Concrete is a non-ecological material due to very high amounts of virgin materials used for its obtaining, significant energy levels being spent for their extraction and processing. The production of Portland cement is a major factor responsible for greenhouse gas emissions. Substituting a part of the cement by waste with puzzolanic properties, such as the fly ash, will lead to a decreasing of used cement and a consequent reduction of the pollutants generated by its obtaining. The present study aimed to investigate the effects of 10%, 20% and 30% volume replacement of cement by fly ash on the concrete density, compressive and split tensile strengths. The experimental results revealed that fly ash adding had a negative effect on the compressive strength of the obtained concrete, but a positive effect on its density. Replacing up to 20% volume of the cement by fly ash led to improved split tensile strength of the concrete. From the point of view of the fly ash quantity and concrete properties ratio, the obtained concrete with 20% volume of cement replaced by fly ash showed the optimum results.