Ultrasonic and impact spectroscopy monitoring on internal sulphate attack of cement-based materials

• Published in: Materials & design 2017-07, Vol.125, p.46-54
• Main Authors: Genovés, V., Vargas, F., Gosálbez, J., Carrión, A., Borrachero, M.V., Payá, J.
• Format: Article
• Language: English
• Subjects: Acoustic spectroscopy; Chirp signal; Microstructure; Non-destructive test; Sulphate attack; Ultrasonics
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2017.03.068

An exhaustive monitoring of an internal sulphate attack of Portland cement-based materials is addressed. Four series of Portland cement mortars with different amounts of gypsum (0%–2% SO3 respect to the cement by mass) were monitored by means of physical, microstructural and non-destructive tests, studying specimens with a low expansion rate to examine the sensitivity of the applied techniques. The expansion analysis has shown the suitability of a fitting model, allowing the examination of two characteristic parameters: the characteristic time of the expansion reaction and the maximum amplitude of the expansion. In the mechanical analysis, higher values of Rc and Rf were attained as the gypsum content decreased. A microstructural analysis (thermogravimetry and FESEM) supported ettringite formation and expansion process. These results have been correlated with non-destructive tests: impact resonance acoustic spectroscopy and ultrasonic measures. The dynamic modulus and ultrasonic pulse velocity have closely predicted the stiffness of the specimens. The total material attenuation (absorbed energy of the chirp signal ultrasonic wave) presented different trends, showing clear differences for the most damaged series (2% SO3). Attenuation supplied interesting information about the hardening process and the microcracking effect due to a mortar expansion higher than 0.04%. The novelties of this study are the exhaustive monitoring of an internal sulphate attack, as well as the examination of the sensitivity of brand new NDT techniques when this damage process overlaps with the curing process. [Display omitted] •Ettringite determined by HRTG rises as the initial amount of gypsum increases and with the curing time in pastes.•According to vibrational tests, expansion of less than 0.04% does not have a significant effect on the dynamic modulus.•Chirp signals (100kHz to 1MHz) were successfully used for assessing material wave attenuation and ultrasonic pulse velocity.•The attenuation monitoring is presented as an interesting procedure for the assessment of low-level expansion processes.•Traditional techniques and new NDT using broadband signals were successfully correlated to determine the damage.