Characterization of supplementary cementitious materials by thermal analysis

Abstract

Working Group 1 of RILEM TC 238-SCM 'Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)' is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700-1000°C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required.

Influence of Activators on Mechanical Properties of Modified Fly Ash Based Geopolymer Mortars

“…The analyzed bound water of the hydrate phases (H) and the Ca(OH) 2 content (CH) were calculated from the weight loss curve expressed as a percentage of the dry sample weight at 1000 • C (m 1000 ) using Equations (4) and (5) based on literature [39][40][41][42]. The CaCO 3 content was determined similarly with Equation (6).…”

Comparison of calcined illitic clays (brick clays) and low-grade kaolinitic clays as supplementary cementitious materials

“…The dehydroxylation of the kaolinite, illite and smectite occurs at temperature intervals that partially overlap, but may allow their differentiation in DTG curves (see e.g., Refs. [4,25]). Under the present experimental conditions, the mass losses due to dehydroxylation of kaolinite, illite and smectite were found at approximately 400-600, 600-700 and 800-900°C, respectively.…”

Influence of Graphene Nanosheets on Rheology, Microstructure, Strength Development and Self-Sensing Properties of Cement Based Composites

“…Thermogravimetric analysis (TGA/DTA) was used to determine the behavior of cement-based composite at elevated temperature. According to available literature, few reactions occur due to heating of the cement based mortar: (a) 180-300 • C bonded water loss from C-S-H and carboaluminate hydrate; (b) 430-480 • C dehydroxylation of portlandite (calcium hydroxide); and (c) 600-780 • C decarbonation of calcium carbonate [37,[42][43][44][45][46][47]. The thermal analysis of both specimens (with and without GO) are presented in Figure 6b while the weight loss values in different regions are given in Table 5.…”