Prediction of physical-mechanical properties of hollow interlocking compressed unstabilized and stabilized earth blocks at different moisture conditions using ultrasonic pulse velocity

Abstract

This paper aims to investigate the effectiveness of ultrasonic pulse velocity (UPV) method to evaluate the physical-mechanical properties of hollow interlocking compressed unstabilized and stabilized earth blocks (ICSEBs) at different moisture conditions. The objective is to establish correlations between destructive and non-destructive tests. To this end, unstabilized and cement (4%, 6%, 8% and 10% by weight) stabilized blocks were prepared and characterized for density, porosity, linear drying shrinkage and water absorption, compressive strength, flexural and splitting tensile strength, and UPV at 28 days in air-dry, oven dry and wet states. Additionally, X-ray diffraction and scanning electron microscopy (SEM) tests were performed to identify the effect of cement content on microstructure and phase composition. The relationships among physical-mechanical parameters and UPV were evaluated. Finally, a statistical regression analysis was conducted, and empirical equations are proposed to predict the mechanical resistance of ICSEB in terms of moisture content, cement content, dry density and UPV. Results indicate that both moisture content and cement content have a significant effect on physical-mechanical properties and UPV of ICSEBs. The compressive strength, flexural and splitting tensile strength, porosity of ICSEBs reduces with an increase in moisture content while density increases for all cement contents. However, the addition of cement significantly improved the block properties. As the cement content increases from 4 to 10% the compressive strength, flexural and tensile strength increase by about 3.7, 5.4 and 6.5 times in air-dry state, respectively. It was observed that mechanical response of blocks is more sensitive to water content than cement content. Cement content ≥ 6% is recommended for production of durable ICSEB. Microstructural investigation confirmed that addition of cement content reduces the pores and densifies the microstructure. In unstabilized blocks, UPV reduces with an increase in moisture content; whereas in stabilized blocks higher UPV is obtained in air-dry state followed by wet and oven-dry states. A strong correlation exists between UPV and physical-mechanical properties. The proposed equations obtained from statistical analysis are capable of predicting the compressive strength, flexural and splitting tensile strength with fair accuracy. These findings confirm that UPV can be effectively used for assessing the performance of ICSEBs.