Recycled concrete paving block waste as a selected sustainable substitute for natural aggregate in cement composites

This study examines the impact of replacing natural aggregates with second-quality sorted concrete paving block (CPB) aggregates in mortars and concretes. Substitution levels varied from 0 % to 100 % for fine aggregates in mortars and 50 % for fine and/or coarse aggregates in concretes. The research analysed the properties of the waste material, including particle size distribution, porosity, water absorption, and density. For mortars and concretes, the evaluated parameters encompassed workability, consistency, density, compressive strength, electrical resistivity, and microstructure. The findings indicate that mortars incorporating CPB aggregates necessitate higher dosages of superplasticizers to achieve desired workability. This requirement is attributed to the increased cement content per unit volume and the finer particle size of the recycled aggregates. Early compressive strength of mortars peaks at a 50 % recycled aggregate content due to a reduced effective water-to-cement ratio, while 100 % substitution of fine aggregate leads to a significant decrease in compressive strength. Concretes with recycled aggregates exhibit comparable or superior early compressive strength relative to reference concrete, but after 28 days, all concretes with recycled aggregates display lower strength. The 28-day compressive strengths are 65.9 MPa, 64.8 MPa, and 62.3 MPa for 50 % replacement by fine, coarse, and a combination of both aggregates, respectively. These results surpass those achieved in similar studies. Durability assessments suggest that concrete mixtures with CPB exhibit trends comparable to reference concrete, indicating moderate resistance to chloride penetration. Overall, the findings suggest that utilizing sorted CPB aggregates is a viable approach to replacing natural aggregates in mortars and concretes.本研究探讨了在砂浆与混凝土中，采用经分选的次级混凝土铺路砖（CPB, Concrete Paving Block）骨料替代天然骨料的影响。砂浆中细骨料的替换率范围为0%至100%，混凝土中细骨料和/或粗骨料的替换率为50%。本研究分析了该废料的多项性能，包括粒径分布、孔隙率、吸水率与密度。针对砂浆与混凝土，本次研究评估的参数涵盖工作性、稠度、密度、抗压强度、电阻率与微观结构。研究结果显示，掺入CPB骨料的砂浆需更高剂量的超塑化剂，才能达到预期的工作性，这一需求源于单位体积内水泥用量增加，以及再生骨料颗粒更细小的特性。砂浆的早期抗压强度在再生骨料掺量为50%时达到峰值，这是因为有效水灰比降低；而细骨料100%替换则会导致抗压强度显著下降。掺加再生骨料的混凝土，其早期抗压强度与基准混凝土相当，甚至更优；但养护28天后，所有掺再生骨料的混凝土强度均低于基准混凝土。细骨料、粗骨料以及两者复配取代50%时，对应的28天抗压强度分别为65.9MPa、64.8MPa与62.3MPa，上述结果优于同类研究的成果。耐久性评估结果显示，掺入CPB骨料的混凝土混合料的性能变化趋势与基准混凝土相近，表现出中等的氯离子渗透抗性。整体而言，本研究结果证实，采用分选后的CPB骨料替代砂浆与混凝土中的天然骨料是切实可行的方案。