Avaliação das alterações do módulo de elasticidade estático para concretos em situação de incêndio submetidos a resfriamento lento e rápido instantâneo.

Abstract

Concrete exposed to high temperatures has its properties modified, such as modulus of elasticity, characteristic resistance to compression and traction, porosity, and in addition to these changes, cracking, dilation, color changes and chipping can also occur. Due to the fact that concrete is a heterogeneous material, the study of this material must be deepened for a better understanding of its properties. For this reason, the objective of this work is to evaluate the changes in the static modulus of elasticity of Portland cement concretes subjected to fire conditions under slow and fast cooling conditions. For this, the experimental program was developed with three concrete mixes using basaltic aggregate. After drawing up a dosage diagram using the IPT/EPUSP method, lines were defined to achieve compressive strength at 28 days with fck equal to 20 MPa, 30 MPa and 40 MPa, which were exposed to temperatures of 100 °C, 300 °C, 450 °C and 600 °C; subdivided into two cooling groups, slow and fast. From the characterization tests, the changes in the modulus of elasticity, compressive strength and tensile strength, absorption and porosity were monitored. The results indicated a reduction in mechanical properties and an increase in absorption as the temperature rises. Verifying that there is a great influence of microcracks in all tests performed, the modulus of elasticity of the concretes was changed regardless of the mix and the type of cooling applied. The correlations between the modules and the other properties were accompanied by an increase in the microcrack of the concrete in addition to the loss of water and decomposition of the concrete phases generated by the dehydration of portlandite and decomposition of CS-H.