NDT Use in Evaluating the Form Removal Time for a Large Diameter Tunnel Concrete Lining

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Title: NDT Use in Evaluating the Form Removal Time for a Large Diameter Tunnel Concrete Lining

Author(s): T. R. Harrell

Publication: Special Publication

Volume: 112

Issue:

Appears on pages(s): 153-164

Keywords: concretes; form removal; nondestructive tests; penetration tests; thermocouples; tunnel linings; General

Date: 1/1/1989

Abstract:
A case history of methods used to evaluate the allowable form removal time for a large diameter tunnel concrete lining is presented. To meet schedule requirements, a concrete placement was to be made every alternate day. A triad of testing was done to evaluate the time at which the reusable, self-propelled, steel-skinned form could be stripped from an existing placement. This testing consisted of field-cured cylinders and nondestructive testing that included embedded thermocouples in the concrete placements and penetration-resistance testing. Reference curves and tables were developed for use in the form removal evaluation. Statistical methods were used on test data obtained from results of testing done with the actual concrete mix to be used in the placements. Control curves were then developed. Target values were selected to be used in determining when the concrete was of sufficient strength to allow for the form removal.