Tag Archives: A−Substructure

Protecting Infrastructure from Major Floods

All photos courtesy Kryton International

All photos courtesy Kryton International

by Jeff Bowman, B.Sc., Greg Maugeri, and Sarah Rippin

Major flooding has dominated international news in recent years. While it may not be occurring more frequently than it was 50 years ago, due to growing infrastructure, the impact is certainly greater. Since 1949, the U.S. population has doubled, leading to a rapid increase in the construction of the urban environment. Most cities are unprepared for these rare increases in water levels—initiatives to protect infrastructure from major damage too often occurs only after the destruction.

Concrete is the modern world’s most commonly used building material, employed twice as much as other major building materials—steel, aluminum, wood, and plastic—combined.1 Concrete walls naturally protect against structural damage that can be caused by the effects of nature.

Looking back in history, many century-old structures stand longer than those erected in the last 50 years. This is largely due to reinforcement methods—instead of using solid stone, most U.S. infrastructure contains reinforcing steel embedded within poured concrete. As the priorities of construction methods shift to increase productivity and streamline scheduling, long-term durability often takes a backseat.

Feeling the effects of flood damage
In 2012, Hurricane Sandy ravaged the Atlantic coastline. The ferocious storm was among the worst disasters to ever hit the United States, causing tens of billions of dollars in damages and losses. The storm surged more than 4 m (13 ft) above the average low tide, leaving millions without power, causing severe flooding, and leaving properties destroyed.

One such flooded building happened to house the server farm for a well-known company’s global financial transactions. The server farm was located in a large warehouse building on West Street in Manhattan, more than two blocks from the Hudson River.

The most damaging issue in the storm’s aftermath was the street-level power plant running the server infrastructure was dramatically flooded. The mechanical room took 750 mm (2 ½ ft) of flooding during the hurricane, which was foreseen by neither owners nor builders when the servers were installed.

After the waters receded, engineers worked with waterproofing experts to come up with a way to protect the vital systems from potential flooding in the future. They opted to surround critical systems with waterproof concrete half-walls that could stand up to hydrostatic pressure.

For this Manhattan server room project, the concrete-to-concrete joints of the walls were constructed using the same crystalline technology to fully tank the room. To provide extra protection, a slurry coat containing the same crystalline properties was applied to the outside of the walls.

For this Manhattan server room project, the concrete-to-concrete joints of the walls were constructed using the same crystalline technology to fully tank the room. To provide extra protection, a slurry coat containing the same crystalline properties was applied to the outside of the walls.

Even under normal circumstances, if soil around a below-grade structure’s foundation is saturated with water to 1 m (3 ft) or more above the ground level, the water’s force causes pressure on the concrete. The walls absorb the moisture like a sponge, leading to cracks and ensuing water infiltration, rebar corrosion, and mold. In a flash flood, similar water pressure is applied to concrete structures.

Waterproofing concrete from the inside out
The project team knew waterproofing the server farm would require a robust assembly that could withstand the sudden onset of a large volume of water. Typical concrete structures built in the past 50 years are waterproofed solely on the positive side (i.e. wet side) using surface-applied paints or membranes. These surface barriers are vulnerable to damage during construction, which can lead to waterproofing failure. In the case of the server farm, the water pressure of a flash flood (and the debris it carries) could damage a membrane and leave the servers vulnerable at the most critical moment.

The slow effects of water damage to an aging building can be accelerated by flooding, which adds force to aging materials and pushes moisture into concrete. This moisture stays within the concrete even after the building is cleaned up, and can cause mold and mildew growth over time. The moisture can also collect around the steel reinforcing rebar within the concrete, causing corrosion that spreads throughout the structure. Additionally, the rebar expands as it corrodes, cracking the concrete and adding to the deterioration.

To make concrete truly ‘waterproof’—which means both preventing water passage and resisting hydrostatic pressure—many contractors have embraced a long-term, permanent approach. Using an integral system, usually in the form of a powdered admixture added directly to the concrete itself, the entire mass of concrete can be made the waterproofing barrier. The system should include properties which work to protect steel from corrosion, saving structures which incur water damage fewer repair or replacement costs down the road.

In late 2010, the American Concrete Institute (ACI) published a new report on chemical admixtures for concrete called ACI 212.3R-10, Report on Chemical Admixtures for Concrete. This document contains a new chapter focused entirely on permeability-reducing admixtures (PRAs). Chapter 15 embodies research dating back nearly five years, with volunteers from across the industry spending countless hours and untold effort into its development.

The result is a valuable resource for concrete users, with the greatest value of the new chapter being its clear categorization of permeability-reducing admixtures into two divisions:

  • permeability-reducing admixtures for non-hydrostatic (PRAN) conditions; and
  • permeability-reducing admixtures for hydrostatic (PRAH) conditions.

Dampproofing admixtures
Used for PRAN conditions, dampproofing admixtures reduce water absorption via treatment with repellent chemicals (e.g. soaps or oils) or partial pore-blocking (i.e. fine particle fillers). Since resistance to water under pressure is limited or non-existent, these admixtures are not suitable for concrete exposed to this situation.

For the Manhattan data center project, the critical systems were surrounded by waterproof concrete walls, which incorporated a crystalline concrete waterproofing admixture.

For the Manhattan data center project, the critical systems were surrounded by waterproof concrete walls, which incorporated a crystalline concrete waterproofing admixture.

Waterproofing admixture
Waterproofing admixtures are specified for PRAH conditions. They reduce water penetration via a pore-blocking mechanism (e.g. crystalline growth or polymer plug). Given these materials are sufficiently stable to resist water under pressure, they are suitable for use in watertight construction, such as basements and water tanks.

Corrosion considerations
Not all flood damage to concrete structures is immediately apparent. Even after the water recedes, there is still a risk of rebar corrosion, especially if the flooding involved salty ocean water.

Corroded rebar can weaken a buildings vital support network, and the damage can quickly spread. Reducing water permeability effectively lowers opportunity for this, thereby increasing the structure’s longevity. Of course, not all corrosion-inhibiting admixtures (waterproofing or otherwise) are created equal.

The University of Hawaii recently released the results of a 10-year study on the corrosion of reinforced concrete exposed to a marine environment.2 Concrete panels were placed in the tidal zone of Honolulu harbor—a highly corrosive environment due to chlorides in the ocean water, as well as constant weather fluctuations.

Corrosion can be prevented in concrete in two primary ways. If the permeability of the concrete is very low, the penetration of water and chlorides will be minimized, preventing corrosive conditions from developing. Alternatively, the concrete can be treated with corrosion-inhibitors that act to chemically inhibit corrosion at the surface of the steel once corrosive conditions develop. For real projects, both methods can be used, but for research purposes only one additive was used in each test mix.

The Hawaii program used a good quality, control concrete (water/cement [w/c] ratio of 0.40) that would be considered durable. Even so, the control (i.e. plain concrete) showed corrosion induced cracking and rust residue after 10 years. The other materials evaluated included two supplemental cementitious materials (SCMs)—fly ash and silica fume—as well as four corrosion-inhibitors and three PRAs.

By implementing long-term waterproofing solutions to key areas, the Manhattan server room will withstand high water exposure caused by any future massive flooding.

By implementing long-term waterproofing solutions to key areas, the Manhattan server room will withstand high water exposure caused by any future massive flooding.

At the study’s conclusion, the report published in 2012 made the following recommendations to minimizing corrosion:

  1. Use a W/C ratio as low as possible, but not greater than 0.40.
  2. Include fly ash with at least 15 percent replacement of cement, or silica fume with at least five percent replacement of cement. Mixing must ensure the fly ash and silica fume, in particular, are well-distributed throughout the concrete.
  3. Include a calcium nitrite admixture at minimum dosages of 20 L/m3 (4 gal/cy).
  4. As added protection, consider including a proprietary hydrophilic crystalline product at two percent by weight of cement.

These findings are particularly relevant because they are based on field exposure in a harsh costal environment. This is the best type of testing because the exposure simulates the actual service conditions of a real structure. Laboratory tests are generally designed to provide accelerated results using conditions that do not always model real life. Many products may perform well in a short-term laboratory experiment, but perform poorly over the long term in actual conditions.

Wall joints and entryways
Certain water entry points are particularly sensitive when exposed to hydrostatic pressure. For example, water can easily penetrate through the joints where walls meet in a corner, or where the wall meets the floor. Tie-holes should also be treated as possible leakage points, and with a product that is effective under hydrostatic conditions, especially if in a below-grade location.

It can be difficult to predict how vulnerable a concrete joint is until it is too late, so it is important to mitigate any concerns well in advance by administering a permanent jointing system that can permanently withstand high water pressure, without breaking down and becoming an entry point for moisture.

Unsuspecting entryways are another issue. Insufficient waterproofing of the concrete is not the only way water can infiltrate an interior space during a major flood. In many cases—including the aforementioned building housing the server farm in New York—there are strong enough winds and water pressure to simply break through windows or doorways.

Boarding up these entrances is an effective protection measure in many cases, but this is time-consuming and, in some cases, impossible. Installing flood-resistant doors, gates, and window protectors upon the construction of the building helps ensure the structure can be protected quickly and efficiently when facing a flood.

If all entrances cannot be flood-proofed, protecting below-grade concrete from water damage from both the positive and negative side is a vital step in ensuring a building’s longevity.

Not all flood damage is immediately apparent. Even after the water recedes, there is still a risk of rebar corrosion for concrete structures.

Not all flood damage is immediately apparent. Even after the water recedes, there is still a risk of rebar corrosion for concrete structures.

The concrete barriers, designed by engineers for the server building in Manhattan, contained a system that would work with water under pressure, rather than against it. Hydrophilic technology (from the Greek hydros, meaning water and philia, meaning friendship) absorbs water rather than repelling it, effectively using the water contact to its advantage.

This process is employed in crystalline admixtures and surface-applied cementitious crystalline products, which transform water into microscopic crystals. These crystals permanently block the pores of the concrete, preventing water from penetrating and moisture from remaining within the wall. As time goes on, the crystalline product remains dormant in the concrete, and reactivates upon the presence of moisture, throughout the entire life of the structure.

For the New York project, the finished wall took on crystalline waterproofing in three different applications:

  • as an admixture added directly to the concrete mix;
  • as a surface-applied brush-on (i.e. to the positive side—on the outside of the walls facing any potential water penetration into the building); and
  • within the concrete joints as a two-part physical and chemical barrier.

By using these extra enforcements, engineers could guarantee the protection of this vital server farm should a flooding event at the level of Hurricane Sandy occur again.

Preparing for the future
With climate change and the increases in water-related damage to cities and areas around the world, it is becoming more apparent drastic steps need to be taken regarding the way we build, and the materials we use. In order to gain full insight, it is critical to pay attention to new innovations based on proven techniques, which reflect both sustainability and durability. Staying up to date with the new tools, research, and reports can help us to know what we can do to protect our structures from costly damage and early deterioration.

Notes
1 Visit cementtrust.wordpress.com/a-concrete-plan. (back to top)
2 For more see the report, “Performance of Corrosion-inhibiting Admixtures in Hawaiian Concrete in a Marine Environment,” by Joshua Ropert, MS, and Ian N. Robertson, PhD, SE. Visit www.cee.hawaii.edu/reports/UHM-CEE-12-04.pdf. (back to top)

Jeff Bowman, B.Sc, is a technical manager at Kryton International Inc. He earned his bachelor’s degree in chemistry from the University of British Columbia, and has extensive experience in the development and use of various construction products for the repair and waterproofing of concrete, specializing in crystalline admixtures and repair materials. Bowman has written numerous articles on waterproofing technologies and has contributed to international publications on this topic. He can be reached at jeff@kryton.com.

Gregory Maugeri is the CEO and managing partner of New England Dry Concrete, which specializes in solving cementitious waterproofing problems with crystalline materials. He has decades of construction and waterproofing experience; his company has been awarded the (ICRI) Project of the Year. Maugeri can be contacted via e-mail at greg@dryconcrete.com.

Sarah Rippin is a multimedia coordinator for Kryton. Over the past eight years, she has worked within the construction and marketing industries, and now uses both visual and written communications to promote and draw awareness to the importance of concrete waterproofing. She can be contacted at srippin@kryton.com.

Designing with Activated Fly-ash Cement Concretes

Photos courtesy CeraTech USA

Photos courtesy CeraTech USA

by Ivan Diaz-Loya, PhD

With evidence of climate change bringing awareness to greenhouse gas (GHG) emissions, the sticking point for concrete construction is the amount of embodied carbon in the material. Most of this embodied carbon comes from production of portland cement—the fine powder that hydrates and ‘glues’ sand and stone together to produce concrete.

Approximately 600 kg (1322 lb) of carbon dioxide (CO2) is released into the atmosphere for every ton of cement produced.1 This may not sound like much, but when the expected global cement output is 3.4 billion tons for 2013, it means roughly 2 billion tons of CO2—five percent of all manmade GHG emissions—will be released to the atmosphere as part of the cement production process.2

To bring this to the specifier’s perspective, when a cubic yard of portland cement concrete is specified to have a cement content of 249 kg (550 lb), that cubic yard of concrete already has around 149 kg (330 lb) of embodied carbon generated from cement production alone.

This figure shows typical shrinkage values of activated fly ash cement concrete tested per ASTM C157, Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, at 50 percent relative humidity (RH).

This figure shows typical shrinkage values of activated fly ash cement concrete tested per ASTM C157, Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, at 50 percent relative humidity (RH).

Concrete carbonation
Part of these emissions is recaptured throughout the concrete’s life when hydrated portland cement reacts with the CO2 in the atmosphere to form calcium carbonate—a process called carbonation. However, it is uncertain how much CO2 is reabsorbed into the concrete. Washington State University’s associate professor Liv Haslebach states in the article, “Concrete as a Carbon Sink,” published on Portland Cement Association’s (PCA’s) website, that although there have been numerous studies, no one has been able to put an accurate number to the amount CO2 recaptured though carbonation.3

A 2007 study by Claus Pade and Maria Guimares, “The CO2 Uptake of Concrete in a 100-year Perspective”, estimates the amount of CO2 recaptured through carbonation is between 33 to 57 percent over a century.4 Whatever the actual number, it only stands to reason by the time the hydrated cement in concrete fully carbonates, the structure will have reached the end of its service life, and another structure will be built using more portland cement concrete to replace the old one. Therefore, even in a perfect scenario where 100 percent of the CO2 is recaptured through carbonation and no new growth occurs, a revolving amount of CO2 is being maintained in the atmosphere as old structures decay and new ones are built.5

This graph shows moisture vapor emission rates (MVERs) of portland cement and activated fly-ash cement concrete tested per ASTMF 1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.

This graph shows moisture vapor emission rates (MVERs) of portland cement and activated fly-ash cement concrete tested per ASTMF 1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.

Alternative binder systems
PCA calls portland cement the “building block of the nation’s construction industry.” While portland cement will likely continue to be used for generations, there are alternative binder systems available for the production of concrete. One of these alternatives is fly ash—the fine powder filtered out from the flue gases resulting from the combustion of coal. Fly ash is typically rich in silica, alumina, and calcium oxide (CaO) in many cases. During the power production processes, fly ash moves rapidly from combustion to room temperature, forming tiny spheres composed mainly of reactive glass; the material has an appearance and fineness similar to portland cement.

This image shows placement of activated fly-ash cement concrete at the Port of Savannah—an application where concrete will be subjected to abrasion and loads of 55,791 kg (123,000 lb) from overhead mobile gantry cranes.

This image shows placement of activated fly-ash cement concrete at the Port of Savannah—an application where concrete will be subjected to abrasion and loads of 55,791 kg (123,000 lb) from overhead mobile gantry cranes.

Fly ash can be easily activated using a small amount of alkalis in the form of hydroxides or pH-neutral hydro-carboxylic acid salts to form a strong and durable binder that can replace portland cement in the production of concrete. Although fly ash has long been used to partially replace portland cement (sometimes up to 30 percent), total replacement of portland cement virtually eliminates all greenhouse gas emissions associated with the production of the cementitious binder in concrete.

Fly ash is typically produced from the combustion of coal to produce electricity, less than 35 percent of which is repurposed for beneficial use. The “2011 Coal Combustion Product (CCP) Production and Use Survey Report,” released by the American Coal Ash Association (ACAA), recorded only 23 million tons of fly ash were reused out of the 60 million tons produced in 2011.6 As such, approximately 37 million tons of fly ash could have been employed to produce activated fly-ash cement concrete instead of being sent to landfills. While some of this fly ash may have been lower quality, much of it could have been blended with high-quality material rather than disposed of.

Benefits of activated fly-ash cement
Activated fly-ash cement concrete not only offers environmental benefits, but also performance benefits, including:

  • improved volume stability;
  • mix design flexibility;
  • high early strengths;
  • low water vapor transmission at early ages; and
  • resistance to corrosive and high temperature environments.

Mix design flexibility
Concrete mixtures using activated fly-ash cement are proportioned in the same way as their traditional counterparts; in many cases, they even follow the same guidelines given by the American Concrete Institute (ACI). After all, it is still concrete with only the powder being different. The main difference is the addition of the activating liquid; at typically less than 24,815 mL/m3 (5 gal/yd3) of concrete, it is less than two percent of the total volume of the concrete mixture.

The type of activator may vary, but sodium hydroxide and sodium silicate are typically used in combination to activate low or moderately low calcium fly ash (i.e. <15 percent CaO). Hydro-carboxylic acid salts, which have a pH close to neutral, can be used for fly ash with higher calcium contents. Since portland cement mixtures can have a pH higher than 13, concrete practitioners are already accustomed to the level of alkalinity that fresh sodium hydroxide/sodium silicate-activated fly-ash mixtures can exhibit.

This graph shows the weight loss of portland cement and activated fly ash cement concretes exposed to different acids, tested per ASTM C267, Standard Test Methods for Chemical Resistance of Mortars, Grouts, and Monolithic Surfacings and Polymer Concretes.  Image courtesy American Concrete Institute’s (ACI’s) May 2013 Concrete International

This graph shows the weight loss of portland cement and activated fly ash cement concretes exposed to different acids, tested per ASTM C267, Standard Test Methods for Chemical Resistance of Mortars, Grouts, and Monolithic Surfacings and Polymer Concretes. Image courtesy American Concrete Institute’s (ACI’s) May 2013 Concrete International

Nevertheless, handling concentrated solutions, especially of sodium hydroxide, may be challenging to certain ready-mixed concrete operations because of its high alkalinity. Hydro-carboxylic acid salts on the other hand, are neutral by pH and produce fresh activated fly ash cement concrete with a pH of around eight. Once the concrete hardens, the pH raises to around 12, which is necessary to protect reinforcing steel from corrosion.

Hydro-carboxylic acid salts activate (or modify) high calcium fly ash by allowing the formation of a solution equilibrium, and the solubility of fractions of the fly ash that do not normally react when mixed with water alone. Then, when calcium aluminosilicate hydrates nucleate and grow, they produce a predictable set time and normal, but accelerated, strength development.

Volume stability
Another benefit of using fly-ash cement is the reduction of water necessary to achieve workable concrete mixtures compared to portland cement mixtures. This allows for fly-ash cement concretes with low water-to-cementitious (w/c) ratios, and the main reason the concrete exhibits low drying shrinkage. Drying shrinkage values of activated fly-ash cement concrete range from 100 to 300 millionths, while regular concrete values range from 400 to 800 millionths after 28 days. This important feature reduces the potential for cracking and can speed up construction times for concrete flatwork and foundations.

Vapor emission rates at early ages for floorcoverings
For floorcoverings and coatings applied over concrete, activated fly-ash cement offers a tremendous advantage given its inherent rapid drying. When flooring materials are applied over concrete with high moisture vapor emission rates (MVER), moisture can condensate beneath the floor covering and dissolve the alkalis in concrete, raising the pH. These conditions can break down the adhesive and cause failures in the flooring such as blistering and delamination. Months can pass from the time the concrete is placed until it has acceptable MVER levels (typically 1.45 kg/100 m2 [3 lb/1000 sf] daily) to apply a low MVER floor covering. This can leave installers with the choice of meeting the construction schedule or waiting for the concrete to dry. Activated high-calcium fly-ash cement concretes do not require wet curing and dry quickly, allowing flooring systems with the most stringent placement requirements to be placed in less than three weeks.

The picture shows the placement of activated fly-ash cement concrete for a high-temperature application at a steel fabrication business in Bakersfield, California. Photos courtesy CeraTech USA

The picture shows the placement of activated fly-ash cement concrete for a high-temperature application at a steel fabrication business in Bakersfield, California. Photos courtesy CeraTech USA

Resistance to corrosive acids
Activated fly-ash cement concrete also offers high chemical resistance, mainly due to a combination of two factors:

  • its low w/c ratio, which can be 40 to 50 percent less than typical portland cement mixtures, resulting in a denser concrete (approximately 80 kg/m3 [5 lb/y3] more than portland cement concrete) that restricts the ingress of destructive agencies; and
  • calcium in activated fly-ash cements is combined in a less soluble form than in portland cements.

Portland cement concretes contain a high proportion of calcium hydroxide, which is highly soluble in most acids. This causes the material to quickly decompose. Conversely, activated fly-ash cement concretes have no excess calcium hydroxide, making them more resistant to corrosive acids.

Resistance to heat and temperature changes
The reaction products of activated fly-ash cements decompose at higher temperatures than those of portland cement, making them able to withstand such conditions. Additionally, because the overall thermal properties of concrete also depend on the characteristics of the aggregate being used, it is important how heat travels into, and through, the material.

Many heat-related failures in concrete happen not because hydration products decomposed, but rather due to temperature changes in the structure, which create a tremendous amount of thermal stresses. An example is when a heated glass jar bursts when exposed to ice-cold water. The higher density of activated fly-ash cement generates two important changes in the thermal properties of concrete: higher heat capacity and thermal conductivity.

Although low thermal conductivity is one of the most sought-after features in most construction materials, it is not as desirable in more brittle (and thus thermal stress-susceptible) materials like concrete. Activated fly-ash cement concretes absorb heat more slowly, and dissipate heat more rapidly through its concrete structure than portland cement concrete because of thermal conductivity which effectively reduces the thermal stress on the concrete. For example, an activated fly-ash cement concrete slab raises its temperature more uniformly, having a lower temperature gradient between the top and bottom of the slab. These features are not only desirable in high temperature exposure applications, but also in regular concrete flatwork applications as they minimize the potential for curling and cracking caused by daily temperature fluctuations.

Placement of a pedestal base for a nitric acid absorber using activated fly-ash cement concrete in Tuscumbia, Alabama, to alleviate corrosion damage.

Placement of a pedestal base for a nitric acid absorber using activated fly-ash cement concrete in Tuscumbia, Alabama, to alleviate corrosion damage.

Photo 4

In the past, activated fly ash cement concretes were only accomplished in highly controlled lab conditions and were impossible for field applications. While this perception still remains for many, the reality has changed. Activated fly-ash cement are now being used as a one-for-one replacement for portland cement concretes in many applications.

In 2009, Missoula Federal Credit Union (MFCU) built the first Leadership in Energy and Environmental Design (LEED) New Construction (NC) v2.2 Platinum-certified building in Montana using 100 percent fly-ash concrete (i.e. portland cement-free) as the main building material. The concrete mixture incorporated recycled glass as aggregate, and was used to build the footings, foundation walls, floor slabs, interior components, column surrounds, and roof beams. Montana State University developed the concrete mixture and worked with local contractors and architects to design and build the new branch office for MFCU. Researchers at Louisiana Tech University have also been running field tests since 2008 to create confidence in activated fly-ash cement concrete.

These ingredients can be easily introduced to existing ready-mixed concrete plants. Activating liquids can be plumbed into the plants in the same way most admixtures are currently used and given most plants already have a dedicated silo for fly ash, there is no need for setting up additional storage for it. Leading designers and specifiers have started taking notice of the capabilities and advantages activated fly ash cement concretes provide to their clients.

In July 2012, the Georgia Ports Authority used activated fly-ash cement to replace part of the lane where overhead mobile gantry cranes operate in the Port of Savannah. The Federal Highway Administration (FHWA) is now looking at the potential use of activated fly-ash cement concrete in rigid pavements and other transportation structures by signing cooperative research agreements (CRADAs) with leading producers of activated fly-ash concrete.

From start to finish, the reconstruction of a military base’s “hush house” for engine testing was recently completed with activated fly-ash cement concrete to alleviate deterioration from high, intermittent temperatures.

From start to finish, the reconstruction of a military base’s “hush house” for engine testing was recently completed with activated fly-ash cement concrete to alleviate deterioration from high, intermittent temperatures.

Photo 5

The Department of Defense (DOD) has also been using activated fly-ash cement concrete regularly to the replace concrete slabs that receive impingement heat from vertical takeoff and landing aircraft. Military bases throughout the United States, and internationally, have successfully been using activated fly-ash cement concretes for more than a decade now in the construction and rehabilitation of surface and aviation transportation infrastructure.

This graph shows typical strength development curves of concrete using high calcium fly-ash activated concrete with hydrocarboxilic acid salts as binder.  [CREDIT] Data courtesy Patel et al’s, “Green concrete using 100 per cent fly ash-based hydraulic binder,” Proceedings of the 2012 Concrete Sustainability Conference (Seattle).

This graph shows typical strength development curves of concrete using high calcium fly-ash activated concrete with hydrocarboxilic acid salts as binder. Data courtesy Patel et al’s, “Green concrete using 100 per cent fly ash-based hydraulic binder,” Proceedings of the 2012 Concrete Sustainability Conference (Seattle).

Since activated high-calcium fly-ash cement relies on its hydraulic activity to harden and gain strength, it can be considered hydraulic—this a candidate for meeting ASTM C1157, Standard Performance Specification for Hydraulic Cement. Conversely, for fly ash with a lower calcium content—typically Class F per ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete—ASTM Committee C01 on Cement recently formed a task group to develop standard test method for testing compressive strength of alkali-activated fly ash and natural pozzolan cement. This test method is expected to be the base for the development of future specifications.

Conclusion
The current social and cultural forces shaping the construction industry are increasingly calling for materials in addition to meeting performance requirements and being produced with environmental responsibility. With regulations looming, it is difficult to predict what will happen in five, 20, or 50 years. On the bright side for fly ash, the EPA is now considering other options, none of which label the material as hazardous waste. 7

Activated fly-ash cement offers a solution by providing a value-added product while reducing the use of portland cement and associated emissions, and recycling a coal combustion product into beneficial construction materials, reducing landfill and disposal facilities.

Notes
1 For more information, visit www.globalcement.com/news/item/1806-decoupling-carbon-emissions-from-cement-production. (back to top)
2 Visit www.nature.com/news/green-cement-concrete-solutions-1.12460. (back to top)
3 Visit www.cement.org/tech/carbon_sink.asp. (back to top)
4 For more information, see Claus Pade and Maria Guimares’ “The CO2 uptake of concrete in a 100-year perspective” from the International Symposium on Sustainability in the Cement and Concrete Industry held in Lillehammer, Norway in 2007. (back to top)
5 For more, visit www.nrmca.org/greenconcrete/concrete%20co2%20fact%20sheet%20june%202008.pdf. (back to top)
6 Visit, www.acaa-usa.org/associations/8003/files/Final2011CCPSurvey.pdf. (back to top)
7 Visit www.epa.gov/epawaste/nonhaz/industrial/special/fossil/ccr-rule/ccrfaq.htm#3 (back to top)

Ivan Diaz-Loya, PhD, joined CeraTech Inc., in 2011 as a research engineer to help develop a better understanding of activated high-calcium fly-ash cement concrete. He holds a PhD in engineering from Louisiana Tech University, where his research focused on the material. Diaz-Loya is a member of American Concrete Institute (ACI) and ASTM where he chairs a task group developing a test method for compressive strength of alkali-activated fly ash cement mortars. He can be contacted by e-mail at ivan.diazloya@ceratechinc.com.