Study on the mechanical properties of modified rammed earth and the correlation of influencing factors

Abstract

The main ingredients of traditional rammed earth walls are plain soil, which decreases the compressive strength and water resistance performance of the rammed earth buildings. To promote the application of rammed earth in traditional buildings, varying additional materials were added to modify the rammed earth, and the water stability and compressive strength of modified rammed earth were investigated. Firstly, the plain soil in Northwest Sichuan was selected as raw material, and seven groups of modified rammed earth standard specimens were fabricated by mixing cement, fiber, sand and gravel or soil stabilizer. Then, the compressive strength tests, water stability tests, and splitting tensile strength tests were performed. After the tests, the failure modes, load displacement curves, compressive strength, and splitting tensile strength of the specimens are analyzed. Furthermore, the correlation between varying parameters and compressive strength, water absorption, and splitting tensile strength of specimens are studied, and the micro mechanism of modified rammed earth is discussed. It indicates that the porosity of the modified rammed earth is reduced and generates a more compact and stable microstructure, which improves the compressive strength, water stability and splitting tensile strength of the modified rammed earth. The hydration products generated by the cement hydration process wrap and connect the soil particles, which fill the gap between the soil particles. By performing variance and correlation analysis, it is found that the variation of fiber types had significant effects on water-saturated compressive strength, water absorption，and compressive strength, and the corresponding correlation coefficients are 0.766， −0.701，and 0.534，respectively. By performing value analysis, SN5 (mixed 8% cement + 20% sand +20% gravel + 0.05% polypropylene fiber) exhibits the better mix proportions and the lower cost.