According to John Sheath, strategy and marketing manager at Ash Resources, the addition of fly ash to a concrete mix substantially boosts the workability of the concrete.
“This is one of the major reasons why concrete producers and contractors prefer working with fly ash mixes,” Sheath says. “They are easier to handle, place and finish.
“The presence of the spherically shaped particles of fly ash in the mix also cuts the water content by between 6 and 12%,” he says.
Adding fly ash to the mix to produce lower slump concrete means the concrete can be placed more easily because of its improved plasticity. On the other hand, higher slump concrete can be produced at the same water content as CEM 1-only concrete.
“Segregation and bleeding of the concrete are reduced because of the increased cohesiveness of a fly ash mix,” Sheath continues. “This enhances form finish and sharpness of detail. The presence of fly ash in a mix also allows coarse, clean sands to be used without negatively affecting workability.”
During the hydration of cement, heat is generated which causes the concrete temperature to rise, accelerating the setting time and strength gain of the concrete. “In the case of mass concrete, such rapid temperature rises increase the chances of thermal cracking, leading to reduced concrete integrity and durability. By partially replacing Portland cement with fly ash the rate of heat generation is reduced as a result of the fly ash’s pozzolanic reaction with lime occurring over an extended period of time,” he adds.
Ash Resources. South Africa’s leading supplier of fly ash, is also one of the world leaders in fly ash technology. The company turns waste products from Eskom’s coal-fired power stations into beneficial products for the building industry – so reducing waste to landfill and contributing to the formulation of high performance concrete