Paving With Roller Compacted Concrete_tcm45-341209

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Roller compacted concrete (RCC) has had a lotof attention in the past seve ral years becauseof its growing acceptance for use as mass con-c rete in dam construction. Howe ve r, a re c e n t

d e velopment is the increasing use of RCC as a com-p a ra t i vely low cost, durable paving material to carry heavy loads. The U.S. Army Corps of Engineers has ac-cepted it for airc raft parking apro n s, taxiways and oth-er pavements at military installations, and thus stim-ulated interest among all those concerned with

p a vement constru c t i o n .Roller compacted concrete as used for pavements is a

d ry portland cement concrete material which is consol-idated by external vibration using heavy vibra t o ry ro l l e r sor similar equipment. It is normally dryer than a no-slump consistency and must be stiff enough to supportthe compaction equipment. RCC for pavement con-s t ruction is generally placed with an asphalt paver orsimilar equipment, modified to accommodate the stiff consistency of RCC and the thicker lifts used.

The most obvious advantage of using RCC pave m e n tis lower cost, achieved pri m a rily by the use of lower costequipment and fewer workers than with conve n t i o n a lc o n c rete pave m e n t s. In some cases, lower cost aggre-gates can also contribute to the saving. The term RCCp a vement is normally considered to refer to installations w h e re the RCC is the we a ring course, without any otherapplied surf a c i n g .

BACKGROUND OF DEVELOPMENTCo n s t ruction technology similar to that of the RCC

p a vement has been available for many years in pave-ment base construction. There is even a re c o rd of tru e

roller compacted concrete used for pavements at the Yakima, Washington airport in 1941. Although theequipment was pri m i t i ve by today’s standard s, and themix design and control we re likely less than perfect, thatp a vement has served well. It is still in use, with only athin asphalt overlay added during 45 years of serv i c e.

How RCC pavement compareswit h t reated bases and RCC for dams

Use of RCC for pavements evo l ved from the use of soilcement and cement treated base (CTB) courses. Al-though equipment for batching or feeding and mixing has developed from that used for the base courses, RCCfor pavements re q u i res better controls on pro p o rt i o n-ing. Also, a true paver or layd own machine is norm a l l y

STATE OF THE ART:

Paving with r ollercompacted concreteExternally vibrated dry concrete mix provides durable support for heavy wheel loads

BY OSWIN KEIFER JR.DIVISIONMATERIALS ANDPAVINGENGINEERU.S. ARM Y CORPS OF ENGINEERSNORTH PACIFIC DIVISIONPORTLAND, OREGON

Fort Lewis RCC test road surface. Close-up of t he 3 ⁄ 4-inchaggregate pavement at about 1 year, showing a nonraveledtransverse crack. These cracks formed at 40 - to 8 0-footspacing throughout the road project.



used for placing and finishing the RCC pavement whileless sophisticated placing and spreading equipment isoften used for CTB or soil cement. The RCC pave m e n tmix has considerably more cementitious material than

C T B, and differs from most soil cement in that it con-tains coarse aggre g a t e.The most important difference between RCC pave-

ment and CTB or soil cement is that the RCC is designedto be a true portland cement concrete pavement withs t ru c t u ral strength at least comparable to that of con-ventional portland cement concre t e, and often higher.The RCC pavement is also designed to have resistance tothe abrasion of traffic, durability when exposed to seve re we a t h e r, and a surface finish and straightedge tolera n c es a t i s f a c t o ry for the usual re q u i rements of the traffic in-vo l ve d .

RCC for pavements differs significantly from RCC for

d a m s, which is simply a form of low - c e m e n t - c o n t e n tmass concre t e. The RCC pavement mixes have a muchhigher cement and paste content and much smallercoarse aggre g a t e. Typical cementitious material con-tents (cement plus poz zolan) range from 500 to 550pounds per cubic yard, and the maximum size of coarse aggregate is usually near 3 ⁄ 4 inch. These factorsalong with a different approach to mix design pro d u c ea much more workable mix than that used for dams, al-though it is still a no-slump mix, stiff enough to supportv i b ra t o ry ro l l e r s.

EARLY APPLICATIONS IN CANADA Although the United States was making slow pro g re s s

in the seventies with RCC dams, only one small RCC testp a vement section (12x105 feet) was installed at the U.S. A rmy Wa t e rways Ex p e riment Station in Vi c k s b u rg, Mi s-sissippi in 1975. Howe ve r, engineers and contractors inBritish Columbia, Canada we re having excellent re s u l t susing RCC pavement as a base with a thin we a ring sur-face of asphaltic concrete for building heavy-duty pave-ments for dockside storage are a s. The material prove dp a rticularly appro p riate for containerization yards and

piggyback trailer park s, and it was decided to try RCC asa combined base and surfacing or total pavement. Theattitude was: “The RCC is perf o rming so well. Why do weneed the asphalt surf a c i n g ? ”

This line of thinking led to construction in 1976 of afull RCC pavement for a log sort yard at Ca ycuse in thec e n t ral part of Va n c o u ver Island, British Columbia. Thef o rest products industry was then facing stiff enviro n-mental regulations which made it impractical to contin-

ue the common practice of sorting and yarding logs inthe waters throughout the timberland. But dry- s o rt y a rds in that climate would immediately become hugemud holes unless surfaced. Since asphalt was impra c t i-cal at many isolated sites, the decision was made to try RCC .

RCC paving procedures at Caycuse,Briti sh Columbia

The log sort yard at Ca yc u s e, built in the fall of 1976,included 4 acres of 14-inch-thick RCC pavement placedin a two-lift operation on a 6-inch crushed rock base.Fi ve more acres we re added in 1979. A local pit-ru n

s a n d - g ra vel with maximum size about3

⁄ 4 inch was used.The 8-inch bottom lift had an 8-percent cement content,and the 6-inch top lift was made with 12 percent cement(about 5.1 sacks per cubic yard ) .

Co n s t ruction equipment and pro c e d u res at Ca yc u s e were similar to those used on later jobs. An easily trans-p o rtable continuous type mixing plant, one whichcould be erected in about 2 days, was set up near theconstruction site. The mixing was done in a twin-screw pug mill. Aggregate was fed to the mixer with a belt con-ve yor having vo l u m e t ric (gate) controls on the feed tothe belt. Cement was fed from a silo onto the ribbon of a g g regate on the belt by means of a vane feeder. Wa t e r was metered and fed to the mixer through a spray bar. A second belt conve yor picked up mixed RCC from thed i s c h a rge of the pug mill and elevated it to the tru c k loading point. A small gated transfer hopper located atthe end of the conveyor reduced segregation at the con-ve yor discharge and allowed trucks to change withoutstopping the plant.

Trucks hauled the concrete to the placing site anddumped into the hopper of a conventional self-pro-pelled asphalt pave r. The paver spread the RCC to a uni-f o rm lift meeting the desired line and grade with a “f i n-i s h e d” surface ready for compaction with heavy steel-wheel vibra t o ry ro l l e r s. Usually the vibra t o ry ro l l e r s we re followed by ru b b e r- t i red rollers and then a finalpass of a non-vibra t o ry steel-wheel ro l l e r. A smallamount of compaction was provided by vibra t i n g s c reeds on the pave r. The paver could be electro n i c a l l y c o n t rolled from a string line or ski operating on the adjacent paved lane. Mo re commonly manual contro l s we re used. An allowance of about 10 to 15 percent extradepth was made to cover compaction during ro l l i n g .Cu ring, commonly provided by sprinklers attached to apipe irrigation system, usually continued for 14 days.

Ends of a broken t est beam from t he Fort Hood, Texas t ankstand (1984) show internal structure of the RCC pavement.



Since the conventional asphalt pavers available couldhandle only about 10 inches in an RCC lift, anything thicker had to be two-course construction. The speci-fied sequence of two-course construction re q u i re dplacing the second course within an hour of the first,but with no treatment of the surface of the first lift. Eachlane of pavement was placed immediately adjacent tothe previous lane, with the longitudinal constru c t i o n joint formed by leaving a 12- to 18-inch unrolled strip at

the edge of the preceding lane and rolling it after thesucceeding lane had been placed in contact with it. If the operation was shut down overnight, the edge of thelast lane was cut back to a ve rtical face with a motorg rader or similar equipment and then the new lanebutted up against this face the next day. No tra n s ve r s e joints we re formed; the pavement was simply allowed toc rack as shrinkage occurred. The tra n s verse cracks didform, reasonably straight across the pavement, from 40to 70 feet apart.

Performance record at Caycuse When we inspected these pavements in De c e m b e r

1983, and again a year later, the Ca ycuse pave m e n t s we re in excellent condition in spite of seve re service con-d i t i o n s. The larger log stackers apply up to 240,000-pound loads on two-wheel axles, and off-road tru c k sb ringing in logs have a gross weight of 120 tons. In addi-tion, the pavement is subjected to intense abrasion aslogs are pushed across the surf a c e. Almost no stru c t u ra lp roblems we re found, and the surface was in exc e l l e n tcondition. There we re few open longitudinal constru c-tion joints. Many tra n s verse cracks we re tight; most we re1 ⁄ 16 to 1 ⁄ 8 inch wide, with a few up to 3 ⁄ 8 inch. No attempt hadbeen made to seal the cracks or otherwise work on them,but there was no sign of offsetting or ra veling, and thec racks we re causing no pro b l e m s.

This pavement is in an area with numerous cycles of f re ezing and thawing, although winter tempera t u re sseldom go below +20 degrees F. There was no evidence w h a t e ver of any fre eze-thaw deteri o ration even though,like other RCC pavements, the Caycuse pavement con-c rete is not air entrained. Co res taken from the pave-ment had compressive strengths from 3000 to 5000 psi, with most of the results bunched in the 4000- to 4200-psi range.

Since 1976 other similar RCC pavements have beenbuilt in we s t e rn British Columbia for log sort yards anddock are a s, using essentially similar construction pro-c e d u res and with similar good resul ts and serv i c ere c o rd s. Some projects have used only portland cement,but more commonly a mixture of 25 percent fly ash and75 percent portland cement has been used.

RCC installed in severe climat e areaThe first major RCC pavement built in a really seve re

climate was an 11-mile haul road from the Bull Mo o s eCoal Mine to a railhead at Tumbler Ridge, the newe s tt own in Canada. This is about 75 miles southwest of

Dawson Creek, beginning point of the Alcan Highway inn o rtheast British Columbia. Along with the road there was also a 6-acre load-out at the railhead, built in the latefall of 1983 over extremely poor subgra d e. The load-outa rea has 7 inches of RCC with no other surfacing. Thero a d — 6 1 ⁄ 2 inches of RCC plus 1 1 ⁄ 2 inches asphalt surf a c-ing—was designed with no base course, but in many ar-eas of poorest subgrade the contractor put down a gra n-ular base as a working platform .

The RCC mix had 12 percent cementitious materi a lby weight, half portland cement and half natural poz-zolan from a local sourc e. It was designed for a flexura ls t rength of 450 psi at 56 days. Two pavers operated inechelon, one about 150 feet behind the other in the ad- joining lane. Cu ring was by water truck for the first few h o u r s, followed by an application of asphalt emulsion.Much of the RCC froze hard the night after it was placed.

We inspected this work in the summer of 1985 be-cause of great interest in the durability of RCC pave m e n tin extremely seve re climate. The asphalt surfacing on theroad has deteri o rated considera b l y, but the RCC has per-f o rmed ve ry well, with the only distress spots show i n g

w h e re subgrade support was extremely poor. In theload-out area where the RCC is exposed without others u rfacing, it seemed to be in perfect condition, show i n g no sign of fre eze-thaw deteri o ration. The road is usedby 7-axle coal trucks with a gross weight of 80 tons, op-e rating 24 hours per day year ro u n d .

EXPERIENCE IN THE UNITED STATESMe a n w h i l e, use of RCC pavement began in the Un i t e d

St a t e s, at first only by the U.S. Army Corps of En g i n e e r s.In 1983 a small area of RCC pavement was placed on atank road at Fo rt St e w a rt, Ge o rgia by the Wa t e rways Ex-p e riment Station, using troop labor from the post. Al-though the road was placed in an area of poor subgra d eusing rather pri m i t i ve paving methods, the users havebeen most pleased with the finished pro d u c t .

Tank area built at Fort HoodThe first significant RCC pavement in the Un i t e d

States was constructed at Fo rt Hood, Texas by the Fo rt Wo rth Di s t rict of the Corps of En g i n e e r s, aided by the Wa t e rways Ex p e riment Station, in August 1984. This wasa large parking area for tanks and other tracked ve h i c l e ss u r rounding a maintenance shop. An 18,000-square - y a rd area of 10-inch pavement was placed in one lift, ata cost of about $58 per cubic yard in place.

The RCC mix contained 300 pounds of portland ce-ment and 160 pounds of fly ash per cubic yard. Most of the RCC contained 1 1 ⁄ 2-inch maximum size aggre g a t e,g raded to ASTM C 33 specification, with separate finea g g re g a t e. This aggregate size did pose some pro b l e m s.T h e re was a tendency tow a rd segregation during han-dling, and the surface finish was not as good as had beenobtained with smaller aggre g a t e s. A small area was made with 3/4-inch maximum aggre g a t e, and this mix han-dled much better.



Weather was also a problem at Fo rt Hood. A temper-a t u re of 100 degrees F with the wind blowing made i tdifficult to pre vent exc e s s i ve drying of the surf a c e. Ori g-inally it was planned to saw joints similar to those inconventional concrete pavements; this proved imprac-tical and the pavement was left unjointed. In spite of d i f f i c u l t i e s, beams sawed from the pavement tested at800 to 900 psi, well above the specified flexural strengthof 650 psi.

Test road built at Fort Lewis

In t e rest in RCC pavement is really booming in the Pa-cific No rt h west, in part because of information coming in from British Columbia. The Seattle Di s t rict of theCorps of Engineers built the first RCC pavement in thisa rea in October 1984. Du ring construction of this testroad at Fo rt Lewis, Washington, many visitors from sur-rounding areas came to observe, and afterw a rd a live l y i n t e rest in RCC pavements developed in the commerc i a lf i e l d .

The Fo rt Lewis test road was 23 feet wide, 700 feetlong, and 8 1 ⁄ 2 inches thick. It was constructed in a port i o nof a well-used gra vel road from which 8 1 ⁄ 2 inches of sur-facing and base had been re m oved so the finish grade of the RCC would match the former surface gra d e. Se ve ra lva riables we re tried during this construction so thattheir effectiveness could be compared. The road wasbuilt in two lanes and on two different days so that there would be cold construction joints, both longitudinal andt ra n s ve r s e. Two different mixes we re used (see table).Mix A, used for about two-thirds of the test road, includ-ed portland cement, fly ash and natural gra vel. Mix B,used for the other third of the work, had only port l a n dcement and a crushed 5 ⁄ 8-inch maximum size aggre-

gate—an asphaltic concrete aggregate used by the Wa s h-ington De p a rtment of Tra n s p o rtation, with 7 to 10 per-cent passing the No. 200 sieve.

The pro p o rtioning (feeding) and mixing equipment we re essentially the same as that used in British Co-lumbia (described on page 291), but two aggre g a t efeeds we re needed for Mix A because it had both coarseand fine aggre g a t e. Tra n s p o rt ing, paving and ro l l i n g p ractices we re also like those used in Br itish Co l u m-bia. The number of passes with the ru b b e r- t i red ro l l e r was va ried to study the effect. The general opinion wasthat two passes helped tighten up the surf a c e, but morepasses tended to degrade it. The 3 ⁄ 4-inch gra vel mix (Mi x A) placed and finished wel l, alt hough the 5 ⁄ 8- i n c hc rushed asphalt aggregate mix was even easier to han-dle and finish.

Both mixes consistently produced RCC surfaces to ana ve rage 3 ⁄ 16-inch tolerance when measured tra n s ve r s e l y with a 10-foot stra i g h t e d g e. Tra n s verse cracks deve l o p e dat 50- to 80-foot spacings. Early strength tests on beamss a wed from the pavement showed Mix B (no fly ash) 30to 40 percent stronger than Mix A (see table).

New paver at Port of Tacoma freight yardEarly in the spring of 1985, the Port of Tacoma, Wash-

ington began building the first of three freight handling areas along trackage at the docks, each having 35,000 to50,000 square yards of 12- to 17-inch RCC pave m e n t .These paved areas are designed for storage of larg ef reight containers, parking of piggyback tra i l e r s, andfor the operation of “piggy-packer” straddle cranes withaxle loads of 205,000 pounds, which handle the fre i g h tcontainers.

The RCC mix was designed with 450 pounds of port-

Vibratory roller was t he only compaction equipment neededfollowing the paver at Portland Airport. Specificationsrequired rolling to begin within 10 minutes of placementand to be completed within 60 minutes from start of mixingat t he plant.

Material/property Mix A Mix B

P ortla nd c ement 350 pounds 520 pounds

Fly a sh 180 pounds —(Class F)

C oa rs e a gg reg ate 1935 pounds , 3500 pounds ,3 ⁄4-inch gravel 5 ⁄8-inch, crushed

S a nd 1560 pounds —

Wa ter 168 pounds 203 pounds(20.3 g a llo ns ) (24.5 g a llo ns )

28-da y flexura l 600 ps i 800 ps istrength

90-da y flexura l 690 ps i 960 ps i

strength

RCC MIXES FOR FORT LEWIS TEST ROAD,PER CUBIC YARD



land cement, 100 pounds of fly ash and the same 5 ⁄ 8- i n c hc rushed aggregate used in the Fo rt Lewis test section. Onthe first area, the low bidder’s price was $1,764,000 forRCC, compared with $2,275,000 for a conventional port-land cement concrete option.

The first two RCC projects at the Tacoma docks we rebuilt with equipment similar to that previously de-s c ribed, but on the third project a Ge rman paver new tothis country was used. The machine is similar to Ameri-

can asphalt pave r s, but heavier duty, capable of laying anRCC lift of 12-inch compacted thickness. It wasequipped with two tamping screeds which can compactthe material to 94 to 95 percent of modified Proctor den-sity as it comes out of the pave r. Thus the single ro l l e rf o l l owing did l ittle additional compaction, causing al-most no settlement of the pavement surface—a gre a ta d vantage in maintaining finish tolera n c e s.

RCC at Port land International AirportEarly in 1985, the Po rt of Po rtland, Oregon invited bids

for construction of 41,000 square yards of airc raft park-ing apron for 747 jumbo jets at Po rt land In t e rn a t i o n a l

A i r p o rt. Because of long term loading conditions, bothp o rtland cement concrete and RCC we re considered asa l t e rn a t i ves to asphalt concre t e. The plans and specifi-cations we re pre p a red for RCC and asphalt concrete al-t e rn a t i ve s. When the bids came in, port officials selectedthe cheaper RCC altern a t i ve, which was almost 25 per-cent below the lowest asphalt bid. Total cost of the RCC was $40.73 per cubic yard in place.

The 14-inch pavement was placed in two lifts on 4 to6 inches of granular base. The mix consisted of

• 488 pounds portland cement

• 119 pounds fly ash• 260 pounds water

• 3256 pounds 3 ⁄ 4-inch-maximum aggre g a t e

per cubic yard. The aggregate was a modified Ore g o nState Highway gradation, crushed material with 5 to 10p e rcent passing the No. 200 sieve. The water-(cement +p oz zolan) ratio was 0.43.

The two equal lifts we re placed with a paver similar tothe one used at Tacoma. The rectangular apron wasp a ved longitudinally in widths va rying from 18 to 24 feet.Each longitudinal lane was divided into three sections sothat the paver could get back to the beginning of the lanebeing paved to start placing the top lift before the bot-tom lift was over 60 minutes old, as re q u i red by the spec-i f i c a t i o n s. The single paver with vibrating screed was fol-l owed by a single vibra t o ry ro l l e r. The speci ficat ionscalled for burlap curing mats and fog spray 24 hours perday for 7 days. Cu ring compounds we re not permitted asan altern a t e.

STRENGTH, DURABILITY SUGGESTWIDER USE OF RCC PAVEMENT

A 1985 survey by the Po rtland Cement Associations h owed more than 283,000 square yards of completedroller compacted concrete pavement in the Un i t e dSt a t e s. The Seattle Di s t rict of the Corps of Engineers now has under contract at Fo rt Lewis the construction of ap a rking area for tracked vehicles around a maintenances h o p. This job invo l ves 16,000 square yards of 8 1 ⁄ 2- inch

RCC pavement with a mix similar to the5

⁄ 8-inch cru s h e da g g regate mix used at Fo rt Lewis (Mix B. in table). Atleast 12 additional projects are under active considera-tion in the U. S.

Durability of RCC pavementsOne quality that was of concern when RCC was first

c o n s i d e red for pavement use was its durability when ex-posed to fre eze-thaw conditions. This concern led to in-vestigation of the RCC pavements in British Co l u m b i a —at Ca ycuse with years of fre eze-thaw cycle exposure, andat Tumbler Ridge where extreme cold conditions arecommon. Nothing thus far has shown the RCC to have

any problems with fre eze-thaw durability in serv i c e.The Corps of Engineers Wa t e rways Ex p e riment St a-

tion and Cold Regions Re s e a rch and En g i n e e ring Labo-ra t o ry have been doing labora t o ry studies to determ i n e what qualities the RCC material has that would protect itf rom fre eze-thaw damage. No one has re p o rted being able to get air- e n t raining agents to work with RCC ma-t e ri a l s, but there is speculation that entrapped air vo i d sin the in-place RCC may lend some measure of dura b i l-ity to it.

Good strengt hs; expanded use predict edSt ru c t u ral design for RCC pavements has thus far been

similar to that used for conventional pavement, basedon the strength attained in the RCC. We do not expectthat this will change. The RCC pavements tend genera l-ly to have higher flexural strengths than conve n t i o n a lc o n c rete pave m e n t s. The test project at Fo rt Lewiss h owed that the RCC had about 100 psi higher flexura ls t rength than conventional concrete with the same ce-ment content at 14, 28 and 90 days. This may be due toboth the lower water-cement ratio and the high degre eof consolidation for RCC .

O ri g i n a l l y, RCC was considered only for such uses ass l ow speed pave m e n t s, parking lots and roads fort racked ve h i c l e s. Howe ve r, recent uses have begun toindicate that it may be suitable for higher quality, higherspeed pave m e n t s.

P U B L I C AT I O N # C 8 6 0 2 8 7Copyright © 1986, The Aberdeen Gro u pAll rights re s e r v e d

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Paving With Roller Compacted Concrete_tcm45-341209