Scc report

CE 241: Concrete Technology

Spring 2004

Report #1:

Self-Consolidating Concrete

Frances Yang

March 9, 2004

Self-Consolidating Concrete Frances Yang CE 241 Spring 2004: Report #1 March 18, 2004

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Table of Contents Abstract ...........................................................................................................................3 Introduction ...................................................................................................................4 Definition........................................................................................................................5 Chemical Admixtures....................................................................................................8

Superplasticizers.........................................................................................................8 Viscosity Modifying Admixtures...........................................................................13

Mix Proportioning.......................................................................................................11

Benefits of SCC............................................................................................................14 Standards.......................................................................................................................15 Application ...................................................................................................................18 List of Figures: Figure 1: Basic workability requirements for successful casting of SCC. .............6 Figure 2: Properties of aggregates influencing SCC characteristics. ......................7 Figure 3: Effect of Superplasticizer .………………………………………….8 Figure 4: Optimum combination of superplasticizer and w/c ratio…….….... 10 Figure 5: Proper fine aggregate content for SCC…………………………… 13 Figure 6: Slump Flow and L-box Tests…………………………………...….17 Figure 7: V-funnel Test…………………………………………………….. 17


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Abstract

Self-consolidating concrete is a concrete that exhibits high deformability while maintaining resistance to segregation. This paper investigates the technology behind creating SCC, including its components and mix proportioning techniques. It highlights numerous benefits in using SCC and refers to the various tools used to parameterize its properties. Precautionary measures that should be taken in developing and working with the mix are discussed. Lastly listed are some exemplary applications.


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Introduction

Understanding self-consolidating concrete is becoming more and more important as the use of this type of mix becomes ever more popular. Meanwhile, the higher level of technology it involves requires a higher level of expertise on the part of those who develop it. Its benefits can achieve enormous labor and cost savings, but only if carried out correctly. This paper will cover what constitutes a self-consolidating concrete, how it works, and its applications. Exploring these topics includes looking at the components of SCC that make it different from normal concrete. These are primarily the aggregates and chemical admixtures. This paper also includes some of the research that has been conducted in these areas. Supplying the reader with this knowledge will then allow pointing out the many benefits and common pitfalls in using self-consolidating concrete. Once understanding the mix itself has been developed, this paper presents the more commonly used instruments for measuring and defining SCC properties. Finally, some successful applications around the world will be presented. This paper is not an all-inclusive summary of the research that has been done to advance the technology, nor does it set down a specific formula for creating an SCC mix. Rather, it recognizes that there are numerous methods and recommendations proposed by experts and tries to explain the fundamental reasoning behind each. In this way, the continually advancing field of self-consolidating concrete makes it an exciting study.


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Definition SCC which stands for Self-Consolidating Concrete, or Self-Compacting Concrete, has many other names. It is also called High-Workability Concrete, Self-Leveling Concrete1, or Flowing Concrete.2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement.3 It is in want of a standard definition, but may be nominally considered a concrete mix of exceptional deformability during casting, which still meets resistance to segregation and bleeding.4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar.5 Because of its low viscosity during pouring, self-consolidating concrete can fill heavily reinforced areas under its own weight, without applying vibration. SCC is also used to create “super-flat” floors (1mm over a length of 4m) without post-pour leveling.6 The highly flowable nature of SCC is due to very careful mix proportioning, usually replacing much of the coarse aggregate with fines and cement, and adding chemical admixtures. It depends on the sensitive balance between creating more deformability while ensuring good stability, as well as maintaining low risk of blockage. See Figure 1.

1 Sebastien Rols, Jean Ambroise, Jean Pera, “Effects of Different Viscosity Agents on the Properties of Self-Leveling Concrete,” Cement and Concrete Research 2 P. Kumar Mehta, Paulo J. M. Monteiro, Concrete: Microstructure, Properties and Materials, 2nd edition, October 2001. 3 Van K. Bui, Yilmaz Akkaya, and Surendra P. Shah, “Rheology Model for Self-Consolidating Concrete”, ACI Materials Journal, November-December 2002. 4 M. Lachemi, K.M.A. Hossain, V.Lambros, P.C. Nkinamubanzi, N. Bouzoubaa, “Self-consolidating concrete incorporating new viscosity modifying admixtures”, Cement and Concrete Research 5 Kamal H. Khayat, Patrick Paultre, and Stephen Tremblay, “Structural Performance and In-Place Properties of Self-Consolidating Concrete”, ACI Materials Journal, Sept-Oct 2001. 6 Rols et al.


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Figure 1: Basic workability requirements for successful casting of SCC. 7

Creating this type of concrete involves playing with the many factors that affect deformability and segregation. These factors include water to cement ratio and the numerous properties of the aggregate: volume, size, distribution, and spacing, void content, ratio between fine and coarse, surface properties, and density. See Figure 2. More importantly, though, chemical admixtures play a key role in the common techniques used today.

7 Khayat et al.


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Figure 2: Properties of aggregates influencing SCC characteristics. 8

In fact, since there is not yet a standard definition for SCC, it has been contended that a better term would be SCT, or Self-Consolidating Technology, because it is the technology behind the chemical admixtures that allows the creation of this highly workable and stable mix.9 Usually a mix with high fines content, low water-to-cement ratio, and less coarse aggregates becomes too stiff to work effectively. At the same time, a high viscosity mix through greater fines and higher water content would have problems with segregation, strength, and durability, among many other important concrete properties. However, these all-important qualities can now be spared from sacrifice in order to achieve highly flowable and stable mixes, due to recent improved technology in admixtures.

8 Bui et al. 9 Joe Nasvik, “The ABCs of SCC”, Concrete Construction, January 2002.


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Chemical Admixtures The two principle chemical admixtures in SCC are a synthetic high-range water reducer (superplasticizer) and a viscosity modifying admixture (VMA). These may be used by themselves but are more commonly used together.10 Superplasticizers Superplasticizers are a water-reducing admixture that causes a significant increase in flowability with little effect on viscosity.11 For example, the addition of 0.3 to 1.5 percent (by weight of cement) conventional superplasticizer to a concrete mix with 50-70 mm slump increases slump to 200-250 mm.12 See Figure 3.

Superplasiticizers have been on the market for more than 30 years. However, these had the problem of retarding intial set and inhibiting complete hydration of cement particles. The new generation of superplasticizers is based on polycarboxylated ethers, which act as powerful cement dispersants that require less mix water to provide dramatic increase in flow. Some of these have also been engineered to set more rapidly and provide more complete cement hydration. Polycarboxylate-based superplasticizers are now available from about 50% of the producers of ready-mix concrete in the US, truly opening up the market for SCC.13 The primary negative effect when adding superplasticizer alone to concrete is that the mix may have a tendency to segregate and bleed. There are two paths to avoid this problem, involving modifying mix proportions and use of viscosity modifying admixtures. More about each will be discussed later.

10 Nasvik 11 Hajume Okamura, “Self-Compacting, High Performance Concrete”, Concrete International, July 1997. 12 Mehta and Monteiro 13 Nasvik

Figure 3: Effects of superplasticizer. (Okamura)


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Segregation can also occur with a normally consolidating concrete if over-vibrated.14 Another limitation of superplasticizers is that the concrete will lose its high-consistency in 30-60 minutes, reverting back to its original slump. Therefore, there is only this short window of time between mixing and placing. For precast concrete, this is usually not a complication. In fact, in precast, it is often desirable to have this short duration before regaining stiffness, especially for steam curing, which is a more rapid way to cure concrete.15 On the other hand, the high slump loss characteristic that occurs with adding superplasticizer may pose a serious problem for ready-mix concrete. On the job site, many other factors may cause a time delay between mixing and pouring. Such unforeseen occasions could lead to wasted concrete and labor, if not requiring more for repair. Researchers have discovered two methods of dealing with this problem.16 The first is to perform repeat dosages of superplasticizer after slump loss, to maintain workability over several hours. After the second or third dosages, however, the concrete mix may become prone to segregation. The second strategy is to add a retarding agent to the admixture, which may maintain the increased slump for 2-3 hours. Such admixtures with these retarding agents are termed low-slump-loss superplasticizers and have been used in hot-weather concrete where the high temperature induces quicker setting times.17 Several tests have been performed on superplasticized concrete vs. control mixes. The following table shows how several important properties of SCC achieved with superplasticizers compare to those of low-slump and high-slump control mixes:

14 Khayat et al. 15 Mehta and Monteiro 16 Mehta and Monteiro 17 Mehta and Monteiro


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Table 1: Experimental Results Comparing Properties of Mixes with and

without Superplasticizer Properties of Mixes with Superplasticizer

Compared to high-slump(watery concrete)

Compared to low-slump (75 mm)

Slump Loss Faster Setting Time Retardation Slight Segregation & Bleeding Slight Comp & Flex Strength Not much difference Freeze-Thaw Durability Overall satisfactory Permeability Overall satisfactory Drying Shrinkage Less No difference The superplasticizers used were melamine sulfonate and naphthalene sulfonate and increased slump of the control mixture from 75 mm to 215 and 230 mm, respectively.18 The primary purpose behind using superplasticizers is in achieving highly flowable concrete while maintaining low water and high fines content. Low water-to-cement ratio is a principal factor enhancing strength, durability, permeability and shrinkage. See Figure 4. The latest generation of this

admixture allows retaining high performance in these categories while making an otherwise unworkable concrete highly flowable during the time required. Superplasticizers can be expensive, adding about $5 per cubic yard of concrete. However, savings in labor and time quickly outweigh the additional cost.

18 Mehta and Monteiro.

Figure 4: Optimum combination of superplasticizer and w/c ratio. (Okamura)


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Mix Proportioning The portioning of the mix is extremely important in developing an effective SCC. This involves either modifying the cement paste, or carefully tuning the aggregates, or both.19 The interlocking of coarse aggregates is integral to the strength of the concrete.20 With coarse aggregate, changing interparticle spacing most practically changes the flowability of concrete. Interparticle spacing depends on particle size distribution and the cement paste. The cement paste must work with the coarse aggregates to fill the interstitial voids for a given particle size distribution of aggregate and produce a desirable interparticle spacing. Several researchers have produced mixture proportion guidelines from their tests, in terms of ratios between coarse and fine aggregates, and cement to solids. 21 Others recommend development of an optimum paste using recommended additional values for such characteristics as aggregate surfaces, aggregate shape, difference in density between aggregate and paste.22 As mentioned previously, careful mix proportioning is critical for optimizing the performance of the flow-enhancing superplasticizers, which introduce the danger of segregation to the mix. Coarse aggregates tend to settle with the introduction of superplasticizer, which causes segregation. There are two paths one can take to avoid segregation due to superplasticizers. The first path is to strictly incorporate a smooth distribution of fine aggregates without increasing cement. This will enhance cohesion without requiring more water, which leads to problems with shrinkage and curling. Nasvik recommends 20-25% of this be fly ash, because it has the property of increasing slump flow.23 Monteiro recommends replacing approximately 5% of coarse aggregates with sands, up to 10% if coarse sand.24 A well-graded aggregate mix, however, is not always available, since many producers lack the more sophisticated equipment and material to do so. In this case, mix the designer could pursue a second path, which is to replace a 19 Bui et al. 20 L. J. O’Flannery and M. M. O’Mahony, “Precise shape grading of coarse aggregate,” Magazine of Concrete Research, October 1999. 21 Aaron .w Saak, Hamlin M. Jennings, and Surenda Pl Shah, “New Methodology for Designing Self-Compacting Concrete”, ACI Materials Journal, v.98 no. 6, November-December 2001. 22 Bui et al. 23 Nasvik 24 Mehta and Monteiro


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portion of the coarse aggregate with cementious content. This could be any combination of fly ash, ground limestone25, granulated furnace slag,26 sand, and cement. With the introduction of more cement in a gap graded mix, more water is needed to completely hydrate the cement. Thus, two potentially deleterious effects arise due to needing more water: higher heat of hydration and segregation and/or bleeding. Therefore, when taking the second path, use of pozzolan is recommended, since it reduces the added heat of hydration, and use of viscosity modifying admixtures, to provide stability.27 More about viscosity modifying admixtures later. Air entrainment can also be added as necessary to enhance freeze-thaw performance.28 Otherwise, air content between 1.5% and 2.3% in non-air-entrained content has been suggested to maintain workability and flowability.29 Some caution must be taken if the concrete needs to be transported significantly after adding high-range water reducers or viscosity modifying admixtures. Both can destabilize the air-voids of the mix, but proper proportioning can produce concrete resistant to freezing and thawing.30 Overall, correct proportioning of the fine and coarse aggregates, cement paste, water and additives is critical. Increasing w/c can increase deformability of the paste, but can reduce cohesiveness.31 Higher fines content can provide the less segregation. However, more fines, as well as manufactured sand or inconsistency in fine aggregates, also leads to higher shrinkage, creep, and warping potential, a particular concern for flat slabs.32 Okamura recommends using 50% coarse aggregate, 40% fine aggregate, 0.9 to 1.0 w/c in volume, and changing the superplasticizer dosage for the needed self-compactibility.33 See Figure 5.

25 Lechemi et al. 26 M.K. Hurd, “Self-Compacting Concrete”, Concrete Construction, January 2002. 27 Nasvik 28 Hurd 29 Lachemi et al. 30 Kamal H. Khayat and Joseph Assaad, “Air-Void Stability in Self-Consolidating Concrete,” ACI Materials Journal, July-August 2002. 31 K. H. Khayat, “Workability, Testing, and Performance of Self-Consolidating Concrete”, ACI Material Journal, May-June 1999. 32 Nasvik 33 Okamura

Figure 5: Proper fine aggregate content for SCC as recommended by Okamura.


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Viscosity Modifying Admixtures Viscosity Modifiers are used to stabilize the rheology of SCC. They essentially thicken the mix to prevent segregation.34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate, which further inhibits flow and increases viscosity. At the same time, added VMA causes a shear-thinning behavior, decreasing viscosity, when there is an increase in shear rate.35 There are various types of VMAs, most of which are composed of either polymer or cellulose-based materials, which “grab and hold” water. The most important aspect is that they do not change any properties of the mix besides viscosity.36 One of the most well-known VMAs is welan gum, which is a natural type of water soluble polysaccharide. When used in large quantities, it has proven very effective in stabilizing the rheology of SCCs.37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets. Currently, these commercial brands and welan gum are known to be very expensive, increasing cost of the mix by at least 20%. Consequently, there is a great deal of ongoing research in the materials sciences, often with financial support from industry, to develop cheaper VMAs with equally reliable high performance. One study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs. Performance of four mixes with each of these new VMAs was compared to two types of control mixes, one with welan gum and a one with a commercial VMA from a Canadian producer. Results showed that performance of the newly developed admixtures matched, or even beat, the control mixes in properties of slump flow, segregation, bleeding, flow time, setting time, and compressive strength. An important characteristic to note is the increase in setting time caused by addition of VMAs. This occurs “because the VMA polymer chains become absorbed onto cement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting.”38

34 Nasvik 35 Lachemi et al. 36 Nasvik. 37 Rols et al. 38 Lachemi et al.


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Another study at the National Applied Science Institute of Lyon in France tested three new viscosity agents: starch, precipitated silica, and industrial starch waste. They found that aqueous solutions of 20% precipitated silica and, to a lesser extent, 10% starch performed as the best viscosity agents. In particular, both allowed limited segregation and bleeding, contributed to high 28-day compressive strength, allowed limited permeability, and therefore good durability. The only property negatively affected was drying shrinkage, which increased 50% due to the reduction in coarse aggregate. To prevent cracking and ensure the concrete develops its potential strength and durability, measures should be taken towards proper curing. Overall, these agents could be suitable as alternatives to welan gum.39 VMAs can be used alone, but are more commonly used with superplasticizers. In this combination, the superplasticizers take on the role of enhancing flow while VMAs act to provide stability. All the while, careful aggregate proportioning still plays a key part. The three acting together can create remarkable SCC, but quality control of each of these materials and over their proportions becomes that much more critical. In particular, use of superplasticizer makes the mix extremely sensitive to slight changes in water content. Benefits of SCC The technologically advanced components of SCC work together to create a mix that produces numerous benefits. It offers many advantages for contractors, ready-mix producers, and precast concrete fabricators: For Contractors:40,41,42

Reduced vibration effort and noise during placing Ability to fill complex forms with limited accessibility More uniform distribution in areas of closely bunched reinforcement Rapid pumping of concrete Uniform and compact surface Less surface voids and need for rubbing and patching Improved aesthetics of flatwork for less effort

39 Rols et al. 40 Bui et al. 41 Mehta and Monteiro 42 Hurd


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Reduced labor and construction time For Ready-Mix Producers:43,44

Better perception from customers by offering a technically advanced, higher value concrete mixture

Offers a product that saves customers time and money Faster truck turnaround More efficient use of mixing equipment and delivery Easily expands variety of products offered without adding more

equipment (eg, tilt-up, flatwork, walls, etc.) Improved aesthetics of final product

For Cast-in Place Fabricators:

All the above, plus Controlled environment allows easier quality control Easier to achieve qualities of an optimally designed mix Can better guarantee properties due to tight quality control Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC, they need an increased understanding of SCC’s complex nature. Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users. At the same time, developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics. Standards As mentioned before, there are as yet no standard definitions or specifications for SCC. The term workability includes flowability, mouldability, cohesiveness, and compactibility of fresh concrete. Flowability is related to consistency. Cohesiveness is a measure of compactibility and finishability, usually measured by ease of dowelling and visual judgement of resistance to segregation.45 Given that workability is so broadly defined by numerous other factors, measuring the properties of High-Workability Concrete has gone in all directions. 43 Nasvik 44 Bui et al. 45 E. Chidiac, O. Maadani, A. G. Razaqpur and N. P. Mailvaganam, “Controlling the quality of fresh concrete,” Magazine of Concrete Research, October 2000.


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Some believe SCC should not be defined as a new product. New products require all new testing and approval from ACI and ASTM. Since it is still a developing technology, many appreciate the flexibility to develop mixes according to project requirements, currently the industry practice. Until test methods to quantifiably characterize the concrete mix are standardized, the following are several industry measurement standards used for the time being.46 Flowability: This characteristic is often termed “slump flow” as opposed to “slump” because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much, the height difference becomes too little to accurately correlate with the flowability of the mix, not to mention the difficulty in measuring the height of the slumped sample. Therefore, slump flow is measured as the horizontal distance of spreading. Usually, this dimension is 20-30 inches.47 In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation efforts. See Figure 6. The flow diameter (Fd) is the mean diameter measured in two perpendicular directions.48 Some researchers recommend a slump flow value between 500 to 700 mm. At less than 500 mm, the mix may have trouble flowing in a confined space. Slump flow exceeding 700 mm could lead to segregation of the mix.49

46 Nasvik 47 Nasvik 48 Bui et al. 49 Lachemi et al.

Figure 6: Slump Flow and L-box Tests (Nasvik)

Figure 7: V-funnel Test (Lachemi)


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The L-box test measures the ability of SCC to flow in a confined space. It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow.50,51 See Figure 6. Another way to measure deformability through restricted areas is the V-funnel test. See Figure 7. After concrete is filled into the funnel, the bottom outlet is opened and the time until flowing stops is measured. To be termed an SCC, it is generally required that this flow time be less than 6 sec.52 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-3/4 inches (or 50 cm) in diameter in the slump flow test.53 Bui et al. states that the flow time of SCC should be no larger than 12 seconds.54 Stability: Stability is the characteristic of SCC to resist segregation. It is often quantified with the Visual Stability Index, which ranges from 0 to 3 in increments of 0.5.55 Another, more exact segregation test, is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min. The segregation index (SI) of a stable concrete should be less than 5%.56 Current Action: ASTM C 09.47 subcommittee is in the process of voting on a terminology standard and standard methods for conducting the slump flow test. They are

50 Bui et al. 51 Nasvik 52 Lachemi et al. 53 Nasvik 54 Bui et al. 55 Nasvik 56 Lachemi et al.


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also developing a way to use existing compressive strength test methods on SCC.57 Another fresh concrete property in definite need of study is formwork pressures, in particular, the effects of SCC’s changing viscosity characteristic. Long-term evaluation also needs to be made specifically in areas of creep, shrinkage, and modulus of elasticity.58 Application SCC technology originated in Japan in the early 1980s,59 arising out of durability concerns due to poor compaction on the job site.60 Use of SCC quickly became widespread in Japan, especially since the government implemented a plan to use SCC for 50% of all concrete jobs by 2003. It then spread to Europe in the 1990’s after invention of polycarboxylate superplasticizers. In the UK, The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction.61 In the US and Canada, SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh. It is also available as specialized admixtures combining superplasticizer and viscosity modifiers.62 Given how important maintaining mix quality of SCC is for its successful performance, using SCC demands increased attention and skill. In particular, superplasticizer dramatically increases the sensitivity of the mix to water. This allows little room for error in mix proportioning, which can become problematic in-field when weather and timing can not always be controlled by the contractor. In light of this, most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plant compared to in-field.63 However, the industry has shown eagerness to expand its use. Whereas in 2000, only about 10% of the precast industry had tried SCC, by 2003, the number jumped to almost 90%, of which 40% used it on a regular basis.

57 Nasvik 58 Hurd 59 Bui et al. 60 Okamura. 61 Hurd 62 Hurd 63 Hurd


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Some notable projects have utilized SCC in Canada. One is the Toronto International Airport, where concrete had to be pumped upwards from the ground to form 101-foot tall columns. Another project in Vancouver, B.C used SCC so little patching would be required for highly visible, outrigger columns.64 In Asia, SCC was used for a monolithic foundation mat in Singapore where the concrete needed to reach massive dimensions in a short amount of time. In the US, a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City.65 SCC has also shown successful application for residential projects, such as homes for Habitat for Humanity in the Houston area.66

64 Hurd 65 Mehta and Monteiro 66 Hurd


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Conclusion

In conclusion, self-consolidating concrete is an exciting technology that has found many successful applications. Although the concept has been around for a few decades, new products are still emerging and better mix proportioning strategies are still in development. The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward. Meanwhile, multiple viscosity modifying admixtures are available, while researchers continue to seek better and cheaper recipes. While there is no set definition for SCC yet, for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC. The absence of an established industrial standard for SCC allows more creativity in tailoring a mix to specific job requirements. At the same time, the lack of standards means devising a successful mix depends on the expertise of the producer and contractor. Therefore, it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCC’s extremely promising technology.


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References

1. Sebastien Rols, Jean Ambroise, Jean Pera, “Effects of Different Viscosity Agents on the Properties of Self-Leveling Concrete,” Cement and Concrete Research

2. Van K. Bui, Yilmaz Akkaya, and Surendra P. Shah, “Rheology Model for Self-Consolidating Concrete”, ACI Materials Journal, November-December 2002.

3. M. Lachemi, K.M.A. Hossain, V.Lambros, P.C. Nkinamubanzi, N. Bouzoubaa, “Self-consolidating concrete incorporating new viscosity modifying admixtures”, Cement and Concrete Research

4. Kamal H. Khayat, Patrick Paultre, and Stephen Tremblay, “Structural Performance and In-Place Properties of Self-Consolidating Concrete”, ACI Materials Journal, Sept-Oct 2001.

5. Joe Nasvik, “The ABCs of SCC”, Concrete Construction, January 2002. 6. Hajume Okamura, “Self-Compacting, High Performance Concrete”, Concrete

International, July 1997. 7. L. J. O’Flannery and M. M. O’Mahony, “Precise shape grading of coarse aggregate,”

Magazine of Concrete Research, October 1999. 8. Aaron .w Saak, Hamlin M. Jennings, and Surenda Pl Shah, “New Methodology for

Designing Self-Compacting Concrete”, ACI Materials Journal, v.98 no. 6, November-December 2001.

9. E. Chidiac, O. Maadani, A. G. Razaqpur and N. P. Mailvaganam, “Controlling the quality of fresh concrete,” Magazine of Concrete Research, October 2000.

10. Kamal H. Khayat and Joseph Assaad, “Air-Void Stability in Self-Consolidating Concrete,” ACI Materials Journal, July-August 2002.

11. K. H. Khayat, “Workability, Testing, and Performance of Self-Consolidating Concrete”, ACI Material Journal, May-June 1999.

12. M.K. Hurd, “Self-Compacting Concrete”, Concrete Construction, January 2002. 13. Aaron .w Saak, Hamlin M. Jennings, and Surenda Pl Shah, “New Methodology for

Designing Self-Compacting Concrete”, ACI Materials Journal, v.98 no. 6, November-December 2001.

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