**9. Biowaste additives**

Biomass and agriculture waste can be great additives or even replacements to cement in concrete and mortar. Because cement is a key building material that accounts for 8–10% of total CO2, there is a critical need to replace cement in order to reduce greenhouse gases (GHGs) such as CO2, which are responsible for global warming [42].

The research of agricultural wastes as extra ingredients in mortar and concrete, as well as replacements for aggregates, resulted from the quest for alternative materials for cement. Agricultural wastes are readily available, inexpensive, and have high reactivity in concrete, which has increased researchers' interest in these materials. The effective use of these elements in concrete will result in a green manner of disposing of enormous amounts of trash that might otherwise have caused environmental harm.

Bassam et al. provide an excellent review on previous studies that use rice husk waste as a replacement for cement. The influence of rice husk on concrete characteristics such as workability, flexural strength, splitting tensile strength, density, compressive strength, modulus of elasticity, durability abilities, and sustainability is reported [43].

Not only the biomaterial itself but also its byproduct ashes can be used for making a sustainable cementitious material.

Blessen et al. provide a comprehensive review based on previous research and current developments in concrete using biomass ashes from agricultural farming wastes, ashes from bamboo leaves, date palm, rice straw, olive waste, elephant leaves, banana leaf and plantain peels, rice straw, wheat straw, olive waste, and corn cob as pozzolanic materials in cement concrete [44].

Some plants can be harmful and dangerous to the environment like the aquatic plant *Myriophyllum spicatum*, which is an invasive and noxious. Saleh, et al.

incorporated this plant into cement for safe immobilization of radioactive isotopes and other hazardous waste. Results show the cementation of dry solid waste generated during phyto-remediation was effective in immobilizing these wastes [45].
