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Update on PCA R&D 07-10a

Investigating the Effect ofPotassium Acetate on Concrete

Durability

Larry Sutter

Director, Michigan Tech

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Overview

Work has been performed in the areas:

Literature review

Repeating previous tests

Exploring effects of KAc on silica solubility

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Silica Dissolution Literature Review

Geology/Geochemical

Dissolution of different silicates in the presence of organicacids (carboxylates) were covered

In all cases, dissolution rates and/or solubility increased

with the addition of small amounts of OA (0.10.5 M)

Conditions did not match those found in pore solns but

effect of carboxylate addition were reproducible

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Silica Dissolution Literature Review

Industrial water treatment

Colloidal silica (analogous to reactive aggregate) deposits

commonly foul process cooling water circuits

Several treatment methods for the removal of silica use

carboxylates (formates and acetates) to dissolve silica

Polycarboxylates having one to five acetate groups are very

effective

Increased pH serves to increase solubility even more

Carboxylates increase the solubility limit of silica and also

increases the dissolution rate

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Silica Dissolution Literature Review

Steel slag dissolution

One paper described a novel approach dissolving steelmaking slags in acetic acid to sequestor CO2w/ Ca

dissolved from slag forming CaCO3

Reported complete dissolution in a solution of 33% acetic

acid and 50Cboth Si and Ca dissolved completely

Silica gel stability greater at >70C allowing researchers to

filter silica out thereby making higher grade CaCO3

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Progress to Date

Completed modified ASTM C1260 procedure utilizing

glass beads for reactive aggregate at 4C, 20Cand 38C with similar results to previous work

Although ASTM C1260 tests were reproducible

they do not align with observed distress

Upon review of ASR chemistry, performed literaturereview of silica dissolution which resulted in

modification of experimental approach.

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New Experimental Approach

Focusing on silica dissolution as a primary driver since

the deicing regime appears to provide conditions forgreatly enhanced silica solubility

Performing solubility tests based upon ASTM C289 - 07

Standard Test Method for Potential Alkali-Silica

Reactivity of Aggregates (Chemical Method)

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Modified ASTM C289

ASTM C289 is a chemical method of evaluating

potential reactive aggregates based upon theamount of silica dissolved during a 24 hour digestion

at 80C in 1N NaOH

Modification of method consists of replacing NaOHwith reactant of interest; 1N KOH, saturated Ca(OH)2,

as-received KAc deicer and KAc deicer + Ca(OH)2as

well as 1N NaOH

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Modified ASTM C289

Both solids and solutions are being characterized

full solution chemistries via XRF

solids by optical and SEM analyses with elemental

mapping.

Using local reactive chert for aggregate tests

Potential paste alteration is being evaluated with

tests conducted on neat cement paste

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C289 Test Progress

Three test have been performed with reactive chert

Solutions are at lab for analysis

Solids are being analyzed, preliminary results follow

One neat cement paste run has been completed.

Solutions are awaiting shipment to lab. Solids are

being analyzed

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Control NaOH KOH

Ca(OH)2 K-Ac K-Ac & Ca(OH)2

Polished thin section of carbonate chert, crossed polars.

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Control NaOH KOH

Ca(OH)2 K-Ac K-Ac & Ca(OH)2

Polished thin section of carbonate chert, SEM EDXelemental map for silicon.

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Control NaOH KOH

Ca(OH)2 K-Ac K-Ac & Ca(OH)2

Polished thin section of carbonate chert, SEM EDXelemental map for calcium.

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Control NaOH KOH

Ca(OH)2 K-Ac K-Ac & Ca(OH)2

Polished thin section of carbonate chert, SEM EDXelemental map for potassium.

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Control NaOH KOH

Ca(OH)2 K-Ac K-Ac & Ca(OH)2

Polished thin section of carbonate chert, SEM EDXelemental map for sodium.

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Future work

Continue studies on KAc effects on silica solubility anddissolution rates

Spratt aggregate is on-site and being prepared for testing

Additional aggregates are being identified with particular

interest in moderately reactive aggregates (SiouxQuartzite)

Cement paste alteration studies will continue. A matrixof cements having different properties (alkali content)

will be developed and procured for testing

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What happens to sand if you put it in 12 molal NaOH soln at 200 C?

JENDOUBI F., MGAIDI A., EL MAAOUF M., The Dissolution Kinetics of Sand as Function of Particle Size,

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, VOLUME 76, p. 233-238, 1998.

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5 minutes later.

JENDOUBI F., MGAIDI A., EL MAAOUF M., The Dissolution Kinetics of Sand as Function of Particle Size,

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, VOLUME 76, p. 233-238, 1998.

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50 minutes later.

JENDOUBI F., MGAIDI A., EL MAAOUF M., The Dissolution Kinetics of Sand as Function of Particle Size,

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, VOLUME 76, p. 233-238, 1998.