The growing interest in saving materials and energy, in parallel with the growing concern for environmental issues and the uncertainty in the evolution of the economy, encourages the research for ways into full or partial replacement of the constituent elements of composite materials. Due to its many advantages, concrete is widely used composite, and in general, the most used material in construction. Being also the second most used substance (after water) in the world, it is inevitable that its impact on the environment is significant and unavoidable. Knowing that the production of cement clinker produces large amounts of carbon emissions worldwide, ways are sought to reduce the required amount of cement through the manipulation of other components of concrete. Thus, new materials can be added that would replace the cement and reduce the need for it. The focus is placed on materials that are usually leftovers from other industrial processes and have no other purpose, so they end up in a landfill. The ash obtained from the combustion of wood biomass is a material that is a good candidate for researching its potential to replace cement in cement composite materials. The ash obtained by burning wood biomass is a material that is often thrown away or used in small quantities for individual household needs.

The aim of this paper is to investigate the influence of the different percentages of ash in relation to cement, on some of the mechanical properties of fresh and hardened concrete: consistency, content of fresh concrete, compressive strength and density at the age of concrete of 3, 7 and 28 days. By increasing the amount of ash, and thus decreasing the consistency of the fresh concrete, insignificant differences are observed in the measured pore content and density of the samples. Compressive strength shows decrease with increasing amount of ash.