UITS concrete are minimized when sand ratio is 45%. As water cement ratio increases, the peak stress and elastic modulus decrease, while the peak strain increases. Additionally, Poisson's ratio of UITS concrete increases and then decreases with increasing iron tailings sand content while decreases with the increase of water cement ratio. Poisson's ratio is maximum when iron tailings sand content is 50%. Comparatively, sand ratio exerts little effect on Poisson's ratio. On the basis of experimental studies, the formulas for elastic modulus, Poisson's ratio, peak stress and strain of UITS concrete are presented, and a model for predicting stress-strain relationship of UITS concrete is established. The predicted results agree well with test data.