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Based on systematic analysis, evaluation and synthesis of a 30 000 strong data matrix generated from 213 studies from 33 countries published since 1968, this paper details the extent of research that has been undertaken and discusses the effect of fly ash (FA) on the carbonation and carbonation-induced corrosion of concrete. It is shown that FA as a cement component, such as those adopted in BS EN 197-1:2011, increases the carbonation rate of concrete, both when concrete is designed in terms of equal water/cement ratio or strength, though with the latter to a lesser extent. This increase in carbonation has also been confirmed for in-service concrete. The net effect of FA content on the carbonation of concrete is dependent upon the combination of mix design, curing and exposure related parameters. FA in concrete is also shown to increase the corrosion of reinforcement, which can only be overcome by increasing the cover to reinforcement, concrete strength, or a combination of the two, beyond those specified in standards such Eurocode 2, BS EN 206-1:2013 and BS 8500. Contrary to the commonly held view, this study shows that the relative rate of carbonation of FA concrete with reference to corresponding Portland cement concrete remains similar under accelerated and natural carbon dioxide exposures.

This paper describes the shrinkage of concrete made with recycled aggregates derived from demolition of concrete structures and is based on the 18 500 data matrix generated from 286 studies published in English from 38 countries since 1978. Relative to natural aggregates, the shrinkage of concrete increases at a decreasing rate with coarse recycled concrete aggregate content, giving an average increase of 33% at 100% natural aggregate replacement. This difference between the performance of the two concretes decreases with increasing ambient humidity and concrete strength. Increase in concrete shrinkage with fine and all-in recycled concrete aggregate and other recycled aggregates was found to be too high and variable to make them unsuitable for use in structural concrete. The assessment of the Eurocode 2 (2004), ACI 209·2R (2008) and Bažant-Baweja B3 (2000) models showed that, although the accuracy of the three models is similar, the shrinkage of concrete containing coarse recycled concrete aggregate is generally underestimated. Methods are proposed for determining the shrinkage of concrete made with coarse recycled concrete aggregate together with using Eurocode 2, as well as for minimising its effect on the shrinkage of concrete for a given strength and workability by reducing its cement paste content.

This study presents an analysis of a 30 000 strong data matrix derived from 227 studies originating from 35 countries since 1968. Similar to the fly ash effect, the carbonation of concrete increases with the incorporation of ground granulated blast-furnace slag (GGBS), but the rate increases as GGBS content is increased. This effect is greater for concrete designed on an equal water/cement (w/c) basis to the corresponding Portland cement (PC) concrete than on an equal strength basis. The Eurocode 2 specification for XC3 carbonation exposure in terms of the characteristic cube strength of concrete (or its w/c ratio) may need to be increased (or decreased) with the addition of GGBS. Other influencing factors, including GGBS fineness, total cement content and curing, were also investigated. In some cases, the carbonation of in-service GGBS concrete has been estimated to exceed the specified cover before 50 years of service life. Measures to minimise the carbonation of GGBS concrete are proposed. Fully carbonated reinforced GGBS concrete is assessed to show a higher corrosion rate. In relation to PC concrete, the carbonation of GGBS concrete is essentially similar when exposed to 3-5% carbon dioxide accelerated or indoor natural exposure, and the conversion factor of 1 week accelerated carbonation equal to 0·6 year is established. Introduction BackgroundGround granulated blast-furnace slag (GGBS), a by-product of iron manufacture, because of its latent hydraulic nature requires alkali activation, from Portland cement (PC) for example. Indeed, the use of GGBS in combination with PC in concrete (GGBS concrete) has long been acknowledged. The first blast-furnace slag cement works was opened in Germany in 1865 and specifications for GGBS use with PC began to appear in Germany towards the end of the nineteenth century and in the UK during the early part of the twentieth century (BSI, 1923). The allowable proportion of GGBS as a cement component increased from about 30% in the 1910s to 90% in the 1970s (BSI, 1968).With sustainability increasingly an issue, and sustainable construction materials seen as central to the sustainability agenda, the use of increasingly high proportions of GGBS in attempts to reduce the carbon dioxide footprint of cement used in construction has become attractive. Its use is now covered by all the major standards, such as BS EN 197-1 (BSI, 2011), and permissible GGBS content can be as high as 95% (known as CEM III/C cement).Notwithstanding the above, as durability forms a major element of concrete specification and is directly connected with sustainable construction, issues related to durability need to be carefully examined. In terms of chemical composition, GGBS can be assumed to improve the resistance of concrete to chloride ingress (and thereby reduce the risk of reinforcement corrosion), sulfate attack and alkali-silica reaction. However, despite the great deal of research undertaken, with 227 published papers in the English medium from 35 countries mainly since 1985, consensus on the effec...