Development of geopolymer pervious concrete with improved engineering properties and environmental benefits
Creators: name: Huang, Wei
Publisher: name: No Publisher Supplied
Year: 2023

description: Pervious concrete can be applied as pavement surface to develop a permeablepavement system, allowing in-situ infiltration of rainwater, which helps to protect natural hydrologic balance and prevent heavy precipitations from flowing into storm drains with water as effluent. However, relatively low mechanical strength of conventional pervious concrete largely limits its application. Geopolymer is a relatively new class of cementitious materials that have brought attractive focus as its good engineering performance and environmental benefits. It is desired to fabricate pervious concrete using geopolymer for superior performance with reduced carbon footprint.This dissertation aims to develop geopolymer pervious concrete that have improved engineering properties and environmental benefits than traditional Portland cement pervious concrete. The multi-aspect performance of geopolymer based cementitious paste and pervious concrete are evaluated, including geopolymer paste formulation and modification, geopolymer pervious concrete mixing design and performance evaluation, numerical modeling for geopolymer pervious concrete by discrete element method (DEM), and Life-Cycle assessment (LCA) for conventional and geopolymer based pervious concrete incorporating recycled concrete aggregate (RCA) and carbon fibers. The geopolymer cementitious paste was successfully synthesized with the use of metakaolin (MK) and fly ash (FA) under ambient curing condition with high mechanical strength and stability and was further modified by certain amount of granulated blast furnace steel slag (GBFS), Portland cement (PC) and carbon fiber for improved strength and reduced drying shrinkage. XRD and SEM results indicated that the presence of GBFS led to better integrity and reduced crack and void contents for the geopolymer paste. The highest compressive strength of geopolymer paste modified with 2% carbon fiber, 33% Portland cement and 10% GBFS could reach 73 MPa, which was higher by 55% and 65% compared to that of non-modified geopolymer and ordinary Portland cement pastes, respectively.The geopolymer pervious concrete was prepared with better engineering properties than that of conventional cement pervious concrete, including higher mechanical strength, better freezing-thawing, abrasion and flexural fatigue resistance. Porosity was found to be a dominant factor influencing mechanical strength and permeability of pervious concrete. While the clogging test of geopolymer based pervious concrete showed no difference with that of PC based one. When the porosity is the same, smaller aggregate size induces higher compressive but lower splitting tensile strength. Incorporating sand is crucial for improving the compressive strength and freezing-thawing durability of pervious concrete but reducing the splitting tensile strength. The FA based pervious concrete presented higher flexural strength and could sustain slightly longer under fatigue test by the same stress ratio than that of PC based pervious concrete.The DEM modeling results indicated that the tensile strength and shear cohesion of paste-aggregate bond presented significant influence on compressive strength of pervious concrete model, while its splitting tensile strength was mainly influenced by tensile strength of paste-paste and paste-aggregate bonds. The numerical strength test simulation showed that the calibrated model was reliable to predict mechanical properties of pervious concrete under different porosity levels. The validation results indicated the feasibility of reducing paste content while maintaining considerable strength. However, the smaller sized aggregate caused greater compressive but smaller tensile strength of the previous concrete.Geopolymer pervious concrete presented lower GHG emissions but higher or comparative energy consumption than those of cement based pervious concrete. Carbon fiber caused significant increase in splitting tensile strength for metakaolin based pervious concrete due to good bonding effect with metakaolin paste, but less improvement in strengths for other pervious concrete mixtures. However, incorporating carbon fiber increased environmental impacts significantly. RCA presented slightly higher environmental impacts than those of natural coarse aggregate. The avoided landfill by RCA would only reduce the total environmental impacts of pervious concrete by 5%~10%. The MK based pervious concrete might be a suitable substrate for incorporating RCA or carbon fiber, resulting in acceptable strength reduction or environmental impact increase, respectively. However, RCA and carbon fiber should not be used together into pervious concrete as that would make the pervious concrete has neither engineering performance nor environmental benefit.