Durability

SOLUTIONS

APPLICATIONS

RESOURCES

CASE STUDIES

THINKERS

www.ConcreteThinker.com

Benefits > Durability
Stands up to natures forces

The New American Home® Incorporates Cement-Based Solutions for Efficiency, Durability

Concrete Builds a Strong Case for Sustainability in New Model Home

Durability is the ability to last a long time without significant deterioration. A durable material helps the environment by conserving resources and reducing wastes and the environmental impacts of repair and replacement. Construction and demolition waste contribute to solid waste going to landfills. The production of new building materials depletes natural resources and can produce air and water pollution.

The heavily traveled Wacker Drive replacement in downtown Chicago was designed for a 75 to 100-year life. (PCA No. 16263)

The design service life of most buildings is often 30 years, although buildings often last 50 to 100 years or longer. Most concrete and masonry buildings are demolished due to obsolescence rather than deterioration. A concrete shell can be left in place if a building use or function changes or when a building interior is renovated. Concrete, as a structural material and as the building exterior skin, has the ability to withstand nature’s normal deteriorating mechanisms as well as natural disasters.

Durability of concrete may be defined as the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties. Different concretes require different degrees of durability depending on the exposure environment and properties desired. For example, concrete exposed to tidal seawater will have different requirements than an indoor concrete floor. Concrete ingredients, their proportioning, interactions between them, placing and curing practices, and the service environment determine the ultimate durability and life of concrete.

These 3x5-ft concrete panels with decorative finishes were displayed outdoors in the relatively severe weather in the Skokie, Illinois, area (near Chicago). With only a few exceptions, their appearance changed very little after more than 40 years of exposure to bright sun-light, wind, snow, acid rain, freezing and thawing, hot summers, and cold winters (PCA No. 2101)

High Humidity and Wind-Driven Rain: Concrete is resistant to wind-driven rain and moist outdoor air in hot and humid climates because it is impermeable to air infiltration and wind-driven rain. Moisture that enters a building must come through joints between concrete elements. Annual inspection and repair of joints will minimize this potential. More importantly, if moisture does enter through joints, it will not damage the concrete. Good practice for all types of wall construction is to have permeable materials that breathe (are allowed to dry) on at least one surface and to not encapsulate concrete between two impermeable surfaces. Concrete will dry out if not covered by impermeable treatments.

Portland cement plaster (stucco) should not be confused with the exterior insulation finish systems (EIFS) or synthetic stucco systems that have become popular but may have performance problems, including moisture damage and low impact-resistance. Synthetic stucco is generally a fraction of the thickness of portland cement stucco, offering less impact resistance. Due to its composition, it does not allow the inside of a wall to dry when moisture gets trapped inside. Trapped moisture eventually rots insulation, sheathing, and wood framing. It also corrodes metal framing and metal attachments. There have been fewer problems with EIFS used over solid bases such as concrete or masonry because these substrates are very stable and are not subject to rot or corrosion.

Ultraviolet Resistance: The ultraviolet portion of solar radiation does not harm concrete. Using colored pigments in concrete retains the color in concrete long after paints have faded due to the sun’s effects.

Inedible: Vermin and insects cannot destroy concrete because it is inedible. Some softer materials are inedible but still provide pathways for insects. Due to its hardness, vermin and insects will not bore through concrete. Gaps in exterior insulation to expose the concrete can provide access for termite inspectors.

Moderate to Severe Exposure Conditions for Concrete: The following are important exposure conditions and deterioration mechanisms in concrete. Concrete can withstand these effects when properly designed. The Specifier’s Guide for Durable Concrete is intended to provide sufficient information to allow the practitioner to select materials and mix design parameters to achieve durable concrete in a variety of environments.

Resistance to weathering, including freezing and thawing (from www.cement.org)

Resistance to Freezing and Thawing: The most potentially destructive weathering factor is freezing and thawing while the concrete is wet, particularly in the presence of deicing chemicals. Deterioration is caused by the freezing of water and subsequent expansion in the paste, the aggregate particles, or both.

With the addition of an air entrainment admixture, concrete is highly resistant to freezing and thawing. During freezing, the water displaced by ice formation in the paste is accommodated so that it is not disruptive; the microscopic air bubbles in the paste provide chambers for the water to enter and thus relieve the hydraullic pressure generated. Concrete with a low water-cementitious ratio (0.40 or lower) is more durable than concrete with a high water-cementitious ratio (0.50 or higher). Air-entrained concrete with a low water-cementitious ratio and an air content of 5 to 8% will withstand a great number of cycles of freezing and thawing without distress.

Chemical resistance (from www.cement.org)

Chemical Resistance: Concrete is resistant to most natural environments and many chemicals. Concrete is virtually the only material used for the construction of wastewater transportation and treatment facilities because of its ability to resist corrosion caused by the highly aggressive contaminants in the wastewater stream as well as the chemicals added to treat these waste products.

However concrete is sometimes exposed to substances that can attack and cause deterioration. Concrete in chemical manufacturing and storage facilities is specially prone to chemical attack. The effect of sulfates and chlorides is discussed below. Acids attack concrete by dissolving the cement paste and calcareous aggregates. In addition to using concrete with a low permeability, surface treatments can be used to keep aggressive substances from coming in contact with concrete. Effects of Substances on Concrete and Guide to Protective Treatments discusses the effects of hundreds of chemicals on concrete and provides a list of treatments to help control chemical attack.

Resistance to Sulfate Attack: Excessive amounts of sulfates in soil or water can attack and destroy a concrete that is not properly designed. Sulfates (for example calcium sulfate, sodium sulfate, and magnesium sulfate) can attack concrete by reacting with hydrated compounds in the hardened cement paste. These reactions can induce sufficient pressure to cause disintegration of the concrete.

Like natural rock such as limestone, porous concrete (generally with a high water-cementitious ratio) is susceptible to weathering caused by salt crystallization. Examples of salts known to cause weathering of concrete include sodium carbonate and sodium sulfate.

Confederation Bridge, spanning the Northumberland Strait between Prince Edward Island and New Brunswick, was specifically designed for high durability in a severe environment and a 100-year life. The bridge has to resist freezing and thawing, seawater exposure, and abrasion from floating ice. (PCA No. IMG15714)

Sulfate attack and salt crystallization are more severe at locations where the concrete is exposed to wetting and drying cycles, than continuously wet cycles. For the best defense against external sulfate attack, design concrete with a low water to cementitious material ratio (around 0.40) and use cements specially formulated for sulfate environments.

Seawater Exposure: Concrete has been used in seawater exposures for decades with excellent performance. However, special care in mix design and material selection is necessary for these severe environments. A structure exposed to seawater or seawater spray is most vulnerable in the tidal or splash zone where there are repeated cycles of wetting and drying and/or freezing and thawing. Sulfates and chlorides in seawater require the use of low permeability concrete to minimize steel corrosion and sulfate attack. A cement resistant to sulfate exposure is helpful. Proper concrete cover over reinforcing steel must be provided, and the water-cementitious ratio should not exceed 0.40.

Corrosion resistance (from www.cement.org/)

Chloride Resistance and Steel Corrosion: Chloride present in plain concrete that does not contain steel is generally not a durability concern. Concrete protects embedded steel from corrosion through its highly alkaline nature. The high pH environment in concrete (usually greater than 12.5) causes a passive and noncorroding protective oxide film to form on steel. However, the presence of chloride ions from deicers or seawater can destroy or penetrate the film. Once the chloride corrosion threshold is reached, an electric cell is formed along the steel or between steel bars and the electrochemical process of carrions begins.

The resistance of concrete to chloride is good; however, for severe environments such as bridge decks, it can be increase by using a low water-cementitious ratio (about 0.40), at least seven days of moist curing, and supplementary cementitious materials such as silica fume, to reduce permeability. Increasing the concrete cover over the steel also helps slow down the migration of chlorides. Other methods of reducing steel corrosion include the use of corrosion inhibiting admixtures, epoxy-coated reinforcing steel, surface treatments, concrete overlays, and cathodic protection.

Resistance to alkali-silica reaction (ASR) (from www.cement.org/)

Resistance to Alkali-Silica Reaction (ASR): ASR is an expansive reaction between reactive forms of silica in aggregates and potassium and sodium alkalis, mostly from cement, but also from aggregates, pozzolans, admixtures, and mixing water. The reactivity is potentially harmful only when it produces significant expansion. Indications of the presence of alkali-aggregate reactivity may be a network of cracks, closed or spalling joints, or movement of portions of a structure. ASR can be controlled through proper aggregate selection and/or the use of supplementary cementitious materials (such as fly ash or slag cement) or blended cements proven by testing to control the reaction.

Abrasion resistance (from www.cement.org/)

Abrasion Resistance: Concrete is resistant to the abrasive affects of ordinary weather. Examples of severe abrasion and erosion are particles in rapidly moving water, floating ice, or areas where steel studs are allowed on tires. Abrasion resistance is directly related to the strength of the concrete. For areas with severe abrasion, studies show that concrete with compressive strengths of 12,000 to 19,000 psi work well.

Why does concrete crack?

Concrete, like most materials, will shrink slightly when it dries out. Common shrinkage is about 1/16^th of an inch in a 10-foot length of concrete. The reason contractors place joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint, where concrete cracks due to shrinkage are expected to occur. Control or construction joints are also placed in concrete walls and other structures.

Why do concrete surfaces spall?

Concrete spalling (or flaking) can be prevented. It occurs due to one or more of the following reasons.

1.) In cold climates subjected to freezing and thawing, concrete surfaces have the potential to spall if the concrete is not air-entrained.

2.)Too much water in the concrete mix will produce a weaker, more permeable and less durable concrete. The water-cementitious ratio should be as low as possible (0.45 or less).

3.) Concrete finishing operations should not begin until the water sheen on the surface is gone and the excess bleed water on the surface has had a chance to evaporate. If this excess water is worked into the concrete because finishing operations have begun too soon, the concrete on the surface will have too high of a water content and this surface will be weaker and less durable.

BOOKMARK

Bob Harris' Guide to Stained Concrete Floors (2004)

Bob Harris, Decorative Concrete Institute, Item Code LT283, 100 pages

Guide to Stained Concrete Floors is a 100-page, full-color resource with detailed information and practical tips on staining concrete interior floors. This publication is available for $35 at the Portland Cement Association Bookstore.

Bob Harris' Guide to Stamped Concrete (2004)

Bob Harris, Decorative Concrete Institute, Item Code LT284, 144 pages

Available for $45. The guide covers topics of vital importance for anyone planning to stamp concrete, including: - Nine sources for stamping design ideas - Maximizing your profits by knowing what to charge - Concrete mix considerations for stamping concrete - Site conditions affecting stamped concrete work and how to prepare or avoid them - How to prepare concrete for stamping, including tips for striking off and finishing - Three important steps to applying color hardener - Tools that are essential for successful stamping - How and when to start stamping - Important issues to avoid when stamping - Fixing minor flaws in stamped concrete work - Effective techniques for the application of sealers - 10 ways to promote and sell your stamped concrete work - How to distinguish your stamped concrete work from competitors

Design and Control of Concrete Mixtures, 14th Edition (2002)

S.H. Kosmatka, B. Kerkhoff, and W.C. Panarese, Portland Cement Association, Item Code EB001, 372 pages

Available for $50 Definitive reference on concrete technology covers fundamentals and detailed information on freshly mixed and hardened concrete. Extensively updated and expanded, this new edition discusses materials for concrete, such as portland cements, supplementary cementing materials, aggregates, admixtures and fibers; air entrainment; procedures for mix proportioning, batching, mixing, transporting, handling, placing, consolidating, finishing, and curing concrete; precautions necessary during hot- and cold-weather concreting; causes and methods of controlling volume changes; commonly used control tests for quality concrete; special types of concrete, such as high-performance, lightweight, heavyweight, no-slump, roller-compacted, shotcrete, mass concrete and many more. Applicable ASTM, AASHTO, and ACI standards are referred to extensively.

Effects of Substances on Concrete and Guide to Protective Treatments (2001)

PCA #IS001, 36 pages

Available for $3. Improve concrete’s durability by knowing what chemicals attack it and what you can do to protect it. A comprehensive list of materials, a description of their effects on concrete, and recommended protective treatments are given. Also listed are dozens of products suitable for protecting concrete, including a list of coating manufacturers with addresses, phone numbers, and websites.

Masonry Designers' Guide, Fourth Edition (2004)

Portland Cement Association. Item Code: LT201

Available for $98. This book is one of the most popular design and teaching resources related to masonry because it provides comprehensive coverage, extensive code references, and numerous practical examples.

Masonry Mortars (2004)

Portland Cement Association. Item Code: IS040

Available for $5.28. This document includes coverage of mortar properties and current masonry standards used in the United States and Canada. Discusses component materials, batching and mixing procedures, the use mortar in hot and cold weather, and special techniques of mortar production.

Specifiers Guide to Durable Concrete (2005)

PCA No. EB221, 72 pages

Available for $30. This publication is an instruction guide and basic reference for those responsible for writing and implementing concrete specifications. This reference covers the basic concepts of concrete technology as it relates to durability, and is intended to be a companion and supplement to Design and Control of Concrete Mixtures. It provides sufficient information to allow the practitioner to select materials and mix design parameters to achieve durable concrete in a variety of environments. It also warns the user when expert help is recommended. Maintenance requirements to assure long-term performance are provided Several case studies provide real-world examples.

Concrete: The Choice for Sustainable Design

Taking Shelter from the Storm, Building a Safe Room inside your House (2004)

FEMA. Publication Number 320

This is a guide to building safe rooms within houses in high risk weather area. It has information on how to assess, plan, and build a safe room.

A Sustainable Future: Creating the Legacy - The Story of the Earth Rangers Centre (2005)

Cement Association of Canada

Everything about the Earth Rangers Centre has been planned to make it a model of sustainable development. The $23 million building houses a wildlife hospital capable of handling 5,000 animals a year, a theatre and interactive displays for visitors and student tours, and a world class veterinary training and research hospital. To show you how the Centre was built, video footage was captured at regular intervals during its construction, transferred to QuickTime files and available for download.

Changes In Store (2006)

Wal-Mart showcases green concrete technologies at its store in Texas.

This 4 page article was originally featured in the May 2006 edition of Concrete Producer Magazine, by Hanley Wood. Wal-Mart testing a range of green strategies at this prototype store in McKinney, TX. Along with other green strategies, concrete was used as interior finish flooring, reducing VOC's and maintenance, and pervious pavement in the parking area to improve ground water quality and quantity.

Concrete Reinforcing Steel Institute (2006)

An industry resource website

ICF Points to LEED (2006)

Insulating Concrete Form Systems contribute to LEED credits

This two page .pdf summarizes the credits available to designers and building owners when using high performing insulating concrete forms in wall construction. Documents available for download to ICFA members.

National Ready Mixed Concrete Association

Industry resource for ready mixed concrete.

Polished Concrete Can Be Green (2007)

L&M Concretenews, January, 2007: Volume 7, Number 1

A durable, long lasting, attractive polished concrete floor is a value-loaded option within the reach of almost any facility today.

Tile Roofing Institute

Website of non-profit industry association.