Editorial for the Special Issue on Sustainable Composite Construction Materials, Volume II

The use of sustainable composite building materials is essential for developing infrastructure that benefits the environment while reducing energy consumption. As global efforts to combat climate change intensify, the construction industry faces growing pressure to lower its carbon emissions. This requires the development of materials with reduced embodied carbon-both in production and use-without compromising strength or performance.

This Special Issue of the Journal of Composites Science, featuring 13 research articles, contributes to this global effort by presenting scientific insights and advancements in eco-friendly materials and sustainable construction practices. The studies focus on low-impact materials, recycling, and circular economy principles applied to construction. Collectively, these works demonstrate how interdisciplinary research can transform traditional building methods to be more sustainable. Topics include the use of expanded perlite and clay aggregates, and the incorporation of agricultural and industrial by-products. Together, these papers exemplify the productive collaboration between academia and industry in advancing sustainable construction. Below is a brief overview of the featured studies:

Whwah et al. [Contribution 1] investigated how water-to-cement (W/C) ratios and fine aggregate compositions influence concrete performance when natural sand is replaced with expanded perlite aggregate (EPA). Eighteen mixes were tested for strength, density, thermal properties, and workability. The optimal mix (W16-100%EPA) provided the best balance between compressive strength, reduced density, and improved thermal insulation, supporting EPA’s suitability for both structural and non-structural applications.

Almeida et al. [Contribution 2] examined lightweight mortars incorporating expanded clay as a partial fine aggregate replacement. Six formulations were evaluated for physical, mechanical, and durability properties. The results showed that expanded clay reduces density and enhances workability without significantly compromising strength, offering benefits in energy efficiency and material savings-especially in applications requiring lightweight and thermally efficient elements.

Daouadji et al. [Contribution 3] explored interface sliding in composite I-steel–concrete beams reinforced with composite plates. Using analytical modeling based on elasticity and strain compatibility, they demonstrated that optimizing shear stud placement and adhesive bonding enhances stress distribution and minimizes slippage, improving overall structural performance.

Pivák et al. [Contribution 4] addressed the incompatibility of Portland cement with historical masonry, highlighting the advantages of lime-based binders for restoration. The study emphasizes their flexibility, permeability, and mechanical compatibility with heritage materials, ensuring long-term preservation and structural harmony.

Simon et al. [Contribution 5] analyzed foamed concrete incorporating lightweight aggregates. Findings showed that density reduction can be achieved with minimal loss in strength, while thermal insulation and reduced embodied carbon make such mixes ideal for non-structural, sustainable construction applications.

Mohammed et al. [Contribution 6] evaluated self-compacting concrete (SCC) incorporating fly ash, silica fume, and metakaolin as partial cement replacements. The study found that these additives improve workability, strength, and durability, with each contributing unique performance benefits. Optimized blends reduce carbon emissions while maintaining high performance for modern infrastructure.

Sapata et al. [Contribution 7] benchmarked mechanical and durability properties of 3D-printed concrete, focusing on anisotropy caused by layer orientation. Print direction significantly affected compressive and flexural strengths, while interlayer weaknesses impacted durability. The study provides essential insights for optimizing print planning and mix design in structural 3D printing.

Kadhim et al. [Contribution 8] studied walnut shell ash (WSA) as a replacement for limestone filler in hot mix asphalt. Mechanical and volumetric properties improved up to 60% replacement, enhancing Marshall stability and void structure. Beyond this level, performance declined. WSA offers an environmentally beneficial, high-performing option for asphalt mixtures when used optimally.

Huang et al. [Contribution 9] evaluated olive tree pruning sawdust (OTPS) as a sustainable substitute for sand in lightweight mortars. Calcium hydroxide treatment improved workability and strength retention. Mixes with up to 10% treated OTPS matched control strengths, while higher contents reduced performance. The results indicate OTPS’s potential for sustainable, low-density mortars.

Stel’makh et al. [Contribution 10] reviewed the potential of low-grade calcined kaolinitic clay as a partial replacement for Portland cement. When thermally activated at 700–850 °C, even impure clays exhibit strong pozzolanic activity, enhancing concrete strength and durability. The study highlights significant CO₂ reduction potential, particularly for developing countries.

Anwajler et al. [Contribution 11] examined recycled plastic waste (RPW) as a partial aggregate replacement in concrete. While RPW reduced density and thermal conductivity, excessive replacement (over 20%) weakened mechanical strength. Optimal mixes balanced insulation and strength, supporting RPW use in non-structural, sustainable construction.

Oya-Monzón et al. [Contribution 12] also investigated OTPS as an industrial by-product in mortar formulations. Incorporating 10% pretreated OTPS improved porosity and maintained adequate strength, promoting circular economy practices and the reuse of agricultural residues.

Boakye et al. [Contribution 13] presented further findings on calcined impure kaolinitic clay as a cost-effective cement alternative. Thermal activation between 700–900 °C produces highly pozzolanic materials that improve concrete strength and durability. The study emphasizes the scalability and environmental benefits of using abundant low-grade clays in developing regions.