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Impact of Sulfate Activation of Slag Cement on the Performance of Coarse Recycled Aggregate Concrete
No full textThe global construction industry is facing increasing pressure to adopt sustainable practices, driving the search for alternatives to conventional concrete. This research investigates the development of eco-friendly concrete by replacing virgin coarse aggregates with recycling plant-based coarse recycled aggregates (CRAs) and utilising Portland slag cement (PSC). While PSC-CRA based concrete offers environmental advantages, it typically exhibits lower early-age strength and durability, limiting its practical application. To address these limitations, a systematic experimental study was conducted to evaluate the efficacy of sodium sulfate (Na2SO4) as a chemical activator to the binder. This research comprehensively assessed the impact of the activator on compressive strength, water absorption and resistance to hydrochloric and sulfuric acid attacks. Microstructural characterization was also performed by scanning electron microscopy (SEM) to understand the underlying performance enhancement mechanisms. Key findings reveal that Na2SO4 activation significantly improved early-age strength, achieving a target strength of 40 MPa even at 100% CRA (i.e., NC100) replacement and enhanced durability properties. SEM analyses confirmed the formation of denser hydration products (i.e., CSH and CASH gels) and ettringites, correlating with the observed improvements. Also, carbon dioxide emissions (CO2) and cost implications demonstrated the environmental and economic benefits of activated PSC-CRA-based concrete. This study validates the potential of Na2SO4 activated PSC-CRA based concrete as a viable and sustainable construction material, offering a practical solution to the performance deficiencies of non-activated PSC-CRA based concrete mixtures and contributing to the advancement of sustainable construction practices
Deploying 3D Concrete Printing for Large-Scale Building Construction in Saudi Arabia: A Case Study
No full textThis paper details the successful large-scale implementation of 3D concrete printing (3DCP) for the construction of large building in remote area of Saudi Arabia. As one of the first religious buildings in the region constructed using additive manufacturing, this project showcases 3DCP\u27s technological and environmental potential for contemporary building. In order to ensure sustainability and cost effectiveness, the mosque was constructed using a COBOD BOD2 gantry printer and a customised concrete mix made up of 99% locally sourced materials and 1% CEMEX D-fab admixture. To maximise thermal insulation and accommodate mechanical, electrical, and plumbing (MEP) systems, the structure included a dual-layer wall system with two outer layers that were each 5 cm thick and separated by a 10 cm cavity. In comparison to traditional methods, the project achieved impressive metrics, such as a 30% increase in energy efficiency, a 50% reduction in construction time, and an 80% labor savings. The printer reached a maximum build height of 5.54 meters while operating at a production rate of 350 linear meters per hour. With its ability to withstand thermal stress, chloride ion penetration, and cracking in extreme weather conditions, the concrete mix showed exceptional durability. With an overall average compressive strength of 33.52 MPa, which is higher than the design strength of 30 MPa, compressive strength tests produced consistent average results across all phases. Through creative reinforcement techniques, accurate automated layer calibration, and environmentally friendly building methods, this case study demonstrates the scalability and adaptability of 3DCP in harsh climates. Significant accomplishments include a 40–50% decrease in carbon emissions and an 85% reduction in material waste, with effective waste as low as 2-4 percent. The findings support 3DCP as a groundbreaking approach to durable, effective, and ecologically friendly building, providing a replicable framework for approaching public, industrial, and residential developments worldwide
3D RBSM Conduit Model for Simulating Moisture Transport in Compressively Damaged Concrete
No full textThis study investigates the simulation of moisture transport in concrete under compressive damage using the 3D RBSM Conduit model. The model combines stress-strain responses from concrete compression experiments with detailed crack data, providing a realistic representation of crack development under varying load conditions. By implementing both unlubricated and lubricated compression tests, different failure modes were observed, influencing penetration patterns. Simulations show that the distribution of cracks significantly accelerates moisture penetration within the concrete. Notably, uniformly distributed cracks, typical of lubricated tests, facilitate deeper and faster moisture transport compared to more localized cracks observed in unlubricated tests. This study validates the effectiveness of the 3D RBSM Conduit model in integrating mechanical simulations with moisture transport simulations, offering theoretical and practical insights for understanding and mitigating moisture-induced deterioration in concrete
Shear and Compressive Joint Behaviour of Concrete Floating Structure for Offshore Wind Turbine
No full textJapan\u27s commitment to growing renewable energy generation from 30 to 45 GW has intensified the focus on offshore wind turbines. Due to the presence of extensive deep-sea waters, the installation of fixed turbines is impractical, making floating structures a more viable option. For supporting structure of said turbines, concrete is preferred over steel as it offers various commercial and technical benefits. However, the response of concrete in offshore environment is still under consideration. When considering rationalisation of construction, pre-casting of modules is one option, however in that case, it is necessary to clarify the behaviour of the joints. This research includes comparative compressive joint behaviour analysis to observe the behaviour of concrete with and without joint under air condition. Additionally, it investigates the shear joint behaviour of concrete floating structure subjected to static loading conditions, both under air & water. In order to keep it simple, only prestressed PC bar is provided between the two concrete modules. The experimental setup under this research includes four cases; Case 1 for Compressive fracture behaviour of monolithic concrete module in air, Case 2 for Compressive fracture behaviour of concrete module with joint in air, Case 3 for Shear fracture behaviour of joint in air and Case 4 for Shear fracture behaviour of joint in water. The experimental results depict that the concrete modules containing joint shows almost the same (approximately 7% lesser) compressive strength than that of monolithic concrete. Additionally, it is observed that the concrete modular joint, exhibit similar joint shear strength (about 6% lesser) in water submerged conditions as compared to under air scenario. The above findings significantly contribute to the growing knowledge on the behaviour of concrete in offshore environments and provide valuable insights into the optimisation of such structures for enhanced durability under harsh conditions
Durability of Cement-based Materials in Deep Seas: A Review of Chemical Aspects with New Results
No full textThe application of cement-based materials in deep-sea environments presents serious durability challenges due to high hydrostatic pressure and low temperatures. This study reviews previous research and presents new findings from field exposure tests, including a 3-year exposure at 3500 m depth. Portland cement (PC) and blast furnace slag (BFS)-blended systems exhibited severe degradation, with BFS-based specimens showing complete disintegration. Microstructural analysis revealed calcium leaching, C–S–H decalcification, and secondary phase formation such as ettringite and Mg-based hydrates. In contrast, calcium aluminate cement (AC) demonstrated excellent resistance, retaining its shape and chemical integrity even after long-term exposure. Thermodynamic modelling partially supported these observations, indicating hydrate destabilisation at low temperatures. Additional tests confirmed that AC mortar can be stored as slurry and placed underwater without segregation, offering both chemical and practical advantages. Despite these findings, questions remain regarding in-situ mechanical performance, phase transformation behaviour, and binder optimisation. To address these, we have launched a new deep-sea durability research project aimed at identifying and validating next-generation binders for subsea infrastructure
Interaction of Cementitious Systems Containing Nontraditional and Natural Pozzolans (NNPs) with Chloride-based Deicers
No full textGiven the growing scarcity of traditional supplementary cementitious materials (SCMs), interest in non-traditional and natural pozzolans (NNPs) is increasing. While much of prior research has focused on fundamental physical properties and mechanical performance, durability - particularly scaling resistance - remains a concern for concrete exposed to deicing salts. This study evaluated the matrix-deicer interactions of paste samples containing 25% of 11 different NNPs - including three calcined clays (CCs), three volcanic ashes (VAs), two fluidized bed combustion ashes (FBCs) and three ground bottom ashes (GBAs). Paste samples were exposed to CaCl2, MgCl2 and NaCl solutions and subjected to 50 freeze-thaw cycles per ASTM C672. At the end of the exposure period, differential scanning calorimetry (DSC) and quantitative X-ray diffraction (QXRD) were used to assess changes in the amounts of originally formed phases, such as Ca(OH)2 and AFm/AFt content, and identify new phases such as Friedel’s salt and brucite. The findings were correlated with chemical composition of the NNPs, particularly their alumina content. Additionally, concrete slabs containing the least reactive NNP from each group were tested per ASTM C672 using a 4% CaCl2 solution. Results from paste and slab tests were consistent, showing that low chloride-binding capacity is associated with poor salt scaling resistance
Effect of Backfills on the Corrosion Protection Performance of Galvanic Anode in RC Member
No full textGalvanic anodes can supply corrosion protection current to steel by simply connecting them to steel in concrete and can prevent corrosion of steel for a long period. Furthermore, they are attracting interest because they do not require continuous monitoring nor other maintenance. Galvanic anodes are composed of a sacrificial metal, such as zinc, covered with backfills. The backfills contribute to a stable supply of corrosion protection current by maintaining the galvanic anode at a high alkaline level and by having high water retention. Their properties closely relate to the lifetime of the galvanic anode and its corrosion protection performance. Therefore, with the purpose of verifying the effect of backfill materials on the corrosion protection performance of galvanic anodes, we investigated the corrosion protection performance of galvanic anodes with three different backfills and without backfills on steel in chloride contaminated concrete. The results showed that the galvanic anodes with backfill exhibited higher corrosion protection performance, with larger values of depolarisation and corrosion protection current. It was also found that backfills affect the depolarisation and corrosion protection current, indicating that the corrosion protection performance of the galvanic anodes is affected greatly by the backfills. Furthermore, the influence of the external environment, such as temperature and humidity, was found to be different depending on which backfill is employed
Utilising \u27Filter Cake\u27 for Low-Carbon Non-structural Concrete: A Sustainable Approach to Waste Management
No full textScott Bros (SB) Ltd.’s recycling plant for soil and aggregate washing is projected to generate 225,000 tonnes of residual waste material, known as \u27filter cake,\u27 annually. This high-volume, low-value waste stream presents significant management and disposal challenges. This study explores the potential of using \u27filter cake\u27 as a raw material in low-carbon non-structural (non-standard) concrete production, contributing to the circular economy. The research aimed to develop low-carbon concrete by maximising recycled ingredients and minimising CEM-I content. Concrete cube samples (150 mm) were prepared, cured, and tested according to BS 8500 and BS 12390 standards. The study investigated the 28-day compressive strengths of six concrete mixes with varying CEM-I replacement levels (10%, 30%, 50%, and 70%) and different aggregate sources (recycled vs. virgin). A generic mix proportion of 1:2:4 was used to achieve design strengths of 10-20 MPa. The highest compressive strengths (23 MPa) were achieved by mixes with SB recycled aggregates but without \u27filter cake,\u27 indicating the suitability of such aggregates as greener alternatives to virgin aggregates. Mixes with 10% and 30% CEM-I replacement achieved compressive strengths of 16 MPa and 14 MPa, respectively, balancing CEM-I replacement and strength performance. Higher CEM-I replacements (50% and 70%) resulted in poor strength performance (7 MPa and below). This type of concrete is best suited for non-critical, non-load-bearing applications such as pavements, driveways, and backfill material in pipework
An Architecture PH-UNet-Mask based on Multi-task Joint Learning: Exploration in Real-time Segmentation of Concrete Corrosion
No full textPixel-level segmentation of corrosion-induced damage in underground reinforced concrete (RC) structures is crucial for structural health monitoring but remains challenging due to complex backgrounds and the need for real-time models suitable for on-site inspections. To address these limitations, this paper introduces PH-UNet-Mask, a lightweight multi-task deep learning architecture designed for robust damage segmentation in challenging underground environments. The proposed model integrates Haar wavelet downsampling (HWD) within its encoder to preserve crucial edge details and employs a Parallel Channel-Spatial Attention (PCSA) module to adaptively refine feature representation by explicitly modelling spatial-channel dependencies. A key innovation is a multi-task joint learning framework featuring a dedicated decoder branch that generates a structural mask; this mask is utilised by the primary decoder to effectively suppress background noise interference before performing fine-grained, multi-class damage segmentation. The model was trained and validated on a newly developed RDS dataset, comprising 3336 annotated images captured in real underground parking structures. Experimental results demonstrate that PH-UNet-Mask significantly outperforms baseline and state-of-the-art segmentation models, achieving mF1-Score of 89.75% and mIoU of 82.30%. Ablation studies systematically validated the individual contributions of the HWD, PCSA, and background masking components to the overall performance enhancement. Furthermore, the model exhibited high robustness against variations in training data size and achieved real-time inference speeds (10.5-13 FPS). This work provides an effective and computationally efficient solution for automated, pixel-level detection and classification of critical RC corrosion damage types, enabling accurate quantitative assessment and facilitating proactive structural maintenance strategies in demanding underground settings
On Closed-Form Preintegration for a Class of Mixed-Invariant Systems in SEₙ(3)
No full textA large class of nonlinear systems in engineering and robotics evolves on geometric manifolds, such as fixed-wing aircraft, quadrotors, etc., whose kinematic motion can be described using Lie groups, in particular SEn(3) . The existing techniques involve numerical integration methods such as Runge-Kutta integration to propagate their motion forward in time. However, these methods are approximate solutions and do not respect the geometric constraints of the nonlinear differential equation, leading to higher computational costs and numerical integration errors. To this end, we propose a geometric closed-form approach to solve the initial value problem for a class of nonlinear systems that evolves on the SEn(3) Lie group. Through numerical simulations, we show that our closed-form solution is more efficient than the Runge-Kutta 4th -order (RK-4) integrator and reduces floating-point operations by 45% in a strapdown-inertial-navigation (SINS) case study. We believe that the efficiency and accuracy gains of our approach warrant the general adoption of this method for numerical integration in applications such as SINS