Effects of Natural and Accelerated Aging on Oak CrosstiesI

Transcription

1 308 AMERICAN WOOD-PRESERVERS' ASSOCIATION 1987 Effects of Nturl nd Accelerted Aging on Ok CrosstiesI Poo Chow Profess-or, Wood Science, Deprtment of Forestry S. L. Lewis Former Grdute Student University of Illinois, Urbn, IL A. J. Reinsehmidt Technicl Mnger, Trck Reserch, Technicl Center Assocition of Americn Rilrods, Chicgo, IL nd E. J. Brenberg Professor & Project Leder, Deprtment of Civil Engineering, University of Illinois, Urbn, IL Judgements of the technicl qulity of wood crosstie products hve been bsed on ctul in-use performnce. However, it tkes t lest 20 to 30 yers to obtin results. New wood crosstie mterils re t severe mrket disdvntge due to the length of time neceesry to prove their worth. Thus there is need to develop short-term test method which cn be used to predict the long.term in-service performnce of wood crossties. A cyclic ccelerted ging technique tht is dptble s routine qulity control method in the mnufcturing or developing of red ok crosstie products ws developed. Six cycles of this ccelerted ging technique my be equivlent to more thn 20 yers of nturl ging depending on the property Used to relte ccelerted nd nturl ging. A 95 percent confidence intervl of plus nd minus three yers borders this reltionship. A curviliner reltionship is better fit thn liner model in relting certin properties to tie-ge, becuse these properties re decresing their rte of chnge, i.e., leveling off with ge. The MOE in compression is more sensitive thn hrdness modulus to the ccelerted ging process- Vrious properties of seleeted creosote-treted red ok crossties were significntly ffected by both the tie-ge nd the number of cycles of the developed ging technique. Keyword= Accelerted ging, compression, creosote-treted, crosstie, hrdness, modulus of ets ticity, nturl wethering, red ok. Introduction Wood crossties hve been used in the United Sttes since 1831 (Bescher, 1977). Creosote treted crossties ccount for more thn 30 percent by volume of the treted wood products mrket; mrket which utilizes more thn 500 million ft' (14.16 million mn) of stnding timber nd produces 1.46 billion dollrs worth of merchndise nnully (AWPA, 1982, USDA, 1981). It is pprent tht the use of wood for crossties is n importnt segment of the forest products industry. However, wood crossties must remin competitive with lterntive tie mterils, such s concrete nd steel, in order to mintin mrket shre nd prevent deleterious effects on the wood preserving nd timber production industries. Judgements of the technicl success or filure of these crosstie products hve lwys been bsed on ctul in-use performnce. This is the most ccurte method of evlution; however, it tkes long time ' This is refereed pper. to obtin results. The service life of treted wood ties on minline trck in the United Sttes is typiclly 20 to 30 yers nd rnges up to 40 yers (Bescher, 1977; Blum, 1942; Miller nd Houghton 1981). Regrdless of their potentil, newly developed crosstie mterils re t severe mrket disdvntge due to the length of time necessry to prove their worth. For prcticl purposes, evlution of these new tie products must be done through the use of ccelerted ging tests which llow for the rpid evlution of the resistnce of crosstie mterils to long-term service conditions. Thus there is need to develop suitble short-term test methods nd to estblish correltions between these short-term test results nd long-term in-service performnce of wood crossties. Tble 1 lists those fctors tht my significntly ffect the service life of crosstie (Bescher, 1977; Hope, 1983; Msters, 1982; nd USDA, 1973). Hinson (1985) nd Hope (1983) reported tht the reltive importnce of the degrdtion fctors vries with the chnging chrcteristics of ril trffic, environmentl conditions, trck chrcteristics, minte- - t-yi, 5; =05' 411

2 AMERICAN WOOD-PRESERVERS' ASSOCIATION 309 nnce, qulity of preservtive tretment, nd Mechnicl filure, primrily splitting or checking, crosstie species. In the pst, filure of crossties hs is the cuse for removl of the mjority of the hrdgenerlly been due to biologicl decy. Since the wood crossties. dvent of the diesel locomotive nd seled roller It is importnt to relize tht resons for removl berings, ril trffic hs become more severe; tht of ties from trck re determined on the bsis of is. greter tonnge crried per yer, lrger nd visul ppernce nd decy presence. Ties re relonger crs, incresed xle lods, nd higher speeds. moved from trck becuse of the suspicion of poor The filure of cross ties in mechnicl (non-biolog- performnce bsed on the experience of the tie finicl) mode hs become more common. Bescher spector. There is no efficient method of determining (1977) lso found tht the resons for tie filure re ' tie filure bsed on mesured mechnicl properties. different for different species. Over 60 percent of It is desirble to compre mechnicl properties of the ok ties were removed becuse of splits while ccelerted ged ties with those of nturlly ged only 5 percent of the pine ties filed due to splits. ties; however, there is no dt on the mechnicl Tble 1. Degrdtion Fctors Affecting the Service Life of Crossties I. Wethering Fctors A. Temperture (elevted, cyclic depressed) B. Wter C. Temperture Moisture Interctions (i.e. freeze thw) II. Biologicl Fctors (primrily fungi) III. Stress Fctors A. AbrAsion nd Compression due to bllst B. Impct Compression due to verticl ril lods C. Impct Bending due to verticl ril lods D. Spike loding due to lterl ril lods IV. Incomptibility Fctors A. Chemicl degrdtion due to presence of rusting metl nd high concentrtions of cidic slts B. Physicl degrdtion due to prticulte mtter under tie plte during loding V. Use Fctors A. Qulity nd Frequency of Mintennce (i.e. spike removl, dzing, type of bllst) B. Trck geometry (i.e. curves, ties per mile) C. Accidents (derilment, drgging equipment,spills)

3 310 AMERICAN WOOD-PRESERVERS' ASSOCIATION sj properties of nturlly ged ties. There is need to determine the mechnicl properties of crossties t vrious ges. The most importnt properties for ties tht re sensitive to the ging process nd indictive of the servicebility would be side hrdness nd compression perpendiculr to grin. These properties hve been shown to be sensitive to wood degrdtion to degree reported by Thompson (1980). Chow (1977, 1983) lso found hrdness of wood is ffected by moisture chnges. McLen (1932, 1953, 1954) found tht dry het is generlly not s severe s moist het, but stem heting is more severe thn heting in wter; nd lso found heting to be more severe on hrdwoods thn softwoods nd ttributed it in prt to the higher cetic cid content in hrdwoods. Acetic cid ccelertes the disintegrtion of wood. Plte-cut, seson-checks nd split creted by repeted wetting nd drying of the wood surfce from rin, dew, snow, nd high humidity hve been considered the principl cuses of cross tie filure. A preliminry study (Chow et l., 1986) indictes tht cyclic rtificil ging test ppered to be n effective wy of reducing the modulus of elsticity (MOE) in compression perpendiculr to grin nd hrdness modulus of 2 by 2 by 6 in. (5 by 5 by 15 cm) red ok blocks. Ech cycle of ging test consists of the following procedure: minutes under wter nd 25-inch (10 cm) vcuum, minutes under wter nd 170 psi (1.75 kg / cm") pressure, 3. 3 hours of steming t 250 F (121 C) nd 15 psi (103.4 kp), hours of oven drying t 220'F (104 C), nd 5. 3 hours in 0 F (17.8 C) freezer. The 6-cycle ging test found tht the rpid deteriortion which occurred in the smll red ok blocks ws not occurring in the full-size, 7 by 9 by 18 in. (18 by 23 by 46 cm) creosote-treted red ok ties. A longer steming portion of the cycle ws necessry to chieve n dequte level of dmge on the fullsize crossties. Tests lso found tht the steel tie plte inhibits movement of het nd moisture into the crosstie. For this reson, further ccelerted ging tests should be conducted on crossties without tie plte ttched. Objectives The mjor objectives of this study were s follows: 1. To determine the effects of ging, both ccelerted nd nturl, on the surfce ppernce, modulus of elsticity (compression perpendic- ulr to grin), side hrdness nd hrdness modulus of red ok crossties_ 2. To estblish reltionship between short-term nd long-term ging of red ok crossties in terms of the following properties:. Compressive lod perpendiculr to grin (I) Modulus of elsticity (MOE) (2) Mximum deflection (3) Lod t 0.04 in. (0.1 cm) deflection b. Side Hrdness (1) Hrdness (2) Hrdness modulus c. Totl re of surfce checks (surfce qulity) Mterils 1. Nturlly Aged Red Ok Crossties: With the id of the Norfolk Southern Rilrod Compny, 38 red ok crossties were selected from 0.2 mile (0.32 km) long section of trck t Sdorus, Illinois in June of This section ws minline running est-west with single line of trck. The line crried MGT per yer t mximum speed of 50 miles per hour (80.5 km / hr.) over grde tht vried from to feet per 100 feet (0.06 to 0.18 m 130,5 m). This trffic generlly consisted of 10 to 12 trins per dy with 100 to 150 crs per trin. The heviest cr nd engine weights were estimted t 130 tons over four xles nd 300 tons over six xles, respectively. The line ws tngent (stright) nd consisted of 115 lb. (52 kg) continuously welded ril plced on 13 by 7.75-in. (33 by 19.7 cm) steel tie pltes. Two spikes per tie plte were used to secure the ril nd tie pltes to the crossties, which were supported by bllst. The crossties were 7 by 9 in. (18 by 23 cm) in cross section nd 8.5 ft. (2.6 m) in length when instlled. The ties were supplied to the rilrod by three creosote-col tr treting plnts over the lst 45 yers. The treting plnts were locted in Mdison (Illinois), Knss City (Missouri), nd Indinpolis (Indin). The most recent ties were believed to be from the Mdison plnt nd Boulton-dried before tretment. Most of the older ties were thought to hve been ir dried before tretment. Tble 2 shows tht selected ties were ssigned to seven different ge groups, A through G, bsed on visul ppernce nd ny identifying mrks. The oldest of the ties selected ws 44 yers old s determined by dte nil. Ties were selected minly on the bsis of visul ppernce. The ges of 12 ties were obtined in the field by the presence of dte nils nd dte stmps. The ges of 6 more ties were determined fter removl from the trck by the presence of dte stmps.

4 AMERICAN WOOD -PRESERVERS' ASSOCIATION 311 Tble 2. Nturlly ged red ok crossties specimens. Age Group A D E F G Yers Totl First prt Second prt Totl Six red ok ties were desired in ech of the seven ge clsses, As red ok ties could not be differentited from white ok ties in trck, more thn six ties were selected for ech clss in hopes of obtining the desired number of red ok ties. A totl of 71 ties were tken from the trck. In the lbortory, red ok ties were seprted from white ok ties by the use of solution of sodium nitrite on fresh-cut, untreted surfce from the center of the tie. This hs proven to be relible method for seprting red ok nd white ok (Miller et l., 1985). Ech tie ws cut into two pieces, with one piece gong to the Assocition of Americn Rilrods' Lbortory in Chicgo nd the other piece going to the Wood Science Lbortory t the University of Illinois in Urbn, Illinois. Ech piece contined tie plte re. One piece from ech crosstie ws used in this study. From Tble 2, it cn be seen tht groups A, C, E, nd F ech hd less thn six Ted ok ties. The second piece from two red ok ties in group A, one red ok tie in groups C nd E, nd the two red ok ties in group F were lso included in this study to bring the number of red ok specimens per ge clss up to six. This provided for t lest six specimens in ech ge clss except for group F, which hd only four specimens. Thus totl of 44 specimens from 38 nturlly ged red ok crossties were used. 2. Accelerted Aging Red Ok Crossties: Twenty-four new red ok crossties which were pressure treted to 7 pounds per cubic foot (112 kg / nr') with 60 / 40 creosote-col tr preservtive were obtined. These crossties were seprted into three groups bsed on the method by which they were sesoned. Eight ties were ir-dried, eight ties were vpor-dried, nd eight ties were Boulton-dried. The crossties were provided by the Norfolk Southern Rilrod Compny. Ech crosstie mesured pproximtely 7 by 9 by 18 in. (18 by 23 by 46 cm). Procedures 1. Nturlly Aged Crossties: Moisture content redings were tken with _resistnce type moisture meter t penetrtion of 1 in. (2.54 cm) t vrious loctions on the ties t the time of removl from the trck. Moisture content redings were lso tken when the ties were tested t bout 70 F (21 C) room temperture. Compression perpendiculr to grin tests were performed on the tie plte re of the tie. The lod ws pplied through movble crosshed of the universl testing mchine nd crried through short section of 115 lb. (52 kg) ril to 13 by 7.75-in. (33 by 19.7 cm) tie plte nd in turn to the crosstie. Becuse the ends of the tie plte were rolled, the length of the plte ws considered to be in. (32.7 cm) when clculting the bering re of the lod. The re of the spike holes, which totlled in. 2 (27.3 cm') ws subtrcted from the tie plte re. This left bering surfce of 9.54 m. 6.4 cm 2 ). The compression tests were conducted t speed of in. (0.061 / cm) of crosshed deflection per minute nd were crried out to lod level of 24,000 lb. (10,886 kg) which. creted stress level of bout 250 psi ( kp) on the wood bering surfce. In previous study Chow et l. (1986) found tht the ASTM D-143 hrdness test, by using steel bll tht ws only in. (11.28 mm) in dimeter, did not provide relible hrdness vlue for the tretedcrosstie. If the test ws conducted on knot or just bove hidden check or split cvity, the results obtined would over or under estimte the proper test vlues. These problems could be solved by incresing the size of the steel bll used so s to "verge out" ny vrition of surfce hrdness in loclized res of the crosstie. For these resons, hrdness tests were performed using 2-inch (5.1 cm) steel bll tht ws imbedded into the surfce of the side of the tie t

5 AMERICAN WOOD-PRESERVERS' ASSOCIATION 31L the plte re. The lod ws trnsferred from the crosshed to the steel bll using steel plte with circle cut into it to ccommodte the bll. The hrdness tests were conducted t speed of 0.25 in. (0.635 cm) of crosshed deflection per minute nd were conducted until the steel bll ws imbedded 0.25 in. (0.635 cm) into the crosstie. A hrdness testing pprtus ws constructed tht held the steel bll, prevented it from moving lterlly, nd ws ble to mesure the penetrtion from the surfce of the wood. It ws decided to test the plte re of the tie in hrdness since hrdness is best suited to indicte the tie's resistnce to plte cutting, which occurs only under the tie plte. Properties clculted from compression tests included modulus of elsticity (MOE), lod t 0.04 in. (0.1 cm) deflection, nd mximum deflection. For selected ties, the re of surfce checks ws mesured. By subtrcting the re of the surfce checks from the bering re, reduced bering re ws determined. This ws used to determine n MOE bsed on reduced bering re. Properties determined from hrdness tests were hrdness (mximum lod) nd hrdness modulus. Hrdness modulus is equl to the lod under the proportionl limit divided by the depth of penetrtion (Chow et el., 1983). Ties were conditioned to the moisture contents ner the level of the fiber sturtion point of red ok. Vrition in moisture content under the fiber sturtion point is known to ffect the mechnicl properties of wood. 2. Accelerted-Aging of Crossties: The eight ties from ech of the three sesoning groups were processed through six cycles of the following ccelerted ging schedule s shown in Tble 3. One cycle is pproximtely 48 hours. Due to limittions in the size of the processing equipment, the ties were processed in sets of two. The ties were tested before nd fter the completion of every cycle. Testing consisted of perforthing compression perpendiculr to grin, hrdness tests, mesuring the dimensions of the tie, nd the length nd width of ll surfce checks on the:top of the specimen. The mesuring of the surfce checks ws done with ruler to the nerest eighth of n inch for both width nd length. All compression nd hrdness tests were crried out in the sme mnner s those for the nturlly ged tie specimen with the exception tht hrdness tests were performed on the bottom surfce of the Tble 3. Lbortory Aging Schedule Condition Exposure Period Purposes Vcuum soking (25 in. or 63.5 cm. Mg., room temp.) Pressure soking (170 psi or 1,172 kp, room temp.) Freeting (0 F or 17.8 C) 30 minutes' Mximum swelling occurs in wood 30 minutes' Mximum swelling occurs in wood 3 hours To simulte winter Steming (250 F or 121 C, 15 psi or 30 minute wrmup + 10 hours temperture Therml degrdtion of wood fibers Oven drying (220 F or 104 C) 9.5 hours Shrinkge occurs to crete checks. Conditioning (70 F or 21 C, bout 22 hours PO:=60% R.H.) q 0

6 AMERICAN WOOD-PRESERVERS' ASSOCIATION 313 crossties so s not to ffect the bering re for future compression tests. RESULTS AND DISCUSSION 1. Nturlly Aged Crossties: The moisture contents t the time of removl were generlly bove the fiber sturtion point. The moisture contents one inch below the top surfce of the tie under the center of the tie plte re were virtully ll bove the fiber sturtion point (bout 25 percent moisture content). Exceptions were some ties in group G, where moisture contents under the tie plte vried down to 23 percent. Severl ties in groups D through G vried ll the 'wy down to 17 percent moisture content but the verges for ll groups were close to or bove the fiber sturtion point. The ties tht hd moisture contents tht were below the fiber sturtion point were in the older ge groups. It is thought tht the incresed number nd size of checks in older ties enble them to dry out more rpidly thn younger ties. Moisture content redings t testing, under the tie plte re on the side of the tie t mid height, vried t or ner the level of fiber sturtion point. Averge vlues for ech group re shown in Tble 4. Tble 4 shows tht the older ties hd lower moisture content t the time of testing. Since the older ties hd lower moisture content When removed from the trck, it my be pproprite to consider the lower moisture content s prt of the nturl ging process. This would provide better estimte of strength in service thn if the moisture contents were djusted. The vlues for ech mechnicl property were plotted ginst ge group nd curves were fit to the dt using ordinry lest squres liner regression. Two curves were determined for ech property, one being P, the mechnicl property s liner function of yers, nd the other being Log (P) s liner function of yers (Steel et l., 1980). Ech tie ws ssigned the midpoint of the group ge rnge s its ge i.e., group A ties were 3 yers old, group B-8 yers old,... group G-33 yers old. In ddition to the seven ge groups tht consisted of crossties tken out of trck, n eighth group of new crossties, representing n ge of zero, ws lso included. This group consisted of the 24 ties tht were to be used for the ccelerted ging procedure. Tble 5 gives regressions of vrious properties on ges of nturlly ged red ok ties. Figures I through 3 re exmples of sctter plots showing the dt vlues nd the regression line tht ws fit to this dt. Ech property hs two sctter plots, one for the liner model, P = + b (Cycles), nd one for the log-liner model, Log (P) = + b (Cycles). Tble 4. Averge moisture contents t testing. Group Averge moisture content Rnge A C D E F All of the regressions in Tble 5 re significnt t the one percent level. The coefficient of determintion, R 2, cn be used to determine the goodnessof-fit of the regression line to the dt. The coefficient of determintin for the regressions vries from 0.24 for the log-liner model for hrdness modulus s function of cycles up to 0.74 for the log-liner models for mximum deflection, MOE, nd MOE using reduced bering re s function of cycles. For some properties, the rte of chnge of the property ppers to be nonliner. The rte of reduction in MOE nd lod t 0.04 in. (0.1 cm) deflection decreses while the rte of chnge in mximum deflection in compression seems to increse. For these properties, the log-liner model his the better fit. Generlly, the R 2 vlues were higher for the logliner model thn for the liner model except. the hrdness modulus nd surfce check properties. Those regressions involving properties pertining to compression ccounted for more of the vrition in the dependent vrible thn did those regressions involving hrdness properties. All the intercepts nd coefficients possess non-zero vlues t the one percent level of significnce. 2. Accelerted Aging of Crossties: The vlues for ech mechnicl property were plotted ginst number of ging cycles for ech sesoning group. Ordinry lest squres regression ws used to fit two curves to the dt. One curve ws of the form P = + b (Cycles) nd the second ws of the form Log = + b (Cycles), where P represents the mechnicl property (Steel et l., 1980). Seprte regression curves were determined for ech sesoning group. These curves re shown in Tble 6 nd Figures 4 through 6. Tble 6 gives the dependent vribles, the model used, the estimtes of the prmeters, the significnce of the prmeters, nd the coefficient of determintion for ech regression. Figures 4 through 6 ech show the three regression equtions determined for specific property nd model. The three lines in ech figure re

7 314 AMERICAN WOOD-PRESERVERS' ASSOCIATION identified by the letters A, V or B. A stnds for irdried, V stnds for vpor-dried, nd B stnds for Boulton-dried. Tble 6 shows tht ll models re significnt t the 1 percent level. With the exception of the regression coefficient in the liner model for hrdness modulus of ir-dried ties, ll intercepts nd regression coef- ficients possess non-zero vlues t the one percent level of significnce. Most of the regressions show tht the rtes of mechnicl degrdtion due to ccelerted ging between the ir-dried ties nd the vpor-dried ties were very similr. The comprisons show tht the only significnt differences between the ties from Tble 5. Regressions of Properties on Ages of Crossties Significnce of: Property & Model Eqution Model Intrcpt Coeff log-liner MOE: liner P' (Yrs) ** ** ** 0.71 Log(P) (Yrs) ** ** ** 0.74 mx. deflection:c liner P" (Yrs) log-liner Log(P)= (Yrs) ** ** ** 0.62 ** ** ** 0.74 lod t 0.04 inches: liner 1:} (Yrs) ** ** ** 0.53 log-liner Log(P)= (Yrs) ** ** ** 0.68 hrdness: d liner P=, (Yrs) log-liner Log(P)= (Yrs) ** ** ** ** ** ** hrdness modulus: e liner p" (yrs) log-liner Log(P)= (Yrs) ** *.* ** 0.30 ** ** ** 0.24 reduced bering re: liner P= (Yrs) ** ** ** 0.35 log-liner Log(P)= (Yrs) ** **- ** 0.34 _MOE using reduced re: liner P= (yrs) ** ** ** 0.60 log-liner Log(P)= (Yrs) ** ** ** ** denotes significnce t the p=0.01 level. b In psi, 1 kp = x psi. In in., 1 cm = x in. d In lb., 1 kg = x lb. e In lb. /in., 1 INT / cm = x lb. /in. f In in. 2 2, 1. cm = in. 2.

8 AMERICAN WOOD-PRESERVERS' ASSOCIATION Sctter Plot of Log(MOE) vs. Age Lg(MOE) (Yers) o : El 0 B 3.6 I I t i i i i u ctul vlues Yers Predicted vlue Figure 1 The effect of nturl-ging on the MOE (psi) in compression of red ok crossties (semi-log form), 1 &P -= X psi.

9 316 AMERICAN WOOD-PRESERVERS' ASSOCIATION Sctter Plot of Log(Mx. Defl.) vs. Age Log(Mx. Defl.) (Yers) Log(Moxlmum Deflection) g D ctul vlues Yers predicted vlue Figure 2 The effect of nturl-ging on the compressive deflection (in.) of red ok crosstie (semi-log form), 1 cm = x in.

10 AMERICAN WOOD-PRESERVERS' ASSOCIATION Sctter Plot of Log(Hrdness) vs. Age Log(Hrdness) (Yers) 3.9 ṟ-7 Log(Hrdnes3) U 8 B U i 3 I I I I I I - I I I I I I I 1 I I ctul vlues Yers predicted vlue Figure 3 The effect of nturl-ging on fce hrdness (lb.) of red ok crossties (semi-log form), 1 kg = x lb.

11 318 AMERICAN WOOD-PRESERVERS' ASSOCIATION Tble 6. Liner Regressions of Properties on Number of Aging Cycles Property, Model & Sesoning Group Regression Eqution Significnce of: Model Intrcpt Coeff 2 R Modulus of Elsticity: b liner: ir dry (Cycles) ** * * ** 0.47 vpor dry P (Cycles) ** ** ** 0.64 P= (cycles) ** ** ** 0.67 boult. dry log-liner: ir dry Log(P) (Cycles) ** ** ** 0.45 vpor dry Log(P)i= (Cycles) ** ** ** 0.67 boult. dry Log(P) (Cycles) ** ** * * 0.67 Mximum Deflection: c liner: ir dry P= (Cycles) ** ** ** 0.34 vpor dry P (Cycles) ** ** ** 0.50 boult. dry Pi., (Cycles) ** ** ** 0.59 log-liner: ir dry Log(P)p (Cycles) **,** ** 0.39 vpor dry Log(P) (Cycles) ** ** ** 0.50 boult. dry Log(P)** (Cycles) ** ** ** 0.63 Lod t 0.04" Deflection: liner: ir dry (Cycles) ** ** ** 0.27 vpor dry P= (Cycles) ** ** ** 0.18 boult. dry P= (Cycles) ** ** ** 0.49 log-liner: ir dry Log(P)= (Cycles) * * 0.35 vpor dry Log(P) r-.0453(Cycles) ** ** ** 0.26 boult. dry Log(P) (Cycles) ** ** * * 0.53 Hrdness: d liner: ir dry P= (Cycles) ** ** ** 0.63 vpor dry P= (Cycles) ** ** ** 0.63 boult. dry (Cycles) ** ** ** 0.43 log-liner: ir dry Log(P) (Cycles) ** ** ** 0.74 vpor dry Log(P)n (Cycles) ** ** ** 0.61 boult. dry Log(P) (Cycles) ** ** ** 0.47

12 AMERICAN WOOD-PRESERVERS' ASSOCIATION 319 Tble 6. (continued) Property, Model & Regression Significnce ) of: Sesoning Group Eqution Model Intrcpt Coeff 2 R Hrdness Modulus: e liner: ir dry P= (Cycles) ** ** vpor dry P= (Cycles) ** ** ** 0.63 boult. dry P= (CycleS) ** ** ** 0.54 log-liner: ir dry Log(P)= (Cycles) ** ** ** 0.17 vpor dry Log(P)= (Cycles) ** ** ** 0.60 boult. dry Log(F)J (Cycles) ** ** ** 0.58 Reduced sering Are: liner: ir dry P= (Cycles) ** ** ** 0.74 vpor dry P= (CyCles) ** ** ** 0.33 boult. dry P= (Cycles) ** ** ** 0.38 log-liner: ir dry Log(P)= (Cycles) ** **. ** 0.73 vpor dry Log(P)= (Cycles) ** ** ** 0.33 boult. dry Log(P)= (Cycles) ** ** ** 0.37 MOE w/reduced Are: liner: ir dry P= (Cycles) ** ** ** 0.44 vpor dry P= (Cycles) ** ** ** 0.62 boult. dry P= (Cycles) ** ** ** 0.63 log-liner: ir dry Log(P)= (Cycles) ** ** ** 0.41 vpor dry Log(P)= (Cycles) ** ** ** 0.64 boult. dry Log(P)= (Cycles) ** ** ** 0.63 ** denotes significnce t the p=0.01 level, -- denotes no significnce. b In psi, 1 kp = x psi. In in., 1 cm = x in. d In lb., 1 kg = lb. e In lb./in., 1 N/cm = x lb./in f In in., 1 cm = in..

13 320 AMERICAN WOOD-PRESERVERS' ASSOCIATION 4.65 Regression Lines of Log(MOE) = Cycles Three Se3orting Groups w 0 v ,4 4.35, , i Aging CycIe Figure 4 The effect of ccelerted-ging cycle on compressive MOE (psi) of red ok crossiies (A --= ir-dried, V = vpor-dried, B = Boulton-dried), I kpa = X psi.

14 AMERICAN WOOD-PRESERVERS' ASSOCIATION Reg. Lines of Log(Hrdness)=Cycles Thre Sesoning Croups Log (Hrdness) Aging Cycles Figure 5. The effect of ccelerted-ging cycle on fce hrdness (lb.) of red ok crossties (semi-log form) (A = irdried, V = vpor-dried, nd B = Boulton-dried), 1 kg = X lb.

15 322 AMERICAN WOOD-PRESERVERS' ASSOCIATION Reg. Lines of Reduced Are-=Cycles Three Sesoning Groups e O C C C Aging Cycles Figure 6 The effect of ccelerted-ging cycle on reduced tie-plte re (in') of red ok crossties cused by checks nd splits (liner regression form), 1 cm' = X in'.

16 AMERICAN WOOD-PRESERVERS' ASSOCIATION 323 these two sesoning methods were the rte of increse in surfce checking (shown by differences in the regression coefficient), nd the originl vlue (intercept term) nd the rte of chnge (regression coefficient) in hrdness. Boulton-dried ties show significnt differences in intercept terms for ll properties from the ir-dried nd vpor-dried ties. However, the rte of chnge in the property is similr for ll three groups for MOE, mximum deflection, nd lod t 0.04 in. (0.1 cm) deflection. As should be expected, the intercept term for reduced bering res for ll groups ws similr since initilly ll ties hd very few if ny checks. The irdried ties hd the lrgest regression coefficient for reduced bering re while the vpor-dried ties hd the smllest. It is likely tht the increse in checking is similr between the vrious groups of ties but the size of checks my differ considerbly. The ir-dried ties tended to hve t lest one or more lrge checks while the other groups my hve hd the equivlent re of checks but in much smller checks. 3. Reltionship of Accelerted Aging to Nturl Aging:. Correltion: The intent of this study ws to numericlly relte ccelerted ging to nturl ging nd thus determine quntittive mesure of durbility. A reltionship in the form of: Yers of Nturl Aging = f (Accelerted Aging Cycles) ws desired. This reltionship ws determined by lgebriclly solving the two independent regression equtions: P = f1 (Cycles)... [I] Yers = f 2 (P)... [2] Yers = f 2 [f, (Cycles)]... [ 3 ] The symbol "P" denotes mechnicl property. The results shown in Tble 6 gve equtions f 1. The regressions of ccelerted ging were clculted gin with the dependent vrible being yers insted of P. The liner regression equtions from both types of ging were combined. These gve equtions of the form: Yers = + b (Cycles) Tble 7 presents equtions 1 nd 2 nd the re-, suiting eqution 3 for ech property, model, nd sesoning group. In Tble 7 "Y" represents yers, "C" represents ccelerted ging cycles, "P" represents the property or log of the property used to relte cycles to yers. Also "AD" represents irdried, "VD" represents vpor-dried, nd "BD" represents Boulton-dried. b. Confidence Level of Predicting Models: Tble 7 provides equtions relting ccelerted ging cycles to yers but does not provide mesure of how ccurte this reltion is. It is possible to pre- dict confidence intervl bout ny point in these equtions. A 95 percent confidence intervl bout these equtions would denote tht bsed on the dt collected in this study, the confidence intervl would hve 95 percent probbility of including the true vlue t ny one point. Ninety-five percent confidence intervls for the expected vlue of yers from ech eqution were determined s outlined below (Steel et l., 1980). The two independent equtions below were used to clculte the vrible "yers". P 1 = b (Cycles,) from ccelerted ging.. [4] Yers, = rn n(p,) from nturl ging... [5] The vrince of the estimte of yers, V (Y), is equl to the vrince of estimted yers due to eqution 4, V 1, plus the vrince of estimted yers due to eqution 5, V2. V1 nd V2 were clculted s follows: V 1 = [x 0 ' (x'x) - 'ix o ]n 2 4, MSE1... [6] where x o = the mtrix contining the desired vlues of.the independent vribles, i.e., 1 nd Cycles I representing the intercept term nd Cycles vrying from 0 to 6. x o ' = the trnspose of mtrix - x o the inverse of mtrix contining the sum of squres of x for eqution 4 n = the estimted coefficient from eqution 5. MSE1 = the men squre error from eqution 4. V 2 = [1 31 (X'X) - 'P]oNISE2... [ 7 ] where P = the mtrix contining the desired vlues of the independent vrible, i.e., 1 nd predicted P-1 representing the intercept nd predicted P corresponding to the desired vlue of cycles. = the trnspose of mtrix P (rx) -1 = the inverse of mtrix contining the sum of squres of x for eqution 5. MSE2 = the men squre error from eqution. The vrince of the estimte of yers cn be used to determine the confidence intervl in the following mnner. Limits on the Confidence Intervl = estimted yers ± t(v[y])os. where t = tbulted t sttistic for the pproprite degrees of freedom nd probbility level. In this cse, p = nd there re 66 degrees of freedom, from published t-tbles, t -= 2.0.

17 324 AMERICAN WOOD-PRESERVERS' ASSOCIATION Tble 7. Reltion of ging cycles to yers. P=f (Cycles) Yers=f (P) Yers=f (Cycles) Property Eqution 1 Eqution 2 Eqution 3 MOE (Compression perpendiculr to grin): Liner: AD P= (C) 1= (P) VD P= (C) sme s bove BD P= (C) sme s bove Y= (C) 1= (C) Y= (C) AD VD BD Log-liner: P= (C) P= (C) P= (C) Y= (P) sme s bove sme s bove Y= (C) 1= (C) Y= (C) Mximum Deflection: b Liner: AD P= (C) VD P= (C) BD P= (C) Y=-I (P) sme s bove sme s bove Y (C) Y= (C) Y= (C) AD VD BD Log-liner: P= (C) P=-I (C) P= (C) Y= (P) sme s bove sme s bove 1= (C) Y= (C) 1= (C) Hrdness: Liner: AD P= (C) VD P= (C) BD P= (C) Y= (P) sme s bove sme s bove 1= (C) 1= (C) 1= (C) AD VD BD Log-liner: P= (C) P= (C) P= (c) Y= sme s bove sme s bove (P) 1= (C) 1= (C) 1= (C) Hrdness Modulus: d Liner: AD P= (P) VD P= (P) BD P= (P) Y= (P) sme s bove sme s bove Y=I (C) 1= (C) Y= (C) AD VD ED Log-liner: P= (C) P= (C) P= (C) 1= (P) sme s bove sme s bove Y= (C) Y= (C) Y=I (C) In psi, 1 kp = x psi. b In in., I cm = x in. In lb., I. kg =,2.205 x lb. In lb./in., 1 N/cm = 0.571x lb./in.

18 AMERICAN WOOD-PRESERVERS' ASSOCIATION 325 The confidence intervl vries with x. The further x is from the verge x used to determine the confidence intervl, the wider the confidence intervl. Exmples of confidence intervls re given in Figures 7, 8, nd 9. These confidence intervls re bout the equtions determined by combining the liner regression equtions tht involve the modulus of elsticity in compression. These re the first three equtions in Tble 7. The grphs show the confidence intervl becoming wider t the ends of the known vlues for cycles. Tble 8 shows the rnge of the confidence intervl for ech property, sesoning group, nd type of model. All vlues in Tble 8 re for 95 percent confidence intervls. For the properties determined from the compression perpendiculr to grin tests, the confidence intervl is ±2 to 3 yers. The confidence intervls for hrdness properties hve wider rnge, from ±3 to 5 or 6 yers. The compression properties gve more consistent vlues, with intercepts rnging from 0 to 7 yers with most being between 3 nd 5 yers. According to the equtions constructed from the regressions involving MOE, 6 cycles of ccelerted ging is equl to 16 to 20 yers of nturl ging depending on the sesoning method. The 95 percent confidence intervl for x = 6 cycles is less thn ±3 yers for the eqution obtined by solving the liner regressions involving MOE. The compression perpendiculr to grin properties seem to provide better nd more consistent reltionship between ccelerted ging nd nturl ging. The reduced bering re criteri provides very consistent confidence intervl between ± 2.8 yers. Summry nd Conclusions This study involved the testing of nturlly ged nd ccelerted ged 7 x 9-in. (18 by 23 cm) cross- Result of Liner Eqtns Air Dried Ties Yers (Cycles) Cycles Figure 7 Prediction of tie ge by using the number of cycle of ccelerted ging test in term of MOE (psi) in compression - (bsed on tests dt of ir-dried red ok crosstie specimens), 1 kp = x psi.

19 326 AMERICAN WOOD-PRESERVERS' ASSOCIATION Result of Liner Eqfns Vp.Dried Ties Yers (CycIes) Cycles Figure 8 Prediction of tie ge by using the number of cycle of ccelerted ging test in term of MOE (psi) in compression (bsed on test dt of vcuum-dried red ok crosstie specimens), 1 kp = X psi.

20 AMERICAN WOOD -PRESERVERS' ASSOCIATION 327 Result of Liner Ecitns BILDried Ties Yers (Cycles) Cycles Figure 9 Prediction of tie ge by using the number of cycle of ccelerted ging test in term of MOE (psi) in compression (bsed on test dt of Boulton-dried red ok crosstie specimens). I kpa = psi.

21 328 AMERICAN WOOD-PRESERVERS' ASSOCIATION section pressure treted red ok crossties. Conclusions tht cn be drwn from this study include: 1. The elstic properties in compression perpendiculr to grin nd surfce hrdness properties re significntly ffected by cyclic ccelerted ging nd nturl wethering. 2. The modulus of elsticity in compression perpendiculr to grin is more sensitive thn hrdness or hrdness modulus to ccelerted ging tretments of het nd moisture. 3. Simple liner regression cn ccount for up to 74 percent of the vrition in compression perpendiculr to grin properties, including mod- Tble 8. Confidence Intervls About the Equtions Relting Accelerted Aging to Nturl Aging. Confidence Intervls consist of: Property & Estimted Y + the vlues in this tble. Sesoning Group Liner Equtions Log-liner Eqution Modulus of Elsticity: ir dry vpor dry boult. dry Mximum Deflection: ir dry vpor dry boult. dry Lod t 0.04" Deflection: ir dry vpor dry boult. dry Hrdness: ir dry vpor dry boult. dry Hrdness Modulus: ir dry vpor dry boult. dry Reduced Bering Are: ir dry vpor dry boult. dry MOE w/reduced Are: ir dry vpor dry boult. dry

22 AMERICAN WOOD-PRESERVERS' ASSOCIATION 329 ulus of elsticity nd mximum deflection in nturlly ged crossties. 4. Certin properties, including modulus of elsticity, mximum deflection, nd lod t 0.04 inches show better fit when curviliner reltionship is used. This indictes tht these properties re leveling off with ge. 5. There is more vribility in mesurement of hrdness properties thn in compression perpendiculr to grin properties. 6. There re differences in the mechnicl properties of red ok crossties tht hve been sesoned by different methods. However, the rte of chnge of these properties due to ccelerted ging my be consistent between sesoning tretment groups. 7. A reltionship hs been determined between the six-cycle ccelerted ging process nd nturl ging. Confidence intervls of pproximtely three yers border this reltionship. Six cycles of ccelerted ging my be equivlent to more thn 20 yers of nturl ging depending on the property used to relte ccelerted nd nturl ging. 8. The mechnicl properties of some selected inservice red ok crossties obtined from trck in the Midwest hs been determined. 9. The ging nd degrdtion of wood crosstie ppers to be n extremely complex process involving mny fctors nd interctions. This study demonstrtes tht the wethering of red ok crossties my be s importnt fctor of degrdtion s biologicl deteriortion nd stress. Acknowledgment This study ws supported by funds dministered through the Assocition of Americn Rilrods; nd the Affilited Lbortory Core Progrm, College of Engineering, nd the Deprtment of Forestry, Illinois Agriculturl Experiment Sttion, University of Illinois, Urbn, Illinois We re grteful to Mr. W. S. Lovelce, Ms. J. J. O'De, nd Mr. J. E. Hinson, Norfolk Southern Rilwy Compny, Alexndri, Virgini, lso Kerr- McGee Chemicl Co. for the red ok crossties used in this study; nd to Mr. R. L. Lntz, Mr. M. A. Frnck, nd Mr. N. L. Hwker, Koppers Compny, Illinois, for the ok crossties used in the preliminry investigtion of this experiment. Mr. M. D. Roney, CP Ril, Quebec, Cnd, nd Mr. J. B. Miller, Snte Fe Rilrod, Chicgo, nd Mr. R. H. Bescher, Ohio, provided vluble counsel for the experiment. Literture Cited Americn Wood-Preservers' Assocition Sttistics. Proceedings, AWPA, 78. AWPA, Stevensville, MD. Bescher, R. H. 1977, Creosote crossties. Proceedings, AWPA, Stevensville, MD. Blurn, B Service rendered by vrious species of tie in the northwest. Proceedings, AWPA, 38: AWPA, Stevensville, MD. Chow, P Hrdness of wood flooring nd siding. Illinois Reserch, 19(2):16. University of Illinois Agriculturl Experiment Sttion, Urbn, IL. Chow, P., P. Dzilowy, nd P. Russo Veneered fiberbord pnels: effects of moisture nd testing speed on hrdness properties. Furniture Design nd Mnufcturing, Feb Chow, P. A. J. Reinschmidt, E. J. Brenburg, nd S. L. Lewis Lbortory tests on rtificil wethering of Quercus rubr crosstie. Int. Res. Gr. on Wood Pres. Doc. IRG/WP/2252. Sweden. 7 p. Hinson, J. E Wood ties in '85, the chllenge nd the promise. Crossties 66(7): Hope, L. G The severe-service crosstie. Crossties 64(10). McLen, J. D Studies of het conduction in wood-prt II. Results of steming green swed southern pine timbers. Proceedings, AWPA, 28: Effect of steming on the strength of wood. Proceedings, AWPA 49: AWPA, Stevensville, MD Effect of heting in wter on the strength properties of wood. Proceedings, AWPA 50: AWPA, Stevensville, MD. Msters, L Predictive service life testing of structurl nd building components. In structurl uses of wood in dverse environments. Ed. R. W. Meyer nd R. M. Kellogg. Vn Nostrnd Reinhold Co., New York, NY. Miller, D. J. nd P. R. Houghton Perform= nce of western wood species s crossties in minline rilrod trck. Forest Products Journl 31(5): Miller, R. et l Identifying white ok logs with sodium nitrite. Forest Products Journl 35(2): Steel, R. G. D. nd J. H. Torrie Principles nd procedures of sttistics. Second Edition. McGrw-Hill Book Co., Inc., New York, NY. Thompson, W. S Effect of preservtive tretments nd exposure conditions on the mechnicl properties nd performnce of wood. In how the environment ffects lumber design: ssessments nd recommendtions. USDA Forest Service, Forest Products Lbortory, Mdison, WI. U. S. Deprtment of Agriculture, Forest Service, Forest Products Lbortory Wood Hndbook. Agric. Hndbook No. 72. U.S. Deprtment of Agriculture The biologic nd economic ssessment of pentchlorophenol, inorgnic rsenicls, creosote. Volume 1: Wood preservtives. Technicl Bulletin No

23 330 AMERICAN WOOD-PRESERVERS' ASSOCIATION Discussion HARRY GREAVES: Did you find tht ny of your ccelerted ging regimes cused n increse in the mobility of the creosote in the treted ties. I m prticulrly thinking of the steming, oven drying nd conditioning phses. MR. CHOW: It is very interesting to know the condition in Austrli nd I think in the United Sttes. We re lso going in the sme direction s wht you sy. Your question bout loss of creosote due to ccelerted ging, is true. Especilly the first nd second cycle in the utoclve where we re steming the creosote treted ties. We try to simulte the rins nd the sun. We determine some of the creosote content fter ech cycle. But fter six cycles there is still quite lot of creosote left in the ties. JEFF BROADFOOT: Wht plns do you hve to incorporte mechnicl dmge into your overll picture. I noticed tht wsn't included in the ccelerted ging process nd its reltionship to tie life (i.e., is there ny reltionship between mechnicl dmge spect in your ccelerted tie ging process?) MR. CHOW: The question ws whether or not the mechnicl dmge on the tie ws included in the lb ccelerting test. One of the slides show tht the left hlf of ech tie went to the Assocition of Americn Rilrods lb. They re plnning to do some impct nd dynmic test in their lb in Chicgo. Tht is prt of the purpose. We only conduct the sttic test t the University of Illinois. I m only responsible for this end in the lb nd I don't know their pln. Mr. Victor Shfrenko of AAR is here nd you my be ble to get some nswers from him. He is the representtive of the Assocition of Americn Rilrods. J. N. R. R000loK: This study nd the conclusion developed do not tke into ccount the influence of decy. Would you like to comment on the effect of decy on limiting tie life? MR. CHOW: In the pst I think the tie inspectors removed the tie bsed on the ppernce nd decy which re mjor fctors to remove the tie from the trck. In this study we only tried to isolte the decy fctor. Right now we just study the wethering effect. In the lter phse of the study we shll include decy or fungi effect in the sme kind of tests. All of the tests we conducted on red ok ties hd the tie ges from brnd new up to 30 yers old. Ties deteriorte in kind of similr rte nnully. When ties rech 20 yers old, decy or fungi my strt to grow in them. This is just my guess. We re plnning to study this topic using different kind of fungus species in the future. SESSION CHAIRMAN Roo: Thnk you very much, Dr. Chow: Our next pper is entitled "Recent Reserch on.alkylrnmonitn Compounds in the U. S." by A. F. Preston, P. J. Wlcheski, P. A. McKig nd D. D. Nichols. Aln Preston will present the pper.