Ecological problems such as natural resource depletion and massive quantities of waste for disposal are now guiding progressive civilization towards sustainable construction. The reduction of natural resources and the discarding of debris into open landfills are the two main environmental concerns. As a result, managing these solid wastes is a major challenge worldwide. In comparison to disposal, insufficient landfills, ecological degradation and the economic load on the relevant agencies, recycling and reusing waste materials have a considerable influence. Waste fiber has been studied for use as a cement-based composite (CBC) ingredient. Recycling waste fibers not only makes the cement composite more cost-effective and long-lasting but also helps to reduce pollution. Plastics, carpets and steels are among the various types of waste fibers reviewed in this study for their applications in cement-based materials. The mechanical properties of CBCs with different kinds of recycled-waste fibers were explored, including their compressive, flexural and splitting tensile strength and durability properties. The use of recycled fibers in the construction industry can help to ensure sustainability from environmental, economic and social standpoints. As a result, additional scientific research is needed, as well as guidance for more researchers and experts in the construction sector to examine the unknown sustainability paths. The barriers to the effective implementation of waste fiber recycling techniques in the construction sector were reviewed, and various solutions were proposed to stimulate and ensure their use in CBCs. It was concluded that CBCs containing recycled fibers provide a long-term and cost-effective alternative for dealing with waste materials.

Concrete is a multiphase composite material composed of coarse aggregate, cement mortar, and interface transition zone (ITZ). It is of great significance to study the effect of ITZ and coarse aggregate on chloride microscopic diffusion behavior for predicting the service life of reinforced concrete (RC) structures. By introducing the random distribution function, a random coarse aggregate model considering the randomness of the thickness of the ITZ was established. Furthermore, a two-dimensional (2D) chloride ion diffusion mesoscopic model was developed by specifying different diffusion properties for different phase materials of concrete. Moreover, the effects of coarse aggregate rate, ITZ thickness, and ITZ diffusion property on chloride ion diffusion behavior were investigated in this paper. The research showed that the aggregate has hindrance and agglomeration action on chloride ion diffusion. Although the volume content of the ITZ was very small, less than 0.2% of the total volume of concrete, the effect of the ITZ on the chloride diffusion in concrete cannot be ignored. More importantly, the mechanism of promoting chloride diffusion in the ITZ was revealed through the chloride diffusion trajectory. The research revealed the transmission mechanism of chloride ions in the meso-structure of concrete and provides theoretical support for the design of RC structures in coastal areas.

As supplementary cementitious material, glass powder has been widely used in concrete, and many investigations on the mechanical properties of glass powder concrete have been carried out. However, there is a lack of investigations on the binary hydration kinetics model of glass powder-cement. Based on the pozzolanic reaction mechanism of glass powder, the purpose of this paper is to establish a theoretical model of the binary hydraulic kinetics model of glass powder-cement to investigate the effect of glass powder on cement hydration. The hydration process of glass powder-cement mixed cementitious materials with different glass powder contents (e.g., 0, 20%, 50%) was simulated using the finite element method (FEM). The numerical simulation results are in good agreement with the experimental data of hydration heat in the literature, which verifies the reliability of the proposed model. The results show that the glass powder can dilute and accelerate the hydration of cement. Compared to the sample with 5% glass powder content, the hydration degree of the glass powder decreased by 42.3% for the sample with 50% glass powder content. More importantly, the reactivity of the glass powder decreases exponentially with the increase in the glass particle size. In addition, the reactivity of the glass powder tends to be stable when the glass particle size is greater than 90 μm. With the increase in the replacement rate of the glass powder, the reactivity of the glass powder decreases. When the replacement rate of the glass powder is greater than 45%, the concentration of CH reaches a peak at the early stage of the reaction. The research in this paper reveals the hydration mechanism of glass powder and provides a theoretical basis for the application of glass powder in concrete.

In karst area, the quality of punching pile-forming is generally not high, and pile defects is a problem. In order to evaluate the punching pile-forming quality better, this paper introduces the fuzzy comprehensive evaluation theory. This paper constructs the fuzzy comprehensive evaluation model of karst area, and divides the inspection and evaluation indexes of punching pile into two levels, the expert scoring method is adopted to determine the evaluation weight at all levels; The comprehensive fuzzy operator of multiplication before addition is adopted because it has obvious weight function and comprehensive degree; The principle of maximum membership is used to determine the quality level of pile foundation detection. The model is applied to an engineering case, and the evaluation effect is good.

Internal curing can improve the water supply needed for shrinkage compensation in ultra-high-performance concrete (UHPC). This study investigated a magnesium oxide expansive agent (MEA) combined with presaturated perforated cenospheres (PCs) in a cement-silica fume-blended industrial by-product system. Setting time, flow spread, compressive strength, autogenous and drying shrinkage, internal relative humidity, hydration heat, thermogravimetric behavior, mercury-intrusion-accessible pore structure, and local morphology were examined. MEA alone reduced shrinkage but decreased flow spread and compressive strength as its dosage increased. At a fixed MEA dosage, the PC-containing mixtures showed lower shrinkage and higher flow spread and strength, alongside delayed setting. M6P8 showed 62.8% lower autogenous shrinkage at 168 h after final setting and approximately 76% lower drying shrinkage at the end of the 180-day drying test than Ref. It achieved a 28-day compressive strength of 157.0 MPa, close to the Ref mean of 156.0 MPa. Higher PC dosages were associated with higher late-age internal relative humidity and, relative to MEA alone, higher cumulative heat release and lower intrudable pore volume. These observations are consistent with reduced self-desiccation and continued hydration, but do not directly measure PC water release or MgO hydration. PC replacement simultaneously reduced cement content and introduced stored water; the observed response therefore represents combined effects and does not establish a synergistic interaction.