Om Materialprøvningens Udvikling i Norden
Og om Statsprøveanstaltens Virksomhed

WMF________ •| 156 ■ the cavities would certainly give respect. explain why well burnt circumstances can stand ners during the test of resistance to frost in spite of its displaying a strong capillary attraction. Finally, it cannot be taken for granted that because the water is moving easily in a brick, the same should be the case with the ice. A study of the shape of valuable informations in this There remains to bricks under certain the »strap test« but not the usual test of the La- boratory. As already mentioned this must be due to deficient ho- mogeneity in the bricks concerned. This want of homogeneity may of course assert itself in many ways, and it would be too long to account for the modes of ex- pression of this want in its various shades. But in the following we shall try lo explain how absence of homogeneity can become apparent in different ways under the various tests of resistance to frost and in nature when acted upon by the frost. Let us, for instance, imagine that fig. 21, p. 62 shows a brick produced by a material, sandy in itself, but where owing to deficient working there is a stripe A of not sandy material. We further imagine that the brick has been burnt so hard that the very clay-substance has become vitrified while the sandy material is as yet rather much absorbing. We shall now see how such a brick will stand actions of frost in the following 3 cases: The usual test of the Laboratory. The »strap test«. Frost in nature. 2) 3) 1) We now fancy that the freezing case with the poration from the side B will try to rise through the brick, but here it meets the stripe A not allowing of transition of the water. Then the consequence is that the shell situated between A and B is pushed off. 2) On the same brick being, however, clasped into a strap, so that free evaporation can take place from all the planes of the brick, it will in all probability not be the least damaged. the brick is placed on the bottom of stretcher-side B turned down. Eva- thus becoming impossible, the water