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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
Application of CNT/CF Cement Composite Sensor for Corrosion Monitoring in Chloride-Exposed Reinforced Concrete
No full textThis study investigates the use of a conductive cement composite containing carbon nanotubes (CNTs) and carbon fibres (CFs) as a reference electrode for corrosion monitoring in reinforced concrete. For comparison, stainless-steel reference electrodes were also prepared. Both CNT/CF cement composite and stainless-steel electrodes were immersed in a 10% NaCl solution for three months to simulate a chloride-rich marine environment. The open circuit potential (OCP) of both reference electrodes was measured against a standard silver/silver chloride electrode (SSCE) over time. Two reinforced mortar samples and one reinforced concrete sample were tested under different exposure conditions. In Experimental Program 1, a mixed-in NaCl contamination approach was employed by incorporating NaCl into cylindrical concrete samples at concentrations ranging from 0% to 1.2% by binder weight. Corrosion current was measured using the linear polarization resistance (LPR) method with the three reference electrodes. In Experimental Program 2, mortar blocks were immersed in a NaCl solution following the NT Build 443 standard, and corrosion initiation was monitored through OCP measurements over time. In Experimental Program 3, reinforced concrete blocks with varying cover depths were subjected to rapid chloride ingress using a 30 V potential for 24 hours, following the NT Build 492 standard. The OCP of embedded rebars was then measured using all three electrodes. Results indicate that the CNT/CF cement composite electrode maintained a stable potential (~-220 mV vs. SSCE) regardless of chloride exposure, while the stainless-steel electrode exhibited potential variation over time. Corrosion monitoring using CNT/CF electrodes demonstrated reliable OCP measurements, faster stabilization, and consistent correlation with SSCE, confirming their suitability for long-term monitoring in chloride-exposed structures
Enhancing the Durability of Concrete Structures through Digital Twins and Advanced Numerical Simulation
No full textThis study applies a digital twin–based multi-scale and multi-physics simulation framework for durability assessment of reinforced concrete (RC) structures. The framework integrates thermo-hygro-chemical and structural analyses using DuCOM–COM3 to capture time-dependent deterioration processes such as fatigue and corrosion, and to assess their effects on structural performance under realistic environmental and loading conditions. Two case studies illustrate the methodology. The first addresses the fatigue behaviour of RC bridge slabs under moving wheel loads in both dry and wet environments. Numerical simulations reproduced field-observed deterioration patterns, including top-surface disintegration in wet conditions, and led to the development of a simplified predictive equation to support inspection planning and maintenance scheduling. The second case focuses on a corroded RC jetty superstructure in a marine environment. Field-calibrated chloride ingress and corrosion models were applied to evaluate long-term performance under alternative repair scenarios. Analyses showed that surface coating can be highly effective when both moisture and oxygen ingress are restricted, and that unmitigated corrosion not only reduces load-carrying capacity but also alters failure modes despite apparent structural redundancy. In both cases, the calibrated digital twin reproduced the present damage state and projected future deterioration under different intervention strategies, providing a rational basis for determining the scope and timing of repairs. By embedding inspection data and site-specific environmental histories into a unified material–structure simulation from the time of construction, this approach supports evidence-based lifecycle management and the development of durability-focused design provisions. These findings highlight the potential of combining digital twin technology with advanced numerical simulation to bridge the gap between material degradation modelling and structural performance assessment in concrete infrastructure
Machine-Learning PCI Forecasts for Concrete Pavements: Evidence from a Nigerian Airfield
No full textThis study develops data-driven Pavement Condition Index (PCI) forecasting for rigid (jointed concrete) airfields to support maintenance planning, risk mitigation, and lifecycle analysis. Traditional PCI surveys per ASTM D5340 are manual, time-consuming, and subjective, motivating machine-learning alternatives. Using panel-level observations, five models predict next-year PCI from readily available variables: prior-year PCI, annual aircraft traffic, temperature, and rainfall. The models include ordinary least squares (linear), ridge, lasso, random forest (RF), and a feedforward artificial neural network (ANN). All models performed well on held-out validation data; the ANN was best, achieving ��2 = 0.985, MSE = 0.286, MAE = 0.397, and RMSE = 0.534. The ANN architecture comprised one input layer, three hidden layers (128, 64, 32 neurons), and one output layer, with diagnostics indicating no material overfitting. Despite limited data, results show strong potential for accurate short-term PCI prediction in rigid airfields. Main limitations stem from the small sample size and potential generalisability issues. Future work should expand datasets, add predictors (e.g., soil type, traffic mix, slab age, joint spacing, deflection data), and assess ensemble and probabilistic models. The approach can help authorities estimate short-term deterioration and prioritise budgets for timely interventions