CHARACTERIZING TEMPERATURE INDUCED STRENGTH DEGRADATION AND EXPLOSIVE SPALLING IN ULTRA HIGH PERFORMANCE CONCRETE

Event Date/Time: 
August 2, 2017 - 1:00pm
Event Location: 
3546D Engineering
Speaker: 
Mahmood Sarwar
MS Thesis Defense

ABSTRACT

Significant research and development in concrete technology have led to the evolution ofultra-high-performance concrete (UHPC). UHPC possesses excellent durability and ductility characteristics, and exemplary tensile and compressive strength properties. Therefore, owing to its superlative properties UHPC is being progressively used in infrastructure and must satisfy fire resistance requirements. Yet, evaluating fire resistance requires knowledge of elevated temperature mechanical properties, and unfortunately such properties are lacking. Furthermore, exploratory investigations reveal UHPC's composition and construct precipitate the temperature engendered dilapidation of its strength, and it is highly susceptible to fire induced spalling. To fulfill this integral gap, a comprehensive experimental study was undertaken to develop temperature induced degradation in compressive strength, stress-strain behavior, and elastic modulus, along with the fire induced spalling behavior of UHPC. Variables were introduced to the testing program through varying the content of steel fibers, hybrid design consisting of steel and polypropylene fibers, and varying the application of heating rate. Furthermore, UHPC's results were compared to four conventional concretes tested, and recommendations as prescribed in ASCE (1992) and Eurocode 2 (2004). Results from the experimental testing reveal the compressive strength and stress-strain behavior of UHPC deviates from conventional concretes, and there is a vast disconnect amongst the experimental results and recommendations prescribed in codes. Moreover, successful testing of UHPC at and above 300°C, was only possible through drastically reducing the heating rate to less than 0.75°C/min. Otherwise, employing higher heating rates induces explosive spalling at temperatures as low as 190°C. When the rate of heating is more than 0.75°C/min, coupled with high thermal gradient reaching its peak later during the heating process, it increases the risk of explosive spalling in UHPC.