The effect of specimen size on deterioration due to external sodium sulphate attack in full immersion studies

A rapid and reliable performance test will enable fast and suitable selection of binder for each service environment. In order to evaluate the possibility of using smaller specimens to accelerate the sulphate resistance tests, Portland cement mortar specimens of sizes 20 × 20 × 160 mm, 25 × 25 × 280 mm and 40 × 40 × 160 mm were continuously immersed in 50 g/l sodium sulphate solution and various physical and microstructural characteristics were evaluated at different ages. Additionally, the depth of deterioration and the alteration in binder chemistry was investigated using microCT scan and SEM-BSE along with EDX analysis. The XRD pattern confirms that expansion of specimen is related to the fraction in the cross section altered by the formation of ettringite and gypsum. The expansion and evolution of flexural strength showed a close correlation, notwithstanding a concurrence between the depth of deterioration and evolution of dynamic modulus. This paper discusses the relevance or possibility of using various test methods and their consistency in sulphate attack measurements. The investigation shows that smaller specimens can be considered as a means to accelerate the typical immersion test method for sulphate attack.