Physical and mechanical properties of fly ash concrete

Abstract

As the construction revolution increases nowadays, the demand of building raw materials increases as a result. The whole world started to search for alternative raw materials in order to reduce the cost in the first place of the construction projects. Fly ash is a group of materials that can vary significantly in composition. It is residue left from burning coal. Fly ash is a pozzolanic material, which means it’s a siliceous or siliceous-and-aluminous material that reacts with calcium hydroxide to form cement. When portland cement reacts with water, it produces a hydrated calcium silicate (CSH) and lime. The hydrated silicate develops strength and the lime fills the voids. Properly selected fly ash reacts with the lime to form CSH–the same cementing product as in portland cement. This reaction of fly ash with lime in concrete improves strength. Typically, fly ash is added to structural concrete at 15-25 percent by weight of the cement, but up to 70 percent is added for mass concrete used in dams, rollercompacted concrete pavements, and parking areas. Special care must be taken in selecting fly ash to ensure improved properties in concrete. This report presents an experimental study on the physical and mechanical properties of fly ash concrete. In these experiments, a total 48 cubes with 100 x 100 x 100 mm and 48 beams with 100 x 100 x 500 mm were casted with different percentage of fly ash. The first set was without fly ash as a control set. While the other five sets consist of 5%, 10%, 15%, 20%, and 25% dosage of fly ash from each mix volume. All the cubes and the beams were tested for the failure under increasing load. The behavior of fly ash cubes and beams was studied comparing with the normal concrete set. Concrete mix with 25% of fly ash got the highest compressive strength value in 90 days of the concrete age with 37.6 MPa while concrete mix with 10% of fly ash got the highest flexural strength value in 90 days of the concrete age with 3.97 Mpa. Concrete mix with 20% of fly ash got the highest slump value with 93 mm which is considered to have the best workability value among all samples tested. The experimental results show better slump, flexural and compressive strength of the fly ash concrete comparing to the normal concrete set in general.