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Cement replacement with brick powder and concrete powder in sludge solidification

Abstract Soil solidification with cement is widely adopted to improve soil strength and stiffness. However, a large amount of cement may be consumed for ideal soil solidification. Therefore, a method was proposed using waste powders crushed from discarded brick and concrete as alternative materials to partially or fully replace the cement in soil solidification. The influence of the substitution rate and particle size of waste powders on the efficiency of solidification was studied. Scanning electron microscopy (SEM), water content analysis, direct shear tests, and unconfined compression tests were conducted at varying curing days. The results revealed that a lower substitution rate or smaller particle size generally led to denser soil structures and lower water content of the sludge. The unconfined compressive strength, cohesion, and internal friction angle of solidified sludge decreased slightly within around 6% when the substitution rates gradually grew to 40% and reduced by 19% approximately with the particle size rising from 0.045 mm to 1 mm. Besides, compared with brick powder, the concrete powder had a more positive impact on solidification. Consequently, the concrete powder with the smallest particle size of 0.045 mm and substitution rate less than 40% is recommended for replacing cement in solidification.