Long History of Concrete

[Pages:4]HIST ORY R EPORT? N O . 6 4

Virginia takes its cont inuously reinforced concrete pavement (CRCP) seriously, so much so that the Virginia Department of Transportation (VDOT) undertook a rig orous analysis of the performan ce of its CRCP to identify be st practices for extending t he pavement se rvice life with minimal maintenance.

Long History of Concrete

Virginia has th e t hird larg est st ate-mainta ined hig hway system in the count ry, just behind North Carolina and Te xas (anothe r CRCP sta t e). VDOT built its first concrete pave me nt in 1913 and its first CRCP in 1966 on Inte rst ate 64 t hrough Richmo nd, Virginia's state cap ital. VDOT curre ntly has ap proximat ely 561 lane-miles of CRCP in se rvice, abou t thre e-quarter s of it on interstate highways and the remainder on st ate roads .

CRCP is, simply, conc rete pavement th at is reinforced with longit ud i-

~ nel steel bars. No transverse co nt ro l joints are needed . The reinfo rcing bars control the widt h of

the transve rse cracks that form and ho ld t he m closed. The t rans ve rse cracks do not impair the structural integ rity of the pavement .

Because of its g rea ter durability, lo ng er life expectancy, and minimal maintenan ce requirements, CRCP can provide th e best long-t e rm value of any pavement typ e .

CRCP circa 1970 (photo below): At 52 miles , '-64 west of Charlottesville wa s the longest stret ch of road opened to t he st at e a t on e tim e. The entire segmen t wa s built wit h CRCP.

"The key to attaining a long-lasting, safe, and economical CRCP is in learning from its performance.When we apply the lessons learned from our in-place pavement, we can build a better product in the future ."

- Andy Mergenmeier; P.E., VDOT Materials Engineer

~n c e- E n h a n C i n g Forensics

Most (Rep has performed satisfac-

~

torily over its intended service life and

well beyond.

For select (Rep segments that we re showing signs of wear or dist ress, VOOT performed extensive pave? ment condition surveys, which included field visits, coring, shoulde r trenching, la borat ory testing, and ana lysis of historic al data.

VOOI's pla n of action involves the collective effo rts of pavem ent d esign

e ngine er s. materials en g ine er s,

resea rchers, an d t he construction ind ustry. NEarly results are p romising," says Mohamed Elfino, P.E" Ph.D" Assistant State Materials Engineer with VOOT.

"Our resear ch has give n us m o re

confi dence that we unde rstand the behavior mechanisms an d how to improve upon past performance. In a way, that's what engineering is all about. N

VDOT has imp lemented improveme nt s to their CRCP design an d construction protocols on several highway p roje ct s now und e rway in the state, as described in the followi ng sections.

La r g e r Aggregate I mproves D urobi l ty

The long-pro mise d western loop arou nd Richmond , is near completion. A ne w hig hway, State Route 288, through Powhata n and Goochland Counties an d completion of the existing highway in Chesterfield County will bring a much-needed tr ans portat io n alternative to central Virginia.

Portions of existing SR 288 south of the city we re constructed wit h CRCP in 1989. CRCP will be used for the adjacent Chesterfield County portion of the p roject, which consists of adding new through-lanes in the me dian of the e xisting roadway, a total of approximately 6 miles.

"when constructed pr operly, it 's a good pav ement," not es Trenton Clark, P. E., VDOT Pavement Program

Engineer. "Based on the life-cycle cost analysis, the cost of CRCP would be within 10 perce nt of that of othe r pavements. We chose CRCP to be compatible with the existing pavement."

Several important findings from VDOT's pavement analysis have been incor porated int o the CRCP design for SR 288. For example, AASHTO #357 aggregate is being used in the concrete mix instead of #S7. #3S7 is a larger agg regate with a higher percentage in the on e - to two-inch range . NHaving more rock means that the amount of cement paste is reduced, which will le ad to reduced shri nkage an d cracking," says Clark. Nit's a more d urable mix."

VDOT 's Lessons Learned abo u t CRCP

Through extensive research and evaluation, VDOT has narrowed down the main factors influencing the long-term performance of continuously reinforced concrete pavement (CRCPJ in the state: material characteristics, pavement design, and construction practices. Here's what VDOT has concluded.

Slab T hickn ess a nd Stee l Cont ent

VDOT recom mends using a sla b of adeq uate th icknes s to reduce t he she ar stress at t he level of the reinfor cing steel cause d by bending mo men ts in t he slab. Depending on the site condition s, slab thickness may need t o be increased by up to 2 inches.

VDOT reco mme nds incre asing the t ot al amou nt of longitudinal reinforci ng steel from 0.65 percent to 0 .70 percent t o improve the crac k spacing, with t he goal of ha ving t ransverse cracks spaced 4 to 6 feet apart. VDOT also re comme nd s using transve rse reinforcing bar s spaced every 4 fe et t o support the longitudinal steel an d t o keep any longitud inal cracks tight (should they occur).

- - Poo r S ubgra de Calls fo r Thi c ker C RC P

. .., "- - ,,-,,!",, " . Traffic on US

,- ---- ~-

Rout e 29 , the

ana lysis of several pavement options. Although costs were dose, VOOT

) US

29

( "Lynchburg

Expressway," is

chose CRep for the mainline pavement. "We believe that (Rep will provide the

~==4

[NORTHI

anything but express . When built, US 29 was the preferred

best st ructu re, given the high traffic counts we expect this pavement to e xpe rience," says Don French, P.E., Dist rict Materials Eng inee r for VDOI's

route around the

lynchburg District.

"City of Seven Hills," but is now heavily congested with numerous stoplights and strip malls . VDOT's new US 29 Lynchburg/ Mad iso n He ig ht s Bypass project, 20 miles in total lengt h including connection projects, ramp, and loo ps, will provide an alternate route.

The project is underlain with "horrible" re sid ual micaceous silt, according to French. To compensate, VDOT is treating the top 8 inches of subgrade with cement (12 percent by volume), installing a 3-inch asphalt drainage layer under the pavement, and constructing a 12-inch-thick (R(P

VOOT pe rforme d a life-cycle cost

section (t he thickest so fa r in Virginia).

Again, recommendations made from VDOI's extensive (Rep analyses were incorp orate d into the design . For instance, the outermost la ne will be 14 feet wide to accomodate wheel loads at the pavement/ghoulder interface.

Concr ete P r o pe r t ie s

VDOT is alt eri ng t he concrete mix de sign for CRCP wit h th e objective of minimizing crac k widt h and increasing crack sp acing . VDOT has determined th at with larg er-sized agg re gate, concrete shrink age an d cracking is re d uce d. Large r agg re ga te is also expected to provide better aggregate interl ock, which will red uce the amount of crac king and improve lo ad t ran sfe r across th e cra ck.

Wi d er Outside Lan e s For the outside lane s, VDOT recommen ds using a 14-

foot -wid e lane while still de lineating (wit h white-line st riping) a 12-foot -wide lane. The extra two fee t width be comes pa rt of t he shoulder an d provides edge su pport equal to a fullwidt h tie d sho ulder without th e jo int .

The pavement on t he tr uck lane itself expe rience s interior loading as oppo sed to edge lo ading . This e xtra ed ge su pport red uces the po tential for ed ge failures and punchouts.

continlUl d on back

~-

~ G 00 de o n s t r u c t .i o n Great Pavement

e reates

Interstate 64 begins in Norfolk,

being widened. Currently under

runs in a tunnel under the Chesapeake

reconstruction is a 3-mil e-long seg-

Bay into Hampton and Ne wpo rt News , ment of 6-lane pavement that is bein g

and then travels all the wa y west to

demolished and rep lace d with

St. Louis, Missouri. 1-64 in the

8 lanes of CRCP.

Tidewater area of Virginia was built in the late 19505 to mid 19605 as a 4-lane freeway .

INTERSTATE

"The location of t he reinforcing ba rs within the section has a b ig impact on t he

Se ver al portions were con -

succe ss of t he pavement ,"

st ruct ed with (Rep, including

says Boykin. To th is en d, the

one 8-inch-t hick, 7-mile-long

reinfo rcing bars are being

se gment in Hampto n t hat is still

installed manually on chair

in se rvice, not having been

overlaid. uThe esc> has pro-

supp orts, rat he r t han me chanica lly thr o ug h tube fe eders

vide d ex celle nt perfo rmance

t hat have give n VOOT troub le

and has needed virtually no

in th e past.

mainte nance," notes George Boyki n, VDOT Dist rict Materials Eng ineer for t he Hampton Roads District .

Boykin also believes t hat const ructio n quality and rigo r in co nst ruct ion inspect ion is crit ica l with CRCP. "[f t he cont ractor pays care and attention

To day, t raffic vo lumes have far

du ring construction, CRCP is a great

outpaced capacity, and segments of

pavement. I don't see an y reason not

[-64 th rough the Tidewater are a are

to use it."

C o n s t r uct i o n Quol ity ...continu"dfrom in5id.

"CRCP is a complex st ructural system," says Andy Me rgenme ier, P.E., State Materials Engineer with VOOT. "We' ve found that t he long -t e rm performance of the pave me nt d e pe nd s on the qua lity of construction."

VOOI's main conclusion is th at mechanical plac ement (tube -fed) of reinforcement-in which re inforcing ba rs are fed through tubes directly into t he wet concrete-can result in less dependable re inforcing bar placement . VOOT has fo und that the reinforcing bars placed this way we re sometimes too high or too low

within the concrete slab, reading t o pre mat ure failures.

VDOT is now re commending that the longitud inal re inforci ng st eer be place d on con tinu ou s runne r chairs, with d ip s attached at pla nned widt hs, rather th an with the tube-fed syste m. The chairs allow t he slab to be po ured mon o lit hically, which re d uce s the probability for cord joints at the reinf orcing st eel th at have res ulted from pour ing two [ayers of concrete with t he feed-tu be syste m.

Virginia's Smart Road is a 5.7mile-long limited-access highway that will eventually provide a direct route between Int erstate 8 1 and Blacksburg in southwest Virgin ia. The Smart Road se rves as a st ate -of-t he-art resear ch lab fo r te st ing new t ransportation technologies, including pavem e nt types.

A D.8-mi[e-[ong section of th e Smart Road was co nstr uct e d with CRCP to allow t esti ng of variou s hypotheses about pav ement material performance and characteristics.

On e such research area particularly impo rtant for Virginia is the subgrade dr ainage layer. Half of the CRCP section was constructed using a Portland cement open-g raded drainage laye r and the other using an asphalt cement open-graded drainage layer.

Researchers are using groundpenetrating radar to mon itor the cha nge in mo isture in the drainage laye r and pav ement over tim e. Riding surf ace smoothness and texture are also being monitored. Results of this research are forthcomi ng.

CRCP

contlnuo",ly ,oln lo"od co n c ro .. p .. omon,

Concrete Reinforcing St eel Institute

CRSI 933 North Plum Grove Road

Schaumburg, IL 60173 ?2005

De, igned by Con""y

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download