Calcium carbonate (CaCO3) whisker, as a new type of microfibrous material, has been extensively used in the reinforcement of cementitious materials. However, the combined effect of CaCO3 whisker and fly ash on mechanical properties of cementitious materials under high temperatures was still unknown. In this study, the coupling effect of CaCO3 whisker, and fly ash on mechanical properties of the cement was investigated. Two sets of cement mortars were fabricated, including CaCO3 whisker-based mortar which contained 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% CaCO3 whisker as cement substitution and CaCO3 whisker-based fly ash mortar which contained 30 wt.% fly ash in addition to 0 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, and 20 wt.% CaCO3 whisker as cement substitution. Mass loss, compressive strength, and flexural strength of these two sets of specimens before and after being subjected to high temperatures of 200°C, 400°C, 600°C, 800°C, and 1000°C were measured. Based on the results of the aforementioned tests, load-deflection test was performed on the specimen which exhibited the superior performance to further study its mechanical behavior after exposure to high temperatures. Moreover, microstructural analysis, such as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), was conducted to reveal the damage mechanism of high temperature and to illustrate the combined effect of CaCO3 whisker and fly ash on high-temperature resistance of the cement. Results showed that fly ash could improve the high-temperature performance of CaCO3 whisker-based mortar before 600°C and limit the loss of strength after 600°C.

Cement concrete pavement accounts for a large proportion of the road network due to its excellent mechanical strength and durability. However, numerous microcracks are generated due to the high brittleness of concrete, which poses a threat to the service life of concrete pavement. Currently, simultaneous addition of fibers and polymers is a feasible approach to resolving the issues associated with the brittleness of concrete. This study explores the properties of concrete mixtures containing different levels of polypropylene fibers and water-borne epoxy. Additionally, fly ash is also introduced to concrete mixtures. The tests performed include slump, compressive strength, flexural strength, shrinkage, depth of water penetration, and abrasion. The results indicate that water-borne epoxy, at all levels, contributed to improving the weak interfacial bonding between polypropylene fibers and concrete. In addition, the combined incorporation of polypropylene fibers and water-borne epoxy could improve the mechanical and durability properties of concrete, with the combined utilization of 0.1% polypropylene fibers and 10% water-borne epoxy exhibiting the best performance. Moreover, with the incorporation of 10% fly ash into concrete, the mechanical strength and abrasion resistance experienced a slight reduction, while the workability, drying shrinkage resistance, and impermeability were improved. The current findings indicate that the combined utilization of polypropylene fibers and water-borne epoxy at appropriate levels is beneficial for application in pavement; however, in spite of superior drying shrinkage resistance and impermeability, the incorporation of fly ash into concrete pavement should be properly treated according to the actual engineering conditions.

In order to further enhance the reinforcing effectiveness of polypropylene (PP) fibers on pavement concrete, waterborne epoxy (WBE) was introduced in this research and its effect on the flexural properties and freeze–thaw resistance of PP-fiber-reinforced concrete was evaluated. Compressive-strength tests, flexural-strength tests, three-point bending tests, freeze–thaw cycling tests and a scanning electron microscopic observation were carried out to analyze mainly the influence of WBE on the flexural properties and freeze–thaw resistance of PP-fiber-reinforced concrete. WBE contents of 0, 5%, 10%, 15% and 20% by weight of the cement were employed. The experimental results indicated that WBE was beneficial to improving the flexural properties of PP-fiber-reinforced concrete. With increasing content of WBE, the flexural strength and the peak load showed significant increases. Although a slight degradation in the abovementioned flexural parameters was observed when the WBE content was above 15%, the deflection at the peak, the fracture energy and the fracture toughness still showed an upward trend. In addition, the freeze–thaw resistance of PP-fiber-reinforced concrete was improved remarkably with the increasing addition of WBE content, leading to smaller mass loss and higher residual flexural strength. Moreover, microstructural images revealed that with the addition of WBE, the PP fiber/concrete interfacial bonding was effectively improved, and the concrete matrix tended to be denser as well, which provided higher resistance for crack initiation and propagation. In consideration of maximally improving the flexural properties of PP-fiber-reinforced pavement concrete, and while ensuring the compressive strength and meeting the freeze–thaw requirements, it was recommended that the content of WBE in PP-fiber-reinforced concrete should be 15%.