This study investigates the fresh state and short to long-term mechanical properties of three optimized LowCarbon Concretes (LCCs). These LCCs use a ternary blend of supplementary cementitious materials (SCMs) consisting of ground granulated blast furnace slag (GGBFS), fly ash (FA) and silica fume (SF) to achieve a high (80 %-90 %) ordinary Portland cement (OPC) replacement ratio. Their fresh state properties and short (3 days, 3d) to long term (96d) mechanical properties were compared with traditional OPC C40 concrete with 40 MPa 28d cylinder characteristic compressive strength and three single blend SCM concretes (using SF, GGBFS, FA only) with 70 % OPC replacement ratio. Tests results confirmed that the optimized LCCs showed good slump values with balanced initial and final setting times when compared with C40 and single blend SCM concretes. For mechanical properties, while the optimized LCCs showed lower early (3d and 7d) compressive strength gain than C40 and single blend SF SCM concrete, they showed higher long-term strength gain from 28d to 96d. For flexural and indirect tensile strengths and elastic modulus, the optimized LCCs showed better short and long-term performances when comparing with C40 and all single blend SCM concretes. Finally, microstructural analysis using field emission scanning electron microscopy and x-ray diffraction confirmed the existence of a denser matrix, continuing hydration and pozzolanic actions supporting their enhanced flexural and tensile strength performance.

This study reports experimental and analytical investigation on long-term durability and microstructures of Low-Carbon Concrete (LCC) developed using optimized ternary blends of ground granulated blast furnace slag, fly ash, and silica fume as sustainable alternatives to Ordinary Portland Cement (OPC). Three LCC mixes compliances for 40, 32, and 25 MPa grades concretes were designed with high-volume of 80%, 85%, and 90% OPC replacement, respectively. Their durability performance, including abrasion resistance, chloride penetration, water absorption, and total shrinkage was evaluated up to one year and benchmarked against similar grade OPC concretes. Results showed that all three LCCs mixes outperformed the OPC concretes in compressive strength by 2-4% at 28-days (28d) and 36-65% at 365d. Similarly, LCCs mixes reported 19% and 68% improvement in abrasion resistance, 84% and 89% in chloride penetration resistance, 38% and 66% in water absorption resistance, and 53% and 47% reduction in total shrinkage when compared with OPC concretes at 28d and 365d, respectively. More importantly, it is found that unlike OPC concretes for which their long-term strength and durability performances were positively correlated to the concrete grade and OPC content, the long-term compressive strength of LCCs was only weakly correlated to the OPC content while their durability performances are positively correlated to the percentage of supplementary cementitious materials (SCMs) rather than their concrete grades. Microstructural analysis of LCCs identified the synergistic effects of high-volume ternary SCMs blends which resulted a denser, more refined matrix, and explained their correlations with the improved long-term strength development as well as superior durability. Furthermore, a new empirical model was proposed for the total shrinkage of LCCs. The findings confirm that these developed LCCs could provide a low-carbon alternative for infrastructure applications that demand high durability performance.

Recycling industrial waste into construction materials is becoming a fundamental strategy, offering a hopeful path toward sustainable construction practices. This study focuses on the innovative reuse of end-of-service wood and crumb rubber to develop environmentally favorable materials. Their high availability, lightweight properties, and high-energy absorption capacity make them highly suitable as additives in masonry unit production. Furthermore, using them with sustainable binding material, such as geopolymer, enhances the overall sustainability of the masonry, facilitating rapid strength development and enhancing durability while providing increased protection against fire and weathering. The study involved the development of an optimal mix design, which can potentially be used for the production of load-bearing and non-load-bearing masonry units. This was achieved by examining various proportions of wood, as well as combinations of wood and rubber, using a partial–factorial experimental design. The results show that wood-to-binder ratios ranging from 0.2 to 0.4 can potentially be used for the production of wood–geopolymer masonry units. Additionally, a ratio of 0.3 (with 50

This study develops three new Low Carbon Concrete (LCC) mix designs with characteristic cylinder compressive strengths of 32 MPa (C32), 25 MPa (C25), and 20 MPa (C20). By using a Taguchi design of experiment (T-DoE) model and combined it with Grey relational analysis (GRA) and Principal component analysis (PCA) for multi-response optimization, sixteen trial mixes employing supplementary cementitious materials (SCMs) to replace 80 % to 95 % of ordinary Portland cement (OPC) were tested. Three factors namely, OPC replacement percentage, ground granulated blast-furnace slag (GGBFS) to fly ash (FA) ratio, and silica fume (SF) to binder percentage were considered. Optimization results led to three LCC mix designs with 80 %, 85 %, and 90 % OPC replacement. Their compressive strength, split tensile strength, flexural strength, elastic modulus, and slump were evaluated. Confirmation tests showed that the 80 %, 85 % and 90 % OPC replacement mixes respectively satisfied requirements for C32, C25, and C20 concretes. Carbon footprint study showed that the LCC mixes led to significant reduction of carbon footprint when compared with OPC concrete. Finally, microstructure analysis was conducted to study in the microstructure characteristics of the LCCs.

Previous studies have suggested that incorporating crumb rubber into concrete enhances impact resistance and energy absorption. However, these studies often overlook the associated reduction in compressive strength when crumb rubber replaces fine aggregates, leading to comparisons between concretes with different strengths. This study addresses this gap by investigating the dynamic behaviour of two geopolymer concrete mixes, G1-25R and G2-0R, both designed to achieve similar compressive strengths despite their differing compositions. Mix G1-25R includes 25% crumb rubber replacement of fine aggregates and a binder composed of 90% fly ash and 10% Ground Granulated Blast Furnace Slag (GGBFS), while Mix G2-0R has no crumb rubber and uses only fly ash as the binder. Dynamic performance was assessed using a drop tower setup across six testing configurations. Results indicate that both mixes exhibit comparable peak impact forces and energy absorption capacities, which is attributed primarily to their similar compressive strengths. Although G1-25R’s crumb rubber content enhances ductility in static compressive tests, this increased ductility does not significantly influence dynamic resistance when compared similar strength geopolymer concrete with no crumb rubber. These findings suggest that crumb rubber can be effectively recycled in geopolymer concrete, providing comparable impact resistance and energy absorption to traditional concrete.

This study investigates the energy absorption behaviour of Geopolymer Crumb Rubber Concrete (GCRC), a sustainable alternative to conventional concrete that replaces fine aggregates with crumb rubber derived from waste tyres and eliminates Portland cement through the use of alkali-activated binders. The research focuses on the effects of incorporating 25 % crumb rubber, with and without sodium hydroxide (NaOH) pre-treatment, on the static and dynamic performance of GCRC under localised concentrated loading. A total of 138 cube specimens (100 mm) were tested using a semi-spherical striker in both quasi-static and drop-weight impact regimes across a mid-range energy spectrum (75-105 J). This testing configuration, designed to simulate localised impact scenarios, offers a novel approach not previously applied to GCRC. Results show that untreated crumb rubber significantly increases normalised dynamic energy absorption by 41-59 % relative to control mixes, primarily due to the reduction in compressive strength. NaOH pre-treatment improves matrix bonding and restores peak impact force, but results in a 15-25 % reduction in normalised energy absorption due to increased stiffness and reduced ductility. A comparative analysis of mixes with similar compressive strengths confirms that strength, rather than rubber content alone, governs energy absorption per unit of strength. The experimental data generated in this study also provide a valuable reference for calibrating existing material models or validating new ones, enabling more accurate numerical simulations of GCRC under impact loading. These results serve as a foundation for future structural-scale testing, modelling, and design of impact-prone infrastructure components.

In recent years, timber has emerged as a sustainable alternative material in structural engineering. However, due to its orthotropic nature, the mechanical properties of timber vary significantly concerning its grain direction, presenting challenges in its application, particularly in bolted connections perpendicular to the grain, as it causes the joints to fracture prematurely and causes damage to the bolted timber frame when subjected to tensile strain. This paper presents an experimental study on the effects of such loading configurations on timber connections in order to have a comprehensive understanding of the failure mechanisms, as it becomes essential to assess the real capacity of brittle failure modes in timber connections. This paper investigates experimental data from timber connections loaded perpendicular to the grain, taking into account differences in loaded edge distance. Using image-based data, the study penetrates the strain field of bolted timber connections, revealing insights unreachable by conventional laboratory measurements alone. Through image-based analysis, crucial parameters such as crack initiation load and fracture patterns at failure load are evaluated, enhancing the understanding of timber connection behavior. This study also explains the image-based analytic approach to strain field measurement in various cross-sections of timber connections.

Although manifold empirical studies have identified the mechanical properties of crumb rubber concrete (CRC), a comparative analysis of economic and environmental benefits between CRC and ordinary Portland cement concrete (OPCC) is not explored. In this paper, a quantitative meta-analysis between CRC and OPCC is conducted to explore optimized design strength, and a comparative analysis of the economic and environmental benefits of the two materials is undertaken. Considering cost price as the economic index and CO2 emissions per cubic meter of concrete as the environmental index in the materialization stage, CRC and OPCC were compared with different mix designs to achieve grades of similar strengths. Upon replacing less than 20% of natural fine aggregates in concrete with crumb rubber, while retaining the cement content, an increase of 6% in the cost price was achieved for CRC with 30–40 MPa strength grade. Apart from the aspect of mining and transportation of natural aggregates, the reduction of CO2 emissions by means of CRC adoption was verified in the treatment process of waste tire incineration. The results show that CO2 emissions from CRC decreased by 15–17% when compared with OPCC for 30~40 MPa grade concrete. The research conclusion can serve as a theoretical basis for the engineering application of CRC with the same strength, and make certain contributions to the industrial application of crumb rubber aggregates and the sustainable treatment of waste tires.

In pursuits of sustainable infrastructure, development of Low Carbon Concrete (LCC) is vital for the construction of Low Carbon Structures (LCS). For LCS to be widely applied, it is imperative that LCC exhibits the required mechanical and durability characteristics. This necessitates an understanding of constituents such as supplementary cementitious materials (SCMs), recycled aggregates (RA) and fibres that influence LCC mechanical and durability behaviours. However, based on materials characterisation, previous studies reveal significant variations in LCC mechanical properties and durability behaviours. Therefore, this review seeks to comprehend the effect of different types of SCMs, RA and fibres on key mechanical properties and durability behaviours of LCC. It also provides insights on improving LCC mechanical properties and durability behaviours, drawing from extensive research outlooks on materials characterisations, mix proportioning and curing conditions and summarises existing literature on LCC carbon footprint analysis. Finally, it identifies potential research directions for future studies including analytical models to enhance the mechanical properties and durability behaviours of LCC.

Many critical concreting activities require the determination of the in-place concrete strength. It can be costly to wait too long to execute these activities, but acting too early can have a negative impact on structural performance. Conventional moulded concrete cylinders and alternative strength assessment methods such as the maturity method are commonly used to assess concrete's in-place strength. This study is focused on a special case when the maturity method is applied for evaluating concrete strength in cold weather at an early age. Specifically, the study proposes an alternative method for calibrating the activation energy, an input for the maturity method. Concretes cured at two different temperatures are used to calibrate the activation energy. The maturity method based on this activation energy predicted the cold weather concrete's compressive strength satisfactorily. It was also found that for a successful application of the proposed activation energy calibration, the two temperatures should represent the expected minimum and maximum temperature at the site. Furthermore, the results showed that the maturity method based on the proposed activation energy calibration method performed better than the conventional cylinder method.

Rigid pavements at military airfields experience surface deterioration within 6–18 months of construction. The cause of this degradation is mainly due to combined exposure to repeated heat shocks from jet engine exhaust and spilled aviation oils (hydrocarbons). Surface degradation occurs in the form of disintegration of aggregates and cement paste into small pieces that pose severe risks of physical injury to maintenance crews or damage to an aircraft engine. Since coarse aggregates typically occupy 60–80% of the concrete volume, aggregates’ thermal properties and microstructure should play a crucial role in the degrading mechanism. At high temperatures, concrete with lightweight aggregates is reported to have better performance compared to concrete with normal-weight aggregate. Thus, the present study carried out a detailed investigation of the mechanical and thermal performance of lightweight aggregate concrete exposed to the combined effects of high temperatures and hydrocarbon oils simultaneously. To replicate harsh airfield operating conditions, standard-sized concrete cylinders were exposed to elevated temperatures using an electric oven. Additionally, a mixture of equal parts of aircraft engine oil, hydraulic oil, and kerosene was applied before each exposure to high temperatures. To identify the resistance of different concrete with various lightweight coarse aggregates, pumice, perlite, lytag (sintered fly ash), and crushed brick were used as lightweight coarse aggregates in concrete. Also, basalt aggregate concrete was used as a reference. After curing, cylinders were tested for the ultimate strength. Later, after every 20 cyclic exposures, three cylinders from each aggregate type were tested for residual comprehensive strength, thermal, chemical, and microstructural (SEM) properties. Overall, concrete with crushed brick aggregate and lytag used in this study showed superior resistance to the simulated airfield conditions. The findings of this study will provide valuable insights to select an appropriate coarse aggregate type for military airfield pavement construction, aiming to effectively minimize surface spalling.

Concrete is one of the most widely used construction materials, with cement being a key component. However, cement production is associated with a significant carbon footprint. To address this issue, there is a growing demand to partially replace cement with less carbon-intensive binders to create sustainable concrete structures. The chemical composition of these new binders changes the fire resilience requirement of sustainable concrete, which affects the design of concrete slabs. Consequently, changes in concrete volume and cement quantity are expected in the construction of sustainable concrete slabs. This study aimed to investigate how the changes in fire resilience requirements influenced the changes in concrete volume and cement requirements for slab construction. The study involved designing numerous concrete slabs with different spans, loads, and durability conditions as per standard, focusing on minimising the slab thickness. The slabs were then redesigned to meet various fire resilience requirements, and the changes in concrete volume and cement content were compared with the standard design. The study's findings indicated that changes in fire resilience requirements significantly affected concrete slab design, leading to adjustments in concrete volume and cement quantity. Therefore, the study highlighted the importance of considering fire resilience in the design and construction of sustainable concrete structures with implications for the cement industry and construction sector, which are significant contributors to global carbon emissions.

Foam concrete has been used in various real-life applications for decades. Simple manufacturing methods, lightweight, high flowability, easy transportability, and low cost make it a useful construction material. This study aims to develop foam concrete mixtures for various civil and geotechnical engineering applications, such as in-fill, wall backfill and soil replacement work. A blended binder mix containing cement, fly ash and silica fume was produced for this study. Its compressive strength performance was compared against conventional general purpose (GP) cement-based foam concrete. Polypropylene (PP) fibre was used for both mixtures and the effect of various percentages of foam content on the compressive strength was thoroughly investigated. Additionally, two types of foaming agents were used to examine their impact on density, strength and setting time. One foaming agent was conventional, whereas the second foaming agent type can be used to manufacture permeable foam concrete. Results indicate that an increase in foam content significantly decreases the strength; however, this reduction is higher in GP mixes than in blended mixes. Nevertheless, the GP mixes attained two times higher compressive strength than the blended mix’s compressive strengths at any foam content. It was also found that the foaming agent associated with creating permeable foam concrete lost its strength (reduced by more than half), even though the density is comparable. The compressive stress–deformation behaviour showed that densification occurs in foam concrete due to its low density, and fibres contributed significantly to crack bridging. These two effects resulted in a long plateau in the compressive stress–strain behaviour of the fibre-reinforced foam concrete.

As the environmental impact of modern society continues to escalate, the construction industry actively pursues environmentally friendly materials to revolutionize its practices. Recycling, especially repurposing end-of-service materials and industrial wastes, emerges as a pivotal strategy offering a promising path towards sustainable construction. This study focuses on the innovative reuse of end-of-service wood, crumb rubber, and cenosphere with geopolymer binder to produce sustainable alternatives to masonry units. The study was conducted in two stages. In the first stage, cube samples were produced and tested to establish an optimal mix design. Results indicated that as the relative volume of waste increased, the compressive strength decreased. The compressive strength of the wood geopolymer composite decreased from 25 MPa to 4 MPa as the wood-to-binder ratio increased from 0.1 to 0.5. An increasing trend was observed for density with the increase of the rubber-to-wood ratio. The compressive strength also increased with the increase of the rubber-to-wood ratio for most of the investigated ranges. As fly ash is gradually replaced by cenospheres, a significant decrease in compressive strength was noted, about 70% and 80% for wood-to-binder (ratios of 0.2 and 0.3, respectively). In the second stage, three distinct types of masonry units were produced and tested based on the optimized mix design. The compressive strength results indicated promising performance, with wood-geopolymer masonry units exhibiting a strength of 8.39 MPa, wood-rubber-geopolymer masonry units achieving 8.32 MPa, and wood-cenosphere-geopolymer masonry units resulting in 7.33 MPa. While these values fell below the target 10 MPa, it is noteworthy that wood-geopolymer masonry units and wood-rubber-geopolymer masonry units met the minimum compressive strength requirements of some standards and demonstrated significantly better ductility compared to traditional masonry units. The results showcase significant promise in the viability and performance of these innovative masonry units.

The environmental impact of non-biodegradable rubber waste can be severe if they are buried in moist landfill soils or remain unused forever. This study deals with a sustainable approach for reusing discarded tires in construction materials. Replacing ordinary Portland cement (OPC) with an environmentally friendly geopolymer binder and integrating crumb rubber into pre-treated or non-treated geopolymer concrete as a partial replacement of natural aggregate is a great alternative to utilise tire waste and reduce CO2 emissions. Considering this, two sets of geopolymer concrete (GPC) mixes were manufactured, referred to as core mixes. Fine aggregates of the core geopolymer mixes were partially replaced with pre-treated and non-treated rubber crumbs to produce crumb rubber geopolymer concrete (CRGPC). The mechanical properties, such as compressive strength, stress–strain relationship, and elastic modulus of a rubberised geopolymer concrete of the reference GPC mix and the CRGPC were examined thoroughly to determine the performance of the products. Also, the mechanical properties of the CRGPC were compared with the existing material models. The result shows that the compressive strength and modulus of elasticity of CRGPC decrease with the increase of rubber content; for instance, a 33% reduction of the compressive strength is observed when 25% natural fine aggregate is replaced with crumb rubber. However, the strength and elasticity reduction can be minimised using pre-treated rubber particles. Based on the experimental results, stress–strain models for GPC and CRGPC are developed and proposed. The proposed models can accurately predict the properties of GPC and CRGPC.

The effectiveness of hemp shives for the internal curing of concrete has been experimentally investigated in the current study. The effect of internal water embedded through pre-saturated hemp shives on concrete curing was assessed by comparing the strength and shrinkage response of a hemp-concrete composite to those of a traditional concrete mix. Three different hemp shive sizes and two different curing conditions (sealed and unsealed) were considered to replicate typical curing conditions at construction sites. Strength results were compared to a Control Mix subjected to standard laboratory curing conditions. It was observed that the compressive strength of the hemp-concrete composite increased with the reduction of particle size and dosage of hemp shives. The mix that included 1 % shives in the size range 1 to 2 mm was identified as the optimum mix achieving a strength up to 83 % to that of the Control Mix. Importantly, a reduction in unrestrained shrinkage was observed for this mix compared to the control samples. Microstructural analysis of the hemp-concrete composite confirmed that continued hydration took place due to the presence of internal water supplied by the hemp shives. As a result, with the inclusion of saturated hemp shives the process of cement hydration and strength gain continued for a longer period even in the absence of external curing water compared to that of traditional hydration.

This study investigates the feasibility of an alternative structural health monitoring (SHM) technique for an existing, post-tensioned, prestressed concrete bridge in Niigata, Japan. Currently, a static SHM system is in place to detect the progress of damages within the bridge. However, the existing system cannot properly monitor the structural health of the bridge including the periodic vibration, which is one of the damage-sensitive features of interest. Therefore, to effectively detect the real-time performances of the bridge, a three-dimensional (3D) Finite Element (FE) model was developed as a reference and verified using on-site load-deflection test results. After validating the reference FE model, different damage scenarios, such as degradation of concrete, corrosion & rupture of steel tendons and missing tendons, were incorporated in the FE models. Based on non-linear structural and Eigenvalue analyses, natural frequencies and mode shapes of the bridge remain constant even after careful consideration of all types of damages in the FE model. However, vertical displacements are observed to increase for the damage scenarios. Although the effect of tendon rupture and corrosion showed negligible influences on the vertical displacement, the deterioration of the concrete largely influenced the vertical displacement. Additionally, crack widths were found to vary with damage types. Brifely, this study recommends some effective indicators to monitor the structural conditions of the bridge using FE analysis (FEA).

The construction industry is facing increased demand for adopting sustainable ‘green’ building materials to minimise the carbon footprint of the infrastructure sector to meet the United Nations 2030 Sustainability Goals. Natural bio-composite materials such as timber and bamboo have been widely used in construction for centuries. Hemp has also been used in different forms in the construction sector for decades for its thermal and acoustic insulation capability owing to its moisture buffering capacity and thermal conductivity. The current research aims to explore the possible application of hydrophilic hemp shives for assisting the internal curing of concrete materials as a biodegradable alternative to currently used chemical products. The properties of hemp have been assessed based on their water absorption and desorption properties associated with their characteristic sizes. It was observed that, in addition to its excellent moisture absorption capacity, hemp released most of its absorbed moisture into the surroundings under a high relative humidity (>93%); the best outcome was observed for smaller hemp particles (<2.36 mm). Furthermore, when compared to typical internal curing agents such as lightweight aggregates, hemp showed a similar behaviour in releasing its absorbed moisture to the surroundings indicating its potential application as a natural internal curing agent for concrete materials. An estimate of the volume of hemp shives required to provide a similar curing response to traditional internal curing techniques has been proposed.

Surface degradation at parking aprons of military airfields concerns jet aircraft safety. It is caused by the disintegration of coarse aggregates in concrete. This study aims to understand the effects of repeated exposure to various aviation oils and high-temperature on concrete constituent materials. An airfield exposure condition was created to expose samples made with different water to cement ratios (w/c). Samples were tested for residual mechanical properties, thermal conductivity, specific heat, thermogravimetric and microstructural analysis. Results show that the w/c ratio of concrete significantly influences the residual strength of the exposed samples. Moreover, aviation oils react with ordinary concrete at higher temperatures and produce harmful salts. Besides, thermal incompatibility between the aggregates and cement paste triggers microcracks in cement paste and thermal cracks in the coarse aggregate. Due to the simultaneous thermal and chemical attack, concrete suffers the disintegration of aggregates and flake-like concrete pieces on the top surface.