Various Durability Aspects of Calcined Kaolin-Blended Portland Cement Pastes and Concretes

Abstract

The use of calcined clay, in the form of metakaolin (MK), as a pozzolanic constituent for concrete has received considerable attention in recent years, due to the lower CO 2 emission of this supplementary cementitious material compared to the production of a classic portland cement. Furthermore, concretes incorporating MK show some improve durability properties. In this paper, the durability of concretes and cement pastes with MK as partial replacement of cement (10 and 25 %) has been investigated in comparison with CEM-I materials one. Water porosity, chloride migration and diffusion, electrical resistivity and natural and accelerated carbonation tests have been performed. In addition, microstructural study is performed to better understand the results on the durability indicators. The cement pastes microstructure was characterized not only by usual techniques such as mercury intrusion porosimetry, XRD and TGA-DTA, but also by 29 Si and 27 Al NMR spectroscopy. For example, Friedel's salt (chemical binding) has been quantified by 27 Al NMR spectroscopy and XRD on cement paste. In addition, the progress of the durability properties for various water curing times has been investigated. Results show an evolution of the properties, as a function of the cement replacement degree by MK, such replacement increases durability against chloride penetration but decreases resistance to carbonation. The aluminate phases equilibrium is modified in concrete with metakaolin in comparison with a CEM-I one. Both chemical and physical chloride binding increases with MK replacement. In addition, since portlandite quantity decreases in cement materials with MK, these materials are less resistant to carbonation process for a same exposure condition (time and CO 2 concentration).

Effect of supplementary cementitious materials on carbonation of cement pastes

“…Consequently, it is not obvious to understand why ettringite would be more stable than AFm phases in these conditions. Moreover, it is well known that AFm phases can react with carbonates (CO3 2-) to form monocarboaluminates [4], [36][37][38][39]. However, in the present study, XRD showed no ettringite or monocarboaluminate in TC samples in comparison to Ref samples (figure 6).…”

“…When polymerizing, the C-S-H chains release water and this water is probably evaporated during the time in carbonation chamber (RH 65% and T=20°C). Consequently, there is probably a coupling effect between carbonation and drying as reported [39,40] and it will be discussed in the following section. 29 Si NMR.…”

Use of metakaolin as supplementary cementitious material in concrete, with focus on durability properties

“…[44] also associated the phenomenon with the metakaolin pozzolanic reaction, which consumed CH responsible for slowing the carbonation rate. A similar argument was provided by Saillio et al [45], who showed a trend of CH decrease and carbonation depth increase with increasing metakaolin content and exposure time.…”

Calcined Clay as Supplementary Cementitious Material

“…Quite a large group of papers on durability are focused on cement systems with calcined kaolin. Saillio et al [ 202 ], as well as Yazıcı [ 203 ], have analysed various aspects of the durability of concrete and mortars produced with metakaolin addition. Tafraoui et al [ 204 ] gave a brief literature review on the durability of ultra-high performance concrete containing metakaolin.…”