.IIWA-AR-80-001 Skid Research Program May 1981 J. R.
Contents
1. Position the truck and trailer as level as possible Jack up the trailer and position the calibrator under the left wheel Place a block of equal height under the right wheel A wood block is preferable to a concrete or similar block as it is not likely to break Lower the trailer onto the calibrator and block Use the jack to level the trail er hitch Zero the calibrator bill i eg eee pue H H 4 M ee eee ee ET ed SS Se ic MERC Rc e m M o n IT y Re ee M M PMT a o Pg a PEPPER ERREUR a e i k Le RI i A 1 Operating Instructions ML 550E and ML 250H Page 6 start the truck and turn on the equipment Allow the normal 15 minute warmup period so the equipment has time to stabilize Set both re corder sensitivity switches to the 1 mv position Press the ZERO RECORD button and adjust both position controls on the recorder so the pens are at Zero Release the ZERO RECORDER button and again zero the re corder this time using the left and right BALANCE controls on the con trol eonsole The F S controls should both be at approximately their mid range positions at this time Lock the trailer brakes using the toggle switch LOCK BRAKES located inside the locked compartment on the drivers side Add the desired wheel load with the calibrator in 100 pound increments and with the left SENSITIVITY control on the recorder adjust the pen to read one 1 major division for each 1002. amp walk around inspection of the truck and trailer should be made Check all tires for cuts and E 2 Fs Operating Instructions ML 350E and ML 350H Page 3 fay for correct air pressure Pay particular attention to the pressure in the skid tires THIS IS IMPORTANT Correct pressure is 24 pounds and this pressure must be maintained If skid tire pressure is in correct the recorded torque readings will be wrong Make certain that the trailer hitch is fastened tightly and that the safety chains are properly fastened Finally be sure that all elec trical water and any other connections are properly made Fill the water tank on the truck with CLEAN water Be sure the drain valve on the truck is closed Turn the instrument console on and allow at least I5 minutes warmup time before attempting any testing SEC 2 2 CONTROLS AND THEIR FUNCTIONS Ihe instrument console is the heart of the skid tester It controls all functions of the unit Located behind the passenger seat is a high quality Topaz brand inverter which is used to convert twelve volts DC to 120 volts 60 Hz AC This voltage is used to provide power for the timer and the strip chart recorder The inverter used is capable of providing 250 watts of power continuously but only a frac tion of that amount is used in the skid tester The inverter is con servatively rated and operated and can be expected to provide many years of service unless it is abused in
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4. district num ber 2 county number 3 route number 4 section designation 5 alternate section designation 6 direction of data col lection 7 date of data collection 8 time of data collec tion and 9 pavement temperature Prior to the start of 25 TYPICAL SKID INVENTORY PRINTOUT o1injeaioduo g 43uouoAed OUI o3eq 5052279134524 Auninq UOTjooeuTq UOI329Sg 9j UJlo1IV A uogos ojnoy AzuneD 984072510 a 0 ri M 4 in d A t Spoo UOTi19OTjTI3UOSDI 120100984044 1202009 354042 120300884143 pou ejeg 3sej en3ov 1204008341 4 3 120500783944 120600733944 QiequnN PTAS peedg TFH OT QiequnN 4S L Soueq JO ON iequnwN eueT FIGURE 9 26 data collection for a highway section the inventory crew inputs the identity code into the inventory data collec tion unit in digital form which is then printed on paper tape printout and stored on the magnetic cassette tape After each skid test is completed the skid code is printed on a paper tape printout and stored on magnetic tape for future use The twelve digit skid code provides six distinct and necessary pieces of information i lane number 2 number of lanes 3 test number 4 log mile 5 speed and 6 average SN Upon completion of tests in each county the cassettes and paper printouts are forwarded to the Planning and Research office for editing and processing A Wang Mini Computer Model 2200T as s
5. for Skid Testing Trailer Project No HROC 29 Skid Testing Trailer 1 General Information from 26 State Highway Departments on design and specifications of their skid testing trailers has been reviewed and analyzed We found that many of these trailers are of the same basic design but have minor differences as necessitated by the nceds or desires of each state After considering the various possibilities available it is proposed that the unit consist of a two wheel towed trailer incorporating a water laying system for spreading water under the tires a braking system for applying the braking action strain gauge bridges transducers used in measuring skid resistance and pavement skid test tires The testing unit must be designed to meet all requirements of ASTM E274 65T latest revision 2 Trailer Specifications Detailed specifications will include the following mm The tra ler shall be a two wheel side by side design of rugged con struction the vertical center of gravity Shall be less than 22 inches above the tire road interface The distance between the center line of the wheels shall be 60 5 inches The tow hitch shall be midway between the wheels transversely and 100 inches longitudinally ahead of the axle center line It shall be as low vertically as practicable and in no case higher than the wheel center line height A hinged stablizing strut with a caster shall be provided for supporting the trailer near the hi
6. manual T ton Single speed rear axle and other special equipment necessary to control and operate the skid trailer Detailed specifications include l Capacity Manufacturer s gross vehicle weight rating of 10 000 lbs 2 Net Design Payload Minimum of 5 000 lbs 3 wheelbase Shall be at least 125 inches and no more than 133 inches 4 Engine Shall be an eight cylinder model of not less than 390 cubic inchs displacement and develop not less than 225 net horse power at manufacturer s rated speed Shall be equipped with a mechanically operated tachometer The engine shall have sues ficient output in conjunction with the selected transmission and rear axle ratio to maintain 70 mph when testing on a pave B 1 10 ll 12 13 ment surface having a skid resistance of 75 SN and when fully loaded i e full crew water tank filled and required load on trailer Cooling System Shall be equipped with heavy duty radiator to provide adequate cooling Transmission Shall be heavy duty synchromesh Front Axle Shail be solid I ee with a rated capacity of not less than 3 500 1bs Rear Axle Manntactaracts rated capacity not less than 7 200 lbs Single speed with dual wheels and shail be capable of a top test speed of at least 70 mph Types of Wheels Seven only steel disc with proper rims for tire equipment furnished Not less than the standard SAE eee fied tire chain clearance of 1 65 inches shall be maintained be
7. IMPLEMENTATION The Statewide Skid Inventory Program that was develop ed as part of this research project has been incorporated into the Department s overall Inventory Program of streets and highways The initial Skid Inventory Program has been completed and the results have been used to identify high ways or portions of highways where work is needed to correct deficiencies As changes to data collection and storage procedures are needed a modification of skid inventory pro cedures is made 33 10 il 12 13 BIBLIOGRAPHY McCullough F F and Hankins K D Development of a Skid Test Trailer Texas Highway Department April 1965 Stone J and Gulden W Skid Resistance of Highway Pavement Surfaces Georgia Department of Transpor tation June 1974 Ford M C Asphalt Surface Durability and Skid Resistance University of Arkansas March 1978 Cole J H Gleason J G and Dale J L The Design and Construction of a System Utilizing a Trailer to Measure Skid Resistance of Paved Surfaces University of Arkansas January 1976 Csathy T I Burnett W C Armstong M D State of the Art of Skid Resistance Research Highway Research Board Special Report 95 1968 Beaton J S Providing Skid Resistant Pavements Transportation Research Board Record 622 1977 Skid Resistance National Cooperative Highwa Research Program Synthesis of Highway Practice No 14 Highway Resear Bo
8. July 1973 Walter W C Skid Resistance Study Louisiana Department of Transportation and Development June 1977 Bigelow N Skid Trailer Construction Maine State Highway Commission November 1969 Sandvig L D Macgredor L M and Shaffer R K Development and Results of a Skid Research and Road Inventory Program in Pennsylvania Pennsylvania Highway Department August 1968 Ganung G A Development and Implementation of a Skid Test Program in Connecticut Connecticut Department of Transportation April 1971 Revised Skid Code Manual Texas Highway Department APPENDIX APPENDIX A m COST The cost of each piece of equipment contained in the skid inventory unit and the data retrieval system is as follows Item Description Cost l 1972 Chevrolet Truck Chassis 3 852 00 2 Skid Trailer ML 350 HX Soiltest Inc 23 230 00 3 Water Tank amp Body 1 700 00 4 DL 12 Data Logging System Data System 3 440 00 Inc 12 Column Data Printer SN Computer Digital Readout Automatic SN Computation gi Push Button Print Command 5 Skid Trailer University of Arkansas 22 400 00 6 Body and Water Tank 1 759 00 7 Memodyne Data Logger 2 493 00 8 Memodyne Installation 1 030 00 9 Wang 2200T 11 663 00 10 Printer 2221W 5 085 00 11 Floppy Diskette 6 295 00 The original skid testing unit cost 28 782 the first modification cost 3 440 and the second modification cost 27 682 Cost of the data storage and retrieva
9. bridges with a regulated DC power gris is fed to the two track recorder The speed will be obtained from a DC electrical tachometer generator that is driven by a take off from the towing vehicle s speedometer driver The recorder shall be a specially modified two channel pressurized ink recorder with two event markers Speed of response shall be such that not more than one second is required for full scale deflection All controis are preset A dual chart drive allows use of the recorder during test operation or in static condition During tests the chart shall be driven at a speed proportional to the tester speed by a speedo meter cable takeoff which is energized by a solenoid clutch assuring that paper is consumed only during test cycles When the skid tester is not in operation a motor drive can be used to move the charts for static calibration and testing A third pen marks a reference pulse on the chart as the last event in the sequence of actions comprising one test The reference pulse shows reference calibration of the output obtained and also the speed at which the test was made The instrument console will be mounted between the driver s and pas senger s custom bucket seats in truck cab It will house the main fuse ammeter voltmeter and recorder timer is in a separate cabinet Also included will be circuit lights for the tester timer water system and brakes and manual control switches to start defeat and stop the t
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12. mph over the expected range of operation The instrumentation must be capable of operating under the vibration conditions normally encountered in the towing vehicle This will require rugged construction and ability of the marking system to operate properly under vibration ao RECOMMENDATIONS The following recommendations are based first on the needs of the Arkansas Highway Department as compared to the budgetary resources avail able and secondly on the vast experience of several states engaged in skid testing activities Therefore we recommend that A The Equipment Division procure a tow truck that meets the speci fications contained in part III of this report B The Equipment Division obtain and install a combination water tank and body on the tow truck Specifications in part III C The skid testing trailer and associated equipment needed for a complete testing unit be obtained from a commerical source D The successful bidder furnishing the skid testing trailer shall install all equipment required on tow truck and trailer cali brate and check out the completed unit Items c and d will be awarded as one contract Pons APPENDIX D ARKANSAS STATE HIGHWAY DEPARTMENT Division of Planning and Research Specifications for skid Number Computer and Printer GENERAL DESCRIPTION The skid number computer and printer is to be used with an existing skid test trailer conforming to ASTM E274 65T specifications I
13. pounds of wheel load Be sure to tighten the lock nut on this control when finished with calibration Now release the trailer brakes and press the CALIBRATE button Make a note of the reading obtained This reading is now the calibrate re ference number and it is used to indicate that the equipment is working properly and that the unit is in calibration Se To calibrate the right wheel repeat the above procedure on that wheel When both wheels are calibrated the unit is ready for road service SEC 3 4 CALIBRATION OF MODELS RECORDING SPEED LEFT AND TORQUS RIGHT Position the truck and trailer as level as possible Jack up the trail er and position the calibrator under the left wheel Use a wood block equal height under the right wheel Start the truck and turn on the equipment Allow a fifteen 15 minute warmup period for the equipment to stabilize Set the recorder sensitivity switch to the 1 mv position on the right channel Set the RECORD switch on the console to the left position Press the ZERO RECORDER button on the console and adjust the right posi tion control on the recorder to indicate zero on the right channel Release the button and again zero the recorder this time using the left BALANCE controli on the console The F S controls at this time should be in their mid range position Lock the trailer brakes using the toggle switch LOCK BRAKES Located in Side the locked compartment onthe drivers side of th
14. should become defec tive necessitating removal for repair or replacement proceed as follows l dack up the trailer and remove the wheels and drums 2 Remove the four 4 bolts which hold the backing plate to the torque tube If your trailer has disc type brakes the calipers must be removed first if your trailer has drum type brakes the calipers need not be removed 5 Remove the five 5 bolts which hold the torque tube to the axle 4 Remove the cover from the small junction box located on the trailer tongue and disconnect the appropriate four 4 wires and shield which is fed through the sealtite waterproofing from the torcue tubes DO NOT REMOVE THE CONNECTIONS GOING TO THE UMBILICAL CORD Mark the cables left and right 5 Pull the disconnected wire out of the sealtite back to the torque tube 6 Using a wheel puller remove the torque tube from the trailer de Install the new torque tube BE SURE THAT THE TUBE IS INSTALLED ON THE CORRECT SIDE The side is plainly stamped on the torque tube E 8 D m k ao pomme qum m i cix Ecc a cp MES NE MMC S rm D Ec cec Econ a ee KE ch nep pnm Spy END ium hoe ee ee eS a UN Rue t o m LL ge E irm reapse co mm onn mv com o i qun ESOS cru ME ER ADEM M CEDE ar d LI Operating Instructions ML 350E and ML 550H Page 9 pay 8 Pull the tube down tight using the five 5 bolts removed in step three DO NOT HAMMER THS TUBE INTO PLACE 9 I
15. ten re quirements were incorporated into the design of Arkansas original tester ST1 a b c d e g h i j meaningful measurements precision of test data minimum data processing balanced coverage and test cycle frequency adequate range of operation high degree of mobility and maneuverability minimum traffic interference structural integrity economy of operation comfort and safety of crew During 1971 several states that had skid testing units were surveyed concerning their skid testing unit Based on information from our survey of the states and the fact that the Arkansas State Highway and Transporta tion Department was not properly staffed nor had adequate facilities for the construction of a skid trailer the most logical economical and desirable alternative was to Requisition the tow truck from the Department s Equipment Division Secure from a local source a water tank and body for the tow eens and Purchase a commercial model skid testing trailer and necessary recording and control equipment with provisions for the installation and hook up ef all components by a successful bidder 10 From the survey information based on the most common use and satisfactory performance a composite tow vehicle for a skid testing unit was characterized This vehicie was to have a GVW rating of 10 000 pounds with a V 8 engine of at least 390 cubic inch displacement Standard cab 4 s
16. the petcocks on the solenoid valves and permit them to drain Dis connect all electrical connections and install the protective cover attached Be sure you drain as much water out of the system as possible ee a rog ocupa ct req ens m n P M P rndt n s RR el NN D 1 E wact VT KE 2 ce Tang i Operating Instructions ms j ML 350E and ML 350H Page 8 rA B TRUCK When preparing the truck for storage open the main and drain valves on the water tank Open the petcock valves on the two water pumps beneath the iruck Install ihe protective cover attached to the electrical connector on the rear of the truck Remove the re corder and store it in a warm place To remove the recorder proceed as follows l Remove the main fuse 60 ampere cartridge type which is located in the locked cabinet 2 Remove the seven 7 silver head screws in each of the side panels 3 lift the panels up and turn them over so they are out of the cabinet 4 Remove the four 4 hex nuts from the bottom plate of the recorder 5 Unplug the cable which is plugged into the recorder from the drivers side Disconnect the three 33 connections from each of the re corder inputs These are located on top of the recorder three on each side at the top rear 6 Lift the recorder straight up and out of the console SEC 6 1 REPLACEMENT OF TORQUE TUBES If a torque tube with its strain gauge transducers
17. Interpretation of a single trace by two people often resuited in difference in the average skid number for a particular skid test In addition storage of the traces for later reference was impossible for obvious reasons The second problem that is listed above also had an adverse effect on the reliability of the data that was being recorded When ST1 was designed the water tank was located at the rear of the tow vehicle see Figure 1 and as the quantity of water in the tank changed the height of the trailer etch also changed which meant that the axis of the trailer was rotated so that it was not parallel to the direction of motion This resulted in an Of up to 5 SN for each test Another area of concern in relation to the reliabil ity of the data was that the relays in the terminal box on the trailer were almost impossible to keep dry When ever a heavy rain fell or whenever the humidty was high the relays would become damp or wet Several different methods and materials were used in trying to seal the box however only limited success was achieved As with any electronic connection that gets wet the relays trans mitted faulty data to the strip chart recorder 15 When STi went into service on April 10 1972 its dependability vas suspect It was in the shop for repairs ae mie as it was working This caused the oper ational cost per mile to be approximately 0 82 per mile driven Therefore it is easy to understand why
18. SOILTEST EVANSYON OPERATING INSTRUCTIONS MODEL DESCRIPTION DATE ML 550E amp ME 550H SKID TESTING TRUCK AND TRAILER 4 5 71 SEC 1 1 GENERAL DESCRIPTION i The Soiltest Skid Tester is designed for the purpose of measuring the amount of resistance to skidding presented to tires er road surface material Two models are available ML 3508 with electric drum brakes ML 350H with air over hydraulic disc or drum brakes in general this instruction manual is BpPrseebie to either model except where specially noted SEC l 2 METHOD OP TESTING A specially instrumented two wheel trailer is towed behind a truck On each wheel is a strain gauge transducer The transducers measure the amount of torque exerted on the axle of the trailer under locked prake conditions on wet pavement ches Phas lie bie m ee ee ee men n A B pnm ni m c yr The towing vehicle carries ihe water supply for wetting ihe pavement i and all necessary instrumentation The instrumentation records test results on a strip chart recorder and it also provides complete control of the tests being conducted SEC 1 3 PHYSICAL DESCRIPTION OF EQUIPMENT The Soiltest ML 350 is comprised of three basic components 1 the towing truck 2 the skid trailer and 3 the instrument console The truck carries the water supply and pumping system and the instrument console The trailer carries the torque measuring strain gauge tran
19. TECHNICAL REPORT STANDARD TITLE PAGE 1 Report No Government ccession No 3 Recipient s Catalog Mo CHWA AR 80 001 d Title and Subtitle 5 Report Date May 1981 6 Performing O ization Cod Skid Research Program ertorming Urganizatian Lode 7 Author s 8 Performing Organization Report Mo J R Westerman 9 Perlarming Organization Nama and Address 10 Work Unit No Arkansas State Highway amp Transportation Dept Post Office Box 2261 Little Rock Arkansas 72203 12 Sponsoring Agency Name and Addres 11 Contract or Grant No HRC 29 13 Type of Report and Period Covered Final ARKANSAS STATE HIGHWAY AND TRANSPORTATION DEPT P O BOX 2261 LITTLE ROCK ARKANSAS 72203 14 Sponsoring Agency Code I3 Supplementary Notes This Project was conducted in cooperation with the U S Department of Transportation Federal Hichway Administration 16 Abstract This report presents the actions taken in the development and 4cquisition of a skid testing unit that would be economical efficient and safe as well as repeatable and reliable while the statewide inventory was conducted This report also con tains specifications and operating procedures 17 Key Words 18 Distribution Statement Skid Resistance Skid Tester NO RESTRICTIONS Security Classif of this report 20 Security Classif of this page 21 No of Pages UNCLASSIFIED UNCLASSIFIED 61 Fo
20. Xv UTE we xo d DERS RE pa Fe s peus gud tet HRS B pai S AT ah SESE HA seas Pape YOK TEL eec YN theme S is Ed PENARE Sex tp DRY Y exW te OY can TF or t E locns TE d F prt E H a pue ES de y a ee sagt ENS MY vy xS Ens ee ERN iH T aperi E 3 PEN Mmm Poses fue ova y Oe WHR vows xo Oy ae oF neck bern M ard GASES si Here vot O XEo 0 x rut re Xo rete ME Iur FLEMEITM ex MAE PIGET Enc ders Gus E H PEE Sores x MEL Lia flows fame s nebula IRA ERTES iA voxa x TUR s Pac ONU a ija Ot ibxegel RE SHAE tow anx Khaaa oe PORAS Bee ME ps ih BESS ERLE Aga t pet POMONA ohY 4 d i F PM rote ees x ELA a RERHRS ngage i ferai vr z ie PExoppAUsavieonpa RE C x MM donee rie ts pq s MEHR fil be i min CIEN H DUX uyk cone tee ata i InDINRMSexz die YWOXO AUBMA y ra s PIE M RSH Sows a Parte Ta E LOREM ween neces EREN acae a Mea SLES HtoKO euro 5 i DT Ra id ev ie ARR a 5 Ever eir xg diet LEER Tal LETRI IS S E pr s E eire Dry A SILL Nee ceri ugg Re Parte EE ae 3 che mete oi BER Poe ELLEN CENA LTEM yk DEET T v NT ee E MA em cano T EH ZUM ET S MIR STl consisted of three main components see Figures No 1 and 2 1 a towing vehicle which carried a water supply a pumpinc system and the instrument console 2 a Skid trailer and 3 an instrument console whi
21. ard Y Giles C G Sabey B E Cardew K H F Development and Performance of the Portable Skid Resistance Tester STP 326 American Society for Testing and Materials 1962 Hankins K D A Program for Reducing Skidding Accidents During Wet Weather Transportation Research Board Record 622 1977 Gramling W L and Hopkins J G Skid Resistance Studies Aggregate Skid Resistance Relationship as Appiied to Pennsylvania Aggregates Pennsylvania Department of Transportation May 1974 Stocker A J and Albert J W Comparison of the Ohio State University and Penn State University Skid System Water Nozzle Texas Transportation Institute August 1977 Stapler W T Stone J S and Chase H D A Skid Resistance Study of Georgia Pavements Georgia High way Department December 1970 Rushing H B Skid Resistance Study Louisiana Department of Highways October 1968 14 125 16 17 18 19 20 2l Mullen W G Whitfield J K Gibson D Cahoon T Dixon W Robinson J Surface Wear and Skid Resistance Properties for Portland Cement Concrete Pavements North Carolina State University May 1974 Highway Skid Resistance ASTM Special Technical Publication 456 American Society for Testing Materials October 1968 An Analysis of the Literature on Tire Road Skid Resistance ASTM Special Technical Publication 541 American Society for Testing Materials
22. ayer thickness shall conform to specifications in ASTM E274 latest revision Ut we The suspension system shall consist of coil springs and shocks adjusted so that when the trailer is properly leaded and level the wheel center line height is never lower than the tow hitch C Recording Instrumentations The instrumentation necessary to control and record all phases of Skid testing shall include the following major components control head including the timer instrument panel two channel recorder water pumps skid trailer instrumentation including the strain gauge bridges solid state timer shall be provided so that the driver of the towing veh cle after making the proper settings can throw one switch and all the equipment necessary to be actuated during a test will be actuated in the proper sequence and for the proper duration The proper sequence shall include all phases of skid test application of brakes release of water control of recording sg pesos E E through custom designed multiflex timer with vernier controls for TE of automatic timing Automatic Eiuins Snail be accurate to 1 100th second on vernier control The recorder sensitivity shall be at least 10 mv input for full scale deflection The strain in the braking system will be measured by strain gauges transducer mounted on the aluminum torque tube concentric to each axle that is between the brake drum housing and axle housing Output from the strain gauge
23. ble that does influence skid re sistance To accomplish this task Dr Jack Cole Mr James Gleason and Mr Jack Helms of the University of Arkansas Department of Mechanical Engineering designed and constructed a random path rapid wear track which would accelerate the i Ford Miller C Jr Asphalt Surface Durability and Skid Resistance Investigation Civil Engineering Department University of Arkansas Final Report March 1978 30 aggregate wear A final report on the design and construc tion of the wear track was published in August 1975 Due to several serious problems in the hydraulic system the system was modified by Dr Cole and Mr Gleason The mod ified rapid wear track will be discussed in the pending final HRC 40 report Operational problems with the wear track prevented coordination of work activities with this project 3l CHAPTER V CONCLUSIONS 1 The initial skid testing unit was adequate for developing and testing procedures to be used in He Inven tory Program but was not sufficient to implement the Inventory Program 2 A newer and improved skid testing unit is recom mended to implement the Inventory Program 3 The procedures developed for collecting storing and analyzing skid data have proven to be excellent in meeting the Department s needs 4 The skid Inventory Program has improved the Department s method of determining priorities for over laying State highways 32 CHAPTER VI
24. ch is mounted in the cab of the towing vehicle between the driver s and passenger s bucket seats Included in the appendix of this report are a compiete set of specifications a brief de scription of ST1 as well as a summary of operational procedures STl was placed into operation on April 10 1972 PERFORMANCE OF SKID TESTING DEVICE After STl had been in operation for several weeks it became evident that STl did not have the capabilities or features that were required to conduct an efficient State wide inventory program over an extended period of time A detailed description of the inventory program that was de veloped for Arkansas hishways ds included in another chapter of this report Some of the problems that were encountered included 1 slow data reduction 2 improper water tank location on the tow truck 3 poorly sealed terminal box on the trailer and 4 extensive maintenance to ST1 Of the problems listed above data reduction was the most frustrating and serious As each skid test was run the two channel strip chart recorder as shown in Figure No 2 and discussed in Appendix C received an electrical input from the strain gauges in the transducer and then graphically 14 displayed the traction force as a strip chart trace Since the data was recorded as a trace an additional hour was required to interpret the results to arrive at an average skid number for each hour that was spent in the field collecting data
25. e Federal Highway Administration The first requirement of this project was to study various skid testing units determine specifications and either acquire or construct a skid trailer In addition to a literature review an informational review was initiated by requesting from various state highway and transportation departments Federal and pri vate agencies a copy of their plans and costs for con struction or purchase of a skid trailer The Department received information from twenty eight states and three private organizations The conclusions of this investi gation are discussed in appropriate sections of this report OBJECTIVE AND SCOPE OF HRC 29 During the 1960 s skid testing research became a high priority of various research agencies Arkansas was no exception The Arkansas Highway Department now named the Arkansas State Highway and Transportation Department did some preliminary skid testing using the stopping distance vehicle method Although this method proved to be adequate for the limited amount of testing per formed the method was too costly time consuming and hazardous Therefore this research project Acquisi tion Calibration and Application of a Skid Trailer was begun on July 1 1970 in an attempt to develop an economical efficient and safe system that could be used to determine the skid characteristics of highway pavements in Arkansas This goal was to be accomplished by meeting the followin
26. e console Add the desired wheel load in 100 pound increments and with the right sensitivity control on the recorder adjust to read one major division for each 100 pounds Tighten down the lock nut on this control so the Setting cannot change The same procedure is used for the right wheel except that the sensitivity control is not used Calibrate the right side to match the left using only the right F S pot to give an equal reading ogi cm m em o m un er yem o c ou o o p a a V de a uan eb Menem Ps eS qu T r TUmEuiAcR3 f fis r MM 7 mE Operating Instructions ML 550E and ML 550H Page 7 e Press the calibrate button with left record and make a note of the amount of deflection Do the same on the right record These read ings will enable you to set the F S pots to their proper calibration point if they should happen to be moved by mistake These readings are for reference only and are used only to indicate that the system is working properly To calibrate the speed set the left selector switch on the recorder to the 5 mv position and zero the pen using the left position control on the recorder Remove the top cover of the console by releasing the trunk clasps on each end Press the CHECK SPEED button on the console This applies voltage from a 4 05 volt standard cell to the circuit and it should produce a speed reading of 48 mph If necessary adjust the sensitivity control on th
27. e recorder to give this reading If 48 mph cannot be reached adjust the locking type pot located to the rear of the battery so the reading is 48 mph Loosen the lock nut to make this adjustment and when adjusted re tighten the lock nut on the pot Adjust the dash meter also by adjusting the locking pot located at the end of the battery Re install the cover and calibra tion is complete SEC 4 1 MAINTENANCE The Soiltest Skid Tester requires a minimum amount of maintenance Tire air pressure in the trailer tires should be maintained at 24 psi This should be checked using the special gauge which is provided with the tool kit The wheel bearings on the trailer should be repacked every 20 000 miles The brakes should be inspected periodically The solenoid valves in the water system may be taken apart for cleaning if it should happen that they do not close tightly This also applies to the relief valves at the top rear of the water tank Valve closure problems may be caused by the presence of foreign matter such as dirt or sand The Service manual provided with the truck should be followed closely with regard to maintenance and lubrication The instrument console requires no special care except for that main tenance noted in the manuals for the recorder timer and inverter SEC 5 1 STORAGE A SKID TRAILER To take the trailer out of service for storage dis connect tne hose connections and lay them out to drain the water Open
28. e torque developed by the left skid tire and the right channel records the torque developed by the right skid tire On some models the left channel is used to record vehicle speed and only the right channel is used to record torque OEC l 5 THEORY OF OPERATION wes Wem P quoa hh ep o s bai EM gt E The Soiltest Skid Tester basically consists of a special trailer towed by a truck At a preselected test speed water is applied to the pave ment to be tested ahead of one or both test wheels as selected and the brakes on the trailer are locked The resultant torque is recorded on a strip chart recorder in the instrument console The water flow i applied to the pavement is designed to leave a film of water 020 inch x 005 inch thick regardless of vehicle speed The torque measured is sensed by balanced bridge strain gauge transducers mounted on special torque tubes These tubes are mounted concentric to the axles of the trailer All test functions are automatically controlled by the timer in the instrument console Pt aH m p mr PER The timer is set so that the test sequence occurs in this order 1 Start recorder 2 Start water flow 3 Calibrate pulse is recorded 4 Brakes lock for 2 seconds 5 Brakes release 6 Water is turned off 7 Recorder stops 8 Timer resets and the unit is ready for the next test SEC 2 1 PREPARATION FOR OPERATION Before any instrument preparations are made
29. eee he foe FF Fi i HU BE IPIS is TIME INVENTORY UNIT FIGURE 5 18 savings has been reaiized in analyzing the data This mod ified skid testing device was used to develop the procedures that are currently being used to conduct the statewide inventory These procedures will be discussed in later sections of this report Even though this unit is still used to check spot locations a newer more advanced skid testing unit was designed and built for the inventory pro gram Except for this brief statement and Figures 4 and 5 no other reference will be made to this unit since it was developed under a different contract Due to excessive down time which was caused by fail ures of various components the trailer was only operational approximately 50 of the time The Department was not satisfied with the trailer s record so the University of Arkansas Mechanical Engineering Department was contracted to design and construct a skid testing system which conform ed to ASTM Specification E274 70 The system as shown in Figures 6 and 7 has been in operation since October 1977 and has been reasonably reliable in its performance A detailed description of the trailer design and construction can be found in Dr Jack H Cole Mr James G Gleason and Mr James L Dale s report The Design and Construction of a System Utilizing a Trailer to Measure Skid Resistance of Paved Surfaces which is available from AHTD or NTIS The third modifica
30. esired position Attain the chosen test speed usually 40 miles per hour per ASTM E 274 65T par 5 1 and press the START button All functions of the test will be per formed automatically At intervals during your test Sequences it is wise to re check the zero of the recorder the balance of the bridge s and the height of the calibrate pulse This will eliminate the possibility of drift in the equipment or inadvertantly moving the wrong knob which could give erroneous results SEC 3 2 OPERATING PRECAUTIONS l Be sure that the truck is NOT moving when you engage the PTO 2 Remove ihe main fuse in the console when any work is being Bono in the console or if panels are removed 535 Do NOT operate the truck with the PTO and pumps running unless the main valve is in the OPEN position and the water tank is full 4 The drain valve should be opened on the tank and the pumps and Solenoid valves in the event of freezing weather This is dis cussed further in the storage section 2 When testing be sure you have an adequate supply of water SEC 3 3 CALIBRATION OF MODELS RECORDING TORQUE ON BOTH RECORDER CHANNELS It is recommended that the Soiltest Skid Tester be calibrated using the Soiltest model ML 360 Dynamic Skid Calibration Unit which in cludes a Soiltest 1000 ib capacity proving ring with a dial indicator a proving ring calibration chart fine thread screw ratchet wrench wheel block and complete instructions
31. est sequence and select right left or both wheel brakes Console will be designed to allow metalari of additional expanded circuitary and more controls and instrumentation D Electrical System Ihe electrical power for the recorder and other systems will be suppiied by a frequency controlled solid state inverter mounted in the vehicle cab and powered by a separate 12 volt battery system When the test system is in operation provisions will be made to disconnect the power supply battery from the truck electrical system to assure that the test system receives nonfluctuating power Provision will be made to tie the power supply battery into the trucks electrical system during the time the recorder is not operating E Water Pumps The water pumps are to be a positive displacement type that delivers water to the water laying system proportional to the forward vehicle speed The pump unit is mounted in the towing truck beneath the water tank F Other Requirements The instrumentation system shall conform to the following overall requirements at ambient temperatures between 40 and 100 F Overall system accuracy 3 of full scale Time stability 10 hours minimum The exposed portions of the system must tolerate 100 relative humidity and all other adverse conditions such as dust shock and vibrations which may be encountered in highway operation The vehicle speed measuring instruments shall provide an accuracy better than 0 2
32. g six objectives 1 acquire or construct a skid trailer 2 calibrate the equipment 3 test existing surfaces 4d test and recommend corrective measures for high or potentially high accident loca tions 5 establish minimum frictional values and 6 develop methods for application of skid technology on a Statewide basis As a result of several modifications to the research proposal and work plan the modified project was conducted in four separate phases 1 literature review and acquisition or construction of a skid trailer 2 establishment of calibration and opera tion procedures 3 establishment of a statewide inven tory system and 4 coordination with HRC 38 Asphalt Surface Durability and Skid Resistance and HRC 40 Rapid Wear Track At the time this project began the staff anticipated that the following benefits would be realized 1 reduced crew size 2 reduced time required at each site to conduct each test 3 reduced cost per test 4 increased efficiency 5 improved water delivery 6 improved uniformity of each test 7 improved accuracy 8 increased mobility and 9 improved safety Implementation of the results of HRC 29 is the continuation of the inventory system that was developed as part of this project The skid resistance of all State highways are coded onto magnetic tape and are updated periodically by the Division of Planning and Research This system provides a forewarning of high way sections approach
33. gin ning point of a test A speed meter is driven by a tachometer generator from the speedometer cable lt A standard cell is located inside the speed meter housing and it is used to determine that the speed meter is in calibration To check the meter press the pushbutton on the meter housing The pointer should deflect to a reading of 48 miles per hour If it does not the meter should be recalibrated by loosening the locking nut on the cali bration pot and while pressing the calibrate button the potentio meter should be moved until the meter does read 48 mph Re tighten the locknut The standard cell used for calibration checking is a long life mercury cell but to insure freedom from possible deterioration of the cell or possible corrosion the cell should be replaced once per year
34. he equipment must be capable of receiving and processing raw data obtained from strain gauge torque transducers or from a modified Gould Brush two channel strip chart recorder model Mark 220 The specified equipment must be capable of rapid acquisition and re cording friction data calculating skid numbers and displaying the skid numbers digitally and in printed form The printer must accept at least ten 10 columns or digits of information through preset inputs by thumb wheels or other acceptable means These inputs will be used for highway number direction of travel date lane number log mile or any other bits of predetermined information selected by the system operator The printer mist be capable of reproducing this information an infinite number of times until reset by the operator GENERAL SPECIFICATIONS General specifications for the equipment are as follows Power Requirements 1 115 120 VAC 60 Hz sine wave 40 watts maximum during printing Signal Input Single ended analog raw force data or unprocessed strain gauge transducer SN data Brake signal nominal 12 VDC amp 1 0 amp Dimensions The unit s must be small enough to mount in the vehicle for compatible installation with existing equipment and instrumentation D 1 Weight PRINTER SPECIFICATIONS 4 Data Columns Printout Data Format Conversion Time Analog to Digital Print Rate Versus Temperature COMPUTER SPECIFICATIONS Compu
35. hown in Figure 10 is used for this purpose In addition it is used for transferring the data to diskettes for storage Programs were developed to retrieve data by route by county and route and any other special data configurations which may be required zy DATA STORAGE AND RETRIEVAL SYSTEM FIGURE 10 28 CHAPTER IV COORDINATION OF HRC 29 SKID PROGRAM WITH HRC 38 ASPHALT SURFACE DURABILITY AND SKID RESISTANCE AND HRC 40 DESIGN CONSTRUCTION AND EVALUATION OF A RANDOM PATH RAPID WEAR TRACK Two projects HRC 38 and HRC 40 were already under way when this project was revised in 1975 Both of these projects dealt with topics which were either directly or indirectly connected with skid resistance Therefore it was logical for the work activities of all three projects to be coordinated throughout the life of each project HRC 38 was a four year investigation of the durability and skid resistance of existing asphalt concrete hot mix pavements The study included field and laboratory evalua tion of the polish characteristics and stripping resistance of 18 most commonly used mineral aggregates in Arkansas Aggregate polishing was accomplished by a small circular wear track that was designed to polish 12 Marshall size specimens at one time with in place specimen frictional measurements obtained by a British Portable Tester The laboratory work included tests of aggregate cast in poly ester Marshall specimens and pa
36. ing dangerous limits Each District is notified promptly if any section of high way has a serious decline in skid resistance since previous testing CHAPTER II SELECTION ACQUISITION AND OPERATION OF THE ARKANSAS SKID TESTING UNIT 1971 EVALUATION OF SKID TESTING DEVICES Since the method of testing has a profound influence on the value of skid resistance measurements it was nec essary that the Department select the most suitable unit for Departmental use The following table compares the various types of testers as to their suitability for research purposes and routine surveys SUITABILITY OF PAVEMENT FRICTION TESTERS FOR ROUTINE USE STOPPING PORTABLE DISTANCE SKID CRITERION TESTERS CARS TRAILERS Meaningful measurement Poor to sood Good Coad to excelient Accuracy of test data Good Poor 10 good Cr ood to excellent Data display Indication Indirectly derived Recording Test frequency Poor Poor Good to excellent Operating range Poor Poor tu good Good to excellent Mobility and maneuverability Good to escelient Excellent Poor to excellent Traffic interference Very high High Low Rugypedness Good Poor Good to excellent Hazard to test crew High Very high Low Recuired test crew minimum 1 2 A 4 1 2 Procurement and operating cost Initia cost average 900 3 500 10 000 te 25 000 Sites tested per day no 8 12 15 25 700 400 Life expectancy ivr 6 2 S Mait and direct cost pez season 50 1 250 1 250 Toia wage
37. inventory if no major difficulties arise Weather and equipment malfunctions have caused long delays in complet ing the inventory A central location in each county was selected and the inventory crew tested to the county line in a spider web type configuration The inventory began in Miller County and moved east until the southern counties had been inventoried The next row of counties would then be inventoried by moving toward the west Skid tests are made every 1 2 lane mile in each direc tion and the tests are staggered every 1 4 mile as shown by Figure 8 Thereby four tests per mile are obtained In the event of a bad test another will be run immediately after the bad test cycle is completed Special tests may 24 also be made on changes of surface type All skid testing is conducted in accordance with ASTM Specifications 1 Mile FIGURE 8 DATA STORAGE AND RETRIEVAL SYSTEM Any discussion of the data storage and retrieval sys tem must begin with a brief discussion of the data that is collected by the skid inventory unit An example of the data is illustrated in Figure 9 As shown in Figure 9 the data is divided into two categories a twenty four digit identity code and a twelve digit skid code The identity code is the name which makes a 5sctioupar set of data unique A complete description of the highway section is contained within the code For example the code is comprised of nine definitive parameters 1
38. l system Items Note All prices are actual dollar values and are not based pa on a base year dollar comparison 8 9 and 10 was 23 043 Funding for the second modification and data storage and retrieval system was through the Arkansas Governor s Office of the Coordinator of Public Safety Due to equipment failure the operational cost of the skid testing unit has averaged 0 82 per mile All cost of operating and maintaining the unit was included in determin ing the operational cost Fm APPENDIX B DESIGN CRITERIA AND SPECIFICATIONS Towing Truck Information from 28 states was investigated to determine the type size make and other pertinent data on tow trucks currently in use It was found pide d wide variety of vehicles from light station wagons to heavy trucks are currently being used Some states perferred to have a light weight vehicle with maximum horsepower engine in order to tre test speeds rapidly and with a minumum of effort Others perferred the heavy trucks which were more cumbersome to handle accelerated more slowly but maintain a constant speed during the test because of greater mass The states using the lighter weight trucks did not indicate any safety problems due to undesirable swaying even though some reports had mentioned this as a reason for selection of heavier units After A sidering the various possibilities it is proposed that we use a one ton truck powered by a V 8 gasoline engine standard cab
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40. nd all supply connections are securely fastened Close the drain valve on the water supply tank on the truck and fili the tank with CLEAN water through the filling port at the top rear of the tank Open the main valve which is also located on the water tank Start the engine of the truck and turn on the POWER switch on the console Be sure to allow at least fifteen minutes warmup time for the equipment to stabilize When warmup time has elapsed press the ADVANCE CHART and ZERO RECORD buttons at the same time and zero both channels of the recorder using the left and right POSITION controls on the recorder itself Now re lease the ZERO RECORD button and re zero the pens using the left and right BALANCE knobs on the console Now press the CHECK CALIBRATE button and adjust left and right F S knobs to read the number deter mined in the calibration of the tester Next depress the clutch and at a dead standstill pull out the FTO knob on the center of the firewall E 4 F SSS eee MR X A M er LL SA BW Ir B er o ta ES PM 248 L k Yi Tus Operating instructions p ML 550E and ML 350H Page 5 ff NOTE In trucks with automatic transmissions this operation is per formed automatically by the timer through a magnetic clutch The tester is now ready for operation and you may drive to your test site When you have reached the highway to be tested be sure you have the WHEEL SELECT switch set to the d
41. neously during cross country travel when testing is not in progress The tires shall be the standard tire for pavement tests ASTM specification E 2459 Two spare wheels complete with rims tires and valve stems shall be mounted on the trailer A safety chain must be provided at the trailer hitch that is capable of holding the trailer in case of hitch failure Fenders will be provided for the wheels of the trailer A removable protection cover for the trailer will be provided Running lights and safety lights should be provided as required by Arkansas and Federal Safety laws Easily operated disconnects shall be provided between the trailer and the towing vehicle for the water air and electronic circuits Spray nozzles shall be mounted on the trailer and connected to the water supply on the towing truck with flexible hose so that water can be sprayed in front of the test tires either right or left or both at the same time They must be so mounted that they can be raised when not being used and will swing upward if they should hit any unexpected object on the pavement to protect them from damage Flexible connections are to be provided where pudeat to prevent stresses from being transmitted to the pump or valves The nozzle configuration shall be such that high velocity water jets are directed toward the pavement surface at an angle that will produce a minimum splash and that water is not applied directly to the tread of the test tire The water l
42. nstall the brake backing plate using the four 4 bolts removed in step two Note If you have disc brakes re install the calipers iO Re install the wheel li Push the new four wire cable and shield through the sealtite and connect it in the junction box Observe the color code carefully the wiring must be connected exactly as it was Re install the box cover l2 To check the new torque tube start the truck and equipment Allow the usual 15 minute warmup and stabilization period Lock the trailer brakes using the BRAKE LOCK switch in the locked compart ment Observe the recorder and note in which direction the pens move If everything is normal the pens will move to the right lf they do not it is an indication that the red and white wires to the torque tube on the incorrect side should be reversed SEC 7 1 MODELS WITH CHART RECORDING OF SPEED In some models of the Soiltest ML 350 the vehicle speed is recorded on the left channel of the strip chart recorder In these models an event mark will be printed on the chart at the beginning of the test sequence only when the right wheel is being recorded If ihe left wheel is being recorded no event mark will appear on the chart SEC 8 1 MODELS WITH ELECTRIC SPEED METER In ML 350 models with an electric dash mounted speed meter an event mark will be printed on the chart on one or both channels depending on the setting of the wheel selector switch The mark snows the be
43. nventory to be of value blanket type cover age of all highways in the State was required Several factors were considered by the Research staff during the evaluation and development of the Inventory Program 1 15 000 miles of State highways were to be inventoried 2 10 000 miles of paved county roads and city streets eventu ally needed to be inventoried 3 a limited amount of fiscal resources would be available to purchase operate and main tain the operation 4 type amount and method of data to be collected during the testing phase 5 data storage and retrieval 6 complexity of equipment operation during data collection 7 frequency of tests 8 direction of testing 23 9 routing of tests 10 number of individuals needed to operate each phase of the program 11 rate that data could be collected and 12 establishment of specific reference points so skid nuzbers could be evaluated for any given section of highway The approach that was selected consisted of a two man crew completing the inventory in one county at a time As a result of this approach a realistic time table for com pleting the skid inventory could be established main tained and modified if needed A Research crew tested the approach and concluded that in most cases one week per county provided iane than enough time to complete the skid inventory in each county By applying the schedule approx imately 75 to 80 weeks would be required to complete the
44. ock right left or both It also feeds water to the proper wheei s Any of the three settings may be used ADVANCE CHART This pushbution allows the operator to run the chart forward without initiating a test cycle This function is very useful as an aid in calibration and balancing CHECK CALIBRATE This button provides a calibration pulse and is used as a reference in calibration Use of this function will be discussed further in the calibration procedure ZERO RECORDER Pressing this button removes all signals from the re corder inputs and allows the operator to balance the recorder to Zero When zeroing the recorder use the position control on the recorder for each channel as marked LEFT AND RIGHT BALANCE These knobs allow the operator to balance the two strain gauges to zero LEFT AND RIGHT FS FULL SCALE This knob adjusts the height of the calibrate pulse and is used to ensure proper calibration This is explained in the section on calibration procedure In the center of the console is the strip chart recorder In normal road testing sequences the sensitivity switches should both be set at the 1 mv position and the chart speed should be set at 25 mm sec Under static test or calibration checks a chart speed of 1 or 5 mm sec can be used to conserve chart paper OBC 3 1 TESTING ON THE ROAD To operate the Soiltest Skid Tester on the highway perform the follow ing operations Be sure that the hitch safety chains a
45. og nized and accepted skidding as a major hazard in high way transportation It was a known fact when this project started that the average travel speed of vehicles had steadily in creased over several years and that this increase in Speed coupled with higher traffic density per mile of highway merely intensified the skidding problem This problem had reached such proportions that the Federal Highway Safety Standard Number 12 required all state governments to have a program for resurfacing or other surface treatment for correction of locations with low skid resistance and high or potentially high accident rates that could be reduced by providing improved sur faces The Federal Highway Administration was charged with the administration of this Standard They ask that the state highway departments compile statewide invento ries of skid values covering all sections of pavement on the state highway system Prior to the Department s purchase of skid trailers the Arkansas State Highway and Transportation Department did preliminary skid investigations by using the stopping distance vehicle method This procedure duse Slew expen sive and hazardous therefore it was prohibitive to conduct a continuing inventory of all state highways using this method Since skid resistance had become a very prominent factor in the field of highway safety the Arkansas State Highway and Transportation Department initiated this project in cooperation with th
46. peed manual transmission single speed axle and be capable of maintaining 65 mph test speeds when loaded This same approach was used for determining the most desirable characteristics of a skid trailer Most of the trailers were designed to meet requirements of ASTM E274 65T and therefore were of the same basic design Since the trailer design had to meet the ASTM requirements the only decisions to be made were which components would be incorpo rated into the trailer A detailed list of requirements and specifications are included in the appendices of this report SELECTION ACQUISITION amp DESCRIPTION OF A SKID TESTING DEVICE As a result of the information from the Department s sur vey of states with skid testing systems previous studies and technical reports on commercially built systems the Department concluded that the only feasible manner of obtaining a skid testing system was to purchase a tow vehicle and then request bids from suppliers of commercially built trailers Soiltest Inc of Evanston Illinois was awarded the contract to supply the trailer an ML 350 H and all the necessary instrumenta tion In future references this skid testing system shall be referred to as STl1 STl was constructed and operated in ac cordance with ASTM E274 li T VOS naro A v CO X f pi T gros Avin Rene PLHI Ros VAPE weeks KOLIK EHI etary x V ROG XO Ayer IECIT TLEUhir HIC NEG SA Lavon RIAM oe gb noxe Bee x n opi he URARTU g Oe
47. rm DOT F 1700 7 8 692 TABLE OF CONTENTS Page Table of Contents 2 List of Figures 3 Chapters I Introduction A General E B Objectives and Scope of HRC 29 5 II Selection Acquisition and Operation of the Arkansas Skid Testing Unit A Evaluation of Skid Testing Devices B Comparison of Two Wheel Testing Devices C Selection and Acquisition of a Skid 11 Testing Device D Performance of Skid Testing Device 14 E Modification of Skid Testing Device 16 III Development of Inventory System A General 23 B Data Collection 23 C Data Storage and Retrieval 25 IV Coordination with HRC 38 and HRC 40 29 V Conclusions 32 VI Implementation 33 VII References VIII Appendices A Cost B Design Criteria and Specifications Towing Truck C Specification for Skid Testing Trailer D Specification for SN Computer E Operating Procedures for Skid Testing Trailer Figure 10 LIST OF FIGURES STl Skid Tester 1 Console in STI Component Positioning in Modified Skid Testing Unit Microcomputer in Inventory Unit Inventory Unit Modified Skid Testing Unit Water Pump Compartment Diagram of Test Pattern Typical Skid Inventory Printout Data Storage and Retrieval System Page 12 13 17 18 18 Zl 22 29 26 28 CHAPTER 1 INTRODUCTION GENERAL The problem of skidding on slippery roads as well as research into methods to prevent it has been present for over forty years Agencies have now fully rec
48. s per season 4 200 8 400 4 200 Cos per site tested 3 45 4 70 0 32 Table from NCHRP Report No 37 The conclusion drawn from the above information was that skid trailers are the most efficient economical and suitable means for determining friction coefficients of pavement surfaces COMPARISON OF TWO WHEEL TRAILER UNITS Results from the 1962 Tappahannock Correlation Study and the Florida Skid Correlation Study were examined to evaluate the degree of standardization which would be achieved by skid test trailers that were constructed in accordance with ASTM Standard Test For Skid Restecance of Pavement Using a Two Wheel Trailer ASTM Designation El74 65T The Department concluded that 1 many types of trailers are capable of accurately determining the coefficient of friction resulting from a steady state skid 2 good agreement existed among trailers which included three different types of force measuring systems and 3 good repeatability was aehleved by the individual trailers Even though a trailer might have the following character istics 1 good repeatability 2 test results which cor relate with skidding accident frequency or risk of skidding on all types of pavement surfaces and over the entire speed range of vehicular traffic it is understood that frictional measurements under seemingly ideal conditions are affected by conditions beyond the control of the operator As a result of our analysis the following
49. sducers water laying nozzles for pavement wetting end water and brake control Solenoids Eel rj ENGINEERING TEST EQUIPMENT FOR SOILS CONCRETE BITUMINOUS PRODUCTS amp CONSTRUCTION MATERIALS Tom EE re ae m mta Ao a m 0 r c Vix cca E Ur CAL I EDT me CE CH MEC CD INO duum o c MUSS P op ie to i LI Li a 9 gt xu RCRUM E Operating Instructions ML 3550E and ML 350H Page 2 The instrument console is located between the drivers and passengers seats inside the cab of the towing truck This console contains all controls for the complete test sequence Once initiated by the START button the test sequence is automatic being governed by a built in timer The console also contains the force measuring recorder Ihe truck has amp manual control for the trailer brakes for use on the highway when not testing The truck and trailer lights conform to ICC regulations The towing truck is equipped with flashing safety lights as standard equipment n electronic speed meter is located on the dashboard of the truck to provide precise Speed indication SEC l 4 TYPE OP INDICATION OF SKID RESISTANCE Ihe instrument console in the truck cab is equipped with a two channel recorder as Standard equipment The torque required to slide the skid tire on a wetted pavement is read directly on the chart as pounds torque when the system is correctly calibrated On most models the left recorder channel records th
50. side the locked instrument cabinet toward the rear is the timer The timer controls the time of each function of the test and the time of the overall test sequence The timer may be easily reset to meet any Special requirements by simply changing the setting of the on and off time of each function as labeled Use caution if you ere chang ing the water and or brake setting so that you do not inadvertantly skid the tires on the pavement before water is applied On the passenger side of this same compartment is the primary instrumen tation fuse block The 60 ampere fuse protects all of the instrumenta tion The fuse should be removed whenever ANY work is being done on the console or if any panels are to be removed In describing the controls it will be assumed that the console is being viewed from the drivers side Controls on the left side panel at the drivers side are as follows START Pressing this switch begins the test cycle Once a test cycle is started all functions of the skid tester are automatically controlled until the cycle is completed DEFEAT Pressing this button will stop a test sequence at any point in its cycle This function might be used under such conditions as bad roads traffic hazards etc 1 qa T ll CUPS onc d m indc xem CC a a rm em 1mm L mi E Operating Instruciions ML 550E and ML 350H Page 4 8 WHEEL SELECT This switch is used to determine which brakes are to l
51. tation Format Input Impedance Input Polarity Front Panel Digital Display Digital Readout Accuracy Timers Thumbwheel data none Skid Number No greater than 30 lbs gross l2 per line consisting of 10 columns thumbwheel data entry by operator 2 columns computed skid number Paper tape pressure sensitive 3 375 inch width characters 110 inch high 100 inch wide spacing between columns 275 inches Over 40 lines foot of tape gt 1 2 4 8 BCD positive true logic Column suppression logic 1 Raw traction force data or unprocessed SN data 400 milliseconds maximum Intermittent duty 100 consecutive lines at 25 duty cycle 20 C for 2 5 lines second Continuous duty 100 duty cycle G 0 C to 40 C for 1 line second x 100 F SN F a h Greater than 100 K Ohms Positive Single ended analog Display remains in memory until reset 0 596 of reading or 1 least signi ficant digit over a temperature range of 09C to 40 C Temperature coeffi cient better than 150 ppnvdeg C Strictly solid state D 2 Timing Sequencing Sampling to begin 0 5 seconds after brake initiation Sampling period l 0 seconds Timing Accuracy At least 0 5 of longest timer go s s APPENDIX E SOILTEST INC n 2205 LEE STREET EVANSTON ILLINGIS U S A SUBSIDIARY OF CENCO INSTRUMENTS CORPORATION e TELEPHONE 312 869 5500 i CABLE
52. tch point when it is uncoupled from the towing vehicle The trailer design shall be such that the service load on each wheel will be 1085 pounds 25 pounds and a down load of from 100 to 200 Jotad will result at the hitch point The trailer axle shall be such that shoe brakes can be accommodated The wheel suspension shall be such that both springing and shock strut damping will be provided The shoe brakes shall be hydraulically actuated with air over the hydraulic system They shall be capable of locking either or both wheels in second holding for the duration of the test normally 2 seconds and releasing the brakes in second Provisions must be made so that either the left wheel or the right wheel can be locked independently or both may be locked simultaneously Brakes will bes automatically applied during test through manually preselection on the selector switch Torque developed by braking action is sensed by two balanced bridge strain gauge systems one at each wheel of the trailer mounted on aluminum torque tubes placed concentrically around the trailer axle inboard of each wheel Output from these strain gauges feeds to the electronic control and recording system Measurement of braking action torque curve expressing the skid resistance force exerted by the t re pavement contact Provision shall be made to provide an interconnection between the towing vehicle brakes and the trailer brakes so that they will be actuated simulta
53. the Depart ment was disappointed in the performance of STl and had the system modified MODIFICATION OF SKID TESTING DEVICE As stated in the previous section STl had several characteristics which the Research staff decided would hinder the efficiency and reduce the effectiveness of a Statewide Inventory Program STl was partially modified to eliminate these characteristics to take advantage of advances in technology and to reduce the overall cost of performing skid tests The first modification was made during the fall and winter of 1974 At that time a DL 12 Data Logging System as shown in Figure 3 which was designed and built by Data System Inc replaced the two channel strip chart recorder as shown in Figure 2 The DL 12 System pri marily consists of two components 1 a SN computer and 2 a 12 column digital printer Since the SN computer analyzed the analog signal from the strain gauges computed and printed an average skid number a significant manpower 16 E H HERE TAN PERE LIES COMPONENT POSITIONING IN MODIFIED SKID 12 Column Digital Printer SN Computer Memodyne Data Logger Primary Control Panel Velocity Indicator Flow Meter FIGURE 3 17 TESTING UNIT TOTIS qM EIE dx tety FEM dE i PLAN A cre e xd RU x ced us H FEES ii tes fasotiecbier P1 p x H jig hes MICROCOMPUTER IN INVENTORY UNIT FIGURE 4 I gd ERE P ERG NN UIN ET bog ore
54. tion of rupture proof tank shall be outside of cab 16 Body Bare chassis on tae 17 Accessories and Special Equipment a Substantial front bumper heavy duty steel attached to frame b Heavy duty T Jack 8 ton capacity 18 Water Tank and Body Capacity of water tank shall be at least 60 cu ft Baffle plates of the same size shall be inserted to divide the tank into Eus equal compartments to prevent turbulence and load shift when truck is in All interior surfaces shall be coated for corrosion resistance A two 2 inch shut Be3 FI 19 off value will be installed to control water flow from tank Manholes at the top of the tank will provide access for iene ing the tank interior Hinged cap will be used for tiis purposes See sketch of tank for more details The final design will be completed after determining which tow truck is obtained Basically the outside dimensions will be approximately 60 x 102 x 24 inches with steps 8 wide on each side Power for water pumps The power on truck shall deliver approximately 20 horsepower 1300 RPM at 40 miles per hour The power take off shall be set up for speed pro portional to the rear wheel speeds and not proportional to engine speeds Note a chelsea type PY 41R C3E is normally used on F 600 Ford with 5 speed forward transmission fos APPENDIX C ARKANSAS STATE HIGHWAY DEPARTMENT Division of Planning and Research SPECIFICATIONS
55. tion of STI was the installation of a Memodyne Data Logger a magnetic cassette tape recorder Additional information will be included in the Data Storage 19 Section of this report A detailed equipment cost list is provided in Appendix A of this report The original skid unit as well as all modification costs are included in the list 20 MODIFIED SKID TESTING UNIT TRAILER AND WATER DELIVERY SYSTEM DESIGNED AND BUILT BY UNIVERSITY OF ARKANSAS DEPARTMENT OF MECHANICAL ENGINEERING 1 Water Tank 2 Hose to Nozzles from Water Tank 3 Fifth Wheel for Speed and Distrance Measurements 4 Water Delivery Nozzle 5 Compartment Containing Water Pumps Figure 7 FIGURE 6 21 PEPEN Ot twos K WATER PUMP COMPARTME FIGURE 7 22 CHAPTER III DEVELOPMENT OF A STATEWIDE SKID INVENTORY PROGRAM The Statewide Skid Inventory Program that is cur rently being used by the AHTD s Division of Planning and Research was developed for the three following reasons 1 a recognized need to maintain a reliable record of potentially high accident locations 2 the need to provide the Department s maintenance personnel with an additional method of identifying hazardous locations that require maintenance and 3 the Federal Highway Adminis tration s Instructional Memorandum on Skid Accident Reduction which required that a comprehensive as well as continuing Skid Inventory Program be established by January 1 1975 For the i
56. tween dual rear tires and between inside dual tires and springs or other chassis parts Tire Equipment 7 50 16 8 ply rating Biber same size all around dual in rear One spare shall be supplied mounted on spare wheel Brakes Air over hydraulic Steering Gear Equipped with hydraulic power assist Cab Manufacturer s standard type cab steel enclosed with two doors Two bucket seats having no less than 19 inches between them The following items supplementing if necessary those items already cataloged as standard cab equipment shall be furnished and in place ae Air conditioning Deluxe factory air conditioner necessary to control instrument temperature and dust B 2 b Deluxe fresh air TO with windshield defrosters c Two 2 outside rear ee eee West Coast Jr s d Dual windshield washers e Two 2 arm rests f Dome light g Floor mat and headlining h Directional lights i Warning lights 14 Electrical System Shall be a 12 volt system with a two belt driven 65 M T alternator with built in silicon rectifier and matching regulator Wiring shall be adequate to handle full output of selected alternator Two 2 REUS anes batteries of not TT than 66 plates 70 amp hr shall be furnished Extra 12 volt battery shall be installed for furnishing power to the recorder and other systems through a frequency controlled sanbaeeeats inverter 15 Gasoline Capacity Not less than 30 gallons Loca
57. vement cores The asphalt mixtures were evaluated for their Marshall stability and immerson compression retained strength The principal find ings are as follows 1 the field tests results indicated a good correlation between SN40 and BPN vaiues 2 the lab oratory tests yieided a good correlation between the Texas 29 polish value from the British wheel and the Arkansas polish value from the accelerated circular track 3 a good corre lation was obtained between the BPN field value and the Arkansas polish value laboratory 4 polish tests on cores indicated that most cores had a higher polisn value than was shown from the parent coarse aggregate in the Marshall polish test the difference in these values was attributed to the fine aggregate that was used in the actual paving istae 5 the data indicated that the Arkansas accelerated polish test results on asphalt mixtures can be used to esti mate minimum SN40 values of the mix in the pavements Dr Miller Ford of the University of Arkansas Department of Civil Engineering conducted the research for the Department and any additional information is available from Dr Ford the Department or the HRC 38 Final Report Asphalt Surface Durability and Skid Resistance which was published in 1978 HRC 40 was to be a fifty four month study to determine the aggregate s influence on the wear characteristics of asphalt concrete hot mix and Portland cement concrete pave ments which is one varia
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