Report of RILEM TC 281-CCC: outcomes of a round robin on the resistance to accelerated carbonation of Portland, Portland-fly ash and blast-furnace blended cements

Abstract

Many (inter)national standards exist to evaluate the resistance of mortar and concrete to carbonation. When a carbonation coefficient is used for performance comparison of mixtures or service life prediction, the applied boundary conditions during curing, preconditioning and carbonation play a crucial role, specifically when using latent hydraulic or pozzolanic supplementary cementitious materials (SCMs). An extensive interlaboratory test (ILT) with twenty two participating laboratories was set up in the framework of RILEM TC 281-CCC ‘Carbonation of Concrete with SCMs’. The carbonation depths and coefficients determined by following several (inter)national standards for three cement types (CEM I, CEM II/B-V, CEM III/B) both on mortar and concrete scale were statistically compared. The outcomes of this study showed that the carbonation rate based on the carbonation depths after 91 days exposure, compared to 56 days or less exposure duration, best approximates the slope of the linear regression and those 91 days carbonation depths can therefore be considered as a good estimate of the potential resistance to carbonation. All standards evaluated in this study ranked the three cement types in the same order of carbonation resistance. Unfortunately, large variations within and between laboratories complicate to draw clear conclusions regarding the effect of sample pre-conditioning and carbonation exposure conditions on the carbonation performance of the specimens tested. Nevertheless, it was identified that fresh and hardened state properties alone cannot be used to infer carbonation resistance of the mortars or concretes tested. It was also found that sealed curing results in larger carbonation depths compared to water curing. However, when water curing was reduced from 28 to 3 or 7 days, higher carbonation depths compared to sealed curing were observed. This increase is more pronounced for CEM I compared to CEM III mixes. The variation between laboratories is larger than the potential effect of raising the CO 2 concentration from 1 to 4%. Finally, concrete, for which the aggregate-to-cement factor was increased by 1.79 in comparison with mortar, had a carbonation coefficient 1.18 times the one of mortar. Supplementary Information The online version contains supplementary material available at 10.1617/s11527-022-01927-7.

Model fitting to concrete carbonation data with non-zero initial carbonation depth

“…Vanoutrive et al [15] observed a statistically significant difference between carbonation of different faces depending on casting orientation. This was also observed in [19], when comparing trowelled (top) and non-trowelled (bottom) surfaces.…”

“…Non-uniformity of carbonation fronts leads to large uncertainty in measured carbonation depths, meaning that variability of the carbonation coefficient from experimental results can also be large, even if taken from the same specimens. The stability of the coefficient has also been found to depend on the duration of the test [15]. In these instances, the variability in K due to choice of linear or non-linear approach may be insignificant when compared to the expected variability in the value.…”

“…These tests are conducted in a variety of laboratory controlled and natural exposure conditions, and can be accelerated by increasing the concentration of CO 2 . Many standards for accelerated test conditions exist, including [11][12][13][14], conditions of which are summarised in [15]. Correctly interpreting results of tests such as these is of importance to performance-based specification of concrete mixes as they enable quick prediction of carbonation behaviour in real-world conditions to be generated [13,14], which can then be used for probabilistic design against failure.…”

“…Acknowledgements The authors acknowledge the financial support of the Engineering and Physical Sciences Research Council (grant numbers EP/N017668/1 and EP/N509620/1).The authors are grateful to the Hanne Vanoutrive, Andreas Leemann, Fritz Hunkeler and their co-authors for the additional experimental data used in this analysis. Where raw data from [21] and [15] was not publicly available, the carbonation depth results were provided by the original authors and used to calculate K values with permission (A. Leemann, personal communication, September 23, 2022),(H. Vanoutrive, personal communication, October 4, 2022).…”

Report of RILEM TC 281-CCC: Insights into factors affecting the carbonation rate of concrete with SCMs revealed from data mining and machine learning approaches

“…However, this information is not available in most cases. It has to be considered that repeatability and reproducibility of the test itself contribute to the scatter (see [51] and section 2).…”