Abstract:
This study focuses on the effect of mixing time on the properties of self-compacting paste systems using supplementary cementitious materials (SCMs) such as Marble Powder (MP), Fly Ash (FA) and Limestone Powder (LSP). These SCMs are industrial waste products of the marble, coal and limestone industry, respectively and their use as replacements of cement aids in their effective disposal while making concrete production more economical and environment friendly. Furthermore, replacement of cement with SCMs results in the reduction of environmental pollution causes by cement production. The parameters studied include powder particle size characterization, flow, strength development, water absorption and calorimetry. In earlier stages, tests were carried out at 3 minute mixing time to determine the optimum replacement levels for all SCMs by replacing cement with 15%, 30% and 45% SCMs by weight. A replacement level of 15% for all SCMs resulted in the highest strengths and was, thus, selected for latter experimentation though in an earlier project, it was estimated at 20%. An increased replacement level for SCMs caused a fall in water demand, in terms of water-powder ratio, but increased superplasticiser demand. An increase in flow was recorded with increasing replacement levels of SCMs except for MP which retarded flow due to increased internal friction and possible early hydration. Increased replacement levels delayed setting times and reduced both water absorption and final strengths of the self-compacting paste systems. Addition of SCMs also resulted in reduced and delayed hydration. The self-compacting pastes containing optimum replacements of 15% SCMs were subjected to varying mixing times of 5 and 10 minutes. Results show a
considerable improvement in strength with increasing mixing time along with greater water absorption. MP exhibits the greatest compressive strength. It can be concluded that higher mixing time results in better compressive strength (though reduced flow and increased flow times) as well as earlier and faster hydration which proves that the use of SCMs can produce concrete that is workable, strong, economical and environment-friendly. It can be concluded that higher mixing time result in better compressive strength as well as earlier and faster hydration which prove that the use of SCMs can produce concrete that is workable, strong, economical and environment-friendly.
