Iano's backfill

Bridge In A Backback

Maine first to use process for stronger bridges (forbes.com, 4/11/2009) describes innovative concrete bridge-forming technology developed at the University of Maine's Advanced Structures and Composites Center.

Formwork for concrete arches is made from lightweight, composite fabric tubular arches that are prefabricated off-site and then folded up for easy transport. Once on site, the arches are inflated into final shape and then filled with concrete. The fabric tubes, made of a carbon-glass fiber blend coated with resin, become an intergral part of the concrete  structure in the finished construction. Erection of formwork and pouring of the concrete arches can all be accomplished in as little as one day's time.

The Center's own web site provides information on a range of technologies in development, such as composite-reinforced structural wood panels, glulams, and more.

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.