News Detail

What Engineers Need to Know About Concrete...but Never Learned in School

8/1/1999

There is a national concern about premature deterioration of our infrastructure, including the concrete. Too many bridges, roads, highways, garages, and water treatment facilities require early repair and/or replacement. Repair and restoration is the fastest growing segment of the concrete industry. This not only drains municipal coffers, postponing new work, traffic delays irritate drivers like you and me.

For years, we have had the technology to produce durable, long-lasting concrete. In Ohio, there is a concrete city street over 100 years old and a 1940 bridge that has never required maintenance. Why are we not able to do such work today?

One reason is that concrete is generally understood by designers as a structural element, not as a material. This is caused by heavy academic pressures to expand engineering design curricula, leaving little time for attention to materials science, especially concrete. In a talk given during the 1994 "Mohan Malhotra Symposium on Concrete Technology—Past, Present, and Future," Kumar Mehta, professor emeritus of the University of California, Berkeley, pointed out:

"...fewer and fewer civil engineering schools are requiring their students to complete courses in quality control and behavior of concrete...The undergraduate and graduate curricula in civil engineering at well-known institutions in the U. S., such as MIT and Stanford, do not seem to contain any courses in concrete technology...The simplest and the most cost-effective solution is to go back to the basics or the root cause for lack of durability, namely the permeability of concrete and the factors responsible for increase in the permeability during service...The most serious problem in concrete technology today is the premature deterioration of concrete structures that are subjected to harsh environments."

During a high-level workshop on "Cement and Concrete Standards of the Future," leaders from ACI, ASTM, NIST, and Canadian and Mexican standards associations agreed: 1) "Concrete durability and how it affects long-term serviceability of a structure are not adequately covered in current codes and standards," and 2) "...meeting a strength requirement does not necessarily assure that a concrete will be durable in a specific environment.

While there are no records that any properly constructed pavement has failed due to low strength, many specifiers nevertheless continue to cite low water/cementitious materials ratios that lead to higher compressive strengths and also increased thickness to improve durability. Prominent research organizations are reporting that, in some applications, high strength can be counter-productive. Apply a dollar sign to the change from 9 in. thick pavements built under the first highway program (and still in excellent condition) to the cost of low w/cm concrete 12-14 in. thick!

In order to draw more attention to this situation, ACI and ASCE will offer a continuing education seminar titled: "Engineering Durable Concrete." The goal: to provide an overview of practical concrete materials and construction technology, to help engineers and constructors make best use of concrete as a material to extend durability and reduce costs."

The seminar will address:

Change — Why is old concrete outperforming new concrete?

Durability — What causes (and how to reduce?) steel corrosion and concrete cracking, spalling joints, ASR, sulfate attack, scaling, D-cracking?

High-performance concrete — Defined as concrete meeting special performance and uniformity requirements that can not always be achieved routinely. Critical characteristics include ease of placement, compaction without segregation, early-age strength, long-term mechanical properties, permeability, density, heat of hydration, toughness, volume stability, and long-life in severe environments.

Concrete as a process — It’s like a jigsaw puzzle – design the parts to fit.

Mixtures — Ingredients, proportions, and how to evaluate them for more than strength.

Constructibility — Design to fit construction operations needs.

Forming, placing, consolidating, and curing — Contract document needs.

Slabs and pavements — Avoiding cracking, spalling, curling, etc.

Testing — Interpreting reports and use of nondestructive testing.

There will be two opportunities to take advantage of this comprehensive program in 1999—November 30 at the ASCE Conference Center in Reston, VA, and December 8 in Dallas, TX. This program is appropriate for senior engineering and construction people.

I urge you to send as many as possible to this worthwhile and illuminating program. For more information and costs, watch for special announcements in the mail.

Jo Coke
President
American Concrete Institute

Back to Past-Presidents' Memo List