Development of high performance concrete containing high calcium fly ash

Abstract

High performance concrete is a kind of concrete with compressive strength at 28 days over 50 MPa, high slump of  20 cm, and large flow of 50 cm without segregation. Low water to cement ratio is a usual practice to achieve the required high compressive strength. The amount of free water is decreased and often more cement is added into the system. However, Portland cement is relatively expensive and if used in large quantities, it can cause heat from reaction and fast setting of concrete, which lead to undesirable fresh concrete properties. This research is aimed to decrease the amount of cement and re-adjust mix proportion of high performance concrete to economize production cost and be able to use high performance concrete with the same quality.

In this research, the researcher re-adjusted the water to cement ratio to control slump and flow value to be more than 20 cm and 50 cm respectively.  The test revealed that when 2.5% of super plasticizer by cement weight was added to the proportion, the compressive strength at 28 days reached 58 MPa with 30% cement reduction by weight. Moreover, when high calcium fly ash was mixed into the system, its work ability further improved, water to cement ratio decreased, and compressive strength increased. The result showed that it largely helped to decrease the use of cement and production cost, and the properties of high performance concrete remained satisfactory.