23 March 2015 Monitoring accelerated carbonation on standard Portland cement mortar by nonlinear resonance acoustic test
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Abstract
Carbonation is an important deleterious process for concrete structures. Carbonation begins when carbon dioxide (CO2) present in the atmosphere reacts with portlandite producing calcium carbonate (CaCO3). In severe carbonation conditions, C-S-H gel is decomposed into silica gel (SiO2.nH2O) and CaCO3. As a result, concrete pore water pH decreases (usually below 10) and eventually steel reinforcing bars become unprotected from corrosion agents. Usually, the carbonation of the cementing matrix reduces the porosity, because CaCO3 crystals (calcite and vaterite) occupy more volume than portlandite. In this study, an accelerated carbonation-ageing process is conducted on Portland cement mortar samples with water to cement ratio of 0.5. The evolution of the carbonation process on mortar is monitored at different levels of ageing until the mortar is almost fully carbonated. A nondestructive technique based on nonlinear acoustic resonance is used to monitor the variation of the constitutive properties upon carbonation. At selected levels of ageing, the compressive strength is obtained. From fractured surfaces the depth of carbonation is determined with phenolphthalein solution. An image analysis of the fractured surfaces is used to quantify the depth of carbonation. The results from resonant acoustic tests revealed a progressive increase of stiffness and a decrease of material nonlinearity.
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J. N. Eiras, T. Kundu, John S. Popovics, J. Monzó, M. V. Borrachero, Jordi Payá, "Monitoring accelerated carbonation on standard Portland cement mortar by nonlinear resonance acoustic test", Proc. SPIE 9438, Health Monitoring of Structural and Biological Systems 2015, 94380D (23 March 2015); doi: 10.1117/12.2084124; https://doi.org/10.1117/12.2084124
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