Australia Finds Many Uses for Sfrc

8/3/2019 Australia Finds Many Uses for Sfrc

http://slidepdf.com/reader/full/australia-finds-many-uses-for-sfrc 1/3

For more than 8 ye a r s, the use of s t e e l - f i b e r- re i n f o rced concre t e

( S F RC) in Au s t ralia has been grow-ing 30 to 40 percent per ye a r. Si n c ean Au s t ralian manufacturer intro-duced enlarged-end steel fibers tothe country in 1975, more than 30ready mixed concrete companiesh a ve supplied SFRC. The materi a l

has been batched by more than 200batch plants, both large automatedcity plants and small port a b l ep l a n t s. It is now included in Au s-t ra l i a’s Swi mmi ng Pool St a n d a rd(AS2785) and its Septic Tank St a n-d a rd (AS1546). Its inclusion in Au s-t ra l i a’s Co n c rete St ru c t u res Co d e(BD2) is being considered now also.

Why use steel fibers?

A ready mix supplier can batchthe enlarged-end steel fibers dire c t-

ly into a transit mixer. No specialdispensing equipment is re q u i re d .Co n t ractors can handle and finish

the concrete with standard concre t eequipment. This makes it faster andeasier to place than concrete re i n-f o rced with mesh or re b a r. It’s alsoc o s t - c o m p e t i t i ve with concrete re-i n f o rced with mesh or re b a r. It re-sists impact and abrasion and it per-mits thinner sections, which re d u c edeadload and the amount of con-c rete needed. Slab thickness can bereduced by 30 to 40 perc e n t .

Floors and roads

Because of its excellent re s i s t a n c eto impact and abrasion, SFRC ori g i-nally was used only for heavy- d u t y floors and pave m e n t s. The Au s-t ralian coal and ore mining indus-t ry uses a lot of SFRC for work s h o pf l o o r s, wash-down pads, and hardstanding are a s. The cotton industry uses it for storage sheds and gins. It

also is used for pavements in con-tainer handling are a s, bus park i n g l a n e s, ro u n d a b o u t s, heavy-duty fac-t o ry floors, and slipformed slabs un-der railway tra c k s.

Since these pro p ri e t a ry steelfibers we re f irst introduced, thefiber manufacturer has deve l o p e dt h ree standard mixes for heavy- d u-t y, light-duty, and residential uses.Because they contain fewer fibers,the light-duty and residential mixescost less, making them economical

for many other uses. Now they alsoa re used for warehouse floors, ten-nis court s, and some re s i d e n t i a lf l o o r s. Though they are n’t usedmuch in highway construction, they a re used for roads with light tomedium traffic, typically at 4- to 43 ⁄ 4-inch thicknesses.

The light-duty mix contains 105pounds of steel fiber per cubic yard

of concre t e. It reaches a compre s-s i ve strength of 5000 psi and a flex-u ral strength of 800 psi. The fiberm a n u f a c t u rer recommends ware-house floor slabs be at least 4 inch-es thick. Thinner slabs are too diffi-cult to place. At free edges andd oweled or keyed joints, slabsshould be thickened to 5 to 6 inches, with the underside sloped 1:10 fro mthe main slab to the edge. Ma x i-mum joint spacing should be 50 feet

for indoor slabs and 30 feet for out-door slabs.

Toppings

S F RC is used in Au s t ralia forbonded, unbonded, and part i a l l y bonded toppings over deteri o ra t e dfloors or pave m e n t s.

Thick, unbonded SFRC toppingsa re placed over badly cracked slabs

Austr al ia finds m any uses forsteel-fiber-reinfor ced concrete

SFRC is cast in place, precast, and shotcreted

Because it resists impact andabrasion, SFRC is used in heavilyloaded areas, such as containerhandling yards, bus parking lanes,roundabouts, bridge nosing joints,railroad track foundations, and factoryfloors.

A thin topping of SFRC can provide anew wearing surface for old timberfloors.



or slabs that must be leveled a larg eamount. A thin layer of sand orc rushed stone is placed over theslab first to separate the topping f rom the original floor. This helpsp re vent crack reflection and elimi-nates the need to match joints in thetopping with joints in the slab. If toomuch headroom is lost because of t h i s, plastic sheeting can be used asa bondbreaker instead. An unbond-ed topping must be at least 3 inches

thick; 4 inches is common. To pro-vide load transfer and to pre ve n tedge curling, joints must be dow-eled. Cu ring is important, as withany SFRC application.

Thin, bonded SFRC toppings areplaced over sound slabs with a wornor unlevel surf a c e. Wo rkshop floors,c o m m e rcial floors, and bridge decksin Au s t ralia have all been re s u rf a c e d with bonded SFRC toppings. Thick-ness va ries from 1.2 to 2.4 inches.Thicker toppings tend to debond

due to curling or differential shri n k-a g e. For a good bond, the existing c o n c rete is scabbled then damp-ened with a bonding agent, such asa 1:1 sand-cement slurry. SFRC isthen placed, vibrated, and finished with a power trowel. Joints in thebase slab will reflect, so joints in thetopping must coincide with them.

Cu ring is re q u i red for 7 days.Pa rtially bonded toppings are

placed over cleaned slabs, withouta bonding agent or a bondbre a k e r.Because the topping must with-stand loads without relying on loadt ransfer to the slab, it should be atleast 2 inches thick. Joints in thetopping must follow joints in the

s l a b.Below-grade walls

The Au s t ralian-made machines h own here digs a trench at thesame time it casts a SFRC wall insidethe trench. The machine can beused to cast basement walls, foun-dation walls, retaining walls, orcanal re vetment walls up to 101 ⁄ 2inches thick and 14 feet deep. Gu i d-ed by a laser beam, it can place con-c rete to within 3 ⁄ 16 inch of an existing

building, with an accuracy of 5

⁄ 32 i n c hover a distance of 440 yard s.

S F RC is crucial to the operation of the machine. Because concrete ispumped into a slipform attached tothe back of the tre n c h e r, there is noaccess to install mesh or re b a r.

Precast panels

S F RC is used to make difficult-to-cast precast panels, such as thinp a n e l s, curved panels, or panels

that are difficult to re i n f o rce with re-bar or mesh.

A few precasters make compositebuilding panels that consist of a

l i g h t weight concrete core sand- wiched between exterior SFRCs k i n s. Due to the lightweight core,the panels re p o rtedly are easy tohandle and erect. One such systemfor residential and commerc i a lbuildings is said to have exc e l l e n tf i re resistance and sound attenua-tion pro p e rt i e s. A 4-inch-thick non-

s t ru c t u ral panel achieved a 4-hourf i re rating. When partially post-ten-sioned, this type of panel also canbe used in load bearing situations.

Precast panels for swimming pools we re one of the first uses of p recast SFRC in Au s t ralia. They costless than laminated asbestos panels.The 3 ⁄ 4-inch-thick, 4-foot squarepanels are set in the concrete baseand secured at the top with a re i n-f o rced or post-tensioned coping. A vinyl liner is placed over the con-

c re t e, so an off-form or hand-trow-eled finish is satisfactory. Pa n e l susually are stack cast. The high-s t rength mortar contains 200pounds of fiber per cubic yard anda c h i e ves flexural strengths of 1450to 1750 psi. Fu l l - s i ze olympic poolsh a ve been built with these curve dand flat precast SFRC panels.

Australian-made machine casts a SFRCfoundation wall at the same time itdigs a trench for the wall. Becauseconcrete is pumped into a slipformattached to the back of the trencher,there is no access to install mesh orrebar.

Loadbearing U-shaped columns for athree-story building were precast usingSFRC to overcome reinforcementplacing problems.

New swimming pools are built byshotcreting SFRC over the poolexcavation; old pools are rehabilitatedby shotcreting SFRC over the oldconcrete or tile.



Precast tanks

Ap p roved by a state authority in1983, SFRC septic tanks are now be-ing formed and spun-cast. A tri a l132-gallon septic tank with 3 ⁄ 4- i n c h -thick spun-cast walls is in exc e l l e n tcondition after 8 years of serv i c e.

In 1983, water tank manufactur-ers started using SFRC also. A 5800-

gallon cylindrical tank has a 3- to 4-inch-thick base and walls that taperf rom 3 inches thick at the bottom to2 inches at the top. A 1300-gallons p h e rical tank having walls l-inchthick was recently constructed as ap ro t o t y p e.

Shotcret ing SFRC

In Au s t ralia, shotcreting of SFRCusually is done by the wet pro c e s s. Itis used for building walls, tunnel lin-i n g s, embankment stabilization, re-

pair of wharf piles, and constru c t i o nand repair of swimming pools. Thesame enlarged-end steel fibers alsoa re made in Oslo for we t - s h o t c re t-ing tunnels in Scandinavia.

For Au s t ralian residential con-s t ruction, expanded polystyre n epanels are set between studs ands h o t c reted on both sides with SFRC .Mesh laid over the pipe frame for af ree form building also has beenc ove red with SFRC shotcre t e.

S F RC is used to repair wharf piles

by shotcreting the pre p a red surf a c eor by pumping SFRC into water-p roof socks placed around the dete-ri o rated piles.

Since 1983, more than 100 in-g round home swimming pools havebeen built with SFRC shotcre t e. Walls usually are about 4 inchesthick. Most do not contain mesh orre b a r, except perhaps for some con-tinuous re i n f o rcement in the bondbeam. Pools up to 56 feet long and 8feet deep have been built in this w a y.

Old pools are rehabilitated by lin-ing the original shell with 3 inches of

S F RC shotcre t e. No special pre p a ra-tion is re q u i red; the SFRC is spra ye dd i rectly onto the old concrete or tiles u rf a c e. To accommodate shri n k a g es t re s s e s, a compressible isolation joint is installed at the top betwe e nthe old pool and the new SFRC lin-i n g .

But is SFRC durable?

In 1971, SFRC beams we re placedin the tidal zone of the upper Syd-ney Ha r b o r. Beams we re re m ove d ,examined, and tested after 21 ⁄ 2, 5,and 10 ye a r s. All of these tests haves h own that SFRC resists corro s i o n .

Although spalling is common for re-i n f o rced concrete in sea water, noneof the SFRC beams has spalled. On ebeam is still immersed and in goodcondition after 15 ye a r s.

S F RC is durable because it gener-

ally has a strength of 5000 psi (or5800 psi, where durability is a majorc o n c e rn). Wa t e r-cement ratio isn o rmally below 0.5. The typical 3-inch-slump mix can be compactedreadily by normal pro c e d u re s.

Ac c o rding to the manufacturer of e n l a rged-end steel fibers, surf a c estaining has been overstated. It oc-curs in salt water conditions, but it’san aesthetic rather than a dura b i l i t y p roblem. Under normal urban con-d i t i o n s, i t will be minimal or nonex-

istent. Staining that does occur willbe localized and will not change theg e n e ral appearance of the concre t e.The surface can be painted or tre a t-ed to pre vent staining.

Editor’s note

This article is based on a paper byWinston A. Marsden, Technical Devel-opment Manager of AWI Fibresteel,Australia. Marsden presented the pa-per, “The Diversifying Applications of

Steel Fibre Reinforced Concrete inAustralia,” at the FRC ‘86 Rilem Sym-posium in Sheffield, England, July1986.

PUBLICATION #C870517Co py right © 1987, The Ab e rdeen Gro u p

All rights re s e rve d

Documents

Australia Finds Many Uses for Sfrc