Materials and Structures最新文献

This recommendation is an outcome of the work carried out by RILEM Technical Committee 309-MCP “Mineral Carbonation for the Production of Construction Materials”. To facilitate exchange in the rapidly developing field of mineral carbonation for construction materials, technical terminology covering specific terms of common interest is proposed. This terminology was developed in an iterative feedback process within the technical committee.

The presented terminology is recommended for use in the field of mineral carbonation technology applied to the production of construction materials and products.

The incorporation of electrically conductive inclusions in structural materials can impart self-sensing functionalities, making them ideal for structural health monitoring applications. However, the use of more sustainable alternatives and their effect on key engineering properties remain largely unexplored, while the adoption of different testing protocols for the characterisation of electrical/self-sensing properties can lead to different results, thus questioning their reliability, even for existing smart composites. This paper investigates systematically the effect of recycled carbon fibres and graphite powder on the mechanical, electrical, transport properties and piezoresistive performance of cementitious mortars. Virgin carbon fibres, at dosages equivalent to those of recycled fibres, were also examined to establish a performance benchmark. Fibre content ranged from 0.05% to 1% vol., while graphite powder was added as sand replacement at contents varying from 0.3% to 3% vol. The effect of existing testing protocols and electrode layout on the piezoresistive performance was also examined, and the associated limitations and challenges are discussed in detail. The results demonstrate the potential of recycled carbon fibres as a cost-effective alternative in smart applications, without compromising electrical and piezoresistive performance. The use of 0.25%vol. of recycled or virgin carbon fibres was found to provide the desirable synergy between structural performance, cost and self-sensing properties, yielding a 50–60% increase in flexural strength, and good piezoresistivity with a gauge factor of 90–110. In contrast, the use of graphite powder resulted in composites with poor self-sensing ability even at the highest content examined (3%vol.), also accompanied by a reduction in compressive strength up to 33%.

Monitoring carbonation in concrete is crucial for assessing the long-term durability of structures, particularly as sustainability efforts increasingly incorporate supplementary cementitious materials (SCMs) to reduce clinker content. While beneficial, SCMs alter the pore structure and pore solution chemistry, necessitating advanced methods to evaluate carbonation progression. Traditional techniques, such as splitting specimens and using pH indicators like phenolphthalein to detect changes in alkalinity, are destructive and primarily designed for ordinary Portland cement (OPC), limiting their effectiveness for SCM-incorporated systems. This paper presents the development of a novel lab-scale carbonation monitoring method based on conductivity measurements in the cementitious matrix. The proposed method examines how carbonation impacts the electrical conductivity of concrete, enabling in-situ monitoring of carbonation propagation in mortar specimens using mini-sensors embedded within the material. These mini-sensors consist of 10 sets of stainless steel 4-point Winner electrodes, spaced 2.54 mm apart, ensuring accurate conductivity measurements. By strategically placing these mini-sensors within the cementitious matrix, real-time measurements can be carried out, allowing for continuous monitoring of carbonation progression. The method provides new insights into how carbonation impacts the electrical properties of concrete, revealing dynamic changes such as a distinct peaking behavior in conductivity at the reactive carbonation front. This feature enables identification of partial carbonation front, which traditional colorimetric methods cannot detect. The results validate the method's effectiveness for OPC system and indicate its applicability when SCMs are incorporated.

Textile Reinforced Concrete (TRC) is a strain-hardening cementitious composite that integrates bi-directional fabric reinforcement within a fine-grained concrete matrix, enabling the development of thin, lightweight structural and non-structural systems. This study investigates the influence of specimen thickness on the uniaxial tensile behaviour of TRC panels, using panels of varying thicknesses—10, 20, and 40 mm, reinforced with coated E-glass textiles. Two sets of TRC panels were analysed: (i) panels with a constant reinforcement ratio and (ii) panels with the same number of textile layers. The displacement and cracking behaviour including crack patterns, spacing, and openings at different strain levels, were assessed using axial extensometers and 2D Digital Image Correlation. The findings reveal a reduction in the first-crack stress with increasing panel thickness, which is consistent with the Weibull model. Additionally, a decrease in ultimate stress and textile efficiency is observed in larger panels though the reinforcement ratio is constant. Such reduction is attributed to a shift in failure mechanisms, from textile fracture to extensive debonding in some of the specimens, as the number of reinforcement layers increases, possibly due to the increase in defects with larger interface (bond) area. Thinner panels exhibit higher crack density, reduced crack spacing, and finer crack widths, at comparable strain levels. For the same number of layers, thicker panels experience wider cracks at a given nominal strain; longer yarn lengths that bridge the cracks are mobilised leading to a Weibull-type size effect, which reduces the load-carrying capacity of the textiles.

In view of promoting the recycling of construction and demolition waste, the re-utilization of Recycled Asphalt Pavement (RAP) as aggregate in structural concrete has been recently proposed and investigated. Although many studies are available on the physical and mechanical characterisation of concrete containing RAP, little is still known about how medium- to long-term durability performances are affected by the partial or total replacement of natural aggregates with RAP aggregate. In this experimental study, several durability-related properties were assessed, with the aim of investigating the possible use of RAP as partial or total replacement of natural aggregates for reinforced concrete applications. In particular, concretes were obtained with increasing RAP contents (from reference mixtures with natural aggregate only, to complete substitution with RAP aggregate), two different cement types (Portland-limestone and pozzolanic), and two water/cement ratios (0.45 and 0.65), representative of two exposure classes for chloride and carbonation induced corrosion. Water sorptivity through capillary suction and water absorption were investigated, together with the resistance to the penetration of carbonation, both under accelerated and natural exposure, and the resistance to the penetration of chlorides, under natural diffusion. Relationships between physical and mechanical properties, such as total open porosity and compressive strength, and durability-related properties were also investigated. Results showed that sorptivity experienced a neat decrease for increasing RAP contents, due to the hydrophobic nature of RAP aggregate, while water absorption was less affected. Resistance to the penetration of carbonation and chlorides were both more clearly affected by other mix design variables, such as w/c ratio and cement type, rather than RAP content.

Lead–zinc mine tailings are hazardous waste that is produced by mining activities. Poor tailings management can lead to heavy metals leaching into the groundwater or surrounding environment if not properly managed. In this study, lead zinc mine tailings were treated using several activation methods to stabilize their heavy metals. Thus, in this study, several activation methods like mechanical, mechano-chemical, and microwave oven activation were applied to stabilize the heavy metals and reuse them effectively in construction. Toxicity-characteristic leaching procedures were performed to analyze the leaching concentration based on USEPA standard limits. A modified sequential extraction procedure (BCR) was used to determine the detailed distribution of heavy metals. 20% of tailings were replaced with cement. Tailings aggregates used in construction reduce the cost of construction and minimize the emissions of CO₂ to the environment as cement consumption is reduced. Characterizations supported the stabilized structure of concrete after activation methods were applied. Overall, it was concluded that activation methods can treat tailings powders and make them suitable for safe utilization in construction. Mechanical activation (200 rpm), mechano-chemical-activation (Graphene Oxide, 0.03%), and microwave oven activation (high power) for 40 minutes was selected for successful applications for concrete based on tailings due to their better-stabilizing effects and cementous properties.

This project aimed to document the mechanical properties, the bonding, and joint performance of trembling aspen to improve its use in Engineered wood products. It also aimed to study the bending characteristic and investigate the failure behavior of full-size beams made of trembling aspen. Non-destructive and destructive tests were conducted on lamellae of trembling aspen (Populus tremuloides Michx) following the ASTM D198. Full-size beams were manufactured following the manufacturing principles outlined in the CSA-O122, the standard for glulam production in Canada, to evaluate the performance of finger jointing, block-shear and delamination, and to establish the glulam's bending strength. Mechanical tests on trembling aspen assessed a 5th percentile value of 13.8 MPa in tension, and 40.9 MPa in bending with a mean modulus of elasticity of 10,343 MPa. The relationship between dynamic and static modulus of elasticity was analyzed and showed a strong correlation, with low relative error, and its feasibility for machine stress rating. The test conducted on the finger joint shows a characteristic value of bending strength of 31.8 MPa. The block-shear and delamination align with the requirement from the standards CSA-O122. The investigation of the bending performance on the glulam made of trembling aspen achieved a mean strength resistance of 30.3 MPa, once modified to be compared with the values from the standard, is lower than the MOR value required from the standard. In addition to the mean modulus of elasticity determined of 9013 MPa, it is also lower than the value from the standard.

This paper presents phase diagrams for Portland cement-slag-fly ash ternary cements. The study investigates various binder combinations of Portland cement, slag and fly ash, ranging from 30–100, 0–50 and 0–50, respectively. The thermodynamic equilibrium of given ternary cement systems was simulated using thermodynamic modeling coupled with simulated degree of reaction of slag and fly ash that vary with the binder compositions. The obtained results suggest that a 56% substitution factor for supplementary cementitious materials is feasible without significantly altering the formation of C–(A)–S–H. Additionally, it is found that ettringite and straetlingite are stable in the same cementitious material combinations, but ettringite becomes unstable in mixtures that favor monosulfate formation. Overall, this study provides a catalogue for selecting an appropriate proportion of binders to create mixes that complement one another, providing characteristics that are specifically tailored to the application. The results may have important implications for designing and optimizing ternary cement compositions.

This paper investigates the mechanical properties and microstructural characteristics of Controlled Low-Strength Material (CLSM) modified with Alkali Activated Solution (AAS), synthesized by combining NaOH and Na₂SiO₃ in a 1:3.29 weight ratio. The study evaluates the flowability, compressive strength, elastic modulus, and tensile strength of conventional CLSM mixes across different water-to-cementitious material ratios (w/cm), humidity levels, and curing periods. These properties are then compared with modified CLSM mixes produced by partially substituting cement in the mix with AAS. The results indicate that AAS modification enhances flowability and significantly improves both early and long-term compressive strength compared to unmodified mixes. The authors performed Scanning Electron Microscopy analysis to evaluate the microstructural characteristics of both control and modified mixes. Microscopic analysis reveals the formation of unique tubular crystal zeolitic structures in modified mixes, contributing to their improved mechanical properties. However, the study also highlights challenges associated with shrinkage and cracking, particularly under low relative humidity curing conditions. These findings provide valuable insights into the efficacy of AAS modification for enhancing the performance of CLSM mixes and underscore the importance of considering both mechanical and microstructural aspects in the mix design.

Metallurgical sludge waste (MSW), a by-product of mining, energy, and metallurgical industries, has shown potential as a substitute for traditional aggregates. This research article focuses on studying the properties of concrete incorporating MSW itself and recycled concrete aggregate (RCA) containing MSW at both early and late ages. Great emphasis is placed here on the tests carried out one year after concreting. A total of ten concrete mix proportions were prepared with varying amounts of MSW and RCA, including a reference mix. In order to investigate the effects and role of MSW on the durability properties of concrete mixes, several laboratory tests, their numerical evaluation and energy dispersive spectroscopy were carried out. The investigation aims to provide insights into the performance, durability and long-term behaviour of MSW concrete.