Fire-induced damage assessment of cementless alkali-activated slag-based concrete

Abstract

According to recent studies, concrete made with alkali activators and slag is a potential construction material. To ensure the safety and durability of concrete structures after a fire, it is crucial to assess the material properties and determine the extent of the damage. This paper investigated the effect of elevated temperatures (25 °C, 100 °C, 250 °C, 500 °C, 700 °C and 900 °C) on the properties of cementless alkali-activated slag-based concrete. In this regard, 216 cubic samples with eleven mixes were designed according to the literature and then prepared. Two categories of tests were utilized: nondestructive and destructive tests. The nondestructive evaluations included visual inspections, mass loss, and the measurement of ultrasonic pulse velocity (UPV) of the specimens. The destructive tests were conducted to determine the post-fire mechanical properties, including stress–strain curves, compressive strength, and strain energy. Microstructural analyses (EDS,SEM, and XRD) were performed to evaluate microstructural and chemical composition changes after exposure to high temperatures. According to the results, exposing slag-based concrete samples to less than 500 °C can enhance their compressive strength. The reduction in strength for slag-based concrete ranged from 22% to 59% at 700 °C, showing a considerable improvement compared to normal concrete. Afterward, regression-based models were proposed to bridge the nondestructive evaluations to the destructive measurements, yielding appropriate predictions with the highest R-factor of 0.96.