The effect of the size of grog in fire-clay bodies. . 12 -ZOl 812 GftOG Fig. 20.—Series 1. Relation between grog composition and modulus of rupture of bodies burned to cone 14 28 Technologic Papers of the Bureau of Standards In series i to 4 the modulus of rupture at cone 12 bears anapproximate relation to porosity. The strength-porosity curve(Fig. 26) consists of two parts. From body 1A (4 to 8 grog) tobodies in series 3 (12 to 80 grog) strength increased with increase ofporosity, due to small cracks which developed in drying and didnot heal in burning. In series 4 (20 to dust grog) and
The effect of the size of grog in fire-clay bodies. . 12 -ZOl 812 GftOG Fig. 20.—Series 1. Relation between grog composition and modulus of rupture of bodies burned to cone 14 28 Technologic Papers of the Bureau of Standards In series i to 4 the modulus of rupture at cone 12 bears anapproximate relation to porosity. The strength-porosity curve(Fig. 26) consists of two parts. From body 1A (4 to 8 grog) tobodies in series 3 (12 to 80 grog) strength increased with increase ofporosity, due to small cracks which developed in drying and didnot heal in burning. In series 4 (20 to dust grog) and part of series3 strength decreased with increase of porosity, the degree of vitrifi- 8-IZ <?ro«. SO-^-O GROG Fig. 21.—Series 2. -\Z-ZO GROG Relation between grog composition and modulus of rupture of bodiesburned to cone 14 cation being the governing factor. In series 5 (4 to dust grog)there was no relation between porosity and modulus of , for bodies containing grog of different sizes, porosity maygive entirely wrong indications of strength. The surface factor, however, does afford an accurate means ofjudging the strength of such bodies. In Figs. 27 and 28 surfacefactor of the grog portion of the bodies is plotted against modulusof rupture. The curves are straight lines except that some are of Size of Grog in Fire-Clay Bodies 29 parabolic form in the lower part; that is, for larger grog relation holds for all the series at all three heat is more exact in series 1 to 4 than in series 5 to 7, because thelatter contain comparatively large particles which are not dissolvedby the clay to anywhere near the same extent as are the smallparticles. (
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