Abstract:
This thesis describes the development of high strength concrete by using fly ash asa replacement of cement. The parameters to be investigated are the optimum of water-cementratio, sand-aggregate ratio, slump of concrete, compressive strength, and cost of high strengthconcrete made from Hong Kong fly ash and that from normal weight concrete.Experiments were conducted to obtain the optimum water-cement ratio by usingcement content of 450,500 and 550 kg/m3 and varying the water cement ratio of 0.22, 0.24,0.28 and 0.30. To determine the optimum sand-aggregate ratio, the concrete with cementcontent of 450 kg/m3 was used with the sand-aggregate ratio of 25,30,35,40 and 45 percentby weight of aggregate. The optimum sand-aggregate ratio is the concrete mix with the highestcompressive strength. mer the optimum sand-aggregate ratio was found, this sand-aggregateratio and water content were use to investigate slump and compressive strength of concretewith cement content of 450, 500 and 550 kg/m3. This amount of cement content was alsoreplaced by fly ash of 0, lo,20 and 30 percent by weight of cement plus fly ash. Compressivestrengths of fly ash concrete cube specimen of 10 x 10 x 10 cm were tested at the age of 3,7,28,56 and 91 days.The results showed that the optimum water cement and sand-aggregate ratios were0.26 and 0.40, respectively. The average slump of concrete with 10 and 20 percentreplacement of fly ash was 22.3 cm while that of normal concrete was 14.7 cm. However, theslump of fly ash concrete reduced to 11 .O cm with the present of fly ash 30 percent. Thecompressive strength of fly ash concrete with cement content of 450 to 550 kg/m3 and fly ashof 0 to 30 percent in the mix ranged from 760 to 850 Ksc at 91 days. Cost of fly ash concretewas found to be higher than that of normal concrete. Although fly ash concrete is more costlythan the normal one, it gives a higher slump and non segregation behavior. These advantagesof fly ash concrete will bring it to be more preferable to be selected in construction ascompared to normal concrete