Case Studies in Construction Materials最新文献

The value-added recycling of waste polypropylene (PP) as asphalt modifiers has been a popular research topic in recent years, but high blending temperatures and asphalt smoke emissions are difficult issues that have not been solved. Therefore, this study innovatively used phthalic anhydride (PA) and catalysts (NHPI or BPO) to mechanochemically turn waste PP into different reaction products as bitumen-use PP modifiers (PPM(N) & PPM(B)). To well understand the physicochemical characteristics of PPMs, thermogravimetric analysis, torque rheology, and scanning electron microscopy were adopted and analyzed. Furthermore, the penetration, softening point, viscosity, storage stability, and dynamic shear rheology (DSR) tests were also carried out to study the performance differences of their PP modified asphalt (PPMA(N) & PPMA(B)). The main results showed that the PPM(N) continues being degraded with PA, but BPO-degraded PP conversely gets chemical connections with PA. With the effects of NHPI and BPO, all PPMs can improve the deformation resistance of virgin bitumen, even at higher temperatures, but as the PA content increases, this performance will gradually deteriorate for PPMA(N) and shows a slight improvement for PPMA(B). The appropriate use of PA can decrease the mixing temperature of PPM(N) with virgin bitumen and improve the storage stability of PPMA binders, and will not significantly sacrifice the resistances of its PPMA(N) to deformation, while with the addition of PA, the mixing temperatures of PPM(B) and virgin bitumen will not be decreased as expected and the resistances of PPMA(B) to deformation remain unchanged. Overall, the proposed mechanochemical method can work out to well address the high-quality recycling and reuse issue of waste PP for its large-scale application in asphalt pavement.

The large accumulation of molybdenum tailings (MoT) has resulted in a series of hazards, including environmental pollution, damage to water resources, and increased risk of geological disasters. This study employs ordinary Portland cement (OPC) and fly ash (FA) stabilization of MoT sand and seeks the optimal mix ratio through experimentation. The strength properties of MoT sand stabilized with different proportions of OPC and FA are studied and analyzed through unconfined compressive strength tests, splitting tensile strength tests, and splitting rebound modulus tests. Additionally, the microstructure of MoT sand stabilized with OPC and FA is analyzed using scanning electron microscopy (SEM). The results indicate that with an increase in OPC content, the compressive strength, splitting tensile strength, and splitting rebound modulus all increase. With an increase in FA content, the compressive strength gradually increases, while the splitting tensile strength and splitting rebound modulus show a trend of initially increasing and then decreasing. The results show that the optimal mix proportion for OPC and FA-stabilized MoT sand is 7 % OPC content and 15 % FA content. This mixture is suitable for a heavy traffic base of expressways and class I highways, as well as for an extra heavy traffic base of class II and below highways. The research results can provide reference for using OPC and FA stabilized MoT sand as roadbed material.

The purpose of this study is to further investigate the strength size effect and failure mechanism of asphalt mixtures and clarify the strength parameter conversion relationship between standard and non-standard size samples. The article established an improved microscopic model for uniaxial compression and indirect tensile testing of asphalt mixtures based on laboratory and discrete element simulation tests. The effects of thickness and gradation on the uniaxial compressive strength (UCS) and indirect tensile strength (ITS) of asphalt mixtures were studied. The loading rates of the UCS and ITS tests were set at 2 mm/min and 50 mm/min, respectively. Additionally, the tensile-compressive stress distribution, crack propagation, and strength contribution rates of different contact types within the sample were investigated during the virtual model loading process. The reliability of the model was validated through laboratory test results. Finally, the strength parameter conversion relationship between standard and non-standard size samples was investigated. The study found that the UCS of asphalt mixtures decreases with increasing thickness, while the ITS increases with increasing thickness, with average reduction and increase rates of 70.69 % and 24.18 %, respectively. The contact fracture ratio and the strength contribution rate of the aggregate-asphalt mortar contacts both exceed 50 %, indicating that the fracture of these contacts is the primary cause of asphalt mixture failure. The use of small-sized samples instead of standard samples in practical applications is promising. These research work outcomes can serve as a theoretical basis for designing asphalt pavement materials and acquiring existing asphalt pavement material parameters.

The steel tubes with geopolymer recycled concrete (GRC) infill are actively seeking environmentally friendly and low-carbon building materials as alternatives in the process of promoting sustainable development, maximizing the use of waste materials and resources, and reducing consumption of natural resources and environmental pollution. In this paper, three types of steel tube specimens with GRC infill were proposed, i.e., the geopolymer recycled concrete-filled steel tube (GRCFST), geopolymer recycled concrete-filled double skin steel tube (GRCFDST), and geopolymer recycled concrete-filled double section steel tubes (GRCFDSST). These GRC-steel tube structures were tested under axial compressive loading, and the influence of some crucial factors on bearing capacity, ductility and strain distribution of specimens was considered, such as the slag content, and the types of steel tube section and the replacement rate of recycled aggregate. The experimental results show that the steel tube can provide effective confinement for geopolymer recycled concrete and thus compensate for the adverse effect induced by recycled aggregate. The slag content has less effect on the bearing capacities of the GRCFDSST specimen compared with the GRCFST and GRCFDST specimens due to the stronger confinement effect of the former. The ductility of GRCFDSST specimens is better than the other steel tube specimens under the same parameter conditions. This study, building on existing literature, provides new insights and design recommendations for the mechanical performance of concrete-filled steel tube structures by using geopolymer recycled concrete as a filling material.

Over the last two decades, foam concretes (FCs) have been used for several light-weight applications demanding low strength; however, their use for Reinforced Concrete (RC) applications is limited since high macrovoid amounts result in weaker matrices. The use of high w/c and the overlapping of macrovoids have been identified as critical factors constituting a permeable microstructure in FC systems. Since corrosion performance is a critical aspect in the design of RC members and that the durability parameters of concrete, such as its porosity, pore size distribution, and permeability, play a vital role in restricting the diffusion of chloride ions, particularly in the cover region of members, it is imperative to determine these properties and understand the material behaviour or characteristics. In the current study, five FC mixtures (GF0 to GF4) were produced using ground granulated blast furnace slag (GGBS) and fly ash (FA) as replacements for cement and sand, respectively, at different dosages, considering both economic and environmental aspects. The principal objective of the study is to determine the pore- and permeability-related properties of produced FCs, assess their corrosion performance, and ascertain their suitability for RC applications by comparing their performance with that of conventional M25-grade concrete. Also, the influence of the combined effect of GGBS and FA addition and the individual effect of FA addition were assessed.

The research findings showed that FCs had a higher water absorption capacity and porosity compared to M25 concrete. In addition, the inclusion of GGBS and FA resulted in a decrease in water absorption by 8%–19% and a decrease in porosity by 23%–36% compared to the control FC mixture. The Mercury Intrusion Porosimetry (MIP) results indicated a substantial enhancement in gel pores, threshold, and critical pore diameter, while the size of the larger capillary pore decreased by 90% to 95% when GGBS and FA were added compared to the control FC mixture. The scanning electron microscopy (SEM) analysis and binary images from the image analysis revealed the presence of uniformly distributed and distinct macrovoids formed by foam. These macrovoids were predominantly found within the size range of 7.1–100 µm. The addition of GGBS and FA particles to FC mixes resulted in a significant improvement in the chloride ion permeation (CIP) class, reducing it from 'High' to 'Very Low' compared to M25 concrete. The Accelerated Corrosion Test (ACT) results obtained from FCs demonstrated a significant increase in cracking time ranging from 30% to 323%, as well as a notable decrease in mass loss ranging from 56% to 85% when compared to M25 concrete. The Fourier transform infrared (FTIR) and energy dispersive spectroscopy (EDS) analysis results revealed the presence of corrosion products, including feroxyhyte, akageneite, and Friedel's salt crystal, in both FCs and M25, indicating the occurrence of corrosi