Update on PCA R&D 07-10a Investigating the Effect of

Potassium Acetate on Concrete Durability

Larry SutterDirector, Michigan Tech Transportation Institute

Overview

• Work has been performed in the areas:

– Literature review

– Repeating previous tests

– Exploring effects of KAc on silica solubility

Silica Dissolution Literature Review

• Geology/Geochemical– Dissolution of different silicates in the presence of organic

acids (carboxylates) were covered– In all cases, dissolution rates and/or solubility increased

with the addition of small amounts of OA (0.1 – 0.5 M)– Conditions did not match those found in pore sol’ns but

effect of carboxylate addition were reproducible

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

Silica Dissolution Literature Review

• Steel slag dissolution– One paper described a novel approach dissolving steel

making slags in acetic acid to sequestor CO2 w/ Ca dissolved from slag forming CaCO3

– Reported complete dissolution in a solution of 33% acetic acid and 50°C – both Si and Ca dissolved completely

– Silica gel stability greater at >70°C allowing researchers to filter silica out thereby making higher grade CaCO3

Progress to Date

• Completed modified ASTM C1260 procedure utilizing glass beads for reactive aggregate at 4°C, 20°C and 38°C 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 literature review of silica dissolution which resulted in modification of experimental approach.

New Experimental Approach

• Focusing on silica dissolution as a primary driver since the deicing regime appears to provide conditions for greatly enhanced silica solubility

• Performing solubility tests based upon ASTM C289 - 07 “Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method)”

Modified ASTM C289

• ASTM C289 is a chemical method of evaluating potential reactive aggregates based upon the amount of silica dissolved during a 24 hour digestion at 80° C in 1N NaOH

• Modification of method consists of replacing NaOH with reactant of interest; 1N KOH, saturated Ca(OH)2, as-received KAc deicer and KAc deicer + Ca(OH)2 as well as 1N NaOH

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

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

Control NaOH KOH

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

Polished thin section of carbonate chert, crossed polars.

Control NaOH KOH

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

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

Control NaOH KOH

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

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

Control NaOH KOH

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

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

Control NaOH KOH

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

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

Future work

• Continue studies on KAc effects on silica solubility and dissolution rates

• Spratt aggregate is on-site and being prepared for testing

• Additional aggregates are being identified with particular interest in moderately reactive aggregates (Sioux Quartzite)

• Cement paste alteration studies will continue. A matrix of cements having different properties (alkali content) will be developed and procured for testing

What happens to sand if you put it in 12 molal NaOH sol’n 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.

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.

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.