Curing Practices for Concrete Pavements (2023)

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31   C H A P T E R   3 Introduction The curing of concrete is widely recognized as a critical step for achieving high-quality long- lasting concrete pavements. While the most common curing practice is the application of membrane-forming curing compounds, the compound specifications, including application rates and quality control (QC)/quality assurance (QA) practices, differ among DOTs from state to state. The timing of the curing application—a critical item that is important to the success of the curing process—also differs among DOTs. State DOTs’ practices also vary with respect to additional curing measures taken to protect the concrete during adverse weather conditions. A survey of state DOT curing practices for concrete pavement construction is addressed in this chapter based on responses to specific questions regarding the following topics: • Extent of DOT use of concrete pavements • Curing procedures allowed by DOT specifications • Curing material types used and specifications • Application rates and details • Pre-certification process • How the timing of the curing is established, including objective and subjective evaluations • Pre-construction evaluation of curing • Approaches followed to ensure the specified application of the curing (QA) • Use of support software • Use of sensors to aid curing procedure or QA evaluation • QC requirements in specifications • Weather conditions under which concrete paving is permitted • Additional curing measures required when paving under adverse weather conditions • Procedures taken if early-age cracking occurs • Accelerated construction • Internal curing Practices of State DOTs The presentation of responses to the survey question is organized into the following general categories: • Inventory of Concrete Pavement Mileage • Specification of Curing Concrete Pavement Construction • Types, Rates, and Evaluation of Curing • QC/QA of Concrete Curing • Adverse Weather Curing • Specialty Concrete Curing Survey of State Pavement Curing Practices

32 Curing Practices for Concrete Pavements The survey questions associated with the summary of the responses are provided with the associated tables or figures illustrating the responses and also listed in Appendix A. A tabulated summary of responses is provided in Appendix B. A tabulated summary of curing specifications of the responding State DOTs is presented in Appendix C. Inventory of Concrete Pavement Mileage Figures 20, 21, and 22 pertain to concrete pavement use in three different aspects. Figure 20 indicates a wide range of lane-miles distributed across several states. Figure 21 pertains to con- crete pavement constructed in the last 15 years. Figure 22 refers to pavement construction Q2. How many lane miles of concrete pavements does your agency maintain? Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 0 1 to 99 100 – 999 1,000 – 4,999 5,000 – 9,999 10,000 – 14,999 15,000 – 19,999 20,000+ Figure 20. Lane miles maintained (95% response). Q3. How many lane miles of concrete pavements has your agency constructed in the past 15 years? Responses 0.0% 5.0% 10.0% 15.0% 20.0% 25.0% 30.0% 35.0% 40.0% 45.0% 50.0% 0 to 99 100 – 999 Other (Please specify in the box below) Figure 21. Lane miles constructed in last 15 years (82% response).

Survey of State Pavement Curing Practices 33 Q4. How many lane miles of concrete pavements does your agency plan to construct in the next 5 years? Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 0 to 1 1 to 99 Other (Please specify in the box below) Figure 22. Lane miles planned in next 5 years (82% response). planned for the next 5 years. A conservative estimate of concrete paving in the near future would entail at least 5 million cubic yards of concrete. Given this amount of work in the future, curing is an important aspect to be addressed in future specifications and ties into the data illustrated in Figure 23. Specification of Curing Concrete Pavement Construction Results in Figure 23 indicate that over 90% of surveyed state DOTs have construction speci- fications that address curing, while approximately 10% maintain special provisions for curing. Approximately 3% do not construct concrete pavement since they do not specify curing. Q5. Does your agency have construction specifications/special provisions for curing of concrete pavements? Please check all that apply. Responses 0.0% 20.0% 40.0% 60.0% 80.0% 100.0% Yes, specification Yes, special provision No Figure 23. Use of construction specifications/special provisions for curing of concrete pavements (92% response).

34 Curing Practices for Concrete Pavements Question 6 refers to the provision of a link to the agency construction specifications for curing concrete pavement. A summary of specification requirements is included as a table in Appendix C. Figure 24 summarizes the responses to a question regarding the types of curing materials/ methods specified for concrete pavement construction. It can be assumed that all agencies specify an ASTM Type II curing compound that essentially includes a white pigment to visually track the spray application. Few agencies specify the use of a Type I compound. Other curing methods were bought to light by a survey question illustrated in Figure 24: • Polyethylene sheeting (68%) • Wet burlap or BurLene® (62%) • Cotton mats (21%) • Water spray, fogging, or misting (38%) • Evaporation retarders (18%) The data regarding these other curing methods can be examined from two perspectives (depicted in Figure 24) in terms of the four FHWA climatic regions in the United States (39). One comparison is related to wet versus dry regions and the other to freeze versus no-freeze Q7. What curing materials does your agency specify or allow for concrete pavement construction specification? Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% 100.0% ASTM Type I or equivalent curing compound. ASTM Type II or equivalent curing compound. Polyethylene sheeting. Wet Burlap or BurLene. Cotton mats. Water spray, fogging or misting. Evaporation retarders. Figure 24. Curing materials specified or allowed for concrete pavement construction (87% response).

Survey of State Pavement Curing Practices 35 regions. ese comparisons are in each circumstance comparing usage between either the dry and wet zones or the freeze and no-freeze zones and are displayed in Figure 25. e use of polyethylene sheeting and wet burlap or BurLene display the greatest distinctions among these comparisons in relation to their greater usage in wetter and colder climates. Examining the survey response data from the perspective of a dry-freezing climate, agencies allow for the use of polyethylene, wet burlap or BurLene, water spraying or fogging, and even evapo- ration retarders in this climate category. Experiences with these types of curing technologies suggest that they release less moisture and may, under certain conditions, have greater application to con- crete paving. Another climatic-related dimension regarding the use of polyethylene sheeting and wet burlap or BurLene may be related to cold weather paving, for which these curing methods oer a certain degree of insulation against damage due to low temperatures. See Figure 26 for more data. Few agencies responded to Question #8 of the survey: “Of those curing materials checked above, please list in the box below the combinations that include either a Type I or II curing compound your agency would allow to be used and the criteria, if any, associated with the use of that combination.” Figure 25. LTPP climatic regions. LTPP is an AASHTO/TRB program to evaluate pavement test sections around the country. 0% 10% 20% 30% 40% 50% Polyethylene Sheeting Wet Burlap or Burlene Cotton Mats Water Spray, Fogging Evaporation Retarder Wet Dry Freeze No Freeze Figure 26. Curing methodology versus climatic region.

36 Curing Practices for Concrete Pavements Nonetheless, the following Type I/II combinations were noted: • After the use of cotton mats and evaporation retarders together • With water spray and fogging • After the use of wet burlap or BurLene used when plastic shrinkage cracking occurs • After the use of cotton mats • With polyethylene Even though most state DOT specifications do not take advantage of the potential curing benefits that can be derived from strategic application of specific curing measures involving combinations of different curing technologies, some agencies have specified combinations to address when occurrences such as plastic shrinkage cracking occur. One agency requires the use of fogging if there is a delay in the spray curing operation to keep the surface of the concrete moist until spraying operations can resume. Another agency requires the use of silane with the curing compound. Agencies are recognizing a need to address certain types of weather condi- tions and events with key combinations of construction methodology and curing technolo- gies to mitigate undesirable effects. Relative to the response to Question 9, Figure 27 illustrates the specification distribution of the different types of curing compounds, including wax-based, water-based, and resin-based. Two of the survey respondents indicated a poly-alpha-methylstyrene resin compound in the “other” category. Use of wax-based and resin-based compounds is nearly equal compared to infrequent use of water-based compounds among the agencies that responded to the survey. Use of wax-based and resin-based compound data climatically is illustrated by the bar chart in Figure 28. Examination suggests little evidence to support variations in use between the curing compound types among the different climatic zones. The list of the standard curing compound specification requirements used by the responding state DOTs is shown in Appendix C. This data was assembled from review of the specification documents requested as part of the survey questionnaire. Question 10 refers to the brand of curing compound. The data is not included in this report in compliance with NCHRP rules. Q9. Type of curing compound specified or allowed by your agency. Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% Wax based Water based Resin based Other (Please list in the box below) Figure 27. Type of curing compound specified or allowed for concrete pavement construction (87% response).

Survey of State Pavement Curing Practices 37 Types, Rates, and Evaluation of Curing The data shown in Figure 29, which pertains to measures taken by state agencies to pre-qualify curing materials for construction, is presented with respect to: • Certification from AASHTO, National Transportation Product Evaluation Program (NTPEP) • Approval by the state DOT product evaluation office • Testing conducted at DOT chemistry/materials laboratory to verify performance • Certification of approval from other State DOTs • Other methods The survey question related to the data shown in this figure was generated to gain insight into how state agencies qualify materials (i.e., curing compounds) for curing hardening concrete. Several agencies qualify their curing materials via NTPEP or their agency product evaluation office. Others conduct curing compound qualification testing in their own laboratory or testing facilities. The intent of the “other methods” choice in the questionnaire was to identify other pre- qualify methods different from the choices listed; nevertheless, all responses in that category simply referred to ASTM C309 testing requirements that would be followed as such by a testing labora- tory or agency. It is also pointed out that approximately two thirds of the respondents have a process in place to identify unacceptable curing materials or processes, as noted in Table 2. The data shown in Figure 27 pertains to measures taken by state agencies to pre-qualify. Figure 30 illustrates data summarized in Appendix C regarding the rate of spray application used by agencies. A benchmark for manufacturer-suggested curing application rates for most curing compounds has ranged from 180 to 200 ft2/gal (which is also the rate used for ASTM moisture evaporation testing). However, many agencies use rates much greater than that shown in Figure 30. Nonetheless, the data shown in Figure 31 contrasts with the data shown in Figure 30 since a number of agen- cies use manufacturer-suggested rates for their project specifications. The alternative is to deter- mine rates via laboratory testing or other means. The drawback to this approach is the typical lack of connection between the rate of application used to conduct ASTM C156/309 testing and 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% Resin Based Water Based Wax Based No Freeze Freeze Dry Wet Figure 28. Curing compound use versus climatic region.

38 Curing Practices for Concrete Pavements the rate of application used under field conditions. Even though agencies have special provisions for determining the applied rate of application under field conditions, it can be assumed that the rate of application used to qualify a curing compound for field use would be applied at the same rate if there were no established criteria to determine otherwise. Furthermore, relative to the data in Figure 31, one agency indicated they determined the specified rate based on past experience. Others stated that they did not use a specified rate as much as they emphasized full coverage and a minimum time to apply the curing after pav- ing. One agency specified the application of the curing compound in two passes with a mini- mum delay time between coats. Each pass was required in two directions (which is likely to reduce gaps and promote uniformity in the application process). Another agency stated that slab thickness was used as a criterion to dictate what the specified rate of application should be. Q11. What pre-qualifications and/or standard qualifications measures does your agency undertake for approval of a curing product? Please check all that apply. 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% Other methods (Please list in the box below) Certification of approval from other State DOTs. Testing conducted at DOT chemistry/materials laboratory to verify perfromance. Approved by state DOT product evaluation office Certification from AASHTO, National Transportation Product Evaluation Program (NTPEP) Re sp on se s Figure 29. Pre-qualifications and/or standard qualifications measures for approval of curing (89% response). Q12: Does your agency have a process for identifying unacceptable curing process? Answer Choices Responses No. of state responses Yes 65% 22 No 35% 12 Total: 34 Table 2. Agencies using a process for identifying unacceptable curing processes (87% response).

Survey of State Pavement Curing Practices 39 The data illustrated in Figure 32 pertains to the method of application: • Self-propelled mechanical sprayer for slip-formed pavement • Hand-held sprayer for slip-formed pavement • Self-propelled mechanical sprayer for side-formed pavement • Hand-held sprayer for side-formed pavement • Hand-held sprayer for odd paving widths and shapes • Hand-held sprayer for after form removal and/or sawed joints All agencies use mechanical spraying for curing slip-formed paving, and most also allow some form of hand-held spraying. Hand-held spraying is used with slip-form paving and for filling in areas that cannot be reached with mechanical spraying. Q13. What is (are) the specified rate(s) of application allowed by your agency? Please choose from the following ranges: Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% One gallon per 50 ft2 -100 ft2 surface. One gallon per 101 ft2 - 150 ft2 surface. One gallon per 151 ft2 - 200 ft2 surface. Other Figure 30. Specified curing rates (85% response). Q14. Based on your response, what criteria does your agency use to determine the rate of application? Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% Manufacturer’s recommendation Laboratory testing results (no responses) Other Figure 31. Criteria to determine rate of curing (82% response).

40 Curing Practices for Concrete Pavements QC/QA of Concrete Curing The data illustrated in Figure 33 shows the means to determine the specified time to apply the curing compound after paving: • By agency specification • By the engineer’s judgment • By the contractor’s judgment • None Q15. What method of application does your agency specify or allow to apply a curing compound? Responses 0.0% 20.0% 40.0% 60.0% 80.0% 100.0% Self-propelled mechanical sprayer for slip-formed pavement. Hand-held sprayer for slip- formed pavement. Self-propelled mechanical sprayer for side-formed pavement. Hand-held sprayer for side- formed pavement. Hand-held sprayer for odd paving widths and shapes Hand-held sprayer for after form removal and/or sawed joints Figure 32. Method of specified application to apply curing compound (85% response). Q16. How is the criteria for the time of curing established? Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% By agency specification. By the Engineer’s judgment. By the Contractor’s judgment. None Figure 33. Criteria for time of curing (87% response).

Survey of State Pavement Curing Practices 41 It appears that most agencies have specified this item for many years with perhaps little reason to vary it. Nevertheless, some agencies do allow the decision to cure to be determined by the project engineer or the paving contractor. The factors/data considered to determine the time of curing as shown in Figure 34 include: • None • Data from embedded sensors (e.g., maturity meter) • Data from handheld sensing device(s) • Weather condition data • Visual observation data (disappearance of sheen from the concrete surface) • Other test of method data? Most agencies use visual observation to determine when to apply a curing compound. These observations focus on when bleed water has evaporated from the surface of the concrete or when the sheen has dissipated. Others use a time limit, usually no more than 30 minutes after finishing, before applying the curing (with one exception of 15 minutes). Few use any type of instrumentation or sensors to monitor conditions, although one agency uses an embedded sensor and weather station data (e.g., relative humidity, wind, temperature) to monitor evaporative conditions during curing operations. The questionnaire includes a question regarding measures taken to verify the rate of curing application during paving operations. The choices shown in Figure 35 include: • Use of a calibration template on pavement surface • Curing bridge calibration (e.g., speed of travel) • Other (i.e., curing of a pavement test strip) Most respondents chose other measures, which consisted of: • Visually inspecting items such as pattern of spraying (which assumes hand-held spraying) • Checking of use rates using a prescribed test standard • Conducting a test strip Q17. What factors/data is (are) used by the criteria checked above? Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% None Data from embedded sensors (e.g., maturity meter). If so, list the type of sensors Data from hand held sensing device (s). If so, list the device(s) Weather condition data. If so, list the type of weather data Visual observation data (disappearance of sheen from the concrete surface). Other test of method data? (Please specify in the box below) Figure 34. Factors affecting time of curing (87% response).

42 Curing Practices for Concrete Pavements • Making comparisons to a whiteness standard • No checks Figure 36 refers to practices to qualify uniformity of the sprayed application. Uniformity is a key factor in curing quality; the choice of practices selected were: • Visual inspection for any spots or bands of gray • Inventory of the amount of curing material used • Scheduled cleaning/inspection of spray nozzles • Application rate measurements • Other Most agencies simply check uniformity visually (one agency used photographic evidence for whiteness), but other practices included conducting an inventory of the amount of curing compound applied to the concrete surface, as noted in Figure 36. Fewer agencies check on the rate of applica- tion, which is closely associated with conducting an inventory (one agency used a field protocol for this determination). Regularly conducting cleaning of the spray nozzles indirectly affects uniformity. QA procedures and methods (Figure 37) are always of great importance to owner/agencies; moreover, it is of interest to explore those practices in the paving industry for curing as follows: • None • Volatile organic compound (VOC) validation • Verification of full coverage on flat and vertical surfaces Q18. What qualification measures/testing does your agency undertake to verify the proper application rate, quality of spraying and applicators’ proficiency? Please check those that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% Use of a calibration template on pavement surface Curing bridge calibration (e.g., speed of travel) Other (i.e. curing of a pavement test strip). Please list in the box below items such as degree of uniformity, proper dosage rate, etc. Figure 35. Measures to qualify rate of application of curing compound (69% response).

Survey of State Pavement Curing Practices 43 Q19. What QC measures are required to ensure uniformity of curing application? Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% None Visual inspection for any spots or bands of gray. Inventory of the amount of curing material used. Scheduled cleaning/inspection of spray nozzles. Application rate measurements. Other (Please list in the box below) Figure 36. Measures to qualify uniformity of curing application (85% response). Figure 37. QA requirements for curing (87% response). Q20. What QA requirements are specified for curing? Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% None Volatile organic compound (VOC) validation. Verification of full coverage on flat and vertical surfaces. Visual/photographic inspection for whiteness. Other (Please specify in the box below) • Visual/photographic inspection for whiteness • Other A significant portion of the agencies surveyed (illustrated in Figure 37) do not have QA proto- cols for curing; moreover, most do not check for VOC content, although nearly 10% address it in their curing specifications (see Appendix C). A greater number of agencies use visual techniques to check for either full coverage or whiteness. Agencies that responded to the other category listed items such as ASTM C309 or similar testing. Figure 38 indicates the use of software to meet curing needs associated with paving operations. Again, most agencies do not use software for this purpose, although some do use HIPERPAV

44 Curing Practices for Concrete Pavements software, which simulates the effects of the climate on the hydration and behavior of early-aged concrete paving. The software represents specifically the effects of weather during the curing process on the potential for slab cracking to occur and the optimum time to conduct saw cut- ting operations; one agency, however, did note that it does not represent the effects of the curing compound. Other measures used for curing are specific to an agency curing practice. Figure 39 illustrates the use of various sensors/instruments for monitoring conditions inter- nal to the concrete during curing operations. Again, most agencies do nothing in this regard, while a few employ some technologies to monitor conditions. Some agencies make use of ambient wind speed, relative humidity, and temperature to employ the ACI 305 evaporation chart. This procedure is conducted in a number of ways. One agency requires the contractor to subscribe to a weather service to monitor the project’s ambient conditions. Another agency ensures that the Q21. What software does your agency use for curing QA/QC? Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% None HIPERPAV Customized Excel spreadsheet. Other software (Please explain in the box below) Figure 38. Software tools used for curing QA/QC (90% response). Q22. What sensors are used by your agency to monitor curing quality? Please check all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% None Wind meters. Relative humidity sensors. Temperature gauges or meters. Other (Please explain in the box below) Figure 39. Sensors used for monitoring curing quality (90% response).

Survey of State Pavement Curing Practices 45 rate of application is within ±50 sf/gal of the designated rate for the project. Yet another agency uses maturity meters to track conditions internal to the concrete during curing. Figure 40 illustrates the measures that agencies take to address early-aged uncontrolled slab cracking. This type of distress is often associated with curing quality during and after the curing process; however, it can be due to a variety of causes such as materials (plastic shrinkage crack- ing), construction methods (i.e., saw cut depth and timing), or construction-weather related. Investigating the cause of cracking is of interest as indicated by the high percentage of agencies that do carry out investigations of that nature when the need arises. The most common reaction is to remove and replace cracked concrete, particularly if the cracks are full depth. Alternatively, a number of agencies allow cracked slabs to remain in place (especially if due to drying shrinkage) but at a penalty to the contractor in some cases. Both options are sound, although the main objective is to prevent further cracking. Nonetheless, paving contractors bear the financial responsibility for removal and replacement, as well as revision of the QC plan, to limit additional cracking. Some agencies consider the number and configuration of the cracks in determining whether removal is necessary. Slabs with single longitudinal or transverse cracks that have not spalled can remain in place, while slabs with multiple cracks dividing the slab in three or more segments require replacement. Another example allows for a maximum of 18 panels per lane-mile before replacement is required. Crack repair is allowed as long as no two consecutive panels are cracked; otherwise, they must be replaced. Furthermore, removal must be carried out until a quarter-mile segment of the paving has less than four cracked panels. Cracks left in place require routing and sealing unless the cracks are less than 1.5 m in width. Upon cracking, contractors are typically required to resubmit an action or QC plan to limit the development of uncontrolled cracking. Q23. How does your agency address early-aged uncontrolled cracking? Please check all that apply. Responses 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% Investigate causes. (If checked, please see Q24) Leave slab in place. (If checked, please see Q24) Remove and replace (R&R) slab. (if checked, please see Q24) For the R&R (if checked), please explain the related financial responsibilities associated with the work. Figure 40. Measures to address early aged uncontrolled cracking (87% response).

46 Curing Practices for Concrete Pavements Adverse Weather Curing The bar charts shown in Figures 41 and 42 refer to a question regarding the criteria that agen- cies use to define acceptable and adverse weather conditions relative to curing concrete paving. The criteria for acceptable weather conditions were categorized as: • Temperature (>40oF and <90oF) • Relative humidity (>20%) • Wind speed (<40 mph) • Chance of rain or snow (<60%) • Use ACI 308 evaporation limit criteria • Other The criteria for acceptable weather conditions were categorized as: • Temperature (>90oF or <40oF) • Relative humidity (<20%) • Wind speed (>40 mph) • Chance of rain or snow (>80%) • Use ACI 308 evaporation limit criteria • Other Other criteria pertained to careful assessment of the weather conditions before paving to determine if a placement window was available. Most agencies will allow paving under adverse Q25. What criteria does your agency use to define acceptable weather conditions for paving cured concrete? Check and respond to all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% Temperature (say, greater than 40°F and less than 90°F)? Relative humidity (> 20%). Wind speed (< 40 mph) Chance of rain or snow (<60%) Use ACI 308 evaporation limit criteria Other Figure 41. Criteria for acceptable weather conditions for paving cured concrete (85% response).

Survey of State Pavement Curing Practices 47 weather conditions as long as proper protection measures are taken. For instance, agencies do not allow for paving to start or continue during rainfall. Ambient temperature conditions must be 34°F (1°C) and rising and less than 120°F (48°C) with ACI 308 (Menzel) evaporation chart within limits (>0.2 lb/ft²/h) and concrete temperature <95°F (35°C). Some agencies require an estimate of induced stress versus the strength of the concrete. The contractor is also required to present a cold-weather protection plan if it is warranted. Figure 43 illustrates the responses regarding additional curing measures taken when paving under adverse weather conditions: • Cover the pavement with protective sheeting. • Set up vertical barrier to lessen impact of high wind. • Increase application rate in hot, dry, and high-wind conditions. • Halt paving operations. • Use curing blankets to cover curing compound when anticipating cold temperatures. • In hot weather switch to nighttime paving. • Use evaporation retarders in dry, warm weather to prevent evaporation before curing. • Please add additional clarifications. Most of the additional items are measures that would be taken by a contractor. Halting paving is typically only conducted to allow other precautions to be taken. Additional clarifications as noted are other necessary protections that could be taken to mitigate the effects of adverse weather conditions. Q26. What criteria does your agency use to define adverse weather conditions for paving? Please check/respond to all that apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% None Temperature (>90°F or <40°F). Relative humidity (< 20%). Wind speed (> 40mph). Chance of rain or snow (>80%) Use ACI 308 evaporation limit criteria Other (Please explain in box below) Figure 42. Criteria for adverse weather conditions for paving cured concrete (85% response).

48 Curing Practices for Concrete Pavements Q27. What additional curing measures does your agency consider when paving under adverse weather conditions? Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% Cover the pavement with a protective sheeting. Set up vertical barrier to lessen impact of high wind. Increase application rate in hot, dry and high wind conditions. Halt paving operations. Use curing blankets to cover curing compound when anticipating very cold temperatures. In hot weather switch to nighttime paving. Use evaporation retarders in very dry warm weather to prevent evaporation prior to curing. Chance of rain or snow; if checked, list the % chance and the measures to protect freshly placed concrete. Please add additional clarifications in the box below. Figure 43. Criteria for adverse weather conditions for paving cured concrete (82% response).

Survey of State Pavement Curing Practices 49 Specialty Concrete Curing The survey questionnaire inquired as to the use of internal curing for concrete paving con- struction. Only approximately 10% of responding agencies specified the use of internal curing, as noted in Figure 44. The data illustrated in Figures 45 and 46 refer to the use of high early strength (HES) concrete in concrete pavement repair that involves short lane closure times. Nearly 90% of responding agencies employ the use HES for short-term repair and rehabilitation work. Nearly 80% use a standard ASTM Type II curing compound for this type of construction. Other methods of curing are shown in Figure 44 along with the percentages of use in specifications. Q28. Has your agency included internal curing in concrete pavement construction? Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% 90.0% 100.0% Yes (Please see Q. 29) No (Please see Q.30) Figure 44. Specification of internal curing for paving cured concrete (85% responses). Q31. Does your agency specify curing for high early strength (HES) concrete for replacement slabs or repair patches in concrete pavement rehabilitation projects requiring short lane closures? Responses 0.0% 20.0% 40.0% 60.0% 80.0% 100.0% Yes No Figure 45. Specification of HES concrete on short lane closures (85% responses).

50 Curing Practices for Concrete Pavements Q32. What curing method does your agency specify for HES concrete for short lane closures? Please check all answers apply. Responses 0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0% 70.0% 80.0% ASTM Type I or equivalent curing compound ASTM Type II or equivalent curing compound. Curing blankets Wet Burlap Figure 46. Curing method specified for HES concrete on short lanes closures (72% responses).