Stomping the Alkali-Silica Reaction in Concrete

Mitigating the Alkali-Silica Reaction

in Concrete

Pumice-Blended Cement is the Ideal ASR Mitigator: Economical, Consistent, and Highly Effective

Concrete AssassinIn 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.

Flatline ASRThe 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.

Pumice vs. Fly AshFly 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.

The Ideal SCMPumice 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.

CH is a deleterious compound that fuels the alkali-silica reaction. more of this (CSH) means

stronger, denser concrete.

less CH means the alkali-silica reaction is short-circuited.

—American Concrete Institute

“”

Pozzolans are made up of siliceous or siliceous and aluminous materials that, in !nely divided form, will react with calcium hydroxide to form cementitious materials.

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.

Graph Data from University of Utah Study

0 20 30 40 50 60

0.800.700.600.500.400.300.200.100.00LE

NGTH

CHAN

GE (%

)

IMMERSION (Days)

A C C E P T A B L E L I M I T

100%CEMENT

PUMICEBLENDEDCEMENT

ASTM C1293 (modi!ed)

Concrete Mix designs tested according to a modi!ed ASTM C1293 procedure using Type 1 cement and Highly Reactive coarse and !ne aggregate in an accelerated ASR environment (80° C and 1 N NaOH solution) over 50 days.

Graph Data from University of Texas-Austin Study

The pumice SCM concrete mixture kept expansions below the 0.04% limit of ASTM C1293, validating the results found from ASTM C1567 Accelerated Mortar Bar Test for ASR.

ASTM C1293 (modi!ed mix design)

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.


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.


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.

More Pumice-Blended Cement Advantages

Class 3 Sulfate Exposure Qualification


1 of 2

Class 3 Sulfate Exposure Qualification


2 of 2

High Resistance to Chloride Ion Penetration


Compressive Strength

2 of 2

Compressive Strength

1 of 2

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.

*

Pumice as an SCMS U M M A R Y O F

Sulfate Strength Relative Approx. Workability Minimum Exposure Level to OPC Control Price Problems at Replacement at 28 Days per Ton High Dosages? for ASR (%)

PUMICE Class 3 Class 3 90% 91% $126 NO 15%

15% 25% 15% 25% (replacement)

Average ASR Expansion at 24 months15% 25% (replacement)0.022±0.007 0.015±0.001

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.

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.

TELEPHONE: 1.800.767.4701 x 111

EMAIL: [email protected]

WEBSITE: www.asrmitigator.com

DOWNLOAD THE RESEARCH: hesspozz.com/downloads.html

http://hesspozz.com/downloads.html

http://hesspozz.com/downloads.html

Stomping the Alkali-Silica Reaction in Concrete

Engineering

Transcript of Stomping the Alkali-Silica Reaction in Concrete