Mario Paredes

Precision Statements for the Surface Resistivity of Water Cured Concrete Cylinders in the Laboratory

A rigorous round-robin testing program was conducted for surface resistivity (SR) measurements of water cured concrete cylinders in the laboratory. Fourteen different laboratories participated in this effort, testing twelve different Portland cement concrete mixtures containing a wide range of constituent materials. Also, test results from two different commercially available SR meters were compared for statistical equivalence of the data. The results of this effort have been used to formally document the repeatability (single-operator precision) and reproducibility (multilaboratory precision) of SR measurements in the laboratory.

Limiting Early-Age Cracking in Concrete Bridge Decks

Early-age bridge-deck cracking is a major problem affecting the durability of U.S. bridges. Many factors can cause early-age bridge-deck cracking including change in temperature, hydration, plastic shrinkage, autogenous shrinkage, and drying shrinkage. The presence of cracking may increase the effect of freeze and thaw cycles and may lead to corrosion of reinforcement, which may result in deterioration of the entire bridge. It is crucial to investigate the issue of early-age cracking in bridge decks to provide solutions to improve the safety of U.S. bridges. This research examines the use of different sealing materials to seal the developed cracks while the performance criteria can be achieved. An analytical study was performed to study the importance of major parameters that may affect the transverse deck cracking, such as concrete strength, shrinkage, thermal effect, load patterns, load magnitude, span length, number of spans, and continuity. A finite-element model was developed to investigate the factors affecting tensile stresses and crack tendency. Also, a tool was developed to predict the likelihood and initiation of early-age cracking in bridge decks. The outcomes of this study identify suitable sealant materials and identify a set of recommendations to limit the cracking problem and, hence, resulting in a longer service life to bridges.