Concrete Cracks: A Shrinking Problem?

The shrinkage of a concrete mixture can have a significant impact on the performance of floors on ground. With the increasing demand for structural load-carrying capability and corresponding floor performance, it can be worthwhile to minimize concrete shrinkage. As repairs and maintenance can be costly, good joint performance is essential for industrial concrete floors. Therefore, it is important for slabs to remain in contact with the supporting base (minimal warping) and the joints to have minimal widening.

The shrinkage potential of the concrete mixture must be well understood so proper design and construction methods can result in the expected long-term serviceability for the owner. Even for commercial floors where heavy loading does not occur, concrete shrinkage can result in warping relaxation subsequent to installation of floor coverings or coatings. When surfaces are reprofiled in preparation for installation of floor finishes, slab distortion can result in delamination and buckling of the flooring. Knowledge of potential concrete shrinkage can help minimize such problems. More.

What causes random concrete cracks and can they be avoided?

Random cracks in new concrete slabs are a common complaint from owners. What causes random cracks; what are the best strategies to avoid the occurrence of random cracks; what are reasonable expectations; and do all random cracks in slabs constitute a failure of the concrete?

Random cracks in concrete slabs are most frequently caused by one of the following mechanisms:

• Settlement of the soils supporting the concrete slab
• Restraint of horizontal movement due to fixed foundation elements
• Overloading, applying a load larger than the slab was designed to support
• Restrained drying shrinkage of the slab

More on random cracks.

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New Edition of Concrete Floors on Ground (EB075)

This comprehensive bestseller represents the state-of-the practice for concrete slabs, including high-tech industrial floors, and incorporates information on modern material handling equipment. This latest update covers the design, construction, and repair of concrete floors on ground for a variety of floor classifications; updated thickness design procedure; joint stability; concrete drying shrinkage; floor flatness and levelness; moisture testing and floor coverings; concrete durability; and special floor types including white concrete floors. More information and to order.

At WOC, Decorative Concrete Remains Hot Because It’s So Cool!

This year, the World of Concrete located its decorative exhibits in the Silver Lot adjacent to the Las Vegas Convention Center South Hall. Called “Artistry in Decorative Concrete,” the sixth annual demonstration brought together twelve artists and numerous vendors with varying techniques and products. From stamped, polished, stained, and sprinkled varieties, flatwork continues to receive a lot of attention. In addition, vertical decorative concrete has seen a growth in both interest and techniques. One artist even has life imitating art imitating…concrete construction, his preferred subject matter for painting, from jobsites to equipment to workers. More.

Click here for more about architectural and decorative concrete.

Effect of Cement Fineness on ASTM C1260 Expansion (SN2963)

The Accelerated Mortar Bar Test, ASTM C1260 or CSA A23.2-25A, is a widely used test to detect alkali-silica reactive aggregates. Mortar bars are cast with the aggregate under investigation and the specimens are stored in 1N NaOH solution at 80°C. The expansion at 16 days after casting is taken as an indication of potential reactivity. ASTM C1260 requires the use of portland cement meeting ASTM C150.

In this research, sponsored in part by a PCA Education Foundation Fellowship, the effect of portland cement fineness on ASTM C1260 expansion in conjunction with other potentially influential factors, such as alkali content of clinker, aggregate reactivity, and immersion solution concentration, was studied. The results show that mortar bar expansion increased with higher cement fineness regardless of cement alkali, aggregate reactivity, or soak solution normality. More.

Free Download of Hydrologic Design of Pervious Concrete (EB303)

This 72-page publication describes the fundamental hydrologic behavior of pervious concrete pavement systems and demonstrates basic design methodologies appropriate for a variety of sites and circumstances. It provides an overview and discussion of techniques which can be used for hydrological design, considering the inter-relationship between runoff characteristics, material characteristics, and site geometry. It also provides guidelines for the preliminary selection of appropriate pervious concrete characteristics for specific applications and environments.
For a limited time, you can download a copy free. Offer ends 3/31/08.

Binders for Durable and Sustainable Concrete (LT308)
Written in the context of the new focus on sustainable construction, this interesting and highly readable new volume emphasizes that a thorough understanding of hydraulic binders is essential to making better concrete. Dr. Pierre-Claude Aïtcin, Professor Emeritus at the University of Sherbrooke, shows how ancient binders evolved, leading to today's 'smart' concretes, and suggests that future progress must involve better integration of the cement and concrete industries.

Mitigating Alkali Silica Reaction in Concrete with Supplementary Cementing Materials When Used in Conjunction with Portland Cements Having Alkali Contents in Excess of 1.0% (SN3023) The Canadian standard CSA A23.2-27A Use of Supplementary Cementing Materials for Counteracting Alkali-Silica Reaction requires a maximum allowable alkali content for cement of 1.0% Na₂O_eq. With increasing environmental pressure for cement producers to minimize waste kiln dust, the trend is towards higher-alkali cements, and several now exceed 1.0% Na₂O_eq. The only question is whether the current minimum SCM contents in CSA A23.2-27A need to be increased to account for the use of higher alkali cements. It was concluded that the current SCM levels are sufficient at mitigating ASR and recommendations to amend that standard are made.

Portland, Blended, and Other Hydraulic Cements (IS004)
Newly revised reprint of Chapter 2 of Design and Control of Concrete Mixtures. Discusses the raw materials and manufacture of portland cement—both wet and dry process—and different types of hydraulic cements. Also discusses masonry and expansive cements, and the chemistry of cement. Tables show compound transformations, chemical composition, fineness, and compressive strength requirements of cements. Includes graphs and charts illustrating effect of cement type on sulfate attack, strength development versus cement type and length change of shrinkage-compensating concrete.

For additional technical information, the PCA Library has an extensive collection of books, journals, and other materials on all aspects of cement and concrete. The Library's catalog may be searched at www.cement.org/library. A list of the newest additions to the collection may be found here.

Troubleshooting: Solutions to Concrete Field Problems
March 3-5, 2008

When concrete starts to deteriorate, clients need a person who can think on their feet and come up with solutions...that's troubleshooting. In this course, participants will learn about real-life problems caused by inadequacies in design, construction, and maintenance practices. Using example problems, participants will learn how to come up with suitable solutions. This program is ideal for those with a solid background in concrete technology who need to troubleshoot problems in the field. It is especially beneficial for those who deal directly with clients' concerns, such as consultants, field service representatives, contractors, inspectors, and government personnel. More information and registration.

Click here for a complete listing of Skokie courses for 2008.

CONEXPO-CON/AGG 2008 will be held from March 11-15 at the Las Vegas Convention Center. Held every three years, this exposition will showcase the latest construction related equipment, products, services, and technologies. The event is expected to attract an estimated 125,000 industry professionals from around the world involved in all segments of the construction, aggregates and ready mixed concrete industries, including contractors, materials producers, and government and institutional sector officials.

Pervious Concrete Seminars
PCA and the National Ready Mixed Concrete Association have teamed up with Land Development Today magazine to offer the seminar "Pervious Concrete—A Stormwater Solution."

• February 18, 2008 - Charlotte, N.C.
• March 17, 2008 - Louisville, Ky.
• March 19, 2008 - Springfield, Mo.
• April 14, 2008 - Hartford, Conn.
• April 21, 2008 - Omaha, Neb.
• April 24, 2008 - Nashville, Tenn.
• May 1, 2008 - Philadelphia, Pa.

Chemistry of Cement and Concrete Course
June 2-6, 2008, University of Toronto

Complete listing of industry conferences.