Editor’s Note: This is the first article in a four-part series on materials that enhance the performance of concrete. This segment covers water reducers, which improve the performance of concrete in its hardened state. Future segments will cover curing compounds, fly ash and accelerators.
Click here to read Material Matters: Liquid Curing Compounds.
By Debbie Sniderman
Water reducers are low-viscosity liquids that reduce the water content in cement. ASTM classifies some as either Type A water reducers, which provide low-range water reduction, or
Type F high-range water reducers, which remove 20 to 40% of water from a mix. Today, 95% of precasters use third-generation high-range water reducers, or superplasticizers, which are Type F.
There is also an entire category of mid-range water reducers that isn’t classified or specified by ASTM. Doug Wittler, president of Premiere Concrete Admixtures based in Pioneer, Ohio, explains: “Developed in the 1990s originally to improve the finishability of concrete, they didn’t offer superior water reduction and were considered to be a product that added body or cream and made it easy to finish and work with,” he said. “The mid-range category (was) confusing until approximately 10 years ago, when third-generation water reducers arrived on the market.”
First- and second-generation superplasticizers are melamine and naphthalene based, and provide excellent strength and water reduction. They are still used by precast operations that don’t use self-consolidating concrete, and, according to Wittler, they offer more wiggle room with control.
Third-generation superplasticizers are made from polycarboxylate materials, which provide higher water reduction and can be sensitive to cement characteristics.
“They also allow SCC to be made after understanding the mix design, the raw material components and how they perform in concert with other additives, which can be chosen to do different things,” Wittler said.
How they work
Water reducers work by coating the cement and acting as a dispersant. They spread out cement particles in the mix so more particles become hydrated and more surface area is available for early hydration. The more cement particles hydrated by contact with the mixing water, the greater the compressive strength of the concrete. Water reducers provide more complete and efficient hydration of the cementitious materials in the concrete matrix.
Why they are important
Kenneth Kruse, admixture systems industry director at BASF, said that using HRWRs helps reduce the overall CO2 footprint for a given project, because it allows less cement to be used.
“Ten years ago, the industry didn’t use HRWRs to reduce cement,” Kruse explained. “But now, they allow cement to be taken out. Precasters can use more secondary materials that are sensitive to sustainability and the environmental impact to society and still have the material performance.”
Admixture companies are always producing new water-reducing products. Kruse says the product lifecycle for water reducers is three years due to precasters’ need to produce more economically, faster, and with smaller batch and test times and higher quality standards than ever.
“The components of concrete – cement, aggregate, sand and water – are dug out of the ground and haven’t changed much over time,” Kruse said. “The market requirements have. Normally you serve those by changing the chemistry of the additives, and water reducers are one chemical component of a high-performance mix design that supplements performance enhancements by other materials.”
Durability and more
HRWRs are one component of durability. In any given mix, there will be several admixture ingredients added to achieve the performance needed at the plastic and hardened state of concrete. There are many reasons why water reducers and superplasticizers are used: They:
- increase the density and strength of concrete quickly without delaying the setting time.
- allow a longer window of workability and fast form turnover.
- allow precasters to use less cement, optimize their material costs and use other secondary materials such as fly ash.
- increase the service life and durability of the product with decreased permeability.
Another use for water reducers is set control. Instead of using accelerator additives, HRWRs can speed up or slow down the set of concrete when additional or faster time is needed.
Advancing precasters’ plant work
Precasters want increased strength for two reasons. The first is for durability – early high strength means products can be manufactured faster. By being able to strip the form faster, producers can make more components in a shorter time and increase efficiency. Second is for higher stripping strengths – to consistently produce high-quality finishes.
Another reason it’s important to add water reducers is to be able to produce and perfect a better SCC process, which, according to Kruse, encompasses more than 35% of all concrete poured by surveyed precasters.
Water reducers enable the concrete to flow smoothly with high spread and little or no vibration. Without mechanical manipulation, plants can save labor and eliminate hazards such as the potential for electrical shock or hearing loss from extended exposure to loud noises.
“There’s an enormous amount of positives for using an SCC process that reach all facets of a business: personnel, safety, labor savings, strength, quality of product and turnover time,” Wittler said. “You can strip the bench quicker, release and turn product faster, and create a nice-looking finished product. Because the mix becomes so fluid, without vibration it’s possible to get sharper details and an aesthetically pleasing product.”