Is a nonconical test cylinder fracture a sign that something specific is wrong with the concrete or the test?
There is no published information that serves as a guide to interpreting the meaning of different types of fractures. Normally, a test cylinder should break into two conical end sections with the caps intact. If the break is through the cap or if the specimen splits vertically, a careful check should be made of the quality of the capping material and Saneness of caps and bearing surface. Abnormal fracture and reduced strength may result from wedging action or uneven distribution when thick, irregular caps are used to correct excessively rough surfaces. Very high strength specimens sometimes split along vertical planes even when caps are proper, but splitting may also be evidence of a cap which has flowed and induced lateral forces. Any variation from the cone pattern indicates that the concrete is failing in compression by forces other than direct compression. If so, the true compressive strength may not be obtained. Fracture, in the form of a cone, is valuable in showing that the results of the tests actually represent the compressive strength of the concrete cylinder. The results of any other type of fracture are questionable. To our knowledge there is no way to relate a departure from the cone fracture directly to the cause. Some usual causes are improper molding of the specimen, a weak surface on the specimen, an inadequate cap or eccentric loading.