Statistical Analysis of Concrete Compressive Strengths for California Highway Bridges: Fid-Bau Portal

Statistical Analysis of Concrete Compressive Strengths for California Highway Bridges

Unanwa, Christian / Mahan, Mark

Abstract

This investigation presents results of the statistical and probabilistic analyses of 3,269 normal weight concrete cylinder compression tests used for recently constructed highway bridges in California. A new model for in-place strength of concrete structures is proposed as a function of the specified compressive strength, the normalized 28-day cylinder strength, and age of the structure based on a realistic strength–age relation for hardened concrete. The model prediction indicates that concretes in cast-in-place bridge structures designed with specified compressive strengths of 25 MPa (3.6 ksi), 28 MPa (4.0 ksi), and 35 MPa (5.0 ksi) reach their maximum strengths at about 40 years, with approximately 98% of the maximum strength occurring during the first 10 years. Also, through significance testing on the 28-day cylinder strengths, it was established that the California Department of Transportation practice of using an expected concrete strength instead of the specified strength for seismic design of bridge components is justified. An expression for predicting the 28-day strength of concrete cylinders as a function of the strength of companion cylinders, also proposed herein, could prove a useful tool for quality control of concrete during construction.