Development of Standard Methodology to Measure Sulfate Ions in Post-Tensioned Grouts
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2021-04-01
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Edition:Final Report March 2018 – July 30, 2021
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Abstract:Steel corrosion in the deficient grout however was associated with elevated concentrations of sulfate ions stemming from the adverse influence of excess mix water and grout pre-hydration. There has been discussions for appropriate ways to address sulfate levels in grout including sulfate limits. Various test methodologies can include varying material conditioning procedures including heating, drying, and chemical reactions that can influence the level of sulfate ion aggregation in the test leachate from the initial bulk material. The research sought to identify ion transport mechanisms in and to identify the effects of grout sampling methodologies for deficient grouts. Testing included a proposed inverted-tee test (INT) and a modified incline-tube (MIT) test. It was shown that the different grout products have widely different propensity for segregation and accumulation of sulfate ions, but adverse grout mixing practices such as the addition of 10% mix water above the manufacturer’s recommendation and pre-hydration promoted the development of grout deficiencies including the accumulation of sulfate ions even without external sulfate ion sources. Testing considered the effect of leaching heating, heating time, leaching volume, grout sample mass, and drying temperature. Leaching of larger grout sample mass can yield higher leachate sulfate concentrations, but the concentrations were not commensurate to the larger grout mass. Larger mass to water ratio (1:40) yielded higher leachate and normalized grout mass sulfate concentrations. The sulfate limits expressed as mass relative to the grout sample mass can be implemented to normalize leaching volume and mass size. Current FDOT specifications (30 ppm following current FM 5-618) can be expressed as 3 mgsulfate/ggrout. Assessment of this limit to the corrosion data set developed is consistent with historic data from previous research
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