Abstract
The influence of time on the mechanical behavior of concrete after exposure to elevated temperatures has been studied. Twenty-one self-compacting high-performance concrete mixtures with different incorporation amounts of coarse recycled concrete aggregate (RCA) and three unprocessed waste powder materials have been tested at age of 270 days for residual compressive and flexural strength after exposure to fire. The results have been compared to the results for the same concrete, which have been studied at age of 90 days. A new parameter has been introduced for comparing the responses of concrete to elevated temperatures at different ages; this parameter was the “heat resistance” which expresses the total area under the curve of the relative residual strength (compressive or flexural) after exposing to six temperature degrees (20, 150, 300, 500, 600, and 800 °C). The results showed that the age of concrete has an influence on the response of concrete to elevated temperatures. The heat resistance of compressive strength enhanced with age but the concrete behaved with a tendency different to that at the age of 90 days. The heat resistance of flexural strength has not been affected or slightly decreased but not with more than 10% to that at the age of 90 days. The used waste powder materials were unprocessed waste fly ash, waste cellular concrete powder and waste perlite powder; they proved that using any of them up to 15% as a replacement for cement with 0% or 25% of RCA enhanced the concrete resistance for the fire with time. The main two reasons for changing of residual strength with the time were the changing of water content and the proceeding of hydration of the binder. In general, long ages testing properties of concrete simulate the real behavior of concrete structures accurately.
Highlights
Fire is one of the major hazards to which concrete structures could be susceptible during their service life
The used waste powder materials were unprocessed waste fly ash, waste cellular concrete powder and waste perlite powder; they proved that using any of them up to 15% as a replacement for cement with 0% or 25% of recycled concrete aggregate (RCA) enhanced the concrete resistance for the fire with time
The present study aims at studying the long-term residual strength for twenty-one self-compacting high-performance concrete (SCHPC) mixtures with different replacement amounts of coarse natural aggregate (NA) and cement by RCA and unprocessed waste powder materials, respectively
Summary
Fire is one of the major hazards to which concrete structures could be susceptible during their service life. Results of long-term testing of the mechanical properties of concrete at elevated temperatures could be closer to reality than those of short-term evaluation A limited number of researchers have been studied the residual mechanical properties of SCC after exposure to elevated temperatures and concluded that SCC responses with more deterioration of residual mechanical properties and higher susceptibility to spalling especially at beyond 300 °C comparing with the normal vibrated concrete [3, 6,7,8,9,10]
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