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NRMCA Releases Report on Chloride Limits for Reinforced Concrete

Article provided by the National Ready Mixed Concrete Association

Silver Spring, MD – July 17, 2017 – The National Ready Mixed Concrete Association in collaboration with Dr. Neal Berke with Tourney Consulting Group has completed a research project titled Evaluation of Chloride Limits for Reinforced Concrete Phase A. The research, conducted at NRMCA and Tourney laboratories, was to establish a relationship between the calculated total (initial) chloride content and the measured water-soluble chloride content in hardened concrete at a later age. The ACI 318 Building Code prescribes limits on water-soluble chlorides for concrete.

Concrete mixtures evaluated in this study included Type II and Type V portland cement, Class C and Class F fly ash, silica fume and slag cement. Mixtures with varying water-cementitious materials ratio were evaluated. The initial chloride content of the mixtures was varied between the background amount up to 2% by weight of cementitious materials by adding controlled amounts of calcium chloride. The initial chloride content was verified by measuring the acid soluble chloride content in accordance with ASTM C1152. The water-soluble chlorides were measured at an age between 28 and 42 days in accordance with ASTM C1218, as required by ACI 318-14.

In each case, the measured water-soluble chlorides were less than the initial calculated chloride content and measured acid-soluble chloride content. The estimated initial chloride content determined by calculation of the chloride content of concrete materials and the concrete mixture proportions can be used to ensure that proposed mixtures will conform to the chloride limits stated in the Building Code and specifications. This permits the concrete producer to make adjustments to the mixture before the submittal rather than dealing with measured test results during the project. The research study supports a code change proposal to ACI 318 to permit the calculated total chloride to document conformance with the chloride limits in the Code.

This research work was funded by the RMC Research & Education Foundation and the ACI Concrete Foundation. The complete report can be downloaded here.

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