Question

waht are mechanical of action for the water reduce high rang water reduce ؟

Answer 1

Action of Water Reducers and High Range Water Reducers

1. Water-reducing admixtures improve concrete’s plastic (wet) and hardened properties, while set-controlling admixtures are used in concrete being placed and finished in other than optimum temperatures. Both, when used appropriately, contribute to good concreting practices.

2. Water reducers do essentially that: reduce the amount of mixing water required to obtain a given slump. This can result in a reduction of the water-cementitious ratio (w/c ratio), which leads to increased strengths and more durable concrete.

3.Reducing the w/c ratio of concrete has been identified as the most important factor to making durable, high-quality concrete. On the other hand, sometimes the cement content may be lowered while maintaining the original w/c ratio to reduce costs or the heat of hydration for mass concrete pours.

4. Water-reducing admixtures also reduce segregation and improve the flowability of the concrete. Therefore, they are commonly used for concrete pumping applications as well.Water-reducing admixtures typically fall into three groups: low-, medium- and high-range. These groups are based on the range of water reduction for the admixture.

How they work

When cement comes in contact with water, dissimilar electrical charges at the surface of the cement particles attract one another, which results in flocculation or grouping of the particles. A good portion of the water is absorbed in this process, thereby leading to a cohesive mix and reduced slump.

Water-reducing admixtures essentially neutralize surface charges on solid particles and cause all surfaces to carry like charges. Since particles with like charges repel each other, they reduce flocculation of the cement particles and allow for better dispersion. They also reduce the viscosity of the paste, resulting in a greater slump.

Advantages of Water Reducers and High Range Water Reducers

• reduces the water content by 5-10%
• decreases the concrete porosity
• increases the concrete strength by up to 25% (as less water is required for the concrete mixture to remain workable)
• increases the workability (assuming the amount of free water remains constant)
• reduces the water permeability (due to less water being used)
• reduces the diffusivity of aggressive agents in the concrete and so improves the durability of concrete
• gives a better finish to surfaces (due to all of the above)

In addition, water reducers can be used to provide additional workability at the same water-to-cement ratio.

The main reason to add water to concrete — above and beyond what is needed for the proper hydration of the cement particles — is to improve workability, of course. “The rule of thumb is: 0.22 to 0.25 water-to-cement ratio is required for complete hydration,” says Schlagbaum. Most mixes have water-to-cement ratios of 0.40 to 0.60 primarily for workability purposes, he adds. But keeping the water-to-cement ratio down through the use of water reducers improves the concrete’s hardened properties.