The expanding human population has led to an increased demand for additional buildings and infrastructure, as evidenced by numerous studies (Khatib et al., 2025a). Concrete is the most widely used material in the field of construction due to its various useful properties (Gagg, 2014). A number of these distinctive characteristics are worthy of mention, including but not limited to the following: adequate compressive strength, the availability of the necessary raw materials, relatively low cost, flexibility, the capacity for use in a variety of locations, the possibility of being formed into a range of sizes and shapes, and durability properties. Cement is an indispensable component in the production of concrete. However, the production of one ton of cement results in the emission of approximately 850 kilograms of carbon dioxide (CO₂) into the atmosphere. This substantial emission is attributable to the combustion of fuel and the decomposition of limestone (Wu et al., 2025; Zannerni et al., 2020). Consequently, researchers and professionals have identified the need to explore alternative building materials that necessitate less energy during manufacturing in order to minimize the carbon footprint and foster a sustainable environment (Bawab et al., 2021; Khatib et al., 2025b; Zhang et al., 2023).

Bio-ash materials, which can be derived from various botanical sources such as stems, leaves, husks, straws, and shells, have emerged as a promising solution for replacing cement in various applications. A multitude of studies have demonstrated the viability of bio-ash materials as a substitute for cement in concrete, mortar, or paste (Onsongo et al., 2025). Bio-ash materials are regarded as ecofriendly and cost-effective (ElKhatib et al., 2022; He et al., 2020). Examples of bio-ash materials include rice husk ashes, wheat straw ashes, sugarcane bagasse ashes, palm oil fuel ashes, walnut shell ashes, corn cob ashes, and phragmites australis ashes (Elkhatib et al., 2023; Shebli et al., 2023; Thomas et al., 2021). Bio-ash materials exhibit pozzolanic properties, a characteristic that is attributed to their high content of amorphous silica and alumina (Gunarathne et al., 2019). The replacement of traditional Portland cement in concrete or mortar can be executed in a partial or complete manner, as evidenced by the works of Akbar et al. (2021) and Al-Alwan et al. (2024).

Research has demonstrated that the incorporation of Bermuda grass ash as a partial cement replacement in concrete results in a modest reduction in water absorption (Patnaik et al., 2022). Additionally, the findings of the study demonstrated that the compressive strength of concrete exhibited an increasing trend as the percentage of wheat straw ash increased from 0% to 10%, followed by a subsequent decrease after the percentage of wheat straw ash was increased as a partial cement replacement from 10% to 20% (Shar et al., 2019). The utilization of rice husk ash as a partial substitute for cement has been demonstrated to enhance the durability of concrete, thereby improving its resistance to water absorption, corrosion, sulfate, and chloride (Endale et al., 2023). Moreover, the incorporation of phragmites australis ash as a partial cement replacement has been observed to result in a modest augmentation of the length change of mortar, encompassing expansion, drying, and autogenous shrinkage (Khatib et al., 2023). A body of research has demonstrated the viability of geopolymer concrete, which involves substituting a portion or all of the conventional Portland cement with bio-ash materials. Recent studies have demonstrated that the incorporation of sugarcane bagasse ash as a substitute for cement can enhance the ultrasonic pulse velocity, thereby indicating an improvement in the quality of the mortar. This phenomenon can be attributed to the enhanced internal structure and denser microstructure of the bagasse ash geopolymer matrix (Akbar et al., 2021). Moreover, the tensile strength of geopolymer mortar incorporating sugarcane bagasse ash exhibited higher values compared to the control mix comprising cement (Akbar et al., 2021). A similar trend was observed in the flexural strength measurements. This phenomenon can be attributed to the occurrence of a strong covalent bond, which is formed during the geo-polymerization chain reaction in the bagasse ash-based geopolymer composites. With respect to compressive strength, geopolymer mortar containing bagasse ash demonstrates higher values than those recorded for the control mix. This is attributable to the denser microstructure resulting from the finer particles of the bagasse ash and the polymerization reaction, which leads to a denser and more stable microstructure. However, the geopolymer mix containing bagasse ash demonstrated lower values in terms of water absorption when compared to the control mix. This phenomenon can be attributed to the chain geo-polymerization reaction, which results in the formation of closed packing of bonds, thereby impeding water absorption (Akbar et al., 2021).

This paper analyzes recent studies on the utilization of bio-ash materials, specifically phragmites australis ash (PAA) and walnut shell ash (WSA), as a partial green alternative for cement. Tests of ultrasonic pulse velocity and compressive strength have yielded encouraging results, contributing to the development of sustainable construction.