Tag Archives: Concrete

ASTM celebrates concrete centennial

Concrete Finishers

ASTM International’s concrete-focused committee has worked to improve the material’s use and durability for a century. Photo © BigStockPhoto/FrenchToast

During last month’s round of standards development meetings in Toronto, ASTM International celebrated the 100th anniversary of the group that became Committee C09 on Concrete and Concrete Aggregates.

Since 1914, when a small group gathered to work on methods for making and testing field specimens, C09 has grown to more than 1400 members from 62 countries, maintaining a portfolio of more than 175 standards. Its 50 subcommittees focus on aspects ranging from self-consolidating concrete and chemical admixtures to supplementary cementitious materials (SCMs) and pervious assemblies.

C09 has developed global standards in construction, industrial, transportation, defense, utility, and residential sectors, but the group says its first standard remains one of its most important. ASTM C94/C94M, Specification for Ready-mixed Concrete, was first approved in 1933, but has kept pace with technology changes to present day.

“Looking at C09’s book of standards doesn’t tell the complete story of the committee’s success and accomplishments over the past century,” said committee member Richard Szeczy (president of Texas Aggregates and Concrete Association).

lobo_colin_2014 (2)

Colin Lobo, PhD, F.ASTM, received the ASTM International Award of Merit for Service to Concrete Committee. Photo courtesy ASTM International

“To produce the defining concrete industry documents stakeholders around the world rely on every day has taken countless hours of dedicated effort and cooperation from thousands of international experts,” he continued. “Over the years, C09 has embodied everything that is great about the ASTM process. That itself is truly worth celebrating.”

In related ASTM news, Colin Lobo, PhD, has received the organization’s Award of Merit for Service to Concrete Committee (along with Fellowship). Chair of the ASTM Cement and Concrete Laboratory (CCRL) executive group and senior vice president of engineering for National Ready Mixed Concrete Association (NRMCA), Lobo was lauded for his contributions to specifications for concrete materials, test methods for fresh and hardened concrete, data evaluation, and laboratory assessment.

Insulating concrete forms manufacturers unite as an association

Picture1

A new industry group will promote insulating concrete forms (ICFs).

Photo courtesy Logix ICFs

Four insulating concrete form (ICF) companies have cemented a deal to form a new industry group.

The Council of ICF Industries (CICFI) seeks to promote the construction assembly, which comprises dry-stacked formwork for reinforced concrete, usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for structural walls, floors, and roofs.

The association’s inaugural chair, Andy Lennox, told The Construction Specifier CICFI will seek strategic alliances with related groups and delve into industry-level technical research to raise awareness about the sustainable attributes of these assemblies.

“Overall, construction professionals do not have an appreciation for the speed of construction that ICFs bring to the table, especially for larger commercial structures,” he said. “Many design professionals are also unaware of the size, scope, and range of buildings that have been successfully constructed with ICFs.”

CICFI’s initial membership includes Logix Insulated Concrete Forms Ltd., Nudura Corporation, Quad-Lock Building Systems Ltd., and Superform Products Ltd. According to Lennox, these companies cumulatively represent the majority of the ICF products manufactured in North America.

“Now that our association is officially up and going the implementation and execution begins,” Lennox said. “This association is long overdue, we are excited to get started and we look forward to additional ICF manufacturers joining us as we move forward.”

How Thin is Too Thin?

Evaluating slab thickness in reinforced concrete flat-plate construction
by Dimitri Papagiannakis, PE

Typical flat-plate construction.
Photos courtesy SGH

 

Reinforced concrete flat-plate construction is popular among mid- and high-rise residential construction projects. It provides a great deal of flexibility in the placement of the structure’s vertical load-carrying elements (i.e. columns and walls) without sacrificing the efficiency of the floor framing—as could potentially be the case with steel or masonry.

In the project’s early stages, structural engineers are often asked by architects and owners how thin the slabs in a flat-plate system can be. The question is usually motivated by a desire to achieve taller floor-to-ceiling heights, which can be an important selling feature to end users. There are building code provisions that address minimum slab thickness as a function of the span length and span condition (e.g. continuous versus discontinuous, etc.). There are also practical and economic factors that often influence the design of concrete flat-plate slabs.

The design of reinforced concrete structures is governed by American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete, which provides minimum thicknesses for one- and two-way slabs supporting structural and/or nonstructural building elements. These are intended to limit deflections that may result in serviceability issues with the structure or that may damage architectural building elements.

The prescriptive minimum thicknesses are a function of the span length, continuity conditions, and end restraints of the slab; they are intended to provide a slab section that conforms to code-prescribed deflection limits without the need for the engineer to perform detailed deflection calculations. However, the code also permits the design engineer to specify thinner slabs when calculations are performed showing short- and long-term deflections will not have an adverse effect on structural or nonstructural elements attached to or supported by the slab.

Clusters of mechanical/plumbing penetrations through flat-slab. Slab design must be checked for required additional reinforcement at penetrations.

Clusters of mechanical/plumbing penetrations through flat-slab. Slab design must be checked for required additional reinforcement at penetrations.

Pros of a thinner slab
There are several benefits to specifying thinner slabs from a structural perspective. One obvious advantage is less concrete is required. Consequently, a reduction in concrete also decreases the gravity loads on the vertical load-carrying elements. This will usually result in smaller columns with less reinforcement, and thus a savings in material costs.

A reduction in building mass also has a direct effect on the seismic loads to which a building is subjected. The seismic base shear of a building structure is directly proportional to its seismic weight—a reduction in the seismic weight of a building generally results in proportional decrease in the seismic-load demands to the lateral-load-resisting elements of the building structure, and thus a more cost-effective design. Additionally, reduced building loads may also yield a less-expensive foundation design depending on the proposed system.

Plumbing sleeves placed near columns.  This requires careful review of slab shear capacity.

Plumbing sleeves placed near columns. This requires careful review of slab shear capacity.

Cons of a thinner slab
Depending on the horizontal spans that must be achieved, minimum slab reinforcement may not provide enough strength to support code-prescribed loads. Therefore, additional reinforcement may be required within the slab, negating some of the aforementioned material cost savings.

Thinner concrete sections are also susceptible to punching shear failures and must be carefully evaluated. Under certain circumstances, the avoidance of the punching shear limit state can preclude the use of smaller column cross-sections. The potential for overstressing the slab at the slab/column interface is further exacerbated by the use of slab-column moment frames often employed as part of the lateral-load-resisting system (where permitted by code). The magnitudes of the unbalanced moments and shear stresses at the slab-column connections are highest at the moment-frame locations, and may require use of thickened drop-panels at the columns to resist the applied loads. Alternatively, shear studs may be placed at the column heads to provide the required strength, or larger beam sections may be used around the perimeter to develop moment-frame action in lieu of the slab. These options result in added labor and additional cost for the project.

Flat-plate construction requires a great deal of coordination between the structural system and the mechanical, electrical, and plumbing (MEP) components. Slab penetrations for vertical mechanical and plumbing risers must be evaluated for potential additional required reinforcement. Riser penetrations located around columns must also be carefully coordinated and evaluated, as they can have a significant impact on the punching shear and flexural stresses near the columns, and may require additional flexural or shear reinforcement.

Electrical/plumbing conduit placed within slab.  Coordination is required to avoid over-congestion of conduit (such as shown here) and delays associated with modifying conduit locations in the field.

Electrical/plumbing conduit placed within slab. Coordination is required to avoid over-congestion of conduit (such as shown here) and delays associated with modifying conduit locations in the field.

Electrical conduit is also typically placed within the slab, at mid-height. Sufficient cover must be provided around the conduit and between the conduit and slab reinforcement. The conduit diameter and spacing must be kept within certain limits to prevent it from degrading the slab’s strength or becoming the focus of shrinkage stress cracks. Design and coordination of these items becomes more challenging—and potentially more expensive—as the slab’s thickness, and thus the space within which to fit the components, is reduced.

For thinner flat plate slabs, the increased surface area-to-volume ratio makes it more susceptible to early drying due to a reduction in the heat of hydration (i.e. the reduced concrete mass retains less heat—a key component to the curing process). Higher drying rates increase the likelihood of early-age cracking and, in turn, the slab’s deflections.

This reduction in heat of hydration also becomes a factor in cold-weather conditions, where the freshly poured concrete may be more susceptible to freezing due to lower concrete temperatures than would otherwise be present to help protect the slab. Thinner slabs are also more prone to early-age cracking from the shoring and re-shoring loads typical of rapid construction cycles.

Conclusion
Selecting the most appropriate slab thickness is a critical aspect of a reinforced concrete flat-plate project. Modern engineering methods and the availability of finite-element software provide useful tools for quick and efficient evaluation of flat-plate systems.

The design engineer should assess the feasibility of reducing the slab thickness beyond the prescriptive limits provided by the code, and should communicate to the owner and design team the implications of doing so (e.g. additional reinforcement, connection detailing requirements, coordination issues, etc.). As mentioned, there are numerous pros and cons to reducing design slab thickness, and each must be evaluated to arrive at the most appropriate conclusion.

DimitriPDimitri Papagiannakis, PE, joined Simpson Gumpertz & Heger (SGH) in 2011 with nearly a decade of structural engineering experience. A registered professional engineer in New York and New Jersey, his work includes design of new building structures and subdivisions, as well as renovations, alterations, repairs, and investigations of existing buildings. He can be reached at dpapagiannakis@sgh.com.

Concrete Moisture Mitigation to Help Floors

Hopps, Emily_36801FAILURES
Emily R. Hopps

Concrete floor slabs contain excess moisture that can damage many types of floor finishes. To address this problem, manufacturers have developed products aimed at mitigating the moisture in concrete. However, not all these products are suited to their intended purpose. Continue reading

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.