Quantitative Effects of Mixture Parameters on Alkali-Activated Binder-Based Ultra-High Strength Concrete at Ambient and Elevated Temperatures

Abstract

This work investigates the effects of mixture parameters on the slump flow and compressive strength of a new type of alkali-activated binder-based ultra-high strength concrete (AAB-UHSC) before and after exposure to high temperatures. The innovative UHSC adopts a combination of sodium silicate (SS) and potassium carbonate (PC) as the activator. Compared with the alkali hydroxide that is currently used in existing AAB-UHSC, alkali carbonate salts are environmental- and user-friendly and cost-effective. Four mixture proportioning parameters, including water/precursor ratio, activator/precursor ratio, silica fume (SF) replacement percentage, and SS/PC ratio, are evaluated regarding their quantitative effects on fresh and hardened properties of AAB-UHSC using Taguchi method. The analysis of variance (ANOVA) reveals that the activator/precursor ratio is the decisive parameter controlling the slump flow diameter of fresh AAB-UHSC, whereas all four parameters have considerable influence on compressive strength of AAB-UHSC at room temperature. Although increasing the activator/precursor ratio increases compressive strength of AAB-UHSC at room temperature, it is adverse for residual strength of AAB-UHSC after exposure to high temperatures. Based on the test results and ANOVA, a mixture proportioning method of AAB-UHSC, which is lacking in existing literatures, is proposed and experimentally validated.