Effect of micro-silica fume and fly ash as a partial replacement of cement on fresh and early strength properties of concrete

Abstract

Concrete is considered as an essential material required in construction. If the decreasing cement quantity used in concrete by replacing it with pozzolanic materials leads to required concrete properties, therefore, decreasing cost and the environment protection is the main goal. The current study investigated the fresh and early strength properties of normal concrete (NC) containing fly ash (FA) and silica fume (SF). FA and SF were together used in this work. The percentages of replacement were at a high level to modify the properties of concrete as well as the control NC mix (without FA and SF only OPC) at water/powder (w / p) ratio of 0.35. Slump test investigated the fresh properties and the compressive strength examined the early strength properties at 3 and 7 days. Results showed that the presence of FA and SF in NC has a negative impact by reducing the workability. For all mixtures, workability was lost with increasing amount of both FA and SF, although the rate of reduction was higher for mixtures with a higher amount of SF. However, the use of superplasticizer can be mitigated this reduction. Also, the results of the strengths of the specimens having these two pozzolanic materials are lower than control NZ specimens, especially at 3 days. Conversely, after 7 days the early strengths of the pozzolanic cubes are approaching values to the strength of control mixture. It is clear that a bit improvement in early strength of mixtures containing FA and SF. However, there is on-going of mixtures to develop its performance. NC with (30% FA + l0% SF) partial replacement of cement can be improved the compressive strength compared with control strength and other concrete mixes.