Abstract
A polymer-modified cement mortar (PCM) is widely used as a repair material for reinforced concrete (RC) structures owing to its excellent strength and durability. However, considering the maintenance of the RC structures and the use period of the structures, the change in the physical properties of the PCM should be evaluated when exposed to various high-temperature environments, such as fires. In this study, the degradation of the mechanical properties (compressive strength and modulus of elasticity), thermal decomposition of the PCM in various high-temperature environments, and the change in the pore structure of the PCM after exposure to high temperatures were quantitatively investigated. A mechanical property evaluation of PCM was performed under three heating conditions: (i) heating in a compression tester, (ii) heating the specimen in an oven to a predetermined temperature and then moving it to a compression tester preheated to the same temperature, and (iii) cooling to room temperature after heating. In the experiment, a PCM specimen was prepared by changing the polymer–cement ratio (polymer content) of ethylene-vinyl acetate (EVA), the most commonly used polymer, to perform a high-temperature sectional test from 200 to 800 °C. In addition, to investigate the change in the PCM mechanical properties in the high-temperature region, in terms of the pyrolysis of EVA, the porosity change and mass change were examined using thermal analysis and mercury intrusion porosimetry. Before heating, the compressive strength of the PCM increased with the EVA content up to 10 % of the polymer–cement ratio. Under the cooling conditions after heating up to 200 °C, the mechanical performance of the PCM was restored, whereas the degradation of the mechanical properties of the PCM without cooling was more pronounced. Furthermore, the mass loss, heat flow, and the total porosity of the PCM increased as the EVA content increased, which is correlated with the degradation of the mechanical properties of the PCM.
Highlights
Polymer-modified cement mortar (PCM) is superior to ordinary cement mortar in terms of strength, durability, chemical resistance, and workability and is widely used for repairing and strengthening reinforced concrete (RC) structures [1,2,3,4]
PCM has shown different physical and mechanical properties than those of ordinary inorganic cement mortar and concrete because PCM is a mixture of polymeric organic material and cement mortar [5,6,7]
Considering the maintenance of RC buildings and the use period of the structures, the change in the physical properties of the PCM when exposed to high-temperature environments, such as fires, should be evaluated [8,9]
Summary
Polymer-modified cement mortar (PCM) is superior to ordinary cement mortar in terms of strength, durability, chemical resistance, and workability and is widely used for repairing and strengthening reinforced concrete (RC) structures [1,2,3,4]. Considering the maintenance of RC buildings and the use period of the structures, the change in the physical properties of the PCM when exposed to high-temperature environments, such as fires, should be evaluated [8,9]. PCM is widely used as a repair material for reinforced concrete structures, when PCM is burned, that is, when it is exposed to a high temperature owing to a fire in buildings that are repaired using PCM, spallation and ignition from the thermal decomposition of the polymer occur and the strength of the structure is expected to decrease [11,12,13,18]. In this study, the mechanical performance (compressive strength and elastic modulus) of the PCM at high temperatures, thermal decomposition, and the variation in the pore structure of the PCM after exposure to high temperatures were experimentally evaluated.
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