Accelerated and natural carbonation of concretes with internal curing and shrinkage/viscosity modifiers
In many parts of the world, corrosion of reinforcing steel in concrete induced by carbonation of the concrete continues to be a major durability concern. This paper investigates the accelerated and natural carbonation resistance of a set of seven concretes, specifically evaluating the effects of internal curing and/or shrinkage/viscosity modifiers on carbonation resistance. In addition to five different ordinary portland cement (OPC) concretes, two concretes containing 20 % of a Class F fly ash as replacement for cement on a mass basis are also evaluated. For all seven concrete mixtures, a good correlation between accelerated (lab) and natural (field) measured carbonation coefficients is observed. Conversely, there is less correlation observed between the specimens’ carbonation resistance and their respective 28 days compressive strengths, with the mixtures containing the shrinkage/viscosity modifier specifically exhibiting an anomalous behavior of higher carbonation resistance at lower strength levels. For both the accelerated and natural exposures, the lowest carbonation coefficients are obtained for two mixtures, one containing the shrinkage/viscosity modifier added in the mixing water and the other containing a solution of the same admixture used to pre-wet fine lightweight aggregate. Additionally, the fly ash mixtures exhibited a significantly higher carbonation coefficient in both exposures than their corresponding OPC concretes.
KeywordsAccelerated testing Carbonation Fly ash Internal curing Natural exposure Viscosity modifier
The authors would like to express their gratitude to the National Council of Science and Technology of Mexico (CONACYT) for the scholarships received by De-Los-Santos and Vázquez for their MsC studies at UANL, to the Scientific and Technological Research Support Program of the UANL (PAICYT) and to CONACYT project number 155363 for the complementary economical support for this project. The authors also thank Charles K. Nmai from BASF Corporation, USA, and Daniel Canizales from BASF Mexico for providing the shrinkage-reducing admixture and the high range water reducer, respectively.
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