Synopsis Friction and adhesion between concrete and form surfaces during the first hours of contact determine the shifting process in slip-form technology and are also of interest in processes involving immediate stripping and in the transportation of ready-mixed concrete. Experimental data are presented on the behaviour of hardening mortar (as a part of concrete obviously coming in contact with mould surfaces) with different mould materials in terms of friction and normal and tangential adhesion, including the aspect of surface cleanliness. These results make it possible to determine the forces required for overcoming adhesion in normal and tangential shifting of the form, and to recommend facing or coating agents for slip-form panels. The results, obtained in small laboratory tests, were then checked by casting 0·15 × l·0 × 2·5 m wall panels in a part of a slip-form.
This paper describes the efforts of the Central Building Laboratory of the Standards Institute of Israel to develop a relatively simple method for in situ nondestructive evaluation of the compressive strength of lightweight cellular concrete used for thermal insulation of roofs. The idea of the developed impact device with sliding drop collar is similar in principal to the well-known soil test method of drop-weight penetration, ordinarily used for field determination of compacted soil density.
Test results show that the depth of penetration is influenced by two main parameters: compressive strength of the concrete and its density. If the unit weight of the cellular concrete is known or predetermined, its compressive strength can be estimated by means of the impact device with a sufficient degree of accuracy. Thus the drop-collar penetrometer may find useful application in in situ quality control of lightweight cellular insulating concretes.
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