Effect of concrete waste dust on the flowability, compressive strength, and ultrasonic pulse velocity of mortar

Abstract

Construction and demolition (C&D) waste, which accounts for approximately 25–30% of total urban solid waste, along with the high CO 2 emissions from the global cement industry, presents a major challenge to achieving sustainable development. One promising approach is the utilization of waste concrete as a supplementary cementitious material (SCM) to reduce both waste accumulation and carbon emissions from cement production. This study investigated the effect of concrete waste dust (CWD) as a partial cement replacement on the fresh, mechanical, and non-destructive properties of mortar, with emphasis on ultrasonic pulse velocity (UPV). Two particle sizes were used: CWD1 (passing sieve #200; 0.075 mm) and CWD2 (passing sieve #360; 0.040 mm), at replacement levels of 10%, 20%, and 30% by cement weight. Tests at 7 and 28 days included flow, compressive strength, elastic modulus, and UPV measurements. All mixtures exhibited good fresh properties without segregation or bleeding. Overall, increasing CWD content reduced compressive strength and UPV values, particularly at replacement levels above 20%. Nevertheless, finer CWD particles (CWD2) demonstrated better performance in maintaining strength and UPV values compared to CWD1, likely due to more effective filler effects. A strong exponential relationship (R 2 = 0.8258) was observed between UPV and compressive strength, highlighting the potential of UPV testing as a reliable non-destructive method for predicting mortar strength. ANOVA analysis revealed that the significant influence on compressive strength occurred only up to certain replacement levels, depending on the particle size of the CWD. These findings support the potential of using CWD as an environmentally friendly cement substitute, provided that the replacement level and particle size are appropriately optimized.

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