Seismic Performance of Corroded and Repaired RC Columns Built using Accelerated Bridge Construction
Presented By: Chris Pantelides
Affiliation: University of Utah
Description: Accelerated Bridge Construction (ABC) is used to construct durable bridges in less time compared to cast-in-place (CIP) bridges. This research examines the reduction in the lateral load and axial compression capacity of ABC constructed columns in seismic regions due to corrosion and methods to restore this capacity. Four specimens were tested under cyclic loads to study the behavior of corroded ABC bridge columns: (i) control with no corrosion; (ii) one with moderate corrosion severity; (iii) one with high corrosion severity; and (iv) one corroded to high severity and repaired. The repair was performed by increasing the column cross-section with a fiber-reinforced polymer (FRP) composite shell filled with non-shrink concrete to increase axial capacity and improve confinement; headed steel bars were used to increase flexural capacity. The specimens were corroded using an accelerated corrosion method to reduce the time for achieving the desired corrosion level. OpenSees was used to develop computational models for simulating the cyclic performance of the corroded specimens. Corrosion effects were considered by reducing the cross-sectional area of the steel bars and their properties such as yield strength, modulus of elasticity, and ultimate strength and strain. Reduction in compressive strength of the concrete was included due to corrosion-induced cracking of concrete and reduction of bond strength between concrete and steel reinforcement. The computational models include bond-slip in the column-to-footing connection, low-cycle fatigue, and buckling of the longitudinal steel bars.
Failure Mitigation of Reinforced Concrete Subjected to Carbonation and Chloride Environments
Presented By: Jun Wang
Affiliation: University of Colorado Denver
Description: This presentation discusses the combined effects of carbonation and chloride migration on the corrosion of reinforced concrete, which frequently occurs for the concrete slab subjected to deicing and carbon dioxide pollution. The pH value and free chloride content in the pore solution are the two major factors of the corrosion for steel reinforcements. During carbonation, the reaction of CO2 and concrete components may reduce the pH and damage the protective layer of the steel surface. Besides, free chloride ions may be released during the carbonation process, which may accelerate the chloride migration and the corrosion rate of steel reinforcement. To address this issue, noncorrosive fiber-reinforced polymer (FRP) bars are used as an alternative to steel bars Unlike steel bars, which require protective passivation to resist corrosion, FRP bars show good properties under low pH value. Given that the components of concrete change during the hydration process, the difference in carbonation reactions for fresh concrete and mature concrete is significant. For fresh concrete, CO2 reacts with unhydrated C3S and C2S; however, CO2 also reacts with hydration products (e.g., CH and C-S-H) for mature concrete. In this study, the carbonation and chloride-induced corrosion development of concrete at various ages is investigated.
Service Life Determination of Reinforced Concrete Subjected to Corrosion
Presented By: Ki Yong Ann
Affiliation: Hanyang University
Description: In determining the service life of concrete structures subjected to corrosion of steel reinforcement, the time to corrosion initiation has been usually taken, of which the concrete structures are nevertheless exempt from structural damage. Thus, to predict the service life more realistically in in-situ, the structural behavior was modelled with respect to yielding, cracking and failure of the structure, assuming that corrosion is evenly propagated from the steel surface. Simultaneously the porosity generated at the steel-concrete interface was taken into account to reflect its buffering of internal stress to concrete. As a result, an increase in the interfacial porosity and steel diameter resulted in an increase in the rust amount to reach cracking by rust formation, whilst the cover depth had a marginal effect on structural performance. Substantially, the steel reinforcement charged with a higher membrane potential or/and greater diameter would extend service life under steel corrosion.
Progress Update on the Delaware Memorial Bridge Deck Rehabilitation - The Largest UHPC Overlay Preservation Project in the US
Presented By: Peter Seibert
Affiliation: UHPC Solutions North America
Description: The preliminary award for the UHPC Deck Rehabilitation Delaware Memorial Bridge (DMB) Structure 1 project by the Delaware River Bay Authority (DRBA) has been awarded to UHPC Solutions as of the abstract submission deadline date. This estimated $70 million project will use 4,700 yd3 of UHPC and will be the largest UHPC overlay installation in the United States to date. The DMB is a suspension bridge structure with 4 lanes, a total length of 10,765 ft, and a 550,000 ft2 deck area. The UHPC preservation of the entire northbound bridge deck is scheduled to occur in 3 phases during the Fall of 2022, Spring of 2023 and Fall of 2023.
This presentation will provide a progress update on two of the three scheduled construction phases of this iconic industry project. Project overview, construction methods, equipment selections, challenges and solutions from a contractor’s perspective will be presented. The UHPC technology, hydrodemoltion, surface preparation, design details, and lessons learned will be discussed. Bridge agencies who seek a cost-effective and long-lasting preservation strategy will learn how UHPC overlays are being installed so that service life of their aging infrastructure can be extended while minimizing traffic interruption during construction.
Chemical Reaction of OPC and High-Volume Fly Ash Concrete with Magnesium Chloride
Presented By: Jialuo He
Affiliation: Washington State University
Description: Magnesium chloride (MgCl2) has been increasingly used in snow and ice control operations for roadways enduring cold weather and its detrimental impact on the integrity and durability of concrete infrastructure has gained increasing attention. This laboratory study investigated the mechanism of chemical reactions of ordinary Portland cement (OPC) and high-volume fly ash (HVFA) concrete with concentrated MgCl2 solution under room temperature. OPC and HVFA mortar specimens were immersed in the 29.8 wt.% MgCl2 solution for 14, 28, and 56 days after 28-day moist curing. The evolution of mechanical properties and gas permeability with respect to the MgCl2 immersion duration was studied. The compressive strength of OPC mortar specimens showed a slight decrease while that of HVFA mortar specimens increased by 19%, after 56-day immersion. The splitting tensile strength of OPC and HVFA mortar respectively increased by 136.5% and 47.1% after 56-day immersion. The MgCl2 immersion also resulted in a reduction of 66.1% and 66.6% in the gas permeability coefficient of OPC and HVFA mortars, respectively. Advanced characterizations including TGA, XRD, and SEM-EDX were conducted to further shed light on the change in chemical compositions and microstructure of OPC/HVFA after MgCl2 immersion and on the associated reaction products with MgCl2 and semi-quantify the profile of multiple elements with respect to the depth to the exposed surface. The results revealed that, unlike salt scaling damage under freeze-thaw cycles, MgCl2 could enhance the hydration of OPC and fly ash under room temperature by producing more Calcium-Silicate-Hydrate phases, which is the main reason for the improvement of mechanical properties.