models agree better with the lab-measured flexural strength than the maturity-based model. However, the modified model is more appropriate for estimation of early hour strength as the conventional model would predict unreliable negative strength for concrete with 2000 m/s shear wave velocity. 900 7 days 3 days 700
14 days
5 days
Flexural Strength (psi)
1 day 500
300
100
2000 -100
-300
2100
2200
2300
2400
2500
2600
2700
2800
2900
Beam Shear Wave Velocity (m/s) Modified Model
Beam
Conventional Model
Figure 23: Example shear wave velocity- strength curves. Substituting Equation (8) into Equation (14) leads to the following relationship between the field-measured shear wave velocity and concrete flexural strength for the long-life concrete mix tested: (15) To combine the benefits of maturity and ultrasonic tomography, a procedure was created using maturity predictive abilities to relate shear wave velocity to strength gain. This proposed procedure is outlined below. Step 1: Conduct laboratory testing of concrete compressive and flexural strengths at various ages. Concrete cylinders and beams should be prepared with the same concrete mix design as expected to be used for the pavement project. Compressive strength and flexural strength should be tested using cylinders and beams, respectively, at various ages, say 6 hours, 12 hours, 18 hours, 1 day, 3 days, 7 days, and 14 days. Concrete maturity should be measured for cylinders
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