Initial Characterization of Geopolymer-Based UHPC Material Properties TR-708A, August 2018

Ultra-high-performance concrete (UHPC) has great potential as a structural material for bridge engineering due to its excellent strength, ductility, and durability. However, the high Portland cement content required by conventional UHPC poses a major obstacle to widespread practical application because of its high cost and CO2 emissions. Introducing any sort of composites as replacements for Portland cement would have a positive impact on the practical applications of UHPC. This research project investigated the mechanical properties (such as compression, tension, bending strength, and modulus of elasticity) of geopolymer-based UHPC and a type of composite UHPC using Iowa materials to explore the feasibility of their use in UHPC for transportation infrastructure. In this study, different ultra-high-performance geopolymer (UHPG) mixes were formulated, their mechanical properties were evaluated, and effects of curing methods on the UHPG strength were investigated. The results indicated that usable UHPG can be achieved through engineered formulation using locally available concrete materials. The UHPG sample made in China and tested at Iowa State University (ISU) showed a compressive strength of 123 MPa (17,868 psi) and maximum compressive strain of 0.0047 micro-strain. The UHPG samples made with a slag-fly ash blend and a liquid (activator solution)-to-binder (slag and fly ash) of 0.27 had 28-day compressive strength of 102 MPa (14,800 psi). When reinforced with 2% (by volume) of polyvinyl alcohol (PVA) fiber, the UHPG mixes developed at ISU exhibited strain and displacement hardening behavior in tension and flexure, indicating significant ductility. Replacement of slag for fly ash improved strengths and elastic modulus, but noticeably reduced the deflection at failure and ductility of UHPG. Steam curing at 50°C appeared to be the optimal condition for the UHPG strength development