Development of Ultra-High Performance Engineered Geopolymer Composites (UHP-EGCs)

This study investigated the possibility of developing novel UHP-EGC materials for the repair and new construction of transportation infrastructure in Region 6 by utilizing locally available resources. To this end, the geopolymers (GPs) in this study were synthesized by activating metakaolin (MK) with potassium silicate and sodium silicate solutions. The solutions were manufactured in the laboratory by dissolving silica fume and potassium hydroxide (KOH) or sodium hydroxide (NaOH) in deionized water. MK-based GP binders, mortars, and fiber-reinforced composites were manufactured and evaluated to determine their density, compressive strength, tensile properties, and slant shear bond strength to Portland cement concrete (PCC). Based on the experimental findings, it was concluded that both MG7500 and FA4404 admixtures improved the workability but reduced the compressive strength of the GP. The inclusion of both microsilica sand and UHMWPE fibers (i.e., plasma-treated and pristine UHMWPE fibers) led to an improvement in compressive strength. Plasma-treated UHMWPE fibers exhibited a higher compressive strength compared to pristine UHMWPE fibers. The uniaxial tensile test results revealed that the composites with pristine and plasma-treated UHMWPE fibers at 1.5 vol.% exhibited robust pseudo-strain hardening (PSH) behavior. Furthermore, the best-performing composite (i.e., composite with plasma-treated fibers) exhibited a tensile strength and strain capacity of 6.65 MPa and 6.26%, respectively. The slant shear test revealed that all the materials passed the minimum requirement (i.e., 28-day shear bond strength greater than 13 MPa) to be used as a repair material. While the compressive strength of the developed GP composites using different techniques reached up to 73 MPa, future research should be directed toward the evaluation of hybrid systems (such as MK and slag) to achieve a compressive strength greater than 120 MPa.

本研究针对第六区域交通基础设施的修复与新建工程，探索利用当地资源开发新型UHP-EGC材料的可行性。为此，本研究通过硅酸钾与硅酸钠溶液激发偏高岭石（metakaolin, MK）合成地聚合物（geopolymers, GPs）。上述激发溶液由实验室自制，具体工艺为将硅灰与氢氧化钾（KOH）或氢氧化钠（NaOH）溶解于去离子水中制得。研究团队制备并表征了基于偏高岭石的地聚合物胶凝材料、砂浆及纤维增强复合材料，测试其密度、抗压强度、拉伸性能以及与硅酸盐水泥混凝土（Portland cement concrete, PCC）的斜剪粘结强度。基于试验结果，研究得出如下结论：MG7500与FA4404两种外加剂均可改善地聚合物的工作性，但会降低其抗压强度；同时掺入微硅砂与超高分子量聚乙烯（ultra-high molecular weight polyethylene, UHMWPE）纤维（包括等离子体处理纤维与未处理原纤维）可提升材料抗压强度，且等离子体处理的UHMWPE纤维相较于未处理原纤维，可使材料获得更高的抗压强度。单轴拉伸试验结果表明，掺入体积分数1.5%的未处理或等离子体处理UHMWPE纤维的复合材料均表现出优异的伪应变硬化（pseudo-strain hardening, PSH）行为。其中性能最优的复合材料（即掺入等离子体处理纤维的试样）的抗拉强度与应变极限分别为6.65 MPa与6.26%。斜剪试验结果显示，所有受试材料均满足作为修复材料的最低性能要求（即28天龄期斜剪粘结强度大于13 MPa）。尽管通过不同工艺制备的地聚合物复合材料抗压强度最高可达73 MPa，但未来仍需开展复合体系（如偏高岭石与矿渣复掺）的相关研究，以实现抗压强度突破120 MPa的目标。