The use of synthetic fibers in fiber-reinforced concretes (FRCs) is often avoided due to the mistrust of lower performance at changing temperatures. This work examines the effect of moderate temperatures on the flexural strengths of FRCs. Two types of polypropylene fibers were tested, and one steel fiber was employed as a reference. Three-point bending tests were carried out following an adapted methodology based on the standard EN 14651. This adapted procedure included an insulation system that allowed the assessment of FRC flexural behavior after being exposed for two months at temperatures of 5, 20, 35 and 50 °C. In addition, the interaction of temperature with a pre-cracked state was also analyzed. To do this, several specimens were pre-cracked to 0.5 mm after 28 days and conditioned in their respective temperature until testing. The findings suggest that this range of moderate temperatures did not degrade the behavior of FRCs to a great extent since the analysis of variances showed that temperature is not always a significant factor; however, it did have an influence on the pre-cracked specimens at 35 and 50 °C.
Self-healing is defined as the capacity of a material to repair internal damage without any external intervention. In the case of concrete, this process can be autogenous, which is the natural capacity of the material. Ultra-High-Performance Fibre Reinforced Concrete (UHPFRC) has a high self-healing potential due to its high binder content with a low w/b ratio and its crack pattern with multiple micro cracks. This paper describes two UHPFRC water reservoirs, which were designed to minimise the volume of concrete used. The design is made of ribbed thin walls where shrinkage cracks are likely to happen. The objective of this work is to study the autogenous healing capability of this concrete in these cracks. The two water reservoirs have internal dimensions of 1.30×0.75×0.70 m³ and with 20 mm thickness in the centre of the walls. These walls displayed cracks (w < 100 μm), which were produced just after casting. Both reservoirs were filled with water, showing apparent water leakage. The cracks were monitored for 30 days, analysing pictures taken with an optical microscope. The results show that UHPFRC is able to heal autogenously under the conditions in this work, recovering completely the water tightness required for the water reservoirs.
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