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Tensile Test Measurements"

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A knowledge of the concrete tensile strength and the elastic modulus is essential for accurate stress analysis of the highly compliant, multi-layered, cementitious composites used to build modern concrete canoes.  Here is how we measured these parameters for our mix in 2001:

We cut tensile specimens from thin, flat sheets of concrete.  Wooden coupons were positioned at the ends of each sample, and the coupons and ends were wrapped with graphite fiber.  The fiber was bonded into place with high-strength epoxy, and holes were drilled in the wooden coupons so that loads could be applied.  Strain gages were mounted axially in the central areas of the test specimens.  Each specimen was hung vertically and loaded to failure by application of weights to the lower end.

We computed the stress in each specimen by dividing the applied load by the cross sectional area.  The elastic modulus of the concrete was computed by determining the slope of the axial stress versus strain plot shown as the blue line in the figure below.

By comparison, the orange line shows the results obtained from a 28-day compression test.