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CHAPTER II.

RESEARCH METHODS AND MATERIALS

2.1 Evaluation of Waterproofing Systems

Two different waterproof bituminous concrete systems were examined in this researchstudy. The first system, consistent with current timber bridge construction practice, uses apreformed waterproofing membrane placed on a preservative treated wood deck and overlaidwith a bituminous concrete wearing surface (Figure-2.1). The second system consists of a treatedwood deck overlaid with a base course of bituminous concrete, a waterproofing membrane, andfinally, a bituminous concrete wearing surface (Figure-2.2). The second system was consideredbecause, in spite of the use of dense graded surface asphalt concrete mixtures, the current practiceof placing a waterproofing membrane directly on top of a flat and level bridge deck may lead tostripping of the asphalt cement from the aggregate due to the buildup of moisture in the asphaltconcrete directly above the membrane. In addition, any water that is allowed to remain stagnantabove the membrane for an extended period of time will be more prone to penetrating anymembrane weaknesses and thereby potentially reduce the functional service life of the wood deckand other bridge components. The bituminous concrete base course can also be used to constructa deck cross-slope into the pavement system at the level of the waterproofing membrane to allowany water that penetrates the wearing surface to flow to the edges of the bridge deck and off thebridge without wetting other bridge members.

Figure-2.1 Existing Timber Bridge Pavement Configuration

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Figure-2.2 Proposed Timber Bridge Pavement Configuration

The testing regime used in this research to evaluate watertightness and bond performanceincorporated three parameters: three waterproofing membranes, two wood preservativetreatments, and two environmental degradation conditions induced by temperature cycling in amoisture saturated condition. Control groups were also evaluated for each study parameter.Duplicate specimens were prepared and tested for each of the study parameters. A total of 160specimens were constructed and tested as shown in the study matrix (Figure-2.3).

Watertightness of each waterproof asphalt wearing surface system was determined bymeasuring the electrical impedance across a test specimen perpendicular to the direction of bondorientation in the pavement materials. The bond strength between each material of both pavingsystems was assessed using a shear test apparatus designed and built for this study. Using aconstant deformation rate, load was applied to one side of the system bond line while the sideopposite was held in a fixed position. Maximum sustained load by the system was recorded foreach specimen along with the location of failure relative to the bond line.

In addition to the laboratory constructed specimens, three drilled cores were taken from abridge deck located on Creekside Drive in East Pennsboro Township, Pennsylvania. The deckwas constructed using the new system design proposed in this research using two asphalt mixturesand a waterproofing membrane. The asphalt mixtures, membrane, and wood species incorporated

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Figure-2.3 Test Matrix for Laboratory Constructed Specimens

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into this bridge were different from those included in the laboratory constructed specimens. Atthe time the cores were taken, the bridge was approximately one year old.

2.2 Specimen Design and Materials

Specimen design was based on the geometry of specimens used in ASTM D 1559"Resistance to Plastic Flow of Bituminous Mixtures Using Marshall Apparatus". In this test, hotmix asphalt is compacted into the shape of a 4 inch diameter by 3 inch thick cylinder using a steelmold and a standardized compaction hammer. For the specimens in this research, this basic shapewas subdivided into two distinct and separate cylindrical sections 1.5 inches thick to allow for theuse of different materials in each lift with a waterproofing membrane placed in between (Figure-2.4). By using this specimen configuration, the bond strength and watertightness of an entireasphalt concrete wearing system was examined.

Figure 2.4 Lab Constructed Test Specimen

To examine current paving practice for timber bridges, a group of specimens wasconstructed with a wood bottom section and a compacted surface hot-mix asphalt concrete in thetop section.

All wood was machined from quarter sawn nominal "2-by" southern pine lumber that waseither left untreated, treated with creosote, or treated with pentachlorophenol. Untreated woodwas used to establish a baseline for future research using other treatment methods, though theperformance of CCA treated lumber is likely to be very similar. It should be stressed that the useof untreated wood in an actual field application is not recommended. Minimum preservativetreatment retention levels were specified as 12lb/ft3 for creosote and 0.60lb/ft3 forpentachlorophenol in accordance with the recommendations of Ritter (1990). Assay results and

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treatment parameters for the treated boards are included in Appendix-A. In the test specimens,quarter sawn lumber was chosen to simulate the grain orientation observed at the paving surfaceof typical glulam deck panels.

The surface asphalt concrete mixture, consisting of asphalt cement and crushed limestoneaggregate no larger than 0.5 inches, was manufactured to Virginia Department of Transportationspecifications for mixture type SM-2AL at a local batch plant. A complete mix design is includedin Appendix-B. In addition, an independent analysis of the asphalt concrete used in this study wasperformed by the Virginia Transportation Research Council. A copy of this analysis is alsoincluded in Appendix-C. This mixture is commonly used for secondary roads in Virginia which iswhere the timber bridges considered in this study are typically located.

Test specimens for the waterproof asphalt concrete wearing surface system proposed inthis research study consisted of a compacted base hot-mix asphalt concrete in the bottomcylindrical section and compacted surface hot-mix asphalt concrete in the top section.

The base asphalt concrete mixture, consisting of asphalt cement and crushed limestoneaggregate no larger than 1 inch, was manufactured to Virginia Department of Transportationspecifications for mixture type BM-2 at a local batch plant. The mixture proportions are includedin Appendix-B. In addition, an independent analysis of the asphalt concrete used in this study wasperformed by the Virginia Transportation Research Council. A copy of this analysis is included inAppendix-C. This mixture is commonly used as a base course for secondary roads. The asphaltconcrete surface mixture was the same material used in the wood-asphalt specimens.

Three different waterproofing membranes were employed in the laboratory specimensconstructed for both systems. They included Bituthene 5000 manufactured by W.R Grace,Petrotac manufactured by Phillips Fibers Corporation, and Protectowrap M400A manufactured bythe Protectowrap Company. Control specimens were constructed with no membrane between thewood and surface asphalt concrete layers to assess baseline watertightness and shear strengthparameters for an unprotected system.

Properties of weight per unit area and unit weight were determined using a one footsquare section of each membrane and a balance capable of measuring to the nearest 0.0001pounds. Thicknesses were determined by obtaining a one foot square section of each membrane,cutting it into four equal size square sections, and measuring around the entire perimeter a total ofeight times (one at each corner and one at the midpoint of each side) with a micrometer capable ofmeasuring to the nearest 0.001 inch. Membrane measurement data is included in Appendix-D.

Measured dimensional properties and physical observations for each membrane areincluded in Table-2.1. The thickest membrane was determined to be Bituthene 5000 and thethinnest was Petrotac, though the thicknesses of Petrotac and Protectowrap M400A were verysimilar. The densest membrane was Protectowrap M400A and the least dense was Petrotac.

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Table-2.1 Measured Dimensional Properties and Physical Observations for MembranesMembrane Thickness

(in)Weight/Unit

Area(lb/ft2)

UnitWeight(lb/ft3)

Observations(at room temperature)

Bituthene5000

0.070±0.004

0.3841 66.15 Most flexible of three membranes.Very sticky.

Petrotac 0.061±0.005

0.2855 55.87 Stiffest of three membranes.Similar to heavy construction felt.

Least sticky.ProtectowrapM400A

0.064±0.002

0.4341 81.36 Similar to Bituthene 5000 exceptfor fibrous material present on topsurface. Slightly less flexible than

Bituthene.

Load-strain properties were determined for each membrane using the procedure outlinedin the draft of a proposed major revision to ASTM D 2523 "Standard Test Method for the Load-Strain Properties of Roofing and Waterproofing Membranes" using 1 inch by 6 inch cutspecimens. Five specimens of each membrane type and orientation were tested after beingconditioned for 16 hours at 73.4ºF, 50% R.H. followed by 16 hours at 0ºF, 50% R.H. The twoorientations considered for each membrane were 0º and 90º relative to the longitudinal axis of themembrane roll. Each specimen was kept at 0ºF until placement into the loading apparatus andeach test was completed within 10 minutes of being placed in the tensile testing machine. Thedeformation used to determine strain was based on the change of distance between loading grips,so any slippage is implicit in the results.

A summary of load-strain properties is presented in Table-2.2 and complete test data isincluded in Appendix-D. For tensile load in the 0º orientation, both Bituthene 5000 and Petrotacwere approximately 19% lower than Protectowrap M400A. In comparison to individual tensileloads in the 0º orientation, tensile load in the 90º orientation was 9% lower for ProtectowrapM400A, 10% lower for Petrotac, and 19% lower for Bituthene 5000. Strain at maximum loadwas highest for Protectowrap M400A and lowest for Bituthene 5000. Loading orientation wassignificant to strain at maximum load only for Petrotac where the result was 30% lower for the 0ºorientation. Energy at maximum load was highest for Protectowrap M400A and lowest forBituthene 5000.

For the Creekside Drive bridge, the cross-section of the bridge deck and pavement systemconsisted of the following (substrate to wearing surface): a creosote treated red maple glulamdeck, Pennsylvania Department of Transportation asphalt concrete base mixture BC-BC, Royston10A waterproofing membrane, and finally, Pennsylvania Department of Transportation asphaltconcrete surface mixture ID-2. The cross section of this configuration is similar to the onepresented in Figure-2.2.

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Table-2.2 Summary of Load-Strain Properties for MembranesMembrane Maximum Load

(lbs)Strain at Maximum

Load(%)

Energy at MaximumLoad

(lbs•in)Mean Std. Dev. Mean Std. Dev. Mean Std. Dev.

Bituthene 50000º 91.6 2.5 19.6 0.8 43.3 2.490º 76.7 3.0 19.8 1.6 40.4 3.7

Petrotac0º 91.9 2.5 55.2 2.8 145.2 10.490º 83.2 3.8 71.6 5.4 158.5 15.2

Protectowrap M400A0º 109.2 5.0 76.1 8.9 257.6 39.390º 100.5 8.3 72.0 4.1 219.7 19.9

Assay measurements taken from the bridge deck indicate an average final creosoteretention level of 15.8 lb/ft3 in the bridge deck. The deck moisture content was 9.4% at the timeof bridge construction. An independent analysis of the asphalt concrete mixtures used on thisbridge was performed by the Virginia Transportation Research Council, a copy of which isincluded in Appendix-C.

2.2.1 Specimen Construction

Specimen construction consisted of several discrete steps including: preparation of 4 inchdiameter by 1.5 inch thick wood specimens, cutting 4 inch diameter circles out of membranesheets, assembling the specimen (asphalt compaction), and constructing a perimeter seal/pondingdam.

2.2.2 Wood Preparation

Nominal 2"-by-12" kiln dried southern pine was obtained directly from an eastern Virginiasaw mill in 16' lengths. Each piece of lumber was ripped in half to yield two quarter sawn 2"-by-6" boards and then cross cut into more manageable 4' lengths to allow for shipment to apreservative treatment facility and additional machining operations.

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Figure 2.5 Drill Press and Hole Saw Used to Obtain Wood Cylinder Substrates

After the boards were pressure treated (where applicable), 4 inch diameter by 1.5 inchthick cylinders were cut using a 4-1/8 inch O.D. hole saw attached to a drill press, see Figure-2.5.Special care was taken to avoid surface defects (i.e., knots, splits) and assay core holes whensawing the cylindrical specimens.

Figure 2.6 Membrane Punch

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2.2.3 Membrane Preparation

To cut the 4 inch diameter circles from the membranes, a punch was fabricated using ashort section of 4 inch O.D. steel tube with a sharpened edge ground against the outside perimeter(Figure-2.6). The membrane was unrolled onto a clean wood surface with the removable backingmaterial facing upward. The punch was placed on top of the membrane and struck on top severaltimes with a heavy hammer until the cutting edge passed cleanly through the membrane material.

2.2.4 Assembly and Compaction of Specimens

Assembly of the test specimens was designed to simulate the rigors that a membrane facesduring a typical bridge deck paving operation. With this in mind, asphalt concrete pavement wascompacted based on ASTM D 1559 "Resistance to Plastic Flow of Bituminous Mixtures UsingMarshall Apparatus". As stated earlier, this test uses a steel mold and a standardized hammer tocompact hot mix asphalt into a 4 inch diameter cylinder.

Initially, asphalt concrete test specimens were made in accordance with the standard testprocedure to determine the theoretical maximum density for both types of asphalt concrete usedin this research. Since only 1.5 inch thick lifts were needed, some preliminary specimens werecompacted to determine the mass of hot mix asphalt and the number of hammer blows necessaryto reach the theoretical maximum density for each pavement material. Though minimumrequirements vary for in place pavement densities based on mixture type, a pavement with adensity at the theoretical maximum exceeds the densities required by the Virginia Department ofTransportation and most other transportation agencies. Through trial and error, it wasdetermined that 700 grams of asphalt concrete compacted with 50 blows applied to one sideyielded a 1.5 inch thick lift at the theoretical maximum density for both SM-2AL and BM-2.

To begin specimen assembly, the steel molds, miscellaneous tools, and previously obtainedhot mix asphalt were heated to approximately 275ºF in a large convection oven. The compactionhammer was placed on a hot plate to bring its temperature up to 275ºF.

For the wood base specimens, a mold was removed from the oven, wood was placedinside at the bottom, and a membrane (if applicable) was pressed onto the wood. Surface mixasphalt concrete was then measured out to the desired mass, placed in the mold on top of themembrane, and spaded 25 times around the perimeter and 10 times in the center. At this point,the mold was fixed in the compaction machine, the temperature of the hot mix asphalt checked tobe sure it exceeded 250ºF, the compaction hammer put in place, and compaction initiated. After50 hammer blows, the mold was removed from the machine and allowed to cool forapproximately 30 minutes before it was removed from the mold.

For the specimens using BM-2 as the base, the mold was removed from the oven, a pieceof release paper was placed in the bottom of the mold, and base mix asphalt concrete was

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measured out to the desired mass and placed in the mold. Compaction of the base mix proceededin a similar manner to that used for the surface mix. The base was allowed to cool forapproximately 20 minutes, a membrane (if applicable) was placed on the base lift, and then asurface mix was added and compacted.

2.2.5 Edge Seal and Ponding Dam

To reduce edge effects, a system consisting of mastic asphalt, a membrane, a PVC plasticcylinder, and a clamp was used to seal the perimeter of each specimen after cooling for at least 24hours, see Figure-2.7. The system was devised to: allow moisture to enter and exit the specimenfrom the top and bottom only; allow ponding of the specimen with a 0.5% NaCl solution tosaturate the surface asphalt concrete thus providing a conductive path should a leak be present inthe membrane; and prevent visco-elastic creep of the asphalt concrete during high temperatureenvironmental exposure. The top surface of each specimen was ponded for the duration ofenvironmental exposure conditioning except for the brief period of time when watertightness andmoisture content measurements were being made. In addition to the edge wrap around thesystem, a plastic or foil wrap (depending on temperature exposure) was fastened over eachspecimen to prevent the escape of moisture from the system.

Application of Masticat Section Interface

Application ofContainment Membrane

Application of PVC PlasticSurround and Clamp

Figure 2.7 Specimen Edge Seal and Ponding Dam

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2.3 Obtaining Creekside Drive Bridge Deck Cores

Three cores were sawn from the bridge constructed using the system designproposed in this research at the locations presented in Figure-2.8. The specimens wereobtained using a water cooled 4 inch I.D. diamond core saw as shown in Figure-2.9. Fortwo of the three specimens taken, the core drill penetrated the full depth of the asphaltpaving system at which point the core sample immediately broke loose from the treatedwood deck indicating that no bond existed between the wood and base asphalt mixture.On the third sample, the base asphalt cracked and broke loose approximately 2 inchesbefore the core drill reached the wood deck, but beyond the waterproofing membrane.The measured depth of surface and base asphalt for each sample is listed in Table-2.3.

After each core sample was removed, the resulting hole in the bridge deck waspatched using a cold mix patching asphalt. Special care was taken to replace the removedmembrane with a new piece at the same height as the existing membrane.

Once the raw core samples were returned to the laboratory, four inch diameter bythree inch thick cylindrical test specimens were prepared by trimming the base asphaltlayer to a height of 1.5 inches using a water cooled diamond blade saw. The surface layerfor each sample was approximately 1.5 inches as paved, so no trimming was necessary.Once the standard specimens were prepared, they were sealed in the manner described inSection-2.2.5.

Table-2.3 Asphalt Lift Thicknesses for Creekside Drive Bridge Core SamplesSpecimenNumber

Surface AsphaltThickness (in.)

Base Asphalt Thickness (in.)

BRA.1 1-3/8" to 1-1/2" 4-7/8"to 5"BRA.2 1-3/8" to 1-1/2" 2-1/2" to 2-3/4" (Broken While Coring)BRA.3 1-3/8" to 1-1/2" 4-1/4" to 4-1/2"

2.4 Environmental Degradation Exposure Cycling

Where applicable, each specimen was exposed to temperature cycle ranges of 0 to40ºF or 90 to 140ºF in accordance with cycle rates described in ASTM C 666 "StandardTest Method for Resistance of Concrete to Rapid Freezing and Thawing". These tworanges were chosen to simulate the temperature effects of cold weather and warm weatherclimates in the United States.

An ASTM C 666 rapid freeze thaw chamber utilizing mechanically controlledrefrigeration and heating units was used to achieve the desired cold temperature exposurecycles, see Figure-2.10. One complete cold temperature cycle was considered to be thechange in temperature at the center of an asphalt-asphalt control specimen starting at40ºF, decreasing to 0ºF, and returning to 40ºF. The internal temperature of an asphalt-wood control specimen was monitored in conjunction with the asphalt-asphalt control

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Figure 2.8 Bridge Core Locations

Figure 2.9 Water Cooled Core Saw Setup on Creekside Drive Bridge

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specimen and temperature data from both was recorded using thermocouples attached to adata acquisition system.

For the warm temperature exposure cycles, an electronically controlled convectionoven was employed, see Figure-2.11. One complete warm temperature cycle wasconsidered to be the change in temperature at the center of an asphalt-asphalt controlspecimen starting at 90ºF, increasing to 140ºF, and returning to 90ºF. As in the coldtemperature chamber, the internal temperature of an asphalt-wood control specimen wasalso monitored. Data from both controls was recorded using thermocouples attached to adata acquisition system.

The length of each exposure cycle in both chambers was typically 4-6 hours. Thecycle length was primarily determined by the thermal properties of the asphalt-asphaltcontrol specimen and chamber loading (i.e., the number of specimens in the chamber).

2.5 Watertightness Test and Procedures

Watertightness of each waterproof asphalt wearing surface system was assessed bymeasuring the electrical impedance across a test specimen perpendicular to the direction ofbond orientation in the pavement materials. Electrical impedance was measured with ameter using a 12 Volt, 97.4 Hertz square wave alternating current power supply. Themaximum measurable impedance with this test instrument is 1.1 MΩ. Test electrodeswere fabricated using 12 gauge copper wire embedded in sponges wetted with a 0.5%sodium chloride electrolyte solution. A concrete block weighing 14.48 pounds was placedon the top sponge to provide a consistent pressure on the electrodes for each test. Thecomplete test apparatus is shown in Figure-2.12.

All watertightness tests were conducted at ambient temperature (65ºF) and whereapplicable, measurements were taken after seven days of ponding with a 0.5% sodiumchloride solution, and after 100 and 200 environmental degradation exposure cycles.After exposure to environmental exposure cycling, each specimen was allowed to stabilizeto room temperature for a 24 hour period prior to testing. Watertightness tests wereperformed on the three bridge core samples after they were ponded for seven days with a0.5% NaCl solution. Prior to watertightness testing, the edge seal clamp on eachspecimen was tightened to help eliminate any conductive path if leaking occurred.

2.6 System Bond Test and Procedures

The bond strength between each material of the paving systems was assessed usinga shear test apparatus in which load was applied at a constant strain rate parallel to thedirection of bond (Figure-2.13). Load was applied on one side of the system bond linewhile the side opposite was held in a fixed position. Fabrication drawings for the bondstrength test apparatus are presented in Appendix-E. System bond strength tests wereperformed at 0, 100, and 200 environmental degradation exposure cycles.

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Figure 2.10 Low-Temperature Cycling Chamber

Figure 2.11 High-Temperature Cycling Chamber

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The bond test strain rate was 0.1 inches/minute and all system bond tests wereconducted at an ambient temperature of 72ºF. Shear load and deformation were recordedfor each specimen. The location of failure relative to the bond line and maximumsustained load were also observed and recorded. The load caused by the weight of thetest fixture is added to the dial load for all reported results. For the three bridge coresamples, system bond strength measurements were taken immediately after thewatertightness tests were performed.

Figure 2.12 Impedance Test Apparatus

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Figure 2.13 Bond Test Apparatus