self compacting concrete offers design potential

8/3/2019 Self Compacting Concrete Offers Design Potential

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he proposed renovations to

Soldier Field Stadium alongChicagos lakefront provide a

creative design that retains some of thelandmark exterior of the existingstructure while offering state-of-the-artamenities and layout inside. Oneingredient in that plan will be precastconcrete stadium tubs that are beingproposed to be made with self-com-pacting concrete, a new material now

just gaining designersattention. The material

offers a range of ben-efits to both designersand precasters, includ-ing aesthetic quality,speed and durability,but its potential is justbeginning to be under-stood.

The design for the Windy Citys new sta-dium calls for tubs lo-cated high overheadfor which the back

sides will be easilyvisible to visitors pass-ing beneath them, saysDon Caithamer, qual-ity assurance managerat J.W. Peters & SonsInc. in Burlington,Wis., the precaster forthe components. I need those pieces tobe flawless, so they present a strong,aesthetic view, he explains. But I dont want to try to have someone up in theair having to rub them smooth once

theyre erected. By using self-compactingconcrete, I wont have to worry about

that. It produces flawless pieces every

time. This material is definitely the wayof the future, from what I see, and its atechnology were going to have to catchup to.

Workability IncreasedSelf-compacting concrete (SCC)

features a concrete mixture thatincorporates high-range water-reducingadmixtures that significantly increase the

materials workability and fluidity. As aresult, it flows quickly into place, fillsevery corner of a form and surroundseven densely packed reinforcement.Self-compacting concrete not only can

speed the casting process, but it offersincreased strength, freeze/thaw durabil-

ity, improved bond strength and great

aesthetic properties, says TonySchlagbaum, group manager of productmarketing for Master Builders Inc. inCleveland, which produces the material.And it can be used in virtually anyprecast concrete application.

Precast manufacturer FinfrockIndustries Inc., in Orlando, Fla., hasfound a variety of uses for the material,which helps the company produce

higher quality andmore durable com-

ponents at a faster rate,says Daniel Finfrock,director of operationsand manufacturing.The company regularlyproduces a number ofcomponents with SCC,including stairs,columns and beams.

SCC works particu-larly well with verticalcomponents that in-clude obstructions to

the form at the top,such as tall columns

with block-outs. Inthose cases, wheretheres a concern aboutensuring that aggregatereaches the bottom ofthe form and doesnt

segregate earlier due to obstructions,there is a huge advantage to using self-compacting concrete, says Finfrock. Adds Caithamer, Its fantastic forinsulated wall panels. Its going to reduce

my overtime dramatically on fast-trackprojects.

Self-Compacting ConcreteOffers Design PotentialOwners and architects can benefit from a new type of concrete that offershigh quality, durability and speed while creating new design options

T

This chart contrasts the compressive strengths that can be gained with self-compacting concrete (SCC), and normal concrete. SCC can attain significantlyhigher early and 28-day strengths.

Self-Compacting Concreteelf-Compacting Concrete

Normal Concreteormal Concrete

9000

COMPRESSIVE STRENGTH

TIME (DAYS)

COMPRESSIVESTRENGTH(psi)

7500

6000

4500

3000

Self-Compacting Concrete

Normal Concrete

1500

01 7 283


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A variety of advantages can be derivedfrom the use of SCC that benefit theowner and designer. These include: High quality. Because the material flowsso readily to fill any gaps, no voids or bugholes develop. This reduces the timeneeded to inspect each component, as well

as any labor or time to rub the piecessmooth to create a smooth finish.

Aesthetically, self-compacting concrete issuperior to anything Ive ever seen, saysCaithamer. SCC virtually eliminates anyholes. It can create flawless pieces. Thatsaves him costs not only in labor to inspectand repair but also by allowing him toeliminate any cost variable to cover piecesrejected due to flaws. Aesthetic value. The smooth finishthat can be created produces an aestheti-cally pleasing component. SCC alsoproduces a consistently lighter color with

reduced discoloration, says FrankKliewer, plant manager with NewcreteProducts Inc., in Roaring Spring, Pa.Pour lines from placer to placer load ofconcrete also are reduced. It producesan improved overall appearance, hesays. Architects and owners who have

seen the pieces weve produced havegiven us very positive comments aboutthem.

Fast production. Because SCC flows sosmoothly, it can be poured quickly andeliminates the need to vibrate the concreteinto tight spaces and around denselypacked reinforcement. That speeds theentire production process. At J.W. Peters,for instance, Caithamer anticipates usingSCC to produce double tee components

The renovation work being proposed for Soldier Field in Chicago will feature precast concrete tubs using self-compacting concrete from J.W.Peters & Sons Inc. The material will provide a flawless finish that eliminates the need for patching, speeding the work considerably.

Precast panels using self-compactingconcrete are shown being poured at theFinfrock Industries plant in Orlando, Fla.The material flows quickly to fill every nookand cranny, leaving no voids and flowingaround densely packed reinforcement.

SCC opens thepotential for more

complex shapes andthinner pieces.

Type Slump/Spread Ranges

Normal


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when he needs to produce a large number.Its hard for me to schedule it now,because I can pour SCC faster than I canget it to the beds, he says. When weneed large quantities, its great, because wecan just keep it moving through the bed,he says. It needs to be leveled after its

poured, but for the most part, I pour itout and Im done.

The speed with which it sets up alsoeliminates the need for steam or heatcuring of concrete to facilitate earlystrength gain, says Master BuildersSchlagbaum. This system will poten-tially allow a precast operation to main-tain regular production cycles of 14 to18 hours without steam or heat andspeed up curing overall, he says. Thisearly strength gain allows fast turn-around and reduced cycle times.

Design flexibility. Because SCC flowsso readily into thin sections and details,it opens the potential for using complexshapes and intricate surfaces. It alsoensures no patching of holes after castingor potential damage to pieces duringvibration. This is especially significant

for delicate panels, such as those withbrick insets, notes Victor Borcea, qualitycontrol manager with Finfrock. AddsPeters Caithamer, Theres simply nohuman or material error that we need tocompensate for when casting any design.That means we can schedule tighter andproduce better looking pieces. Durability. The materials ability toremain stable during and after placementmaximizes the structural integrity anddurability of the concrete, saysSchlagbaum. The admixtures provide a

higher compressive strength than tradi-tional concrete, making it substantiallystronger. It also offers less permeabilitydue to the high consolidation of material,

allowing it to resist chemical attack andimprove the components durability. Itprovides a high modulus of elasticity,ensuring low elastic deformation of the

concrete under dynamic and static loads.

Catching Up To SCCTo be sure, there are some obstacles

yet to be overcome before use of thematerial is widespread. A key one is itscost, as the admixtures and otheradditives create a premium over existingconcrete costs. But the savings that canresult from using SCC effectively giveprecasters a compelling reason to closethe gap on logistics. There is plenty ofcost savings to be captured yet, becausethe full potential hasnt been realized,because were not fully set up to exploit

SCC Cost SavingsThe Newcrete Products Division of New Enterprise Stone & Lime Co. Inc.

in Roaring Spring, Pa., is using self-compacting concrete on a variety ofprojects, including a number of parking structures. The cost comparison it hasmade shows that SCC could cut costs significantly for activities such aspouring and patching pretopped tees.

The cost of using the SCC mixture can easily offset the estimated 3.5%per-yard premium when the savings are extended on a yearly basis, NewcretesFrank Kliewer says. For instance, looking at our production facility we havenoticed a 46% savings in total man-hours per section and a 44% savings inpatching man-hours per section. Analyzing those percentage numbers over the

course of a one-year production time calculates out with significant savings.

The Childrens Hospital University Avenue parking facility in Philadelphia, currently in the erection phase, was designed with precast,prestressed concrete components. Many of the components provided by the Newcrete Products Division of New Enterprise Stone & Lime Co. Inc.,using SCC were pretopped double tees, light walls, shear walls, slabs and inverted tee beams. The material was chosen for the 10-story, 660,550-square-foot project due to the time savings and high performance.

The premium cost will

be reduced asprecasters factor in

their manpowersavings and adjust

their processes.


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the benefits, says Caithamer. Asprecasters become familiar with thematerial, theyll become more effective

at using it and realize cost savings thatoffset the material costs.A key savings for precasters will come

in reduced manpower, which can bevirtually eliminated from the vibrating,repair and patching activities. Being ableto pour such a large quantity of precastquickly also will cut labor on large jobs.When we can minimize productiontime, we can maximize our use of laborand cut the cost on each job,Caithamer says. With labor costs thekey component that drives costs up over

time, using SCC will offer ways to holdproduction costs steady over a longtime.

For instance, Caithamer estimatesthat production of a double tee typicallycan add a $9.44 premium of standardcost per yard of concrete. Using SCCand beds geared to the fast productiontime could reduce the premium to $7.08per yard. Similarly, an inverted teewould add a $12.02 premium per yard,but with no need for inspections forhoneycombing and no time required for

vibrating concrete and the manpowerneeded to oversee that, he can reduce it

to a $7.90 premium. And that doesntcount the elimination of any cushionneeded to compensate for rejected

components.I can quantify the savings that can beachieved while also producing anaesthetically superior product whichis a number I cant really quantify, hesays. But I have to be able to take fulladvantage of its efficiencies to achievethose savings.

Understanding how to exploit the fullbenefits will be the key to using SCCeffectively and extensively, Caithamersays. At the moment, SCC is reallymore advanced than we are, he admits.

We need to catch up to it to take fulladvantage of what it offers. This materialis something completely different, andtheres still room to go for us tounderstand how we can make the bestuse of it for our clients.

Manpower and bed placement aretwo key requirements to adapting to it.It also works best with components thatdont require a troweled finish, notesFinfrocks Borcea. Because of itsviscosity, SCC requires two to threehours to set firmly enough to provide a

troweled finish, compared to traditionalconcrete, which doesnt require that

wait. SCC works well for some prod-ucts but not for all, he says. The ad-vantages in not having to vibrate theconcrete are compelling, because it elim-inates so much time. Its also an idealway to cast stairs and long columns.

Newcretes Kliewer agrees. The com-pany began using SCC in November2000 and went into full production in

March 2001. It has since producedapproximately 20,000 cubic yards andhas used the material on several projects,including five parking structures and awholesale production plant addition. Itcurrently produces approximately 250cubic yards of SCC components perday.

With real manufacturing savings inboth pouring and patching areas as wellas significant quality improvementsmade to date, we have made changes toour two 12-foot double tee lines to take

advantage of the benefits without havingto use additional resources, Kliewersays. Included in the changes was theaddition of 50 feet to the 12-foot-widedouble tee beds to maximize pouringefficiency.

J.W. Peters also intends to adapt tothe material. We have some locationswhere were ready to install a new batchplant, says Caithamer. Well be incor-porating these new admixtures into ourdesigns for those, because this material is

definitely in our future. The onlylimitations are our being able to takeadvantage of its speed. It requires a newmindset. The need for a new mindsetultimately will carry over to designers,who will be able to create more detailedshapes and worry less about strandplacements in complicated components.

I see endless uses for SCC, ultimately, Caithamer says. Our SoldierField project is only one example of where I believe well be using thematerial as we learn more about its best

uses. If I can use it in cases like that one, where Im taking advantage of itsaesthetic value alone, it will pay off dueto the flawless look. Theres still room togo in adapting, and we want to makeadjustments slowly to find the mosteffective approach. But this produces awhole new ballgame, and we intend totake full advantage of it in time.

Craig A. Shutt

SCCs Key AttributesThe two key attributes of self-compacting concrete are its high degree of

workability and its stability during and after placement, according to TonySchlagbaum, group manager of product marketing for Master Builders Inc., inCleveland, which produces a version of the material called RheodynamicConcrete.

The workability of SCC is typically characterized by using a modification ofthe traditional ASTM C 143 slump test method. In the modified procedure,

called the slump flow test, the concrete is not rodded after placement in theslump cone, and the spread of concrete (slump flow) is measured instead ofslump. This test measures the unconfined fluidity of the concrete and gives arelative indication of the degree to which the concrete can travel. The spreadgenerally is between 18 and 30 inches.

The concretes stability is an indication of its ability to resist segregation ofthe paste from the aggregates. Although there is no standard test to measureSCC stability, some of the flow measurements, such as slump flow, provide aqualitative assessment of the concrete stability, Schlagbaum says.

In general, the setting time for Master Builders Rheodynamic concrete isabout 30 to 90 minutes longer than conventional concrete, he notes.Accelerating or retarding admixtures can be used to produce concrete with thedesired setting characteristics.

Rheodynamic concrete mixtures can be used in virtually any precastconcrete application, be it architectural, structural or utility, says Schlagbaum.Different mixtures may be necessary in each project, because each will have adifferent shape, level of intricacy, size, level of reinforcement and coarseaggregate content, he notes. SCC has been used for exposed-aggregate,intricate pieces, structural applications, vaults, culverts and barrier precastapplications.

self compacting concrete offers design potential

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