The concrete admixture industry, which is directly affected by the cement industry, is recovering from negative growth consumption that it experienced in 2011.
The industry experienced a slight rebound of 2.7% in 2012 and is expecting further growth this year.
“The market is competitive from a construction point of view and people are improving their costs to be competitive in terms of projects,” says Chryso construction chemicals manufacturer CEO Norman Seymore.
He adds that, within the cement admixture industry, volumes are showing little growth and there is strong demand for high-performance products to reduce costs.
“The industry is being challenged to deliver high-performance products at the right value,” Seymore says.
He notes that, currently, there are several challenges facing the industry, such as the volatile exchange rate, as the raw materials used in admixtures are imported.
“Cost pressures are currently a major challenge for the industry; however, the acceptance of the application of admixtures is growing. “Traditionally, admixtures were sold to bulk cement users, but cement users in South Africa constitute an even split between bulk users and people who buy cement in bags,” Seymore says.
He notes that the admixture industry is now in its third generation and that, initially, admixtures were made from adapted by-products from other industries, owing to their high service performance in concrete.
“New molecules for third-generation admixtures are designed for performance enhancement,” Seymore says, adding that there are five families of admixtures in the industry – plasticisers, superplasticisers, air entrainers, accelerators and retarders.
Plasticisers are water-reducing agents and when added to a concrete mix, they are absorbed on the surface of the binder particles, causing them to repel each other and deflocculate.
“This results in improved workability and provides an even distribution of the binder particles through the mix,” says Seymore.
He notes that superplastcisers are chemically distinct from normal plasticisers and, although their action is basically the same, they are more marked. When used to produce flowing concrete, a rapid loss of workability can be expected and, therefore, superplasticisers should be added just prior to placing.
“An air-entraining agent introduces air in the form of minute bubbles distributed uniformly throughout the cement paste. “The main types include salts of wood resins, animal or vegetable fats and oils, and sulphonated hydrocarbons,” says Seymore.
He points out that air entrainers are used to improve the resistance of hardened concrete to damage from freezing and thawing as well as its workability, especially in harsh or lean mixes. “They also reduce bleeding and segregation, especially when a mix lacks fines.
“Air entrainment may reduce the strength of concrete and overdosing can cause major loss of strength. “As 1% air may cause a strength loss of 5%, it is important that mixes are specially designed for air entrainment and that the percentage of the air entrained during construction be monitored,” Seymore explains.
He notes that accelerators speed up the chemical reaction of the cement and water, subsequently accelerating the rate of setting and early gain in the strength of the concrete.
“Among the main types of accelerators are calcium chloride, calcium formate, soda ash, potassium chloride and several organic materials,” says Seymore, pointing out that retardants, however, slow down the chemical reaction of the cement and water, leading to longer setting times and slower initial strength gain.
The most common retardants are hydroxylated carboxylic acids, borax, lignins, sugar and some phosphates. They are useful when placing concrete in hot weather, particularly when the concrete is pumped to prevent cold joints that can occur during placing, and in concrete which has to be transported for a long time, he notes.
Seymore adds that many admixtures provide combinations of properties, such as plasticiser combined with retarders or plasticiser combined with air entrainers.
“There are also specialised admixtures, such as pumping aids, pigments, expansion aids and grouting admixtures, and information on their use should be obtained from the admixture suppliers. However, admixtures should never be regarded as a substitute for good mix design, good workmanship or the use of good materials,” he says.
The benefits of using admixtures include cost reduction and the enhanced performance of concrete.
“There are many different types of concrete, such as self- levelling and flowable concrete. All these properties are different to those currently available to the concrete producer and many performance benefits of concrete are driven by admixtures technology,” he notes.
Seymore, who was an alternative director at the Cement and Concrete Institute (C&CI), says the institute’s closing down after 75 years, following the resignation of its main funding members, will leave a gap in the industry.
“I am disappointed that the C&CI closed. It is necessary to have an independent industry body to promote the use of concrete amid alternative construction materials.
I am hopeful, however, that certain aspects of the C&CI will possibly remain in place under different industry bodies, as it has been a major contributor to the industry in terms of education and marketing. Without the C&CI, everyone in the industry will be negatively affected,” he explains.
Seymore notes that people in the concrete admixture industry come from an engineering or construction background and that the industry, in general, is small, but specific.
“The closure of the C&CI will have a significant impact on training within the industry, as it played a big role in training and skills development. The closure of the institute has made it more challenging to educate and train people in the industry,” he concludes.