Design Method for Cemented Sand and Gravel Mix Proportion Using Jaw-Crushed Material

The construction of massive infrastructure projects in Africa suffers from a shortage in natural aggregate materials, such as coarse sand and gravel for cemented sand and gravel (CSG) for hydraulic projects, which would delay progress and raise costs. In response to the scarcity of CSG aggregates and the challenges in the environment-friendly disposal of excavation waste, a design method for the mix proportion of CSG by using jaw-crushed material was proposed, and this method was suitable for similar projects to be constructed in Africa. First, the target grading for coarse aggregates was set based on Fuller’s ideal grading to determine the optimal ratio of jaw-crushed material and smaller stones for gradation adjustment. Second, the target grading for fine aggregates was determined to be the III zone fineness modulus and obtained by seeking the proper ratio of local ultrafine river sand and artificial sand produced from rock grinding. Then, considering the compressive strength, the optimal CSG mix proportion was determined, where both volcanic ash and cement were added as cementitious materials. Finally, the proposed design method for jaw-crushed-material-based CSG was applied in the construction of a temporary overflow cofferdam at the Julius Nyerere hydroelectric power station in Africa, and its feasibility and effectiveness were verified. The results indicate that the optimal ratio between the jawcrushed material and small stones for the coarse aggregate of CSG is 0.85:0.15 (by weight by default unless otherwise specified), the best ratio of ultrafine river sand and artificial sand for the fine aggregate of CSG is 4:6 by weight, the optimum sand content of CSG is 30%, the water-cement ratio is 1.11, and the optimal dosage of volcanic ash is 58.3 kg per cubic meters of CSG (kg/CSG m3). The engineering practice of the temporary CSG overflow cofferdam demonstrates that the use of jaw-crushed material for CSG is feasible, and the proposed CSG mix proportion design method achieved the efficient utilization of jaw-crushed material, which can reduce the environmental impact of excavation waste and ensure the completion of temporary high-quality overflow cofferdam for seasonal floods. This study provides valuable scientific and engineering references for similar CSG projects that may use jaw-crushed material for the design and construction and has important scientific and engineering significance. © 2023 School of Science, IHU. All rights reserved.