THE BASICS OF CONCRETE CHEMICAL ADMIXES
Pouring concrete in cold weather? Need a mix to do a huge project such as a parking garage, or maybe a foundation for a multi-family building that spans an entire city block? Before you even get your concrete tools and equipment on the worksite, you’ve planned how much concrete you’ll need for the job. However, what's in your mix matters, too.
It helps to know about different concrete chemical additives - and how they can make your project go smoother - before you place your cement order.
A concrete masonry contractor may want to change the properties of concrete that cannot be achieved using conventional concrete mixes. Some properties include: water retention, drying time, strength, durability, temperature stability, and aeration (bubble content).
In order to manipulate the concrete to the desired properties, one needs to add chemical powders or fluids that can alter the chemical and physical composition of the concrete at the molecular level.
I know, I know - chemistry. No worries. Yes, this post includes names of compounds for the detail oriented or those just curious (interesting that some concrete additives are also used in the food industry, such as Sodium Nitrate). However, all the average concrete contractor needs to know about the chemistry of additives can be summed up into four categories.
The chemical compounds that are used as concrete additives are known as retarders, accelerators, plasticizers, and bonding agents.
A retarding agent is a compound that slows down the hydration and therefore the curing of concrete. Such agents are themselves hygroscopic (absorbs water) and include sucrose, glucose, and citric acid.
THE BENEFIT: These are useful during large or difficult pours or sites where partial drying is undesirable before the pour is complete.
An accelerator is a compound that speeds up the drying process. Calcium Chloride, Calcium Nitrate, and Sodium Nitrate are the most common, and are drying agents.
THE BENEFIT: The chlorine component is undesirable if there is any steel present, as it may cause corrosion. These are best for use in cold weather.
A plasticizer is a component that has the ability to increase workability of the concrete, using lignosulfonate (a byproduct of the paper pulping industry). This will decrease the viscosity of the material by decreasing the water content without affecting the placement ability.
THE BENEFIT: This treatment improves the strength and durability characteristics.
A bonding agent consists of acrylic or latex polymers that have a wide range of temperature tolerances and corrosion resistance.
THE BENEFIT: This additive is best used for melding old concrete with new concrete.
The dosages of each of these agents depend on what properties need to be manipulated. Usually, they are added in amounts less than 5% of the mass of the cement during the time of mixing.If you have any insights or examples you’d like to add to this post, general concrete tips you’d like to share for a future post, a project success story or other blog section input or feedback, please contact firstname.lastname@example.org. Thanks!