Sulfate resistance of cement with different volumes of fly ash

Abstract

SUMMARY: Sulfate attack is a complex severe set of chemical and physical processes that have great influence on concrete durability by changing the microstructure of the cement paste and concrete. Sulfate resistance of concrete should be obtained including requirements for low-permeability concrete, use of sulfate resistance cement and proper production of concrete. In this paper an extensive experimental research is presented on the possibility of using fly ash as a partial replacement of OPC clinker and its influence on the sulfate resistance of cement. For that purpose, four samples of fly ash from the TPP Bitola were taken in the time period of two weeks. All cement components including fly ash were completely tested from the aspect of chemical composition and physical properties. Two samples of fly ash which showed the biggest difference in their fineness were chosen for further investigations and preparation of cements. Laboratory cements were prepared by varying the quantity of fly ash as replacement of OPC clinker, from 0% to 50%. For all laboratory produced cements complete chemical analysis and determination of the physical and mechanical properties have been carried out. The method of Koch & Steinegger and the recommendations of the Technical Committee of Cement given in CEN/TR 15697 were used for determination of sulfate resistance of the laboratory cements. According to this method, small specimens (prisms with dimensions 10/10/60mm) were prepared and then cured in deionized water and aggressive solution – 4.4% Na2SO4. The corrosion coefficient calculated on the basis of flexural strength of the specimens tested after 56 days in aggressive solution was used as indicator of sulfate resistance of the cements. On the basis of the test results, it is determined that the fly ash and all laboratory cements fulfil the quality criteria defined in the standards. It is also concluded that the cements with 30% fly ash show the best results from the aspect of sulfate resistance.