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：轻集料（lightweight aggregates）是一类具备多孔结构的粒状材料，可用于隔热隔音、园林景观装饰、轻质填充料生产、排水工程、轻质填埋场及基础设施建设，同时也可应用于水培栽培领域。该类材料以黏土质前驱体为原料，经高温烧结制备而成；烧结过程中，玻璃相发生膨胀以捕获反应生成的气体，助熔剂含量与产气物质为该工艺的关键影响因素。 基于上述研究背景，本研究验证了利用花岗岩与大理石切割废料（GMCW）及黏土制备轻集料的可行性。对前驱体的表征工作涵盖比表面积测试（BET法）、激光粒度分析、细度测定、比重与堆积密度检测，同时开展了热分析（ADT/TG）、化学组成分析（X射线荧光光谱法，XRF）以及矿物相分析（X射线衍射法，XRD）。 本研究通过马弗炉在1000℃至1263℃的温度区间内进行烧结，制备了GMCW掺量分别为0、50、60、70、80、90及100%的轻集料试样。对烧结后的混合料开展了多维度性能测试：颗粒密度、吸水率、堆积密度、轻集料变形模量、膨胀指数、质量损失率、干缩指数、外观形貌观测、抗拉强度，以及通过扫描电子显微镜（SEM）表征微观结构。 烧结完成后，本研究获得了颗粒密度小于2.00g/cm³、吸水率小于20%、堆积密度小于0.88g/cm³的轻集料；上述指标为轻集料的分类判定阈值，同时满足结构混凝土用轻集料的合格要求。在核心性能表现上，本研究成功制备了高废料掺量的轻集料，其颗粒密度、吸水率与堆积密度分别为1.56g/cm³、8%及0.85g/cm³，各项指标均符合规范要求；此外，所制备轻集料的抗拉强度为商用轻集料的四倍。