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Roller Compacted Concrete Dams : A Review · Roller Compacted Concrete Dams : ... but at a cost...

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The Masterbuilder | July 2014 | www.masterbuilder.co.in 120 Roller Compacted Concrete Dams : A Review A CI 116 defines RCC as “concrete compacted by roller compaction; concrete that, in its unhardened state, will support a (vibratory) roller while being compacted. RCC is usually mixed using high-capacity continuous mixing or batching equipment, delivered with trucks or conveyors, and spread with one or more bulldozers in layers prior to compaction.RCC can use a broader range of materials than conventional concrete”. About RCC - Roller Compacted Concrete (RCC) has been rapidly developing over the past 40 years and is now commonly used for mass concreting operations typically in a Gravity Dam application. With a widely varied methodol- ogy of design theories and project specific considerations, RCC is not only extremely practical from a constructability standpoint; it is also, along with other advantages, very cost effective. RCC is a mix of cement/fly ash, water, sand, coarse aggregate and common additives, but contains much less water. The produced mix is drier and has no-slump. RCC is placed in a manner similar to paving. The material is deliv- ered by dump trucks or conveyors, spread by small bulldoz- ers or specially modified asphalt pavers and then compacted by vibratory rollers. RCC in Dam Construction - In dam construction, roller compacted concrete began its initial development with the construction of the Alpa Gera Dam near Sondrio in North Italy between 1961 and 1964. RCC had been touted in en- gineering journals during the 1970s as a revolutionary ma- terial suitable for, among other things, dam construction. Initially and generally, RCC was used for backfill, sub-base and concrete pavement construction, but increasingly it has been used to build concrete gravity dams. The low cement Sonjoy Deb, B.Tech, Civil Associate Editor ROLLER COMPACTED CONCRETE
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Roller Compacted Concrete Dams : A Review

ACI 116 defines RCC as “concrete compacted by roller compaction; concrete that, in its unhardened state, will support a (vibratory) roller while being compacted.

RCC is usually mixed using high-capacity continuous mixing or batching equipment, delivered with trucks or conveyors, and spread with one or more bulldozers in layers prior to compaction.RCC can use a broader range of materials than conventional concrete”.

About RCC - Roller Compacted Concrete (RCC) has been rapidly developing over the past 40 years and is now commonly used for mass concreting operations typically in a Gravity Dam application. With a widely varied methodol-ogy of design theories and project specific considerations, RCC is not only extremely practical from a constructability standpoint; it is also, along with other advantages, very cost effective.

RCC is a mix of cement/fly ash, water, sand, coarse aggregate and common additives, but contains much less water. The produced mix is drier and has no-slump. RCC is placed in a manner similar to paving. The material is deliv-ered by dump trucks or conveyors, spread by small bulldoz-ers or specially modified asphalt pavers and then compacted by vibratory rollers.

RCC in Dam Construction - In dam construction, roller compacted concrete began its initial development with the construction of the Alpa Gera Dam near Sondrio in North Italy between 1961 and 1964. RCC had been touted in en-gineering journals during the 1970s as a revolutionary ma-terial suitable for, among other things, dam construction. Initially and generally, RCC was used for backfill, sub-base and concrete pavement construction, but increasingly it has been used to build concrete gravity dams. The low cement

Sonjoy Deb, B.Tech, Civil Associate Editor

ROLLER COMPACTED CONCRETE

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content and use of fly ash cause less heat of hydration while curing corresponding to that of conventional mass concrete. RCC has cost benefits over conventional mass concrete in dams. This includes higher rates of concrete placement, lower material costs and lower costs attributed to less post-cooling and formwork. For dam applications, RCC sections are built lift-by-lift in successive horizontal layers resulting in a downstream slope that resembles a concrete staircase. Once a layer is placed and is initially hardened, it can im-mediately support the earth-moving equipment to place the next layer. After RCC is deposited on the lift surface, small dozers typically spread it in one-foot-thick (300 mm) layers. The first RCC dam built in the USA was Willow Creek Dam in Oregon on a tributary of Columbia River. US Army Corps of Engineers initiated such construction between November 1981 and February 1983. By 2008, about 350 RCC dams ex-isted world-wide. Currently the highest dam of this type is Longtan Dam, at 216 m, with Diamer- Bhasha Dam planned at 272 m. RCC techniques reduced the cost of conventional concrete dam construction and were used in massive con-crete structures with the advantage of limited construction period and cement content. Since the RCC placement rate is much faster and the cost of placement is lower than the cost of conventional concrete, the cost may be reduced by one-half to possibly one-third the cost of conventional concrete. From the overall design criteria, the soils approach to RCC mixture proportioning considers RCC as cement- enriched aggregate and the mix design is based on moisture- density relationships. There is sufficient paste in the RCC mix to fill all the voids in the well graded aggregate for the concrete approach, making no-slump and a fully compacted concon-crete mixture. This approach has a moist consistency than that of the soil approach when the same aggregate type is used. Since there is no ‘‘one procedure’’ which is best and fits all cases, therefore, design needs, materials availability and planned placement procedures are the governing fac-tors for proportioning RCC mixes. Nowadays, several com-pleted RCC dams all over the world, are being constructed in all types of climate. The size of RCC dams has significantly increased where some of the largest dams in the world are now being constructed implementing RCC technology. Con-sidering the RCC development, its application in developed countries, especially the Arab countries, is still limited. Since one of the purposes of constructing RCC Dam (RCCD) is to control floods and redirect them to certain specific passage-way to be optimally used for agriculture and domestic uses, therefore its construction is importantly needed. This impor-tance increases especially when using available local mate-rials in RCCD construction in Egypt, especially Sinai. (Refer Figure 1 for A Typical RCC Dam Construction)

Advantages of RCC Dams

(A) Dams are a vital, but aging, part of our public works infrastructure. The challenge is to find cost-effective repair and replacement methods without sacrificing safety and re-liability. RCC has three key properties that make it uniquely suited for dams: economy, performance, and high-speed construction. It has the strength and durability of conven-tional concrete, but at a cost that rivals earth or rock fill con-struction. RCC can be used to build new dams or to shore

up old ones. (B) It protects dams from over-topping failure, earthquakes, and erosion. It can be placed quickly and eas-ily with large-volume earth-moving equipment. It’s generally transported by dump trucks, spread by bulldozers, and com-pacted by vibratory rollers (Refer Figure 2).

Figure 1: A Typical RCC Dam Construction

Figure 2 : RCC Dam with Large Volume of Concrete under Construction

Advantages of RCC Dams

(A) Dams are a vital, but aging, part of our public works infrastructure. The challenge is to find cost-effective repair and replacement methods without sacrificing safety and re-

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liability. RCC has three key properties that make it uniquely suited for dams: economy, performance, and high-speed construction. It has the strength and durability of conven-tional concrete, but at a cost that rivals earth or rock fill con-struction. RCC can be used to build new dams or to shore up old ones. (B) It protects dams from over-topping failure, earthquakes, and erosion. It can be placed quickly and eas-ily with large-volume earth-moving equipment. It’s generally transported by dump trucks, spread by bulldozers, and com-pacted by vibratory rollers (Refer Figure 2).

(C) Sections are built lift-by-lift in successive horizontal layers so the downstream slope resembles a concrete stair-case. Once a layer is placed, it can immediately support the earth-moving equipment to place the next layer. After RCC is deposited on the lift surface, small dozers typically spread it in thick layers. Workers also place it with motor graders, spreader boxes, and paving machines (Refer Figure 3).

channels, and form grad the first successful application of RCC technology was demonstrated in 1974. The repair of the collapsed intake tunnel of Tarbela Dam proved that the ma-terial had more than adequate strength and durability. The maximum placement of 18,000 m3 of RCC in one day, which is still the world’s record, was a clear evidence of the poten-tial of this new construction method (Refer Figure 4).

Some Examples of RCC in Dams in replacement of Existing Dams:

There have been many dams that were designed as Con-crete Faced Rock fill Dams (CFRD) and changed to RCC as the developments in the designs have proved in many cases that the RCC option proved more economical. One such originally designed CFRD that was changed to RCC was the Al Wehdah RCC dam in Jordan, Figure 5. Al Wehda still re-mains in the top ten fastest constructed RCC dams while 1.4 million m3 RCC dam was placed in 19 months. The recently completed Taum Sauk Upper Reservoir Rebuild Project for the pumped storage facility near Lesterville, Missouri. The original dam was a CFRD and suffered a 215 m long breach after being overtopped and was replaced by a low cementi-tious content (LCRCC) RCC 90 kg/m3 and RCC construc-tion period of just 26 months with an average monthly rate of placement of 88,000m3 with a corresponding maximum daily rate of placement of approximately 14,150 m3. It should be noted that the original CFRD was completed in 1963 and took 4 years to construct. The rebuild project was construct-ed by Ozark Constructers with design being done by Paul C. Rizzo Associates.

Figure 3 : Downstream slope of RCC Dams

(D) RCC has also proven itself in many other types of applications. Older concrete and masonry dams can be buttressed with RCC to increase resistance to earthquake loading and to improve stability to prevent overturning and sliding.

(E) RCC is used as backfill to support conventional con-crete spillways. Due to its high resistance to abrasion, RCC is also used to construct stilling basins, build liners for outlet

Figure 4 : RCC in Dam Spillway

Figure 5 : Al Wehdah RCC dam Jordan

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The project was a huge success and is currently a State of the art “pumped storage” facility as the RCC dam was built in an emergency rebuild operation using nearly all of the existing CFRD material and processing it into RCC for the complete dam structure which includes an emergency spillway.

Another example where a RCC dam was built for an emergency ballast fill behind an earthfill dam was the Sa-luda project in South Carolina USA where an existing zoned earth fill was deemed unsafe as an intensive investigation was done and within and downstream of the dam. After fur-ther analysis, it was apparent that the dam could be subject to Liquefaction and a catastrophic failure could occur dur-ing an earthquake event. As a result of the seriousness of the aging structure it was concluded that an RCC dam be build immediately Downstream of the original dam for safety concerns. This project was a huge success containing some 1 million m3 RCC and achieved a rate of placement of 13,000 m3 in a single 24 hr period.

Design of RCC Dams

The use of RCC offers a wide range of economical and safe design alternatives to conventional concrete and em-bankment dams. Placing RCC in lifts that are compacted by vibratory rollers does not change the basic design con-cepts for dams, locks or other massive structures. Impor-tant considerations that must be addressed include the ba-sic purpose of the dam and the owner’s requirements for cost, schedule, appearance, watertightness, operation and maintenance. A review of these considerations should de-termine the selection of the proper RCC mixture, lift surface treatments, facing treatments and the basic configuration of the dam. The overall design should be kept as simple as possible to fully capture the advantages of rapid construc-tion using RCC technology. Any organization or individual may adopt practices or design criteria which are different than the guidelines contained herein the state of the art in the design of RCC dams and other massive structures. It is not purported to be the standard for design but they should obtained the data bellows:-

- Dam section considerations - Stability especially (Shear-friction factor , Design values

for tensile and shear strength parameters) - Temperature studies and control - Contraction joints - Galleries and adits

- Facing design and seepage control(Upstream facing, Downstream facing & Seepage control)

- Spillways - Outlet works - Tensile strength—Tensile strength of RCC is required for

design purposes, including dynamic loading and in the thermal analysis. The ratios of tensile-to-compressive strength for parent (un jointed) RCC mixtures have typi-cally ranged from approximately 5 to 15%, depending on aggregate quality, strength age, and test method.

ConclusionThe Roller Compacted Concrete (RCC) technology has

been applied in dam construction for about 35 years in the world because of their inherent advantages including speed of construction with consequent reduction in execution time affording significant reduction in cost. As such, more and more RCC dams are being constructed world over in many countries including Algeria, Argentina, Australia, Brazil, Chi-na, Columbia, Cyprus, France, India, Greece, Japan, Moroc-co, Somalia, South Africa, Spain, Thailand, United Kingdom, U.S.A. and U.S.S.R. More than 500 Nos. of RCC dams have been constructed so far. The construction of such types of dams which affords scope for use of fly ash in bulk quantities is highly relevant to countries like India which produce huge quantities of fly ash from thermal stations. Construction of RCC dams has now been universally accepted as a more economical method of dam construction combining safety, aesthetic besides the advantage of cost effectiveness. From the visible trend of RCC dam engineering, a greater number of dams will be constructed of RCC in the near future with further advanced technologies. Besides, greater application of RCC has been for the rehabilitation of existing dams to conform to the present design criteria. It may be opportune at present juncture to be aware of recent advances in RCC technology, innovative methods of construction, contract practices, deployment of modern machinery etc.

Reference

- http://www.ce.berkeley.edu/~paulmont/165/RCC_final.pdf

- http://www.iitk.ac.in/nicee/wcee/article/13_3399.pdf

- http://www.ide.titech.ac.jp/~otsukilab/lecture/advanced%20concrete%20technology 17Roller%20Compacted%20Concrete.pdf

- http://www.rizzoassoc.com/cms/images/stories/site/published_papers/foundation_prep_for_rcc.pdf

- http://keu92.org/uploads/Search%20engineering/ROLLER%20COMPACTED%20CONCRETE.pdf

- http://publications.lib.chalmers.se/records/fulltext/146361.pdf

- http://www.ghd.com/PDF/2008%20USSD%20Conf%20-%20State%20of%20the%20Practice-GERCC%20in%20Dams%20-%20FORBES%20et%20al.pdf

- http://www.geiconsultants.com/stuff/contentmgr/files/0/446bc59d245e7d25b20ef1a6ad3389e9/download/applicationqualit concepts.pdf

- http://www.pozzo.asia/uploads/media/PAPER13_Warren_R.pdf

- http://www.jsce.or.jp/committee/concrete/e/newsletter/newslet-ter05/3-Vietnam%20Joint%20Seminar%20(Uji).pdf

- https://www.wb.bgu.tum.de/fileadmin/w00boi/www/Publikationen/Berichtshefte/Band105.pdfFigure 6 : A Typical Finished RCC Dam

ROLLER COMPACTED CONCRETE


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