Capillary imbibition in cementitious materials: effect of salts and exposure condition
De Brabandere, L. (2021). Capillary imbibition in cementitious materials: effect of salts and exposure condition. MSc Thesis. Ghent University, Faculty of Engineering and Architecture: Gent. xi, 63 pp.
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Document type: Dissertation
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| Abstract |
During its service life, concrete structures are often exposed to harsh environmental conditions. For instance, a building along the coastline exposed to salts or a structure in a city environment exposed toa high concentration of carbon dioxide. Due to global warming, burning fossil fuels for energy and an increasing population, the concentration of carbon dioxide in the atmosphere increases. Penetrating of these aggressive components into the concrete can cause deterioration and corrosion of reinforcement steel. Therefore, the investigation of concrete in different environments is an important topic. A reliable way to assess the transport properties of concrete is capillary imbibition. In this master’s thesis theeffects of different imbibing liquids and exposure conditions on the capillary imbibition phenomenon is studied. Two concrete mixtures with water to cement ratio of 0.4 and 0.6 were used, PC4 and PC6 respectively. The samples were cured in real environmental conditions: city exposed, city sheltered, sea exposed, sea sheltered and also in ideal laboratory conditions as a comparison. Data about the environment conditions (temperature and relative humidity) during those periods was recollected. The concrete mixes were tested after 2 months and 6 months of exposure. The experimental program included performing indirect porosity measurements on site and measuring capillary imbibition after the different exposure conditions. Moreover, different imbibing liquids were also tested.The results showed that regarding the porosity and the capillary imbibition rate (CIR), among the studied exposure conditions, sheltered conditions are the worst ones to cure concrete. Due to a low availability of water to continue the hydration reaction, these samples have the highest capillaryporosity and the highest CIR in comparison to other exposure conditions. Thus, aggressive components that can cause deterioration of the concrete can penetrate into the concrete more easily. Three different imbibition liquids were used: water, 3.5 % NaCl solution and 0.5 % Na2SO4 solution. The influence of the imbibing liquid depends on the w/c and thus the porosity of the concrete. For samples of PC4, the CIR for Na2SO4 as imbibing liquid was lower in comparison to water and NaCl. The sulfates in the solution might cause a pore blocking effect leading to a decreased CIR. For PC6 there was no significant difference between the different imbibition liquids. The influence of the pore blocking effect is probably smaller due to the larger porosity of PC6. The results obtained in this master’s thesis show that the worst condition to cure concrete, regarding transport properties, is sheltered from rain and UV radiation. This should be considered whenestimating the service life of the concrete structure. The imbibing liquid has an effect on transport properties and deterioration mechanisms as well. This can be relevant for concrete structures in marine environment. Further research can be performed to study the influence of chloride ingress andcarbonation on capillary imbibition and transport properties of concrete in general. |
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