Home > Knowledge > Content

Water Reduction in the Concrete Mixing

Water reducers have become so important in concrete, that they could be considered the "fifth" ingredient.

They can be used to: (1) increase slump, (2) lower the water-cement ratio, or (3) reduce cement content.

Water reducers come as Low Range, Mid Range, and High Range Superplasticizers. There are enough different admixtures available that it is possible to select one that meets the need of a particular project whether it is tall columns that need a mix that pumps easily, or an easy-to-finish durable floor slab.

In general, they provide the required slump with less water in the mix, and may provide higher strength concrete without increasing the amount of cement.

Conventional water reducers

Are required to achieve a minimum 5% water reduction. A conventional water reducer can reduce slump by about 1 to 2 inches without the addition of water.

Mid-Range water reducers

Can reduce water content by at least 8% and as much as 15%. They tend to be stable over a wider range of temperatures and tend to give more consistent setting times. These reducers work most effectively in mixes designed to have a slump in the range of 4 to 5 inches.

  • Particularly useful in hot weather concreting by counteracting the accelerating effect of high ambient and concrete temperatures

  • Slow the setting rate of concrete

  • Delay initial set of concrete

  • Keep concrete workable during placement

High-Range water reducers (superplasticizers)

Can reduce water content from 12% to as much as 40% and are typically used in concretes designed to have slumps of 8 to 11 inches. They can be used to either increase slump (by 4 to 8 inches) or lower the water content of hot weather concrete mixes. Used to increase flowability.

Conventional water reducers

Are required to achieve a minimum 5% water reduction. A conventional water reducer can reduce slump by about 1 to 2 inches without the addition of water.

Mid-Range water reducers

Can reduce water content by at least 8% and as much as 15%. They tend to be stable over a wider range of temperatures and tend to give more consistent setting times. These reducers work most effectively in mixes designed to have a slump in the range of 4 to 5 inches.

  • Particularly useful in hot weather concreting by counteracting the accelerating effect of high ambient and concrete temperatures

  • Slow the setting rate of concrete

  • Delay initial set of concrete

  • Keep concrete workable during placement

High-Range water reducers (superplasticizers)

Can reduce water content from 12% to as much as 40% and are typically used in concretes designed to have slumps of 8 to 11 inches. They can be used to either increase slump (by 4 to 8 inches) or lower the water content of hot weather concrete mixes. Used to increase flowability.

High Strength Concrete

Admixtures containing microsilica (condensed silica fume) are used to meet high strength and low permeability requirements.

Benefits include reduced permeability, increased compressive and flexural strengths, and increased durability.

Applications include high-strength structural columns, less permeable parking garage decks, and abrasion resistant hydraulic structures.

Silica fume can be used in concrete to produce compressive strengths approaching 20,000 psi under jobsite conditions. This admixture can be added in a slurry or in a dry form, whichever meets the batching equipment needs. In either case, performance is the same.

Strength Enhancement

Concrete strength enhancement can be achieved through use of superplasticizer admixtures to produce a low water/cement ratio giving high performance concrete.

These admixtures promote a high slump, extremely flowable concrete that achieves high strengths while providing superior workability and pumpability.

High range water-reducing admixtures can also be used for precast/prestressed structures where it is desirable to keep the water/cement ratio to a minimum for low permeability and high early strengths without set retardation.They are also used for concrete requiring high-early stripping strengths.

Fly Ash - Making Concrete Stronger, More Durable, and Easier to Work With

Derived from burning coal, fly ash is a valuable additive that makes concrete stronger, more durable and easier to work with.

Fly ash aids the formation of cementitious compounds to enhance the strength, impermeability and durability of concrete.

Two main classes of fly ash are used in concrete, Class F, and Class C.

Class F

Reduces bleeding and segregation in plastic concrete. In hardened concrete, increases ultimate strength, reduces drying shrinkage and permeability, lowers heat of hydration and reduces creep.

Class C

Provides unique self-hardening characteristics and improves permeability. Especially useful in pre-stressed concrete and other applications where high early strengths are required. Also useful in soil stabilization.

Silica Fume: Early Strength and Reduced Permeability

Silica fume can make a significant contribution to early-age strength of concrete. One pound of silica fume produces about the same amount of heat as a pound of portland cement, and yields about three to five times as much compressive strength.