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.

In this paper, the effect of basalt fiber (BF) on the frost resistance of concrete under different curing conditions was investigated, and its frost resistance mechanism was analyzed. Three different curing conditions (normal curing, short-term curing, and seawater curing) were adopted, and concrete with different BF volume contents was designed. Freeze-thaw (FT) tests were carried out using the rapid freezing method to test the frost resistance of basalt fiber reinforced concrete (BFRC). Additionally, the mass loss rate (MLR), relative dynamic modulus of elasticity (RDME) change, and compressive strength reduction of specimens during the freeze-thaw cycles (FTCs) were evaluated. The results show that when the BF content is 0.15%, under normal curing, short-term curing, and seawater curing conditions, the residual compressive strength of BFRC after FTCs was increased by 5.4%, 28.1%, and 30.9%, respectively, compared to plain concrete. By incorporating BF into concrete, the development of microcracks can be effectively retarded, and damage generation during FTCs can be reduced. In addition, the microscopic morphological characteristics and pore structure characteristics of concrete further elucidate the frost resistance mechanism of BFRC from a microscopic perspective.

Concrete exposed to the tidal zone of the Yellow Sea and bearing Crassostrea gigas (CG) with differing areal coverages was investigated for evidence of biologically induced corrosion prevention. The experimental results indicated that both the chloride ion profile and the neutralization depth of the concrete decreased with increasing CG coverage. Moreover, the water absorption rate and the chloride ion permeability of concrete with the original surface intact also declined with increasing degrees of CG coverage. However, the water absorption rates of three concrete samples with 2 mm of the surface layer removed were similar, as was their chloride ion permeability. Mercury intrusion porosimetry tests indicated that CG significantly reduced the pore structure of the concrete surface layer. SEM observation revealed that the CG cementation membrane and left valve were tightly glued to the concrete surface and had a dense structure. Concrete durability indices showed that high CG coverage greatly improved concrete durability.

A novel polymer concrete (PC) using an aggregate of ceramsite, fly ash and glass fiber was created. Specimens were used in experiments to investigate its anticorrosion properties to determine the viability of its use in flue gas desulfurization (FGD) stacks. The inclusion of ceramsite reduces both the weight and the cost of the material. The effects of ceramsite and glass fiber on the flexural strength and compressive strength of the concrete were investigated. The experimental results showed that ceramsite reduces the flexural strength and the compressive strength of the concrete, but that the glass fiber increases both. Surface resistance to sulfuric acid corrosion and the microstructure of the corroded concrete were investigated. Specimens of the novel PC and the control PC strongly resisted acid corrosion. Although the specimen surfaces deteriorated, the interior structure of the PC was unaffected after 50 days of acid immersion. Processes by which sulfuric acid corrodes PC surfaces were determined.

The hydration degree and compressive mechanical properties of concrete are evaluated in relation to microstructure composition at three curing ages. The analysis focuses on hydration and compressive load-bearing mechanism at the microstructural level. A concrete micromechanism that allows explicit parameters of pore distribution and pore diameter is investigated. Variations of concrete microstructure are measured and analysed over a range of curing ages. Results show that (1) different curing periods have significant effects on the hydration degrees and microstructure of concrete, (2) variations of hydration degrees are the basic reason of changes of pore structure and (3) type of porosity and pore diameter affects mechanical properties of concrete. Microstructure-behaviour relations are established to determine hydration degree and compressive mechanical properties, and facilitate microlevel studies on concrete properties for target-specific applications.

Concrete shrinkage is significantly influenced by the restraint level, and cracking often occurs under specific restraint conditions, thereby adversely affecting structural performance. Investigating the effect of restraint on shrinkage cracking is of great significance for enhancing early-age durability and ensuring structural safety. In this study, four distinct restraint levels (0%, 35%, 55%, and 75%) were established by varying the thickness of the inner steel ring. The influence of varying degrees of restraint on the shrinkage behavior was investigated, with digital image correlation (DIC) and internal strain gauge measurement employed to observe the strain and predict the risk of cracking. As the degree of restraint increases, the inner steel ring inhibits the free radial shrinkage of concrete more significantly, thereby inducing greater tensile strains at both the outer circumferential surface and the interior. The surface strain accumulation far exceeds the interior response due to the drying gradient. During the first 60 h, the shrinkage strain measured by both methods exhibited the most rapid evolution, indicating a critical high-risk period for cracking. These results advance the understanding of restraint effects in concrete and comprehensively clarify the relationship between the degree of restraint and the shrinkage, which accurately captures the evolution of shrinkage, facilitates the transition from empirical to quantitative design for crack-resistant materials and supports their customized optimization under practical engineering loading conditions.