| Show TESTS OF CONCRETE numerous recent accidents in building construction owl owing ng to the failure of con crete give special interest to a bulletin bullet in no just issued by the geological survey showing the results of tests of the strength of concrete beams under many varying conditions dit ions the work reported on consisted of studies of the constituent materials of concrete of its strength when molded into various structural shapes and of the meth by which its maximum strength might be developed through various forms of metallic reinforcement the tests indicate that concrete is unsuitable for use under conditions where it must resist tensile stresses because of the small loads it will sustain and particularly became of the suddenness with which it fails in striking contrast to the behavior of rein in forced concrete which usually shows a gradual development of cracks preceding failure an attempt is made to bring out the comparative para tive values of gravel granite limestone and cinders for use in concrete the effect of age and consistency on strength as shown by the modulus of rupture of the long and short beams and by the ultimate strength of cylinders and cubes and the influence of age and consistency on stiffness which is indicated by the elongation and elasticity the purpose of this series of tests is to determine 1 the effect of age on the strength of concrete 2 the effect of variation in the consistency on the strength of concrete and 3 the effect of different types of aggregates on the strength of concrete the first question is perhaps the most important since an early attainment of considerable sid erable strength and no subsequent decrease in it are essential qualities in concrete indicating how soon a structure may be put to the use for which it is intended many of the accidents reported have apparently been due to putting too early a strain on green cement no attempt is made to generalize the results of the tests nor to draw any conclusions however warranted they may appear from an examination of the data presented it is expected that the bulletin will provoke discussion and in order to promote this extended expressions of opinion or attempted applications of theory to results have been een avoided A running commentary on the ie results of the tests however emphasize 1119 ig points of particular interest and indi eating a few that might lead to interesting conclusions is included in this report when the e results of 52 week tests now in progress be become corae available a thorough analysis 0 of f the ue entire series will be published in an ait other bulletin the e present bulletin can be had had on ap to the director of the e united states geological survey washington D C |
