fter 56 years, the coal-firedpower plant was worn out andobsolete. Corn Products Inter-

national, Westchester, Ill., built the boil-ers and generators in late 1948 to pro-vide steam and electricity for its man-ufacturing plant in Bedford Park, Ill.To replace this resource, Corn Productsis now building a state-of-the-art powerplant that will burn high-sulfur Illinoiscoal and meet all current emissions re-quirements. The State of Illinois pro-vided funding for this purpose. The newplant will cost $97 million and be com-pleted in 2006. Guy Buchner, the en-gineering manager for Corn Products,says the new facility will include a “1.1-million-pound-per-hour, 100-megawatt,circulating fluidized bed boiler.” Abyproduct of the boiler will be high-grade fly ash, which Corn Productsplans to sell—hopefully to the concreteindustry.

ABy Joe Nasvik

For Lindblad Construction,this project was a new high inlow-heat concrete placement

ConstructingaMat Slab

Above: This 41 ⁄2-foot-thick mat slab will support a coal-fired generation plant with aboiler weighing more than 6 million pounds. Right: The precision location of anchorbolts was one of the most important elements of this project (see Fig. 1, p. 3).Lindblad placed “mud mats” to hardware for holding the anchor bolts in position dur-ing placement. Notice the steel mesh on top of the rebar, making it safer for workersto move around while concrete was being placed.

February 2005

The World of Concrete

Corn Products decided to serve asits own general contractor, signing thecontracts for each subcontractor in-volved in the project. It retained ESI ofTennessee in Kennesaw, Ga., to engi-neer the project and to serve as the con-struction and start-up manager. BesidesLindblad Construction’s ability to per-form the concrete work, Corn Productswanted its expertise at setting anchorbolts with high tolerance requirementsand the company’s commitment to job-site safety. Lindblad’s experience mod-ification rate (EMR) of 0.73 and itsprevious year OSHA Recordable Fre-quency Rate of 0.0 was very importantto Corn Products.

The boiler for the project will weighmore than 6 million pounds, and mostof the weight will be suspended fromthe top steel so that its thermal expan-sion won’t affect the slab. The totaldead weight that will rest on this slabwill be over 12 million pounds. To sup-port this, engineers designed a 41⁄2-foot-thick reinforced mat slab. Because ofthe complexity of the mat geometry andloadings, Corn products asked Am-bitech Engineering Corporation of Down-ers Grove, Ill., to verify the design usingPCAMats and STAAD software. MarkStadalsky, Lindblad’s vice president,notes that ironworkers placed 805,000pounds of #10 steel reinforcing bars,generally spaced at 10 inches, but withthe more highly stressed areas at 5-inchcenters. The slab covered 22,800 squarefeet and required 3819 cubic yards ofconcrete coming from three different

yards. It took 79 ready-mix trucks tokeep up with the schedule.

Mass concreteACI 116 defines mass concrete as

“any large volume of cast-in-place con-crete with dimensions large enough torequire that measures be taken to copewith the generation of heat and atten-dant volume change to minimize crack-ing.” The heat generated by the hy-dration of cementitious materials causestemperatures in the center of a slab tobe much higher than at its surfaces.This temperature gradient is the criti-cal thing to remember about mass con-crete since it can cause thermal crack-ing that would compromise the struc-tural strength of the slab.

For practical purposes, accordingto PCA’s Design and Control of Con-crete Mixtures, (Kosmatka, Kerkhoff,and Panarese, Portland Cement Asso-ciation, 2002) slabs and footings morethan 3 feet thick qualify as mass con-crete. Thermal cracking in mat slabscan be managed by the type and amountof cement used, by adding pozzolans,by increasing the amount of reinforc-ing steel, by reducing the delivered tem-perature of the ready-mixed concrete,by using a concrete with a low thermalexpansion aggregate (such as limestoneor granite), and by increasing the sizeof the aggregate. On the jobsite, cov-ering a placement with insulated cur-ing blankets reduces the rate of cool-ing at the concrete surface, helping tokeep the temperature differential within

acceptable limits. So, even with no dan-ger of freezing, insulating blankets willoften be used on a thick mat slab.

Given the 41⁄2-foot thickness of theslab for this project, a mass concretemix design with a low heat of hydra-tion was needed in order to avoid ther-mal cracking. John Gajda, a principalengineer for Construction TechnologyLaboratories (CTL), Skokie, Ill., saysthat concrete temperatures for mass con-crete placements shouldn’t exceed 160ºF. Additionally, based on a simple ruleof thumb, the temperature differentialbetween the center of a placement andthe exterior surfaces shouldn’t exceed35º F to 56º F, depending on the ag-gregate used in the mix. In the devel-opment of the concrete mix design forthis project, Gary Hall, who does qual-ity control for Prairie Materials, Bridge-view, Ill., says it designed the mix notto exceed 130º F.

The mix used contained the fol-lowing ingredients:

Cementitious, including slag 450 poundsSand 1450 pounds#67 limestone (3⁄4 inch) 1825 poundsWater 24.85 gallonsSuperplasticizer Variable rates*Water reducer Variable ratesAir entrainment 51⁄2±11⁄2%Slump 5±1%Design strength, 28 days 4000 psi*The water/cementitious ratio will remain the same. An increase in slump is provided by an increase inthe superplasticizer.

Anchor bolt placementLindblad Construction is known

for its attention to detail and accurateplacement of anchor bolts. The ownerconsidered accurate anchor bolt place-ment to be a vital part of the contract.Before installing the reinforcement,workers marked the location of all theanchor bolts on the subgrade. Next,they cast “mud mats” over those spotsand under the angle support locations(see photo, left). Lindblad’s two onsitesuperintendents then verified the pre-cise location for each anchor bolt as-sembly on the mud mats.

Each anchor location included fouranchor bolts mounted in a steel frame.Workers mounted the frames to the

Concrete Construction � February 2005

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mud mats with concrete anchors. Theangle supports were then attached tohold each assembly securely in place.Ironworkers created a clear space be-tween the anchor assemblies and thereinforcement to insure that there wouldbe no movement during concrete place-ment. A total of 264 bolts were set inthis manner. After the anchor bolts were

set and secured, surveyors checked eachanchor bolt and verified that all of themwere in the proper location.

Forming trench drainsTo anchor trench drain forms, Lind-

blad used a procedure similar to thatused to position the anchor bolts. Work-ers again placed concrete mud beds on

the subgrade under the drains and at-tached angle iron to them with con-crete anchors. Angled supports werealso used. As shown in the photo, ver-tical form panels secured to the angleiron formed the walls of the drain, butthe drain floors were left open. Stadal-sky said that they were concerned thatthe buoyant forces of the concrete againstthe bottom forms would float the drainsout of position. As a result, they plannedto bush-hammer some concrete andplace an overlay cement topping to pro-vide pitch to the drains in each trench.

Placing concreteA private weather service provided

information about weather conditions.Ambient temperatures were around 32ºF when concrete placement started (con-crete temperatures were approximately50º F). Placement started at midnighton a Saturday, and finishing was com-pleted at 10 p.m. on Sunday evening.Windy conditions prompted Lindbladto spray a vapor retarder during place-ment to reduce the effect of surface dry-ing. The slab was covered with poly-ethylene sheeting and wrapped with in-sulated curing blankets the followingmorning, and this was kept in place fora week. Because of the low heat of hy-dration, concrete temperatures didn’treach 85º F on the surface until the fol-lowing Tuesday evening. There were nointernal sensors placed in the slab soits core temperature isn’t known.

One unusual aspect of this job isthat the mat slab was pitched to trenchdrains everywhere, so power screedscouldn’t be used for the placement, ex-cept in small areas. Workers placed pipescreeds at the high points in the slaband hand-struck the concrete. Becauseof the many pitches, finishing machinesweren’t useful either. All finishing wasdone by hand with finishers workingfrom knee boards. The finished surfacewas broom finished.

Lindblad decided to use threePutzmeister Telebelts with maximumreaches of 105 feet to place the con-crete, based on past experience with theequipment. Its goal was to place 9 cubicyards of concrete every 3 to 4 minutesfrom each belt. One ready-mix truckarrived on the jobsite every minute. Afourth Telebelt was kept onsite as an

Concrete Construction � February 2005

Fig. 2. Trench Forming and Bracing System. In order to avoid the possibility of “float-ing” the trench drain formwork, the bottom of the form was left open. By taking thisprecaution, Lindblad knew it would have to bush-hammer some of the bottom of thedrain and establish proper pitch using overlay cements.

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Fig. 1. Anchor Bolt Assembly Anchoring System. The anchor bolts were secured to “mudmats” placed in the subgrade. Angle irons placed at angles and secured to mud matsfixed the anchor bolts in proper position.

emergency standby unit just in casethere was an equipment breakdown.

Lindblad placed the concrete at am-bient temperatures just above freezing,and Stadalsky reports that it was 6 to8 hours later before finishing couldbegin. It took 22 hours to complete theconcrete placement and finishing process.Twenty-three finishers and 15 laborerscompleted the work without incident.

SafetyCorn Products and Lindblad both

consider safety to be the most impor-tant part of the construction process.The construction site is located in aheavy industrial area with constant traintraffic, truck deliveries, and storageareas for chemicals. Corn Products re-quires every worker and guest to watcha safety video before entering the proj-ect to learn the plant’s safety require-ments, including how to safely drivethrough the area. Lindblad set up afund for this job to which Corn Prod-ucts, Lindblad, and the excavation con-tractor all contributed. Cash rewardswere given to workers who submitted

the most innovative safety ideas. Lind-blad calls its program the “Good CatchRecognition Program.” Two recipientsof this award were carpenters who sug-gested that a layer of 6x6-10-10 steelmesh be fastened to the top layer ofrebar to create an easy walking surfacefor finishers and laborers during con-crete placement—eliminating the pos-sibility of injuring feet and ankles bystepping through the holes betweenrebar. Other cash prizes were raffledoff to workers each week there wasn’ta jobsite accident. In addition, for every2 weeks that were accident free, the en-tire workforce was treated to a cateredlunch on the jobsite. There were no ac-cidents on this jobsite.

Planning and executingThe level of difficulty goes up

when constructing mat slabs that qual-ify as mass concrete. “The devil is inthe details,” and, as you can see inthe description of this job, planningand organization were critical to apositive outcome. Lindblad started itsprocess by holding three key meetingswith representatives from all of itsvendors and subcontractors. In thefirst meeting they thought through

the process from traffic control andconveyor placement to truck washout.At the second meeting, they drew plansmarking the locations for everythingbased on the decisions of the first meet-ing, and they discussed back-up plansto cover possible problems. At thethird meeting they met with the own-ers to present and finalize the plan.

The construction of the mat slabwent very smoothly, and there are nocracks in the finished work. The nextstep in the construction process will bethe installation of the boiler and theerection of the building around it. ■

Participants:

Owner and General Contractor: CornProducts International, Westchester, Ill.

Engineer and Construction Manager: ESI Inc. of Tennessee, Kennesaw, Ga.

Concrete Contractor: Lindblad Construc-tion, Joliet, Ill.

Concrete Conveyor Contractor: RuaneConstruction Inc, Frankfort, Ill.

Reinforcing Steel Contractor: GatewayErectors, Burnham, Ill.

Ready-Mix Supplier: Prairie MaterialsSales, Bridgeview, Ill.

The entire surface of the slab waspitched to trench drains like the oneshown here. As a result, much of the slabhad to be “hand struck.”

Finishing concrete placement. Because the heat of hydration of the concrete mix wasso low, finishers waited as long as 8 hours to begin finishing operations. Because ofthe pitches, the entire slab was finished by hand.

Posted with permission from the February 2005 issue of CONCRETE CONSTRUCTION magazine. © Hanley Wood.#1-10277895 Managed by Reprint Management Services, 717.399.1900. To request a quote online, visit www.reprintbuyer.com.

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