MIXING, MOLDING, AND STORAGE. The specimens for the shear and tension tests are mixed, molded, and stored under the same conditions as in the case of beams (pp. 48-53). COMPUTATIONS. The unit shearing stress is found by dividing one-half the shearing load by the area of a vertical section of the test piece. For the tension tests the dimensions of the section and the distance of the break from the center will be given, besides a complete record of the usual information regarding the making of the test pieces. The unit strength and the initial modulus of elasticity will be calculated from the results. A series of parallel tests will be made, including a cylinder for compression tests, so that values for a particular lot of concrete will be obtained, giving the strength in shear, in tension, and in compression, and also the modulus of elasticity for tension and for compression. In the report a complete record will be given of all the materials used in making the test pieces, together with a record of the conditions governing the making, storing, and testing. BUILDING-BLOCK SECTION. OUTLINE OF INVESTIGATIONS. In the building-block section an extensive series of investigations on the properties of building blocks is under way. Five different types of building blocks are used. They are made up of different proportions and different aggregates and are tested at different ages. With each series of blocks a set of cylinders 8 inches in diameter and 16 inches in length are made, and these are stored under the same conditions as the blocks. The blocks are subjected to strength tests in cross bending and compression, and to fire tests to determine what aggregates and proportions offer the greatest resistance to fire. A large number of mortar blocks have been made and many of these have been tested. The schedule of tests now under way comprises the manufacture on five different types of block, mixed in proportion of 1 part typical Portland cement to 2, 4, and 8 parts Meramec River sand, and of damp, medium, and wet consistencies. The strength tests cover periods of 28, 90, 180, and 360 days. This series necessitates the making and testing of 720 blocks and 360 cylinders. In the case of blocks made of concrete, which include aggregates of limestone, gravel, granite, and cinders, proportions of 1:2:4, 1:2:5, and 1:3:6 are used. For convenience in handling, all volumes are reduced to weight and all materials are charged into the mixer by weight. The consistencies which are indicated by the terms damp, medium, and wet are defined as follows: (1) In damp consistency the per cent of water used gives the driest mixture which can be used in all five types of block machines; (2) medium consistency is halfway between the damp and the wet consistencies; (3) in wet consistency the per cent of water used gives the wettest mixture which can be used. The five cement-block machines which are in use were loaned to the laboratories under an arrangement made by a committee of the United Concrete Block Machine Manufacturers' Association, through the courtesies of the following companies: American Hydraulic Stone Company, Denver, Colo.; Miracle Pressed Stone Company, Minneapolis, Minn.; P. B. Miles Manufacturing Company, Jackson, Mich.; Dykema Company, Grand Rapids, Mich.; Century Machine Company, Jackson, Mich. These machines are shown in Pl. XX. . PROGRAMME OF INVESTIGATIONS. The programme that has been adopted as a suggested outline covering all the investigations of mortar and concrete blocks is as follows: I. VARIABLES IN THE MANUFACTURE OF BLOCKS UNDER INVESTIGATION. A. Type of wall block—all plain face and standard ends: 1. With facing. a. One-piece wall block. (1) Hollow block. (a) Down face. x. Single air space. (b) Side face. x. Single air space. (2) Solid block. (b) Side face. b. Two-piece wall block. (1) With metallic bond. (2) Without metallic bond. 2. Without facing. a. One-piece wall block. 1) Hollow block. x. Single air space. y. Double air space. (b) Side face. x. Single air space. A. Type of wall block—all plain face and standard ends-Continued. 2. Without facing-Continued. a. One-piece wall block-Continued. (2) Solid block. (a) Down face. (b) Side face. b. Two-piece wall block. (1) With metallic bond. B. Materials used: 1. Cement, typical Portland. a. Single. (1) Sand. (2) Limestone. (3) Granite. (4) Gravel. (5) Cinder. b. Double, consisting of sand and— (1) Limestone. (2) Granite. (3) Gravel. (4) Cinder. |