Development of lightweight aggregates from crushing of ornamental stones (granites and marbles) and clay

ABSTRACT Lightweight aggregates are granular materials with porous structure used as thermal and acoustic insulation, decoration in landscaping, the production of light fillings, drainage works, light landfills and infrastructure, as well as hydroponics. Manufactured from clayey precursors, sintered at high temperatures, which expand due to a glassy phase to capture the gases generated, being the flux content and substances that form gases, intervening factors of the process. In this context, it was verified the possibility of using granite and marble cutting waste (GMCW) and clay with the objective of developing lightweight aggregates. The precursors were characterized as surface area (BET), laser granulometry, fineness, specific gravity and bulk density in addition to thermal (ADT/TG), chemical (XRF) and mineralogical (XRD) analyzes. Aggregates with 0, 50, 60, 70, 80, 90, and 100% GMCW contents were produced by sintering at temperatures of 1000°C to 1263°C in a muffle furnace. The sintered mixtures were analyzed for their particle density, water absorption, bulk density, modulus of deformation of the lightweight aggregates, swelling index, mass loss, dry shrink index, visual analysis, tensile strength and morphology by scanning electron microscopy (SEM). After sintering, aggregates with particle density less than 2,00g/cm³, water absorption less than 20% and bulk density less than 0,88g/cm³ were obtained, these values being defined as requirements for classifying an aggregate as light and qualified for use in structural concrete. As for the highlighted properties, it was possible to develop lightweight aggregates with high waste content that meet the normative requirements, respectively, with values of 1,56g/cm³, 8% and 0,85g/cm³, in addition to lightweight aggregates presenting tensile strength fourfold higher than the commercial lightweight aggregate.摘要：轻骨料（lightweight aggregates）是一类具备多孔结构的颗粒材料，可应用于隔热隔音、景观装饰、轻质填料生产、排水工程、轻质填埋场与基础设施建设，以及水培种植领域。轻骨料以黏土质前驱体为原料经高温烧结制备，烧结过程中玻璃相发生膨胀以捕获反应产生的气体，助熔剂成分与产气物质为该工艺的核心影响因素。 在此研究背景下，本研究验证了利用花岗岩与大理石切割废料（granite and marble cutting waste, GMCW）及黏土制备轻骨料的可行性。研究人员对前驱体开展了比表面积（BET）、激光粒度分析、细度、比重与堆积密度的表征，并辅以热分析（ADT/TG）、化学组成分析（XRF）及矿物相分析（XRD）。 分别配制GMCW掺量为0、50%、60%、70%、80%、90%、100%的混合料，在马弗炉中于1000℃至1263℃的温度区间内烧结制备轻骨料。随后对烧结产物开展了多项性能测试：包括颗粒密度、吸水率、堆积密度、轻骨料变形模量、膨胀指数、质量损失率、干缩指数、外观形貌分析、抗拉强度测试，并通过扫描电子显微镜（scanning electron microscopy, SEM）表征其微观结构。 烧结结果显示，所制备的轻骨料颗粒密度低于2.00g/cm³、吸水率低于20%、堆积密度小于0.88g/cm³，上述指标为轻骨料的分类标准，且满足结构混凝土用轻骨料的应用要求。值得关注的是，本研究成功制备出高废料掺量的轻骨料，其性能完全符合规范要求，最优样品的颗粒密度为1.56g/cm³、吸水率为8%、堆积密度为0.85g/cm³，且其抗拉强度为商用轻骨料的四倍。