Strains Developed in Concrete During and Subsequent to Hardening.
Final rept. Oct 67-Jul 68,
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MISS
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The recording of unexpectedly large tensile strain readings in early-age concrete by Port Allen Lock and Lackland Air Force Base on the Drilled Pier Test Section DPTS prompted this investigation. Tests were conducted on a smaller scale to ascertain whether the readings were due to instrumental errors, stress-induced strains, or growth of the concrete due to hydration. Three distinct strain meters were installed in a simulated pier having the same mix design as used in the DPTS. They were 1 SR-4 instrumented rebars as used in the DPTS, 2 vibrating wire gage, and 3 Carlson strain meter. The latter two are well-known internal meters for long-term measurements in concrete. Strain and temperature measurements were made on the continually moist concrete during and subsequent to hardening for 3 months. Results showed that the concrete grew during the hydration process but less than observed at the DPTS by at least a factor of 3. This could be explained by the fact that the surrounding medium at the DPTS was clay and could have confined the expansion in the lateral direction. Other interesting facts observed were 1 a low-modulus internal transducer is needed such as the LVDT to measure volume changes before the concrete hardens as well as after it hardens and 2 normal waterproofing techniques for SR-4 gages on steel rebars appear to limit the resolution of the measurement to about or - 50 microin.in. Loads can still be accurately measured by establishing a zero load reading as the sensitivity is hardly affected. Author
- Ceramics, Refractories and Glass