Stomping the Alkali-Silica Reaction in Concrete
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Pumice-blended cement is identified as an effective and economical solution to mitigate the alkali-silica reaction (ASR) in concrete, which can threaten structural integrity. Research from various universities demonstrates that pumice minimizes ASR expansion and enhances overall concrete performance through a pozzolanic reaction that converts harmful compounds into beneficial ones. This innovative approach addresses regulatory challenges regarding fly ash availability, making pumice a viable supplementary cementing material for resilient concrete construction.
Stomping the Alkali-Silica Reaction in Concrete
- 1. Mitigating the Alkali-Silica Reaction in Concrete Pumice-Blended Cement is the Ideal ASR Mitigator: Economical, Consistent, and Highly Effective
- 2. Concrete Assassin In regions with reactive aggregate, the alkali-silica reaction (ASR) is a relentless concrete assassin. There is no way to stop ASR once such chemically-flawed concrete has been placed; no way to contain the slow-motion explosion that map- cracks the concrete and destroys its structural integrity. An infected structure is doomed to fail well before its engineered lifespan.
- 3. Flatline ASR The only way to beat ASR is to account for it in the concrete mix design. That means specifying a supplementary cementing material (SCM) that will short-circuit the ASR chemical train wreck that is triggered by the union of alkali and calcium hydroxide (CH) from the Portland cement, silica from the reactive aggregate, and moisture.
- 4. Pumice vs. Fly Ash Fly ash has long been used as a cheap by-product pozzolan in concrete and has proven effective at mitigating ASR. Tightening EPA regulations on the coal-fired power industry are disrupting the supply of class F fly ash and driving the need to identify a viable SCM alternative.
- 5. The Ideal SCM Pumice is a pozzolan, igniting a secondary reaction within curing concrete that consumes trouble- making CH and repurposes it into a chemical compound (CSH) that fortifies and densifies the concrete matrix. Win-win: ASR is flatlined and overall concrete performance is significantly improved.
- 6. CH is a deleterious compound that fuels the alkali-silica reaction. more of this (CSH) means stronger, denser concrete. lessCHmeansthealkali-silicareactionisshort-circuited. —AmericanConcreteInstitute “ ” Pozzolans are made up of siliceous or siliceous and aluminous materials that, in finely divided form, will react with calcium hydroxide to form cementitious materials.
- 7. Quantifiable ASR- Mitigating Performance Backed by ASTM-standard research, pumice-blended cement proves to be an effective mitigator of the alkali-silica reaction. University of Utah research quantified the performance of pumice-blended cement, including its ability to mitigate ASR. University of Texas at Austin, on behalf of Texas DOT, used Hess Standard Pozz in a two-year study to determine viable commercial SCM alternatives to fly ash in concrete.
- 8. Graph Data from University of Utah Study 0 20 30 40 50 60 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 LENGTHCHANGE(%) IMMERSION(Days) A C C E P T A B L E L I M I T 100% CEMENT PUMICE BLENDED CEMENT ASTMC1293(modified) Concrete MixdesignstestedaccordingtoamodifiedASTMC1293procedureusingType1cementandHighly Reactive coarse andfineaggregateinanacceleratedASRenvironment(80°Cand1NNaOHsolution)over50days.
- 9. Graph Data from University of Texas-Austin Study ThepumiceSCMconcrete mixturekeptexpansionsbelowthe0.04%limitofASTMC1293,validatingtheresults foundfromASTMC1567AcceleratedMortarBarTestforASR. ASTMC1293(modifiedmixdesign)
- 10. Additional Mitigating Factors Reduces the pH of the concrete pore solution by entrapping free alkalis—further squelching ASR. The pozzolanic reaction tightens the concrete matrix to block and control moisture infiltration. What little alkali-silica gel that may form is denied moisture and cannot swell.
- 11. Additional Mitigating Factors The pozzolanic reaction provides for a denser, stronger concrete that is more resistant to the expansive pressure caused by any remaining ASR gel. Allows for use of the standard Portland cement (instead of low-alkali type) and locally-sourced aggregate, reactive or otherwise.
- 12. Additional Mitigating Factors The consistent chemical makeup and performance of pumice-blended cement provides a cost advantage as well as additional benefits to concrete performance and durability that go beyond simply mitigating ASR.
- 14. Class 3 Sulfate Exposure Qualification More Pumice-Blended Cement Advantages 1 of 2
- 15. Class 3 Sulfate Exposure Qualification More Pumice-Blended Cement Advantages 2 of 2
- 16. High Resistance to Chloride Ion Penetration More Pumice-Blended Cement Advantages
- 19. Coefficient of Thermal Expansion * These experiments were conducted to ensure that the pozzolans did not have any detrimental effects on the CoTE value of concrete. *
- 20. Pumice as an SCM S U M M A R Y O F Sulfate StrengthRelative Approx. Workability Minimum ExposureLevel toOPCControl Price Problemsat Replacement at28Days perTon HighDosages? forASR(%) PUMICE Class3 Class3 90% 91% $126 NO 15% 15% 25% 15% 25%(replacement) AverageASRExpansionat24months 15% 25%(replacement) 0.022±0.007 0.015±0.001
- 21. Pumice is the Original Pozzolan The Romans made impressively strong and enduring concrete— stuff with a lifespan of centuries instead of mere decades, like our modern concrete. The magic performance ingredient in Roman Concrete? Pumice.
- 22. ASR Miti•GatorTM The ASR Miti•Gator product is a pure pumice SCM refined from the Hess Pumice deposit in southeast Idaho USA—the purest commercial deposit of white pumice in the world. Used as a percentage of cement replacement, it mitigates ASR and improves concrete performance overall for an economical pennies-per-yard.
- 23. TELEPHONE: 1.800.767.4701 x 111 EMAIL: brian@hesspumice.com WEBSITE: www.asrmitigator.com DOWNLOAD THE RESEARCH: hesspozz.com/downloads.html