Pozzolanic reactivity of a calcined interstratified illite/smectite (70/30) clay. (January 2016)

• Record Type: Journal Article
• Authors: Garg, Nishant; Skibsted, Jørgen
• Is Part Of: Cement and concrete research. Volume 79(2016)
• Page Start: 101
• Page End: 111
• Publication Date: 2016-01
• Subjects: Thermal treatment (A) -- Blended cement (D) -- Amorphous material (B) -- Spectroscopy (B) -- Quartz; Cement -- Periodicals; Cement -- Research -- Periodicals; Concrete -- Periodicals; Concrete -- Research -- Periodicals; Ciment -- Périodiques; Béton -- Périodiques; Cement; Concrete; Periodicals; 620.135
• DOI: 10.1016/j.cemconres.2015.08.006
• Languages: English
• ISSNs: 0008-8846

Abstract

Abstract: Calcined clays can be potential supplementary cementitious materials if effects of heat-treatment on their structure and reactivity are understood. This work reports structural characterization of an interstratified illite/smectite clay, including a quartz impurity, upon heating using 27 Al and 29 Si MAS NMR spectroscopy and ICP-OES analysis. During dehydroxylation (600–900 °C) the Q 3 -type SiO4 sites become disordered and octahedral AlO6 sites transform into tetrahedral sites, resulting in an amorphous material with substantial pozzolanic properties, as demonstrated by reactivity tests and hydration studies of a Portland cement–calcined clay blend. At higher temperatures (above 950 °C), inert Q 4 -type phases crystallize which radically reduce the reactivity. At optimum calcination temperature (900 °C), the amorphous material contains highly dissolvable elemental species as seen from complementary ICP-OES analysis. The quartz impurity exhibits a unique variation in 29 Si spin–lattice relaxation times upon heat-treatment which is ascribed to changes in the concentration of impurity ions in quartz.