To ensure a limited washout loss rate and the self-compaction of underwater concrete, the mix proportion design of underwater non-dispersible concrete is a key technology that has not been completely mastered. In view of this aspect, an orthogonal test study was carried out in this paper on the workability, washout resistance, and compressive strength of underwater non-dispersible concrete. Six factors with five levels were considered, which included the water/binder ratio, the sand ratio, the maximum particle size of the coarse aggregate, the content of the dispersion resistance agent, the content of superplasticizer, and the dosage of fly ash. Using a range and variance analysis, the sensitivity and significance of these factors were analyzed on the slump and slump-flow, the flow time, the washout loss rate, the pH value, and the compressive strength at the curing ages of 7 days and 28 days. The results indicated that the water/binder ratio and the content of the dispersion resistance agent were strong in terms of their sensitivity and significance on the workability and washout resistance, and the water/binder ratio and the dosage of fly ash were strong in terms of their sensitivity and significance on the compressive strength. With the joint fitness of the test results, formulas for predicting the slump-flow, washout loss rate, and compressive strength of underwater non-dispersible concrete were proposed considering the main impact factors.

To promote the efficient utilization of bulk solid wastes, including superfine river sand and fly ash, high-flowing steel-fiber-reinforced mixed-sand concrete (SFRMC) was developed in this study. Superfine river sand and coarse manufactured sand were mixed in a proportion of 4:6 to make the mixed sand. Fly ash, with a content of 30~75%, was blended with 0~12% silica fume on the premise of equivalent activity. The water dosage and sand ratio were adjusted with the volume fraction of steel fiber, which varied from 0.4 to 1.6%, to ensure the high flowability of fresh SFRMC. The mechanical properties, including cubic and axial compressive strengths, modulus of elasticity, splitting tensile strength, and flexural strength and toughness of the SFRMC, were analyzed, accounting for the influences of the contents of fly ash and steel fiber. The predictive formulas for the splitting tensile strength, modulus of elasticity, and flexural strength were proposed by introducing the influencing factors of steel fiber. The SFRMC showed an increased modulus of elasticity with increases in the steel fiber factor, and flexural toughness was enhanced with increased contents of both steel fiber and fly ash.