concrete water reducer plasticizer is a common additive that is used to lower the amount of water in a concrete mixture, increasing its strength. It can also be used to increase the fluidity of a concrete mix, which can improve its placement and workability.
Concrete Water Reducing Admixtures
There are two main types of water reducing admixtures: conventional and high range, or superplasticizers. These admixtures fall under the ASTM specifications C 494 Type A and F, respectively.
Conventional water reducers are designed to decrease the water to cement ratio in concrete, which translates into increased early strengths and greater durability for concrete produced with a low slump. They are typically used in driveways, sidewalks, foundation walls and footers.
Superplasticizers, on the other hand, are designed to increase the water to cement ratio in concrete. They can be used to produce concrete with a low slump, as well as high strength concrete, pumpable concrete and self-compacting concrete.
How Superplasticizers Works
The hydrophobic group in water-reducing admixtures is a large molecule hundreds of times larger than the water molecule (Figure 5.5). It sticks to the surface of cement particles, taking their charges and distracting them from electrical repulsion so that the free water can be released from floe.
The effect of normal water-reducing admixtures on the hydration of concrete is negligible and is therefore not recommended for most applications; however, they can improve dispersion of cement grains in mortars and concrete, which shortens the stiffening time and enhances early strengths at a constant w/c ratio. Some admixtures can even be used in combination with certain types of cements at high dosage levels, e.g., with low tricalcium aluminate content (C3A)-containing cements.