Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
4 C H A P T E R Â 1 Background Concrete curing is widely recognized among state DOTs and industry as an essential con- struction step for achieving high-quality and long-lasting concrete pavements. Curing materials, when applied properly and in a timely manner, will limit moisture loss from pavement surfaces and control temperature of concrete to allow for the continuation of cementitious hydration of the concrete mixture and the development of desired properties of strength and durability, as well as to prevent or mitigate shrinkage cracking. Most state DOTs follow specifications or special provision requirements for concrete pave- ment curing, which may include the types of curing materials used and application rates, as well as timing of application and duration of curing. These specifications and/or special provisions may vary among states in the same climatic region and/or among states in different regions. The differences include type of curing material, rate and time of application, application method, curing measures to mitigate early moisture evaporation, and special curing needs in adverse weather to maintain the overall temperature or prevent drastic temperature differentials within pavement. Although applying water to the pavement surface or covering it with moist materials are considered the most effective means of concrete curing, the most common curing practice for concrete pavements among state DOTs is the application of membrane-forming curing com- pounds because of its ability for rapid application during a fast-moving paving operation that places fresh pavement with large surface areas and sides. Some states in regions with dry and warm weather spray freshly placed concrete with moisture fogging to reduce loss of moisture from the pavement surface to allow finishing and texturing of the surface before applying the final stage of curing with curing compound. Insulation blankets are used by some states and especially in cold regions to prevent drastic cooling of the overall concrete temperature and to limit drastic temperature differentials across the pavement surface and depth. Some of the challenges state DOTs face are determining the proper application rate of the curing compound for their environment, ensuring quality of curing, and identifying ramifica- tions of inadequate, improper, or poor curing on short- and long-term performance of concrete pavements. Some states are experimenting with sensor technology to better assess quality of curing to improve their current curing specifications. Moreover, nomographs are available to estimate pavement surface evaporation. The main objective of this synthesis is to document state DOT practices for curing concrete pavements including, among other aspects, materials, application rates, timing, QC/QA pro- cedures, and specific measures adopted when paving under adverse weather conditions. The information in the report pertains to new concrete pavements, including full-depth overlays, Introduction
Introduction 5 inlays, widenings, and high early strength concrete for pavement replacements. The concepts of internal curing and curing needs for sustainable pavement curing are briefly discussed. Information has been gathered from a literature review, a survey of state DOTs, and case examples of curing concrete-pavement test projects in three states. Information gaps and sug- gestions for research to address those gaps are identified. Report Organization The synthesis report is presented in five chapters and three appendices as follows: ⢠Chapter 1: Introduction ⢠Chapter 2: Literature Review ⢠Chapter 3: Survey of State Pavement Curing Practices ⢠Chapter 4: Case Examples of DOT Curing Practices ⢠Chapter 5: Summary of Findings ⢠References ⢠Appendix A: Survey Questionnaire ⢠Appendix B: Survey Questionnaire Responses ⢠Appendix C: State DOT Specifications/Special Provisions Chapter 2: Literature Review The literature review chapter includes information derived from a wide range of recent and older research publications, including manuals and guides for concrete pavements and materials from ACI, PCA, ACPA, and the Concrete Pavement Technology Center at Iowa State, as well as FHWA publications and select state DOT specifications pertaining to concrete pavement curing. The focus of the literature review is on curing practices for concrete pavement, including new and accelerated pavements for inlays, widenings, and overlays by state DOTs in normal and adverse weather. Curing guides for cold weather and hot weather concrete paving are included, as well as specification requirements for curing from selected states. Effectiveness of individual curing methods and combination of curing methods to achieve best curing and performance outcomes are described. The ramifications of inadequate, improper, or poor curing are also addressed. The chapter includes brief descriptions of the concepts of internal curing method and curing needs for sustainable pavements. Chapter 3: Survey of State Pavement Curing Practices This chapter presents the results of the survey questionnaire prepared and forwarded to state DOT members of the AASHTO Committee on Materials and Pavements (COMP). Responses from 38 states were received, representing 76% of all DOTs. The questionnaire results were ana- lyzed and summarized in tables and graphs and are presented with commentary in this chapter, as well as in Appendices A and B. Chapter 4: Case Examples of DOT Curing Practices Pavement curing test projects in three states (California, Texas, and Florida) were exam- ined and are presented as case examples to supplement other information collected in this synthesis. The three projects discussed in this chapter include the use of sensor technology to evaluate the quality of curing, impact of weather, and ramifications of inadequate or improper curing.
6 Curing Practices for Concrete Pavements Chapter 5: Summary of Findings The report concludes by presenting findings from the information obtained from the survey of state practices, case examples of curing test projects, and the literature review. Technology information gaps are identified and suggested for research to address those gaps. References The report includes a list of the sources of information in the report and makes available to readers more in-depth information on specific aspects of concrete pavement curing practices. Appendices A, B, and C Appendix A contains a copy of the questionnaire as prepared and forwarded to the COMP representative of each state. The survey was prepared using electronic survey software and transmitted electronically to all COMP members for their responses. Appendix B includes a tabulation identifying the states that responded to items listed in each question. Appendix C is a tabulated summary of the specifications received from the responding state DOTs.
