Case study on performance of pumping concrete with super-fine river-sand and manufactured-sand

Natural ecological protection changes the traditional practice for concrete production which faces a situation of the source exhaustion of natural materials, and the sufficient utilization of waste local materials becomes a strategy to reduce the carbon emission in infrastructure construction. This promotes a possible economic production of concrete with mixed-sand composited by coarse manufactured-sand and super-fine river-sand. Due to lack of study on the mixed-sand used for pumping concrete, an experimental study was carried out in this paper. The proportion of super-fine river-sand and manufactured-sand was determined at a target fineness modulus with a gradation in zone-II, the sand ratio of concrete was determined by the closed packing test of aggregates. Twelve mix proportions of mixed-sand concrete were designed by the absolute volume method, considering the content of super-fine river-sand and the sand ratio. The target cubic compressive strength of mixed-sand concrete was 48.2 MPa, while the target pumpability aimed at pumping height of 300 m. The pumpability of fresh mixed-sand concrete was evaluated by multi-indices including slump, slump flow, static segregation rate, pressure bleeding rate and air content, and explained by the rheological property including the indices of yield stress and plastic viscosity. The mechanical property was evaluated by the cubic and axial compressive strengths, the modulus of elasticity and the splitting tensile strength at curing age from 7 days to 56 days. Based on the test results, the absolute volume method for mix proportion design of mixed-sand concrete is rational to keep a consistent unit weight of fresh concrete, the optimal content of super-fine river-sand in mixed-sand is 25%− 35% with a rational sand ratio of 45%− 51%. The developments of compressive strength and tensile strength of mixed-sand concrete are identical to those of conventional concrete. The mixed-sand concrete presents the same relationships to the conventional concrete for the axial compressive strength, the splitting tensile strength and the modulus of elasticity with the cubic compressive strength. However, the splitting tensile strength of mixed-sand concrete is about 90% that of conventional concrete at the same strength grade. Further studies can be conducted to improve the flowability by adjusting superplasticizer and to enhance the tensile strength of mixed-sand concrete.