Agate waste valorization in mortars and concretes: life cycle assessment

ABSTRACT The application of residues from agate beneficiation process (agate powder) in mortars and concretes based on Portland cement is technically viable considering materials mechanical properties and durability. However, there is a lack of studies that assess the environmental profile of the produced materials. This paper aims to evaluate the potential environmental impacts associated to the life cycle of mortars and concretes produced with the application of agate powder in substitution of Portland cement and fine aggregate, respectively. To that, experimental designs defined in previous studies were considered, to perform a cradle to gate analysis, where the following impacts were evaluated, according to CML-IA method: climate change, soil and water acidification, eutrophication, ozone layer depletion, and resources depletion (fossil and non-fossil). Results show up to 30% reduction of potential impacts, for the application of the residue in substitution to Portland cement in mortars. Less expressive reductions are observed for the use of the residue in substitution of the fine aggregate; however, gains on mechanical strength justify the application of the residue in specific cases. Since all the assessed impacts are closely related to cement consumption, the application of the residue to replace cement is considered the most environmentally viable alternative, for the evaluated cases. The participation of the transport processes in all impact categories validates the application of materials locally produced/extracted. Finally, future studies shall consider the performance of the produced materials, in comparison to the reference ones.摘要 考虑到材料的力学性能与耐久性，基于硅酸盐水泥（Portland cement）的砂浆与混凝土中应用玛瑙选矿工艺产生的残渣（玛瑙粉）在技术上具备可行性。然而，目前尚缺乏针对此类制备材料的环境属性开展评估的相关研究。本研究旨在评估分别以玛瑙粉替代硅酸盐水泥与细骨料制备的砂浆与混凝土的全生命周期潜在环境影响。为此，本研究沿用既往研究确立的实验设计，开展从摇篮到大门（cradle to gate）的生命周期评价，依据CML-IA方法对以下影响类型进行评估：气候变化、土壤与水体酸化、富营养化、臭氧层耗竭以及资源耗竭（化石资源与非化石资源）。研究结果显示，在砂浆中以玛瑙残渣替代硅酸盐水泥时，潜在环境影响最高可降低30%。以该残渣替代细骨料时，环境影响的降幅相对有限，但力学性能的提升使得该方案在特定场景下具备应用价值。由于所有评估的环境影响均与水泥消耗量密切相关，在本次评估的场景中，以玛瑙残渣替代水泥被视为环境友好性最优的应用方案。运输环节在所有影响类别中均占有一定比例，这印证了就地生产/取材材料的应用合理性。最后，未来的研究可将制备材料的性能与基准材料进行对比分析。