Tests have been made in order to determine the strength of the mortar for joints by means of an impact test hammer. These tests showed that their results are influenced to a very great extent by variations in the degree of restraint and in the strength of the concrete elements which are adjacent to the joints. Therefore, the impact test hammer can be utilised only to form a rough estimate of the strength of the mortar in joints which are identical in design and construction. A method which is used in the USA to determine the strength by shooting a nail into the concrete or the mortar by means of a nail-driving gun has also been tested. The depth of penetration of the nail serves as a measure of the strength. The scatter in the results was so great that this method was considered to be useless. Another method included in the tests consisted in pulling out a tubular sleeve, which had been fastened with glue in a hole drilled in the mortar. It was found that the pull-out force closely represented the variations in the strength of the mortar. The scatter in the results was small. A drawback of this method is that it requires a relatively large space, and is therefore difficult to use in joints of some types. Previous tests at the Swedish Cement and Concrete Research Institute, Stockholm, have indicated that the rate of penetration of a drill can serve as a measure of the strength of the concrete. However, the tests under review showed that the results obtained by means of this method are in a high degree influenced by the wear of the drill, and above all by differences in sharpness and hardness between various drills. Drilled core cylinders, which ranged down to 15 mm in diameter, have been subjected to compression tests. The small test specimens were sawed and surface-ground by means of a special device for preparation of small test specimens. The respective relations between the size of the test specimen, on the one hand, and the strength and the standard deviation in strength, on the other hand, were determined on test specimens, 15, 28, 50, and 70 mm in diameter. These tests showed that, if a sufficient number of drilled core cylinders is taken from the mortar, its strength can be determined with adequate precision by using test specimens which have a diameter as small as 15 mm. It is only one of the methods covered by these tests, namely, the use of drilled core cylinders, that can be recommended for more or less accurate evaluation of the strength of mortars in joints between precast concrete elements.

  • Corporate Authors:

    Cement och Betonginstitut

    Drottning Kristinas Vaeg 26
    Stockholm 70,   Sweden 
  • Authors:
    • DAHL, G
  • Publication Date: 1975


  • Swedish

Media Info

  • Features: Tables;
  • Pagination: 5 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00125444
  • Record Type: Publication
  • Report/Paper Numbers: 5:75
  • Files: TRIS
  • Created Date: Nov 5 1975 12:00AM