Green and Durable Geopolymer Composites for Sustainable Civil Infrastructure

Abstract

Green concrete, which incorporates industrial byproducts to partially/fully replace portland cement in normal concrete, is not as sustainable as many would like to believe. Like conventional cement concrete, it is a brittle material with low tensile strength and ductility, and therefore susceptible to cracking. Extensive cracking causes many types of deterioration in concrete structures, significantly reducing their service life. Even if the structure is made of more “environmentally-friendly” materials, the short lifespan makes it unsustainable. For establishing sustainable infrastructure systems, a new material technology that combines high material greenness and durability in one concrete needs to be developed. This dissertation is focused on green and durable fiber-reinforced geopolymer composites – Engineered Geopolymer Composites (EGCs) – for civil infrastructure applications. EGCs combine two emerging technologies: geopolymer, which is a cement-free binder material, and Engineered Cementitious Composite (ECC), which is a strain-hardening fiber-reinforced cement composite with high tensile ductility and multiple-microcracking characteristics. This research covers three aspects: development, characterization, and application of EGC. First, a new design method for ductile fiber-reinforced geopolymer composites is proposed to facilitate the development of EGC. It integrates three material-design techniques – Design of Experiment (DOE), micromechanical modeling, and Material Sustainability Indices (MSI) – each of which assists the geopolymer-matrix development, composite design, and environmental performance assessment. With the aid of the integrated design method, an optimized EGC with good compressive strength, high tensile ductility, and enhanced material greenness is systematically developed. Second, fundamental durability properties of the developed EGC are experimentally characterized. Specifically, cracking characteristics, water permeability, self-healing functionality, and sulfuric acid resistance are investigated. Extensive crack-width measurement and water-permeability testing on cracked EGC demonstrate the tightly-controlled multiple cracks and higher water tightness than cracked reinforced concrete (RC). The permeability test also observes a white substance formed inside microcracks of EGC, providing the recovery in water tightness. Subsequent experiments also confirm the stiffness recovery, which demonstrates the self-healing functionality of EGC. In the case of sulfuric acid resistance, acid-exposed EGC specimens show limited surface erosion compared to cement concrete and ECC. Further, no significant degradation in mechanical properties of EGC is observed. Finally, this dissertation explores a promising infrastructure application of EGC. Combined with the characterized durability properties, brief market research and technical-advantage analysis suggest that EGC is promising for large-diameter sewer pipes. In addition, an environmental life cycle analysis (LCA) is conducted to verify and quantify the enhanced sustainability of EGC pipes, in comparison with RC and ECC pipes. The comparative LCA shows the 14% lower greenhouse gas emissions of EGC than RC. Further, it is estimated that, if service life of EGC pipes is more than 1.3 times that of RC pipes, EGC performs best in both energy consumption and greenhouse gas emissions.