Prestressed Concrete Pavement: Instrumentation, Behavior, and Analysis of Horizontal Movements

Transcription

1 38 TRANSPORTATION RSARCH RCORD 1286 Prestressed Conrete Pavement: Instrumentation, Behavior, and Analysis of Horizontal Movements LLIOTT DAVID MANDL, ND H. BURNS, AND B. FRANK MCULLOUGH The long-term work plan for the initial design phase of the MLennan County prestressed onrete pavement (PCP) overlay onsisted of the determination of variables that are relevant to design, the development of models and design proedures, and the study of the effet of environmental fators on PCP slabs. The evaluation of the performane of PCP, with speifi observation of horizontal slab displaements aused by hanges in temperature, is disussed. The behavior of the PCP is haraterized by the results of a field data analysis. The instrumentation of the PCP slabs is desribed, graphs of measured displaements of the slabs for daily temperature yles are presented, and a regression analysis of the slab movements is disussed. Finally, onlusions and reommendations based on the instrumentation program and data analysis are outlined. Prestressed onrete pavement (PCP) takes advantage of the high ompressive strength of onrete to prevent or derease tensile stresses during servie. When a permanent horizontal ompressive stress is introdued to a pavement slab during onstrution, its apaity to withstand traffi and environmental loads is inreased. This ompression of onrete slabs results in a potentially ost-effiient alternative to traditional pavements or pavement overlays. This paper addresses appliations of pavement theory by reporting the analysis of data olleted from in situ PCP slabs on Interstate 35 in Texas. Initial performane of the PCP has been reported previously (1,2), and reent performane has been reported in detail (3,4). The data are used to haraterize the behavior of the slabs aused by environmental loads and to alibrate a model that predits the behavior of PCP. The results of this study are offered as input to an ongoing proess of understanding PCP for the purpose of refining the design proess for its wider implementation. GNRAL BHAVIOR All onrete pavements are subjet to onstant flutuations in temperature beause of daily and seasonal thermal yles. These temperature hanges ause individual pavement slabs. D. Mandel, DeLeuw, Cather & Company, Washington, D.C. 25. N. H. Burns, Department of Civil ngineering, The University of Texas at Austin, Austin, Tex B. F. MCullough, Center for Transportation Researh, The University of Texas at Austin, Austin, Tex to undergo two types of movements: volumetri and urling. Motion that is subjeted to restraint at boundaries or gravity loads auses stress to develop in the onrete. The magnitudes of displaement and stress determine the behavior and ultimate servieability of a pavement. Volumetri Movement Sine PCP slabs are muh longer than they are wide or thik, longitudinal expansion and ontration are the most signifiant volumetri movements. Thermal expansion and ontration of pavement are restrained by fritional fores imparted by the subbase onto the bottom surfae of a slab. When it expands, the slab is subjeted to ompressive stresses aused by the fritional resistane of the subbase. Similarly, when a slab ontrats it is subjeted to tensile stresses. Beause the inherent material properties of plain onrete provide high ompressive strength but low tensile strength, ontration of a slab ditates whether it will rak from a tensile stress that exeeds its tensile apaity. For slab movements that are symmetrial with respet to the longitudinal enterline, a long slab experienes a higher magnitude of tensile stress on ontration than a short slab beause the stress aumulates from the ends of a slab to the middle. The amount of stress aumulation also depends on the fritional harateristis of the subbase; a smooth interfae between the slab and the subbase provides less resistane than a rough one, resulting in an inrease in magnitude of longitudinal movement and a derease in tensile stress. In PCP, the slabs are preompressed so that they an have longer lengths without suffering damage from tensile stresses. Figure 1 illustrates the effet of subbase fritional restraint on the tensile stress in a pavement slab and the ombined effet of frition and preompression on slab stresses. Curling Movement Temperature gradients aross the thikness of the pavement resulting from a time-lag effet of heat transfer from the top surfae to lower regions in the slabs ause urling movements. When the ambient temperature inreases, the top region of a slab experienes a more rapid inrease in temperature than the bottom region. This effet auses the top region to undergo

2 Mandel et al. 39 //X"..' /./.I&'(// i---->-- Movement Movement (& i ;-.,...- i..,.,. --. t F::e Jt! I HI -===+=-=== l H t. k::: --IJ... ==:::J---JI FIGUR 1 ffet of subbase fritional restraint on stress in a onrete slab for a temperature derease and the additional effet of preompression by fore P. a more rapid volumetri inrease than the bottom region. Similarly, when the ambient temperature dereases, the top region experienes a more rapid volumetri derease than the bottom region. The differential in volumetri deformation through the thikness of the pavement auses the slabs to url vertially. This movement of the slabs flutuates onstantly as the temperature gradient aross the thikness of the slab hanges, reversing the diretion of indued urling movement. For long pavement slabs, urling movements an be large, ausing signifiant tensile stress in the onrete. In addition, large urling movements an ause the slab to pull away from the subbase; if enough separation ours, repetitive traffi loads an ause pumping of material from beneath the slab, resulting in large voids under the pavement. PRVIOUS RSARCH The urrent study on the behavior of PCP is an extension of previous researh onduted at The University of Texas at Austin from 1984 to A series of oneptual and experimental investigations into the design and implementation of PCP were arried out during that time. These studies examined several separate aspets of PCP, inluding the appliation of speial prestressing tehniques, the evaluation of projeted in situ parameters, and the formulation of design proedures. The researh provided information required for the design, onstrution, and early-life instrumentation of a 1-mile experimental prototype setion of a PCP overlay loated in entral Texas (1,2,5-9). OBJCTIVS AND SCOP Field work performed on the MLennan County, Texas, PCP overlay from July 1988 to February 1989 is desribed, as well as analytial work performed subsequently. The olletion and analysis of horizontal movement data are overed, as well as instrumentation details. Although urling movement data are available, the results will be reported elsewhere. LAYOUT OF TH PCP The experimental prototype setion of PCP in MLennan County is loated on Interstate 35 southbound, about 15 mi north of Wao. The setion is 1 mi long and ontains a total of 32 prestressed slabs. The slabs onsist of a PCP overlay 6

3 t:! u v : 5 N Q; 9. 1 ::::i z a 11 -, Ul. <1l u V5 a> i:i! Ci FIGUR 2 Layout plan of the MLennan County PCP experimental setion. in. thik over an existing 11-in. jointed onrete pavement (JCP) with an intermediate 3-in. ACP stress-reduing ourse. The pavement is 38 ft wide and onsists of two 12-ft lanes, a 1-ft outside shoulder, and a 4-ft inside shoulder. It has the following dimensions in plan: 9 slabs at 24 ft by 21 ft 7 slabs at 44 ft by 21 ft 9 slabs at 24 ft by 17 ft 7 slabs at 44 ft by 17 ft A layout plan, inluding the joint numbering system of the entire experimental setion, is shown in Figure 2. PRVIOUS INSTRUMNTATION An instrumentation program was arried out during the early life of the MLennan County overlay (2). Measurements taken at that time were intended to provide a verifiation of predited values of onrete stress and slab movements aused by both prestressing and daily temperature yles. The measurement program inluded TRANSPORTATION RSARCH RCORD Determination of daily flutuations in ambient temperature, onrete temperature at middepth of the pavement slabs, and the temperature gradient over the thikness of the pavement slabs; 2. Measurement of horizontal and vertial slab movements and joint widths; 3. Measurement of tendon elongations during stressing operations; 4. Measurement of onrete strain in the slabs; and 5. Determination of onrete strength and modulus of elastiity at early ages. CURRNT INSTRUMNTATION A seond instrumentation program for the MLennan County PCP (overed herein) was arried out to monitor movements of the slabs after hanges in the material properties of the onrete had stabilized and after shrinkage and reep effets essentially were omplete. Information olleted in this instrumentation program was used to haraterize the long-term behavior of the PCP. Field Visits Work performed at the MLennan County PCP site inluded site surveys, preliminary measurements, installation of instrumentation equipment, and data olletion. Data olletion took plae from July 1988 to February During that time six field visits were made. The field visits took plae under varying onditions of moisture and ambient temperaturethree during hot and dry onditions, one during mild and dry onditions, and two during old and wet onditions. Table 1 outlines the five data olletion field visits and an additional trip. The duration of all data olletion periods was 24 hr, wilh lhe exeption of Lhe sixlh fielj visil, whih lasted 48 hr. The array of weather onditions overs the maximum range of temperatures that ourred at the site. It is diffiult to evaluate whether the wet moisture onditions an be onsidered as the extreme onditions; 1988 was a drought year with almost no preipitation from July to Deember. The onditions desribed as "wet" in Table 1 were moist from rain that ourred 1 to 2 days before data olletion. Instrumentation Set-Up Conrete "dead-man" anhors were used to support dial gauges and linear voltage-distane transduers (L VDTs). The anhors onsisted of typial 6-in. by 12-in. onrete ylinders with embedded threaded inserts that reeive 7 /s-in. threaded dowels. Two inserts were installed in ase one failed to funtion. Rubber stoppers proteted the inserts when they were not in use. The anhors were inserted into the soil, leveled, and seured into plae with onrete, about 18 in. from the west edge of the slabs. Then, for eah field visit, a vertial steel dowel with a threaded end was srewed into eah anhor, and horizontal dowels were seured and attahed to the vertials with 9-degree dowel lamps. Dial gauges or L VDTs were then seured to the horizontals. This set-up allowed for the

4 Mandel et al. 41 TABL 1 DATA COLLCTION FILD VISITS Maximum Minimum Ambient Ambient Field Visit Date Temperature Temperature Weather Condition 2 July 26, F 74.8 F Hot, Dry 3 August 6, Hot, Dry 4 August 26, Hot, Dry 5 November 5, Mild, Dry 6 January 21, Cold, Wet 7 February 9, Cold, Wet temporary fabriation of instrumentation supports at the work site and for their removal after data olletion was ompleted for eah field visit. To give the dial gauge and LVDT plunger-pins a positive reation-stop, the slabs were equipped with reeptales. For horizontal movements, steel angles (3 in. by 3 in. by 3/R in.) were bolted onto inserts that were drilled and epoxied onto the edges of the slabs. For urling movements, plasti reeptales were used to provide a smooth and level surfae. ah reeptale onsisted of a 3-in. by % in. by % in. polyvinylhloride pipe that was epoxied to the top surfae of a slab and filled with hot (liquid) sulfur mortar. When the liquid ooled and solidified, a flat and level surfae resulted. A smooth surfae was reated by epoxying a 1 Y2 in. by 1 Y2 in. by Y4 in. plasti square to the top of the sulfur. Temperatures were measured using thermoouples. Six thermoouples were drilled and grouted into the PCP to measure onrete temperature. Two thermoouples were loated at eah of three depths-1 in., 3 in. (middepth), and 5 in. The middle thermoouples were used for orrelation with horizontal movements, and the top and bottom thermoouples were used for orrelation with urling movements. Ambient temperature was measured by plaing a thermoouple in the shade. Q;. :::i z '6..., Q;. :::i z 2 Ui :: :o t 9N e l===='i 9S 9S/6 1N/3 o 1N/6 1 ON e I=-==-=--! 1S 1S/6 1S/3 11N/3 11 N l=====i 11 s Jl us "' (".) Measurement The number of loations on the slabs that ould be instrumented simultaneously was limited by the availability of dial gauges. Figure 3 shows a plan view of the instrumented slabs. Instrumentation loations labeled with "/3" or "16", respetively, indiate third or sixth points along the slab length. During the first three field visits data were olleted from joint loations only so that joint displaement data ould be based on the largest possible sample. For the remainder of the field visits, displaement data were olleted at loations along slab lengths to haraterize the displaements of entire N 12S 13N e l=-===i e.... Instrumentation at nd of Slab O Instrumentation along Slab Length FIGUR 3 Instrumented slabs and instrumentation loations.

5 42 TRANSPORTATION RSARCH RCORD 1286 slabs. The instrumentation set-up allowed for the measurement of horizontal and vertial slab movements with respet to an arbitrary datum. Displaements measured from the first data reading at eah loation for eah field visit. Prevention of rror Several methods for avoiding error in final versions of data were employed. These methods inlude prevention of interferene, redundant readings, and internal heking of data. Interferene was prevented in two ways: steel dowels were enased in foam insulation to prevent error aused by uneven heating from the sun, and temporary masonry walls were onstruted to prevent error reated by wind gusts from traffi. Redundany of data readings inluded two slab temperature readings at eah of the three depths-1 in., 3 in., and 5 in. - and at Joint 1, horizontal slab movements were measured with both dial gauges and L VDTs. The measurements of horizontal slab movements ould be internally heked beause the sum of the movements measured by dial gauges or L VDTs at the ends should add up to the hange in joint opening measured with dial alipers. DATA ANALYSIS This setion desribes the treatment of the field data olleted at the MLennan County PCP. The data inlude measurements of horizontal and vertial slab displaements, joint widths, ambient temperatures, and onrete temperatures at three depths in the pavement. Only the analysis of horizontal displaements and their orresponding onrete temperatures at middepth in the slabs is inluded in this paper. Hankins et al. (3) inluded a omplete listing and graphi presentation of all data. = : Ql Ql.. (/) : N " I.1 o.o ft. slabs - 24 ft. slabs (1/3 point) - 24 ft. slabs (1/6 point) - 44 ft. slabs - 44 ft. slabs (1 /6 point) - 44 ft. slabs (1/3 point)... o (\j N 9. 9.!'? N... <D a; Time (hour:min) g o N FIGUR 4 Average horizontal slab displaements at various times during a 24-hr observation yle for field visit 5. Data for both slab lengths and at intermediate points are shown. DAT A RDUCTION To effetively use the data olleted in the field, a data redution proess was designed and performed. The purpose was to transform field data into numbers that ould be used to haraterize the behavior of the PCP in a onise manner. The proess inluded l. Normalizing displaement data to a ommon axis; 2. "Smoothing" erroneous data by using a redundant reading, or by bakalulating from a losure measurement; 3. Organizing the data by field visit, slab type, and type of instrumentation loation; and 4. Performing a statistial redution of the data. Figure 4 is a typial graph of the horizontal displaement versus time obtained from the redution proess. This graph is for field visit 5 and overs both slab lengths and intermediate points. The omplete set of data may be found in Hankins et al. (3). BHAVIOR ANALYSIS The design of a PCP involves the evaluation of two major aspets of the horizontal slab movements: the harater of slab ativity during temperature hanges and the range of joint widths between slabs. The former is of interest beause stresses in the slab are a diret funtion of displaements. The latter affets the plaement of slabs (in whih the design riteria are meant to avoid extremely wide joint widths and omplete losure of the joints). Slab ativity also affets the range of joint widths, that is, slabs with more ative horizontal movements will ause a larger range of joint widths. Regression Analysis of Horizontal Displaements Analysis of slab ativity for temperature hanges was performed by alulating a series of linear regression equations for horizontal displaements as a funtion of the slab's middepth temperature. This independent variable provided the best orrelation. Figure 5 is a typial graph of slab displaements as a funtion of dereasing and inreasing temperature. Plots for all instrumentation loations are presented in Appendix B as reported by Mandel et al. (4). The equations are linear, in whih the absissa (T) is the onrete temperature at middepth of a slab in degrees Fahrenheit, and the ordinate (Y) is the horizontal displaement from the initial data reading for a field visit. Table 2 shows a ompilation of the regression equations for all field visits, along with oeffiients of determination (R2). All R 2 values are high: two-thirds of the equations have values greater than.95. The lowest value is.854. These data indiate that the linear equations an predit horizontal displaements with a high degree of auray. This regression analysis does not indiate, however, whether stresses in the slab an be predited with a linear model; stresses are a funtion of the aumulation of fritional fores under a slab, and any nonlinear behavior of the subbase fritional restraint ould ause stress magnitudes to vary nonlinearly.

6 Mandel et al _ g a. Cf) Ci ]j : N ' I Dereasing Temperature ---<i- BS N S... 9S/ N/ N/6.,_ 1N Inreasing Temperature -----ss N,.. 9S S/ N/ N/6 --->t-- 1N -.4 L ' ' ' Conrete Temperature ( F} FIGUR 5 Horizontal slab displaements of 44-ft slabs versus hange in onrete temperature for field visit 5. As expeted, the slopes in the equations inrease for the longer slabs. The ratio of slab lengths between the 44-ft and the 24-ft slabs is 1.835, and the ratio between the average values of the slopes in the equations for the slabs is 2.24, 1.31 perent higher. This suggests that the inrease in horizontal ativity with inreased slab length is not linear. The slopes follow logial trends for the various measurement loations. The average slopes for displaements at the joints are 5.89 x 1-3 and x 1-2 in./ F for the 24- ft and 44-ft slabs, respetively. At the sixth points, the average slopes are x 1-3 and x 1-3 in./ F, perent and perent of the slopes at the joints. At the third points, the average slopes are 1.99 x 1-3 and x 1-3 in.l F, perent and perent of the slopes at the joints, and perent and 46.4 perent of the slopes at the sixth points. The horizontal ativity varies approximately linearly with respet to the geometry of the slabs. In addition, it appears that for both 24- and 44-ft lengths, almost the entire slab is moving. Figure 6 shows a graph of the slopes of the regression equations as a funtion of the distane from the enterlines of the slabs. The regression equations do not show a strong trend for various moisture levels. Field visits 6 and 7 took plae under moist onditions; the 44-ft slabs have slightly smaller slopes for these visits, and there is no definitive trend for the 24- ft slabs. One explanation for there not being large differenes for field visits 6 and 7 is that the slabs might not have been ompletely saturated, and therefore expansion and ontration harateristis of the slabs would not have hanged enough to show up in the data. Another explanation is that the horizontal ativity is not very sensitive to hanges in moisture levels. The reason for this would be that the regression equations relate horizontal movements to the onrete temperature at middepth of the slabs. The moisture level might affet the lag time between hanges in ambient temperature and hanges in onrete temperature, but the expansion and ontration harateristis of the slab would not neessarily hange appreiably. The data reveal that horizontal displaements, although behaving almost perfetly linearly in most instanes, show a small amount of nonlinearity in others. The displaements for the 44-ft slabs during field visits 5 and 7 learly exhibit nonlinear variation of displaements with respet to onrete temperature. The nonlinearity of the displaements observed in these two visits is probably beause of either hanges in the rate of heating of the onrete (aused by differenes in the rate of heat absorption by the onrete, whih is aused by differenes in atmospheri filtering of radiation) or a pronouned effet of hysteresis (energy-absorbing apaity) in the fore-displaement behavior of the subbase fritional restraint. It is not possible to draw an exat onlusion for the ause of this effet, but previous researh has indiated that the nonlinear behavior of the subbase frition should be onsidered in the analysis of horizontal displaements of rigid pavement slabs (1). Analysis of Joint Widths The determination of an initial joint width for onstrution of PCP depends on the following fators: The projeted amount of reep and shrinkage that will our during the early life of the pavement, The projeted amount of elasti shortening a slab will undergo during stressing operations, The width requirements for inserting a protetive neoprene seal into the joint, and The expeted range of temperatures and subsequent horizontal displaements that the slabs will experiene throughout their servie lives.

7 44 TRANSPORTATION R SARCH RCORD 1286 TABL 2 RGRSSION QUATIONS FOR HORIZONTAL DISPLACMNTS Coeffiient of Partial Field Visit Measurement Loation Regression quation Detennination 2 24-foot slab (joint) 44-foot slab (joint) Y=(5.374 x 1-3) T Y=(l.281 x 1-2) T R2=.854 R2= foot slab (joint) 44-foot slab (joint) Y=(5.148 x 1-3) T-.558 Y=(l.212 x 1-2) T R2=.884 R2= foot slab (joint) 44-foot slab (joint) Y=(6.76 x 1 3) T.653 Y=(l.27 x 1-2) T R2=.931 R2=.8S foot slab (joint) 24-foot slab (sixth point) 24-foot slab (third point) 44-foot slab (joint) 44-foot slab (sixth point) 44-foot slab (third point) 6 24-foot slab (joint) 24-foot slab (sixth point) 24-foot slab (third point) 44-foot slab (joint) 44-foot slab (sixth point) 44-foot slab (third point) Y=(6.792 x 1-3) T.542 Y=(4.26 x 1 3) T.335 Y=(2.344 x 1-3) T.186 Y=(l.217 x 1 2) T.97 Y=(7.697 x 1 3) T.611 Y=(3.717 x 1-3) T.295 Y=(6.89 x 1 3) T.358 Y=(3.738 x to 3) T.219 Y=(l.887 x 1 3) T.112 Y=(l.16 x 1 2) T.649 Y=(6.948 x 1 3) T.42 Y=(3.138 x 1 3) T.182 R2-<J.991 R2=.982 R2=.993 R2=.983 R2=.97 R2=.932,, R2=.991 R2=.971 R2=.988 R2=.98 R2=.964 R2= foot slab (joint) 24-foot slab (sixth point) 24-foot slab (third point) 44-foot slab (joint) 44-foot slab (sixth point) 44-foot slab (third point) Y=(5.864 x 1 3) T-.542 Y=(3.76 x 1 3) T.335 Y=(l.738 x 1 3) T.186 Y=(l.74 x 1 2) T.97 Y=(6.287 x 1 3) T.611 Y=(2.855 x 1 3) T.295 R2=o.985 R R2=.984 RZ..981 R2=.947 R2=.94 For the urrent study, a sample range of maximum and minimum joint widths was determined; Figure 7 summarizes the results. These maximums and minimums represent a range of ambient temperatures from 17.6 F to F. The joint widths were measured at sribe marks on the joint hardware so that the readings ould be ompared onsistently. The joint edges are not perfetly parallel, so the reported maximum and minimum widths are not neessarily the absolute maximum and minimum widths for the entire length of a joint. In fat, several of the joints between 24- ft slabs were observed to be ompletely losed during hot weather measurements. Joints between 44-ft slabs never ompletely losed. Regression equations were alulated for the joint width data. Figures 8 and 9 show graphs of the joint width data for the two slab lengths along with the orresponding regression equations. Seasonal Slab Operation Overall seasonal behavior of horizontal movements of the slabs is a funtion of daily temperature yles superimposed over seasonal temperature yles. This superimposition auses slabs to operate, on a daily basis, at various seasonal datum values. During the summer season, the joint widths are small, and horizontal displaements our over a range of small joint widths. Similarly, during the winter season, horizontal displaements our over a wide range of joint widths. CONSISTNCY AND RROR ANALYSIS Consisteny Analysis The onsisteny of horizontal displaements gives an indiation of how reliable the measurements are. High onsisteny

8 Mandel et al. 45 u::- Q i x g 1 : - :i 8 O" UJ : 6 "iii Jl Ci a:.. V foot slabs 2 Y = X R = foot slabs Y = X R 2 = g.s::::. u 5..., ft. slabs Y= X R 2 =.927 o...._..._.._._ Distane From Centerline (ft.) FIGUR 6 Slopes of the regression equations in Table 2 as a funtion of distane from slab enterline. Conrete Temperature ( F) FIGUR 8 Regression equation for joint widths between 24-ft slabs. 4 Maximum width 44 foot slabs Minimum width 3 3, 2 "C5..., = "O 5..., 2 44 ft. slabs Y = X R 2 = Joint Number FIGUR 7 Maximum and minimum joint widths for all field visits. o--..._.._,...._.._.._._....., Conrete Temperature ( F) FIGUR 9 Regression equation for joint widths between 44-ft slabs. in the data would indiate a high degree of reliability in analysis and reommendations, whereas wide satter in the data would indiate that any analysis of the data, or any reommendation based on the data, would not be as well founded. The PCP slabs were keyed and dowelled to the subbase at their enterlines so that the middle setion of the slabs would not shift from horizontal movements. Therefore, the slabs were expeted to expand and ontrat symmetrially about their enterlines. Consisteny analysis of horizontal displaement data was performed by omparing the maximum hange in horizontal movement divided by the orresponding hange in onrete temperature for all instrumentation loations and all field visits. Figure 1 shows plots of these values for slab displaements at joints by instrumentation loation for all field visits. Inspetion of Figure 1 shows that onsisteny of slab movements per degree of temperature is generally high. The legend odes refer to instrumentation loations shown in Figure 3. Loation lon shows the most ativity of the 24-ft slabs for the first three field visits, and 9S shows the least. Loation lln generally shows the most ativity for the 44-ft slabs. The magnitude of daily slab ativity for a partiular hange in temperature depends on many fators, inluding the amount of radiant solar heat that penetrates the atmosphere, oeffiient of thermal expansion of the onrete, thermal transmissivity of the onrete, moisture levels, and loal deviations in subbase fritional restraint. It is not possible, with the given data, to pinpoint the reasons for more or less slab ativity at a partiular loation or for a partiular field visit.

9 46 TRANSPORTATION RSARCH RCORD 1286 LL'.2 7S. 9S D 11 CD.!:: BN 1N D 12N B al Ol BS ll 1 12 D C1l.. 9N 11N e 13N m u i.. ClJ.1 ClJ ClJ (.) C1l Ci Cf) "iii N g I ooo...,,..._...w...--jiu.u.wlllll..ij.w.ull..cl...--jlwj.lol..tl..llijlj.1:1.jij_ Field V1s1t Field V1s1t Field V1s1t Field V1s1t Field V1s1t Field V1s1t FIGUR 1 Consisteny of horizontal slab displaements per degree of hange in onrete temperature for all joint loations. rror Analysis rror in horizontal measurements an be heked for internal losure. The sum of the displaements of slabs at a joint should be equal to rh hange in joint width. Therefore, a losure hek was made by omparing the maximum horizontal slab displaement at eah joint for a field visit with the orresponding hange in joint width. As a final hek, the values of the sum of horizontal displaements and the hange in joint width were plotted in Figure 11. A regre sion equatioa was alulated ( h wn on the graph) it shows Llrnl!lit: lupe of the regre ion lin is.98, that the Y-interept i ma ll, and that the oeffiient of partial determination, R2, is.99. A value of 1. for the lope and the R 2 value would indiate a perfet losure for all measurements; thus, overall the error in measurement is small : _.7.6 > ::2;.5.r::.4.3 'Ci...,.2.1 Y =.98X +.95 R 2 = Sum of Slab Displaements (in.) FIGUR 11 Regression equation relating sum of slab displaements and orresponding joint width movements for all joints and all field visits. SUMMARY Slab movements are signifiant. Measurements indiate that entire slabs are moving (Figure 6). Resulting maximum joint widths range from about 1.5 in. to 3 in. Additionally, slab movements orrelate well with onrete temperatures at middepth of the slabs. The tehniques used for measuring slab movements work well. This suess is indiated by small rosshek errors. This study investigated slab movements that our after shrinkage and reep of the onrete have already ourred. The regression equations that result from these movements are basially the same for all data samples. Regression el!uations for the 24-ft slabs have flatter slopes than those for the 44-ft slabs. When the slab temperature rises above about 17 F, joints between 24-ft slabs may lose, as was observed from the tlata. General design equations for prediting slab movements have been developed. The equations are derived by using slopes of regression equations for 44-ft slabs (Figure 6). For MLennan County, PCP joint movements an be predited by t.xj- T = AX + ( L) (T; - T ) where t1x; - r = net joint width at any temperature (T;), in.; t1x = j int width at referene temperature, in.; L = slab length, ft; T = referene onrete temperature, F; and T; = onrete temperature at time i. For any portland ement onrete pavement plaed on a polyethylene sheet the general equation 1s

10 Mandel et al. where a is the thermal oeffiient of expansion of onrete, in./in./ F. CONCLUSIONS AND RCOMMNDATIONS This setion outlines the final onlusions and reommendations of this study organized into the ategories of instrumentation and data analysis. Instrumentation The instrumentation program for this study was highly suessful. The olleted data indiated trends that were diretly parallel with expeted results. The outome of the instrumentation program justifies the following onlusions: The method of using buried anhors to support instrumentation worked well. The supports were extremely stable and therefore provided a reliable foundation for the equipment. The method of measuring displaements by both the dial gauges and L VDTs gave onsistent and idential results. The 2-hr period between measurement readings was frequent enough to haraterize movements but still allowed enough time to gather a large amount of data. The method of measuring temperatures using thermoouples gave aurate and onsistent temperatures. The following reommendations result from experienes that were enountered either during data olletion or as a result of analysis that depends on instrumentation. They are offered as guidelines for any instrumentation program that is designed to measure phenomena similar to those in the program for this study: 1. Although exat effets of moisture levels on magnitudes of displaement were not qualified in this study, future instrumentation programs that investigate environmental effets on pavement should onsider the importane of measuring the moisture level at various depths in the onrete. 2. The onstrution program for experimental protypes should inlude a major onsideration of subsequent determination of material properties. A large sample of material speimens (ylinders, material-test beams, et.) should be made at the time of onstrution so that material properties for longterm investigations an be determined diretly. DATA ANALYSIS The analysis of slab displaements for eah slab length for a field visit allowed for the diret omparison of slab behavior for various seasonal onditions. The use of regression equations to haraterize slab movements was helpful in omparing the behavior of all slabs for all instrumentation loations. Furthermore, the error analysis indiated that measurements were orret and quite aurate. The following points outline speifi onlusions from the analysis of horizontal displaements: 1. The regression analysis of horizontal slab movements shows that displaements an be desribed by a linear equation. The slopes of the equations vary at lose to a linear rate for displaements measured at the joints, the sixth points, and the third points. These data indiate that almost the entire slab moves on a daily basis. 2. Average slopes of the regression equations an be used to predit slab movements as a funtion of temperature. For the 24-ft slabs, the average rate of movement was 5.89 x 1-3 in./ F. For the 44-ft slabs, the average rate of movement was x 1-3 in./ F. 3. The analysis did not show a strong trend for various moisture onditions. This may have been beause the slabs were not ompletely saturated. 4. Maximum and minimum measured joint widths were in. and.263 in. for the 24-ft slabs and 3.2 in. and.983 in. for the 44-ft slabs. 5. Overall seasonal behavior of the slabs indiates that daily flutuations our onstantly, whereas the seasonal data for the movements hange. 6. The onsisteny of slab movements for the entire study is quite high. Standard deviations of movements per degree hange in temperature are.646 x 1-3 and.621 x 1-3 in./ F for the 24- and 44-ft slabs, respetively. 7. Field observation revealed that some joints were ompletely losed for prolonged ambient temperatures in exess of about 1 F (no damage to the slabs or joint hardware ourred). The following reommendations result from the analysis of horizontal movements, as well as field observations: 1. Apparently, less shortening of the slabs ourred during the early life of the 24-ft slabs than was initially expeted. Sine maximum measurements of joint widths for the 24-ft slabs were in., well within servieability limits (about 3.5 in.), there is a wide margin of safety against exessive joint widths. An initial joint width of.5 in. for a 24-ft slab (otherwise onstruted under similar onditions) would prevent the joints from ompletely losing. 2. The joints for the 44-ft slabs always remained within servieable limits. These joints were also set losed at the time of onstrution. No hange is reommended for the initial setting of joints for these slabs. RFRNCS 1. A. Mendoza-Diaz, N. H. Burns, and B. F. MCullough. Behavior of Long Prestressed Pavement Slabs and Design Methodology. Researh Report Center for Transportation Researh, The University of Texas, Austin, September J. R. Maffei, N. H. Burns, and B. F. MCullough. lnslrumenlation and Behavior of Prestressed Conrete Pavements. Researh Report Center for Transportation Researh, The University of Texas, Austin, November K. Hankins,. D. Mandel, N. H. Burns, and B. F. MCullough. Performane Test on a Prestressed Conrete Pavement-Presentation of Data. Researh Report Center for Transportation Researh, The University of Texas, Austin, D. Mandel, B. F. MCullough, and N. H. Burns. Preslressed Conrete Pavement: Instrumentation, In-situ Behavior and Analysis. Researh Report Center for Transportation Researh, The University of Texas, Austin,

11 48 TRANSPORTATION RSARCH RCORD S. J. O'Brien, N. H. Burns, and B. F. MCullough. Very arly Post-Tensioning of Prestressed Conrete Pavements. Researh Report Center for Transportation Researh, The University of Texas, Austin, June N. D. Cable, N. H. Burns, and B. F. MCullough. New Conepts in Prestressed Conrete Pavement. Researh Report Center for Transportation Researh, The University of Texas, Austin, Deember W. S. Chia, B. F. MCullough, and N. H. Burns. Field valuation of Sub base Frition Charateristis. Researh Report Center for Transportation Researh, The University of Texas, Austin, September B. W. Dunn, N. H. Burns, and B. F. MCullough. Frition Losses in Unbound Post-Te11sio11i11g Tendons. Researh Report Center for Transportation Researh, The University of Texas, Austin, November W. S. Chia, N. H. Burns, and B. F. MCullough. ffet of Prestress on the Fatigue Life of Conrete. Researh Report Center for Transportation Researh, The University of Texas, Austin, November Publiation of this paper sponsored by Committee on Rigid Pavement Design.