Engineer. Virginia. Virginia. opinions, findings, and conclusions expressed in this. Highway & Transportation Research Council

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1 OF COLD WEATHER PAVING SPECIFICATION REEXAMINATION BITUMINOUS CONCRETE FOR W. Maupin, Jr. G. Engineer Research opinions, findings, and conclusions expressed in this (The are those of the author and not necessarily those of report Highway & Transportation Research Council Virginia Cooperative Organization Sponsored Jointly by the Virginia (A of Highways & Transportation and Department University of Virginia) the 1978 April 78-R49 VHTRC by the sponsoring agencies.) Charlottesville, Virginia

2 BITUMINOUS RESEARCH ADVISORY COMMITTEE L. ALWOOD, Chairman, District Materials Engineer, VDH&T MR. R. Mr. A. D. BARNHART, District Materials Engineer, VDH&T MR. P. F. CECCHINi, District Engineer, VDH&T MR. J. L. CORLEY, Assistant District Engineer, VDH&T MR. W. A. DENN!SON, District Materials Engineer, VDH&T MR. C. E. ECHOLS, Asst. Prof. of Civil Engineering, U.Va. MR. R. V. FIELDING, Materials Engineer, VDH&T MR. C. S. HUGHES, Assistant Head, VH&TRC MR. A. B. JOHNSON, Assistant Construction Engineer, VDH&T MR. C. G. MCALLISTER, Chief Chemist, Materials Division, VDH&T MR. H. E. MARSHALL, District Engineer, FHWA MR. R. S. THO S, Bituminous Engineer Maintenance Div., VDH&T MR. R. D. WALKER, Chairman, Dept. of Civil Engineering, VPI & SU MR. R. P. WINGFIELD, Assistant Maintenance Engineer, VDH&T ±i

3 cold weather paving specification for bituminous The adopted in 1970 was reexamined to determine its concrete and any need for revisions. Density and temper- effectiveness measurements were obtained on five field projects and ature results and feedback from field personnel were The to recommend (i) changes in the nomograph, (2) a prohibition used paving on a frozen base or when the base temperature is less of 35OF, and (3) allowing the use of a vibratory roller for than SUMMARY observations were made of the rolling practices employed. the 8-minute rolling time, if the required density can be achieved. iii

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5 OF COLD WEATHER PAVING SPECIFICATION REEXAMINATION BITUMINOUS CONCRETE FOR W. Maupin, Jr. G. Engineer Research ambient temperatures experienced in fall and winter Cold cause inadequate compaction of bituminous pavements to an can that results in poor quality pavements. Specifications extent attempt to avoid compaction problems associated with usually have developed a systematic approach to the Investigators in which the cooling rate of a bituminous mat is deter- problem from mat thickness, laydown temperature, base temperature, mined velocity, and solar radiant flux. (1,2) Mathematical relations wind been developed to determine the allowable rolling time in have of the above variables. terms advantages of a specification developed by this approach Two (i) that the purchaser can be assured that the mix will not are beyond a compactable temperature before rolling can be com- cool and (2) that construction may be safely extended into the pleted, 1970 a specification of this type was adopted by Virginia. In it the allowable minimum laydown temperature was specified for In combinations of base temperature and mat thickness. Later various specification was revised to allow the determination of the the purpose of this investigation was to determine the effec- The of the 1974 cold weather paving specifications as presented tiveness section of the Virginia Road and Bridge Specifications in A). The objective was accomplished by observing paving (Appendix by INTRODUCTION cold temperatures by forbidding all paving during winter months. fall and winter months for thick bituminous mats. minimum laydown temperature by use of a homograph (Appendix A). PURPOSE AND SCOPE obtaining pavement densities, and gathering temperature practices, to determine whether the specification is satisfactory and if data is being attained. Data were obtained on five paving compliance projects.

6 feedback from field personnel using the specification Also been considered in the recommendations for revisions. has attempt was made to gather data during periods of cold An temperatures, but in some instances the ambient tempera- ambient (Table i) during October and November of 1976 and projects projects included new construction and two projects were Three included nuclear and core densities, mat thickness, Data practice, base temperature,!aydown temperature, and rolling Job Identification.!.4 Maint. 1.8 solutions of heat transfer equations using the Computer difference method can be used to predict the cooling rates finite DATA C0LLECTION warmed during the day to such an extent that the data were ture useful. Data were obtained at I0 locations on each of 5 not maintenance overlays. measurements of the mat taken periodically after temperature paving. Tab le! Monitored Projects Mix Average Type Type Thickness, Operation Temp. Base Range, OF in. New Const New Const B New Const C Maint RESULTS Verification of Nomograoh

7 bituminous mars. Tegler and Dempsey developed a graphical of to predict the cooling rate.<2] Information that must form provided is time of day, date, amount of sunshine, wind be mix temperature, base temperature, and mat thickness. velocity, and Corlew also developed a simi$ a type of solu- Dickson for the cooling rate of bituminous mats.< ; The computer tion used to predict the cooling rate of a mat under various is conditions. Usually the solar flux and wind ve- environmental are considered constant and the cooling rate is estimated locity curves for various mix temperature and base temperature from newness of the specification and a desire not to impose un- the restrictions on the contractor, the allowable laydown tempera- fair from the homograph were slightly lower than those obtained tures Dickson and Corlew's work. from was established in the present study. Table 2 lists verification predicted time for a fresh mat to cool to 175 F according to the and the measured time. The predicted times represent an Dickson mat temperature (see Figure i) whereas the field measure- average were of the maximum mat temperature at approximately the ments of the mat because of ease of measurement. Because the middle temperature time should be slightly longer than average maximum time, the predicted values compare reasonably well temperature the observed cooling time. Table 2 indicates that the mat with faster than the method by Tegler and Dempsey predicts. The cools verify that the predictive method by Dickson and measurements is reliable and confirm measurements made in a previous Corlew study. 3 nomograph in the specification should be modified to The more closely to the predictions by Dickson and Corlew's conform Contractors are now familiar with the specification and method. modification will help assure that no compaction failures occur. the nomograph should also be modified to include a maximum The rate of 420 psy (3.6 inches). The current specified application laydown temperature cannot be less than that for a 2-inch minimum therefore, the contractor cannot take advantage of heat mat; of mats thicker than 2 inches. Both of the suggested retention are shown in the homograph in Appendix B. revisions combinations. nomograph in section of the specifications was The on Dickson and Corlew's cooling rate curves. Because of based their work was verified by field measurements in Although prior to the drafting of a homograph,(3) additional Virginia

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9 60 o o -t Maximum rature p 165 psy application rate in part (a) of the specifica- The does not agree with the rate of application on the homograph tion an 80OF base temperature and 300OF laydown temperature (maxi- for allowable). The rate of application should be specified at mum 16 0 psy. I00 Upper Surface 8O Average \ O 4O O m 20 Lower Surface Temperature OF Figure!. Typical mat temperature profile. there is a possibility that a base may thaw and be- Because unstable under a hot plant mix, it is preferable that this come mix not be placed on a frozen base. A minimum base tempera- type of 35 of would seem reasonable. ture

10 Density Results and Observations of Rolling Practice observations of rolling practice and density Tabulated are listed in Table 3. results but an examination of the results indicated that the mat low, did not drop below 175 F before breakdown rolling temperature completed. The low densities experienced in these two cases was not the result of a faulty specification. were of the assumptions that was necessary to develop the One was that breakdown rolling can be completed in 15 specification The at (Table ) reveal that very few rolling times project.! minutes therefore, the assumed 15-minute rol in g exceeded breakdown rollers are now required to complete breakdown Two in the 8-minute time period. Vibratory rollers normally rolling less time to complete breakdown rol!ing therefore, a require should be allowed to use a single vibratory roller in contractor of two static breakdown rollers if rolling can be completed lieu 8 minutes. i number of roller passes was generally less than the The required by an established roller pattern. This practice number contributed to the low density (percent compaction) probably on project!c. The density of project 2 was slightly achieved using one breakdown roller and in 8 mi.nutes with two minutes rollers. 0nly one breakdown roller was used on each breakdown appears to be valid. No data were collec ed using two break- time rollers and an 8-minute roiii g time. down

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12 The results of this study have reaffirmed that the i. developed by Dickson and Cor!ew can be used method The data support the assumption made in the original specifi- 2. that the rolling time using one breakdown roller is cation From the limited number of projects observed it appears 3. the specification is producing adequate compaction, if that Modify nomograph ro more closely approximate cooling rare!. by the Dickson and Cor!ew method and extend predictions application rare to 420 psy (3.6 in.). part (a) of section ro read 160 psy rather Change 165 psy so that it will agree with the homograph. than Specify that no paving will be allowed on a frozen base 3. when the base temperature is less than 35 F. or Allow the use of a single vibratory roller operating in 4. vibratory mode for the 8-minute rolling time, if the the required density can be achieved within 8-minutes. CONCLUSIONS to predict the cooling rate of freshly placed bituminous mats. 15-minutes. a satisfactory rolling practice is followed. RECOMMENDED REVISIONS TO SPECIFICATION

13 P. F. Dickson, to the Related " Requirements, Technologists, J. S. Corlew, "Thermal Computations amd of Pavement Compaction Cessation Study G. W., Jr., "Cold Weather Paving Requirements for Maupin, Concrete," Virginia Highway Research Council, Bituminous February REFERENCES i Association of Asphalt Paving Proceedings, 39 Ci970). Vol. Phil!ip A., and Barry J. Dempsey, "A Method Pre- Tegler, Compaction Time for Hot-Mix Bituminous Concrete," dicting Engineering Series No. 43, Engineering Experiment Highway University 0f 'l inois', May Station,

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15 " 180 7O Placing Limitations- Bituminous mixtures shall not See. placed when weather or surface conditions are such that the ma- be cannot be properly handled, finished or compacted. The sur- terial upon which bituminous mixtures are to be placed shall be face time such materials are spread. the Nomograph, Table III-2, shall be used to determine the The reasonably free of moisture at follows: When the bituminous concrete course is less than (a) (165 Ibs. per square y,ard) and one roller is used ll/2-inches the 15 minute breakdown rolling, the surface tempera- for When the bituminous concrete is less than 3/ -inch (85 lbs. (b) square yard) and two or more rollers are used for the 8 per breakdown rolling, the surface temperature of the minute shall be 80" F or above. base When the base temperature is above 80' F, laydown will bc (c) at any mix temperature within the specificatio, permitted concrete intermediate and base courses which Bituminous the rate of application of the Nomograph shall conform to exceed Nomograph requirements for a 2-inch course. The rate of the is based on ; n average weight of 115 pounds per square application per inch of depth. yard the Contractor be unable to complete the breakdown Should the applicable 8 minute or 15 minute period, the placing of within mixture shall cease until sufficient rollers are available, bituminous other corrective action taken, to complete the breakdwon rolling or the specified time. within placing bituminous porous friction course mixture, the When of the mixture shall not be less than 180 F when temperature on the roadway. The weather limitations of Section placed apply to the porous friction course. shall x O" APPENDIX A TABLE III-2 COLD WEATHER PAVING LIMITATIONS 300T OF RATE APPLICATION i LLI I Z i i -'50 m LB/YD o 30 *THE RATE OF.APPLICATION IS BASED ON-.,N AVERAGE WEIGHT OF 115 POUNDS PER SQUARE YARD PER INCH OF OEPTH. minimum lay'down temperature of" the bituminous concrete, except as ture of the base shall be 80 F or above. limits.

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17 280 o " O 400 APPENDIX B Proposed Revised Nomograph COLD WEATHER PAVING LIMITATIONS Rate of Application 300-.= Oo 29O O f O 280 -" 2so O =. 210

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