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.

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.

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.

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.