Sample size requirements for seismic and traditional testing of concrete pavement strength
Additional Document Info
The strength of portland cement concrete (PCC) is one of the major acceptance quality characteristics in most existing specifications and quality assurance programs for PCC pavement. A statistical method is provided for determining the sample size requirements for reliable estimates of PCC parameters for pavement strength. These parameters include compressive strength from cylinders, flexural strength from beams, and dynamic seismic modulus from both portable seismic pavement analyzer and the free-free resonant column seismic nondestructive testing (NDT) methods. The sample size, which refers to the number of tests or measurements for each quality characteristic taken randomly from a lot, is a function of specifications tolerance, buyer's (i.e., agency's) risk, seller's (contractor's) risk, and the standard deviation of the test parameter under consideration. In practice, sample size typically is set on the basis of practical considerations and engineering judgment. Although practicality is an important consideration, there is a need to verify the adequacy of these practices on the basis of sound statistical analysis. The cost of sampling and testing is also discussed. The results of the study reveal that the sample size used in FAA's Item P-501 (which is four beams or cylinders per lot) is relatively small and needs to be increased. A larger sample size can be most cost-effectively achieved if seismic NDT is used because of the rapid and nondestructive nature of these testing methods.