New DURACAL Brand Cement HP Gets Nod From Maintenance Crews in St. Louis
By Pat Martens
MoDOT District Bridge Maintenance Engineer
St. Louis District

Pat Martens, bridge maintenance engineer for the St. Louis district of the Missouri DOT, supervises a recent highway repair using DURACAL Brand Cement HP.

As district bridge maintenance engineer for the Missouri Department of Transportation's (MoDOT) St. Louis District, I oversee the maintenance of over 875 span-type bridges. MoDOT ranks seventh nationally in the number of bridges, and it has been no secret that our agency has had the dubious distinction of suffering with the second most deficient bridges in the country.

There are plenty of old, obsolete bridges in our state. This, combined with other factors including limited funding, the Midwestern climate that features plenty of precipitation and numerous freeze-thaw cycles, and increased volume and loading from trucks, contribute to the dilemma of trying to repair and replace bridges. Throw in the fact that MoDOT has the second lowest gas tax in the Midwest and it's easy to see why we are in the predicament that we are in with our bridges.

10:33 a.m. It took MoDOT crews only a few hours to complete a recent repair using DURACAL HP cement. After the repair area was square-cut and jackhammered (top), a mobile mixer was brought into position (bottom).

In my 18-year career with MoDOT, I have spent 14 years directly involved in the inspection and maintenance program for our state's bridges. We have tried numerous patching products for our state's bridge decks and it seems that when the dust settles DURACAL® Brand Cement, from the Industrial Product Division of United States Gypsum Company, has been our most reliable bridge deck repair product for maintenance operations.

Of the over 68 million square feet of bridge deck on Missouri's state-maintained system, 16.5 million square feet are within our St. Louis District. For over 20 years our maintenance department has predominantly patched our bridge decks with DURACAL Cement. In the summer of 2001, however, we were introduced to a new DURACAL product that recently hit the market. This new and improved product, called DURACAL Brand Cement HP, has been a hit with our crews.

Comprised of calcium sulfate hemihydrate and Portland cement, the new DURACAL HP is a more user-friendly mix and provides the rapid-set capabilities necessary for short work zones dictated by a metropolitan area. According to Mark Lyons, maintenance (bridges) superintendent, who oversees field bridge maintenance operations, and has placed many different patching products, "this is all I want to use now."

Why is DURACAL HP now the product of choice for MoDOT's maintenance forces in St. Louis? There are several reasons.

Moisture from a recent rain shower was blown out with compressed air (top) and DURACAL HP cement was applied below the rebar to assure highest integrity (bottom).

First of all, there are the rapid-set capabilities that are very competitive with other proprietary rapid-set products. We have consistently been getting compressive strengths of 2500 psi within three hours. In addition, the rapid-set gain is achieved with no significant shrinkage cracking, unlike what we have observed with most other quick-setting patch materials, most of which seem to be much more tempermental.

"The DURACAL HP product gives us much higher compressive strengths then with the regular DURACAL cement, and much faster," said Lyons. This is critical in the metropolitan area, where working windows continue to shrink.

Second, the workability of the mix is very user friendly. The crews in the field find it easy to place, consolidate and finish. On a typical St. Louis summer day, the mix has about 10 minutes of working time and gains initial set in about 20 to 30 minutes.

Third, the product can be easily batched and dispensed with a calibrated mobile mixer. This is a big advantage over many of the other rapid-set products that have delicate and precise mixing procedures, requiring a hand-mixer. The mobile mixer allows for higher production rates and it is much easier on the crew. Though if needed, the product can also be applied using a batch mixer.

Preparation of the area to be patched is simple. The outline of the patch should be saw-cut as square as possible, outside the expected area of delamination (as determined by sounding). The repair area is jackhammered out. As long as reinforcing steel is exposed no sandblasting is necessary. Basically, just clean up the reinforcing steel with hand tools and make sure that there is sufficient clearance under the steel for the material to grab to when the gypsum-based patch material is placed. Blow out the area to be patched with compressed air. We use no bonding agents and there is little to no effective shrinkage upon maximum set, so there is minimal stress at the interface with the surrounding concrete. No curing compounds are used on the finished patch. Most other products require wet burlap or other curing methods.

12:30 p.m. A float is used to smooth the patched area. DURACAL HP cement requires no bonding agents and there is little to no effective shrinkage upon maximum set, so there is minimal stress at the interface with the surrounding concrete.

For a maintenance operation, that is about as simple and efficient as a patching procedure gets. No DURACAL HP patches have failed to date, nor have any patches exhibited any signs of distress or cracking.

Recently, our two urban bridge crews and one rural bridge crew combined to work the busy Poplar Street Bridge Complex during a four-night period. The area is extremely congested and requires nighttime lane closures in order to do the work. All of the repairs were made with DURACAL HP cement. Over 1,400 square feet of deck repair was performed during the four nights, and each morning traffic lanes were re-opened for rush hour. Without the use of DURACAL HP cement dispensed through our mobile mixer we could not have accomplished this.

The edges of the repaired area are sealed.

Even inclement weather one night did not hinder production. The quick initial set came in handy when early morning thunderstorms moved through the area. The fast set of the DURACAL HP product did not even require covering with plastic when showers hit shortly after the pour was completed.

DURACAL Brand Cement HP is marketed and distributed exclusively by United States Gypsum Company's Industrial Products Division. For additional information, contact U.S. Gypsum at P.O. Box 806278, Chicago, IL 60680-4124, or call 1-800-487-4431.

3 p.m. Thanks to the quick-setting properties of DURACAL HP cement, the repaired lane was re-opened well before rush-hour traffic.

The Industrial Products Division of U.S. Gypsum Company is a leading producer and marketer of a wide range of industrial products used in manufacturing, tooling, plastics, coatings, construction, agriculture, pharmaceuticals, food processing, statuary, ceramics, road repair, and many other applications.

United States Gypsum Company is a subsidiary of USG Corporation, a Fortune 500 Company with subsidiaries that are market leaders in their key product groups: gypsum wallboard, joint compound and related gypsum products; cement board; gypsum fiber panels; ceiling tile and grid; and building products distribution. For additional information, visit the USG web site at www.usg.com.