This paper aims to investigate the effect of the polypropylene fibre (PP) and basalt fibre (BF), singly or in hybridization, on the workability, mechanical, chloride resistance and pore structure characteristics of concrete. Sixteen mixtures consisting of PP and BF, both at volume content of 0.0, 0.1, 0.2 and 0.3%, were fabricated, and the slump, compressive, splitting tensile, flexural and charge passed were tested. The results show the hybridization of the PP and BF can improve three types of strength of concrete in comparison to their single fibre. Nevertheless, the hybridization is not always conducive, and the synergy of fibres is proposed and divided into positive and negative effects. The combination of the PP and BF both at content of 0.1% achieves the best mechanical performance, and is recommended for practical usage. Incorporating fibres reduces the chloride resistance of concrete, and the hybridization is helpless to this phenomenon; even the reduction is intensified at a highly hybrid fibre volume. However, increasing the curing age can mitigate this adverse effect caused by fibres. Furthermore, the microstructures were explored to elucidate the macro-properties of concrete in terms of interface and pore structure.

The improved properties of ethylene-vinyl acetate (EVA)-modified cement-based materials have not been fully clarified, especially crack resistance and pore structure. The purpose of this research was to investigate the influence of EVA copolymer on the mechanical performances and microstructural properties of cement paste. Strengths, autogenous and drying shrinkage, and water absorption expansion were investigated to evaluate the mechanical properties and volume stability. The ring restrained shrinkage and chloride permeability tests revealed the crack resistance and enhancement of impermeability. The microstructures of EVA-modified cement-based materials were characterized by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques. The experimental results indicated that mixing EVA into cement-based materials increased the flexural strength, reduced the crack propagation and chloride ion penetration, and reduced the negative capillary pressure by improving the water retention. The addition of EVA resulted the remarkable reduction of harmful pores. The optimal mass fraction of EVA powder was approximately 4%.

Determining the rheological properties of cement-based materials and selecting the types and amounts of superplasticisers (SPs) that are appropriate for actual projects are important and topical issues. In this study, the rheological properties of cement pastes with different types of SP were investigated using an AR2000ex rheometer. A colour function method (CFM), in combination with the experimental data, was used to calculate and determine the rheological properties. This paper presents a new selection method (rapid determination system (RDS)) for determining the most suitable SPs. The results show that shear stress, plastic viscosity, normal stress and other mechanical properties are influenced by different volumes and types of SPs. Based on the CFM and RDS, 0·38% HW (a polycarboxylate-type SP) was determined to be the most appropriate.

Lack of post-yield stiffness and corrosion resistance could inevitably result in a considerable loss of seismic performance for steel reinforced concrete (RC) piers. Fibre reinforced polymer (FRP) reinforcement can provide high tensile strength and protection from corrosion. To achieve a better post-yield stiffness and durability for piers, FRP/steel double-reinforced configurations were designed by the proposed flexural-capacity design method. A seismic fragility assessment was also conducted to investigate the effectiveness of design parameters, namely the ultimate tensile strength of FRP reinforcement, elastic modulus of FRP reinforcement, and ratio of steel reinforcement for a double-reinforced configuration to that for a steel RC configuration ( ${\rho }_{\mathit{steel}}/{\rho }_{\mathit{prototype}}$). The results demonstrated that the FRP/steel double-reinforced piers satisfied the mentioned objectives, while the fragility of these piers was a 30.2% less than that of conventional steel RC piers. A 79.9% higher median PGA at the collapse damage state was achieved, when the elastic modulus of FRP reinforcement changed from 164 to 80.7 GPa. An increase in the median PGA of 34.8% can be achieved along with the increase of the ultimate tensile strength of FRP reinforcement. When ${\rho }_{\mathit{steel}}/{\rho }_{\mathit{prototype}}$ was approximately 66%, FRP reinforcement exhibited the highest effectiveness on the seismic performance of piers.