Optimising the usage of fly ash in concrete in the construction of roadworks

Abstract

The use of recycled materials in road construction has been around for many years and with the environment getting severely affected by the daily use of natural resources used in construction, every bit of intervention that can provide a relief to the environment is greatly welcomed. This study looked at one of the ways the industry can play a big role in promoting recycling of by-products such as fly ash, on a larger scale, in the cement and concrete industry, by utilizing the fly ash to the optimum. Concrete mixtures of 35MPa with fly ash partially substituting the cement at four levels, 30%, 40%, 50% and 60%, were produced and numerous tests were performed to determine an optimum amount of fly ash that can be used and still obtain better or comparable concrete to ordinary concrete. Performing concrete tests such as compressive strength, durability, slump and setting was done at the Durban University of Technology and Contest laboratories over a period of one year. Also a cost comparison between the ordinary concrete and fly ash concrete was done. The results obtained during compressive testing showed that although the lowest fly ash content (30%) mixture resulted in higher strength over a year, other mixtures also obtained acceptable and very good strength. The durability index testing showed that utilizing higher fly ash content can also result in concrete with good durability qualities. Using higher fly ash content resulted in very workable concrete with good consistency. Also the cost of producing and working the concrete can be greatly reduced when the amount of fly ash is increased. The fly ash content in concrete can be used up to 50% with positive results in concrete structures and the environment. The transport sector can play a big role in promoting sustainable development by incorporating larger scale use of fly ash in construction.