Self-Consolidating Concrete Serving Faith at Awe-Inspiring Pedestrian Bridge M.L. Nehdi1,2 and K. Al Shareef3 1,2
2
Professor, Department of Civil and Environmental Engineering, Western University, Canada,
[email protected] Senior Consultant, and 3General Manager, Modern Technology Laboratories, Jeddah, Saudi Arabia,
[email protected].
ABSTRACT This paper reports the use of self-consolidating concrete in the construction of the $US 1.2-B Al-Jamaraat Bridge. The pedestrian bridge located in Mina, near Makah in Saudi Arabia is used by Muslims in the annual Hajj rituals. More than one million people can gather at the bridge site during Hajj, which has led to fatal stampedes and accidents in the past. In 2006, the original single tear (ground level and single floor) bridge constructed in 1963 with its various subsequent expansions has been demolished. A four-level segmental bridge with underground tunnels, access ramps, service buildings and helipad towers was constructed and completed in 2009. In total, more than 400,000 m3 (520,000 cu. yd.) of 60- and 80-MPa self-consolidating concrete (SCC) along with 80-MPa steel fiberreinforced SCC have been used in the edge beams, columns and retaining walls, and in stitching precast segmental bridge elements. SCC helped solving reinforcement and duct congestion problems, enhancing finish-ability and accelerating the construction schedule. This large-scale experience with SCC is described in this paper and relevant aspects of the substantial database developed on SCC in this project are discussed.
Keywords: Self-consolidating concrete, fiber-reinforced, reinforcement congestion, retaining wall, finish-ability, Al-Jamaraat Bridge.
1
IN NTRODUCTIION The Jamaaraat Bridge (F Fig. 1) is locaated in Mina, Saudi Arabia near the Holyy City of Makkah. The bridge is used by Muslims in the stoningg of the devil ritual r during H Hajj. The annuaal Hajj, or pilggrimage to Maakah, is amongg the largest mass gathherings in thee world. In 20012, it took place on Octobber 24–27 andd drew about 3 million Muuslims from around thhe planet. The bridge enablees pilgrims to throw t pebble stones at the tthree Jamrah ppillars (Fig. 2)) from either the grounnd level or froom the bridge.. The Jamrah pillars extendd up through thhree openingss in the bridgee. Originally constructeed in 1963, thhe bridge wentt through seveeral expansionns. Yet, until 2006 2 it had a ssingle tier, connsisting of a ground leevel with one bbridge level abbove. During m mid-day peak hhours, over a m million peoplee may gather in the area off the bridge, which w in severaal occasions has led too accidents. S Several fatal stampedes havve been widelyy discussed inn the media. For F instance, on May 23, 1994, a sttampede killedd at least 270 ppilgrims. On A April 9, 1998, around 118 pilgrims were ttrampled to deeath and 180 were injuured. On Marcch 5, 2001, 355 pilgrims werre squashed too death in anoother stampedee. On Februarry 11, 2003, the stoninng of the devvil ritual claim med the lives of 14 pilgrim ms. Another 2551 pilgrims w were killed annd 244 were injured inn a stampede tthat occurred on o February 11, 2004. On Jaanuary 12, 20006, one of the worst stampeedes claimed the lives of o at least 3466 pilgrims and injured 289 m more. The multiple fatal stam mpedes have m motivated rethhinking the maanagement off the large crow wd in the briddge vicinity. major construuction work inn and around tthe Jamaraat Subsequeent to the 20044 incident, Saaudi authorities engaged in m Bridge arrea. The old brridge was dem molished and cconstruction oof a new multii-level bridge w was initiated. The ground and first levels were coompleted to aaccommodate tthe 2006/20077 Hajj (subseqquent to the Jaanuary 2006 H Hajj above), which didd not experiennce stampedess. The two subbsequent levells were complleted for the D December 20007 Hajj. The new bridgge exhibits brroader columnn-free interiorr space. The three cylindriical Jamrah piillars were reeplaced with taller andd several timess longer wallss of concrete to t enable simuultaneous access for more ppilgrims. Mulltiple ramps, access waays, footbridgges, tunnels annd emergencyy exists were built b for easieer access. Botttlenecks weree engineered out through enhanced ccrowd manageement schemees. Large canoopies cover eaach of the threee Jamrah pillars to shade wa (religious ddecree) was isssued to encouurage expandiing the time pilgrims ffrom the deseert sun. Additiionally, a fatw period off stoning betweeen sunrise annd sunset, ratheer than at the traditional t lim mited mid-day ppeak hours.
Figure 11– Aerial view w of Al-Jamaraaat Bridge durring constructiion on Octobeer 31, 2006.
2
(a)
(b)
F Figure 2 – Jam mrah (a) during constructionn, and (b) afterr construction during stoninng the devil rituual.
GE CONSTR RUCTION AN ND NEED FO OR SCC BRIDG The imprrovement of A Al-Jamaraat Brridge and surroounding area was w a project led by the Sauudi Ministry oof Municipal and Rurall Affairs. Thee main contracctor for the prooject is SBG aand the consuultant is Dar Al A Handasah. T The primary ready mixx concrete suppplier for the pproject was BC CS from its A Al-Iskan and M Muzdalifah batch plants. Thee bridge was designed using a moduular concept (Fig. 3) involvving cast in-siitu columns, rretaining wallss and edge beeams, with a s girdder elements. More than onne million cubbic meters of concrete c weree used in the slab cast over precast segmental constructiion of the briidge, among w which about 4400,000 m3 iss grade 60 MP Pa and 80 MP Pa SCC. Usinng SCC was adopted aafter actual coonstruction beggun and regullar high-perforrmance concreete faced diffiiculties in conngested steel and obstrructed access areas. It was determined affter preliminarry trials that S SCC would acccelerate the construction c scheduless, enhance finnish-ability, aand overcomee problems inn casting conccrete elementss having congested steel reinforcem ment. Figure 4 illustrates an example of coongested steell reinforcemennt that is encouuntered in coluumns, retaininng walls and ms and the caasting of a reetaining wall uusing 60-MPaa SCC. Post construction c aanalysis demonnstrates that edge beam using SC CC was instrum mental in meeeting construcction schedulees, reducing pproject delays, enhancing pproductivity, easing labbor demand foor the casting, vibration andd finishing of concrete, c and mitigating prooblems of honney combing or other laack of concrette compactionn.
MATER RIALS AND M MIXTURE DE ESIGN FOR SCC IN AL--JAMARAAT T BRIDGE mixture designns for the 60--MPa and 80--MPa self-connsolidating cooncrete used inn Al-Jamaraaat bridge are Typical m presentedd in Table 1. ASTM A C150 ordinary o portlaand cement waas used. Consiidering that neeither fly ash nnor slag was producedd locally, theirr sustainabilityy benefits are largely comprromised due tto shipping froom overseas. Hence, they p suppllementary cem mentitious matterial. Local were not utilized in this project. Sillica fume wass used as the primary 1/2- and 33/8-inch crushhed granite coaarse aggregatee and natural sand were usedd. The coarse aaggregate wass treated in a double coone crusher to approach cubbic shaped parrticles and to remove r any weeaknesses. Its bulk specific gravity was 2.880 andd its absorptioon was 0.575% %. The sand had a bulk sppecific gravityy of 2.631, abbsorption of 1.605%, 1 and fineness m modulus of 2.885. The combined gradationn of the coarsee aggregate is illustrated in F Figure-5. A conventional c naphthaleene sulfonate superplasticize s er was used inn the 60-MPa SCC, while a polycarboxilaate-based superplasticizer was usedd in the 80-MPA SCC. A ccompatible rettarding admixxture was used in both mixxtures. Chilledd water and crushed iice were usedd for mixing to achieve frresh concrete temperature requirements. No viscosityy modifying admixturee was used. A gaseous expansion admixtture was usedd when SCC w was needed for stitching spaace between precast ellements.
3
(a)
(b)
B and (b)) constructionn of the first Figure 3 – Illustrationn of (a) modulaar design for tthe four-level Al-Jamaraat Bridge, levvel. PERFORMANCE OF SCC AND LESSONS L LEARNED The consttruction of Al-Jamaraat Briddge was carrieed out in a parrticularly hosttile environmeent for fresh cooncrete. The average m monthly tempperature exceeeds 30oC for all months off the year, annd is beyond 40oC betweenn April and October. Moreover, thee traffic to thee job site can ccause substanttial delays. Thhe job site itself has difficult access and is congested with simuultaneous consstruction activvities. Various hot weather cconcreting praactices have been adopted water for mixiing, light coloor paint and includingg shading of cconcrete ingreedients, using crushed ice and chilled w wetting oof burlap on concrete transiit trucks, use of o adequate coombination annd dosage of cchemical adm mixtures, etc. Yet, suchh practices alonne were not suufficient.
4
(a)
(b)
Figure 4 – Illustrationn of (a) exampple of congesteed steel, and 9bb) the actual use u of 60-MPaa SCC in the construction of retaiining walls forr Al-Jamaraat Bridge. T Table 1 – Mixxture proportioons for 60-MP Pa and 80-MPaa SCC Proportiion per m3 off concrete 60-MPa SCC 80--MPa SCC 450 450 27 50 160 150 0.335 0.300 464 336 758 918 1003 18.5 11.4 1.0 2.0 2.0
I Ingredient/Pr roperty ASTM C-150 Cement [kg/m A m3] 3 S Silica Fume [kkg/m ] F Water [kg/m3] Free w w/cm Ratio Aggregate [kg/m m3] 1/2” Coarse A 3 Coarse A 3/8” Aggregate [kg/m m3] 3 N Natural Sand [[kg/m ] N Naphthalene S Sulfonate Supeerplasticizer [kkg/m3] P Polycarboxilat te Superplasticizer [kg/m3] C Compatible R Retarding Adm mixture [kg/m3] E Expansion adm mixture
5
Fiigure 5 – Com mbined gradatiion of aggregaates used in the SCC mixturres versus AST TM C33 envellope.
Indeed, thhe superplasticcizer dosages used (Table 11) may appearr extreme com mpared to that ttypically adoppted in other locations with mild weeather. A paraadigm shift waas implementeed through foccusing on the rheological properties p of mping, rather thhan at the onsset of batch plants. SCC thaat may appear too fluid or SCC at joob site deliverry before pum vulnerablle to bleeding and segregatiion immediateely after mixinng arrived at the job site with w adequate slump flow, passing abbility and resiistance to segrregation and bleeding. A proocedure was aadopted for adjjusting workabbility on the job site uusing a speciffied amount of o chemical aadmixture to minimize thee occurrence oof rejecting ggood quality concrete. Achievingg consistent workability aand mechaniccal propertiess for the 4000,000 m3 of SCC was a particularly challenginng, yet achievvable undertakking. Table 2 shows an evalluation of com mpressive strenngth results foor 60 and 80 MPa SCC C according tto statistical pprocedures ouutlined in ACI 214R-02 (E Evaluation of Strength Testt Results of Concrete)). The coefficiient of variatioon for field coompressive strrength data relevant to conccrete with highher than 35MPa com mpressive strenngth (Table 3..3 in ACI 2144R-02) is conssidered excelleent when the ooverall variatiion is below 7.0-MPa and when thee within test vvariation is bellow 3.0-MPa. It can be obsserved in Tab ble 2 that the vvariation for both the 660-MPa and 80-MPa SCC w was excellent. Figure 6 provvides an illusttration of an exxample monthhly variation of comprressive strengtth for the 60-M MPa SCC. Thhe figure show ws a satisfactoory variation oof measured ccompressive strength. It is to bee noted that inn such a harsh hot weather eenvironment, sseasonal adjusstments of mixxture design aand seasonal variationss in compresssive strength aare to be exppected. For instance, the doosage of retarrder needs to be adjusted accordingg to seasonal ambient tempperature. In hoot summer weeather, concreete gained moore rapid strenngth at early age, yet thhe 28-days to 7-days strenggth ratio tendedd to decrease. This well doccumented trendd is mainly duue to the fact that higheer temperaturee curing leads to less refinedd microstructuure and less efffective hydratiion of cement grains. In the tessting of over one o million cyylindrical conccrete quality ccontrol specim mens from this large-scale SCC work, it was appreeciated that discrepancies inn compressive strength resullts can be due to variations iin sample prepparation and testing methods. m For innstance, signifficant discrepaancy between quality controol data measuured by the conntractor and that by thhe quality conttrol body in thhe project wass primarily linnked to end-suurface preparattion of test cyylinders. The contractor mainly adoppted grindingg of end surfaaces of cylindders, while thhe quality conntrol unit usedd a capping mes led to streength values beelow specificaations. proceduree that proved tto be less efficcient and at tim
6
Table 2 – Evaluation of compressive strength results for 60- and 80-MPa SCC (according to ACI 214R-02) n (Count)
(Average)
74 69 84 88 Control (Table 3.3)
S1 (within test)
S (overall)
V
4.1 3.9
5.9 4.4 Excellent
2.7 3.1
1.6 2.2
V1 (within test) 2.3 2.4 Excellent
60 80
Compressive strength in MPa
80.0 75.0
Measured compressive strength at 28 days 70.0 65.0 60.0
Design compressive strength
55.0 50.0 45.0
Measured compressive strength at 7 days
40.0 Monthly date for compressive strength measurement
Figure 6 – Illustration of an example of monthly variation of compressive strength for 60-MPa SCC. Another lesson to be learned in very hot weather concreting is that the early age curing of quality control cylinders can be very critical. In very hot weather dark plastic or metallic molds used to prepare quality control cylinders on the job site can reach temperatures beyond 70oC. Quality control cylinders would be stored on the job site at above 40oC for the first 24 hours. This had at occasions led to measured compressive strength data below the design value. Cores taken from actual structural members on the job site demonstrated that the below specification strength occurrence is only limited to the quality control cylinders and non-existent in the full-scale structural members. Indeed, there is a size effect so that the small cylinders are much more vulnerable to the effect of the mold and ambient temperature than the much larger full-scale members. It may be necessary to install a temperature controlled curing room on the job site to handle quality control specimens during the first 24 hours. It is therefore recommended that before transposing results from small quality control cylinders to large-scale structural members to conduct non-destructive testing, possibly with some coring in the full-scale structural member. Furthermore, it was observed in this large-scale SCC job that in very hot weather, it is critical to have a superplasticizer dosage beyond the saturation point (usually defined as the dosage beyond which no further reduction in the flow time of a cement grout can be achieved). It is to be understood that the superplasticizer saturation dosage is not constant when the ambient temperature changes and/or when the time of measurement (after first contact between cement and water) increases1-10. While SCC usually saves labor and reduces the concrete casting and finishing effort compared to normal concrete, more skilled labor would be needed for quality control and assurance at batch plants and job sites, particularly to take adequate decisions when the moisture content of aggregates changes, when there are delays in concrete delivery, and when rheological properties are below or above the specified range.
7
It is to be noted that most research on SCC pertains more to small-scale laboratory work1-10, and the engineer still faces challenges to develop cost-effective SCC that does not necessarily require very large binder contents and costly admixtures. Research on economic and resilient SCC, and particularly high-strength SCC for hot weather concreting for instance in tall buildings and for long hauling distance is still needed. CONCLUDING REMARKS About 400 thousand cubic meters of 60- and 80-MPa self-consolidating concrete was successfully produced in hostile hot weather and cast in a difficult access and congested construction site. The SCC achieved consistent workability and mechanical performance. The use of SCC in this awe-inspiring pedestrian bridge which serves the faith of about 1.5 billion people accelerated construction schedules, solved problems of casting concrete in densely reinforced and congestion structural members, and led to better finish surfaces. Particular observations from this very large scale experience with SCC include:
More focus should be on the properties of SCC immediately before pumping and properties should be worked out backwards towards the onset at the batch plant. To produce SCC successfully in hot weather, the superplasticizer dosage will likely need to be beyond the saturation dosage. Compatibility between the cement, superplasticizer and retarder in addition to using crushed ice and shilled water for mixing and adopting other recommended hot weather concreting practices are critical for producing SCC in hot weather. While SCC saves low-skill labor in its casting and finishing, it requires increased skilled labor and intellectual effort in quality control and assurance and in the decision making process to solve issues and variations in materials and properties during construction. In very hot weather, increased attention should be given to the curing conditions of quality control specimens during the first 24 hours on the job site before transport to laboratory curing and testing. Most literature on SCC coalesces around small-scale laboratory work, which does not necessarily transpose to real world full-scale challenges. There is still need for research on economic SCC that is resilient to stringent job site conditions. REFERENCES
1. S. Al Martini and M.L. Nehdi [2011], “Evaluation of use of self-consolidating concrete for hot weather applications”, Concrete Plant International, Issue 5, pp. 66-70. 2. Ghafoori, N. and Diawara, H. [2010], “Remediation of high temperature effects on self-consolidating concrete”, Proceedings of the 6th International Conference on Concrete under Severe Conditions, CONSEC'10, Vol. 2, pp. 1299-1306. 3. S. Al-Martini, and M. Nehdi [2010], “Genetic algorithm-based rheological equations for cement paste at high temperature and prolonged mixing time”, ICE Construction Materials, Vol. 163, Issue 2, pp. 77 – 85. 4. S. Al-Martini, and M. Nehdi [2010], “Effects of heat and mixing time on self-compacting concrete”, ICE Journal of Construction Materials, Thomas Telford, Vol. 163, Issue 3, August 2010, pp. 175 – 182 5. M. Nehdi and S. Al-Martini [2009], “Estimating time & temperature dependent yield stress of cement paste using oscillatory rheology and genetic algorithms”, Cem. & Conc. Res., Vol. 39 , No. 11, pp.1007-1016. 6. S. Al-Martini, and M. Nehdi [2009], “Genetic algorithm-based yield stress equations for concrete at high temperature and prolonged mixing time”, Journal of Computers and Concrete, Vol. 6, No. 4, pp. 343-356. 7. M. Nehdi and S. Al-Martini [2009], “Coupled effects of high temperature, prolonged mixing time and chemical admixtures on rheology of fresh concrete”, ACI Materials Journal, Vol. 106, No. 3, pp. 231-240. 8. S. Al-Martini, and M. Nehdi [2009], “Coupled effects of time and high temperature on rheological properties of cement pastes incorporating various chemical admixtures”, ASCE Journal of Materials in Civil Engineering, Vol. 21, No. 8, 2009, pp. 392-401. 9. M. Nehdi and S. Al Martini [2007], “Effect of temperature on oscillatory shear behaviour of portland cement paste incorporating chemical admixtures”, ASCE Journal of Materials in Civil Engineering, Vol. 19, No. 12, pp. 1090-1100. 10. S. Al Martini and M. Nehdi [2007], “Effect of chemical admixtures on rheology of cement paste at high temperature”, Journal of ASTM International, Vol. 4, No. 3, 17 p.
8
