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.
Highlights
Concrete for special applications such as high-rise buildings, nuclear power plants, tunnels, radioactive waste storage facilities, and military and underground structures should be characterised by high temperature resistance, energy absorption capability, and durability [1,2]
When the steel and polypropylene fibres were added to the mixtures, a decrease in the slump values was observed with the increasing amount of fibres (Table 3)
It was determined that the unit weight of the fresh Ultra-high performance concrete (UHPC) decreases with the increasing steel and polypropylene that the unit weight of the fresh UHPC decreases with the increasing steel and polypropylene fibre content
Summary
Concrete for special applications such as high-rise buildings, nuclear power plants, tunnels, radioactive waste storage facilities, and military and underground structures should be characterised by high temperature resistance, energy absorption capability, and durability [1,2]. 120 N/mm2 [5,6], or according to other researchers 150 N/mm2 [7,8,9], as well as increased durability and high ductility [10] This material is used to improve the bearing capacity of pedestrian footbridges, highway bridges, and the precast lattice-style facade system for buildings and stadiums [10,11]. Its sensitivity to explosive spalling in fire conditions results mainly from its dense structure and low permeability in comparison with normal-strength concrete [12]. These properties make it difficult to release vapour pressure, which leads to physical damage [13].
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