Launch Slideshow

Durable Concrete Chemistry

Durable Concrete Chemistry

  • Specialty admixtures have many benefits, along with some potential limitations.

    http://www.theconcreteproducer.com/Images/20090826-088_tcm77-2105767.jpg

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    Specialty admixtures have many benefits, along with some potential limitations.

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    Steven P. Widoff Photography

    Specialty admixtures have many benefits, along with some potential limitations.
  • A workability-retaining admixture is being used to maintain the workability and consistency of calcium nitrite-treated concretes for construction of two cooling towers at Brayton Point in Fall River, Mass.

    http://www.theconcreteproducer.com/Images/admix-Brayton_tcm77-2105768.jpg

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    A workability-retaining admixture is being used to maintain the workability and consistency of calcium nitrite-treated concretes for construction of two cooling towers at Brayton Point in Fall River, Mass.

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    Charles Nmai

    A workability-retaining admixture is being used to maintain the workability and consistency of calcium nitrite-treated concretes for construction of two cooling towers at Brayton Point in Fall River, Mass.
  • An amine-ester organic corrosion inhibitor was used for the Denver International Airport parking structures.

    http://www.theconcreteproducer.com/Images/admix-DIA%20park_tcm77-2105769.jpg

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    An amine-ester organic corrosion inhibitor was used for the Denver International Airport parking structures.

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    BASF

    An amine-ester organic corrosion inhibitor was used for the Denver International Airport parking structures.
  • A workability-retaining admixture was used to maintain the workability and consistency of calcium nitrite-treated concretes for construction of two cooling towers at Brayton Point power plant in Fall River, Mass.

    http://www.theconcreteproducer.com/Images/admix-DIA_tcm77-2105770.jpg

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    A workability-retaining admixture was used to maintain the workability and consistency of calcium nitrite-treated concretes for construction of two cooling towers at Brayton Point power plant in Fall River, Mass.

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    Charles Nmai

    A workability-retaining admixture was used to maintain the workability and consistency of calcium nitrite-treated concretes for construction of two cooling towers at Brayton Point power plant in Fall River, Mass.
  • High-range water reducers are necessary in the production of self-consolidating concrete.

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    High-range water reducers are necessary in the production of self-consolidating concrete.

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    Joe Nasvik

    High-range water reducers are necessary in the production of self-consolidating concrete.

Waterproofing Admixtures

Watertightness is a key performance criterion for concrete structures designed for the containment, treatment, or transmission of water, wastewater, or other fluids. From a concrete perspective, watertightness can be achieved by using a well-proportioned, low permeability, workable concrete that is properly consolidated and cured. Also, cracking of the concrete must be minimized. Increasingly, waterproofing admixtures, in particular crystalline-based waterproofing admixtures, are being specified for concrete structures where there is a need to minimize water movement through the concrete.


Shrinkage-Reducing and Crack-Reducing Admixtures

The benefits of the durability-enhancing admixtures discussed up to this point can be compromised if the concrete cracks, because cracking will facilitate the ingress of aggressive agents or movement of water through the concrete. Cracking cannot be controlled 100%, but it can be minimized by designing for volume change and also proportioning the concrete for low shrinkage and cracking.

In addition to the traditional methods of reducing drying shrinkage (such as minimizing the total water and paste content of a concrete mixture), shrinkage-reducing admixtures (SRAs) can also be effective. SRAs can reduce drying shrinkage by about 30% to 50% in the long term and provide benefits with respect to the magnitude of curling in slabs-on-ground and cracking overall. Recommended dosages range from 0.5 to 1.5 gal/yd3 and dosages of 0.75 to 1.0 gal/yd3 are typical. In addition to reducing drying shrinkage, a novel crack-reducing admixture (CRA) now available in the marketplace has been shown to provide significantly better performance with respect to the magnitude of cracking and initial crack width, should cracking occur.

Commercially available durability-enhancing chemical admixtures are available today and are very effective. In combination with supplementary cementitious materials, proper concrete mixture proportioning, and good structural design and construction practices, these materials will improve the durability of concrete in aggressive environments.

Dr. Charles Nmai, P.E., is engineering associate/manager, engineering services with BASF Corp.–Admixture Systems, Beachwood, Ohio. He is an ACI Fellow.