Study of Toughness and Macro/Micro-Crack Development of Fibre-Reinforced Ultra-High Performance Concrete After Exposure to Elevated Temperature

Abstract

This study has investigated the changes that might appear in post-peak flexural response. Before the flexural test, prismatic specimens were placed in a furnace chamber and exposed to elevated temperatures of 400, 600, and 800 °C. The flexural toughness test was carried out on two types of concrete: Plain ultra-high performance concrete (UHPC) and UHPC with different types of fibres (steel fibre (SF) and polypropylene fibre (PPF)) at 0.5%, 1%, 1.5%, and 2% volume fractions. During the flexural test in the macro-crack development analysis, the non-contact ARAMIS system was used to perform three-dimensional measurements of strain and displacement. The results of scanning electron microscope (SEM) observations of micro-crack development in UHPC without and with SF/PPF were also presented. The experimental results showed that in some cases, the load–deflection curve of fibre-reinforced UHPC displayed a double-peak response. The first peak signified the UHPC properties, while the second peak represented the properties of the fibres. Under flexural load, the toughness decreased as the temperature increased. Significant decrease in the load–deflection response and toughness were observed for the polypropylene fibre-reinforced UHPC when the temperature approached 800 °C. The SEM observation results showed that the thermal damage of fibre-reinforced UHPC depends on the pore pressure effect, the thermal mismatch, the decomposition of hydration products, and the formation of micro-cracks.

Mechanical Properties of Ultra-High Performance Concrete with Partial Utilization of Waste Foundry Sand

“…The UHPC mixture formulations in this study contained fine quartz sand passed through a sieve to receive a size of <2 mm and coarse basalt stone passed through a sieve <16 mm, type I Portland cement, and condensed silica fume based on previous studies [19,23]. The optimal amount of silica fume was selected based on experience [38].…”

“…Ultra-high performance concrete (UHPC) is considered a very durable material due to its very high strength-to-weight ratio compared to conventional concrete [18]. Nevertheless, on the other hand, it is very sensitive to explosive spalling in fire conditions resulting from its low permeability and dense structure [22,23]. UHPC is usually produced using a high cement content, very fine sand with a grain size below 0.6 mm, water, silica fume, superplasticizers based on polycarboxylate ethers and steel fibres [18].…”

Effect of Elevated Temperature on the Bond Strength of Prestressing Reinforcement in UHPC

“…Some articles describe that due to the thermal interaction (even at relatively low temperatures) between the matrix/steel base fibers, radial cracks of unit length up to tens of µm are formed, which have a very negligible volume, but already have a non-negligible surface [37,68]. Due to their small volume, these pores/cracks are not detectable by mercury intrusion porosimetry.…”

Hybrid Fibres as Shear Reinforcement in High-Performance Concrete Beams with and without Openings

“…The main purpose of this study is to investigate the mechanical behaviour at shearing of RC beams with/without openings, made of HPC (up to 120 MPa), containing long steel fibres and short polypropylene fibres in order to determine the possibility of using different fibre combinations to replace the stirrups in order to improve the shear and flexural strengths, crack control, failure modes as well as ductility. Moreover, based on the experimental results [54], a small amount of polypropylene fibres significantly improved the resistance to high temperature (up to 1000 • C) of hybrid steel/polypropylene fibre-reinforced HPC compared with HPC and steel fibre-reinforced HPC. The response of the RC beams was evaluated based on the crack pattern results, load at the first cracking, ultimate shear capacity, failure modes, toughness, over-strength, ductility, initial stiffness, maximum strength as well as strains.…”