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61Â Â Summary of Findings Findings From the results of the survey responses and literature review, a number of key findings have been drawn: 1. The standard practice among the surveyed state DOTs is to initiate curing measures on pave- ment surfaces and sides as soon as the finishing and texturing of the pavement have been completed. 2. The literature suggests that curing should remain effective until cement hydration has pro- gressed to the degree that the desired concrete properties of strength and durability have been reached, or until it is clear that the properties will develop in the absence of further curing measures. 3. Seventy-five percent of state DOTs surveyed use AASHTO M148/ASTM C309 to specify curing for concrete paving. Responding state DOTs are generally consistent regarding reflec- tance requirements but less consistent in specification requirements regarding evaporation limits or the rate of application. 4. Responding state DOTs in dry, hot, and windy climates undertake initial curing measures during or after placement of the pavement section by applying fog spray (or in rare occa- sions evaporation reducers) to reduce the rate of evaporation and minimize the risk of plastic shrinkage cracking. 5. The survey shows that 70% of the responding state DOTs use insulation blankets in cold weather paving, and 54% of DOTs use them in accelerated paving projects such as slab replacements and lane replacement or widening. 6. All surveyed state DOTs indicated that they use white-pigmented (Type II) curing com- pounds for concrete pavement construction across the full range of weather conditions, both normal and adverse. 7. The literature suggests that internal curing has a high potential to supplement external curing to achieve the desirable properties of strength and durability. The responding states showed only two DOTs using internal curing in concrete paving. Gaps in Information on Pavement Curing Technology and Practices Gaps in information related to curing for concrete pavements were identified based on the survey of the state DOTs and the literature review and are provided later for consideration in future research. Among the information gaps are the following: 1. Practices related to identifying timing of curing among the State DOTs are likely based on contractorsâ experiences, which vary across the countryâs climatic regions. There have been C H A P T E R Â 5
62 Curing Practices for Concrete Pavements some suggestions to use maturity concepts and/or short-term performance data to better define when the application of a curing method should be executed. However, more informa- tion on the use of these devises or other sensor technologies would assist state DOTs to better define the starting time for curing in pavement construction. 2. The literature characterizes the connection between the ASTM/AASHTO standard rate of application for the laboratory test specimens and the associated or specified application rate in the field as almost non-existent. Presently, the state DOTs have little capability to distin- guish between too little (under curing) versus too much (over curing). Information on evalu- ation methods to assess the amount of curing could be better defined if there was a better connection between the test conditions in the laboratory prescribed in ASTM C156/309 and conditions in the field at the time of paving. 3. There is a need for protocols to evaluate new curing regimes relevant to actual field conditions. The Menzel/ACI 308 nomograph for estimating the maximum potential rate of evaporation from a water-covered surface is the only recognizable tool for evaluating curing effectiveness. This nomograph was developed in 1954 with obvious shortcomings regarding both its appli- cability to a freshly cured concrete surface and its capability to yield any kind of critical value that pertains to the performance of modern concrete paving. Improving the relevance of this nomograph or development of new and more appropriate techniques for evaluation of curing would help better define the means and methods to manage the curing process, including the application rate, timing, and duration. Agencies today might be willing to take measures to better monitor and manage curing if the tools were in place to do it. 4. The merits of any type of curing technology, whether external and internal, need to be better characterized to accurately specify and incorporate them under varying climatic conditions throughout a paving day or various construction seasons. 5. Curing techniques and technologies will continue to evolve; tools to evaluate their effective- ness are increasingly necessary. 6. Information about specific contributions of any type of curing methodology to early and later concrete properties, as well to long-term performance of pavements, needs improved defi- nition to encourage state DOTs to specify mixtures with ingredients that have the needed characteristics and properties in the finished product. 7. Sensor technology and related numerical tools have been developed sufficiently to allow for accurate monitoring of the curing quality and to identify deficiencies in concrete curing during construction. More work is needed to further verify their effectiveness and to qualify them as reliable tools for verification of quality and adequacy of pavement curing.
