Modern Gasworks Practice

FOUNDATIONS, GASWORKS BUILDINGS, ETC. 47 Fürther detriment results from the expansion that attends the freezing of the uncombined water. The expansion forces the grains apart, and althougli the hydration shotild contmue after thawing, the consolidation. would be imperfect and the structure lacking in strength. Frost chiefly proves destructive when in the concrete mass there are fissures or hollows. Water collects in such hollows, and the force due to its expansion when frozen is liable to be followed by serious disintegration. Water containing carbon dioxide in solution is undesirable in that the constituents in the cement are liable to be transformed into soluble bicarbonate of calcium. So far as the action of salt or brackish water is concerned, opinions are to an extent contradictory, and when damage occurs it can usually be traced to the eflect of alternate exposure to salt water and air. It is said that crystallization of the dissolved salts then occurs in the pores, and that the expansion brought about by this crystallization causes disintegration. The result of several experi-ments shows, however, that when concrete is carefully made and is constantly immersed in salt water practically no harm results. Where fonndations are above ground level th.e question of shuttcring has to be ■considered, and it is as well to bear in mind that if the boards are given a good coat of lime-washing before use, thcy will come away far more easily and leave a clean ■even surface. Anotlier consideration is that of retort liouse subways, elevator pits, etc., which are sunk below the ground level. It is frequently found that water percolates through the concrete forming the walls, and is liable to give trouble. Various methods may be employed to overcome this, one of thern being the insertion of a thin layer of pitch about half-way through the wall, and extending from top to bottom. An alternative is to paint the face of the walls with two or three coats of some solution such as “ Ironite,” the first coat being rubbed well into the pores and allowed to rust before the next coat is applied. This method is, on the whole, preferable to that of rendering the face of the wall with cement. Allowable Pressures on Various Soils Grave! (firm) with underlying chalk 6 to 7 tons per square foot Firm gravel ...... • 5 „ 6 „ „ „ „ Firm clay ...... • 3 „ 4 „ Gravel (loose) and sand. • 1J „ 21 „ „ „ „ Light earth and sandy loam . 3 4 „ 11 „ „ „ „ Made-up ground (well rammed) 1 2 ” 3 4; >5 >> ff When slabs of concrete for retort bench.es are laid down on any type of clay it will be found profitable to drop a layer of fine sand (from 3 inch.es to 6 inch.es deep) on to the surface of the clay before filling in with concrete. Concrete, being of a homogeneous nature, readily conducts heat, so that in time the moisture is dried up from the clay, with the result that shrinkage occurs, and the whole may be thrown out of level. The strength. of the concrete is a question. to which due thought must be given, and this particularly applies to gasworks undertaking ex-tensions, where there is usually a stock of “ hard-core ” on liand. The gas engineer