Proposed Mix Design Method for Dune Sand Concrete Using Close Packing Model and Mortar Film Thickness Theory

Abstract

Massive infrastructure constructions have resulted in scarcity of river sand resources. Previous studies and applications proved dune sand can partially replace river sand used in engineering to alleviate the supply and demand contradiction of river sand. However, due to the dune sand is finer, rounder and smoother than river sand, determining the appropriate proportion of dune sand for designing engineered dune sand concrete (DSC) remains challenging. To tackle this challenge, a mix design method for DSC was proposed via close packing model and mortar film thickness theory. Specifically, the close packing model was used to confirm dune sand content and sand ratio, then the dune sand and river sand were mixed to obtain engineering-standard mixed sand. The mortar film thickness theory was utilized to determine the mortar volume and to tailor the concrete slump. By proper design, the DSC achieved the 28-d compressive strengths of 50 MPa along with good workability. Increasing the thickness of the mortar film from 0.3 to 0.9 mm leads to significant changes in DSC performance. For per 0.1 mm increase in thickness, there is an average change of 14.25 mm in slump, 11.35 kg/m3 in dry density, 0.90 MPa in compressive strength at 28 d, 15.06 kg/m3 in CO2 emission, 85.3 MJ/m3 in energy consumption, and 1.2 USD/m3 in cost. The designed DSC achieved a relatively low cement intensity (CI) value of 6.23 kg/m3/MPa, implying that DSC exhibits good eco-efficiency. Therefore, the proposed hybrid design approach can guide the design of engineered DSCs with excellent mechanical properties as well as environmental and economic performance.