Apparatus. The large blocks of stone sent in by the field geologist, having been roughly dressed by hammer and chisel, are sawed into cubes by the gang saw (Pl. XI, C, p. 50) and finally ground to exactly 2 inches on an edge by rapidly revolving horizontal cast-iron disks about 18 inches in diameter. Methods. The position in which the blocks were bedded in the quarry is indicated on the stone by the collector and this mark is transferred to the finished cubes. Half of the cubes sawed out of the blocks are then crushed with the bedding plane perpendicular and the other half with it parallel to the direction of application of the load. Previous to the strength tests the cubes are placed in a pan containing one-half inch of water, and their increase in weight measured at the end of twenty-four hours. The water is permitted to flow gently through the pan and is maintained at a constant level by an outlet placed one-half inch above the bottom of the pan. From these data the percentage of absorption is obtained. The weight per cubic foot and the specific gravity are also determined. BEAM SECTION. OUTLINE OF INVESTIGATIONS. NATURE OF THE WORK. The principal work in the beam section consists in the making and testing of plain and reinforced concrete beams. The beams are made of different consistencies, different aggregates, and, in the case of the reinforced beams, of different percentages of steel; the beams are tested at different ages. In addition to making and testing beams, the beam section also makes and tests cylinders and cubes formed of concrete like that used in the beams. Each rod used in the reinforced beams is tested in the beam section and all the materials that are used in the concrete are tested in the constituent-materials section. This gives a complete report of all the properties of the material used and makes it possible to study the effect of different properties on the strength of concrete beams. The first schedule of tests (now under way) in the beam section is given in the accompanying table (p. 38). All the beams, cylinders, cubes, and bond test pieces outlined in this table have been made, and some of the 360-day test pieces have been tested. 15767-Bull. 329-08- -4 Remarks.-Three test pieces identical in composition to be tested at each of the following ages: 30, 90, 180, and 360 days. Three cylinders of each aggregate, theoretically proportioned, to be tested at each of above ages. Three cylinders and three cubes of each aggregate for medium consistency to be tested at each of above ages. Mild steel.-One coupon to be tested from each bar. The above outline of the first three series covers the following parts of the general programme (pp. 16-19): Section III.-B, items 2 and 5; C, item 1. Section IV.-A, items 1, 2, and 3. 24 Variables. The proposed schedule of beam tests is given in the table on pages 40-47. This schedule is only tentative, the object of these tests being to determine the maximum strength of a beam-that is, to determine the amount and character of reinforcement necessary to cause failure by compression in the upper fibers. Many of these tests have been arranged on assumptions which may not be true and which may therefore necessitate a change in the series. |