Concrete Admixture Effects
Concrete color
Concrete color is sometimes called integral color when you are referring to adjusting the concrete color before or during the mixing process. Though there are many different techniques to add a superficial color layer to concrete such as acid stains or paints, adding an integral color to concrete is the best way to ensure color fastness and a low maintenance finished product.
Typically added as powder or liquid by volume, concrete pigments can offer a wide array of earth tone concrete colors. If a white cement and aggregate is used, more dramatic colors can be achieved. In ready mix concrete only earth tones are available without paying substantial additional charges. Earth tone integral mixes are surprisingly affordable and can add dramatic effect for minimal budget.
Set time
Concrete takes 28 days of curing to reach full strength. The initial set time, or the amount of time where the concrete can still be placed and finished, can change depending on a number of different factors. Temperature and humidity as well as direct sunlight will have a dramatic impact on the set time of freshly mixed concrete.
By adding a retarder to the concrete mix you can delay the initial set time of concrete without negatively impacting the workability or finished strength. Retarder is added by percentage volume or by dose when ordered from a ready mix concrete batch plant. Fast initial set can be achieved by adding an accelerant to the concrete such as hydrated calcium. Added by percentage volume calcium will dramatically increase the speed at which concrete becomes hard after mixing.
Finished strength
By adding liquid additives such as acrylic polymer, glue, water reducer, latex or bonding agent you can increase the finished strength of the concrete while also increasing the workability of the concrete. All of the liquid additives fortify the concrete helping to create a stronger bond between the aggregates with the exception of the water reducer. Also available in a powdered form, water reducer increases the viscosity of concrete while reducing the amount of water required to achieve the slump.
Slump refers to the tendency of concrete to slump after being placed in a conical form and is measured in inches. A zero or one inch slump would be very dry stiff concrete and a slump of five or six would be very watery. Since the strength of concrete reduces exponentially the higher the water content of the mix, a stronger concrete can be achieved by reducing the water required to the absolute minimum. Cement requires very little water catalyst to begin the chemical reaction that hardens the cement. Dry pack concrete has the consistency of damp sand and this is more than enough water to actuate cement.
Workability
The workability of concrete refers to the slump or viscosity of the mixed concrete as well as its ability to be placed, floated and finished effectively. Adding liquid latex or acrylic to the concrete will help to create a smooth and creamy concrete texture that is ideal for smooth or detailed finishing such as stamped concrete. By adding glue or bonding agent you can make the concrete slightly less viscous and slight more sticky which is good for bonding new cement to old cement or for three dimensional concrete applications where a form is not used to hold the concrete in place.
Proceed to the section on Concrete Admixtures Types