DESIGN METHOD BASED ON OVERLAY PAVEMENT DISTRESS VISUAL N. K. Vaswani Dr. Research Scientist Senior opinions, findings, and conclusions expressed in this (The are those of author and not necessarily those of report Highway & Transportation Research Council Virginia Cooperative Organization Sponsored Jointly by Virginia (A of Highways & Transportation and Department University of Virginia) 1978 May 78-R26 VHTRC by sponsoring agencies.) Charlottesville, Virginia
VDH& PAVEMENT RESEARCH kdvisory COMMITTEE MR. R. L. F!NK, Chairman, Asst. Maintenance Engineer, VDH&T MR. J. P BASSETT, =avemenr Desig Engineer, VDHgT --{ MR. L. E. BRETT, JR., District eer, MR. R. H. CANODY, District Mate.rials Engineer, VDH&T MR. o. C. CLEVEL :ND, Asst. Secondary Roads Enginee., VDH&T FLR..DONALD HARRIS, Area Engineer, FHWA MR. K. H. MCGHEE, Research Engineer, VHgTRC MR. R. L. MOORE, Residen= Engineer, VDH&T MR. C. H. ROBSON, JR., District. Materials Engineer, VDH&T MR. M. B. VANN, Assistant Ccnstruction Engineer, VDH&T MR. R. D. WALKER, Head, Dept. of Civil Engineering, VPI & SU MR. J. T. WARREN, Management Serv _ces 0f ={._ _. =, VDH&T MR E WINFREY Asst D s --ic" VDH&T W.. Engineer,
method for designing thickness of overlays for A concrete pavements in Virginia is described. In bituminous method thickness is calculated by rating amount this severity of observed pavement distress and determining and total accumulated traffic. Ratings for amount and of each type of pavement distress are tabulated in severity report, and a chart for calculating accumulated traffic daily traffic counts of different classifications of from ABSTRACT vehicles is given. iii
DESIGN METHOD BASED ON OVERLAY PAVEMENT DISTRESS VISUAL N. K. Vaswani Dr. Research Scientist Senior types of distress that affect maintenance rating, The of a pavement are given in Table i. Each type is rated by MR, Types of Distress Affecting MR Value Cracking AC Alligator Rutting rarely observed Distress occasionally observed Distress Rating of Distress by Maintenance Rating of Pavement amount and severity of its occurrence as shown in Table 2. Table i s 0.f Distress No.tation Type Cracking LC Longitudinal Ru Pu Pushing Ra Ravelling Pa Patching Table 2 Amount of Distress Rating Fa_ctor Not Severe Severe Very Severe No Distress 0 0 2 3 4 6 Distress frequently observed 3 6 9
degree of severity is not defined in this report; The it is noted that on interstate pavements none of however, types of distress are rated as being severe. rating factors given in Table 2, maintenance With of each pavement is obtained as rating is rated by extent of damage only and is classified as Pa not severe. being rating values in Table 3, which reflect rating numbers in in Table 2. assigned cracks (LC) Longitudinal cracks (AC) Alligator Not severe 3 Frequent Not severe 3 Frequent Then, by use of equation I MR is obtained as MR- 92.6 2.4(LC) 2.3(AC) 1.0(Ru) 1.0(Pu) 0.9(Ra) 2.3(Pa) (I) method of determining ma ntenance r ting is applied The follows. An inspection trip over an interstate highway results as ±able 3 lllustrative Data for Rating a Pavement Type of Distress Amount Severity Rating (Ru) Occasional Not severe 2 Rutting None 0 Pushing (Pu) Ravelling None 0 (Ra) None 0 (Pa) Patching MR 92.6 2.4x3 2.3x3 1.0x2 = 76.5 applied to provide structural strength are recom- Overlays for maintenance rating values given in Table 4. These mended recommended values are based on AASHT0 Road Test results.
not be justified if pavement were on arterial would system. required thickness of an overlay is dependent on The of asphaltic concrete mix as affected by durability hardening, and stripping of asphalt. An overlay made from age, well-designed mix and properly constructed could perform satisa for I0 to 15 years without surface rejlvenation. For factorily thickness of overlay, a service life of 12 determining Determine accumulated traffic in terms i. 18-kip (8,160 kg) equivalents that of pavement has carried from date of to date of proposed construction Determine accumulated traffic in terms 2.!8-kip (8,160 kg) equivalents of will carry in 12 years after pavement overlay. The percentage ratio of traffic after 3. to traffic before overlay is overlay Tab le 4 Maintenance Rating Values for Overlays Road Classification Rating Roads 83 or less Interstate 71 or less Arterial Roads Roads Primary 60 or less 36 or less Low Primary & Secondary Roads an overlay would be justified for a pavement with an Thus 76.5, if pavement is on interstate system, but MR Thickness of Overlay years is recommended for use. The procedure is as follows. irrespective of any previous overlay. overlay, Figure I to convert traffic count in- Use to 18-kip (8,160 kg) equivalents. (8,160 kg) after overlay 18-kiP (8,160 kg) before overlay x i00. 18-ki
, 0.0 50 igure I. Determination of 18-kip equivalent F traffic count. <Conversion from I. 000. 100 0.0 uni " 18-kip 8,160
Ex amp I e From Figure 2 determine thickness of 4. for percentage ratio of estimated overlay after overlay to traffic before traffic overlay. for an interstate highway pavement that was built Thus, 1967 and had a maintenance rating of 76.5 in 1977, an overlay in be justified. Having determined need for an overlay would thickness of overlay could be calculated as outlined Determination of daily traffic in 18-kip I. equivalents. average daily traffic volume records From average daily traffic volumes on interstate, ( and primary routes are published by arterial for each year) ADT obtained for Department and 18-kip equivalents are given in 1976 5. Figure 1 is used to convert traffic Table Type ADT 18-kip Equivalents Vehicle Figure I) (From axle 6 tire 2 axle I0 tire 3 Trucks (Assume 20% of Buses axle and 80% of 2 3 vehicles) axle 58 320 14 50 lane highway For--four Traffic 2,578 x 0.5 x 0.8 1,031 18-kip. * Design and 2 axle 4 tire vehicles are not considered, because Cars damaging effect on pavement is almost negligible. ir Traffic and Safety Division reported traffic counts include *The directions of travel. One-half reported traffic is both to travel in each direction and 80% of truck traffic assumed assumed to use outside (design) lane. is below. count to 18-kip equivalents. Table 5 ADT Counts and 18-kip Equivalents 2,500 2,850 6 40 Trailer Total 2,578
0 I 2 3 4 i inch 2.3 cm 700 700 600 i600-500 500 4.00 300 300 200 -i00 I00 thickness- inches Overlay Overlay thickness versus traffic carrvin Figure Conversion units" 18-k :p 8 160 kg canacitv.
of accumulated traffic before Determination overlay. could be determined from traffic This or it can be estimated on assumption record x ADT during first year) and (b) 1.47 traffic for each year for a 20-year accumulated ( accumulated traffic after 9 years period x ADT during first year). 4,016 Rate and Accumulated Traffic Growth 5 Percent Growth Assuming Accumulated Rate Traffic 1 365 1 1.05 748 2 I.I0 1,149 3 1.16 1,572 4 1.22 2,017 5 1.27 2,480 6 1.34 2,969 7 1.40 3,480 8 1.47 4,016 9 1.54 4,578 I0 1.62 5,169 II 1.70 5,789 12 1.78 6,438 13 1.87 7,120 14 1.97 7,839 15 2.07 8,595 16 2.17 9,387 17 2.28 10,219 18 2.39 11,091 19 2.51 12,007 20 above example accumulated traffic on road In 1977 at end of ii years of service in daily traffic in 1977 x accumulated traffic rate Design Rate Growth traffic has increased at rate of 5% that year national standard). Table has been a to show (a) growth rate for each developed for a 20-year period ( ADT after 9 years year Table Period of Traffic in Years Growth Rate x 5,169 1,031 1.62 3.29 million 18-kip
of estimated traffic for life Determination overlay. of that life of bituminous mix Assuming overlay will be 12 years, projected in daily traffic Design for 12 years, rate 1,031 x 5, 789 Design of overlay thickness. of two traffics Ratio 18-kip (8,160 kg) after overlay Accumulated 18-k"ip (8,160'kg) 'before overlay Accumulated 5.97 3".29 x I00 180 percent. Figure 2 design thickness of an overlay for this ratio From 1.75 inches (4.5 cm ). is traffic during this 12-year period would be in 1977 x accumulated traffic 5.97 million 18-kip