Feasibility of Najran rocks crushing waste as manufactured sand in the sustainable concrete industry in the Kingdom of Saudi Arabia

Abstract

ABSTRACT The rock crushing process produces powdered materials, and tons of these are buried as waste in low-lying areas, dumped on plains, or stacked on them across large areas, negatively impacting the Najran region’s environment in Saudi Arabia, and later they have been used to create manufactured sand (MS). We have studied the feasibility of using Najran MS in the industry of concrete (whose constituents are cement, sand, gravel, and water) by replacing it partially with natural sand in different percentages (20%, 30%, 40%, 60%, and 80%). Based on the British specifications, the physical and mechanical tests of the aggregate and concrete were performed on the Najran manufactured sand concrete samples and compared to conventional concrete samples. In addition, ultrasound tests and scanning electron microscopy of samples were performed to study their internal characteristics. Through the physical tests that were carried out on the two samples of natural sand and Najran manufactured sand, it was found that, except for the absorption of the manufactured sand, they are within the limits of the required British specifications, where the bulk particle density was 2.6 gm/cm 3 and 2.8 gm/cm 3 and the absorption was 1.85% and 9.94% for both natural sand and Najran manufactured sand, respectively. The gradation of natural sand was classified as medium, and the Najran manufactured sand was coarse, falling within the limits of the gradation. According to the ultrasonic test and scanning electron microscope of the concrete samples, it was found that the density of hardened concrete increases by increasing the percentage of Najran manufactured sand replacing natural sand in the concrete mix up to 40%, where the enhancement was 51.78% and 53.46% for the bulk density and the dry density, respectively, subsequently the density decreases gradually. Eventually, it is found that the optimum content of Najran manufactured sand that required improving the mechanical properties of the produced concrete is 40% replacement for natural sand, which gains enhancements of 13.75% for both compressive strength and flexural strength, and 11.9% for splitting strength, respectively, when compared with the properties of conventional concrete. This study can help to manage and reduce significant environmental pollution problems, as well as develop sustainable, low-cost materials that can be used in buildings by low-income people, particularly in Saudi Arabia.