Materials and Structures最新文献

Portland cement is responsible for a large share of CO₂ emissions in the construction sector, which reinforces the need for sustainable alternatives. In this context, wastes with pozzolanic properties, such as red ceramic waste (RCW), show potential for partial replacement of cement. Every year, dozens of tons of RCW are generated, usually disposed of in landfills or discarded improperly, causing environmental impacts. This study investigated the replacement of 10 and 25% of Portland cement with RCW in concrete. The research introduces innovation by evaluating the performance of the mixtures under elevated temperatures (200, 400, and 600 °C) and conducting a life cycle assessment (LCA) of the developed composites, aspects rarely addressed in the literature. The results showed that the concrete with 10% RCW exhibited higher compressive strength than both the 25% mixture and the control concrete after exposure to 400 and 600 °C. The elastic modulus of the RCW10% mix also stood out, reaching 37.3 MPa, outperforming all other concretes at all studied temperatures. The LCA demonstrated reductions in CO₂ emissions of approximately 9 and 23% for RCW10% and RCW25%, respectively, with additional reductions in the categories of Marine Eutrophication (6 and 16%) and Terrestrial Acidification (8 and 19%) compared to the control concrete.

The effect of different types of fibers and fiber mixes on fresh and hardened properties of commercial ultra-high performance concrete (UHPC) were investigated. Six types of metallic and non-metallic commercially available fibers, including ones commonly used in UHPC and ones not investigated in prior work, were evaluated. Eighteen mixtures with different fiber dosages and combinations are prepared and tested for flowability, compressive strength, flexural properties, and bulk resistivity. Generally, the fibers, with the exception of polyethylene fibers did not affect flowability. All fibers affected mechanical behavior significantly. Depending on fiber type and dosage, compressive strength was − 23 to + 19% of the value of the mixture without fibers. Polyethylene fibers and their blends with steel fibers showed excellent flexural properties. Compared to the control mixture, selected binary mixtures showed improved flexural and compressive strength and synergies. Selected binary mixtures showed improved flexural strength and a lower cost per flexural strength, but a somewhat reduced compressive strength. Clearly, there are complex cost, compressive strength, flexural strength, and flow tradeoffs that can be leveraged based on the required application.

The use of methylene diphenyl diisocyanate (MDI)-based additive to prepare isocyanate-based chemically modified bitumen (IMB) has shown significant advantages for improving pavement performance and reducing environmental impacts. However, the chemical compatibility mechanism of IMB has not been fully elucidated, limiting its further application. To give a detailed interpretation of the chemical compatibility of IMB, both experimental and theoretical investigations were carried out in this study. The molecular interactions in IMB were investigated using quantum chemical calculations and molecular dynamics simulations. In combination with the Fourier-transform infrared spectroscopy (FTIR), dynamic shear rheometer (DSR), fluorescence microscopy (FM), scanning electron microscopy (SEM), storage stability, and Brookfield viscosity tests, the modification mechanism of IMB was analyzed at the molecular level. The results show that isocyanate-based additive and base bitumen have good chemical compatibility. The bitumen molecules can provide active sites for the chemical reactions with isocyanate, resulting in distinct covalent reactions. Since the MDI molecule has a rigid aromatic structure, it can help obstruct the self-association of condensed aromatic sheets within the bitumen after the chemical reactions. As a result, the IMB exhibits desired structural stability. Based on the chemical interactions of MDI and bitumen molecules, the chemical modification eventually leads to significant improvements in the stiffness, elasticity, and viscosity of the IMB. The results of this study contribute to a deeper understanding of the fundamental mechanism of isocyanate modification and provide guidance for the future application of IMB.

Concrete sewer surfaces made with Portland Cement (PC) consistently exhibit deterioration products such as gypsum and amorphous silica, despite relatively high measured in-situ concrete surface pH values (typically 4–2) in relation to the lower expected pH of the attacking acid. This is because the alkalinity of concrete neutralises the sulphuric acid produced by Sulphur-Oxidising Bacteria (SOB), masking the true acidity at the surface. Consequently, the actual pH driving corrosion is problematic to measure directly, yet it is hypothesised to be as low as pH 1. This study investigates the corrosion mechanisms of PC binders under controlled sulphuric acid attack at pH 1, 2, and 4 using a laboratory titration method coupled with reactive transport modelling, and microstructural analyses, i.e., X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Quantitative Evaluation of Minerals by SEM (QEMSCAN). Results show that at pH 1, the most aggressive condition, gypsum and amorphous silica concentrations were highest, with their content decreasing as pH increased. Reactive transport modelling confirmed that reduced availability of SO₄²⁻ and H⁺ ions at pH > 1 limits gypsum formation, implying that SOB must generate acid close to or below pH 1 to account for the observed gypsum formation (and associated surface zonation) on the exposed surface. The significance of this study lies in bridging laboratory, modelling, and field observations to advance understanding of biogenic sulphuric acid corrosion. These insights improve the accuracy of durability predictions and support the development of effective mitigation strategies for concrete sewer infrastructure.

The construction sector is a major consumer of natural resources and a significant contributor to global greenhouse gas emissions. Raw earth construction presents a sustainable alternative due to its availability, recyclability, and low environmental impact. However, its mechanical weakness and sensitivity to moisture remain critical limitations. This study explores the potential of corn starch gel as a bio-based stabilizer to enhance the performance of compressed earth blocks (CEBs). Two types of soils were initially considered: a surrounding soil and Macrotermes sp. termite mound soil. Preliminary analyses revealed that the surrounding soil lacked the physical properties required for CEB production, and only the termite mound soil was retained for further testing. Several formulations incorporating 5%, 10%, 15%, and 20% starch gel (wet mass) were prepared, corresponding to starch contents ranging from 0.24 to 2.5% (dry mass relative to soil). The physical and mechanical properties of the blocks were evaluated, including dry density, unconfined compressive and tensile strengths, shear parameters, and both dynamic and cyclic Young’s moduli. Results demonstrated an improvement in mechanical performance with starch stabilization. The optimal formulation (10M15G), containing 1.36% dry starch, exhibited compressive and tensile strengths of 5.80 MPa and 2.67 MPa, respectively, compared to 2.50 MPa and 0.88 MPa for the unstabilized control (0M0G). The dynamic Young’s modulus also increased substantially, indicating improved internal bonding and stiffness. Shear strength parameters were enhanced, with cohesion increasing from 15.69 to 37.65 kPa and the internal friction angle from 18.3° to 31.8°. A linear relationship between dynamic and cyclic Young’s moduli was established. However, mechanical performance declined beyond the optimal starch content, likely due to the excess water introduced by the gel, which hinders compaction. These findings confirm the effectiveness of corn starch gel as a sustainable stabilizing agent, offering a viable ecological solution for enhancing the structural integrity of raw earth materials.

This study investigates the potential of bio-admixtures derived from Sargassum natans (SN1E, SN2E), Sargassum fluitans (SFE), water hyacinth (WHE), miscanthus grass (ME), and plantain stem (PSE) as sustainable alternatives to polycarboxylic ether (PCE) superplasticizers in cement-based materials. The research examines their effects on rheology, hydration, microstructure, and mechanical properties to assess their suitability for eco-friendly construction applications. Cement pastes and mortars incorporating 0.1% and 1% bio-admixture dosages were analyzed using isothermal calorimetry, thermogravimetric analysis (TGA/DTG), static yield stress measurements, and compressive strength testing at 7 and 28 days. Results indicate that all mixtures containing admixtures exhibited lower initial yield stress values, indicating a liquefying effect initially. At 0.1% dosage, the admixtures exhibited comparable or slightly improved compressive strength relative to the reference (REF), with no significant losses. However, at 1% dosage, PCE, WHE, ME, and PSE showed notable strength reductions, particularly ME, which significantly impaired both 7-day and 28-day strengths. Hydration studies revealed that bio-admixtures exhibited lower retardation effects compared to PCE, with SN1E, SN2E, and SFE promoting early hydration and portlandite (CH) formation. Conversely, ME and PSE exhibited delayed hydration, leading to lower early-age strengths but a more sustained hydration process over time. Thermal analysis further confirmed these trends, with bio-admixture-modified pastes maintaining stable hydration profiles, while PCE exhibited the strongest retardation effect, as evidenced by its lower total weight loss, and reduced CH content. These findings highlight the potential of bio-admixtures as sustainable modifiers in cementitious materials, providing workability benefits while minimizing hydration delay, making them promising candidates for green construction.

Moisture content in porous concrete, which depends on environmental relative humidity, is a key parameter in durability tests of construction materials. Relative humidity affects the amount of free water within the pore network, which serves as a medium for corrosive agents to diffuse through the concrete and reach the embedded steel reinforcement. The correlation between environmental relative humidity and the degree of saturation is described by water vapour sorption isotherms, which address the equilibrium between the sorbed and free liquid phases in the pores at a given temperature. However, limited data are available on water vapour sorption isotherms for alkali-activated materials, and such measurements require long durations to achieve equilibrium at each relative humidity condition. In this research, several kinetic models used in sorption analyses are tested on data from Dynamic Vapour Sorption measurements for alkali-activated binders, with varying microstructures, to predict water vapour sorption isotherms in a realistically shorter experimental timeframe. Among the models tested, the Weibull distribution model best predicts the final measurements at equilibrium, and with the model a new testing parameter termed as mass conversion can be used as an indicator to reduce the experimental duration for determining water vapour sorption isotherms.

With the increasing adoption of low-clinker blended binders to reduce the environmental footprint of cement production, understanding the effect of carbonation on transport properties becomes critical. This study seeks to advance knowledge on the performance of blended cements by evaluating their efficiency in enhancing durability prior to carbonation and by assessing the relative changes in transport properties after carbonation for different low-clinker binder compositions. Transport properties, including permeable pore volume, sorption, oxygen permeability, and water penetration, were investigated for low-clinker cement compositions with clinker factors of 0.65 and 0.5 at two water-to-binder ratios (w/b), incorporating fly ash, slag, limestone, and calcined clay as supplementary cementitious materials (SCMs). After 120 days of curing, the specimens were subjected to accelerated carbonation at 3% carbon dioxide concentration for another 120 days. Results show that low-clinker binders exhibit superior transport properties compared to ordinary Portland cement (OPC) before carbonation. However, post-carbonation, blended binders experienced deterioration in transport performance, while OPC showed improvement. Moreover, the influence of carbonation on transport properties became more pronounced at higher w/b ratios. Overall, the findings highlight how binder type and w/b ratio govern transport behavior in partially carbonated systems, with implications for carbonation progression, corrosion kinetics, and the durability design of low-clinker cements.

Oxidative aging of asphalt binder, is a well-recognized and omnipresent phenomenon that leads to several distress types. As an effective way to tackle it, antioxidants have been introduced in asphalt binders. Although it is well documented that certain antioxidants are effective in preventing the deleterious impact of aging on the physical and mechanical properties of asphalt binders, an in-depth investigation of their impacts on meaningful viscoelastic parameters is yet missing. Therefore, this paper examines two promising antioxidants, namely kraft lignin and zinc diethyldithiocarbamate at two different contents of 3% and 5% binder enhancement, utilizing distress-related rheological indicators. Among others, master curves, the Glover-Rowe and ΔΤc parameters were extracted from Dynamic Shear Rheometer, supporting in general a softening effect for zinc and a stiffening effect for lignin. Ultimately, this work seeks to shed light on the functionality of these antioxidants at the virgin asphalt binder state as well as to comprehensively assess their efficiency after laboratory short- and long-term aging compared to their unmodified counterparts. As such, a Relative Aging Index is introduced to fairly compare the aging capacity of the two antioxidants in all blends. Additionally, the rheological investigation is contrasted with aging-related functional groups via Fourier-Transform Infrared spectroscopy, and the findings indicate that there is sufficient basis for supporting a satisfying correlation between the Glover-Rowe parameter and the carbonyl index. Overall, this study dives into a detailed analysis of the rheological behavior of antioxidant-enhanced binders and provides confidence for the application of zinc on a wide scale.

A functional modification strategy using vermiculite powder has attracted significant attention in asphalt composites due to its tunable interlayer structure and surface modifiability. However, the evolution law of the phase structure of vermiculite powder induced by functionalization treatment and its synergistic regulation mechanism on the multi-scale properties of the crumb rubber (CR) asphalt system have not yet been clarified. Therefore, in this investigation, vermiculite powder was chemically modified through organic intercalation followed by thermal expansion. The resulting organo-expanded vermiculite (OEV) was subsequently incorporated into CR asphalt with furfural-extracted oil (OIL) as an additive. The chemical and microstructural evolution of vermiculite during modification was investigated, and the optimal formulation was determined using response surface methodology and the NAGA-II multi-objective optimization algorithm. Rheological behavior of the modified asphalt at high and low temperatures was assessed, along with the stability of the compound modifier within the asphalt matrix. Additionally, Road performance and noise reduction effects of the asphalt mixtures were also examined. Results showed that organic intercalation and thermal expansion altered the interlayer anions and cations in vermiculite, forming hydrogen bonds, electrostatic interactions, and hydrophobic forces. These changes increased interlayer spacing, surface area, and pore structure, enhancing OEV’s thermal stability and adaptability. The optimal ratios of CR, OEV and OIL were 20%, 3.3% and 5%, respectively. The rheological test analysis of asphalt shows that OIL improves the low-temperature performance of modified asphalt, OEV improves the high-temperature performance of asphalt, and COO modified asphalt has excellent rheological properties at high and low temperatures. In addition, compared with pure CR modified asphalt mixture, COO modified asphalt mixture has significant advantages in high temperature stability, low temperature crack resistance, water stability and noise attenuation. The Analytic Hierarchy Process (AHP) evaluation confirmed the composite’s potential as a sustainable, high-performance material for road engineering applications.