Reclaimed Byproducts Boost Concrete Performance

How waste materials from manufacturing are making longer lasting, more durable concrete for highways and bridges.

by Tom Kuennen, Contributing Editor

The high-performance, high-tech, durable concretes of today and the future have their origins in what were once landfilled waste materials.

Reclaimed, recyclable industrial byproducts now being used in high-performance concrete are providing the durability and strength that portland cement concrete bridges and pavements need to stand up to the traffic loads and maintenance practices of decades to come.

Chief among these byproducts are fly ash, microsilica, and slag, but concrete itself is becoming an increasingly useful recycled product.

Class F and C fly ashes — the reclaimed byproducts of combustion of coal for electric power — are widely accepted for their advantageous effects in conventional PCC, and new, processed, “beneficiated” Class F fly ash makes certain high-carbon C fly ashes practical when used with air-entraining agents.

Silica fume, also called microsilica, is an industrial byproduct from the silicon and ferrosilicon manufacturing industry that imparts high strength to concrete. Microsilica boosts concrete’s compressive strength to as much as 14,400 psi, and it also fills micropores in the concrete to enhance its resistance to chloride infiltration.

Today’s ground, granulated blast furnace slag, the byproduct of steel manufacturing, performs in PCC more predictably than straight slag right out of the mill, making it more reliable. This processed GGBF slag makes concrete stronger and more durable while lowering its heat of hydration.

New research in the lab and the field is validating and setting the rules for use of reclaimed, crushed portland cement concrete itself as aggregate in concretes.

An immediate environmental benefit of the use of reclaimed industrial byproducts in concrete is lessened pressure on landfills, and businesses benefit by savings in tipping fees and the development of a new profit center.

Also, with the use of reclaimed industrial byproducts in PCC, less cement is needed for a given application, which means a reduction in the amount of energy consumed by the cement manufacturing industry, and parallel reductions in carbon dioxide and water vapor emissions from the fuels used in pyroprocessing, and from the calcining process itself.

Added value for agencies

A public road agency which uses reclaimed materials in high-performance concrete benefits from the added value the recycled materials provide, and so do its citizen taxpayers.

This added value can come without significant upfront added costs. High-performance concrete made with reclaimed, recyclable industrial byproducts like coal fly ash, silica fume and GGBF slag result in stronger, more durable structural elements, allowing designers to specify fewer elements, all things being equal, with equivalent first-cost savings.

With the exception of fly ash, reclaimed industrial byproducts in HPC have been used in private-sector structural applications like high-rise buildings since the 1970s, but state transportation agencies and public sector owners have been slow to specify them due to a lack of experience. Now, the Federal Highway Administration and its allies have taken a leadership role in justifying HPC in the United States, and questions are being answered and the word is being spread.

What is HPC?

High-performance concrete, also called “durable concrete”, is an engineered concrete mix made with the classic components of water, portland cement, and fine and coarse aggregates. HPC component materials are selected and proportioned to realize high early strengths, high ultimate strengths, and high durability beyond conventional concrete.

But the ironic fact is that some “waste” materials of a few decades ago now are critical components of high-performance concrete. This trinity of admixtures — fly ash, silica fume, and GGBF slag — add strength and durability to concrete.

High-performance concrete provides enhanced properties in structural precast concrete, including elevated tensile and compressive strengths, and a boosted stiffness (modulus of elasticity).

The benefits of HPC are best experienced in North America’s snow belt. In transportation infrastructure such as viaducts and bridges, high-performance concrete strongly resists penetration of chloride-laden snow and ice melt water. This results in longer life for the reinforcing steel within, and a reduction in spalling, cracking, and associated repairs.

High-performance concrete has Sunbelt applications, too. Ocean-side highways, marine bridges, causeways, piers, and breakwaters all will benefit from use of durable HPC as it protects reinforcing steel from salt water splash and spray.

High-performance and conventional concrete differ primarily in the proportions in which its fundamental elements are mixed, and with the admixtures that are used. A low water/cement ratio, perhaps as low as 0.35, is required, achieved by use of a high-range water-reducing admixture.

Fly ash adds performance

The most common HPC admixture, fly ash, is what’s left from the burning of pulverized coal in electric power plants. The ash particles are collected mechanically or by electrostatic precipitators. About 15 to 20% of burned coal takes the form of ash.

In 2002, the most recent year for which reliable data are available, approximately 76.5-million tons of fly ash were produced, according to the American Coal Ash Association.

Fly ash is a pozzolan, that is, a siliceous and aluminous material that, in the presence of water, will combine with an activator (lime, portland cement, or kiln dust) to produce a cementitious material, according to FHWA’s Fly Ash Facts for Highway Engineers, authored by the ACAA.

In the old days, fly ash went right up the stack, but after controls were placed on air pollution, new technologies made it easier to remove fly ash from the stack stream. This material mostly was landfilled, but high disposal fees and the wish to realize income on a waste product caused utilities to take a closer look at new markets for the pozzolanic material.

Required for federal aid projects

Fly ash use on federal-aid highway projects was encouraged by its classification as a “recovered” product under the federal Resource Conservation and Recovery Act (1976), which generally mandates use of fly ash in cement or concrete in construction projects using $10,000 or more of federal funds.

Twenty years later, in 1996, the Environmental Protection Agency ruled that GGBF slag also was a recovered product under the conservation act, putting it on the same level as fly ash. Now a contracting agency may choose between GGBF slag and fly ash.

State agencies are in violation of the law if either product was not used as a material in qualifying, federally funded projects, unless the agency can show compelling reasons not to. These reasons include that the material is not available at a competitive price within a reasonable period of time, the material doesn’t meet performance specs, or the material is only available at an uncompetitive price.

Class C and F ashes

The American Society for Testing and Materials classifies fly ash into Class C and Class F categories.

Class C has a higher calcium oxide content (CaO, or “lime”), and is derived from lower-Btu western sub-bituminous or lignite coals. Because Class C ashes contain less free carbon than Class F ashes, they work better with certain air entraining agents.

Class F is derived from higher-Btu bituminous eastern coals. While both types perform well, research indicates that Class F fly ash is better suited for fighting alkali-silica reactivity (see related sidebar), a common malady of concrete.

To mitigate the higher carbon content in Class F fly ash, one firm, Separation Technologies, has developed a patented, commercial process and equipment, which will remove excess carbon from fly ash.

“With this energy-efficient technology, an unusable high carbon Class F fly ash can be economically processed to produce a consistent, low carbon (beneficiated) fly ash, ProAsh, that is suitable for use in concrete,” the firm says. ProAsh is made commercially available to the concrete industry through a collaborative effort including Separation Technologies and Master Builders.

Benefits of fly ash

There are many benefits to both classes of fly ash, starting with gains in concrete strength. “Mixtures designed to produce equivalent strength at early ages (fewer than 90 days) will ultimately exceed the strength of conventional portland cement concrete mixes,” reports FHWA in Fly Ash Facts.

Reduced permeability in the finished, cured concrete is another benefit of fly ash. Fly ash reacts with lime and alkalis, creating cementitious compounds that block-up portland cement concrete’s porous structure. Similarly, fly ash provides reduced susceptibility to sulfate attack because it “locks up” free lime, making it less available to react to sulfates.

Fly ash provides improved workability, too, due to the spherical shape and small size of its particles. Its spherical shape lends flowability, “lubricating” the mix, while improved workability can speed construction. This is important for its use in the new self-consolidating concrete mixes just now gaining attention in the United States (see related sidebar).

Fly ash also can reduce bleeding in concrete, because lower amounts of water are required due to its improved workability.

Fly ash produces a lower heat of hydration, because it reacts more slowly than portland cement when substituted for portland cement in mixes. This can benefit mass concrete placement.

Significantly, fly ash results in lowered costs for contractors and government agencies alike. Fly ash generally costs half that of cement. When used as a replacement for portland cement, replacement percentages can vary from 15 to 25%, with even higher amounts in mass concrete placements.

Silica fume and durable concrete

Microsilica, or silica fume, is another industrial “waste” byproduct which would otherwise be landfilled but now has a very prominent role in the development of high-performance concrete.

Silica fume is produced through the reduction of high-quality quartz in an electric arc furnace. The product is condensed from fumes and gases escaping from the furnace and is made up of very fine, round particles of silicon dioxide.

In the 1980s silica fume was widely used in private sector construction for concrete high-rise buildings and parking garages. Now silica fume is moving into bridge decks and bridge substructures, such as the landmark Wacker Drive reconstruction in Chicago.

“Silica-fume concrete can withstand corrosion factors such as harsh weather and deicing chemicals and has been used throughout the U.S. for more than 20 years,” reports the Silica Fume Association, based in Fairfax, Va. “Infrastructure benefits include increased durability, extended concrete life, reduced corrosion of reinforcing steel and increased strength for longer bridge girders. The use of silica-fume in concrete paving will provide additional strength, abrasion resistance, and durability.”

Silica fume’s action in PCC is physical and chemical in nature. Because the silica fume particles are much, much smaller than the cement particles, they fill voids between the cement particles, thus causing a finer pore structure.

As cement hydration begins, silica fume accelerates hydration because its tiny particles provide nucleation sites for hydration, just as microfine atmospheric dust particles cause formation of rain droplets. Microsilica also has the ability to dramatically reduce bleeding, because the silica fume introduces a lot of surface area into the mix, which holds water in place.

And silica fume has a very strong pozzolanic reaction, so that when the cement grains hydrate and generate calcium hydroxide, silica fume reacts to that compound and creates calcium silicate hydrate. Thus more space is filled up in the matrix, which provides much more strength, inhibits water permeability, and boosts chloride ion resistance.

Silica fume actually liquifies concrete at low doses of 3% of cementitious material. The fine silica particles fit in between the cement grains and displace water, enhancing the flowability of the concrete. It actually becomes its own water reducer.

When more silica fume is added — near 5% of cementitious material — the surface area of the

silica fume begins to outweigh its water displacement function, and surface forces begin to have a strong effect. A water reducer, or superplasticizer, or both must be added to overcome the need for more water.

Adding value with GGBF slag

Blast furnace slag is the byproduct of the manufacture of molten iron, resulting from the fusion of limestone and other fluxes with the ash from coke and silica, and alumina from iron ore.

Air-cooled slag has been used for decades for noncritical applications such as railroad track ballast. It has also been landfilled or just left in heaps at steel mills. When manufactured in a controlled process as ground, granulated blast furnace slag, however, it takes on higher value as an admixture to concrete.

According to the American Society for Testing and Materials, GGBF slag must be a cementitious, glassy, granular material formed when molten blast furnace slag is rapidly chilled by immersion in water. This chilling creates a granular product that is then ground to spec and used as an admixture.

Demand for GGBF slag manufactured to spec is such that it is not often seen outside the region in which the iron and steel industry is situated. There are three grades of GGBF slag: 80, 100, and 120. The classification of grades is based on what is called the slag-activity index. Increased compressive strength and flexural strength is expected with GGBF slag grades 100 or better.

Enhancements that GGBF slag brings to concrete include low heat of hydration (ideal to avoid cracking for mass pours), increased compressive and flexural strengths, potential quelling of ASR, enhanced resistance to sulfate attack, and reduced permeability to chlorides.

In 2000, a major mass pour for a bridge pier spread footing illustrated the potential for GGBF slag cement. That May, Lone Star Cement’s Aucem GGBF slag cement — in a 70% substitution for Type II portland cement — was used to lower the heat of hydration in a 2,600 cubic-yard pour for a pier footing for the extension of Page Avenue (State Route D) over the Missouri River in St. Louis County, Missouri.

This pour was only part of a larger application. Aucem anticipated that over 100,000 yards of the GGBF-slag cement mix — about 10,000 tons of slag cement — would go on the job over the next two years.

Control of heat of hydration was the prime purpose for GGBF-slag cement being used. The mass pour concrete mix design called for 50 calories per gram heat of hydration. With the Missouri DOT having a crack spec on this project of 0.03 mm, Breckenridge Material Company, the ready-mix producer, was trying to achieve crack-free concrete. The pours averaged strengths of 4,100 psi in 28 days, and 4,500 in 56 days.

RCA poses challenge

But reused material in PCC pavements and structures is not just limited to reclaimed industrial byproducts as admixtures. Reclaimed, crushed concrete aggregate from demolition materials is undergoing study for use as an aggregate in concrete mixes. It is broadly accepted as a base material, but its use as an aggregate in concrete itself has been problematic.

Reclaimed concrete aggregate is the same as crushed concrete. “It consists of high-quality, well-graded aggregates (usually mineral aggregates), bonded by a hardened cementitious paste,” reports the FHWA in its User Guidelines for Waste and Byproduct Materials in Pavement Construction. This material is generated through the demolition of concrete highways, runways, and structures, which necessarily pile up during reconstruction of transportation infrastructure.

“The [RCA] excavation may include 10 to 30% subbase soil material and asphalt pavement,” the FHWA says. Therefore, initially the RCA is not pure concrete, but a mixture of concrete, soil, and small quantities of bituminous concrete.

Reclaimed concrete material can be used as an aggregate for cement-treated or lean concrete bases, a concrete aggregate, an aggregate for flowable fill, or an asphalt concrete aggregate, the FHWA says. It can also be used as a bulk fill material on land or water, as a shoreline protection material (rip rap), a gabion basket fill, or a granular aggregate for base and trench backfill.

Consistency

A lack of consistency and the need to continuously, exhaustively test RCA for its characteristics has worked against its adoption as aggregate in concrete and asphalt mixes. But the industry is responding with research to establish its utility.

For example, in conjunction with Penn DOT, Maine DOT, Wyoming DOT, and FMC Lithium, an ongoing two-phase study (2000-2004) is looking at the potential danger and means of mitigating ASR in concrete aggregate made of reclaimed, crushed, portland cement concrete from demolition materials.

This project, conducted by Dr. David Gress of the Recycled Materials Research Center at the University of New Hampshire, is focusing on the use of recycled concrete aggregate that has alkali silica reactivity. Previous projects conducted at UNH developed ASR detection methods.

The current project will look at ASR mitigation strategies to control or eliminate ASR in recycled concrete aggregate. A new test procedure for evaluating the use of RCA in concrete with and without mitigation will be proposed to AASHTO for their consideration as a recognized test method. Guidelines will also be developed to allow state DOTs to evaluate a given RCA for recycling in concrete.

New national review of RCA

In 2003, the FHWA undertook a National Review of Recycled Concrete Aggregate use. Its purpose was to capture for technology transfer the most advanced uses of recycled concrete aggregate among state highway agencies.

“We intend to showcase how other [agencies] overcame barriers and advanced the routine use of recycled concrete as aggregate,” the FHWA said last year. “Specific uses or applications will be identified along with their barriers and benefits to implementation. Specifications, construction practices, and implementation challenges will also be documented.” Tech transfer will take place through technical guidance, training, and guide specifications, as necessary.

Minnesota, Utah, Virginia, Texas, and Michigan were selected for an in-depth review of their recycled concrete aggregate programs. A team reviewed their uses of recycled concrete as base aggregate, as concrete aggregate, as asphalt aggregate, and for miscellaneous uses.

The FHWA found that concrete routinely is being recycled into the highways of the United States, but its principal application has been as base material. “The utilization of recycled concrete aggregate as aggregate in hot-mix asphalt and concrete is not as widely accepted in the United States,” the FHWA said.

Among its findings in 2003:

In Texas RCA is bid as an option in construction contracts for non-structural concrete (coarse 100%, fines 20%) and as a base material (100%). Because of the current economic benefits of RCA, the total generated waste flow in Houston is being consumed.

Virginia uses RCA in base, sub-base, synthetic reefs, and embankments. One example of VDOT’s use of RCA in sub-base aggregate is the I-66 project, which won a National Concrete Paving Award after completion. This project was part of a $140-million reconstruction program on a section of I-66 in Fairfax and Prince William Counties.

Michigan allows the use of RCA as coarse aggregate for concrete for curb and gutter, valley gutter, sidewalk, concrete barriers, driveways, temporary pavement, interchange ramps, and shoulders. Recycled concrete aggregate is also allowed as coarse aggregate in hot-mix asphalt and as dense-graded aggregate for base course, surface course, shoulders, approaches and patching. It was widely used in the pavement structure during the 1980s. However, in 1991, a moratorium was implemented on the use of RCA in the concrete pavement slabs.

Texas focus on durability

Texas was one of the first states to participate with the FHWA in constructing high-performance concrete bridges.

Thought to be the first of the new generation of HPC bridges, the Louetta Road overpass on State Highway 249 northwest of Houston was completed in 1994, consisting of two parallel three-span bridges. High-performance concrete was used in the poured-in-place decks, the unique, precast concrete Texas U-beams, and the precast post-tensioned substructures.

This was followed by two bridges on U.S. 67 over the North Concho River near San Angelo in 1997. High-performance concrete was used in the deck, the AASHTO Type IV bridge girders, and the substructure of the eight-span eastbound bridge, and in the deck of spans 1 through 5 of the nine-span westbound bridge.

Now, in Texas, where the first HPC beams and bridges were produced, the emphasis is shifting from mix development and testing to construction technique and contractor reliability.

High-performance concrete bridges are not quite ready for performance-related specifications, said William R. Cox, P.E., and Kevin R. Pruski, P.E., Texas Department of Transportation, in their 2003 Transportation Research Board paper, High Performance Concrete Structures: A Work in Progress.

“Now that concrete strengths normally suited for the majority of bridge structures can be routinely provided by the contracting community, the exciting part of the HPC definition is determining how to get more durable concrete,” Cox and Pruski write.

Success in constructing durable concrete bridges depends on the state being proactive among contractors, they say. “Proper design and detailing go part of the way to success, but even the best design is affected by the fact that for state transportation contracts, the lowest bidder gets the work,” they say.

Therefore, the Texas DOT says it must reach out to the design and construction community to make sure HPC designs are correctly implemented. “[C]rafting precise specifications to instruct contractors, educating the bridge design and construction community on new technologies, and vigorously enforcing contract plans during construction are the keys to obtaining structures that will be around for a long time,” Cox and Pruski say.

The use of fly ash, silica fume, and ground, granulated blast furnace slag in Texas is increasing, they say, and bridge designers and contractors are seeing the benefits of using these materials. TxDOT is continuing to examine methods to specify the use of HPC.

“As contractors gain experience providing concrete that meets prescriptive specification requirements, TxDOT will move toward performance-based specifications,” they say.

Missouri HPC reaches 15,000 psi

In 2002, live load tests showed Missouri’s first HPC bridge was meeting American Association of State Highway and Transportation Officials guidelines, say Yumin Yang, graduate research assistant, and John J. Myers, Ph.D., P.E., assistant professor of civil engineering, University of Missouri-Rolla, in their 2003 TRB report, Live Load Test Results of Missouri’s First High Performance Concrete Superstructure Bridge.

“For its significant economical savings and greater design flexibility, HPC is becoming more widely utilized in highway bridge structures,” the authors say. “High performance bridges with HPC and large diameter prestressed strands are becoming attractive to designers.”

This HPC mix — with design compressive strengths between 10,000 and 15,000 psi — has been successfully produced with conventional materials and concrete production methods. Bridge A6130 is the first fully HPC superstructure bridge in Missouri, report Yuan and Myers.

The bridge has high-strength concrete girders with a high performance concrete cast-in-place deck. The precast, prestressed girders utilize 0.6-inch diameter strands and high-strength concrete.

Like Missouri, Tennessee has studied its high-performance concrete jointless bridges with integral abutments, write David J. Knickerbocker, Prodyot K. Basu, D.Sc., Vanderbilt University, Department of Civil & Environmental Engineering, and Mark A. Holloran, P.E., and Edward P. Wasserman, P.E., Tennessee DOT, in their TRB paper, Recent Experience with High Performance Concrete Jointless Bridges in Tennessee.

Two bridges were built as part of the FHWA’s nationwide initiative to implement HPC in bridge structures. Performance of the two bridges is observed through all stages of construction and service to date, via material testing, bridge instrumentation for both short- and long-term performance monitoring, and live load testing.

“The up-to-date observed performance of the bridges reveals the success of such bridge construction,” they write. “Local contractors were found to be capable of producing concrete to meet increased requirements in strength and durability parameters. 

Class F Fly Ash Can Fight ASR

Use of Class F fly ash will quell the appearance of alkali-silica reactivity, or ASR, a bane of concrete from coast to coast.

Alkali-silica reactivity is a chemical reaction that occurs between alkalis contributed primarily by cement, and a reactive form of silica from reactive aggregate, which form an alkali/silica gel. Under the right conditions — particularly enough available moisture — the gel will expand and produce stresses and damage in the concrete.

Over time, this expanding ASR gel exerts tremendous internal pressure that can lead to cracking of the concrete. This cracking can provide pathways for potentially deleterious materials such as water, sulfates, and chlorides to the interior of the concrete matrix, which in turn can lead to serious durability issues such as freeze/thaw damage, sulfate attack, or steel corrosion.

It’s acknowledged that ASR doesn’t destroy concrete per se. Rather, ASR-compromised concrete is weakened so that day-in, day-out wear-and-tear becomes prematurely destructive. Clues to ASR’s destructive chemical reactions include map and longitudinal cracking in bridge decks and pavements, and longitudinal cracking in structural columns.

This cause-and-effect pattern that ASR sets off has caused ASR to be dubbed the “AIDS” of concrete.

The best way to avoid ASR in new concrete is to take precautions in the mix design. These include testing aggregates for reactivity, consideration of the use of low-alkali cements, use of suitable pozzolans like ASTM C-618 Class F fly ash, use of lithium-based admixtures, and a basic knowledge of the historical performance of all the materials used.

Use of nonreactive (“innocuous”) aggregates can be specified, but these may not always be available locally. Aggregates can change in composition from one end of the pit or quarry to the other. And their positive identification may be difficult.

Use of low-alkali cement may help forestall ASR where the potential exists, but it may not be always available. Similarly, control of the alkali content of cement can be problematic, because of the diverse sourcing of cement these days, and new regulations restricting fugitive dust from cement plants. Now, captured high-alkali cement dust often is returned to the finished cement product, thus increasing its ASR potential.

Class F Fly Ash Plays Role in Self-Consolidating Concrete

Self-consolidating concrete can enhance the strength and durability of concrete used in precast bridge elements, according to Celik Ozyildirim, Ph.D., P.E., principal research scientist, and D. S. Lane, senior research scientist, Virginia Transportation Research Council, authors of the 2003 Transportation Research Board paper, Investigation of Self-Consolidating Concrete.

For their research on SCC in a concrete arch bridge project, Type II cement with 20% replacement of cement with Class F fly ash was used.

“Conventional concrete tends to present a problem with regard to adequate consolidation in thin sections or areas of congested reinforcement, which leads to a large volume of entrapped air voids and compromises the strength and durability of the concrete,” the researchers write. “Using [SCC] can eliminate the problem, since it was designed to consolidate under its own mass.”

The results showed that with tweaking of the mixture proportions, SCC can be produced successfully and provide many benefits to the transportation agencies and the construction industry.

Self consolidating concrete is different than conventional concrete in that it has a lower viscosity and, thus, a greater flow rate when pumped, they say. As a consequence, the pumping pressure is lower, reducing wear and tear on pumps and the need for cranes to deliver concrete in buckets at the job site.

To achieve a high flow rate and avoid obstruction by closely spaced reinforcing, SCC is designed with limits on the nominal maximum size of the aggregate, the amount of aggregate, and aggregate grading, say Ozyildirim and Lane. However, when the flow rate is high, the potential for segregation and loss of entrained air voids increases.

These problems can be alleviated by designing a concrete that has a high fine-to-coarse-aggregate ratio, a low water-cementitious material ratio, good aggregate grading, and a high-range water-reducing admixture. Viscosity-modifying admixtures are also used to reduce the tendency for segregation and enhance the stability of the air-void system.

In a laboratory phase of this research, all mixtures contained Type II portland cement and Class F fly ash, which was added at 20% of the total cementitious material. The coarse aggregate was crushed granite gneiss with an NMS of 25 mm and was prepared by blending aggregates retained on the 19.0, 12.5, 9.5, and 4.75-mm sieves, each 25% by weight. In a field test phase of the project, mixes were produced at a precast plant and a prestressing plant.

Strength and permeability tests of the consolidated samples provided a baseline for evaluating the need for consolidation. Freeze-thaw resistance was also determined in the field mixtures. Moist-cured beams were tested.

Lab and field results indicated SCC is feasible, which led to a field application involving an arch bridge in Fredericksburg, Virginia, the researchers say. This project was an excellent candidate for SCC because the arches are heavily reinforced, thin, curved sections that would be difficult to construct with conventional concrete.

Ozyildirim and Lane came to the following conclusions:

• SCC that flows into formwork and through reinforcement under the influence of its own weight can be made such that no external vibration is required.
• Although careful proportioning and batching are needed, SCC can be produced with locally available materials.

For More Information

More information on reclaimed industrial byproducts in portland cement concrete and their role in the ongoing shift to high-performance concrete is available from these sources:

The Web site of the Recycled Materials Resource Center at the University of New Hampshire contains an abundance of easily accessible research on all areas of recycled materials in transportation infrastructure construction. Visit them at www.rmrc.unh.edu.

The Turner-Fairbank Highway Research Center of the FHWA has an entire online guide to recycled materials in portland cement concrete, asphaltic concrete, and road bases. You may view User Guidelines for Waste and Byproduct Materials in Pavement Construction at www.tfhrc.gov/hnr20/recycle/waste/begin.htm.

The Environmental Council of Concrete Organizations is a coalition of national cement and concrete groups dedicated to publicizing the environmental benefits of building with concrete. Visit them and browse ECCO’s online Reference Library and download technical documents at www.ecco.org.

More information on FHWA’s ongoing research in Recycled Concrete Aggregate (suitability of aggregate composed of reclaimed, crushed portland cement concrete) is available at www.fhwa.dot.gov/pavement/rca.htm.

The uses of fly ash in construction are promoted by the American Coal Ash Association. Visit them and access their research at www.acaa-usa.org. Its 36-page glossary of terms is particularly useful, and may be downloaded at www.acaa-usa.org/PDF/epri-coal_ash-origin-disp-use.pdf (free Adobe Acrobat Reader required).

Power Point files describing use of silica fume (microsilica) that can be viewed directly in your Internet browser or may be downloaded from the Web site of the Silica Fume Association at www.silicafume.org/general-concrete.html,

Read more about ground granulated blast furnace slag, and conventional slag, on the Web site of the National Slag Association, www.nationalslagassoc.org.

The Slag Cement Association has an abundance of interpretive materials and documentation of slag cement performance in various applications. Visit them at www.slagcement.org. 

Reprinted from Better Roads Magazine
January 2004

Click Here to return to article index