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Loess soils have always been among the most problematic soils, according to engineers. Due to the sensitivity and vulnerability of this soil type, researchers are constantly looking for different solutions to improve and stabilize this soil using different methods. In the present study, a mixture of lime and rice husk ash (LRHA) was used to modify the loess soil of the Golestan province, Iran. Lime and RHA were mixed in a ratio of 2:4 and with different contents of 2.5, 5, 7.5, 10 and 12.5% of the dry weight of the soil. To study the effect of curing on the strength properties, the samples were cured and tested for 7, 18 and 28 days. Atterberg limits, modified Proctor, unconfined compressive strength (UCS) and scanning electron microscope tests (SEM) were performed. It was found that increasing LRHA content increased the value of UCS at different curing times, such that UCS increased about five times by the addition of 5% LRHA to the loess at the end of 28 days. As the curing time increased, the optimum amount of the additive also decreased. The results showed that combining the soil with LRHA is an effective method for improving and stabilizing loess soil. According to the results of the study, the optimum value of 5% additive is economically and technically recommended. [ABSTRACT FROM AUTHOR]

Pervious concrete (PC) provides multiple benefits, including reducing stormwater runoff, purifying water, recharging groundwater, and reducing the heat island effect. This study aims to determine an effective way to reuse municipal solid waste incinerator (MSWI) fly ash (FA), MSWI bottom ash (BA), and rice husk ash (RHA) as single or binary partial replacements for ordinary Portland cement (OPC) in PC. The ashes and PC specimens were characterized via X-ray fluorescence spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the PC quality. The main components of the ashes were similar to those of OPC, suggesting that the ashes could be reused as cement materials; however, the cementitious activity of the ashes, especially MSWI FA, was relatively low. All ashes except 1100 °C MSWI FA met the standard requirements and can be applied as pozzolanic materials. The three PC specimens with binary replacements containing RHA (550, 700, and 900 °C) and MSWI BA (1100 °C) showed a synergistic effect and exhibited a higher 90-day compressive strength than the other specimens with single and binary ash replacements containing RHA (550 and 900 °C). The water permeability ranged between 0.106 and 0.391 cm/s, and the TCLP-released metal concentrations from all specimens met the regulatory standards of Taiwan. The results indicated that replacement with MSWI BA and RHA in cement materials provides an acceptable compressive strength and water permeability. [ABSTRACT FROM AUTHOR]