No abstract

Core tests can give the most reliable information when studying concrete of structures.Rotary core drilling with type ST-1 hard-alloy bits were used in Soviet practice until recently for boring out cores. Owing to the presence in concrete of components having a different strength and the rapid wear of hard-alloy cutters during drilling, cores with a wavy and partially damaged surface are extracted. Testing of such specimens gives underestimated inindices of the properties of concrete characterized by a large scatter, whereupon the underestimation and scatter are higher, the smaller the diameter of the core. Hard-alloy bits have a low wear resistance and rarely provide a sufficiently large core recovery. All aforementioned shortcomings can be eliminated to a considerable extent by using diamond drill bits (Fig. i) [1], the results and experience of using which are given below.