FEBRUARY

2014 1Concrete Plant InternationalNorth America Edition

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SPECIAL PRINTCPI 01/14

SPECIAL PRINT | CONCRETE TECHNOLOGYEnCon United supports fabrication of precast liner segments for Seattle highway tunnel usingadvanced batching system

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CONCRETE TECHNOLOGY

Hank Giles, Advanced Concrete Technologies (ACT), USA

Reinforcing world's largest highway tunnel

The 7,000-ton 326-foot-long by 57.5-foot-diameter self-contained TBM will advancealong its course by using hydraulic jacks topush against successive precast concretereinforcement rings, each consisting of tensegments (see figure 1) weighing about37,500 pounds each. Most segments meas-ure 18.5 feet long, 6.5 feet wide and twofeet thick. Several smaller segments com-bine to form a key section at the top of eachring. A complete tunnel reinforcement ringweighs in at approximately 375,000pounds. The reinforcement rings are 2.65inches narrower on the keystone side, allow -ing the builders to curve the tunnel in almostany direction by rotating and aligning eachnonsymmetrical ring. According to Jason Lien, EnCon United'svice president of design, the firm was chosenfor the tunnel project because the contrac-tor wanted a facility with a long trackrecord and PCI certification. The 21.5-acreEnCon Washington, LLC, precast facility inPuyallup, Washington, just 35 miles fromthe tunnel location, was an ideal choice. EnCon Washington has been in continuousoperation as a PCI certified plant since1999 and is a wholly owned subsidiary ofEnCon United, based in Denver, Colorado.EnCon Washington was already a long-time producer of precast retaining walls,median barriers, sound barrier panels, andcommercial wall panels--most products pro-

duced to Washington State DOT standards.EnCon site's proximity to the tunnel con-struction site, large storage yard, andEnCon's existing fleet of gantry cranes wasa critical advantage. "We learned we won the business in late2008 and began planning immediately forthe expanded facility we would need toproduce the tunnel segments," explainsLien, project manager for the expansion ofthe EnCon Washington plant. The plant will produce thousands of individ-ual segments to meet the need for morethan 1,400 complete reinforcement rings.The total volume of concrete required bythe tunnel liner will amount to approximately118,000 cubic yards.

Advanced batching system required

EnCon Washington's original plant reliedon ready mix to meet its needs. "We werealready in the process of moving a drybatching plant from our Atlanta operationup to Washington and using our own mixertruck," Lien notes. "Our existing ready mixarrangement was really not meeting ourneeds in terms of production scheduling,mix consistency and costs. Once welearned we had been selected for the tun-nel, and saw what was required, we knewwe needed a high volume, highly precisebatch plant." The plant expansion includes nearly41,100 additional square feet of enclosed

EnCon United supports fabrication of precast linersegments for Seattle highway tunnel using advancedbatching system

Advanced Concrete Technologies, Inc., Greenland, New Hampshire, 03840, USA

The 6.8 magnitude Nisqually earthquake that struck eastern Washington State in 2001 shook a wide area of the U.S. Northwest, damagingnumerous structures including many roads and bridges. The damage and subsequent repairs of a 1950s era reinforced concrete double-decker highway led to an ambitious replacement plan that includes the world's largest diameter highway tunnel. On July 30th, an $80 milliontunnel boring machine (TBM) departed its 80-foot deep launch pit near the Seattle waterfront. The TBM – the world's largest – arrived inApril 2013 from Osaka, Japan, and its 41 pieces were lowered into the launch pit for assembly. At speeds of up to 35 feet per day, the earth-worm-like TBM will burrow its way below nearly 200 buildings and a maze of subsurface infrastructure for nearly two miles, surfacing justsouth of Lake Union in the fall of 2014.

Figure 1: The system shown above is used to install a gasket on each newly cast tunnel segment prior to yarding. Each segment weighs approximately 37,500 lbs.

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space, a rail-based carousel productionline and flying bucket concrete delivery sys-tem, a sophisticated segment mold system,and highly automated concrete batchingsystem from Advanced Concrete Techno -logies (ACT). There are also speciallydesigned trailers to transport the finishedsegments. "The equipment and specifica-tions for the tunnel segments were specifiedin the contract; however, the selection of thebatching system was up to us," Lien says.

"We needed a system that could produce alarge volume of concrete in a short periodwith high levels of consistency and wouldallow us to easily break into the tunnel linerproduction cycle now and then to pull outmix for our other DOT precast operations." Lien and his team looked at several batch -ing systems, but ultimately chose theMobilMat Mo4500 system from ACT/Wiggert (see figure 2). "Other batch plantvendors were somewhat competitive on

price; however, we had greater confidencein the ability of ACT to deliver on time andmeet our specific needs," Lien explains."We knew we had a carousel productionsystem coming, the building laid out, andwe had a delivery mechanism. We neededa batch plant vendor that could work with-in the confines of those specifications anddeliver on demanding requirements. It hadto be a design-build solution--essentially aturnkey plant."

Figure 2: Under construction. The new ACT MobilMat Mo4500-5-PCS batching solution is positioned to feed EnCon'snew tunnel segment production line as well as its preexisting precast retaining walls, median barriers, sound barrier panels, and commercial wall panel productionlines. The new batch plant arrived from the Wiggert factory pre-assembled, pre-tested, wired and plumbed (air and water). One of the twocement silos shown here is dedicated to Portland Type 1 cement, and the other silo is split with one side containing silica fume and the otherground-granulated blast-furnace slag (GGBFS).

Figure 3: The new EnCon batch plant features a five-compartment,885-ton capacity aggregate storage system from ACT that includesdrive over dump hopper and conveyor system (shown here) thatautomatically ensures the correct aggregates are loaded into associ-ated bins.

Figure 4: Shuttle belt above aggregate storage bunkers providesautomated distribution of aggregates into one of five aggregatebins.

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CONCRETE TECHNOLOGY

The ACT automated MobilMat Mo4500-5-PCS batching solutionprovides four cubic yard output with continuous cycle times of just afew minutes per batch. The plant is pre-assembled, wired andplumbed (air and water) at the factory and tested prior to shipping.The system includes the following elements: • HPGM 4500 high-shear planetary mixer from Wiggert & Co.

with true four-cubic-yard consolidated concrete output. Mixerequipped with two dis-charge gates to enable easy distributionto both the tunnel segment production via flying bucket or to theprecast panel production area via Tucker delivery vehicle.

• Five-compartment aggregate bins with 885-ton capacity automat-ically charged via a drive over dump hopper and a conveyorsystem (see figure 3). An automated aggregate handling system(see figure 4) ensures correct aggregates are loaded into associ-ated bins. The bins were fabricated on site from precast panelsaccording to ACT drawings (see figure 5) to provide sufficientcapacity within predetermined footprint. Galva nized cones havedual batching gates for precision fast/slow aggregate batchingonto a weigh belt (see figure 6).

• Steam heated aggregate bins ensure precise batching temper-atures. Aggregate moisture levels are automatically monitoredand compensated for in the mixer to maintain the perfectwater/cement ratio. Temperature probes in each aggregatebin and the mixer ensure concrete temperature is maintainedensuring fast stripping strength.

• Continuous level monitoring of aggregate bins and cementitioussilos prevents overfilling and enables suppliers to log in onlineto check stock levels for just-in-time restocking.

• Two cement silos contain approximately 300 tons of cementi-tious material. One silo is dedicated to Portland Type 1cement, the other is a split double wall silo, one compartmentstores silica fume and the other stores ground-granulated blast-furnace slag (GGBFS).

• PC-based PCS Control system with user-friendly interface andremote call stations provides flexible control, maintenancereminders, recipe recall, complete production history, and real-time batch control."Batching history and quality control arecritical," Lien says. "Through the ACT PCS controls, we cantrack everything, including aggregate temperature, batchweights. With the connection to our system for vendors, theordering process has basically gone away, which is a huge sav-ings in time and coordination when you're dealing with the vol-umes we are."

• Hydrotester aggregate moisture probes automatically adjustsbatch weight compensating for varying moisture in order tomaintain mix design and batch yield.

• Hydromat microwave mixer probes automatically measuresmix moisture and calculates final batch water quantity to main-tain perfectly consistent W/C ratio for each batch.

• Automatic high pressure mixer and flying bucket cleaning sys-tem reduces cleanout time and extends equipment life. "Wehave defined automated cleaning times that fall within employ-ee break windows and we could not clean the system in theallotted timeframe without this automated system," Lien notes.

• Centrally located Eco-Clean water reclaim system treatsapproximately 10,000 gallons of process water daily. Theplant generates about 3,000 gallons of grey water from plantcleaning and an additional 7,000 gallons from steam curingoperations. The process water is automatically treated to meettough Washington State turbidity and pH standards before dis-charging.

• Precision admixture metering system pumps precise admixturedoses by weight.

Project management

The Denver-based Lien served as project manager on-site at theEnCon Washington facility during plant construction and start-up. "I

Figure 6: Weigh belt and galvanized dual-gate batching conesbelow aggregate storage bins for precision batching of aggregatecomponents.

Figure 5: At left in this diagram is the ACT MobilMat Mo4500-5-PCS batch/mixing plant. At right, five steam-heated aggregatebins hold up to 900 tons and discharge onto weigh belt that in turnempties into a skip hoist to feed the HPGM 4500 high-shear plane-tary mixer from ACT/Wiggert. Steam heating is required to meetexacting temperature requirements for the high early strength tunnelsegment mix. This extra moisture is accounted for by the batchplant's PCS computer control system and moisture probes in theaggregate bins and mixer.

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CONCRETE TECHNOLOGY

acted as the liaison between the variousvendors and the general contractor," Lienexplains. "I worked closely with ACT. Thebatch plant was essentially a perfect fitupon delivery. ACT provided layout anddesign assistance, including completedrawing and specification (see figure 7)that were made part of the drawings keptby the engineer of record."

One challenge in particular--aggregatestorage--required a creative solution. "Wehad a predetermined space for about 900tons of aggregate storage and the metalbins we originally specified would not pro-vide the storage volume within the allottedfootprint," Lien notes. "EnCon Design engi-neered and detailed the prestressed\pre-cast aggregate silos and ACT providedreview of bins for compatibility into theoverall batch plant plan. We not onlyachieved the space/storage objective weneeded, but also saved about $200,000building them on site."

The tunnel liner segment plant has been infull production since February 2013 andhas already produced thousands of seg-ments. The segments are transported viatruck from the Puyallup plant to the southerntunnel portal at varying rates. The special-

ly designed trucks can carry two segmentsat a time due to their extreme weight. The segment production line includes 11main workstations. The segments ride onspecial rail carts through each workstation,which include:

• Opening Mold – open the form• Stripping – remove product from Form• Cleaning – Clean Form / Oiling• Insert Placement – place insert in form,

includes bolting hardware for purposeof attaching the segment to others atthe job site.

• Reinforcement Placement – place cagein mold

• QA – quality assurance positionwhere the finished mold is inspectedfor compliance before casting.

• Casting – place concrete in mold andvibrate using seven built-in vibrators ineach mold (see figure 8).

• Screeding – remove excess concretefrom surface

• Finishing – hand finishing of exteriorsurface of segment

• Wash – Final clean of mold exteriorprior to curing chamber

• Curing Chamber -- segments cure forseven hours and 12 minutes to achieveminimum 2,500 psi stripping strength

Critical mix parameters

The concrete mix used to produce the tun-nel liner segments is engineered to providestripping strength of 2,500 psi after sevenhours of curing, and a minimum strength of7,000 psi after 56 days. The segments arestored in the EnCon Washington yard dur-ing that time (see figure 9). According toLien, the company is actually achieving 56-day strengths in the range of 10,000 to12,000 psi, which provides an extra levelof confidence that the segments can easilywithstand the demands of transportation,and the extreme hydraulic pressure exertedon them to drive the TBM forward.

Each segment requires approximately ninecubic yards of concrete. The mix is deliv-ered via a flying bucket system to the cast-ing station. Every 50th segment is carefullymeasured using a 3D laser-based scanningsystem.

"The high shear mixing precision batching wesee with the ACT/Wiggert batching plant isdefinitely helping us exceed the earlystrength and 56-day strength goals," Liensays. "We are using a very stiff mix with aone inch slump, so the speed and consisten-cy of the batching system is critical. Given

Figure 7: From above, the new EnCon plant is a model of efficiency with many automated features to save on labor and enhance quality. Fromthe automated aggregate loading and batching system, to the automated ACT MobilMat batching system, computer control and continuousmoisture monitoring ensures that they dry mix required for tunnel segment production always meets & exceeds design requirements.

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CONCRETE TECHNOLOGY

the water contained in the aggregates, weonly add about 39 pounds of water toeach yard to hit our target water/cementratio. We have a very short window--a shortpot life--and fast mixing and delivery speedis essential."Lien notes that even if it were possible to getthe volume and particular mix design froma ready mix supplier, the consistency andquality would not be sufficient. "Qualityand record keeping is paramount--we canonly get that using our own batch plant," henotes. "Not to mention, our cost to produceconcrete with our own batching system isabout $25 less per yard compared to de-livered ready mix. That's a saving of about$3 million over the life of the project."

Segment assembly

Rail mounted carts haul the tunnel segmentsfrom the southern portal along the complet-ed section of the concrete tunnel to an over-head conveyor that transports them to thelining system. The TBM system uses two vac-uum powered erector arms to place the tun-nel liner segments. Bolts and dowels areused to secure the segments to form a com-plete ring. The TBM then moves forwardusing massive hydraulic jacks that push offthe latest ring.

With the new ACT/Wiggert concrete mix-ing batching plant, EnCon is able to deliverthe highest quality precast concrete withsignificant production savings over conven-tional methods.

"With this plant expansion we are achiev-ing improvements in quality, lower laborand material production costs at the sametime achieving increased product strength,"Lien notes. "This investment positions ourcompany for future growth and flexibility todeliver precast concrete products that meetmarket demands. We're extremely proud tobe playing a key role in the developmentand delivery of this important transporta-tion system. Thanks to all our vendors andour dedicated crew, we are producing thehighest quality precast products possible."

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FURTHER INFORMATION

Advanced Concrete Technologies, Inc.300 Portsmouth AvenueGreenland, New Hampshire, 03840, USAT +1 603 4315661F +1 603 4315547info@concretebiz.comwww.concretebiz.com

Encon Washington, LLC5415 - 189th Street EPuyallup, WA 98375, USAT +1 253 8462774F +1 253 8469628www.enconwashington.com

Figure 9: Completed tunnel segments arestored in the EnCon yard for about 56 daysbefore delivery to the tunnel construction sitein Seattle. The fully enclosed plant addition,shown here, enables continuous productionin all types of weather.

Figure 8: Skilled operators watch over every step in the tunnel production process. Here, aflying bucket has just filled the segment form. Powerful vibrators, built into the form system,ensure complete and thorough consolidation.