Concrete Blocks.

Progress, Volume XVI, Issue 10, 1 June 1921, Page 238

Concrete Blocks.

the President of the Concrete Institute of London (Mr. E. F. Etchells), in .his presidential address at the annual meeting of the -1920-21 session, made some interesting comments, on the construction and manufacture of concrete -blocks. In dealing with the development of concrete block construction, he dealt with its possibilities and also called attention to some of the earlier unfortunate experiences in the use of concrete blocks. In a considerable number of houses built with concrete blocks the wet drove through the walls, and in some instances the blocks were so porous as to make the houses unfit for habitation, but this was not to

decry block construction in itself. It was evidence of ignorance on the part of those who made the blocks, because, if no attempt was made to fill up the voids in the shingle, for instance, it could not be expected that the concrete would be watertight. Also in many houses erected a few years ago there was a great tendency to vertical cracks, not only through the joints but across the blocks themselves, which made it impossible to keep a dry interior. These defects, however, were being overcome. A principal cause of cracking in concrete buildings, especially in houses, was poor foundations, but there was a preponderating percentage of straightline cracks in cottages built of concrete blocks due to contraction and expansion under temperature changes. When a cottage was put up in the summer time under the conditions he had mentioned there was bound to be contraction, and stresses would be set up in the concrete. These stresses would necessarily be very much greater at certain points than others, and cracks would result. The provision of meshed reinforcement across the places most likely to crack would be useful, but in any case it was desirable to use only matured blocks. If they followed the information in,the manufacturers’ catalogues, which sometimes said that the blocks could be used after four days, they deserved to have trouble.

After enumerating in detail the advantages of concrete blocks and some of the essential points to be remembered in connection with their use, Mr.

Etchells touched on the question of their manufacture. He said that with regard to the manufacture of blocks with Portland cement there were four principal methods of ensuring that moisture would not penetrate to the interior of the buildings; the Erst depended upon the use of a continuous cavity or air gap, the inner and outer sides of the wall being connected with ties of suitable material. The second depended upon the use of a sheet of impervious material, such as bitumen, or even steel plate. In this method the sheets of impervious material were laid and lapped between the inner and outer leaves of the wall, and suitable metal ties were used. The third depended upon the use of some waterproofing compound being mixed with the concrete. The fourth depended upon the use of dense concrete made of impervious materials without voids, it being considered that concrete itself is a water-resisting material. The water-resisting properties of concrete varied immensely. He had seen instances of water pouring through 30 inches of brick and ballast concrete short of sand, and through 15 feet of concrete in a dam. On the other hand, he had seen specimens of concrete, less than I inch in thickness, perfectly dry when used in walls of cisterns. The question of using additional cement or patent compounds in order to ensure water-tightness was, after all, a matter of relative cost, and at the present time the prices of certain proprietary compounds tended to approach prohibitive figures. It was obvious when making cement watertight that there should be enough sand to fill up the voids in the coarse material. There should be more than sufficient cement paste to fill up all the voids in the sand, and if the sand filled up all the voids in the coarse material and the Portland cement paste filled up all the voids in the sand, where was the water to get through? It could only get through if they left out one of the ingredients.