A Study of Ground Mea Moh Fly Ash as a Pokolan for Increasing Concrete Strength

Abstract

This paper purposed the use of Mae Moh fly ash as a pozzolan for increasingconcrete strength. Fly ash was ground to increase its fineness and used as a replacementof cement. Setting times of cement-fly ash paste, flow, and compressive strength ofmortar containing different fineness of fly ashes were investigated. Mortar cube of5-cm was used to determined its compressive strength. The mix proportion of cementitiousmaterials (cement+fly ash) to sand was 1 to 2.75 with water to cementitious materialsratio of 0.59. Three different fineness of fly ashes were used. There were the ungroundfly ash with Blaine fineness of 3730 cm²/g, the 6-hr ground fly ash with Blaine finenessof 5563 cm²/g, and the 12-hr ground fly ash with Blaine fineness of 17727 cm²/g.Cement was replaced by fly ash 0, 15, 25, and 35 percent by weight of cement. The flyash mortar cubes were tested for compressive strength at 1, 3, 7, 14, 28, 60, and 90 days.

The results revealed that use of fly ash in the mix resulted in the increaseof setting times of cement-fly ash paste. With the same mix proportion, the finer flyash reduced the setting times of cement-fly ash paste. Flow of mortar increased withthe use of fly ash in the mix not more than 25 percent, but, decreased with the amountof fly ash higher than 35 percent. For the same mixture, the higher fineness of fly ashreduced the flow of mortar. All the compressive strengths of the mortar mixed withunground fly ash were lower than the standard mortar strength. The use of finer fly ashincreased the rate of development of compressive strength of fly ash mortar. Only theground fly ash mortar gave higher compressive strength than the standard mortar strength.With 15 percent of the finest fly ash in the mix, the compressive strongth of fly ash mortarwas equal to or higher than the standard mortar strength at 7 days. With the amount ofthe finest fly ash 25 and 35 percent in the mix, it took about 14 and 28 days, respectively,for the fly ash mortars to gain the same strength as of the standard strength.