Análise experimental do efeito spalling e da resistência residual do concreto com e sem fibra de polipropileno

Abstract

High performance concrete (CAD) structures become susceptible to spalling when exposed to intense heat. The occurrence of explosive chips is intensified in these cases due to the low permeability of the concrete and the consequent increase in pore pressure caused by the high temperature. The residual compressive strength, in turn, determines the severity of damage generated by material overheating followed by abrupt cooling. This property is influenced by the type of cooling used. To reduce fragmentation in CADs, polypropylene fibers (FPP) are applied, since at 170 °C the fiber material melts and creates alternative paths for the passage of water vapor, consequently reducing pressure damage. NBR 15200 does not specify calculation procedures for the design of concrete structures in fire situations according to the type of concrete, making analyzes necessary in this area. For this reason, the study seeks to analyze the occurrence of chipping in concrete with and without polypropylene fibers in their composition, evaluate the performance of concrete after its immediate cooling and collaborate with the structuring of experimental procedures for evaluating these properties. For this, 36 specimens (CPs) were tested at 150 °C, 300 °C and 450 °C, being 18 CPs of CSF (Concrete without FPP) and 18 CPs of CRF (Concrete with FPP), to evaluate the effect spalling and residual compressive strength. However, after carrying out the tests, the CSF obtained a compressive strength of 39.05 MPa and the CRF of 37.05 MPa. The compressive strength of the first test for CSF was reduced by 32% at 150 °C and 12% at 300 °C and 450 °C, while CRF showed a reduction of 19%, 29% and 22% at temperatures of 150 °C, 300 °C and 450 °C, respectively. For the second test, CSF exhibits a 4%, 22% and 37% reduction while CRF reduces 11%, 6%, 26% at 150 °C, 300 °C and 450 °C, in that order. Among all samples, only one CSF specimen suffered explosive chipping at a test temperature of 450 °C. Therefore, it is proven that polypropylene fiber contributes to minimizing the spalling effect and helps to preserve the compressive strength of concrete when subjected to temperatures above 300 ºC.