Page 480 - New Trends in Eco efficient and Recycled Concrete

430 New Trends in Eco-efficient and Recycled Concrete

14.2.5 X-ray diffraction

X-ray diffraction (XRD) renders information on the structure and chemical compo-
sition of crystalline phases, based on the scattered intensity and direction of an
X-ray beam striking the sample (Parrish, 1993). Since concrete systems contain
crystalline aggregates and a variety of crystalline and partially crystalline phases,
XRD is one of the most prominent analytical techniques for their analysis (Tabikh
and Weht, 1971; Christensen et al., 2003; Snellings et al., 2014). The main advan-
tages of XRD analysis application to cement-based materials are the ease and speed
of measurement and its accuracy compared to traditional phase analysis methods
(Snellings et al., 2014). Only a small sample is required, either in the form of finely
ground powder or as a solid section (Parrish, 1993). XRD analysis is fundamental
for the identification of cement phases, aggregates and supplementary cementing
components, to distinguish between mixtures and various types of solid solutions
and polymorphs, and to distinguish between amorphous and crystalline states
(Parrish, 1993) and renders knowledge of chemical reactions occurring in the syn-
thesis and hydration of cements (e.g., Christensen et al., 2003; Guedes et al., 2013;
Setina et al., 2013; Abo-El-Enein et al., 2014; Colombo et al., 2018). In recent
years, the use of XRD in concrete research further extended based on the develop-
ment of quantitative analysis tools that allow to estimate phases fraction in concrete
with high accuracy (Whitfield and Mitchell, 2003; Scrivener et al., 2004b; Korpa
et al., 2009; Snellings et al., 2014; Roychand et al., 2017). Another breakthrough
arose with the possibility of online investigation of the phases present over time
using synchrotron radiation (Christensen et al., 2003; Raki et al., 2003; Snellings
´
et al., 2010; Schlegel et al., 2012; Alvarez-Pinazo et al., 2014). Synchrotron X-ray
radiation computed micro-tomography has also been used by several researchers to
directly examine the three-dimensional internal microstructure of cement and con-
crete, including phases distribution, pore structure and the ITZ (e.g., Bentz, 2007;
Promentilla et al., 2008; Landis et al., 2016).

14.2.6 Mercury intrusion porosimetry
Pore structure characteristics comprising pore fraction, size distribution, tortuosity
and connectivity, play a key role on the engineering properties of cement-based
materials (Cnudde et al., 2009). In this context, a variety of experimental techniques
are used for its characterisation, including BET specific surface area, NMR spec-
troscopy, small-angle neutron scattering, X-ray micro-tomography and BSE image
analysis of polished sections (Promentilla et al., 2008; Cnudde et al., 2009; Pˇ rikryl,
2015). However, the most well-established and thoroughly used technique is mer-
cury intrusion porosimetry (MIP) (Abell et al., 1999; Katrin and Dirk, 2006;
Guedes et al., 2013; Ru ¨bner et al., 2015; Wenzel et al., 2017) despite its well-
known limitations when applied to materials with irregular pore geometry such as
concrete (Abell et al., 1999; Kumar and Bhattacharjee, 2003; Bonen, 2006). MIP is
a simple and quick indirect technique where mercury is forced into the pores of the
sample by gradually increasing intrusion pressure; at each discrete pressure