EFFECT OF FLY ASH FINENESS ON COMPRESSIVE, FLEXURAL AND SHEAR STRENGTHS OF HIGH STRENGTH-HIGH VOLUME FLY ASH JOINTING MORTAR

In this research, the compressive, flexural, and shear bond strengths of high strength-high volume fly ash mortar containing high calcium fly ash (HCFA) of various finenesses were studied. The mortars were made from ordinary Portland cement (OPC), HCFA, sand, water, and Type D admixture. The HCFA was from Mae Moh power station in the north of Thailand. Three types of HCFA fineness viz., as-received coarse fly ash (CF), medium fineness fly ash (MF, passed sieved No. 100), and fine fly ash (FF, passed sieve No. 200) were used to replace OPC at the levels of 0-70 % by weight of binder. The results showed that the high strengthhigh volume fly ash mortars with satisfactory 28-day compressive strengths between 70.0 and 114.0 MPa, shear bond strengths between 7.2 and 18.0 MPa, and flexural strengths between 15.9 and 27.6 MPa were obtained. Test results also indicated that the use of FF gave significantly higher strengths than the use of CF and MF. Specifically, the compressive strength of mortar containing 50%FF was very high at 110.0 MPa. The FF could thus be used to improve the strengths of high volume fly ash mortar for uses in various architectural and structural works requiring high strength products.