EFFECT OF QUARRY DUST AND BILLET SCALE ADDITIONS ON THE PROPERTIES OF FLY ASH BRICKS

Abstract- This paper reports the effect of addition of quarry dust and billet scale on the properties of fly ash bricks. Bricks were made with fly ash and cement and varying percentages of quarry dust and billet scale. All the mixtures were made to be flowable in fresh state. The bricks were then tested for strength, modulus of rupture, ultrasonic pulse velocity, initial rate of suction, water absorption, and efflorescence. The strength of bricks ranged from 0.8 MPa to 18.9 MPa, modulus of rupture ranged from 0.13 MPa to 3.7 MPa, water absorption from 15 to 32 %, and initial rate of suction between 0.27 and 2.21 kg/m^sup 2^.min. All the bricks were categorised as non-efflorescent. It is concluded that the optimum ratio of fly ash and billet scale and quarry dust and billet scale is 1:1 to get improved strength. Furthermore, it is shown that fly ash bricks incorporating 25% of quarry dust and billet scale gives reduction in the various properties observed. Modulus of rupture ranged between (2.5-3.7) MPa for series C and in (0.13- 0.25) MPa for series D. The minimum permissible limit of modulus of rupture of brick is 0.65MPa [2]. Modulus of rupture test was performed on clay brick and cement brick and the results were 1.6 MPa and 1.8 MPa respectively. Therefore, fly ash bricks produced from series C showed higher values for modulus of rupture. However, fly ash bricks from series D showed less values of modulus of rupture than that of conventional bricks. Modulus of rupture increased with the increase of fly ash and billet scale and optimized at 1:1 fly ash and billet scale as indicated in Fig. 4. Recycling of billet scale solely in the matrix may reduce the modulus of rupture as it may disintegrate due to attrition between the constituent materials during mixing, thereby weakening the bond. However, further tests are necessary to confirm this. Consequently, modulus of rupture will be reduced since it is more sensitive than compressive strength to voids and micro-crack [24]. However, fly ash as powder material may fill the voids in the mix when mixed with billet scale enhancing the modulus of rupture [23]. A similar trend was found in Fig. 5 which illustrates the relationship between modulus of rupture and QD+BS. Result for UPV at 28 days ranged between (1.8-2.6) km/s for series C and between (0.5-0.8) km/s for series D as shown in Table 3. The acceptable range of UPV of brick is (1.453-2.758) km/s [13]. UPV test was performed on clay brick and cement brick a