Lightweight Aggregate as Internal Curing Agent to Limit Concrete Shrinkage
Drying shrinkage is a principal cause of cracking in concrete structures. The cracking can be accommodated or modified so that the performance of the overall structure is not affected. This is not true for bridge decks where drying shrinkage cracking combines with plastic shrinkage, settlement, and thermal cracking to lower the durability of the deck by allowing water and deicing chemicals to penetrate the concrete and increase the susceptibility of the reinforcing steel to corrosion. Work is underway at the University of Kansas to develop concrete mixtures that will minimize concrete shrinkage to minimize cracking in bridge decks. It has been well established that the lower restraint provided by lightweight aggregates (LWAs) can lead to increased drying shrinkage compared with mixtures containing normal aggregates, and if not adequately prewettted, the unsatured pores lead to greater water demand during construction and result in inadequate water for hydration. Due to the absorption and desorption properties of the aggregate, vacuum-saturated LWAs can readily provide an internal source of water to increase hydration and lessen the drying effects on a concrete mixture. The effectiveness of prewetted, vacuum saturated (PVS) light-weight aggregates as an internal curing agent to reduce concrete shrinkage is evaluated for curing periods of 7 and 14 days in this paper.
Lightweight aggregates as an internal curing agent for low-cracking high-performance concrete
i Acknowledgements ii List of Figures vi List of Tables vii Chapter 1 Introduction and Background 1 1.1 General Information 1 1.2 Development of Aggregate Replacement Methodologies 3 1.2.1 Internal Relative Humidity and Autogenous Shrinkage 4 1.2.2 Optimizing the Effects of Lightweight Aggregates 7 1.2.3 Influence of Pore Structure on Internal Curing 10 1.2.4 Mixture Proportioning 13 1.2.5 Benefits of Internal Curing in Sealed and Unsealed Conditions 16 1.2.6 Optimum Replacement Levels of LWA for Internal Curing 18 1.3 Applications of Internal Curing 20 1.3.1 Pavement Application 20 1.3.2 Field Application Challenges 22 1.3.3 New York Department of Transportation 24 1.4 Previous Work at KU 25 1.5 Summary 33 1.6 Scope 36 Chapter 2 Experimental Program 37 2.1 General 37 2.2 Materials 37 2.2.1 Cement 38 2.2.2 Mineral Admixtures 39 2.2.3 Admixtures 40 2.2.4 Fine Aggregate 40 2.2.5 Coarse Aggregate 41 2.2.6 Lightweight Aggregate 42 2.3 Laboratory Work 44 2.3.1 ASTM C 157 Free-Shrinkage Specimens 44 2.3.2 Free Shrinkage Measurements and Data Collection 45 2.3.3 Casting 47 2.3.4 Curing 47 2.3.5 Drying 48 2.3.6 ASTM C39 Strength Cylinders 48
Corrosion protection system for construction and rehabilitation of reinforced concrete bridges
Corrosion of metallic structures has a significant impact on the USA economy. In a recent study, the total direct cost of corrosion was determined to be $276 billion per year, of which the costs associated with the infrastructure represent 16.4%, a sizeable portion. The dollar impact of corrosion on highway bridges is considerable. The average annual direct cost of corrosion for highway bridges (including steel) was estimated to be $8.29 billion. Based on the annual cash outflows, the analysis shows that indirect (user) costs can exceed the direct cost by a factor of ten or more. The paper presents details on various methodologies presently used for rehabilitation of reinforced concrete bridges. In addition, the rationale for calculating annual cost of corrosion is discussed. A brief synopsis on various corrosion protection systems for the new construction is also provided.