Carbonation resistance of GGBS concrete

Abstract

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...

Influence of loading and cracks on carbonation of RC elements made of different concrete types

“…It is important to highlight that these mixes did not have equal strength and that the rank order is likely to different when based on comparative strength rather than w/b. suggested that the carbonation resistance of GGBS concretes is lower than that of PC concretes with a similar w/b ratio, especially when the GGBS content is greater than 20% [Lye et al 2016]. However, according to several studies, concretes with 50% GGBS content have more or less the same carbonation resistance as PC concretes with a similar w/b ratio [Osborne 1992, Polder et al 2014 or similar strength grade [Bamforth 2004, Bouzoubaa andFoo 2005].…”

“…In particular, it has been observed that 'green' concretes containing SCM, particularly where Portland cement is directly replaced, can have lower resistance to carbonation than traditional ones (e.g. [Papadakis 2000, Khunthongkeaw et al 2006, Lye et al 2015, Lye et al 2016). More recently, the positive effect of carbonation on the CO2 balance of the concrete industry has also attracted attention of researchers (e.g.…”

“…[Sanjuan et al 2003, Castellote et al 2009, Visser 2014, Cui et al 2015). Although full consensus has not been reached, it has been recommended to keep the partial pressure of CO2 between 3%-5%, in order to obtain results similar to natural conditions; in particular, this has been shown for 'green' concretes containing fly ash and blast furnace slag [Lye et al 2015, Lye et al 2016. Among the factors which affect the rate of carbonation, loading and associated cracking have received limited attention and most research has been restricted to Portland cement concretes and effects of tensile stresses caused by static and cyclic loading [Castel et al 1999, Alahmad et al 2009, Jiang et al 2015.…”

The development of a low carbon binder produced from the ternary blending of cement, ground granulated blast furnace slag and high calcium fly ash: An experimental and statistical approach

“…However, the presence of GGBS in high content could lead to increasing the depth of carbonation due to the reduced calcium hydroxide produced during hydration [26,27]. Therefore, in order to produce a ternary blended cement with better performance than binary blending of GGBS-OPC cement, High Calcium Fly Ash (HCFA), a waste material that is produced from the burning process in local power plants, has been used in addition to OPC and…”

Durability Design Method Considering Reinforcement Corrosion due to Water Penetration

“…It is assumed that the standard curing described in Section 4.7 is applied on site. So far, for some cases, the durability design for carbonation led to excessive cover thickness when blended cement was used because a larger carbonation depth has been reported in concrete involving blended cement (Horiguchi et al 1994;Lye et al 2015Lye et al , 2016. The durability design for water penetration can avoid such problems, and the performance of the blended cement can thus be appropriately evaluated.…”