Structural Effects of ASR on Concrete Structures

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Extensive mapped crack on the surface of concrete structures can be a scary observation for public, or even most structural engineers. There is a common belief among material and structural engineers that the Alkali Silica Reaction (ASR) is always harmful for a concrete structure. It is scary to drive under a ASR affected bridge. Despite this observation and speculation, no major collapse has been reported as a result of ASR cracking. In this article, we will briefly review the structural effects of ASR on concrete structures.

Structural Effects of ASR on Concrete Structures

Structural Effects of ASR on Concrete Structures

The following summarizes the effects of ASR on structural properties of concrete:

* Expansion

The swelling nature of ASR gel increases the chance of expansion in concrete elements.

* Compressive Strength

The effect of ASR on compressive strength can be minor for low expansion levels, to relatively higher degrees at larger expansion. (Swamy R.N 1986) points out that the compressive strength is not very accurate paramater to study the severity of ASR; however, the test is done because of its simplicity.

* Tensile Strength / Flexural Capacity

Researches show that ASR cracking can significantly reduce the tensile strength of concrete; therefore reducing the flexural capacity of beams. Some research on bridge structures indicate about 85% loss of capacity as a result of ASR.

* Modulus of Elasticity/UPV

The effect of ASR on elastic properties of concrete and ultrasound pulse velocity (UPV) is very similar to tensile capacity. The modulus of elasticity is shown to be more sensitive to ASR than pulse velocity.

* Fatigue

ASR reduces the load bearing capacity and the fatigue life of concrete (Ahmed T 2000).

* Shear

ASR enhances the shear capacity of reinforced concrete with and without shear reinforcement (Ahmed T 2000).

Summary

As we see, ASR can generally impact major structural properties of concrete, however, it can sometime improve the structural response. The following presents two contradictory effects of ASR cracking:

1- A wide range of results were reported from negligible changes to significant improves for failure load of reinforced ASR-affected reinforced beams in comparison with non-ASR affected beams. An improvement up to 1.5 times of non-ASR affected reinforced beams has been observed. Such improvements are related to a self-prestressing effect named “hogging effect”. This is because of the concrete expansion difference between the tension and compression zones. Even strength improvements in shear strength of ASR affected deep concrete beams have been reported.

2- ASR cracks provide direct paths for the penetration of severe ions into concrete such as chloride ions of deicing slats. These severe ions can speed up the corrosion of steel rebar within concrete. In other words, ASR cracks eliminate the protective effect of concrete cover.

Public Safety Comes First

Despite the fact that the ASR affected reinforced elements have demonstrated no significant capacity decrease, the public safety is not compromised. It is risky to pass under an overhead ASR affected structure because of the risk of spalling of cracked concrete. Precautionary measures should be performed to minimize such risks even though ASR can strength the structure from the structural point of view.


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6 thoughts on “Structural Effects of ASR on Concrete Structures

  • Hi. Thanks for the informative post. I have been a specialist concrete repair and protective applicator for the past 25 years. ASR is a major problem with so many structures built about 20 year’s ago and even the new ones not being protected. Concrete is not waterproof and moisture in the concrete is causing most of the problem. Seal the concrete and solve the problem. I have been applying Hydrogel and Silane coatings for years with great success in sealing the structures. I have been working on an application method of application in the tidal zone and under water and recently succeeded in doing so. We can now solve the permeability issues above and below water. Let me know if you have any interest in this application method. Thanks again for your interesting post

    • i’m interested in the application of sealing corroded part of reinforced concrete above the roof slab of my building.
      i thank you for your advice in naming the best material used and the procedure to be followed in doing this treatment

  • La investigación es muy Interesante; en Perú tienen representante técnico?? Podrían enviar información en español

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