lnslde ntanufacturlnHYBRID NNETHODHANDLES HIGH-PROFILETUNNEL PROJECTPu ltrusion/filament wi nd i ng com bi nation creates corrosion - resistantcomposite rock bolts for city's storm-water containment system.

strength, 90 to 95 percent of the world's supply stillis. However, composite rock bolts are graduallygaining marketshare in both permanent and tem-porary installations, because composite materialsoffer two inherent advantages over steel - high cor-rosion resistance and cuttability. For the SydneyHarbor tunnel and similar projects, where rockbolts must remain in place for the tunnel's life,composites are replacing stainless steel because oftheir superior corrosion resistance over extendedtime periods. \d/hile some rock bolts have self-lock-ing mechanisms, most, including those for theSydney tunnel, are grouted in place using a poly-mer resin or cementitious grout, which encapsu-lates and protects ttre bolt from corrosion. A care-fully selected, corrosion resistant resin formulationin both the bolt and the grout provides exlra pro-tection for the Pultron bolfs fiber$ass componentin the alkaline conditions present in most rock andall concrete. In temporary shoring applications,composite bolts are replacing stainless steel boltsbecause the latter are removed only with great dif-ficulty and cost. When construction machinerymills further through the tunnel strata, grindingout the grouted-in steel is time consuming, and thesteel damages the rotating cutter heads. But com-posite bolts are relatively easy to cut and don'tharm the equipment.

Pultron custom-designs rock bolts to meet spe-cific application requirements. When a tunnel is cutthrough rock, the physical forces that stabilized therock are altered. Rockbolts redistribute shear andtensile stresses in the rock face, preventing collapseof the tunnel. Bolt designs can vary widely, basedon the rock strata, which at any stage of a projectcan change, requiring a revision of load-bearing,shear, torsion and other mechanical and perfor-mance specifications. "It's almost as thoug;h you'remaking individual rock bolts for each customer,"

B

gryrior to the 2000 Summer Olympic Games,

ffihost city Sydney. Australia bulJrt the 21.77€ ftl6.5m diameter, 14.66 mle/23.6 km long,525 ft/l6Om deep Northside Storage Tunnel. Rainwater from Sydney's average 47 tnch/1,194 mmannual rainfall had previously flushed road oils,animal waste and other contaminants into stormdrains, polluting Sydney Harbor. The tunnel nowdirects storm run-off away from the harbor andstores it until the nearby Northhead wastewaterplant can process it. The sandstone walls of thetunnel are secured by 100,000 composite rockbolts, manufactured for Cutabolt Pty Ltd., the

Sydney-based contractor that supplied the bolts, byPultron Composites Ltd. (Gisborne, New Zealand).Designed for 70 years of service, the bolts are man-ufactured with a Pultron-developed hybrid processthat integrates filament winding heads inline with-pultrusion machinery and substitutes an opencure chamber in place of the heated die commonlyused for molding and curing pultruded parts.

Traditionally, rock bolts have been made fromsteel and, because of its low cost per unit of

Cuttable composite rock boltswith matng threads and nut,ready for installation in a mineor construction hllrnel.

COMPOSITES IEGHNOL0GY www.coMposrrEsTEcH,coM

comments Pultron technical director Peter

Holdsworth. "Almost all are mine-specilic and engi-

neered very precisely to the conditions. A certainmine will need a certain rock bolt - and then the

strata or other conditions might change in that

mine and call for a change of bolts."

RESIN KEYS BOTT PERFORMANCEResin formulation is a critical production step and

the key to final performance characteristics. "A

high degree of cure is essential in a rock bolt, and

every bolt type has a very specific resin formula-

tion," Holdsworttr explains, adding, '.We have hun-

dreds of formulations entered into our computer

database." To select the appropriate resin formula,

Pultron first performs a statistical design analysis,

usually using Trial Run software written by SPSS(Chicago, Illinois), a producer of software products

that span the process analysis spectrum. Pultron

analyzes the formulations in its computer database

and compares these formulations with the perfor-

mance requirements for the specific application'This analysis process allows them to derive the opti-

mum formulation for the requirements. Pultron's

Composite Materials Research division then deter-

mines the optimum reactivity and degree of cure for

various resin/catalyst combinations suggested by

the analysis, using a Modulated Differential

Scanning Calorimeter (MDSC). Resin viscosityvaries from 500 to 5,000 cps, depending on specif-

ic requirements. 'The MDSC gives a very accurate

measurement of the degree of cure we can get for a

specific formulation," Holdsworth says. 'That can

be translated into the mechanical properties that

are required." Having identified a trial formulation,the computer-controlled mixer blends enough forprototype parts, pultrusion trials are run, and trial

parts are tested to validate the design. The MDSC is

also used to inspect the cured product for cure level

and glass transition temperature (T$. (The mlxes

and formulations are stored for 10 years to permit

traceability, in compliance with ISO 9002 docu-

mentation requirements.)

DESIGN ACCENTS CORROSIONRESISTANCEOf equal if not greater importance, the Sydney tun-

nel called for corrosion resistance to storm-waterrunoff. To meet this requirement, Pultron modified

POLYPLEX isophthalic polyester (isopolyester) resinpurchased from Nuplex Industries Ltd. (Auckland,

New Zealand). The resulting isopolyester formula-

tion coupled with an isopolyester resin grouting

material protects the rock bolt fiom alkaline degra-

dation.Though Nuplex has licensing agreements with

key resin producers, such as Reichhold, Scott

Bader and Ashland, marketing manager Phil

Wilkinson says the company designs and makes

more than 70 percent of the polyester resins it sells

in its own research and development facilities. The

company exports its own polyester resins, gel coats

and other composite materials throughout the

Asian Pacilic region.Specifications called for high tensile, shear and

torque strength - mechanical properties that

delined the quantity and type of lineal fibers

required. After analysis, Riltron engineered an

0.866 inch/22 mm diameter,9 ft./2.8m long, solid

fiber$ass bolt to exceed the specified minimum ten-

sile load requirement of 30tons or 60,000 lb

{27,215.54 k$ and theminimum shear strengthrequirement of 21,750 psi(150 Mpa), with torquestrength exceeding 110lb/ft (150Nm). Pultronused Owens Corning'spultrusion-grade E-glassroving, achieving a70 per-cent fiber content bYweight in the cured part. Each 9 ft long bolt weighs

4.4 lb (2k9, about one-fourth the weight of an

equivalent steel bolt. Though bolt weight was not a

major factor in the Sydney project, Holdsworthpoints out that a "lightweight bolt is almost always

an advantage, because it is faster and easier to

install and helps keep transport costs down."

Bolts are anchored in the tunnel wall with a pre-

installed, cartridge-type resin grout. Bruno Haag'

product development engineer for Pultron,

describes the typical grouting procedure: Fot the 22

mm diameter bolt, a hole about 28 mm in diameter

and long enouglr to accommodate the bolt is drilled

into the strata and a 25 mm diameter resin car-

tridge is pushed into the hole. An interna.l mem-

brane separates the resin from a fast-acting catalyst

in the cartridge until the bolt is inserted with a

rotating motion. A cutting edge on the bolt end (see

Step 8, p. 37) ruptures both the inner membrane,

mixing the catalyst and resin, and the cartridge's

exLerior lilm (typicalty Mylar), allowing the catalyzed

resin to flow fieely into the interstices of the sur-

rounding rock. When the bolt is home, rotation is

stopped, and the resin hardens in about 16 sec-

onds. Then, a nut and large-diameter washer are

applied and tightened.

PROCESS ADAPTED TO BOLTSPECIFICATIONSSince a somewhat rough, deformed surface bonds

more securely with the resin grouting than wor-rld a

smooth rod, Pultron made substantial changes to

the pultrusion equipment and process, notably the

incorporation of winding heads and replacement of

the standard heated die with an open curing cham-

ber. Built in-house, Pultron's pultrusion machines

=I

3

Pultron-manufactured fiber-glass composite rock boltsinstalled in a 21.77 ft diameter,i4.66 mile long turmel tlatdirects storm water runoffaway from the harbor inSydney, Australia, stodng itrmtil it can be processed.

COMPOSITES IEGHNOI0GY reaRunRY 2oo2

After resin wetout, roving brmdles re led ttrougfr sizing bushingsand into parallel preform tooling {view shov"n at set-up).

A diamond-coated saw blade cuts the rods to preprogfarnrned leng;thas the cut-off saw moves downstream, its motions slnchronizedwith puller speed for continuous operation.

The fomed packages re continuously filament wound by electri-cally-driven winding heads, and the womd package moves into theentry to the cure zone (view shown at machine start-up).

A lO-inch length at one end of the rod is gromd dom about 0.10-inch and spimled in Pultrons custom, proprietary plunge grindingsystem.

The wound rods then enter the pre-heated, tunnel-shaped curing oven, whichreplaces the pultmsion die. Here they curethoroughly, with no post-cure requfed, ata temperature ranging from 300"F to350'F (150'C to 180'C). (Process emis-sions are drawn off through a small pipe atthe exit end of the cure chamber.) Curedbolts are pulled from the cure tunnel bythe reciprocating pair of grippers/pullers,which alternately clamp and pull/releaseand retract. Bolts move down the line tothe cut-off station, where they are auto-matically cut to pre-programmed length.Enclosed in a sealed steel box frame, awater-cooled, diamond-coated saw bladeand cutting table travel downstream, sgr-chronZed with puller speed, so that partscan be cut to length on the fly. Cut lengthcan be adjusted without stopping themachine. For operator safety, the frameincorporates a negative-pressure dust-col-lection system.

An FRP nut and a large diameter wash-er will be threaded on the exposed bolt endat installation, to compress the rock strataand/or provide an attachment point forauxiliary equipment (e.g., safety mesh, to

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have two hydraulically driven, computer-controlled, reciprocating pullers with air-operated gripper platens. Each puller hasa maximum six-ton pulling capacity (12tons, total). Holdsworth notes, however,that the pulling force required for rock-boltpultrusion is normally less than a ton. Themachine is capable of single- or multiple-stream production at speeds up to 13 ft(4m) per minute and has a maximum grip-per envelope of 24 inches by 4 inches (600mm by 100 mm).

During machine setup, dry rovings arepulled from racks at the upstream end ofthe machine, threaded through the resinbath and the winding and curing stations,then tied off on the puller. Once ttreaded,the machine is started, the resin mix ispumped into the bath, and the cure cham-ber is heated to the calculated tempera-ture. At this point, the machine is ready tobegin pulling product.

In the first step of the process, rovingsare wetout in the ambient temperatureresin mix bath. The specified mix ingredi-ents are dispensed by a computerized dis-penser and the first batch is mixed using aturbine mixer. Holdsworth points out that

the resin tank is designed for minimumsurface area exposure. 'We keep the bathdeep and the surface area as small as pos-sible to minimize emission of VOCs.Measured operator exposure to stgene islow - about I /20th of the legal allowablelimit," he says. New T,ealand limits long-term s{rene exposure to a maximum of 60parts per million (ppm).

The wet-out fibers pass through sizingbushings, to strip off surplus resin, andinto parallel forming tools, where the twostreams of the rod are formed.Consolidated to a degree by this process,the preforms are then pulled through thewinding station, where electrically-drivenheads wind glass roving or a proprietarythread hased on the application) aroundthe rods at a 30' angle. This step furthercompresses the fibers, contributes to cir-cumferential strength and introduces thedesired slightly roughened, deformed sur-face to the bolt.

'Winding is a critical step," Haag pointsout. "High internal pressures can developduring the cr;re cycle, and unless it's man-aged properly these pressures can cause aloss of dimensional stability or cracking."

COMPOSITES TEGHNOI0GY www,coMposrrEsrEcH,coM

The womd rods cure as they pass through the heat hmnel

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Fltjt

shield workers from small debris dislodged Threaded, glass-reinforced nylon nuts and and is gradualy replacing open resin

from tunnel walls). An innovative sec- washers are injecilon molded in separate baths with closed injection dies.

The two product streams are pulled through the line by two com-puter-controlled, reciprocating gripper/pullers at speeds up to 13 ftper mnure.

The opposite end of the rod is angle-cut, foming an edge that wilcut into the cartddge and mix the resin and catalyst that will groutthe rock bolt into the tumel wall durine installiation.

To create the threaded end ofthe bolt, a $ms-reinforced nylon com-pound is injection molded into the rod. The spiraled end of rod is

inserted into the mold. The mold closes and the compound is ram-injected onto the rod, forming a sinusoidal thread as it flows along

the die path provided by the spiral groove.

ondary process readies the rod end toaccept the nut. Pultron fust plunge-grindsabout 10 inches of the bolt end on a high-speed, dedicated grinder, designed andbuilt in-house for this purpose. Thisremoves about 0.10 inch (2.50 mm).Grinding the threaded end of the bolt per-

mits formation of the thread prolile whilemaintaining the bolt's outside diameter, ina final injection-molding step. "If we just

molded the thread over the cured bolt, thethreaded end wouldn't frtthe 22 mm nut,"Holdsworth explains. After grinding, a spi-ral groove is cut into the now 0.689 inch(17.5 mm) diameter ground rod end. Thusprepared, the bolt end is inserted into aninjection-molding machine, where a splitmold clafirps over the end of the bolt. Areinforced nylon compound is ram-inject-ed at 3,000 psi (20 Mpa) pressure, forminga sinusoidal ttrread (seated in the ground

spfal groove) with an 0.275 tnch (7 mm)pitch.

Finally, the bolt's opposite end is cut atan angle, forming the chisel-like edge thatcuts through the grout cartridge.

processes.

INNOVATION SPURS GROWTHA composite rock bolt manufacturer since1985, Pultron started with a simple pul-

truded rod for an Australian coal mine andsince has developed a wide range of rockbolt types. One, a "pumpable" rock bolt, ispultruded as a hollow tube. At installation,grouting resin is pumped though the tube,and flows back out between the rock andthe tube exterior. to achieve the desiredfull encapsulation. Pultron also makes agroutable thermoplastic rock bolt of whatHoldsworth describes as "highly orientat-ed polyethylene." In high-strain applica-tions, the bolt's more gradual yield (akin

to that of steel) accommodates greater

movement in the strata before breakage,forestalling catastrophic failure. Failureoccurs at about 9 percent elongation, com-pared with about 2 percent for thermosets.

Pultron also pultrudes standard angle,channel, bar, rod, tube and specialtyshapes. The companyhas also done exten-sive research into injection die pultrusion

Beyond New Zealand and Australia,Pultron now exports 75 percent ofits prod-

ucts - from rebar to sail battens - to 69other countries. As its sophisticationgrows in both analytical design and com-puter-controlled manufacturing, Pultron'scomposite rock bolts are proving theirworth even in competition with low-coststeel and stainless steel. The demonstrat-ed longevity and cuttability of compositesin this application is bound to captureincreased attention among cost-consciouscivil engineers and infrastructure con-struction firms worldwid.. @

- DonrtaK. Datttson, SeniorWriter

For more information the companies andproducts disctls,sed in this artble, circle theappropriate number on the Reqder SeruiceCard: Nuplex Industries Ltd.., 242; OwensCorning, 243: Pultron Composites Ltd., 244;SPSS, 245, pultrusion Jabrbatiry, 246; i4jec-

tion molding, 247: data/analgsis soflutare,248: E-glnss, 249; isopolgester resin, 25O:polgethybne, 25 7 ; engineeruq plnstics, 2 52.

COMPOSITES TEGHN0I0GY rrsnunRY 2oo2