Accelerated and natural carbonation of concretes with internal curing and shrinkage/viscosity modifiers

Abstract

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.

Sustainability-based decision support framework for choosing concrete mixture proportions

“…where, 400 and 10000 ppm are the CO 2 concentrations in the environment and accelerated conditions, respectively. The factor of 1.47 is similar to those obtained by previous researchers for other tropical climates [29,30]. Such region or climate dependent factors could be used to convert short-term accelerated carbonation data to the natural carbonation coefficients.…”

“…Since this would require several years of measurements, it is more practical to determine an accelerated carbonation coefficient, k CO2,accl , from tests conducted in the laboratory under high CO 2 concentrations. A suitable conversion factor to obtain k CO2,nat from k CO2,accl could be used, if available for the relevant environmental conditions; conversion factors reported in literature range from 0.07 to 0.5 [26][27][28][29][30], depending on the CO 2 concentrations in the accelerated and natural environments, and the climatic conditions. In this study, concrete prisms of 100 9 100 9 500 mm were cured for 28 days in a moist room followed by 14 days of air-curing at the temperature and relative humidity of 25°C and 65% R.H., respectively, after which they were subjected to 1% CO 2 concentration in a chamber having the same conditions.…”

Blending organic material with municipal solid waste incinerator bottom ash to promote in-situ carbonation in road base

“…The mean pH of the control BA sample was 12.07 initially, and decreased to 9.78 by the end of the 63-day experiment. It is well-known that carbon dioxide results in carbonation (Chimenos et al, 2000; Durán-Herrera et al, 2015; Forteza et al, 2004), and this result confirms previous findings that BA is carbonated naturally by atmospheric carbon dioxide. The pH of the blended samples followed a similar trend as the control BA sample at the beginning of the experiment.…”

Effect of concrete carbonation on natural frequency of reinforced concrete beams

“…Changes in modal damping ratio were inconsistent with the changes in frequencies. According to the results from previous research (Duran-Herrera et al, 2015; Silva et al, 2014), carbonation itself does not degrade the concrete strength. However, it decreases the alkalinity of the concrete and, thus, depassivates the passive layer of steel reinforcement there.…”