Residual Compressive Behavior of Self-Compacting Concrete after High Temperature Exposure—Influence of Binder Materials

Abstract

This paper presents an experimental investigation of the compressive behavior of high-strength self-compacting concrete exposed to temperatures up to 600 °C. Ten different concrete compositions were tested, in which part of the cement (by weight) was replaced by three different mineral additives (5–15% metakaolin, 20–40% fly ash and 5–15% limestone). The stress–strain curves, compressive strength, modulus of elasticity and strain at peak stress were evaluated from uniaxial compression tests. Scanning electron microscope micrographs were also taken to evaluate the damage caused by the high temperatures. A sharp decrease in mechanical properties and an increase in peak strain were observed already after 200 °C for all mixes tested. The different mineral additives used in this study affected the variations of residual compressive strength by 24% and peak strain by 38%, while the variations of residual modulus elasticity were 14%. Comparing the obtained results with the recommendations for compressive strength given in regulatory code EN 1992-1-2 for high strength concrete, it can be concluded that the strength loss observed in EN 1992-1-2 at temperatures up to 400 °C is too conservative. The Popovics model for the relationship between stress and strain provided a good approximation for the experimentally determined stress–strain curves at different temperatures.

Recovery Behavior of the Macro-Cracks in Elevated Temperature-Damaged Concrete after Post-Fire Curing

“…It is believed that the mechanical and physical changes during exposure to high temperatures is the cause of the deterioration of the service abilities of concrete [4][5][6]. These changes include thermal-induced cracks and pores [7], the evaporation of water, and the decomposition of hydrated cement [5]. The mechanical changes and chemical changes are correlative.…”

“…For example, the water evaporates at temperatures over 100 • C, and with the increasing temperature, the pressure of the water vapor increases. This can cause micro-cracks around the pores or even spalling [7,8], and, on the contrary, it Materials 2022, 15, 5673 2 of 13 also creates an internal autoclaving condition, resulting in the further hydration of nonhydrated cement up to 300 • C [9]. At high temperatures, the hydrated cement decomposes, which causes the shrinking of the cement matrix, while the aggregate expands, and the discrepancy of the thermal deformation introduces cracks in the cement matrix and the matrix-aggregate interfaces.…”

Review of Residual Mechanical Properties of Concrete Mixed with Different Admixtures at High Temperatures

“…The data collected to be included in the analysis of this study are presented in Table 2. They included the shape and dimension of the specimens, W/B ratio, heating rate, types of coarse aggregate and admixtures used, and the mechanical properties of concrete measured in each study [13][14][15][16][17][18][19][20][21]. As for the criteria for data collection from existing literature, those that measured compressive strength among the mechanical properties of concrete were included.…”