Investigation of macro void development of different cement mortars exposed to sulphate attack by computerized tomography

In this study, void structure development of different cement mortars exposed to sulfate attack was investigated by Computerized Tomography (CT). For this purpose, the types of cement to be used as cementitious materials in the study were PC 42,5 R (CEM I) and SDC 32,5 (SRC). Prismatic mortar specimens with the dimensions of 40 x 40 x 160 mm and 25 x 25 x 285 mm were produced by using these cements. Firstly, physical properties of cements were determined by standard consistency, setting time, soundness, specific gravity and specific surface tests. Produced mortar specimens were exposed to the effects of 5% concentrations of MgSO4 and Na2SO4 in addition to standard curing conditions. Length change, water absorption, capillary water absorption and compressive strength tests were performed at different ages. In addition to these tests, the void structure developments of mortar specimens were investigated by CT. Moreover, microscopic analyses of mortar specimens were carried out at the ages of 28, 70 and 180 days.A custom made image processing program was developed using Matlab software to analyze the CT images. With this developed program, quantitative analyses were performed on the obtained CT images. Utilizing the statistical analyses, several comparisons were made on the obtained experimental results.According to the obtained test results in the study, it was determined SRC more resistant to the sulfate attack than CEM I. The maximum macro void ratio, the biggest loss of compressive strength and maximum length change measurements occurred in the mortar specimens were exposed Na2SO4 solution with 5% concentration. On the other hand, it was determined SRC having high sulfate resistant. The biggest degradation among the produced specimens was occurred to expose Na2SO4 solution with 5% concentration in CEM I specimens. The images obtained from SEM exhibited that all the mortar specimens under sulfate attack experienced intensive formation of portlandite and ettringite. Void ratios for the all CEM I and SRC mortar specimens cured with water increased after a certain time. The results obtained from CT image analyses were confirmed by the results obtained from water absorption tests. As a result, CT has proven as a non-destructive testing method to be a functional and sensitive yet complex method in the investigation of macro void structure development of cement mortars exposed to sulfate attack.