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Performance-Based Design of 3D Printable Cement Composite Using Locally Available Materials
No full textProportioning 3D printable materials using locally available resources offers significant environmental and economic benefits while supporting local communities. This study proposes a performance-based design approach to adapt these materials into printable mixtures, focusing on key fresh and hardened properties. Binder combinations made with locally available materials were initially optimized for enhanced packing density and flow characteristics. Optimized candidates were narrowed down using a radar chart method based on multivariate criteria closely linked to printing performance.The printability of the optimized cement composites was subsequently validated. Developing such print materials enhances the cost-effectiveness of 3D printing in construction and expands its applicability to remote regions
Advancing Underwater Construction with 3D Printing: A Two-Stage Approach
No full textUnderwater concreting presents a unique challenge, requiring advanced materials and construction methods to endure harsh submerged environments. Traditional techniques often encounter difficulties in adapting to the dynamic underwater conditions. In contrast, 3D concrete printing (3DCP) offers a revolutionary alternative, enabling automated, precise, and highly customizable fabrication of resilient underwater structures. This study introduces a two-stage cementitious 3D printing system that dynamically adjusts accelerator dosages at the nozzle, optimizing printability in submerged conditions. Evaluations in both air and underwater settings reveal that real-time dosage control effectively addresses critical challenges, overcoming the limitations of pre-mixed underwater admixtures (reduced flowability and compromised strength) while adapting to environmental changes. These findings underscore the transformative potential of two-stage 3DCP, advancing both innovation and sustainability in underwater construction by offering unprecedented control over material properties. This approach lays the foundation for more efficient, durable, and environmentally friendly solutions in the evolving field of 3DCP
Enhancing Early Strength Development through CO2-Induced Hydration Acceleration
No full textThis study investigates the accelerating effect of gaseous CO2 on cement hydration.The addition of up to 0.2% CO2 by weight of cement during the mixing process led to increased compressive strength after 24 hours and greater heat release during the acceleration phase. However, higher concentrations negatively affected workability and hydration kinetics, resulting in lower compressive strength
Tailoring Ultra-High-Performance Concrete Toughness with Carbon Fibers: Linking Microstructure and Fracture Energy
No full textThis paper presents a multiscale experimental study on the effect of carbon microfiber reinforcement on the fracture behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC).Various fiber lengths (0.1–6 mm) and contents (1.2–20 kg/m³) were tested, linking microstructural features obtained via X-ray computed tomography (CT), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) to mechanical performance. Results show that a dosage of 6 kg/m³ of 3–6 mm fibers offers a balance between workability and fracture resistance, with fracture energy increasing up to 195% compared to plain concrete. This research provides insights for optimizing fiber type and content in UHPFRC for structural applications
Recovery of Silica as SCM from Olivine using Oxalic Acid-enabled Chemical Comminution
No full textUsing supplementary cementitious materials (SCMs) to substitute cement or clinker, as a decarbonization strategy, is limited by the shortage of conventional SCMs like GGBS, fly ash, and silica fume. Meanwhile, mafic/ultramafic minerals are unlimited to be processed for SCMs production. In this study, oxalic acid is used to dissolve olivine ((Mg, Fe)2SiO4) to produce amorphous silica. Results show that high purity amorphous silica could be successfully obtained and the yield can be up to 93.42%. This process endows the extra value of olivine alongside being used for carbon storage
Sustainability Assessment of Jointed Plain Concrete Pavements and Fibre-Reinforced Concrete Pavements
No full textEnsuring sustainability of construction and maintenance is critical to the widespread application of fibre-reinforced concrete (FRC) for pavements, which offer higher performance and increased service life. However, investigations in terms of economic and environmental impact assessments are essential for assessing the extent of benefits from this technology. It is important since a large volume of concrete is being consumed for pavement construction worldwide and leads to significant environmental issues, including carbon emissions, resource extraction, energy consumption, air pollution, etc. Consequent to this understanding, this research focuses on the comparative life cycle assessment (LCA) to investigate the environmental impacts of the two rigid pavement options viz., jointed plain concrete pavements (JPCP) and FRC pavements (FRCP). The environmental impacts are mainly compared in terms of greenhouse gas (GHG) emissions expressed as CO2 equivalent and endpoint indicators such as effect on human health, ecosystem toxicity, and extent of resource utilization. LCA includes a cradle to grave analysis. The impact assessment is performed using SimaPro software. The functional unit used is 1 km stretch of road designed for the same traffic spectrum and service life of 30 years. The inventory includes primary data of fuel and energy consumption for construction operations collected from actual sites. All other background data is taken from existing literature, databases, and other sources available on the web. Based on LCA, FRCP exhibits better environmental performance than JPCP. The impact is heavily skewed towards cement utilisation and a material optimisation based on binders will improve the sustainability value of such systems. The study supports green design policies for a more sustainable transportation network
Microstructure Characterisation of Alkali-Activated Fly Ash-Slag Paste at Elevated Temperatures
No full textAlkali-activated fly ash-slag (AAFS) cured at ambient temperature has been considered as a promising eco-friendly alternative to traditional cement-based binders, offering reduced carbon emissions and enhanced durability. However, understanding how these materials respond to extreme conditions, particularly at high temperatures, remains a critical area of study. Therefore, it is essential to investigate this material for ensuring their reliability in fire-prone and high-temperature environments. This paper presents a systematic experimental study on microstructural and damage evolution in AAFS paste exposed to elevated temperatures (from 20 °C to 800 °C) in terms of changes in phase assemblage and pore structural characteristics as well as crack initiation and development, using a series of advanced characterisation techniques including backscattered electron microscopy (BSEM) coupled with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Mercury Intrusion Porosimetry (MIP). Experimental results indicate that at temperatures up to 200 °C, minor shrinkage cracks appear due to water evaporation, while significant crack widening occurs between 200 °C and 600 °C as phase decomposition and thermal expansion mismatch accelerate damage. At 800 °C, viscous sintering leads to partial densification, reducing microcrack connectivity despite the extensive degradation of amorphous reaction products. EDS and XRD results reveal the decomposition of C-A-S-H and transformation of gels into more cross-linked N-A-S-H gels, accompanied by crystallisation of nepheline and gehlenite. This significantly changes the microstructural integrity of the matrix in AAFS paste. This study establishes a direct correlation between microstructural changes and damage evolution in AAFS paste, offering critical insights into its high-temperature/fire resistance applications. These results hold significant implications for advancing the use of sustainable, cement-free materials in fire-resistant infrastructure and heat-intensive environments
Development of Mesoscale Model for Volumetric Deformation of Cementitious Materials in Deep-Sea Environment
No full textThis study developed a mesoscale mechanical model capable of reproducing the volumetric deformation behaviour of cementitious materials in deep-sea environments. In the analysis, the rigid-body spring model (RBSM), a mesoscale mechanical model, was integrated with a truss network model (TNM) capable of evaluating mass transport, forming the RBSM-TNM framework. To assess the volumetric change of the skeleton under hydrostatic pressure, a creep model was applied to the mechanical springs representing the mechanical response of the skeleton. Additionally, the truss network model was employed to evaluate water penetration from the surface. Furthermore, based on the concept of poromechanics, the model was designed to generate mechanical springs representing the stress contribution of pore water, depending on the water penetration amount. By assuming that the volumetric strain of the skeleton induced by hydrostatic pressure is equivalent to the volumetric change of the pore, the pressure exerted by the pore water on the skeleton was calculated based on the strain and elastic modulus of the skeleton. Consequently, the proposed model demonstrated its capability to reproduce, to some extent, the characteristic volumetric deformation behaviour of cementitious materials in deep-sea environments
Utilisation of Semi-naturally Carbonated Steelmaking Slag as Concrete Aggregate
No full textSteelmaking slag has emerged as a promising material for low-carbon concrete, owing to its ability to sequester CO₂ through carbonation. However, CO2 sequestration by steelmaking slag and its utilisation is still far from practical application due to the high energy consumption and cost of the accelerated carbonation process. Anticipating that optimising the pre-natural carbonation during storage would reduce the energy and cost for accelerated carbonation, this study focused on the natural carbonation potential of steelmaking slag. In addition, the applicability of naturally carbonated steelmaking slag as aggregate for concrete was investigated. The long-term exposure experiment simulating outdoor storage demonstrated that CO₂ sequestration through semi-natural carbonation reached 18-107 kg-CO₂/t-slag depending on the particle sizes, indicating the significant potential of semi-natural carbonation during storage. CaCO₃ layer was found on the slag surface, and the presence of polymorph CaCO₃ and crystallisation of calcite was suggested. The compressive strength (after 7 days of sealed curing) of concrete incorporating semi-naturally carbonated steelmaking slag was comparable to those made with natural aggregate or steam-aged steelmaking slag, demonstrating the potential for its use as aggregate. The CO₂ emission intensity of concrete using semi-naturally carbonated steelmaking slag was 69 kg-CO₂/m³, representing a 49% reduction compared to natural aggregate. The natural carbonation of steelmaking slag has the noteworthy potential to sequester CO2 at a low cost and in an energy-saving manner. It can also contribute to the decarbonisation of concrete