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TECHNICAL PAPER

Figure 19: Granite exposed to elevated temperature, Haneefa et al., 2013 [21]

of granite vary with their sources. Moreover, the distribution The petrography of river sand mortar exposed to elevated
of mafic mineral draws different textures, or appearances as temperature is illustrated in Figure 20. Figure 20 (a) dictates
discussed earlier in this paper. Thermal incompatibility of extensive staining of weathered feldspar grain exhibiting
constituent minerals in aggregates (in terms of specific heat brownish red colour. Microcline with twinning lamella, and
capacity, and coefficient of thermal expansion) consequences weathered quartz are also present in the section. Figure 20
cracks in aggregates. Table 6 represents the thermal properties (b) depicts the transgranular mineral staining of feldspar
of some major minerals present in the aggregates [66] . In typified by a profile, red in colour; along with disrupted, and
the case of multi-mineral tiled textured rocks, variations in widened cleavages. Figure 20 (c) provides alkali feldspar phases
these thermal properties of minerals may impart deferential (converting into clay minerals) are ferric oxidized along with
unaltered quartz grains. Figure 20 (d) illustrates the weathered
expansion at elevated temperatures and contraction at ambient quartz (bright phase in the middle) with iron pop outs due to
temperatures. The phenomena ultimately result in cracks and thermal effects. Similarly, Figures 20 (e and f) provide different
consequent degradation in concrete. levels of staining, and iron dust. All these disintegration
Haneefa et al. [63] tested siliceous based river sand and limestone mechanisms make the siliceous river sand of a granitic origin
aggregate mortars for use in a fast breeder reactor at 550°C with inferior to mono-mineral aggregate, like limestone in strength
wide ranges of w/c ratios and four types of cement. Irrespective performances.
of cement type or w/c, limestone mortar was superior in On another note, the staining of minerals due to ferric oxidation
compressive and flexural strengths after thermal exposure. as a result of thermal effects in aggregate can be qualitatively

Table 6: Thermal properties of some major minerals in aggregate, Lane et al. [72]

MINERALS AVERAGE LINEAR COEFFICIENT OF SPECIFIC HEAT × 10 J/kgK, AT 27°C
3
THERMAL EXPANSION × 10 /°C
-6
Quartz 11.5 to 12 0.75
Orthoclase, microcline 6.5 to 7.5 0.77
Pyroxenes, and amphiboles 6.5 to 7.5 0.75 (For pyroxenes)
Calcite 4.5 to 5 0.86
Muscovite - 0.86

THE INDIAN CONCRETE JOURNAL | AUGUST 2022 27