As regards tiles, the Committee expresses the wish, as in the case of roofing slates, that experiments should be made to find out what quantity of water can be absorbed by a square metre of tiles, fixed just as they really are in practice upon a frame inclined at the minimum angle adopted for roofs, by subjecting this frame to a regular shower of known intensity for a given time.
The test shall be made with at least three whole tiles which have been previously immersed for forty - eight hours, as described in § 5. A glass tube of .035 mm. internal diameter and .11 height shall be placed horizontally and fixed with pure cement at about the middle of the upper surface of each tile. The tube, closed at the top by an indiarubber cork, shall be put into communication with a reservoir giving a head of water of. 1 m.
By means of a reservoir placed under the lower surface, the water passing through each tile shall be collected.
The perviousness shall be estimated by the volume of water which has passed through in an hour, after the experiment has been continued for twenty-four hours.
1 In the case in which the time of immersion is to exceed forty-eight hours, if it is wished to shorten the experiment, use may be made of the process of imbibition by means of the exhausted receiver, as described for tests of natural building-stones (Note of the Commission).
The test of resistance to frost shall, as much as possible, be made upon whole products. The trial can, however, be made with fragments. In this case, the cut or broken parts of the specimens should be protected by a varnish or a thin coating of tallow, in order to leave free for the penetration of water only those faces usually seen.
The correct tests of resistance to frost, carried out as directed in the case of natural stones, shall comprise:
In making these trials, note must be taken of the following details:
1. For the immersion, distilled water at a temperature of +15° to +30" C. shall be used, or, in default of distilled water, drinking water at the same temperature, which presents no inconvenience when it is not required to determine the quantity of soluble salts.
a. The specimens shall be exposed to a temperature of - 15° to - 20o C.
3 The duration of exposure to the cold shall be four hours.
4. Thawing shall be effected by complete immersion of each specimen in distilled or drinking water at a temperature of +15o to +20o. (In the case of natural stones, a volume of 500 cubic centimetres is prescribed for a specimen containing 7 cubic centimetres.) For specimens tested in a state of imbibition after an immersion of twenty-four hours, the thawing is effected in damp air and not in water. During the interval separating successive freezings and thawings, the specimens are kept in closed jars to prevent a too great loss of the absorbed water; care is moreover taken, before subjecting to cold again, to plunge them into water for a few moments so as to keep them, during the whole test, in about the same state of imbibition as that in which they were at the beginning of the experiment].
(1) The examination of the specimens with a magnifying-glass, with a view to ascertaining whether cracks or splits have occurred in those products which have been subjected to successive frosts and thaws twenty-five times.
(2) The determination of the loss of weight of the frozen specimens.1
There must be used for these tests at least - three specimens soaked in water for twenty-four hours; three specimens saturated with water.
The test of resistance to rupture by crushing shall be made on pieces of nearly cubical shape, obtained, for example, in the case of ordinary bricks, by placing two half bricks one over the other and binding them together by a thin layer of pure Portland cement.
The surfaces of compression shall be rendered exactly parallel by a coating of similar aste.
As in the case of natural building-stones, the tests of resistance to crushing shall be made with lever apparatus or hydraulic press.
The objects should be placed between the compressing plates, covered by a sheet of thin pasteboard; it is advisable that one of the two compression plates should be movable in every direction.
The dimensions of the surfaces exposed to pressure shall be noted in the report of the experiment at the same time as the resistance offered per square centimetre.
The test shall be made upon at least three objects from the same specimen.
The average of the results given shall be calculated.
It will be well to make the test with two series of objects, one in the dried state, the other in a state of imbibition, the degree of imbibition being noted.