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Update on PCA R&D 07-10a Investigating the Effect of Potassium Acetate on Concrete Durability Larry Sutter Director, Michigan Tech Transportation Institute. Overview. Work has been performed in the areas: Literature review Repeating previous tests
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Update on PCA R&D 07-10a Investigating the Effect of Potassium Acetate on Concrete Durability Larry Sutter Director, 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
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. Control NaOH KOH Ca(OH)2 K-Ac K-Ac & Ca(OH)2
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