Evaluation of the rheological and mechanical behavior of the synthesized geopolymer with residue waste

ABSTRACT The sustainable construction of the future, besides low energy consumption and greenhouse gas emissions must also adopt the principle of reusing wastes generated by the production chain that impact the environment. One of the most impacting wastes generated by the aluminum production chain is fly ash. Geopolymers are cementitious materials with a three-dimensional structure formed by chemical activation of aluminosilicates. According to studies some ashes have proven to be suitable sources of Al and Si for the geopolymerization reaction. One of the most important aspects in the commercializing these products is their behavior in a plastic state. The workability of fresh geopolymer paste can be measured using several common tests used for Portland cement concrete, such as flow and slump; however, a more in-depth characterization of their rheology is essential for understanding their basic setting mechanisms. The objective of this work was to evaluate the rheological behavior of the Davidovits (SiO2/Al2O3) geopolymer paste at 2.65; 3.04 and 4.11. The mechanical resistance to compression at 24 hours, 7 days and 28 days of geopolymer cure was also evaluated. The geopolymerization reaction was conducted at ambient temperature of 28°C and 15 Molar sodium hydroxide (NaOH) and 10 Molar sodium silicate (Na2SiO3), were used as the activator. Fly ash and metakaolin were used as source of Al and Si was used. XRD, XRF, SEM techniques were used in the characterization of raw materials and geopolymers. The geopolymer with a lower Davidovits ratio of 2.65 presented better workability in its fresh state and higher mechanical strength at 40.80 MPa compression with 28 days cure at ambient temperature. The Herchel Bulkley rheological model was the one that was best adjusted to the geopolymers.

摘要：未来可持续建筑除需满足低能耗与温室气体减排要求外，还应遵循再利用生产链产生的环境影响型废弃物的原则。铝生产链产生的极具环境影响的废弃物之一为粉煤灰（fly ash）。地质聚合物（geopolymer）是通过铝硅酸盐化学活化形成的具有三维结构的胶凝材料。相关研究表明，部分粉煤灰可作为适用于地质聚合反应的铝、硅源。该类产品商业化过程中的关键要点之一为其塑性状态下的性能。新鲜地质聚合物浆体的工作性可采用硅酸盐水泥混凝土常用的多项测试方法进行评估，例如流动度与坍落度测试；然而，对其流变学特性进行更深入的表征，对于理解其基本凝结机理至关重要。本研究的目的为评估Davidovits（SiO₂/Al₂O₃）比值分别为2.65、3.04和4.11的地质聚合物浆体的流变性能，同时测定该地质聚合物养护24小时、7天及28天时的抗压力学强度。本研究在28℃的室温条件下开展地质聚合反应，采用15摩尔浓度的氢氧化钠（NaOH）与10摩尔浓度的硅酸钠（Na₂SiO₃）作为活化剂，以粉煤灰与偏高岭土作为铝、硅源。采用X射线衍射（XRD）、X射线荧光光谱（XRF）、扫描电子显微镜（SEM）等技术对原材料及地质聚合物进行表征。结果表明，Davidovits比值为2.65的地质聚合物展现出更优的新鲜状态工作性，且在室温养护28天后的抗压强度可达40.80 MPa。赫尔施-布尔克利流变模型是最适配该类地质聚合物的流变模型。