Lightweight Concrete for 's Highway Bridges by James E. Roberts, Director, Engineering Service Center, Chief Structures Engineer, California Department of Transportation Introduction turallightweight concrete, incorporating the The California Department of Transportation latest t~chnolQ.gical developments. Qu~stions (Caltrans) has used expanded shale structural regarding the shear stren.gth an~ ductile per- lightweight concrete for bridge construction formance of structural lightwelgh~ co~crete as a substitute for normal weight concrete for hav~ pr~mpted res~arch at the Urnverslty of b th 1 t f Id b .d d k d Callforrna at San DIego, funded by Caltrans. o repacemen o o er n ge ec s an widening, and new bridge construction on the Background California State Highway S~stem f?r the past Caltrans bridge engineers have designed and forty five years. A 1986 Desl~n Polic.y Memo constructed expanded shale structurallight- sugg~ststhe use of structural lightw~~gh~con- weight concrete bridges or bridge compo- crete III deck replacement and rehabilitation at nents since the mid 1950's. The use was ~ '.'.'h~I':~!00.:l!agg~~g.a:~~ ~~ unsuit primarily iurdc;l:k:c;Ic;IIlc;IIr~rcr-teduceme-d able, as a cost e~fectl~e ~aten~ for long span load imposed on supporting superstructures, structures, and III seismIc regions where su- bents, abutments and foundations. The addi- perstructure dead loa;d nee~s to .be reduced. tional weight imposes severe problems on Examp~es of four ~aj?~ projects Illustrate the foundation design in a highly active seismic d.urabllity and reliability of a pr?perly .de- zone. A total of 15 major bridges have been signed and constructe~ structural lightw~lght designed with structural lightweight concrete aggregate co~crete b?dge. Cost comparisons decks. There have been several bridges de- o~ st:ructural li~~twel~ht aggregate structures signed using structural lightweight aggregate bid III co~petition With struc~ral steel and concrete for the entire superstructure to fur- normal weight concrete al~ern~ti~e.structur~s ther reduce substructure design requirements demo?strate the economIc viability of this in poor foundation materials. Two of those matenal. have been in service for several years. .The ?utstanding performance of Caltrans ' Structural lightweight concrete has been used lightweight concrete bnd¥~s u~de~he~vy traf -for decks with the typical normal weight con- fic, and the.close ~ompetition III ~Iddlllg su.g- crete topping or polyester concrete overlays gests that lightweight aggregate IS a matenal b t al h b tru ted . u sever ave een cons c WIth out which should be considered III future bndge t .E. ht fth b .d h b . designs, especially in earthquake country Oppln.g. Ig O ese n g~s ave een III where dead load is such an important factor in place. III e~cess of 30 years With no apparent seismic design. The known consistent creep, detenorati~n of ~e deck concrete. In 19~7 shrinkage and modulus of elasticity properties stru~tural lightweight .concrete. was used III of lightweight aggregate concrete remove any portions of the conventionally relllforced con- doubts about performance as Caltrans' struc- crete box girders on the Tenninal Separation tures have shown. The industry advances in Interchange at the west end of the San controlling lightweight aggregate moisture Francisco-Oakland Bay Bridge. Lightweight content have considerably reduced the han- aggregate was used to bring the concrete dling and finishing problems of earlier years. stresseswithin reasonable limits while simul- Preliminary plans to bridge two large bod- taneouslysatisfying the aesthetic requirements ies of water in the Bay Area of the site. In the mid 1960's, the San with long span structures over 1.5 miles (2.4 Francisco-OaklandBayBridgewasconverted km)inlengthhaspromptedCaltranstoreview to one-way traffic on each level, requiring and update the overall policy on use of struc- continued on next page Portland Cement Association

strengthening of the upper deck to carry mod- alternatives to the bidders as possible. The concrete alternative would be competitive. ern truck traffic. Since it had previously car- design assumptions for structural lightweight When the study was completed it concluded ried only automobile traffic, substantial concrete creep and modulus of elasticity were that the savings in substructure would offset strengthening of the deck support system was obtained from historical data maintained by the additional cost of lightweight concrete required and lightweight aggregate concrete the manufacturer. aggregate and the Caltrans designers prepared decks were used to reduce those requirements. two alternative designs for the final bidding. It had been assumed after the study that the five Napa Bridge column bent required for the normal weight The Napa River Bridge was designed in concrete alternative could be reduced to three 1973-74 and constructed in 1975-77. It is a columns for the lightweight alternative. un- thirteen-span continuous post-tensioned fortunately, during final design some difficult cast-in-place structural lightweight concrete foundation problems caused by underground box girder with a total length of 2230 ft (680 utilities were encountered and the total sav- m). It carries four lanes of State Highway 12 ings anticipated in foundations were not over the NapaRiver, immediately south of the achieved. The normal weight concrete alter- city of Napa and about 35 miles (56 km) native was estimated at $29. 78 million and the northeast of San Francisco. It was designed as Figure 2 Napa River Bridge lightweight concrete alternative was estimated an alternative to a structural steel girder sys- at$30.56 million. The normal weight concrete tem. Both alternatives were advertised. Seven The successful bidder, Guy F. Atkinson alternative was low bid at $ 26.35 million, a bids were received. Six bids were for the Company of South San Francisco, California savings of $ 3.43 million below the lowest prestressed concrete box girder, including the proposed an alternative construction method Engineer's Estimate foreitheraltemative. With lowest bid of $10.96 million. The seventh bid from that assumed by the designer. The the proper site conditions, the lightweight alter- was for the structural steel girder; it was the Caltrans Standard Specifications forconstruc- native would have been extremely competitive highest bid at $16.66 million. tion contracts provide this option to bidders. and may have been the lowest bid. The com- Atkinson chose to construct the bridge as a The bridge superstructure is constructed petitive position of lightweight aggregate con- modified form of segmental construction by entirely of expanded shale structural light- crete is close enough to warrant further designs. building segments up to 100 ft (30.5 m) in weight aggregate and has shown no signifi- From the perspective of the owner agency, the cant problems during its 20-year life. Spans length on steel falsework towers (see Figure competition generally results in a lower bid, range from 150to 250ft (45.7 to 76.2 m) over 1). The long segments were partially regardless of the successful alternative. the main river navigation channel and are post-tensioned and the falsework removed and relocated asconstruction progressed across supported on 100 ft (30.5 m) nonnal weight San Juan Creek Bridge the valley. Figure 2 shows a general view of concrete piers and prestres3sedconcrete piling. This bridge is on State Route 74 east of San The 11,000 cu yd (8410 m )of structurallight- the completed bridge. ~ -~ weigfit-concrete utilized expanded shaleaggre- Jua!l Capistrano in Orange County. It is de- Benicia-Martinez Bridge Widening signed as a 267-ft (81.4-m) two-span pre- gate produced by Port Costa Materials at their stressed structural lightweight concrete box- Port Costa, California plant, located approxi- The Benicia-Martinez Bridge is a 7200-ft girder structure as an alternative to a hard rock mately 20 miles (32 km) from the bridge site. (2195-m) deck truss carrying four lanes of Interstate 680 over the Carquinez Straits ap- concrete structure. Structural lightweight con- This bridge is not only an economical alter- crete is being used to generate some competi- native in direct competition with structural steel proximately 30 miles (48 km) Northeast of tion in bidding in Southern California. The but is an aesthetic award winner in national San Francisco. The bridge was completed and bridge provides a 42 ft (12.8 m) roadway and competition. It has been inspected annually opened to traffic in 1962 and utilized a struC- is replacing a deficient older bridge. The project since 1977 and there are no apparent problems turallightweight concrete deck with normal with the structural lightweight concrete. weight concrete topping. In 1988 plans were is scheduled for completion and advertising in completed to widen the bridge deck from four late 1997. to six lanes to handle increasing traffic. In Future Plans for Structural order to minimize the additional reinforce- ment of the existing deck truss, the deck Lightweight Concrete widening was also designed and constructed Two major crossings of the Carquinez Straits of expanded shale structural lightweight con- at the northeast end of are crete with a polyester concrete overlay. The being planned and the use of structurallight- deck widening project was completed in June weight concrete superstructures is being con- 3 sidered at both sites. The 1991. A total of 2600 cu yd (1990 m ) of structural lightweight concrete was used in the site is on Interstate 80 at Vallejo where two deck widening. A parallel five lane bridge is bridges carry the east and west bound lanes. The west bound bridge was erected in 1927 Figure 7 Nopo River Bridge during currently being designed with a structural lightweight concrete superstructure. and is severely overloaded by the current truck construction. loads. A new westbound bridge has been The design drawings and bid documents Street Viaduct financed and design studies are underway. were based on the assumption that the bal- This bridge is a ten-Iane 3500-ft (1067-m) Several alternatives were studied, including a anced cantilever method of construction would viaduct carrying Interstate 105, the Century structural lightweight concrete segmental be used. All final camber and prestressing Freeway, over an industrial area with complex bridge superstructure. In any bridge con- diagrams as well as assumed form traveler foundation problems. At the request of the structed at this site the decks will be con- loads were indicated on contract drawings Port Costa expanded shale lightweight con- structed of structural lightweight concrete. based on this assumption. Optional details for crete aggregate producer, the Department al- The Benicia-Martinez site is on Interstate precast girder segments were also provided on lowed a consultant to prepare conceptual de- 680, upstream of the Carquinez site, and par- the contract drawings to provide as many signs to show that a structural lightweight allel to the bridge which was recently wid-

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DEFORMED BARS -cont'd Structural Intermediate Hard Cold-twisted I Corrugated Square Bar Corrugated Square Bar Yield min., 33,000 40,000 50,000 Type A Type B 55,000 (379) psi (MPa) (228) (276) (345) {IIJ~7J.~ ~/I-J! 1-,4~ 55,000 (379) 70,000 (483) UUU] lJ[j--~=~--1[JI Tensile, 55,000 n/a to to Rolledfor ConugetedBar Co. psi (MPa) (379) min 70,000 (483) 85,000 (586) Deformations were not standard, and in Defo17lled Steel Bars for Concrete Reinforce- fact very dissimilar compared to present mark - e~ [~i3[~ ment, designated A 305-50T. A 305 required Corrugated Round Bar Corrugated Square Bar ings. Most were patented and particular to the minimum deformation heights, a maximum Type C Type D producing mill, and were labeled cup, corru- angle of the deformations with respect to the Lug Bar -Type A Lug Bar- Type B gated, lug, herringbone, or by the name of the bar axis, deformation spacings per foot, and inventor, such as Havemeyer, Elcannes, the overall length of the deformations. Scofield, or Thacher. Bar sizes were also not It was not until 1964 that A8TM A 408, standard, with each manufacturer publishing a Special Defo17lled Round Bars, namely #148 list of sizes available from that mill. Shapes (44 mm diameter) and #188 (57 mm diam- were round, square, oval, flat with either raised eter), originally 1-1/2 in. (38 mm) sq and 2 in. lugs or depressed dimples. A conservative (51 mm) sq, now round with the same cross- estimate of the steel grade of the reinforcing sectional area, became available in the same bars furnished for a concrete structure built grades as A 15. In the same year (1964), Herringbone Bar between 1910 and the mid 1920's would be A8TM adopted two higher strength grades of Havemeyer Square Bar Havemeyer Round Bar structural grade. reinforcing steel: A 432-64, yield 60,000 psi Effective January 1, 1928, the U.S. De- (414 MPa)min., tensile 90,000 psi (621 MPa) partrnent ofCommerce recommended that the min., and A 431-64, yield 75,000 psi (517 "Standard" for new billet reinforcing bars be MPa) min., tensile 100,000 psi (690 MPa) intermediate grade. In effect, this suggested min., for sizes #3 (10 mm diameter) through not specifying structural grade reinforcing #188 (57 mm diameter). bar. It is interesting to note that in 1928, A 15- flffl Finally, in 1968, A8TM adopted A 615-68 Elcannes Bar 14 was still in effect. During the decade of the titled Standard Specifications for Defo17lled 1920' s, the producing mills standardized rein- Billet Steel Bars for Concrete Reinforcement. forcing bar to: 1/4 in. (6 mm) rd; 1/2 in. (13 A 615 incorporated previous A 15, A 305, A Wing Bar- Type A Wing Bar- Type B mm)rd; 1/2 in. (13 mm)sq;5/8in. (16mm)rd; 408, A 431, and A 432 into one specification, 3/4in,(19mm)rd;7/8in. (22 mm)rd; 1 in. (25 and also eliminated structural grade steel and BfIiiiiiiilJ mm) sq; 1-1/8 in. (29 mm) sq; 1-1/4 in. (32 plain round reinforcing bar, listing three grades: mm) sq; 1-1/2 in. (38 mm) sq; and 2 in. (51 Or40 (276MPa yield strength) and Or 60 (414 Rolled lor Trussed Concrete Steel Co. mm) sq. During the same decade, each mill MPa yield strength) in sizes #3 ( 10 mm diam- developed its own deformation or brand pat- eter) through #18 (57 mmdiameter) and Or 75 ffI:IlJ tern with a quality mark "N" for new billet, (517 MPayield strength) in sizes#ll (35 mm New Rib Bar plus a letter or symbol designating the produc- diameter), #14 (44 mmdiameter), and#18 (57 ing mill. Thus, intermediate grade new billet mm diameter) only. reinforcing bar became typical into the 1930' s In conclusion, it is reasonable to assume through the 1940's As a historical note, the 1/ that a reinforced concrete structure built in the 2 in. (13 mm) sq size was eliminated in 1942 period 1910 through 1927 was reinforced with as a war emergency measure. structural grade (Or 33 or 228 MPa yield In 1950, ASTM revised the specifications strength) deformed reinforcing bars, and from pertaining to new billet reinforcing bars. 1928 through 1963 with intermediate grade ASTM A 15-50T changed all reinforcing bars (Or 40 or 276 MPa yield strength) deformed to round, designated #3 (10 mm diameter) reinforcing bars. Of course, during these same through #11 (35 mm diameter), replacing 3/8 periods higher strength steel reinforcing bars in. (10 mm) rd through 1-1/4 in. (32 mm) sq. were available and may have been used or #2 or 1/4 in. (6 mm) rd was not classified as specified for a particular project; however, deformed, and was available only as plain unless specific data are available regarding the round. However, A 15-50T still listed plain grade of the material supplied to that project, and deformed reinforcing bar with the same conservative judgment would use the forego- three grades: structural, intermediate and ing values of the grade of steel when evaluat - hard. At the same time, ASTM issued Tenta- ing an "elderly" structure. tive Specifications for the Deformations of

Printed in U.S.A. PL279.0lD