Ultra-high performance concrete (UHPC) is a novel class of concrete that has superior mechanical properties and durability characteristics. Although UHPC exhibits exceptional performance at room temperature, the behavior of UHPC under fire conditions can be of concern due to faster degradation of strength and modulus properties with temperature, as well as its high susceptibility to fire-induced spalling. Since UHPC is a new construction material, there is limited information on its fire performance. This session will invite research and industry groups to share information on the fire performance of UHPC with students, faculty, researchers, and practitioners. Attendees will learn about the current fire problems in UHPC, recognize knowledge gaps and research needs, and practical solutions for improving UHPC fire performance.
Fire Performance of Ultra High Performance Concrete (UHPC) Double with Insulated (DWI) Wall Panels
Presented By: Mark Green
Affiliation: Queen's University
Description: The growing applications of Ultra High Performance Concrete (UHPC) in structures, particularly high-rise buildings, have prompted recent developments in Double Wythe Insulated (DWI) panels. These panels incorporate UHPC wythes and an insulating core, such as expanded polystyrene. While promising research on UHPC materials at high temperatures has been conducted, intermediate-scale and full-scale fire testing is necessary for further assessment of the full DWI panels. The two main objectives of this research are to quantify the thermal properties at high temperatures of small-scale UHPC specimens reinforced with various types of fibres and to conduct fire tests which experimentally assess the performance of UHPC DWI panels in fire conditions. Intermediate and full-scale panels have been developed for fire testing against the ASTM E119 and CAN ULC S101 temperature time heating curve. Information stemming from this test series will allow for a way forward for this system, which could include recommendations for refinement (e.g. to the mix design to reduce concrete spalling, or to the shear connectors to enhance composite action), contributing to its development and application in North American construction.
Fire Performance of Carbon Nano-fibre Ultra-High-Performance Fibre Reinforced Concrete at the Material Leve
Presented By: Raafat El-Hacha
Affiliation: University of Calgary
Description: This investigation aims to examine the effect of various parameters on the performance of Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) at room temperature and under fire exposure. The effectiveness of adding steel fibres (SF) and polypropylene fibres (PPF) to enhance the fire performance of UHPFRC will be studied to reach the most efficient volume ratios for the SF and PPF fibres in terms of fire resilience at the material level. The mechanical and thermal properties of the UHPFRC at room temperature and various elevated temperatures (200, 400, 600 and 800°C) for steady and transient states. The tests (compressive and flexural strengths, combustibility and thermal properties) will be performed for 1.5% and 2.0% by volume of SF while keeping the percentage of PPF at 0.2%.
Effect of Autogenous Self-healing on Post-fire Cured Ultra High-performance Concrete
Presented By: Liberato Ferrara
Affiliation: Politecnico di Milano
Description: Mechanical properties of Ultra High-Performance Concrete (UHPC) degrade when exposed to elevated temperatures, even more than ordinary concretes due to its dense microstructure. Concerning, in particular, the special application of nuclear power plants, in which UHPC can find a promising use, concrete can be subjected to moderately high temperature (usually lower than 400°C) along the working life, this making of interest the study on the influence and persistence of UHPC's innate self-healing capabilities over the thermal degradation. In this context, the paper focuses on an experimental study of UHPC recovery ability by autogenous self-healing after being exposed to high temperatures. The UHPC specimens have been made with hybrid fibres, that is, polypropylene and steel fibres, and have been pre-cracked up to a cumulative crack width of 0.3 mm under 4-point flexural test. The pre-cracked specimens have been exposed to a temperature of 200 °C or 400 °C, with an heating rate of 1 °C / minute from room temperature and kept at the target temperature for two hours, with a following slow cooling at a rate of <1 °C / minute. The specimens have been kept in the lab environment for 24 hours after reaching room temperature. Then they have been tested for residual flexural capacity or allowed to self-heal under water immersion for six months. The damage and healing evolution have been monitored periodically using ultra-sonic pulse velocity survey and digital microscope inspection. Nevertheless, the thermal degradation, during the healing period, UHPC showed a significant recovery in terms of strength assessed by ultra-sonic pulse velocity tests.
Development of Ultra High-Performance Concrete for Fire Resistance Applications
Presented By: Venkatesh Kumar Kodur
Affiliation: Michigan State University
Description: In recent years, the construction industry has shown significant interest in the use of high- performance concretes (HPC) in buildings and infrastructure projects due to enhanced strength, durability, and sustainability solutions these HPC’s offer over conventional (normal-strength) concretes (NSC). Ultra-high-performance concrete (UHPC) is one such high performing cementitious material which possess higher compressive and tensile strengths, as well as enhanced ductility characteristics. These properties allow the design of more slender structural members with reduced conventional steel reinforcement.
Conventional concretes possess good fire resistance properties and hence concrete structures made of NSC exhibit high fire resistance. However, number of research studies have clearly shown that HPC structures exhibit lower fire resistance properties, as compared to NSC structures. Specifically, HSC (high strength concrete) and UHPC types undergo rapid degradation of strength at elevated temperatures and are also susceptible to explosive spalling under severe fire conditions. These poor fire resistance properties, together with reduced cross-sectional sizes in HSC and UHPC structural members, can lead to lower fire resistance in structural systems.
UHPC, which is currently used mostly in bridge applications, has great potential for use in buildings, but has to meet stringent fire resistance ratings as prescribed in building codes. While there are no specific fire resistance requirements for bridges currently, recent fire incidents in bridges have stimulated a debate on the destructive impact of fires on bridges and the need to mitigate such fire hazard in bridges through the provision of fire resistance to structural members.
To address the fire problem associated with HSC and UHPC structures , a series of characterization tests, fire resistance experiments and numerical studies have been carried out, both at material and structural level.