RESUMEN
Ultra High-Performance Concrete (UHPC) is a cement-based composite material with great strength and durability. Fibers can effectively increase the ductility, strength, and fracture energy of UHPC. This work describes the impacts of individual or hybrid doping of basalt fiber (BF) and steel fiber (SF) on the mechanical properties and microstructure of UHPC. We found that under individual doping, the effect of BF on fluidity was stronger than that of SF. Moreover, the compressive, flexural, and splitting tensile strength of UHPC first increased and then decreased with increasing BF dosage. The optimal dosage of BF was 1%. At a low content of fiber, UHPC reinforced by BF demonstrated greater flexural strength than that reinforced by SF. SF significantly improved the toughness of UHPC. However, a high SF dosage did not increase the strength of UHPC and reduced the splitting tensile strength. Secondly, under hybrid doping, BF was partially substituted for SF to improve the mechanical properties of hybrid fiber UHPC. Consequently, when the BF replacement rate increased, the compressive strength of UHPC gradually decreased; on the other hand, there was an initial increase in the fracture energy, splitting tensile strength, and flexural strength. The ideal mixture was 0.5% BF + 1.5% SF. The fluidity of UHPC with 1.5% BF + 0.5% SF became the lowest with a constant total volume of 2%. The microstructure of hydration products in the hybrid fiber UHPC became denser, whereas the interface of the fiber matrix improved.
RESUMEN
Reflection cracks are one of the most common problems in semi-rigid base pavement. Setting a stress absorption layer can effectively delay the occurrence of reflection cracks, but further improvement is still needed in its interlayer bonding performance and anti-reflection crack performance. Considering the excellent crack resistance of basalt fibers and the good elastic recovery ability of rubber asphalt, it is considered worthwhile to incorporate them into traditional stress absorption layers to improve performance. To simulate the actual pavement layer effect, composite specimens consisting of a cement-stabilized macadam base + basalt fiber rubber asphalt stress-absorbing layer + AC-20 asphalt mixture surface layer were prepared to evaluate their performance through interlayer direct shear tests, interlayer tensile tests, three-point bending tests, and overlay tests (OTs). To determine the optimal fiber blending combination, four fiber lengths (3 cm, 6 cm, 9 cm, 12 cm) and four fiber proportions (120 g/m2, 140 g/m2, 160 g/m2, 180 g/m2) were selected respectively. The specific effects of basalt fibers with different lengths and dosages were analyzed. The results show that compared with the absence of fibers, the improvement of interlayer bonding performance of rubber asphalt with basalt fibers is not significant, and it has certain limitations; however, the improvement of anti-reflective crack performance is significant, with an increase of up to 305.5%. This indicates that the network structure formed by basalt fibers and rubber asphalt stress absorption layer can effectively absorb and disperse external loads, causing an excellent crack resistance effect. Meanwhile, the results indicate that the main factor affecting its interlayer bonding strength and anti-reflective crack performance is the fiber content. Based on the comprehensive analysis of the performance and economy of the stress absorption layer of basalt fiber rubber asphalt, the optimal fiber parameter combination recommended is as fiber length 9 cm and fiber content 160 g/m2. These results can provide a reference for the design and performance evaluation of basalt fiber rubber asphalt stress absorption layer, and have certain application value.
RESUMEN
In the context of green and low-carbon development, energy saving, and emission reduction, hot recycling technology (RT) has been researched, which is divided into hot central plant RT and hot in-place RT. However, due to the aged asphalt binders, the shortcomings of hot recycled asphalt mixtures have become apparent, as in comparison to new asphalt mixtures, their resistance to cracking was inferior and the cracking resistance deteriorated more rapidly. Therefore, it was very necessary to focus on the improvement of crack resistance of hot recycled asphalt mixtures. Basalt fiber has been proved to be able to effectively improve the comprehensive road performance of new asphalt mixtures. Therefore, this paper introduced basalt fiber to hot central plant recycled and hot in-place recycled asphalt mixtures, in order to improve the crack resistance of asphalt as a new type of fiber stabilizer. Firstly, six types of SMA-13 fiber asphalt mixtures were designed and prepared, i.e., hot mixtures with basalt fiber or lignin fiber, hot central plant recycled mixtures with basalt fiber or lignin fiber, and hot in-place recycled mixtures with basalt fiber or lignin fiber. Secondly, the trabecular bending test, low-temperature creep test, semi-circular bending test, and IDEAL-CT were used to comparatively study the changing patterns of low and intermediate temperature cracking resistance of hot recycled mixtures with conventional lignin fibers or basalt fibers. Finally, Pearson's correlation coefficient was used to analyze the correlation of the different cracking resistance indicators. The results show that the low and intermediate temperature cracking resistance of hot central plant recycled mixtures increased by 45.6% (dissipative energy ratio, Wd/Ws) and 74.8% (flexibility index, FI), respectively. And the corresponding cracking resistance of hot in-place recycled mixture increased by 105.4% (Wd/Ws) and 55.7% (FI). The trabecular bending test was more suitable for testing the low-temperature cracking resistance of hot recycled asphalt mixtures, while the IDEAL-CT was more suitable for testing the intermediate-temperature cracking resistance. The results can provide useful references for the utilization of basalt fiber in the hot recycling of SMA-13 asphalt mixtures.
RESUMEN
Reclaimed asphalt pavement (RAP) has been widely utilized because it is an environmentally friendly and economical material. The performance of recycled asphalt mixtures will deteriorate gradually with the secondary aging process of asphalt, including the self-healing property. To further understand the self-healing characteristics of asphalt after secondary aging, taking 70# petroleum asphalt, SBS-modified asphalt, and extracted old asphalt mastics as objects, the fatigue self-healing test and fracture self-healing test were conducted to simulate the intermediate-and low-temperature healing behaviors of different asphalt mastics. The impact of healing time, healing temperature, and aging degree of mastics on the healing performance was systematically investigated. The results show that the original unaged asphalt mastics present excellent fatigue healing properties with an index of 0.796 and 0.888 for 70# petroleum and SBS-modified asphalt mastics, respectively. The secondary aging process causes significant impact on the healing properties, leading to a great drop in the corresponding index, which decreased to 47.5% and 72.5% of that of the unaged ones. The fracture healing ability of all mastics was much inferior to the fatigue healing. After secondary aging, the fracture healing index values of 70# petroleum asphalt, SBS-modified asphalt, and extracted old asphalt mastics were all as low as around 0.3, indicating similar performance can be found in the secondary aged SBS-modified asphalt mastics and 70# asphalt mastics. Overall, after secondary aging, the fatigue damage of SBS-modified asphalt mastics can be cured effectively by self-healing, but the fatigue and fracture self-healing properties of 70# asphalt mastics are difficult to recover. These results could provide an innovative view to understand the fatigue and fracture healing characteristics of recycled asphalt pavement after secondary aging.