Ivan R. Lasa

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.

Control of cathodic protection in bridges without disconnecting protection current: passivity verification technique (PVT)

Abstract Standards for monitoring the performance of cathodic protection systems on reinforced concrete structures actually recognised are based on the measurement of the polarised potential of the reinforcement (polarisation/depolarisation, E–log I tests). A new methodology to measure this performance has been developed based on the passivation of the rebar rather than on the level of potential polarisation. This new technique is based on electrochemical impedance spectroscopy measurements using a modulated confinement of the applied current. The results are not quantitative, but properly inform on the passivity of the rebar under protection and its resistance to corrosion. The new technique has been evaluated in the laboratory using sacrificial and impressed current systems. In the present paper results obtained with this technique were compared to results achieved by standard polarisation methods and were found to be in agreement. The new technique is faster than standard methods and does not require interruption of the cathodic protection current.

Corrosion of Post-Tensioned Tendons with Deficient Grout, Part 1: Electrochemical Behavior of Steel in Alkaline Sulfate Solutions

Severe corrosion recently documented in Florida post-tensioned bridges were related to grout segregation that created deficient grout with characteristics of having low chloride content, high sulfa...