Hiran D. Yapa

In tandem with global urbanization and infrastructure development, the escalating demand for concrete has prompted a search for eco-friendly alternatives against the extraction of river sand for fine aggregate. This study investigates the use of blended sea sand and manufactured sand (M-sand) as an alternative to river sand in concrete, with a focus on mechanical properties and durability. In Stage 1, three control concrete mixes—comprising river sand (RS), sea sand (SS), and M-sand (MS)-were tested alongside blends in which M-sand replaced sea sand at 25%, 50%, and 75% proportions. Evaluations included particle size distribution, compressive strength, workability, and durability via accelerated corrosion and chemical exposure tests. Results identified the 50% sea sand–50% M-sand blend as the optimal mix. In Stage 2, this optimal blend was further assessed against RS and SS concretes for mechanical properties (elastic modulus, splitting tensile strength) and durability characteristics (water absorption, density, void content, and chloride penetration resistance). Stage 3 focused on determining a permissible chloride content for the blend using accelerated corrosion testing. A chloride threshold of 0.05% was established, at or below which the durability performance remained comparable to the control mixes. These findings highlight the potential of SS–MS blended concrete as a sustainable alternative to traditional fine aggregates in construction.

Processed sea sand has emerged as a viable alternative to traditional fine aggregates in the Sri Lankan construction industry. Despite its economic and environmental advantages, concerns over residual seashell content have limited its widespread adoption by local contractors. Residual seashell content, typically ranging from 1% to 3% after processing, has raised concerns about its impact on the performance of concrete. This study systematically investigates the influence of seashell fragments, with a content of up to 5%, on the fresh, mechanical, and durability properties of sea sand concrete and mortar. Experimental results indicate that workability remains stable, with minor variations across the tested range of shell content. Compressive strength remains relatively consistent from 0% to 5% seashells, indicating that seashell content does not significantly impact the strength within this range. Durability tests reveal minimal effects of shell content on concrete performance within the tested shell range, as indicated by results for water absorption, rapid chloride penetration, and acid exposure testing. Accelerated corrosion indicates that the typical shell content does not increase corrosion risk; however, high shell content (>3%) can compromise corrosion durability. Overall, these findings demonstrate that the mechanical and durability performance of sea sand concrete remains uncompromised at typical seashell content levels (1–3%), supporting the use of processed sea sand as a sustainable and viable alternative to traditional fine aggregates in Sri Lankan construction.

Reinforced concrete dapped‐end beams (DEBs) represent a unique structural type with the presence of recessed ends. The beam configuration is ideal for structural connections. However, the recessed area is structurally a disturbed region, and is vulnerable to embedded reinforcement deterioration. This study explored the potential of strength assessment of impaired DEBs via an analytical approach. A kinematics based model (KBM) was opted, and it was subjected to significant modifications to account to suit with distinct structural defects that were common to DEBs. The extended model (EKBM) was validated using experimental results available for eight beams. Both the load and failure mode predictions from the EKBM were found to be more accurate than those from the KBM, where the EKBM prediction offset was within a fair range of −23% to 15%. Furthermore, a parametric analysis was carried out to investigate the sensitivity of shear reinforcement deficiency and of reinforcement corrosion in the joint region on the beam load capacity. It revealed that the first two shear links were the most critical links. The load reduction was linearly proportional to the area reduction of reinforcement due to corrosion, however, the trend deviated from that at some combined deficiencies. The corroded reinforcement length was rather insensitive to the resulting beam strength.

Recently, machine learning-based prediction models have gained considerable popularity in predicting the compressive strength of concrete using results from Non-Destructive Testing (NDT) methods. This research considers NDT results from Rebound Hammer (RH) and Ultrasonic Pulse Velocity (UPV) tests for concrete samples with different concrete grades. 270 test samples were considered for the analysis using different machine learning techniques such as Multi-Layer Perceptron (MLP), Long Short-Term Memory network (LSTM), and Convolutional Neural Network (CNN). Concrete compressive strength results are obtained from Destructive Test (DT) results of the same for the purpose of labelling. Each model's performance is evaluated through the computation of the Coefficient of Determination (R²), Mean Square Error (MSE), and Mean Absolute Percentage Error (MAPE). The findings of this study underscore the potential of machine learning techniques in predicting concrete compressive strength based on Non-Destructive Test (NDT) results. The analysis findings suggested that employing UPV and RH data in conjunction with a trained MLP model to be an effective approach for accurately estimating the compressive strength of concrete specimens. The outcomes of the research serve as a valuable reference for researchers and industry practitioners alike when assessing in-situ concrete compressive strength through Non-Destructive Testing (NDT) methods.

Biochar is a well‐known sustainable and effective additive used in mortar/concrete to improve its mechanical properties. However, its potential to improve the impact resistance of concrete is still unexplored. This paper investigates biochar's effectiveness in improving the strength and impact performance of alkali‐activated slag concrete (AASC). Five AASC samples with 0%, 2%, 4%, 6%, and 8% rice husk biochar (RB) were employed in an experimental program. The strength and the impact resistance were tested, and the latter was assessed over a drop‐weight test conforming to the ACI Committee 544 guidelines. The crack propagation of the impact‐tested samples was examined using micro‐CT images. The results showed that adding RB up to 6% improved, notably the 28‐day compressive strength of AASC. At 6% RB, the strength enhancement was 44.6%, whereas no additional gain was observed at the 8% RB blend. More importantly, except for the 8% RB sample, the impact resistance was considerably augmented with the RB level increment. The increment in the impact number at the first crack and the failure in the 6% RB sample were as high as 185% and 180%, respectively. The reduction in the solution/binder ratio of the mix with the addition of biochar and the internal curing effect of biochar were deemed to be responsible for these improvements. However, possibly due to biochar's brittle characteristics, the increase in RB dosage from 6% to 8% reduced the impact resistance drastically.

Concrete half-joint beams (HJB) are characterised by local reductions in the overall beam depth at the support and are ideal for structural connections. However, the beam joint region is vulnerable to deterioration and design/detailing shortcomings. Non-linear numerical modelling of the behaviour of a series of impaired reinforced concrete HJBs was conducted in this study. The major defects considered were unavailability of diagonal bars/U bars, shear reinforcement inadequacy and reinforcement corrosion. The numerical simulations captured global and local behaviours of the beams. The load capacity prediction discrepancy was in an impressive range of −16.7% to +1.5%, in contrast to the predictions of the commonly used strut-and-tie model in the range of −39.2% to 16.9%. Subsequently, an experimental study was established using finite-element modelling to explore the retrofitting potential of defective HJBs using the deep embedment (DE) technique. The strength enhancement was almost 30% and the internal load paths and the failure mode of the defective beam were favourably altered with the post-installation of the retrofitting element. The DE technique was thus identified as an ideal option for the retrofitting of impaired HJBs.

In the past, asbestos siding, roofing, and ceiling sheets became more popular than conventional materials due to their high strength-to-weight ratio, durability, and low cost. However, it was later identified that most types of asbestos are carcinogenic and are responsible for major lethal diseases. In terms of developing a substitute for asbestos, different alternative organic fibers have been investigated as sustainable solutions. Therefore, this article reviewed the usability of organic fibers from wood, banana, bamboo, and coconut coir, which are locally available and abundant in the region, as a substitute for asbestos in the fiber cement industry in Sri Lanka. The quantitative physicomechanical properties of organic fiber and fiber cement composites were evaluated, and the effect of treatment methods on durability was discussed. The previous literature revealed that organic fiber cement thin sheets have comparable mechanical properties in comparison to composites reinforced with asbestos. Furthermore, this study found that these organic-fiber-based composites are energy-efficient and have improved fire resistance. However, the long-term performance is questionable. Hence, further studies on fiber treatment methods and composite durability are needed. Additionally, a comprehensive cost analysis of organic fiber cement composite is recommended to introduce organic fibers into commercial products.

The geometric reduction prevailing in dapped-end concrete beams forms a disturbed region into the beam-ends. Consequently, material deterioration- and reinforcement-detailing issues prevailing in the end region cause a series of structural distresses. In this light, distresses in dapped-end beams and potential retrofitting options are reviewed in this paper. It is found that the choice of the retrofitting configuration is governed considerably by the prevailing defect. The strength enhancement could be as high as 40%–50% upon the choice of correct configuration whereas possibly be negligible upon inappropriate selection. Generally, the use of diagonal bars and plate jacketing are promising with steel applications. The bars can be prestressed to enhance the retrofitting efficiency. For fibre-reinforced polymer applications, inclined/horizontal stripping and fabric wrapping are impressive approaches, while combined systems show better results. The review also identifies the required future research for formulating comprehensive retrofitting guidelines.