LIMESTONE FILLER USED AS CEMENTITIOUS MATERIAL

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21st Century Dam Design

Advances and Adaptations

31st Annual USSD Conference

San Diego, California, April 11-15, 2011


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On the CoverArtist's rendition of San Vicente Dam after completion of the dam raise project to increase local storage and provide

a more flexible conveyance system for use during emergencies such as earthquakes that could curtail the regions

imported water supplies.The existing 220-foot-high dam, owned by the City of San Diego, will be raised by 117

feet to increase reservoir storage capacity by 152,000 acre-feet. The project will be the tallest dam raise in the

United States and tallest roller compacted concrete dam raise in the world.

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advertising or promotional purposes and may not be construed as an endorsement of any product or

from by the United States Society on Dams. USSD accepts no responsibility for the statements made

or the opinions expressed in this publication.

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Limestone Filler 259

LIMESTONE FILLER USED AS CEMENTITIOUS MATERIAL IN THE MIXFOR THE LARGEST RCC DAM IN EUROPE: LA BREA II

Rafael Ibez de Aldecoa1

Gonzalo Noriega2

Antonio Sandoval

3

Miguel Sanz4

ABSTRACT

La Brea II is a roller-compacted concrete (RCC) straight gravity dam located on the

Guadiato River, about 25 km southwest to the city of Cordoba in Southern Spain. With aheight of 119 m, and RCC volume of 1.4x10

6m

3-out of a total of 1.6x 10

6m

3of

concrete placed-, La Brea II is the largest RCC dam built in Europe. The use of a high

(230 kg/m3)

cementitious content RCC mix, of which 70% was to be flyash, required atotal flyash consumption of roughly 225,000 t during a planned 20 month construction

period. This would have required an average flyash supply of approximately 11,000t/month, with peaks on the order of 21,000 t/month and 1,100 t/day. In depth market

investigation showed that, even monopolizing the flyash supply available from severalSpanish and Italian thermal power plants, it was very uncertain to fulfill the target.

Therefore an alternative using a second type of mineral admixture that would reduce the

need for flyash was carefully studied.

The chosen option was to use a limestone filler that complies with the European Standard

EN 197-1 as a suitable mineral admixture with required cementitious properties, whichcould be used by cement manufacturers to produce certain types of common cements.

The use of this limestone dust in the RCC mix for La Brea II, in a proportion of 20% byweight with respect to the total cementitious materials, resulted in satisfactory long term

concrete strengths that met the project requirements and exceeded all expectations.

La Brea II RCC dam is owned by AcuaSur, the designer for the Construction Design

was Idom, the site engineer Initec Infraestructuras, and the contractor Dragados S.A.

INTRODUCTION AND BACKGROUND

Flyash as a mineral admixture to replace a certain amount of cement has been widely

used for decades, due to the favorable properties that it provides to the concrete, whetherit be in its fresh state, making the placement easier, or in its hardened form reducing the

heat of hydration and providing greater strength in the long term. All of these benefits are

1Head Hydraulic Works Division, Dragados S.A., Avda. Camino de Santiago, 50, 28050 Madrid, Spain,

[email protected][Member of SPANCOLD]2Portugues RCC Dam Construction Manager, Dragados-USA, Road PR10, km 5.5, Ponce, PR 00731,

[email protected][La Brea II RCC Dam Construction Manager]3Water Supply and Irrigation Technical Manager, acuaSur, Pza. Cuba, 9, 41011 Seville, Spain,

[email protected][La Brea II RCC Dam Project Manager]4Hydraulic Works Division, Dragados S.A., Avda. Camino de Santiago, 50, 28050 Madrid, Spain,

[email protected]


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260 21st Century Dam Design Advances and Adaptations

very adequate to mass concrete for dams. In addition to those technical advantages, the

use of flyash often reduces the overall cost for cementitious material.

In Europe, the Standard EN 197-1 Composition, Specifications and Conformity Criteria

for Common Cements, gathers the classifications of the common cements. In such

classifications there appear various types of cement that incorporate, in differentproportions, flyash obtained from electrostatic precipitation in the thermal power plants

fed with pulverized coal. These cements include CEM II/A-V, CEM II/B-V, CEM II/A-

M, CEM II/B-M, CEM IV/A, CEM IV/B, CEM V/A, CEM V/B, etc. Since the late1970s and early 1980s, the use of flyash as a substitute for the clinker in the

cementitious material for concrete dams has broadened. This substitution started at the

order of 30%, and over time it reached up to 50% in conventional concrete dams. Unlessnoted otherwise, all percentage values shown in this paper are by weight. The

incorporation of flyash in the cementitious content could take place in the concrete batch

plant of the project or at a cement factory, adopting in this second case, one of the on-factory cements previously mentioned.

In the early and mid 80s the technique of roller compacted concrete for dam construction

was introduced in some countries, including Spain. In this type of dam the substitution ofthe clinker using flyash was even greater, common percentages of flyash being from 60%

to 70% above the total of the bonding material.

Flyash, a by-product of coal thermal power plants, was a relatively inexpensive product

and available in unlimited quantities meeting the needs of a huge concrete dam.

However, with time it became an expensive product and hard to get in large quantities,due to the fact that most of the Spanish coal thermal power plants (as probably in many

other countries too) have much of their production engaged, directly or through anintermediary, with the companies producing cement. The benefits mentioned previously

from using flyash have enormously increased the employment of the type II, IV and V

cements that incorporate flyash, in a variety of uses besides building concrete dams.

Upon undertaking the construction of La Brea II Dam in Cordoba, the largest RCC Dam

in Europe and due to the problem of not having enough flyash available to satisfy the

required high consumptions, the search for alternative solutions was compelling.

NEEDS OF FLYASH FOR LA BREA II

After scheduling of the job, which involved a very strict deadline, the specific needs of

most important materials that dictated the critical path of the job were determined. Based

on the required RCC volume and construction schedule, the need for flyash wasestimated as follows:

Total volume of RCC =1,400,000 m3

Execution time = 20 months

Typical dosage of cementitious material = 230 kg per cubic meter of concrete Flyash percentage of total cementitious material (by weight) = 70%


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Average monthly consumption of flyash = 11,000 t/month Peak monthly consumption = 21,000 t/month Peak daily placement of RCC = 7,000 m

3/day

Peak daily flyash consumption = 1,100 t /day

Given the extent of the needs of flyash an extensive market investigation was undergonewhich showed that even supplying ash from various Spanish thermal power plants and

supplementing with ash from Italian power plants, it would be very uncertain to meet the

project requirements.

In addition, some of the thermal power plants we relied on as our main sources of supply

of flyash could not guarantee a minimum supply since production was impacted byunpredictable factors such as the climate. In years where the hydrology is favorable the

needs of production of electrical energy with thermal power plants diminishes and vice

versa. Additionally, the power plants have mandatory maintenance stops, and in somecases these stops coincided with the months of highest RCC placement at La Brea II.

Therefore we were forced to seek alternatives to reduce the need of flyash for the job,

without altering the planned schedule of RCC placement.

ALTERNATIVES TO FLYASH AS THE ONLY MINERAL ADMIXTURE

We proceeded with another extensive market investigation of cement manufacturers to

search for other possible admixtures besides flyash. The study focused on two main

aspects including use of commercially available cement customized to meet specificrequirements of the project, and use of natural pozzolans, ground granulated blast furnace

slag (GGBFS), or limestone filler as a second admixture to reduce the need for flyash.

In principle, customizing cement for a large-sized job like La Brea II is feasible.

However, the solution of using a sole product like cement type CEM II, III, IV or Vsupplied from a cement factory was not economic for various reasons. For instance, the

composition of the cement customized for the requirements of our case did not agree

with the standard production of cement factories, and a high level of consumption (nearly

30,000 t/month during peak months) posed problems of supply to their regular customers.Those problems could be solved, but always at extreme cost. Therefore, the approach to

customize a single type of cement was not studied further.

The other possible solution was to mix a cement type CEM I with two mineral

admixtures on site. This approach was perfectly acceptable since some factory-

manufactured cements already incorporate two or even more admixtures, as it is the caseof cement types CEM II-composed, CEM IV and CEM V (from European Standard EN

197-1).

The second aspect of the study was to find a second source of mineral admixture that

would decrease the need of flyash. The sources of supply for natural pozzolans, GGBFS

or limestone filler were searched and evaluated. Of the first two materials no conclusive


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possibilities of reliable supplies were found. However, some potential limestone filler

sources were found.

The investigation then focused on locating a limestone filler source that would comply

with the properties required for it to be considered as an active mineral admixture with

cementitious properties. The possible use of limestone filler for such endeavor was basedon the following published standards and practices:

Standard EN 197-1 contemplates limestone filler as a possible component of acommon cement, as long as it meets predetermined technical requirements;

Standard EN 197-1 contemplates cements with limestone filler additions of up

to 35% (e.g. types CEM II/A-L and LL, and types CEM II/BL and LL); Standard EN 197-1 contemplates cements with limestone filler additions

together with other additions, including flyash (e.g. types CEM II/A-M and

CEM II/B-M); ICOLD Bulletin N

o126 State of the Art of RCC Dams, Section 3.2

Cementitious Materials cites limestone filler as a possible source foradmixture; and The use of limestone filler as an active mineral admixture was considered by

the Joint Venture which Dragados was part of in the laboratory tests performed

for the RCC dam of Sa Stria, in Sardinia, Italy. [3]

Based on the supply availability and previous study results, we chose limestone filler as a

possible source of second admixture to be further tested and investigated.

CHARACTERISTICS OF CHOSEN LIMESTONE FILLER

The limestone filler that was finally chosen came from an industrial installation in the

vicinity of Estepa, in the province of Seville, about 105 km away from the damsite. The

following are the main characteristics of the chosen limestone filler (the values shown inparenthesis are those required in Standard EN 197-1):

CaCO3content = 99% by mass (75%)

Clay content 0.7 g/100 g (< 1.20 g/100 g)

Total Organic Carbon (TOC) content 0.10% mass (< 0.20% for cements type

LL and < 0.50% for type L) Density = 2.822 g/cm

3

Fineness (Blaine) = 454 m2/kg

Although the material very comfortably complied with the Standard EN 197-1, it wasdecided to do particular additional tests, with the objective of determining if the

limestone filler complied with specific requirements of a flyash for its use as an active

mineral admixture in a common cement. The following were the tests made for thispurpose (the values in parenthesis are those required in European Standard EN 450-1 for

flyash):


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Fineness, retained in # 0.090 mm = 16% (not specified) Fineness, retained in # 0.063 mm = 20% (not specified) Fineness, retained in # 0.045 mm = 30% (< 40%)

Strength Activity Index at 7 days = 76.7% (not specified) Strength Activity Index at 28 days = 83.5% (> 75%)

Strength Activity Index at 90 days = 86.7% (> 75%)

Additionally, the tests for the Strength Activity Index were also made in compliance with

Standard ASTM C-618 in which, as a bonding material, a mixture of 80% clinker + 20%flyash (limestone filler in this case) must be used instead of the 75% clinker + 25% flyash

specified in the European Standard. The results are (the values in parenthesis are those

required in Standard ASTM C-618):

Strength Activity Index at 7 days = 81.8% (> 75%) Strength Activity Index at 28 days = 85.7% (> 75%) Strength Activity Index at 90 days = 87.2% (not specified)

The test results demonstrated that the strength activity of the chosen limestone filler met

the requirements specified for a flyash, and therefore it was proved that the filler materialwould make its contribution to the development of RCC strength.

MODIFICATIONS NEEDED AT THE CONCRETE PLANT

The concrete plant, consisting of two twin batching-mixing plants for a joint production

of 500 m3/h of RCC, was at the beginning designed to work with two different

cementitious materials. The storage capacity foreseen for the bonding materials was

planned with 6 silos of 1000 t capacity each, enough so as to have a reserve on the jobequivalent to 5 days of peak placement of RCC. In principle we had foreseen 2 silos for

cement and 4 silos for flyash.

Working with three different cementitious materials we changed the above approach; we

assigned 2 silos for cement, 3 for flyash and 1 for limestone filler. But the main problem

that turned up was the transportation of the bonding materials to the concrete plants,

which at the beginning were to be three lines of pneumatic conveyors, one for every twosilos, designed for a unitary performance of 50 t/h.

Each of the two concrete plants was arranged with 2 silos of 100 t and 2 weighing scalesto work with only two cementitious materials. Therefore, two of the three bonding

materials had to be pre-dosed and pre-mixed before arriving to these silos. To establish

the process, tests were made with the three products, verifying their density, fluidity, etc.Those results allowed us to assign a supply line for the cement and the other two lines for

the flyash+filler mix, with a dosage for these, by flow, in the required proportions.

The synoptic chart Fig. 1, showes the fittings and operation of the system to feed from the

6 big master silos of 1000 t to the four small 100 t silos above the concrete plants. Fig. 2

shows an aerial view of the concrete production facilities.


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Figure 1. Synoptic chart of the cementitious materials pneumatic transport system

Figure 2. Aerial view of the plant for RCC production

Fine aggregate silos(2 x 1300 t)

Wet belts

Coarse aggregate silos (3 x 3600 t)

Water cooling plants

Cementitious silos (6 x 1000 t)

Mixing plants 4 mixers x 4 m3

Ice flakes plants (2 x 90 t/day)

Batching plants 2 x 250 m3/h


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The mixture of flyash and limestone filler is produced in the bins of two of the pneumatic

transport lines, acting over the speed of the corresponding screw conveyor feeders whosevalues are adjusted by means of a variable-frequency drive. The proportions of the

mixture depend on the respective speed of each screw conveyor of flyash and filler that

feed the bin. Once the dosage to use is known, these speeds depend on the bulk density of

the two products. Reliability of the mixture is controlled by means of swing detectors forthe screw conveyors and material flow detectors at the drop toward the bins.

TENSILE AND COMPRESSIVE STRENGTH REQUIREMENTS FOR THE RCC

First of all, indicate that the design age for the RCC strengths was established at 180

days. Concrete with high mineral admixture content (depending on the mineraladmixture) usually continue gaining strength well beyond the age of 90 days. This control

age of 90 days is typical for conventional concrete dams, in which the proportion of

cement substituted by mineral admixture is usually lower than in RCC dams, and was ofcommon use in RCC dams some years ago. But in modern RCC projects the control age

has been expanded to at least 180 days, and preferably one year.

Taking into account the high increase in strength obtained from 180 days to one year,further discussed in the next section, it would have been more appropriate for this project

to have selected one year for the design age instead 180 days. We have to recognize that

when developing the Construction Design for the job, it was to be the first dam design inSpain in which a design age beyond 90 days was to be implemented, and we remained a

bit conservative in this respect.

The required strengths in the Specifications of the Construction Design of the project

were the following:

Direct tensile strength of RCC cores across lift joints = 0.875 MPa at 180 days

This value was derived from the maximum value of the vertical tension obtained in a

finite elements thermal stress-strain analysis [5] [Fig. 3] which resulted in 0.75 MPa

(discarding isolated higher values located in singular areas, as in the corners of the

galleries), allowing for a rounded safety margin of +15%. This margin could seem verystrict, but we counted also on the certainty of the RCC strength improvement beyond 180

days and, additionally, the damsite is located in an area with very low seismicity.

Compressive strength of RCC cylinders = 17.5 MPa at 180 days

Other large RCC dam projects were considered where the actual ratio between the twoaforementioned strengths was found to be mostly in the range of 16 to 18 (e.g. Beni

Haroun in Algeria [6] and Porce II in Colombia [2], among others). To be on the safe

side, we adopted a value of 20 for such ratio, which led to a compressive strength of0.875 x 20 = 17.5 MPa for the design age.


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It should also be mentioned that at the time of elaborating the Construction Design, the

possibility of using a mineral admixture other than flyash in the RCC mix was notconsidered at all.

Figure 3. Figures from the finite elements thermal stress-strain analysis

MIXTURE PROPORTIONS USED AND STRENGTHS OBTAINED

Based on review of the results from the previous laboratory tests, the Full-Scale Trial

(FST) placement that was carried out in November 2006 used an RCC mix with 220

kg/m3of total cementitious materials of which 40% was pure cement (EN 197-1 CEM

I/42,5 R-SR), 40% flyash, and 20% limestone filler. Concrete set retarders were also

tested during the Trial placement.

Fig. 4 shows cores 3 m-long and 120 mm in diameter extracted from the FST. Afterwards

they were prepared to perform direct tensile strength tests across lift joints [Fig. 5].

Figure 4. Cores 3 m-long, 120 mm-diameter, extracted from the Full Scale Trial


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Figure 5. Direct tensile strength test on jointed core performed at laboratory on site

The RCC compressive strengths obtained at 90 days at the Trial Placement were lower

than those inferred from the previous laboratory tests. Although it was estimated that at

180 days the strengths would surpass the target value established in the Specifications, itwas decided to begin the placement of the RCC in the body of the dam with a slightly

richer dosage of cement, with the idea of eventually adjusting the cement content

downward as we obtained more consistent statistical results of the strengths during thecourse of RCC placement.

The three most significant mixes used were:

Mix 1: 230 kg/m3total cementitious, with 43.5% cement + 43.5% flyash + 13% filler

Mix 2: 230 kg/m3total cementitious, with 35% cement + 45% flyash + 20% filler

Mix 3: 230 kg/m3total cementitious, with 30% cement + 50% flyash + 20% filler

The compressive strengths obtained with each one of them are shown in Fig. 6.

Emphasis must be made on the high compressive strength values attained at 365 days.For example, Mix 3, the mostly used for construction, showed the amazing improvement

of strength from 90 days (R90) to one year (R365), resulting in:

R365/R90= 29.5/18.6 = 1.59

or an increase of nearly 60% from the 90-day strength.


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From 90 days to the design age of 180days, the RCC strength increase was:

R180/R90= 24.5/18.6 = +32%

From the design age of 180 days to one year, the RCC strength increase was:

R365/R180= 29.5/24.5 = +20%

The similar ratios for Mix 2 were:

R365/R90= 31.1/21.4 = +45%

R180/R90= 28.0/21.4 = +31%

R365/R180= 31.1/28.0 = +11%

Figure 6. Compressive strengths of the different RCC mixes

Regarding the direct tensile strength of RCC cores across lift joints corresponding to damconstruction, all the tests were performed at approximately the design age of 180 days.

The results were, on average:


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Mix 2: 1.47 MPa at approx. 180 days

Mix 3: 1.12 MPa at approx. 180 days

For comparison, the RCC mix used in construction of Beni Haroun RCC Dam in Algeria

[6] had:

225 kg/m3total cementitious, with 36% cement + 64% flyash (+ 0% limestone filler)

that was very similar in cement and mineral admixture contents to Mix 2 of La Brea II

Dam. The aforementioned ratios for Beni Haroun Dam were:

R365/R90= 33.1/23.8 = +39%

R180/R90= 29.0/23.8 = +22%

R365/R180= 33.1/29.0 = +14%

Although the sources of materials (e.g. cement, flyash, aggregates, etc.) were different forthe two projects, a preliminary comparison indicate that Mix 2 of La Brea II (45% of

flyash and 20% of limestone filler) produced compressive strengths similar to those of

Beni Haroun (64% flyash and without limestone filler), with comparable increase ofstrength from 90 days to 180 days and a year. In fact, the strengths were slightly higher in

the case of the mix with limestone filler.

The above comparison between the compressive strengths of the two dams is quite

consistent, due to the fact of the similarities of both mixes evaluated. In Table 1 there is asummary of the main characteristics of both mixes, in order to have a better evaluation of

the similarities and differences between them.

The direct tensile strength of RCC cores across lift joints in Beni Haroun, where all the

test were performed at approximately 90 days (the design age for that dam), was in

average 1.50 MPa, similar to that of Mix 2 of La Brea II, but at a lower age (90 days

instead 180 days).

Nevertheless, it is difficult to compare results of direct tensile strength tests of RCC cores

across lift joints from two different dams, even having similar RCC mixes, becausebonding at the joint is influenced by multiple factors apart from the mix itself (and within

this mainly the cementitious content and the volumetric paste/mortar ratio compared with

the compacted sand void content), for example the RCC placement temperature, the airtemperature and weather conditions during the exposure time, the exposure time, the

conditions of surface curing during the exposure time, the conditions of surface

cleanliness prior to next lift placement, the spreading and compaction process (e.g.occurrence of segregation, type of compactor and number of passes), the lift thickness

(although it is extensively standardized to 30 cm), etc.


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Table 1. Summary of main characteristics of RCC mixes used at La Brea II and Beni

Haroun dams

In summary, RCC mixes with 20% limestone filler in compliance with EuropeanStandard EN 197-1 were mostly used in construction of La Brea II Dam. The chosen

limestone filler as a substitution of the same quantity of the flyash led to long-term RCC

strengths very similar to those expected of only flyash.

CONCLUSIONS

At present in several countries, including Spain, the high demand coming from cement

manufacturers for the flyash produced by coal thermal power plants makes it increasingly

difficult to purchase huge quantities of flyash to be used in construction of large concretedams, although such practice has regularly resulted in technical and economic benefits

during the past decades.

This has promoted a search for alternative admixtures that will reduce the need for the

flyash. In the case of La Brea II RCC Dam, a limestone filler which is in compliance

with European Standard EN 197-1 has been found and used for substituting portion of theflyash as a mineral admixture for RCC.


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The results obtained using the chosen limestone filler with a proportion of 20% of the

total cementitious material, together with 50% flyash (45% in certain phase of the job),have been as satisfactory as those expected with the use of 70% flyash as the only

mineral admixture.

It is important to point out that difficulties of adapting the batch plant for concreteproduction could arise when trying to work with three different cementitious products.

Figure 7. Aerial view of the completed La Brea II RCC Dam

REFERENCES

[1] R. Ibez de Aldecoa. Construction of La Brea II Dam, Spain. Proceedings ofInternational RCC Dams Seminar & Study Tour, Atlanta, USA, March 2007.


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[2] R. Ibez de Aldecoa, M. Dunstan & R. Noriega. La Presa Porce II de HCR enColombia: Proyecto, diseo de la mezcla, construccin y comportamiento. Proceedings

of VII Jornadas Espaolas de Presas, Saragossa, Spain, May 2002.

[3] R. Ibez de Aldecoa & L. Gutirrez. Laboratory previous tests for Sa Stria Dam(Italy) performed using three different mineral admixtures. Proceedings of 4th

International Symposium on RCC dams, Madrid, Spain, November 2003.

[4] F. Romero, A. Sandoval, R. Ibez de Aldecoa & G. Noriega. Plans for the

construction of La Brea II Dam in Spain. Proceedings of 5th

International Symposium

on RCC dams, Guiyang, China, November 2007.

[5] F. Rueda, N. Camprub, G. Garca & J.M. Pardo. Thermomechanical analysis of

La Brea II Dam during its construction process: evaluation of potential thermalcracking. Proceedings of 22

ndCongress on Large Dams, Q.84, R.31, Barcelona, Spain,

June 2006.

[6] M. Sanz. Construction of Beni Haroun Dam (Algeria). Proceedings of 4th

International Symposium on RCC dams, Madrid, Spain, November 2003.

LIMESTONE FILLER USED AS CEMENTITIOUS MATERIAL

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