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Advanced High-Performance Materials for Highway Applications: A Report on the State of Technology

Chapter 3, Candidate Concrete Materials

Engineered Cement Composites

Description

ECCs are high-performance, fiber-reinforced cement-based materials. ECCs are similar to conventional fiber-reinforced concrete (FRC) in terms of its constituent materials, except coarse aggregates are not used (these adversely affect the ductile behavior of the material) and lower fiber contents are employed (typically 2 percent or less by volume) (Li 2005). Furthermore, unlike FRC, ECC is a micromechanically designed material, which means that the mechanical interactions between the fiber, cement matrix, and interface are taken into account by a micromechanical model which relates these individual constituent properties to an overall composite response (Li 2005). The end result is a highly ductile composite material nicknamed "bendable" concrete by many researchers.

Some of the characteristics of ECC materials include the following (Li 2005; Yang et al. 2009; PCA 2009):

  • High tensile ductility (strain capacities of 3 to 5 percent, about 300 times that of conventional concrete).
  • High fracture toughness.
  • Autogenous healing of hairline cracks.
  • Higher compressive strengths.
Applications

Because of its light weight, ECC has perhaps the greatest potential for use on bridges, bridge decks, and other highway structures.

Benefits

The benefits of ECC are similar to those offered by conventional FRC materials, such as improved structural integrity, resistance to plastic shrinkage, and improved post-cracking behavior. However, ECC goes beyond conventional FRC by also offering high tensile ductility and the potential for autogenous healing of hairline cracks.

Costs

No cost data are currently available regarding ECC. The unit cost of ECC is higher than conventional concrete, but because of its greater strength and ductility, reduced cross sections (and hence less material) may be required for a given application.

Current Status

ECC has seen use as a repair material for a bridge deck in Michigan, for a lightweight composite bridge deck in Japan, and as an infrastructure patching material in Japan and the United States. More widespread use and monitoring of in-service performance of ECC are needed to establish its viability.

For More Information

Li, V. C. 2005. "Engineered Cementitious Composites." Proceedings, Third International Conference on Construction Materials: Performance, Innovations and Structural Implications, Vancouver, Canada.

Portland Cement Association (PCA). 2009. Bendable Concrete. http://www.cement.org/tech/cct_con_design_bendable.asp. Accessed September 2, 2009.

Yang, Y., M. D. Lepech, E. H. Yang, and V. C. Li. 2009. "Autogenous Healing of Engineered Cementitious Composites Under Wet-Dry Cycles." Cement and Concrete Research, Vol. 39, No. 5. Elsevier Publishing.

Titanium Dioxide - Modified Concrete

Description

Titanium dioxide (TiO2) is widely used as a white pigment in a number of products, such as paints, coatings, plastics, and toothpaste. In addition, TiO2 is a potent photocatalyst that can break down almost any organic compound it touches when exposed to sunlight in the presence of water vapor (Frazer 2009). Recently, research has been conducted in adding TiO2 to cement mortar to diminish the polluting effect of exhaust gases; in particular, nitrogen oxide is removed from the air and broken down into more environmentally benign substances that can be washed away by rainfall.

One product available that uses TiO2 is TX Active® "smog-eating" cement manufactured by Italcementi over the last 10 years. A stretch of concrete pavement in Bergamo, Italy, was coated with a layer of TX Active, with claims of odor reductions within 4.5 mi2 (11.7 km2). This product was named one of the top 50 inventions of 2008 by Time magazine.

Applications

Although TiO2-modified concrete could be used in almost any type of application, it may have greatest potential for use in urban areas where the levels of nitrogen oxides are greatest due to the higher volumes of traffic. In addition, the inclusion of TiO2 helps maintain the whiteness of the cement, which may be important for certain aesthetic applications.

In addition to being used in conventional concrete, a thin layer of TiO2 has been added to paver blocks used in urban street construction in Japan.

Benefits

As described above, the greatest benefit associated with the use of TiO2 is the conversion of noxious nitrogen oxides into more environmentally friendly compounds.

Costs

No cost data are currently available, but costs for TiO2 modified concrete are expected to be higher than for conventional concrete.

Current Status

There is considerable interest in the use of TiO2 as a means of reducing nitrogen oxides, although some researchers believe that a more direct way of reducing nitrogen oxides (through improved automotive emission controls) may be more appropriate. Several cities, including London, are contemplating the use of TiO2 in paving applications.

A test section that incorporates TiO2 in the upper lift of a two-lift concrete pavement is under construction near Chesterfield, Missouri (as of September 2010). As part of the test section construction, Missouri DOT performed a detailed study of the concrete incorporating TiO2.

For More Information

Beeldens, A. 2006. An Environmental Friendly Solution for Air Purification and Self-Cleaning Effect: The Application of TIO2 as Photocatalyst in Concrete. Belgian Road Research Centre, Brussels, Belgium.

Federal Highway Administration (FHWA). 2005. Long-Term Plan for Concrete Pavement Research and Technology - The Concrete Pavement Road Map: Volume II, Tracks. HRT-05-053. FHWA, Washington, DC.

Frazer, L. 2009. Titanium Dioxide: Environmental White Knight? http://www.ehponline.org/docs/2001/109-4/innovations.html (accessed September 9, 2009).

Jayapalan, A. R., B. Y. Lee, S. M. Fredrich, and K. Kurtis. 2010. "Influence of Additions of Anatase TiO2 Nanoparticles on Early-Age Properties of Cement-Based Materials," Transportation Research Record: Journal of the Transportation Research Board, No. 2141, 41 - 46.

TIME. http://www.time.com/time/specials/packages/article/0,28804,1852747_1854195_1854176,00.html

Trautman, B. 2010. "Characterization of TX Active Cement," presentation at the National Open House on Two-Lift Concrete Paving near Chesterfield, Missouri. Missouri Department of Transportation, Springfield, MO.

Pervious Concrete

Description

Pervious concrete is a special type of concrete made of cementitious materials, water, admixtures, and narrowly graded coarse aggregate (Tennis, Leming, and Akers 2004). Containing very little or no fine aggregate and just enough cement paste to coat the aggregate, a system of interconnected voids (typically 15 to 35 percent) is created that provides a permeable concrete material capable of draining water very quickly (ACI 2006). Typical properties of pervious concrete include the following (Obla 2007):

  • Slumps less than 0.75 in. (19 mm).
  • In-place densities of 100 to 125 lb/ft3 (1,602 to 2,002 kg/m3).
  • Compressive strengths from 500 to 4,000 lb/in2 (3.4 to 27.6 MPa).
  • Flexural strengths from 150 to 550 lb/in2 (1 to 3.8 MPa).
  • Permeability from 2 to 18 gal/min/ft2 (81.5 to 733.4 L/min/m2).
Applications

Pervious concrete has been used in a number of different applications, including parking areas, greenhouse floors, tennis courts, residential parking lanes, pedestrian walkways, pavements needing acoustic absorption characteristics, swimming pool decks, and low-volume roadways (ACI 2006). Pavement structures using pervious concrete are not intended to be subjected to heavy truck traffic. While pervious concrete has been successfully used throughout the warmer climates of the United States, there are some concerns about its use in areas subjected to severe freeze - thaw cycles. The National Ready Mixed Concrete Association has developed guidelines for using pervious concrete in areas prone to freeze - thaw conditions, focusing on such things as designing the pavement to limit the amount of saturation and incorporating a proper subbase course (NRMCA 2004).

Benefits

Pervious concrete offers a number of benefits, including the following (Chopra et al. 2007):

  • Pervious concrete essentially serves as a retention pond, significantly reducing surface water runoff and reducing the need for curbing and storm sewers.
  • Pervious concrete "filters" storm water that run through it, removing pollutants that would otherwise enter the groundwater, streams, or storage ponds.
  • By allowing water to pass directly, pervious concrete helps recharge groundwater supplies.
  • Pervious concrete helps improve road safety because of reduced hydroplaning potential.
  • Pervious concrete can help absorb noise emissions.
Costs

The cost of pervious concrete can vary depending on the region, the type of application, and the size of the project, but some data suggest that pervious concrete can be 15 to 25 percent more expensive than conventional concrete.

Current Status

The use of pervious concrete has increased significantly in the last several years, perhaps largely because it is considered an environmentally friendly, sustainable product. The use of pervious concrete is among the "Best Management Practices" recommended by the U.S. Environmental Protection Agency and other agencies for the management of stormwater runoff on a regional and local basis. The inclusion of a pervious pavement is given additional LEED (Leadership in Energy and Environmental Design) credits, and a number of cities (including the City of Chicago in its "Green Alleys" initiative) and companies (including Wal-Mart) are incorporating pervious concrete into their construction programs.

For More Information

American Concrete Institute (ACI). 2006. Pervious Concrete. ACI 522R-06. American Concrete Institute, Farmington Hills, MI.

Chopra, M., M. Wanielista, C. Ballock, and J. Spence. 2007. Construction and Maintenance Assessment of Pervious Concrete Pavements. Final Report. Florida Department of Transportation, Tallahassee, FL.

Kevern, J. T., V. R. Schaefer, K. Wang, and P. Wiegand. 2010. "Performance of Pervious Concrete Mixtures Designed for Roadway Overlay Applications," Proceedings of the International Conference on Sustainable Concrete Pavements: Practices, Challenges, and Directions (pp. 239 - 250), held in Sacramento, California, September 15 - 17, 2010, Federal Highway Administration.

National Ready Mixed Concrete Association (NRMCA). 2004. Freeze - Thaw Resistance of Pervious Concrete. National Ready Mixed Concrete Association, Silver Spring, MD.

Obla, K. 2007. "Pervious Concrete for Sustainable Development." Proceedings of the First International Conference on Recent Advances in Concrete Technology, September 2007, Washington, DC.

Tennis, P. D., M. L. Leming, and D. J. Akers. Pervious Concrete Pavements. Engineering Bulletin EB302. Portland Cement Association, Skokie, IL, and National Ready Mixed Concrete Association, Silver Spring, MD.

Self-Consolidating Concrete

Description

Self-consolidating concrete (SCC) is a high-performance concrete that can flow easily into tight and constricted spaces without segregating and without requiring vibration (Szecsy and Mohler 2009). First used in the 1980s, the key to creating effective SCC is the development of a mixture that is not only fluid but also inherently stable so as to prevent segregation. Flowable properties are typically achieved with one or more of the following mix design attributes (Lange et al. 2008):

  • High cementitious materials content (greater than 750 lb/yd3 [445 kg/m3]).
  • Inclusion of next-generation superplasticizers (possibly in combination with a viscosity-modifying admixture).
  • Inclusion of mineral admixtures (e.g., silica fume, fly ash, ground-granulated blast furnace slag), which help reduce the potential for segregation.
  • Careful selection of aggregate volume and gradation. In particular, low aggregate volume and smaller coarse aggregate size are often needed to improve flow around steel reinforcement to reach restricted areas.

The flowability of SCC is measured in terms of spread when using a modified version of the slump test (ASTM C 143), and it typically ranges from 18 to 32 in. (457 to 813 mm) depending on the project requirements (NRMCA 2009).

Applications

SCC has been used in a variety of applications, including architectural concrete, columns, residential structures, beams, tanks, footers, and pumped concrete (NRMCA 2009). A recent construction project in Illinois used SCC for over 20 mi (32.2 km) of retaining wall structures along an interstate highway (Lange et al. 2008).

Benefits

There are a number of benefits associated with the use of SCC, including the following (NRMCA 2009):

  • Faster placement rate with no mechanical vibration and less screeding, resulting in savings in placement costs.
  • Improved and more uniform architectural surface finish with little to no remedial surface work.
  • Ease of filling restricted sections and hard-to-reach areas.
  • Improved consolidation around reinforcement and improved bond with reinforcement.
  • Improved pumpability.
  • Improved uniformity of in-place concrete by eliminating variable operator-related effort of consolidation.
  • Shorter construction periods and resulting cost savings.
  • Reduction or elimination of vibrator noise, potentially increasing available hours for construction in urban areas.
Costs

Although the material production costs for SCC are higher than for conventional concrete, overall cost savings can be realized with SCC because of increased productivity and reduced labor requirements.

Current Status

SCC continues to see increasing growth in usage in the construction industry, particularly in structural applications. Because of its unique properties, significant research has been performed to develop new test methods for characterizing SCC mixtures, such as the slump flow (ASTM C1611), the J-ring (ASTM C1621), and the column segregation (ASTM C1610) tests (Szecsy and Mohler 2009). Some research is also being conducted to identify suitable SCC mixtures for slip-form paving applications.

For More Information

American Concrete Institute (ACI). 2007. Self-Consolidating Concrete. ACI 237R-07. American Concrete Institute, Farmington Hills, MI.

Lange, D. A., L. J. Struble, M. D. Dambrosia, L. Shen, F. Tejeda-Dominguez, B. F. Birch, and A. J. Brinks. 2008. Performance and Acceptance of Self-Consolidating Concrete: Final Report. FHWA-ICT-08-020. Illinois Department of Transportation, Springfield, IL.

National Ready Mixed Concrete Association (NRMCA). 2009. Self-Consolidating Concrete. http://www.selfconsolidatingconcrete.org/. NRMCA, Silver Spring, MD.

Szecsy, R., and N. Mohler. 2009. Self-Consolidating Concrete. Publication IS546D. Portland Cement Association, Skokie, IL.

Wang, K., S. P. Shah, D. White, J. Gray, T. Voigt, L. Gang, J. Hu, C. Halverson, and B. Y. Pekmezci. 2005. Self-Consolidating Concrete - Applications for Slip-Form Paving: Phase I (Feasibility Study). Report TPF-5(098). Federal Highway Administration, Washington, DC, and Iowa Department of Transportation, Ames, IA.

Sulfur Concrete

Description

Sulfur concrete is made from sulfur collected from the petroleum refining process and coal ash from coal-burning power plants (FHWA 2005). The process applies vibration and pressure to a mixture of heated sulfur and coal ash, with the result being a dense, strong material that is highly resistant to acid and other chemicals. Sulfur concrete gains strength very rapidly, and can achieve compressive strengths in excess of 9,000 lb/in2 (62.1 MPa) within 1 day (ACI 1993). The materials are impervious to moisture permeation and extremely resistant to attack by mineral acids and salts.

Applications

Sulfur concrete may be suitable for use in applications where conventional PCC may not be appropriate, such as saline environments or in areas exposed to chemicals or acids. Possible applications include industrial floors, bridge decks, tanks, pipes and pipe linings, and tunnel linings.

Benefits

The primary benefits of sulfur concrete are its rapid strength gain, dense matrix, and excellent durability and resistance to acids and chemicals. In addition, it has an environmental advantage, since it is produced using by-product and waste materials.

Costs

Cost data for sulfur concrete are not available.

Current Status

Although widely researched in the 1970s and early 1980s, sulfur concrete has not seen significant usage or research activity in the last decade. But given its high early strengths and resistance to chemicals and salts, there may be renewed interest in evaluating the suitability of sulfur concrete in transportation applications.

For More Information

American Concrete Institute (ACI). 1993. Guide for Mixing and Placing Sulfur Concrete in Construction. ACI Publication 548.2R-93. American Concrete Institute, Farmington Hills, MI.

Federal Highway Administration (FHWA). 2005. Long-Term Plan for Concrete Pavement Research and Technology - The Concrete Pavement Road Map: Volume II, Tracks. HRT-05-053. FHWA, Washington, DC.

Autoclaved Aerated Concrete

Description

Autoclaved aerated concrete (AAC), sometimes referred to as autoclaved cellular concrete (ACC), is a lightweight precast structural product made from silica sand (AAC) or fly ash (ACC), gypsum, lime, cement, water, and an expansion agent (aluminum). It is an economical and sustainable construction block/panel material that provides thermal and acoustic insulation, as well as fire and termite resistance. While AAC is primarily manufactured for use in commercial, industrial, and residential buildings, it has potential application in the highways arena in the form of sound barrier walls for traffic noise mitigation.

AAC has been a popular building material in Europe for over 50 years and was first introduced in the United States about two decades ago. The manufacturing process involves grinding the sand (or fly ash) and gypsum to a consistency of powder and then mixing in the lime, cement, water, and aluminum (powder or paste form) (PCA 1991). After mixing, the slurry is poured into greased molds up to two-thirds of their depth (for load-bearing panels, rust-protected steel reinforcement mats are positioned into the molds prior to casting). The aluminum agent reacts with calcium hydroxide and water to produce hydrogen gas, which aerates the mixture (millions of microscopic, finely-dispersed cells) and causes it to expand by more than double in volume. The molds are placed in a pre-curing room for several hours, after which the semi-solid material is cut using steel wires to form the sizes required for the building elements. The material is then placed in an autoclave for 10 to 12 hours, whereby the steam pressure hardening process causes the sand to react with calcium hydroxide to form calcium silica hydrate, which increases its strength.

Depending on the application, the final AAC product is about 80 percent air by volume and has a density of approximately 45 lb/ft3 (720.8 kg/m3). The average minimum compressive strength of AAC ranges between 750 and 1,000 lb/in2 (5.2 and 6.9 MPa). A typical noise reduction coefficient for unpainted AAC is 0.15, as compared to 0.02 for conventional concrete and 0.07 for concrete masonry. Also, the R-value for an AAC block 8 in. (203 mm) thick is about 13.28, as compared to 0.98 to 2.30 for a block of conventional concrete 8 in. (203 mm) thick (PCA 1991).

Manufactured panels are generally available in dimensions of 8 to 12 in. (203 to 305 mm) thick, 24 in. (610 mm) wide, and lengths up to 20 ft (6.1 m). Manufactured blocks are generally made 24, 32, and 48 in. (610, 813, and 1219 mm) long, between 4 and 16 in. (102 and 406 mm) thick, and 8 in. (203 mm) high. AAC can be cut or trimmed on-site with a handsaw to achieve the desired fit.

Construction of highway sound barrier walls using AAC typically consists of installing post (concrete or steel) and post foundations at specified intervals along the side of the road, and then setting and stacking the AAC panels into place between the posts to the specified height. Maintenance and repair are generally limited to individual panel replacements or cementitious patches to small damaged areas.

Applications

As previously described, in the highway arena AAC precast blocks and panels are generally most suitable for use as sound barrier walls along high-speed, high-volume highways located in noise-sensitive environments. In a similar application, they can be integrated with retaining walls and bridge parapets (Schnitzler 2006).

Benefits

AAC precast blocks/panels provide a highly effective, economical, and sustainable approach toward mitigating highway traffic noise. They possess excellent noise-dampening properties, are 100 percent recyclable, and, because they are lightweight and can be easily modified to size, can be installed quickly and efficiently.

Costs

The cost of AAC sound walls relative to other types of sound walls is highly variable and depends in large part on project location. Projects distantly located from the few places of manufacture will experience higher initial costs due to the additional transportation costs. On the other hand, the initial cost of precast AAC is reduced by the fact that the material can be installed more quickly than some other forms of sound walls.

Current Status

There are now only a few AAC/ACC manufacturing facilities in the United States. Although only a few States (e.g., Arizona, Georgia) have constructed significant amounts (estimated 100+ mi [161+ km]) of AAC sound barrier walls, it is expected that the beneficial properties of the material and the speed at which it can be installed will result in increased usage in the future.

For More Information

Barnett, R. E. 2005. "Autoclaved Aerated Concrete: A Lime-Based Technology." Proceedings, International Building Lime Symposium, Orlando, FL.

Portland Cement Association (PCA). 1991. "Autoclaved Cellular Concrete - The Building Material of the 21st Century." Concrete Technology Today, Vol.12, No. 2. Portland Cement Association, Skokie, IL.

Schnitzler, S. 2006. "Autoclaved Aerated Concrete as a Green Building Material." Applied Research Paper on Sustainability and the Built Environment. University of California at Davis, Davis, CA.

Geopolymer Concrete

Description

The term geopolymer represents a broad range of materials characterized by chains or networks of inorganic molecules.1 There are nine different classes of geopolymers, but those of greatest potential application for transportation infrastructure are composed of alumino-silicate materials that may be used to completely replace portland cement in concrete construction. These geopolymers rely on thermally activated natural materials (e.g., kaolinite clay) or industrial by-products (e.g., fly ash, slag) to provide a source of silicon (Si) and aluminum (Al), which are dissolved in an alkali-activating solution and then polymerize in chains or networks to create the hardened binder. Some of these systems have ancient roots, and have been used for decades, often being referred to as alkali-activated cements or inorganic polymer cements. Most geopolymer systems rely on minimally processed natural materials or industrial by-products to provide the binding agents, and thus require relatively little energy and release minimal amounts of CO2 during production. Since portland cement is responsible for upward of 85 percent of the energy and 90 percent of the CO2 attributed to a typical ready-mixed concrete, the energy and CO2 savings through the use of a geopolymer can be significant.

The major drawback of current geopolymer technologies is their lack of versatility and cost-effectiveness compared to portland cement systems. Although numerous geopolymer systems have been proposed (most of which are patented), most suffer from being difficult to work with, requiring great care in production while posing a safety risk due the high alkalinity of the activating solution (most commonly sodium or potassium hydroxide). In addition, the polymerization reaction is very sensitive to temperature and usually requires that the geopolymer concrete be cured at elevated temperatures, effectively limiting its use to precast applications. Considerable research is underway to develop geopolymer systems that address these technical hurdles, creating a low-embodied energy, low-CO2 binder that has properties similar to portland cement. In addition, research is also focusing on the development of user-friendly geopolymers that do not require the use of highly caustic activating solutions.

Applications

Currently, geopolymer concrete has very limited transportation infrastructure applications, being primarily restricted to international use in the precast industry. A blended portland-geopolymer cement known as Pyrament® (patented in 1984) has been used for rapid pavement repair, a technology still in use by the U.S. military along with geopolymer pavement coatings designed to resist the heat generated by vertical takeoff and landing aircraft.

Potential applications of geopolymers for bridges include precast structural elements and decks as well as structural retrofit using geopolymer fiber composites. To date, none of these potential applications is beyond the development stage.

Benefits

Benefits to be derived from the use of geopolymer concrete fit squarely into enhanced sustainability through increased longevity and reduced environmental impacts. The geopolymer systems under development for transportation infrastructure possess excellent mechanical properties and are highly durable, and therefore would result in increased longevity when used in harsh environments such as marine structures or pavements/structures exposed to heavy and frequent deicer applications. Furthermore, these systems rely on the use of industrial by-products (e.g., fly ash, slag). Most significantly, the widespread use of geopolymer concrete would significantly reduce the embodied energy and CO2 associated with the construction of concrete transportation infrastructure, significantly reducing its environmental footprint.

Costs

The cost of geopolymer concrete is unknown, as it is still under development. The raw materials are not expensive and the equipment needed for geopolymer concrete is similar to that used to produce and handle conventional PCC. Systems need to be developed that are more user-friendly and less hazardous and that ideally can be used for cast-in-place applications at ambient temperatures. One concern is that many of the geopolymer systems that have been developed are patented, which will increase the cost of implementation.

Current Status

Research into geopolymer applications is at a fever pitch, from small startup companies to major international efforts. Australia and Europe have led significant past research efforts, but there has been a dramatic increase in research in the United States in recent years as interest in developing low-CO2-emitting cementitious binders continues to grow. The first transportation application will likely be from the precast industry, but as of yet, there are no known producers of precast geopolymer concrete in the United States.

For More Information

Davidovits, J. 2002. "30 Years of Successes and Failures in Geopolymer Applications - Market Trends and Potential Breakthroughs." Proceedings of Geopolymer 2002 Conference. Melbourne, Australia.

Davidovits, J. 2008. Geopolymer Chemistry and Applications. Institut Géopolymère. Saint-Quentin, France.

Hardjito, D., S. Wallah, D. M. J. Sumajouw, and B. V. Rangan. 2004. "On the Development of Fly Ash-Based Geopolymer Concrete." ACI Materials Journal. Vol. 101, No. 6. American Concrete Institute, Farmington Hills, MI.

Lloyd, N., and V. Rangan. 2009. "Geopolymer Concrete - Sustainable Cementless Concrete." 10th ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues. ACI SP-261. American Concrete Institute, Farmington Hills, MI.

Rangan, B. V. 2008. Fly Ash-Based Geopolymer Concrete. Research Report GC 4. Curtin University of Technology, Perth, Australia.

Rangan, B. V. 2008. "Low-Calcium, Fly-Ash-Based Geopolymer Concrete." Concrete Construction Engineering Handbook. Taylor and Francis Group, Boca Raton, FL.

Tempest, B., O. Sanusi, J. Gergely, V. Ogunro, and D. Weggel. 2009. "Compressive Strength and Embodied Energy Optimization of Fly Ash Based Geopolymer Concrete." Proceeding: 2009 World of Coal Ash Conference, Lexington, KY.

Van Dam, T. 2010. "Geopolymer Concrete," FHWA TechBrief, Publication No. FHWA-HIF-10-014, Federal Highway Administration, Washington, DC.

Hydrophobic Concrete

Description

Hydrophobic concrete is produced by introducing admixtures that shut down the active capillary transport mechanism and reduce absorption levels to less than 1 percent, as tested under the BSI 1881-122 procedure (CP 2006). While ordinary low water/cement ratio concrete absorbs from 3 to 5 percent, hydrophobic concrete absorbs less than 1 percent. Hydrophobic concrete has a long history of use in Australia, Asia, and Europe, and experience in the United States dates back to about 1999 (CP 2006).

Hycrete, Inc., of Carlstadt, New Jersey, markets a family of products that provide waterproofing and corrosion protection when added to concrete, thus rendering a hydrophobic material. These admixtures effectively seal internal capillaries that are responsible for water penetration into concrete, making the resultant product completely waterproof. As a result, for below-ground structures, external waterproof membranes, coatings, or sheeting treatments are no longer required, which increases productivity. The use of hydrophobic material also makes the concrete completely recyclable at the end of its life since it is the presence of those external waterproofing membranes that make concrete unsuitable for recycling. In addition, the product also provides corrosion protection by forming a protective coating around the steel reinforcement.

Applications

Primary applications for hydrophobic concrete include subgrade walls and slabs, elevated decks for parking structures, plazas and green-roof systems, tunnels, transportation infrastructure, and marine facilities (CP 2006). In the highway field, the most logical use of these hydrophobic concrete is in the construction of bridges, and several highway agencies have constructed experimental bridge projects featuring Hycrete admixtures (Wojakowski and Distlehorst 2009).

Benefits

As described in the preceding paragraphs, the primary benefits provided by hydrophobic concrete are the following (CP 2006; Wojakowski and Distlehorst 2009):

  • The concrete is effectively waterproofed since the internal capillaries are sealed. This eliminates the need for any external waterproofing for below-ground structures, an activity that can be time- and weather-sensitive, so the overall construction schedule can be accelerated.
  • The corrosion of embedded steel is prevented or reduced, not only by reducing the permeability of the concrete but also by forming a protective layer around the steel.
  • A key environmental benefit is that concrete that would otherwise be waterproofed externally (through toxic chemicals and volatile organic compounds) can now be fully recycled at the end of its service life if it employed hydrophobic admixtures. In addition, concrete constructed with the Hycrete waterproofing admixtures has earned credit under the LEED program since savings in time and materials are realized.
Costs

Cost information on hydrophobic admixtures is not available. In applications where external waterproofing would otherwise be used, it is estimated that the use of hydrophobic concrete can save contractors between 20 and 60 percent (CP 2006).

Current Status

The use of hydrophobic concrete appears to be growing in the commercial structural industry, but in the highway arena only a few agencies have been experimenting with the technology, primarily in bridge applications. Among the agencies that have been evaluating this technology are the Connecticut, Kansas, New Jersey, and Ohio DOTs, and the U.S. Army Corps of Engineers (Wojakowski and Distlehorst 2009).

For More Information

Concrete Products (CP). 2006. "Hydrophobic Concrete Sheds Waterproofing Membrane." Concrete Products, Vol. 109, No. 1.

Wojakowski, J., and J. Distlehorst. 2009. "Laboratory and Field Testing of Hycrete Corrosion-Inhibiting Admixture for Concrete." Proceedings, 2009 Mid-Continent Transportation Research Symposium, Ames, IA.

Ductile Concrete

Description

Ductal® is an ultra-high-strength, portland cement FRC premix that has been developed by the French cement manufacturing company Lafarge, in collaboration with two other French industrial groups, Bouygues and Rhodia. This material is designed to have high strength and high ductility, while also capable of being placed over a wide range of fluidities (from dry-cast to self-placing) depending upon the application. The manufacturer indicates that, in addition to the Ductal material's high strength and ductility characteristics, its microstructure makes it more resistant to freeze - thaw cycles, resistant to sulfates and various corrosive solutions, and resistant to abrasion and shocks (Lafarge 2010).

The components of the Ductal mix are cement, silica fume, mineral fillers (nano-fibers), water, fibers (metallic or organic), sand, and superplasticizer (Lafarge 2010). While the primary material is delivered as a dry premix, the metallic fibers (high carbon metallic) or organic fibers (polyvinyl alcohol), admixtures (superplasticizer), and water are added to the premix by the end user. Depending on the end-use application, the fibers typically make up 2 to 4 percent of the mix, whereas fibers typically make up 1 percent of the mix in more traditional fiber-reinforced mixes (Gerfen 2008).

Three different Ductal® products are available:

  • Ductal®-FM: Ductal® premix with metallic fibers. Suitable for structural civil engineering applications such as load-bearing structures.
  • Ductal®-AF: A variation of Ductal®-FM that includes the same mechanical properties and incorporates excellent standardized fire-resistance behavior.
  • Ductal®-FO: Ductal® premix with organic fibers. Suitable for architectural applications such as wall panels, furniture, canopies, etc.

Strengths for the Ductal-FM premix are reported to be 23,000 to 33,000 lbf/in2 (159 to 228 MPa) for compressive strength and 4,000 to 7,200 lbf/in2 (28 to 50 MPa) flexural strength; while the Ductal-FO premix yielded slightly lower compressive strengths of 17,000 to 22,000 lbf/in2 (117 to 152 MPA) and flexural strengths of 2,200 to 3,600 lbf/in2 (15 to 25 MPa) (Klemens 2004).

Applications

Because the premix contains no large aggregate (i.e., the aggregate is in the sand-sized range), the combination of the fluidity of the material and the lack of need for traditional rebar reinforcement allows this material to be used in many different structural and nonstructural applications. While the material can be mixed in standard industrial type mixers, most applications to date have been precast concrete (Klemens 2004). Among the civil engineering and structural applications are structural beams, truss type structures, decks of steel bridges, slabs, panels, light poles, crash barriers, noise walls, pipes, blast protection, and vaults.

In 2006, the first North American Ductal® highway bridge was completed in Wapello County, Iowa, the result of 5 years of collaborative work between FHWA, Iowa DOT, Iowa State University, and Lafarge (CIF 2007). A simple, single-span bridge with a three-beam cross section utilized three 110-ft (33.5 m) Ductal girders with no rebar for shear stirrups. This project won a 2006 PCA Concrete Bridge Award.

Benefits

Because of its unique combination of strength, ductility, and durability, the manufacturer describes the following advantages of Ductal® over more traditional materials (Lafarge 2010):

  • No need for conventional reinforcement.
  • Great improvement of durability, with a resistance to permeability 50 times better than conventional high-strength concrete.
  • Resistance to aggressive environments and loading from blasts.
  • Permits the use of much thinner sections.
  • Provides complete freedom on the shape of the section.
  • Reduces the concrete volume of a structural member to only one third to one half of its conventional volume.
  • Dramatically reduces the structural weight to be supported by a structure.
  • Provides both direct and indirect cost savings.
Costs

While no reported material cost was found in any published resources, the manufacturer claims that the increased durability of the material does lead to reduced future maintenance costs.

Current Status

The Ductal material is available in the United States in several different formulations that are tailored to match the performance requirements of individual applications. Most of the experience to date has been in structural applications, with at least one highway bridge project constructed in the United States.

For More Information

Construction Innovation Forum (CIF). 2007. Ultra-High Performance Ductile Concrete. Construction Innovation Forum, Walbridge, OH. Available at www.cif.org/noms/2007/09_-_Ultra-High_Performance_Ductile_Concrete.pdf.

Gerfen, K. 2008. "Thin Is In, Abroad." Architect, June 2008. Hanley Wood LLC, Washington, DC. Available at www.architectmagazine.com/transportation-projects/thin-is-in-abroad.aspx.

Graybeal, B. A. 2006. Material Property Characterization of Ultra-High Performance Concrete, Report No. FHWA-HRT-06-103, Federal Highway Administration, Washington, DC.

Klemens, T. 2004. "Flexible Concrete Offers New Solutions." Concrete Construction, December 2004. Hanley Wood LLC, Washington, DC.

Lafarge. 2010. Ductal. Available at www.ductal-lafarge.com/wps/portal/Ductal/Homepage. Lafarge, Paris, France.


1 http://www.geopolymer.org/science/introduction

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Updated: 05/22/2012
 

FHWA
United States Department of Transportation - Federal Highway Administration