Iano's backfill

Pollution-Reducing Cement

A Concrete Step Toward Cleaner Air (Businessweek.com, 11/8/2006) reports on the use of concrete formulated with photocatalytic agents in the construction of walls and slabs at the Italian Pavilion of the Venice Biennale. In the presence of light, Italcementi Group's TX Active proprietary cement used in the concrete mix breaks down carbon monoxide, nitrogen oxide, benzene, and other pollutants into less harmful compounds such as water, nitrates, and carbon dioxide. The basic ingredient in TX Active, a blend of titanium dioxide, can be added to cement, mortar, paints, and plaster. Full-scale tests of the product in repaving projects in other locales have resulted in up to 60% reduction in measured pollutants.

The Vatican's Jubilee Church in Rome, 2003, (image above) was the first project to use TX-Active cement concrete.

Smog-Eating Concrete May Soon Cover US Buildings (ENR March 5, 2007) reports on the anticipated arrival TX-Active cement products in the United States via Italcementi Group's US subsidiary Essroc Cement Corp, though no specific projects are named. According to ENR, the titanium dioxide cement mix was first formulated to produce concrete with a brilliant white color, and it's pollution reducing properties were only appreciated later.

Superabsorber (transmaterial, March 8, 2007) describes the Superabsorber system designed by Douglas Hecker and Martha Skinner of fieldoffice that combines sound absorbing and photocatalytic air pollution reducing properties in sponge-like highway sound barrier walls. 

See also: Anti-Pollution Paint

Ultra-High Performance Concrete

Iowa Bridge Gives Glimpse Into the Future (Ascent, Designing With Precast, Summer 2006) describes the use of extraordinarily high-strength concrete in precast beams for the Mars Hill highway bridge in Wapello County, Iowa.

The "bulb tee" beams  (photo left) were cast with a proprietary concrete mix from Lafarge North America capable of producing concrete with compressive and tensile strengths as high as 30,000 psi and 7000 psi, respectively. (For comparison, conventional concrete is typically specified with compressive strength in the range of 2500 - 5000 psi, and taller buildings are being designed with concrete with compressive strengths as high as 10,000 - 20,000 psi.) Among the reported benefits are:

• A lighter, thinner structural member: The bulb tee beams used in the Mars Hill Bridge have webs 4-1/2 inches wide, compared to 6-1/2 inches for a conventional precast bulb tee, bottom flanges  5-1/2 inches deep, compared to 7-1/2 inches for a conventional tee, and top flanges 2-3/4 inches deep, compared to 3-3/4 inches for a conventional tee.
• The more dense concrete results in a structural member that is more resistant to the effects of weather and road salts, and that should be longer-laster.
• Reduction in the need for conventional steel reinforcing: Aside from the prestressing strands, the only other steel reinforcing in the Mars Hill Bridge beams are U-shaped bars used to develop bond between the precast beams and the cast-in-place concrete bridge deck. There are no stirrups or other conventional reinforcing steel.

More Info
For more about Lafarge Company's proprietary Ductal concrete, see Iano's Backfill Flexible Concrete.

Recycled Waste In Concrete Construction

Slab Alternatives From Recycled Waste (Architecture 04/2006) describes two proprietary Swiss systems from using recycled waste products in concrete to provide lighter-weight, better-performing concrete products.

Cobiax Technologies manufactures a system of hollow recycled polyethylene plastic spheres integrated with steel reinforcing cages that may be used to construct sitecast or "semi-precast" concrete floor slabs. This slab system can span from approximately 5 to 20 meters (15 to 65 feet) with thicknesses ranging from 230 to 580 mm (9 to 24 inches), capabilities roughly comparable with sitecast concrete one-way joist systems or precast concrete hollow core slabs.

In comparison to conventional concrete systems, the manufacturer claims weight savings of up to 35%, and additional potential savings through reduction in construction time and simplification of concrete forming requirements.

Geofil manufacturers glassy spheres from recycled waste, with sizes ranging from 2 to 25 mm (1/16 to 1 inch) in diameter. When added to concrete, the manufacturer claims a lighter-weight material with improved heat resistance and higher insulating values is produced. 

Concrete Residential Construction On The Rise

Concrete Homes Gain Significant Market Share (Portland Cement Association's Concete Homes Newsletter, November/December 2004) reports that 211,000 homes employing concrete wall systems were built in the year 2003. This amounts to 16% of all new single-family homes built in that year, an increase of 2% from 2002.

Types of construction included in these figures include insulating concrete formwork (ICF), autoclaved aerated concrete (AAC), concrete masonry, precast concrete, and others.

Flexible Concrete

Flexible concrete offers new solutions (Concrete Construction, December 2004) describes a highly ductile concrete produced under the trade name "Ductal". Flexible concrete differs from conventional reinforced concrete primarily in the absence of large aggregate in the concrete mix and the substitution of steel or organic fiber reinforcing for standard mild steel reinforcing.

The key to the behavior of the material is the creation of a highly regular matrix of fine aggregate interspersed with the reinforcing fiber in the concrete mix. The result is a material with greater strength and ductility than conventional reinforced concrete. Compressive strengths as high as 33,000 psi and flexural strengths as high as 7200 psi are claimed. Under extreme loading the material exhibits ductile behavior more similar to steel than conventional reinforced concrete. Ductile concrete also exhibits low porosity, reduced creep under sustained loading, and reduced drying shrinkage.

The high flexural strength of ductile concrete allows new possibilities for slender concrete elements. For example, curved concrete shell canopies for the a Calgary light rail transit station span 18 by 20 feet and are only 3/4 of an inch thick.

More Info:
Lafarge Ductal Home (click at top-right to view English version of site)
See also U-M researchers make bendable concrete (University of Michigan, May 4, 2005) press release for news of a similar developments at this university. Video links also included.

New Concrete Technologies

Nanometers? Tiny sensors embedded in concrete will collect physical and chemical data, Architecture Record, 04.04, reports on a National Science Foundation grant for the development of tiny passive sensors for inclusion in concrete to allow long term data collection pertaining to the physical and chemical characteristics of that material.

Each monitoring device consists of four or five sensors, known as micro-electromechanical systems or MEMS. According to the developer, Advanced Design Consulting, each MEMS is no larger than the size of the period at the end of a sentence. Monitoring devices will be added to the concrete mix and can measure properties such as pH, moisture content, temperature, and concentrations of chloride, sodium, and potassium ions throughout the life of the material, starting when it is freshly mixed and up to 100 years in age. The monitoring devices have no internal power source and rather are activated, powered by, and transmit data to a handheld monitoring device.

The goal is to allow more timely and accurate assessment of chemical and physical changes in concrete, such as changes in alkalinity, that can signal the onset of rebar corrosion and deterioration in highway bridges, pavements, and other concrete structures. With early warning of such changes, repairs can be made earlier and more cheaply, thereby extending the life of the concrete structure at lower cost.

Carbon fiber reinforcement requires less cover, Concrete Construction, April 2004, reports on C-Grid, a a new carbon and epoxy based concrete reinforcing material. According to the article, C-Grid can be used for applications ranging from concrete countertops to structural precast double-tees. The product can be used in place of welded wire mesh. Because it is non-corrosive, it requires less concrete cover and therefore permits thinner, lighter concrete sections. Because of its low thermal conductivity, C-Grid is also suitable for connecting the inner and outer portions of precast concrete insulated sandwich panels without loss in R-value. Current applications use C-Grid for secondary reinforcing and shear transfer reinforcing, but not for primary tension reinforcing.

More Information
TechFab
Altus Group

Light-Transmitting Concrete

Concrete casts new light in dull rooms, Optics.org, 11 March 2004, reports on a new concrete composite with optical fibers that is reportedly as strong as traditional concrete but also highly translucent. Dubbed LiTraCon, the material consists of cast blocks with an embedded array of optical fibers that allow light to pass through walls constructed of the material. According to twenty-seven year old inventor Áron Losonczi, “Thousands of optical glass fibers form a matrix and run parallel to each other between the two main surfaces of every block. Shadows on the lighter side will appear with sharp outlines on the darker one. Even the colours remain the same.”

See also Luccon.

Carbon Fiber Concrete Reinforcing

Precast concrete technology replaces steel with carbon fiber to produce thinner panels, Building Design & Construction, 02-02, reports on the use of carbon fiber reinforcing in wall panels and double tees to produce precast units that are up to 66% lighter and one-third thinner than conventional units. The reduced weight and size of these units can contribute to cost savings in transportation, erection, and the building superstructure.

According to the article, primary reinforcing in the precast units is steel, while a 1 mm (0.04 inch) high-strength, resin-bonded carbon fiber grid is used for secondary and shear transfer reinforcing. The carbon fiber reinforcing requires only 1/4 inch of concrete cover, compared with 3/4 inch to 3 inches of cover required for conventional steel.

More Information
Altus Group, CarbonCast Brochure

Reinforced Concrete and Fire

Fending off the flames, Structural Engineer, January 2004, discusses the performance of structural concrete in building fires, and advocates the virtues of this material's inherent resistance to the damaging effects of fire. Some topics discussed include:

The Benefits of Reinforce Concrete Construction
This article touts the benefits of concrete's inherent fire resistance, including for example:

• Application of additional fireproofing material is not required
• Connections are not vulnerable and do not require special attention for fireproofing
• Concrete walls and slabs are well suited to containing the spread of fire
• The added protection afforded by concrete construction can lead to lower building insurance rates
• Reinforced concrete structures typically survive building fires with only minimal structural repairs required
• Redundancy in concrete structures reduces the risk of structural failure due to fire


• Concrete in fire does not generate smoke or toxic gasses

Rational vs Empirical Design Methods
Two strategies are available for fire safety design. Rational design is the more complex and more expensive to perform. It consists of using fire test data, analysis of materials behavior at high temperature, and consideration of other thermal effects, to evaluate the performance of a particular structure under assumed design conditions. In other words, the structural behavior of a particular structure under building fire conditions is analyzed on a case-by-case basis. More on these techniques can be found in the Concrete Reinforcing Institute's Reinforeced Concrete Fire Resistance manual. Rational design is most appropriate when its results are likely to lead to sufficient cost savings to justify the extra effort required in design.

Empiricle design relies on standardized fire test results dictating design parameters such as critical member thickness, minimum concrete cover for reinforcing, etc. This is the design strategy most commonly applied to typical building projects.

Concrete Firesafe Design
The remainder of the article focuses primarily on empirical design methods. The predicted fire-resistance rating of concrete members is provided in a number of tables, relating factors such as aggregate material, restraint conditions, concrete cover for reinforcing, and type of structural member.

The discussion of lightweight concrete is noteworthy. Most commonly formulated with lightweight aggregates such as expanded clay, shale or fly ash, lightweight concrete has a density of 90 to 120 pounds per cubic foot, compared to approximately 150 lb/cu. ft. for normal weight concrete. Generally speaking, lightweight can expect to achieve a higher fire resistance rating than normal weight concrete due to its lower thermal conductivity.

Portland Cement Gets Greener

[This image shows a rotating cement kiln used in the manufacture of Portland cement. The scale is deceiving. Note the small human figures standing on the facility floor toward the bottom right of the image.]

The Portland Cement Association (PCA) is in the later stages of spearheading changes to the formulation of portland cement according to the ASTM C 150 standard. By allowing the inclusion of up to 5 percent ground limestone, PCA estimates annual enivironmental benefits including:

• Reduction in raw materials use of 1.6 million tons
• Reduction in energy use of over 11.8 trillion BTUs
• Reduction in carbon dioxide emissions of over 2.5 million tons
• Reduction of cement kiln dust of over 190 thousand tons

According to PCA's November 13, 2003 press release, the proposed changes will result in a 2.6 percent reduction in carbon dioxide emissions per ton of product, part of PCA's longer-term goal to reduce such emissions by 10 percent between 1990 and 2020. PCA also claims to have reduced energy consumption in the manufacture of portland cement by 33 percent since 1975.

More Information:
The manufacture of portland cement is discussed on pages 469 - 471 of the textbook. Issues of sustainability in concrete construction are discussed on pages 472 - 473.
PCA's Cement Basics page provides information on the formulation of portland cement, blended cement, and hydraulic cement, and provides links to additional related topics.

Pervious Concrete

Pervious Concrete Pavement: A Win-Win System, Concrete Technology Today, August 2003, a three times a year newsletter from the Portland Cement Association, discusses concrete pavements with high porosity. Also known as no-fines concrete or porous concrete, this 50-year old technology is gaining renewed attention for its ability to contribute to improved storm water management.

Unlike conventional concrete mixes, the aggregate in pervious concrete is narrowly graded. By omitting smaller sized aggregates, and limiting the amount of cement paste, interconnected voids may constitute 15% to 35% of the final concrete after curing. The interconnected void spaces allow water to pass through the concrete and percolate into the ground below. According to the article, percolation rates of pervious concrete may range from 2 to 18 gallons per minute per square foot of surface. The large percentage of void space also makes pervious concrete lighter and less strong than conventionally formulated concrete. Its compressive strength may range from 500 psi to 4000 psi, and its density may vary from 100 to 120 pounds per cubic foot.

This article provides more information about mix design for pervious concrete, its application to various site pavement applications, and its benefits related to federal clean water regulations.

Falling Water Restoration

Restoration wrapping up at Fallingwater, Fine Homebuilding January 2004, reports that the structural portion of the $11.5 million restoration started in 1996 is coming to a close.

VSL, the concrete restoration company hired to implement the repairs, provides additional details regarding the structural repairs on their web site, including:
--Explanation and diagrams of the posttensioning reinforcement of the main cantilevers, consisting of bundles of 13 1/2-inch steel cables
--Project background and description of structural steel channels and fiber reinforced polymer bars used to reinforce other parts of the structure.

Future restoration includes waterproofing, finishes, furnishings, and landscaping.

More information:
The textbook discusses posttension and other prestressing concepts on pages 493 - 499.
VSL Falling Water Media Coverage provides additional links to articles and media coverage of the Falling Water Repair project.
Western Pennsylvania Conservancy provides information about the building, and visiting Falling Water.
The Frank Lloyd Wright Building Conservancy provides information about conservation efforts related to all of Frank Lloyd Wright's projects.

13 - Concrete Construction Links

This article contains external links to resources on the Web relevant to Chapter 13 Concrete Construction.

Cement & Concrete FAQ

From the Portland Cement Association

Concrete Homes

Portland Cement Association's web page promoting concrete construction systems for residential construction.

ConcreteThinker.com

Portland Cement Association's web site devoted to sustainable design with concrete materials.

Durability

Portland Cement Association's web page for information related to resistance toweathering action, chemical attack, abrasion, and other durability factors.

Fly Ash for Concrete

ISG Resources information regarding fly ash for use in concrete.

PCA Library Services

Portland Cement Association's portal to research services, online catalog, journals, links, FAQs, conferences, and more...

Roadmap 2030: The U.S. Concrete Industry Technology Roadmap

Research and innovation strategic vision document, developed by American Concrete Institute and US Office of Industrial Technologies.