Abstract
The prevention and mitigation of spalling in high-strength concrete (HSC) rely on mixing polypropylene (PP) as an additive reinforcement. The dense internal structures of ultra-high-strength concrete (UHSC) result in risks associated with a high thermal stress and high water vapor pressure. Herein, the effects of pore formation and thermal strain on spalling are examined by subjecting fiber-laden UHSC to conditions similar to those under which the ISO-834 standard fire curve was obtained. Evaluation of the initial melting properties of the fibers based on thermogravimetric analysis (TGA) and differential thermal analysis (DTA) demon strated that although nylon fibers exhibit a higher melting point than polypropylene and polyethylene fibers, weight loss occurs below 200 °C. Nylon fibers were effective at reducing spalling in UHSC compared to polypropylene and polyethylene fibers as they rapidly melt, leading to pore formation. We anticipate that these results will serve as references for future studies on the prevention of spalling in fiber-reinforced UHSC.
Highlights
Concrete is a composite material produced by mixing cement, an admixture, water, fine aggregates, and coarse aggregates
In the case of ultra-high-strength concrete (UHSC), the saturation point of the water vapor pressure was closer to the surface due to the denser matrix structure; our observations indicated that the addition of fibers can shift the maximum vapor pressure point within the concrete
We examined the effects of the thermal strain and the water vapor pressure with respect to the melting properties of fibers on UHSC specimens that displayed several grades of spalling
Summary
Concrete is a composite material produced by mixing cement, an admixture, water, fine aggregates, and coarse aggregates. Various methods have been proposed to prevent spalling in HSC, including reduction of the water vapor pressure of concrete by mixing fibers [17,18,19,20,21,22,23,24,25]. UHSC may be vulnerable to spalling due to the small number of internal pores within its structure It is, necessary to reduce the internal water vapor pressure of concrete by adding selected fibers for anticipated fire conditions and to fully examine the influence of thermal stresses that occur during the heating process [27,28,29]. The observed evaluation metrics included the grade according to the spalling property, thermal strain, and water vapor pressure
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