Abstract Ultrahigh performance fiber-reinforced concrete (UHPFRC) is a promising composite material, exhibiting compressive strength of around 150 MPa and flexural strength of up to 45 MPa. Despite its impressive properties, the characteristics of the interfacial transition zone (ITZ) between the fiber and the cementitious matrix, which are similar to those in conventional fiber reinforced concrete, significantly influence the behavior of the composite. Since the fiber surface is in direct contact with the ITZ, modifying this interface presents a promising technique to enhance the performance of the composite. In this context, silanes can be used as coupling agents to improve fiber–matrix interactions. This study investigates UHPFRC with the fibers’ surface functionalized using tetraethoxysilane (TEOS) at different proportions: 0.1, 0.5, and 1.0% silane in surface treatments. The analysis was conducted on both fresh and hardened states, evaluating workability and hydration through calorimetry, and flexural and compressive strength through mechanical testing. The results demonstrated that the addition of 0.5% of TEOS improved workability and hydration, showing 7% more heat released in the acceleration period in comparison to the reference (REF) series. The bending results indicated that the sample with 0.5% TEOS in the treatment resulted in an improvement in strength indices up 15% on maximum load, and a 28-day equivalent compressive strength was achieved.

Cracks in reinforced autoclaved aerated concrete (RAAC) pose significant structural risks, including water ingress, corrosion of reinforcement, and, in extreme cases, potential collapse. The challenge is worsened by the lack of accessible RAAC crack data, making it difficult to develop accurate and consistent detection frameworks. This limitation restricts the ability to perform timely interventions and implement effective maintenance strategies for RAAC cracks. Therefore, the study aims to assess the impact of data augmentation by using StyleGAN3, one of the generative adversarial networks, to address limited RAAC crack data. Furthermore, advanced convolutional neural network architectures were explored for improved semantic segmentation of RAAC cracks. Results revealed that StyleGAN3-generated data augmentation boosted model performance, and the newly developed RAAC-UNet++ model markedly enhanced segmentation accuracy. These findings offer valuable insights for improving RAAC crack detection, ultimately aiding in the effective maintenance and management of RAAC structures.

This paper analyses the mechanical behaviour of steel fibre reinforced concrete (SFRC) subjected to cyclic loading. Fatigue tests were conducted on pre-cracked specimens using a three-point bending setup, considering initial crack widths and load levels representative of the service limit state (SLS). A Weibull distribution was used to establish the S-N-Pf curve. The crack growth rate indicated that inflection points are governed by the quasi- static load-CMOD relationship, transitioning to a damage accelerate stage with reduced post-cracking strength. Energy dissipation analysis revealed a significant increase of this property at lower load levels during the final 80 % of fatigue life, while increases were less pronounced at higher load levels. Maximum energy dissipation occurred at the CMOD corresponding to a 2 % reduction in load-bearing capacity. Visual analysis of SFRC cross-sections suggested that fatigue failure resulted from a combination of persistent fibre pull-out, fibre- matrix damage, and fibre rupture. An improved conceptual model accurately estimates CMOD evolution and suggests that fatigue tests can be shortened by pre-cracking or performing a set number of cycles to stabilize deformation rates. Fatigue life design considerations herein are proposed to the light of results and analysis carried out.

3D Concrete Printing (3DCP) has the potential to support the adoption of digital manufacturing approaches in construction. However, applications are currently limited by the lack of understanding of the structural performance of elements manufactured with this process. The layer-wise fabrication process enables the placement of reinforcement between printed layers. The final reinforcement position depends on the fresh properties of wet material. Moreover, toolpath strategies influence the cross-sectional geometry and concrete anisotropic compressive strength. Understanding the relative importance of these factors as they relate to the mechanical performance of the printed concrete becomes, therefore, critical for 3DCP use. This study addresses this gap through experimental and numerical studies of the flexural behaviour of 3DCP beams with different reinforcement positions and toolpath strategies. The results demonstrate that the toolpath orientation, and hence anisotropy, can be neglected for the cases explored here. Moreover, toolpath orientations perpendicular to the steel reinforcement reduce the risk of shear and delamination failure as cracks align with the vertical interface, thus promoting flexural cracking. The position of the steel reinforcement is the most significant factor: specimens printed with reinforcement closer to the top layers showed increased flexural performance if compared with those printed with the reinforcement closer to the bottom layers.

Purpose Reinforced autoclaved aerated concrete (RAAC) panels have been extensively used in the UK since the 1960s as structural roofs, floors and walls. The lack of a longitudinal, objective, consistent defect data capture process has led to inaccurate, invalid and incomplete RAAC data, which limits the ability to survey RAAC within buildings and monitor performance. Therefore, an accurate, complete and valid digital data capture process is needed to facilitate better RAAC performance and defect monitoring. This paper presents the development of an artificial intelligence (AI)-driven RAAC crack defect capture tool for improving the quality of RAAC survey data. Design/methodology/approach RAAC crack defect image data were collected, curated and trained. A deep learning approach was employed to train RAAC surveyed defects (cracks) images from two hospitals. This approach mitigated unavoidable occlusions/obstructions and unintended “foreign” objects and textures. Findings An automatic RAAC crack identification tool has been developed to be integrated into RAAC survey processes via an executable code. The executable code categorises RAAC survey images into “crack” or “non-crack” and can provide longitudinal graphical evidence of changes in the RAAC over time. Originality/value This paper identifies the role of AI in addressing the intrinsic defects data capture issues for RAAC and extends current debates on data-driven solutions for defect capture and monitoring.

The longevity and viability of construction components in a circular economy demand a robust, data-informed framework for reuse decision-making. This paper introduces a multi-level grading and classification system that combines Bayesian probabilistic modeling with scenario-based performance thresholds to assess the reusability of end-of-life modular components. By grading components across a five-tier scale, the system supports strategic decisions for reuse, up-use, or down-use, ensuring alignment with engineering standards and sustainability objectives. The model's development is grounded in empirical data from precast concrete wall panels, and its explainability is enhanced through decision tree logic and Sankey visualizations that trace the influence of contextual scenarios on classification outcomes. MGCS addresses the environmental, economic, and operational challenges of EoL management–reducing material waste, optimizing value recovery, and improving workflow efficiency. Through dynamic feature weighting and transparent reasoning, the system offers a practical yet rigorous pathway to embed circular thinking into construction industry practices.

One of the most significant challenges facing extrusion-based 3D concrete printing (3DCP) is the anisotropy present in the printed material: under load, the observed performance is typically lower than a cast equivalent and significantly so in certain directions. In addition, the performance is also more variable than cast material. These observations are, in part, due to surface moisture evaporation and air entrapment. Here, we investigate the hypothesis that the printed concrete comprises of agglomerated filament core and skin having distinct properties as a necessary consequence of the printing process. Through novel X-ray computed tomography measurements, we show that printed concrete comprises the core and Filament Interfacial Zone Network (FIZN) and that, in contrast to the cores, the FIZN is found to be free from pores except at boundaries where there is incomplete bonding. Through morphological, chemical and mechanical analysis, the FIZN is also found to contain 20% less sand and 60% more anhydrous cement than the filament cores, while the FIZ material was inferred to have 11% higher compressive strength, 28% lower flexural strength and 22% lower elastic modulus than the core. The findings from this work suggest that anisotropy will always exist and that care should be devoted to the material rheology, printing system and the filaments arrangement in order to produce consistent and predictable hardened material properties.

The primary mechanism of stress transfer between the fiber and the matrix is governed by the interface region between the fiber and the cementitious matrix, which is rich in calcium hydroxide (Ca(OH)2). Calcium hydroxide is a byproduct with low mechanical strength and is intrinsic to the cement hydration process. Leveraging this characteristic, the deposition of silicabased materials on the fibers opens up potential for enhancing the interface region through reaction with Ca(OH)2. In this context, the treatment of metallic fibers with Tetraethoxisilane (TEOS) presents potential for depositing silica on the fiber surface, this may react with this calcium hydroxide and could promote depositions of Calcium silicate hydrates in this region, densifying this interface. In this study, various types of dip-coating treatments of metallic fibers with TEOS were evaluated, using different silane concentrations (0.1 %, 1.0 %, and 10 %) and different alkaline treatments (sodium hydroxide (NaOH) and Ca(OH)2), aiming to obtain a silicarich film. Microstructural analyses of the fibers pre- and post-treatment, mass variation analysis of the fibers post-treatment, as well as tests on the fiber-reinforced composite, including workability, isothermal calorimetry, modulus of rupture (MOR), and compressive strength were conducted. The results showed that silane was deposited on the fiber surface, as indicated by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and there was an increase in fiber mass depending on the TEOS concentration in the functionalization solution. In the composite, greater workability was observed with higher TEOS concentrations, while no clear trend was observed in the calorimetry results, with variations of around 10 % in the induction period and silicates peak heat. In terms of MOR, the samples treated with TEOS showed strength values up to 15 % higher compared to the reference, while no significant increases were observed in compressive strength.

Industries are required to utilize treatment technologies to reduce contaminants in wastewater prior to discharge and to valorize by-products to increase sustainability and competitiveness. Most acid leaching gypsum purification studies have obviated the treatment of the highly acidic wastewater produced. In this work, acidic wastewater from acid leaching purification of post-consumer gypsum was treated to recover a valuable solid product and reusable water. The main aims of this work were to determine the impact of recirculating acidic and treated wastewaters on the efficiency of the acid leaching purification process and to valorize the impurities in the wastewater. Samples were characterized through X-ray fluorescence and X-ray diffraction. SimaPro 9.5 and the ReCiPe 2016 midpoint method were used for the life cycle assessment of three sustainable wastewater management approaches. The reuse of the acidic wastewater did not improve the chemical purity of gypsum. Soluble impurities were precipitated at pH 10.5 as a magnesium-rich gypsum that could be commercialized as fertilizer or soil ameliorant. The alkaline-treated water was reused for six acid leaching purification cycles without impacting the efficiency of the purification process. An acid leaching–neutralization–filtration–precipitation approach demonstrated superior overall environmental performance. Barriers and enabling measures for the implementation of an in-house wastewater treatment were identified.

Plasterboard, which serves as a nonstructural building material, is widely employed for lightweight wall construction and surface finishing in walls and ceilings. Amid mounting concerns regarding product sustainability and the adoption of Net Zero strategies, evaluating the environmental performance of materials has become crucial. This study aims to conduct a comprehensive life cycle assessment (LCA) for wall gypsum plasterboard, aiming to pinpoint areas for potential environmental improvement. The LCA methodology, adhering to established guidelines and considering midpoint impact categories, was employed to quantify environmental impacts across various stages of the plasterboard life cycle—encompassing raw material extraction, plasterboard manufacturing, transportation during all stages, and end-of-life treatment of plasterboard waste. Primary data were sourced directly from a plasterboard manufacturer and recycler and supplemented with secondary data obtained from the Environmental Product Declaration (EPD) and the Ecoinvent 3.9 database. Among the identified impact categories, the human carcinogenic toxicity category emerged as the most affected category, primarily due to the raw material supply stage, followed by freshwater ecotoxicity, which was impacted due to the material supply stage.

This paper presents a novel developed Sprayed Ultra-High-Performance Cementitious Sandwich Panel (SUHPC-SP) for structural applications. The SUHPC-SP features sprayed UHPC outer layers making it suited for structural load bearing applications, and a foamed concrete core layer offering high thermal properties. With the development of enhanced material properties and novel production methods, the established SUHPC-SP can achieve optimal mechanical performance while minimising the volumes of material required. As such, this study assesses SUHPC-SP potential to increase sustainable outputs over reference Brick and Block (B&B) construction; by quantifying and comparing the whole life cycle environmental and economic impacts of the two methods. A comparative life cycle assessment (LCA) of these types of construction products is presented for the first time in this paper. The study found that integrating SUHPC-SP over typical B&B construction can reduce environmental impacts by as much as 500% and costs by up to 180%. This informs sustainable construction decisions, offering an effective alternative to conventional inefficient building methods and materials.

UK industry has recently highlighted concerns relating to the structural safety of Reinforced Autoclaved Aerated Concrete (RAAC) in existing structures, together with a small number of without warning collapses. A broad body of scholarly academic research already exists on AAC in Building Structures, though much less on RAAC. Against the fact that extant research is primarily industry-led, there is a lack of a systematic critical review of the body of academic literature available. To achieve this, the paper systematically reviews 92 academic papers filtered from over 480 published studies on AAC/RAAC, each included after applying an exclusion criterion, from 1980 to 2024. The review identifies four drivers for AAC applications in building structures, namely AAC being: 1) a lightweight material, useful in reducing load transfers, 2) an insulating material, against fire, temperature, and sounds, 3) a sustainable material, of a recyclable nature with relatively low carbon emissions, and 4) an economical material because of its composition and ease of use and application. Moreover, it also identifies the popular areas of AAC application within buildings, the processes involved in its production, the material's behaviour and characteristics, the types of reinforcement, and the modes of AAC failure. Such a review of knowledge from the last 40 years will help scholars identify the understudied research gaps and several untapped research areas that are included in the proposed research agenda.

The early age strength development required for typical wet mix sprayed concrete tunnel lining (SCL) necessitates higher binder contents than strength class cast equivalents, and is dependent on liquid accelerating admixtures specifically formulated to work with CEM I. Consequently, SCL concretes have relatively high embodied carbon contents that are difficult to mitigate using supplementary cementitious materials such as ground granulated blast furnace slag (GGBS). Contemporary low carbon alternatives based on conventional spraying technology achieve a 23 % carbon reduction, although calcium aluminate (CA) based powdered accelerators have the potential to facilitate significantly greater reductions through the replacement of a high proportion of CEM I. The paper reports the trial spraying of a concrete employing a CA based powdered accelerator to achieve 70 % CEM I replacement with GGBS, representing a 57 % reduction in embodied carbon. Partially intermittent spraying led to some statistically significant in-situ material variability in nominally identical test panels. Nonetheless, the material was of consistent good quality evidenced by there being no statistically significant difference in the mean strengths of parallel and perpendicular cores. Early age (up to 24 hours), 28 and 90-day compressive strengths were conformant, although 1 to 7-day strength development was lower than specification requirements. This was attributed to factors unique to the prototype trial set up, which would necessarily be addressed in SCL construction practice. Residual flexural tensile strength ductility performance was also conformant, although requirements relating to immediate post cracking brittleness and absolute residual strength were below that required. Given the concurrent compressive strength conformance, this was attributed to inadequate fibre performance that is easily addressed through fibre type and dosage selection. The aim of demonstrating potential conformance with a contemporary SCL specification mechanical performance requirements was therefore clearly met. Durability related testing, including petrographic and SEM analyses, provided assurance that hydration products were as expected which, along with reduced heat of hydration, demonstrate enhanced potential for overall carbon reduction by meeting the quality requirements associated with single pass permanent SCL.

Background Contaminants and water-soluble salts present in mechanically recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste limit its use as a secondary raw material in plasterboard manufacturing. This research addresses this limitation, developing a novel acid leaching purification technology combined with an improved mechanical pre-treatment for post-consumer gypsum valorization. Methods Laboratory-scale acid leaching purification was performed with a borosilicate beaker, hot plate, and overhead stirrer. Stuccos were produced after calcination of gypsum at 150 °C for 3 hours. Samples were characterized through X-ray fluorescence, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and particle size analysis. Results Acid leaching at 90 °C for 1 h using a 5 wt% sulfuric acid solution was revealed to be the optimum purification conditions. Stuccos produced from purified gypsum under optimum conditions had similar initial setting times to that of a commercial stucco but with higher water demand, which could be reduced by optimizing the calcination conditions. A magnesium-rich gypsum was precipitated from the wastewater. Conclusions Purified post-consumer gypsum with > 96 wt% chemical purity and calcium sulfate dihydrate content was produced. The research recommends acid neutralization prior filtration, use of gypsum particles < 2 mm in size, and stirring speed of 50 rpm to reduce the economic and environmental impacts of the acid leaching purification process at industrial scale. The magnesium-rich gypsum could potentially be marketed as soil fertilizer.

Background: Contaminants and water-soluble salts present in mechanically recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste limit its use as a secondary raw material in plasterboard manufacturing. This research addresses this limitation, developing a novel acid leaching purification technology combined with an improved mechanical pre-treatment for post-consumer gypsum valorization. Methods: Laboratory-scale acid leaching purification was performed with a borosilicate beaker, hot plate, and overhead stirrer. Stuccos were produced after calcination of gypsum at 150 °C for 3 hours. Samples were characterized through X-ray fluorescence, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and particle size analysis. Results: Acid leaching at 90 °C for 1 h using a 5 wt% sulfuric acid solution was revealed to be the optimum purification conditions. Stuccos produced from purified gypsum under optimum conditions had similar initial setting times to that of a commercial stucco but with higher water demand, which could be reduced by optimizing the calcination conditions. A magnesium-rich gypsum was precipitated from the wastewater. Conclusions: Purified post-consumer gypsum with > 96 wt% chemical purity and calcium sulfate dihydrate content was produced. The research recommends acid neutralization prior filtration, use of gypsum particles < 2 mm in size, and stirring speed of 50 rpm to reduce the economic and environmental impacts of the acid leaching purification process at industrial scale. The magnesium-rich gypsum could potentially be marketed as soil fertilizer.

Post-consumer plasterboard waste sorting is carried out manually by operators, which is time-consuming and costly. In this work, a laboratory-scale hyperspectral imaging (HSI) system was evaluated for automatic refurbishment plasterboard waste sorting. The HSI system was trained to differentiate between plasterboard (gypsum core between two lining papers) and contaminants (e.g., wood, plastics, mortar or ceramics). Segregated plasterboard samples were crushed and sieved to obtain gypsum particles of less than 250 microns, which were characterized through X-ray fluorescence to determine their chemical purity levels. Refurbishment plasterboard waste particles <10 mm in size were not processed with the HSI-based sorting system because the manual processing of these particles at a laboratory scale would have been very time-consuming. Gypsum from refurbishment plasterboard waste particles <10 mm in size contained very small amounts of undesirable chemical impurities for plasterboard manufacturing (chloride, magnesium, sodium, potassium and phosphorus salts), and its chemical purity was similar to that of the gypsum from HSI-sorted plasterboard (96 wt%). The combination of unprocessed refurbishment plasterboard waste <10 mm with HSI-sorted plasterboard ≥10 mm in size led to a plasterboard recovery yield >98 wt%. These findings underpin the potential implementation of an industrial-scale HSI system for plasterboard waste sorting.

Reinforced Autoclaved Aerated Concrete (RAAC) is a lightweight, aerated cementitious material with no coarse aggregate, hence the material properties and structural behavior vary significantly compared with “traditional” reinforced concrete. It was a popular form of precast concrete panelized construction in the 1970s, especially in critical infrastructure such as hospitals, schools, and government buildings, and many of these structures are now at the end of their design life. Although the quality of contemporary RAAC precast elements and structures is considered to be good, concerns exist regarding the durability, serviceability and structural reliability of 40–50 year old RAAC panels still in service. Ongoing survey regimes and preliminary site observations and investigations of multiples structures in the United Kingdom have revealed significant problems in a small number of panels such as excessive cracking and deflection, insufficient cover, and reinforcement that is corroding and/or incorrectly placed. This paper therefore presents data on the structural performance and integrity of aged RAAC panels from the 1960s and 70s still in service in the United Kingdom, and presents the outcomes of the most significant and largest research project in the United Kingdom in the last 10 years, which investigated the material properties, structural performance, and monitoring strategies of aged RAAC panels. Structural testing on full scale panels in the laboratory and in situ have been conducted, together with petrographical examination and computational finite element modeling of RAAC panels form different structures and locations around the United Kingdom. The research has developed considerable new knowledge and understanding regarding the structural and material performance of aged RAAC panels and their associated failure modes, which will have significant implications for the repair, monitoring and management of these national critical infrastructure.

The quality control of fibre-reinforced sprayed concrete (FRSC) for tunnel linings has evolved significantly in recent years. One of the main innovations concerns the control of FRSC in the lining using small-scale tests of cores extracted from the tunnel instead of the traditional approach, based on the characterization of panels sprayed on moulds. This study combines experimental and numerical investigations to evaluate if constitutive models derived from small-scale tests, such as the double punch test (DPT) and double-edge wedge splitting (DEWS) test can be used to predict the behaviour of larger panels in the round panel test (RPT) ASTM C1550. Results confirm the link between the new and the traditional approaches. Findings demonstrate that small-scale tests can be considered as a viable method to evaluate the mechanical behaviour of FRSC both in regular quality control programs and for verifying an existing tunnel lining condition.

Background Contaminants and water-soluble salts present in mechanically recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste limit its use as a secondary raw material in plasterboard manufacturing. This research addresses this limitation, developing a novel acid leaching purification technology combined with an improved mechanical pre-treatment for post-consumer gypsum valorization. Methods Laboratory-scale acid leaching purification was performed with a borosilicate beaker, hot plate, and overhead stirrer. Stuccos were produced after calcination of gypsum at 150 °C for 3 hours. Samples were characterized through X-ray fluorescence, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and particle size analysis. Results Acid leaching at 90 °C for 1 h using a 5 wt% sulfuric acid solution was revealed to be the optimum purification conditions. Stuccos produced from purified gypsum under optimum conditions had similar initial setting times to that of a commercial stucco but with higher water demand, which could be reduced by optimizing the calcination conditions. A magnesium-rich gypsum was precipitated from the wastewater. Conclusions Purified post-consumer gypsum with > 96 wt% chemical purity and calcium sulfate dihydrate content was produced. The research recommends acid neutralization prior filtration, use of gypsum particles < 2 mm in size, and stirring speed of 50 rpm to reduce the economic and environmental impacts of the acid leaching purification process at industrial scale. The magnesium-rich gypsum could potentially be marketed as soil fertilizer.