Effects of water ratio on high strength lightweight self-compacting concrete using carbon quantum dots and coir fiber

The aim of this study is to evaluate the effects of the water-to-binder ratio and water-to-sand ratio on the structural properties of high-strength lightweight concrete. To this end, the tested properties included slump, water absorption, density, compressive strength, flexural strength, splitting tensile strength, and modulus of elasticity. Finally, the microscopic features of the concrete were observed by scanning electron microscopy (SEM). The results demonstrated that the compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and high-strength lightweight concrete exhibited inverse relationships with increasing water-to-binder ratios and water-to-sand ratios. In addition, the splitting tensile strength exhibited a more pronounced sensitivity to changes in the aforementioned ratios than did the compressive strength. Microscopic analysis revealed that the incorporation of lightweight aggregate enhanced the mechanical properties at room temperature, conferring both lightweight and high-strength characteristics to the resulting material. Furthermore, on the basis of the aforementioned results, this study presents an effective method for predicting the strengths from water‒sand ratios (w/b and w/s). Additionally, the compressive strength can be optimized through the development of equations. The results of this research have the potential to facilitate the practical implementation of concrete in real-world pavement projects. In other words, the use of oil shale aggregate and clean recycled concrete aggregate for bridge decks resulted in savings of 368 tons of structural steel, 363 tons of suspension and cable, 2060 tons of bridge deck weight, and cost savings of US$320,000 in the pier‒pier portion of the bridge.