Materials and Structures最新文献

Recycling end-of-life tires (EOLT) presents a sustainable solution for addressing a major waste issue in many countries. This study focuses on the reuse of EOLT as construction materials, particularly in the form of EOLT-based rubberised concrete. However, several research gaps hinder the understanding of this construction material for implementation into practice. This study delves into key parameters, including admixture composition, aging, thickness, rubber distribution, and surface roughness, which play pivotal roles in designing and implementing rubberised concrete noise barriers. The paper presents the results of investigations into the performance of fibre-reinforced rubberised concrete when entrained with air, shedding light on flexural toughness and post-crack behaviour. The effects of incorporating fly ash and ground granulated blast furnace slag (GGBFS) as cement replacements are also examined. The acoustic performance of fibre-reinforced rubber concrete is studied, including the impact of sample conditioning (surface saturated dry or dry). The results indicate that air-entraining admixtures, the replacement of coarse sand with tire-derived rubber shreds, and the inclusion of recycled polypropylene fibre significantly enhance the mechanical and acoustic properties of the concrete. For instance, compressive strength improves by 43%, flexural strength by 120% and acoustic performance nearly twice, while water absorption and volume of permeable voids remain relatively unaffected. This study suggests an optimized sustainable mix design with rubber replacing more than 75% of the aggregate volume. It underscores the potential of EOLT-based rubberised concrete as an environmentally responsible construction material, offering enhanced performance across multiple domains, including noise attenuation barriers.

Despite concrete being inherently strong and resilient, durability issues stemming from undesirable cracks can significantly reduce the lifespan of concrete structures or cause costly maintenance and repair procedures. Accordingly, the phenomenon of self-healing holds crucial importance in preserving the longevity of existing buildings. This study particularly focused on utilizing two seawater tolerant bacteria, Marinobacterium litorale, and Halomonas elongata, in cementitious systems to experimentally investigate their overall performances and self-healing capabilities. Bacillus subtilis and Bacillus megaterium, which had proven effective in earlier studies, were used as controls. To gain insight into the self-healing potential of bacterial strains, a comprehensive experimental program including flow table, compressive strength, flexural strength, ultrasonic pulse velocity, and capillary permeability tests were performed. Furthermore, the extent of self-healing was assessed using a digital camera to measure crack closure rates, and the healing products formed within cracks were characterized through FE-SEM–EDX, and XRD. Based on crack closure observations, mixtures containing M. litorale and H. elongata demonstrated superior self-healing performance, particularly in salt water environments. Consequently, both M. litorale and H. elongata exhibited promising mechanical and permeability performance, showcasing similar effectiveness to popular Bacillus strains.

To investigate the debonding process, an in-situ pullout experiment on an indented single polypropylene fiber was conducted using X-ray microtomography. This study utilized mechanically regularized global digital volume correlation (Reg-G-DVC) to measure the deformation fields of the fiber, matrix, and interfaces during interfacial debonding. Reg-G-DVC mitigates the impact of low contrast on measurement uncertainties, ensures the convergence of DVC calculations, and enables the element size to be reduced to improve the spatial resolution. The displacement jumps of the shared nodes between the fiber and the matrix were used to quantify interfacial debonding. The profiles of the normal and tangential components of the displacement jumps exhibited periodic features corresponding to the geometry of the indented fiber as it was pulled out. Additionally, the force–displacement curves displayed multi-peak fluctuations corresponding to the fiber geometry, thereby indicating that the periodic indentation of the fiber enhanced friction and the cohesive force between the fiber and the matrix during the pullout process. The displacement jumps along the fiber was maximum at the embedded initiation and decreased along the fiber toward the embedded end. The aforementioned research demonstrated the advantages of utilizing Reg-G-DVC in measuring displacement fields during interfacial debonding, which provides deformation data for identifying and validating interface models.

This study investigated the physicochemical effects of kaolinite (CK) and montmorillonite (CM) calcined clays on the sulfate balance, early hydration, and artificial pore solution of limestone calcined clay cement (LC³). The effects of fineness, clay dissolution, and ion-adsorption capacity were evaluated by isothermal calorimetry, compressive strength, ICP-OES, and zeta potential within 72 h, respectively. Increasing the fineness of both calcined clays did not significantly affect the sulfate depletion kinetics or the compressive strength and the adsorption of Ca²⁺ ions onto the calcined clay’s surface is not the main factor responsible for differences in sulfate demand. The higher dissolution of ions Al in CK provided an intensified and accelerated formation of ettringite that competes for the available sulfate. We demonstrate that the chemical effects have a significant impact on the sulfate balance of LC³, revealing the lesser impact of alternative clays like montmorillonite compared to metakaolin (MK) which can minimize the problem of accelerated sulfate depletion of LC³ mixes with MK.

Concrete is a heterogeneous multiphase material composed of various solid phases that interact both physically and chemically with each other and with the water filling the pores. Among these solid phases, a crucial role is played by the calcium silicate hydrates (C–S–H), which are the primary products of cement hydration and are primarily responsible for the material’s physical properties. When concrete is subjected to high temperatures, the chemically bound water in C–S–H is progressively released, leading to a degradation in the strength and durability properties of the concrete. Hence, understanding how the dynamics of C–S–H dehydration and the corresponding evolution of hygro-mechanical properties (e.g. strength, permeability, porosity) are related with the characteristic observed phenomenology of spalling is crucial to assess the resistance of a structure under high temperature. Within this context, multiphysics thermo-hygro-chemical (THC) numerical models now play a pivotal role in predicting and analyzing structures’ performance under fire accidents. However, to enhance the reliability of numerical results, properly accounting for the initial hygro-chemical state of the structure just before the accident is of chief importance. This work presents a monolithic fully-coupled unified THC mathematical model enabling the simulation of the full service life of the material: from casting (early-age behavior and curing), through aging, until the eventual occurrence of an accident (high temperature, high pressure, ...). The model provides the evolution of the hydration reaction as a function of time, temperature, and relative humidity, as well as the eventual dehydration occurring at high temperature. The main contribution of this work lies in the proposition of general chemo-physical constitutive relationships that incorporate the influence of the hygro-thermal state of the material as well as that of C-S-H hydration/dehydration in a fully-coupled manner. The evolution of volume fraction of phases and porosity during hydration/dehydration follows Powers’ stoechiometric model, while a novel adsorption–desorption model is proposed to properly account for the irreversibility of chemical damage in the porous microstructure. This enables an alternative, simpler approach requiring only a limited number of experiments for the model calibration. The model is firstly benchmarked by simulating the early-age behavior of a concrete sample, and it is then validated against experimental results of temperature, gas pressure and mass loss under heating. Our results highlight a non-negligible impact of the initial (which in real cases is usually heterogeneous) hygral state on the predicted behavior at high temperature and unravel new perspectives on understanding the physics underlying concrete spalling. The thermo-hydro-chamical code developed in this paper is made available in a GitHub repository.

This paper presents the pull-out bonding behaviour and mechanical performance of recycled carbon fibre (rCF) reinforced concrete based on the recent investigation of fibre reinforced concrete (FRC) with rCF recovered from pyrolysis. Single fibre pull-out tests have been carried out to identify the apparent interfacial shear strength of different types of rCF and virgin carbon fibre (vCF) to identify the fibre matrix connection. Furthermore, a series of tests have been carried out to identify the workability, compressive strength and tensile strength of FRC. Besides rCF, also vCF and steel fibre were used for fabrication of FRC test specimens. rCF have shown the same adhesion behaviour and strength like vCF. Furthermore, the use of unsized or acrylate-based sized rCF creates an adhesion between fibre and matrix material. During the pull-out tests, the failure does not occur as an adhesive crack between fibre and cement matrix, but as a cohesive crack in the cement matrix. The mechanical performance of FRC with rCF was compared with mortar and FRC with vCF and steel fibres. The results of compressive test conducted for FRC with vCF and rCF indicated that the influence of vCF and rCF on the compressive strength of FRC was insignificant. On the other hand, the results of tensile test conducted for FRC with vCF and rCF indicated that the tensile strength of FRC with rCF was at least 14.9% greater than that of FRC with vCF.

Adding steel fibers to concrete essentially improves its post-crack tensile properties. To determine this experimentally, indirect methods, such as flexural tensile tests, are generally used, which allow only indirect conclusions about the material´s tensile properties. In contrast, direct tensile tests provide the desired result immediately, but are difficult to realize. A key parameter affecting the performance of the SRFC is the orientation of the fibers, which is mainly influenced by the manufacturing process. Typically, when the concrete is cast, the steel fibers align with the edges of the formwork. This is commonly called the wall effect. We address these issues, presenting the setup and results of direct tensile tests on bone shaped specimens with three different steel fiber contents. For each content, a series of specimens with a three-sided formwork (i.e. three-sided wall effect and strong influence on the fiber orientation) and a series with cut-out bones (i.e. one-sided wall effect and less influence on fiber orientation) were fabricated and tested. After these tests, the fiber orientation was determined using an opto-analytical method to quantify the influence of the manufacturing methods on the fiber orientation. Comparing the stress-crack-opening relationships shows that the cut specimens at 0.5 mm crack openings have only about 80% of the tensile strength of three-sided formwork specimens. This effect decreases with larger crack openings and vanishes at about 3 mm crack opening. Finally, a new fiber reinforcement index is defined to correlate observed stress in direct tensile tests to fiber content and orientation in direct tensile tests.

Limestone calcined clay cement (LC³) is emerging as an alternative to Portland cement, offering economic advantages, reduced CO₂ emissions, and mechanical properties on par with Portland cement. Central to the effective utilization of LC³ is understanding how the fineness of its components affects its performance. The current study investigates limestone calcined clay cement mixtures composed of kaolinite, illite, and montmorillonite calcined clays and limestone at two levels of fineness. Strengths of mortar cubes were tested at 1, 3, 7, and 28 d and statistical analysis was performed with a 95% confidence level. Additionally, LC³ pastes were analyzed using x-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy, and isothermal calorimetry. The fineness of the calcined clay along with the fineness of limestone is found to be statistically significant for 28-d strength in LC³ mortars made with kaolinitic and montmorillonite calcined clays. All hydrated blends had a hemicarboaluminate phase, whose intensity was related to the fineness of the calcined clay, and the monocarboaluminate phase formation was found to be dependent on both the fineness and type of calcined clay. Porosimetry revealed that LC³ pastes with illite clay have larger threshold pore diameters than those with kaolinite clay. LC³ pastes containing kaolinite have denser microstructures due to C–S–H and hemicarboaluminate formation. Pastes produced with coarse calcined clay and coarse limestone led to a broader, weaker heat development peak and lower normalized cumulative heat. LC³ with kaolinitic clay has the highest normalized cumulative heat, while that with montmorillonite calcined clay has the lowest.

Graphical abstract

The compositional characteristics of cement by-pass dust (CBPD), specifically its alkalinity and salt content, present significant limitations to its reinsertion in cement production. Furthermore, these characteristics give rise to considerable concerns regarding its disposal. The present study investigated the potential for treating CBPD through the application of a direct aqueous carbonation technique. The aim is to assess carbon capture potential of the material and to investigate the impact of the mineralisation process on its composition. The process was conducted under atmospheric pressure, at low temperature (20–60 °C) and for short duration (20–60 min). Different CO₂ quantification techniques were employed to assess experiments efficiency and replicability of the adopted quantification techniques. A Design of Experiment was developed to identify the optimum carbonation conditions in terms of time and temperature. The conditions for CO₂ content maximisation resulted in a fair agreement with the prediction of the response surface methodology. High values in CO₂ uptake (25.1%) and carbonation degree (82%) were achieved, outperforming previous literature studies. Moreover, the mineralisation process significantly reduces the chloride content of CBPD, paving the way for its adoption as a supplementary cementitious material in integrated industrial processes for carbon capture and utilisation.

Laminated veneer lumber (LVL) is a popular engineering wood commonly used in modern wood structures. Australian radiata pine, being one of the prominent fast-growing woods in Australia, exhibits substantial promise for advancement and application in structural LVL. To assess the feasibility of employing Australian radiata pine LVL (RP-LVL) in compression components like columns and walls, the compressive behavior of RP-LVL was experimentally studied. The modulus of elasticity and compressive strength of RP-LVL under different loading directions were determined. Besides, obvious cross-section influences on the compressive failure modes and compressive strength parallel to grain of RP-LVL were found. Variations in compressive failure modes were observed to correspond with distinct cross-sectional sizes in RP-LVL. Both the section depth effect parameter and section width effect parameter of RP-LVL were obtained for further strength analysis of RP-LVL compression components. Taking into account of the cross-section influences, a predictive model for the compressive strength parallel to the grain of RP-LVL was proposed. An excellent correlation between the test results and the predicted results were found, affirming the effectiveness of the proposed predictive method in accurately estimating the compressive strength parallel to the grain of RP-LVL. The results underscored that RP-LVL possessed competitive compressive properties could be provided a great potential for application in civil engineering as compression components.