Durability Assessment of Alkali-Activated Concrete Exposed to a Marine Environment

Abstract

This study investigated the performance of two alkali-activated concretes (AACs) subjected to marine exposure for 2 years. The AACs were synthesized from a low-calcium Class F fly ash (FA) and a blast-furnace slag. Concrete specimens were exposed in a marine environment in a port facility in southern Australia for 2 years. The specimens were subject to a range of nondestructive testing (NDT) techniques, including resistivity, Schmidt hammer, and ultrasonic pulse velocity (UPV) tests. In addition, chloride diffusion coefficients were calculated from concrete cores taken from specimens exposed in the marine environment. Microscopy analysis was undertaken using Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA), and comparative data were taken on laboratory specimens at 28 days. Furthermore, the chloride diffusion coefficients were compared with the results of standard laboratory tests undertaken on the control samples at 28 days, including rapid chloride permeability testing (RCPT) using a 10-V driving voltage, an NT Build 492 test, and a bulk diffusion test, to determine the relationship between the 28-day laboratory tests results and the site performance. The data showed good correlation between the predicted performance based on the 28 day laboratory tests and the 2-year site data. The chloride diffusion of the ground granulated blast-furnace slag (GGBS) concrete agreed very accurately with the predicted value from the modified RCPT test, whereas the performance of FA concrete was superior to that predicted.