Development of a Cell for the Installation of Electrical Resistance Strain Gages in Concrete

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Title: Development of a Cell for the Installation of Electrical Resistance Strain Gages in Concrete

Author(s): Herbert E. Worley and Richard C. Meyer

Publication: Journal Proceedings

Volume: 50

Issue: 10

Appears on pages(s): 121-135

Keywords: no keywords

Date: 10/1/1953

Abstract:
These investigations were conducted to develop a method of adapting SR-4 elertrical resistance strain gages for measurement, of strains in concrete pavements. Previous experiments in which SR-4 gages were incorporated in cells which could be cast internally in concrete indicated that some new water-proofing technique would have to be found which would extend the useful life of such installations. SR-4 gages having a 6-in. gage length were found to indicate strain values which were much more consistant than did shorter gage lengths when used on concrete containing coarse aggregate. A number of experimental cells were made and tested before one was developed that measured strains satisfactorily. The SR-4 gages for this gage cell were cemented between the flattened walls of an expanded poltion of 5/32- or 3/16-in. copper tubing. The copper tubing extended the length of the gage leads and was filled with Petroscne was to keep moisture from entering the gage cell. Specimens in which these thin-walled copper gage cells were cast were tested in the laboratory in compression and in flexure. Strains measured with internal gages compared favorably with those found by similar surface gages with no apparent reinforcing of the concrete by the gage cells. Con-sistency of strain values indicate a good bond between concrete and gage cell. Two rosettes of two gages each were cast in a pavement and a strain investigation was made to determine the workability of these gages. Strains due to a 20,000-lb axle moving load at various speeds and in several wheel lanes were recorded satisfactorily. After having been installed in a concrete pavement for ten months the gages have manifested no decrease in gage to cell resistance. It is believed that gages of this type are waterproof and will remain serviceable for a long time.