Concrete water reducing agents are a type of admixture that performs a specific role in concrete. To begin with, a concrete water-reducing agent reduces the “unit amount” of water that is used during the process of mixing concrete without impacting the concrete’s workability to lower the cement-water ratio which improves the concrete’s strength.
Secondly, a water reducing agent does not lower the mix performance of the concrete (other than the unit water consumption), and can dramatically alter the mix-compound workability of the concrete, lower the consumption of construction energy, and facilitates easier construction.
Lastly, water reducing agents can reduce the time the concrete takes to harden and the cement amount that is used for each concrete unit, thus reducing costs and saving cement. According to the capacity of water reduction, the water reducing agents are available in different categories, including the standard water reducing agents, high-performance PCE based superplasticizer, SNF superplasticizer (sodium naphthalene sulphonate) and other water reducers.
Many of the essential characteristics relating to the concrete are mainly influenced by a ratio (by weight) of w/cm (water to cementitious materials) used in a mixture. By reducing the water, the paste (cement) will achieve a higher density, and this results in a better paste quality. When the quality of the paste increases it yields higher flexural and compressive strength, lowers permeability, increases weathering resistance, improves the reinforcements and bond of the concrete, decreases the volume change that occurs from wetting and drying, and lowers cracking tendencies caused by shrinkage.
What Are WRA (Water Reducing Admixtures)
The use of concrete water reducing agent or water-reducing admixture is defined as “Type A” in the ASTM C 494. WRA mainly impacts the “fresh characteristics” of concrete in the way of decreasing the water used (the amount) by 5% to 12% while still maintaining a specific consistency level measured by “the slump” which is prescribed in the ASTM C 143-90. WRA use may retard or accelerate the time that it takes for the concrete to set.
WRAs designed to retard the setting time to over 3 hours later are classified as WRAs with retarding effects, also known as Type D. WRAs that are commonly used include hydrocarboxylic (HC) and lignosulfonates acids. When using HC acids as a WRA the concrete will require a higher content of water when compared to lignosulfonates. Rapid bleeding is one of the issues for concrete that is treated with HC acids.
Water Reducing Admixtures are mainly used in areas that experience hot and humid weather for the purposes of concrete pumping, tremie, and placing. Careful placement of the concrete becomes a requirement since the “initial” time it takes for the concrete to set will typically occur 1 hour earlier.
It has also been shown that WRA use provides an increased initial compressive strength to the concrete (up to 28 hours) by 10% when comparing it to a control mixture. Another benefit relating to the use of WRA is that the higher density of the concrete is achieved making the concrete a lot less permeable while obtaining higher durability and improving the overall quality of the mixture.