Utilização de cinza moída da usina termelétrica do Pecém como pozolana na produção do concreto convencional

Abstract

On thermoelectric plants, the coal burning is performed to provide heat, vaporizing the water, which mobilizes the turbines, thus generating the necessary movement for the electric energy production. One of the residues of this process is the fly ash, which, if pozzolanic, has a great potential when incorporated into the concrete, since, besides avoiding an expensive deposition, it can even improve the concrete compressive strength. In order to increase pozzolanic activity, the ash went through a grinding process, increasing its specific surface area. To characterize the ash, chemical and physical tests were performed to define if the ash is a pozzolanic material. 30 MPa, 35 MPa, and 40 MPa concretes were tested with addition of ash, and substitution of cement for ash at 0%, 8% and 15% in volume, resulting in a total of 45 concrete mixtures. Chemical and physical analyzes have shown that ground fly ash is in fact a pozzolanic material. The compressive strength analysis were performed by a statistical analysis of variance. For the seven days compressive strengths, in the fly ash incorporated concrete mixtures, both in addition and in substitution, the values were significantly lower than the reference values. The 35 MPa and 40 MPa compressive strength at 28 days was lower at least on one of the percentages (8% or 15%). Only on the 30 MPa mixtures the resistance was maintained, both in addition and in substitution, when compared to the reference. It is concluded that the use of ground fly ash in the studied concretes does not bring any advantage to the concrete compressive strength, which is possibly due to the grain structure breakage caused by the grinding process and the fineness of the particles being quite high.