Fly Ash Used to Create Stronger Concrete

(Engineering News 5-13-2011) Fly ash products manufacturer Ash Resources has introduced a new fly ash additives product to its range – DuraPozzPro.
The new product is the finest form of fly ash the company produces, and is intended for the high-end market. The company gathers fly ash from coal-fired power stations, before processing it and selling it for use in concrete mixtures.
Newly appointed company MD Daniel Pettersson explains the ash particles found in DuraPozzPro pass through a 45 μm sieve, resulting in higher reactivity from a greater concentration of the particles in the amorphous (glass) phase, and stronger concrete.
“DuraPozzPro has a reduced residual carbon content, resulting in a whiter fly ash, and contains less activated carbon, which can adversely absorb concrete admixtures,” he says.
Further, the product requires less water, which helps to create a stronger concrete, while the fine fly ash particles improve the concrete’s workability. The product also enables concrete mixers to reduce the cement content in the concrete.
Pettersson notes that, owing to the increased density of the concrete, Dura-PozzPro is suitable for use in coastal applications, or where the concrete will retain water bodies, such as dam walls.
Ash Resources is currently involved in the construction of the De Hoop dam, in Limpopo, where a new national record for a single continuous concrete pour was achieved late last year, when 103 600 m3 of concrete was placed in 23 days. That is more than double the previous record of 40 600 m3 placed in a month at the Wolwedans dam, in the Western Cape.
The Department of Water Affairs (DWA) reports that a locally developed roller-compacted concrete mix was used in the construction of the R2,55-billion De Hoop dam project.
Pettersson explains that this achievement demonstrates the depth and experience of Ash Resources in guaranteeing product availability on projects of such magnitude. “Ash Resources is supplying about 150 000 t of fly ash overall to the construction site, necessitating up to 40 truck loads a day at the peak of construction,” he says.
Meanwhile, the company is also supplying fly ash to the construction sites of State-owned power utility Eskom’s two new coal-fired power stations, Medupi, in northern Limpopo, and Kusile, in Mpumalanga.
Ash Resources has five plants around the country, supplying about 85% of fly ash to the concrete market. Its strategically positioned plants assist it in providing uninterrupted supplies of fly ash to its project commitments.
“Although logistics prove to be a challenge at times, owing to an unreliable rail network and industrial action, the company strives to supply and succeeds in supplying its customers with the required amount of fly ash, when it is required,” he adds.
Further, the company owns a sophisticated laboratory, which it uses to research concrete technologies. It is currently researching concrete additives which can reduce the amount of cement needed to produce concrete. This will help to further extend the volumes of concrete, while reducing the carbon dioxide emissions associated with producing cement.