Concrete outlook 2005

Residential construction levels off; technology continues to improve concrete performance.

Editor note: Experts at the Portland Cement Association (PCA) (www.cement.org) share its outlook on the concrete and construction industry.

Economic outlook
Ed Sullivan, chief economist at the PCA, predicts residential construction will slow slightly in 2005.

“Higher oil prices will slow overall economic activity, delaying a recovery in nonresidential and public construction; but low mortgage rates will prolong the boom in residential construction,” he says.

He also believes consumer spending will be partially compromised; inflation will run stronger; job gains will be smaller; and sentiment in the consumer and business areas will be more subdued.

That means the level and composition of construction spending will shift. “In retrospect, 2004 represents a year of transition for U.S. construction. The strengthening economy and an increase in interest rates sets the stage for recovery in public and nonresidential activity. The wildcard is oil prices.”

Higher oil prices and slower economic growth translates into three considerations in PCA’s forecast.

First, slower overall economic growth implies a more gradual recovery in capacity utilization and vacancy rates, and generally lowers the expected return on investment for commercial property. The PCA estimates nonresidential construction to gain 9.9 percent in 2005.

Second, slower overall economic activity implies sluggish employment growth which offers a muted improvement in states’ tax base.

“The scars from state fiscal problems will fade slower than anticipated,” he says. With delayed state revenue growth, the PCA predicts public construction will increase only 3.8 percent in 2005.

Finally, mortgage rates will slowly rise, and PCA forecasters believe it will take a 6.5 percent mortgage rate to exert enough pressure to affect single-family construction activity. However, the PCA predicts that tipping point will not happen until the end of the first quarter of 2005. The PCA predicts overall residential construction will decrease slightly by 0.3 percent in 2005 and construction spending is expected to reach an inflation-adjusted level of $745 billion or 2.9 percent growth.

“Through 2008, nonresidential and public spending are expected to assume growth leadership and residential activity will step down to become the growth laggard, although it will maintain historically strong levels.” Sullivan says.

Concrete construction trends
Technology continues to evolve the business of mixing, placing and designing with concrete, says Terry Collins, concrete construction engineer at the PCA. “Self-consolidating concrete (SCC) continues to gain interest, but economics and practicality should drive decisions about its use,” he says.

Producing SCC requires using highly cementitious materials (typically cement plus fly ash or slag), a low water-cement ratio and a large dose of high-range water reducer. Viscosity-modifying admixtures may also be needed.

Collins says forms must be stronger to hold SCC mixes. “With a 16'-tall wall placed at a rapid pace, the pressure at the base of the form could be as high as 2,400 lbs. per sq. ft. or nearly 17 psi. Generally, concrete is placed at a more controlled pace (height vs. time), but forms must be 40 percent stronger to take the pressure.”

High-performance or high-strength concrete is commercially available to attain 20,000 psi or greater. “This higher strength adds great building efficiency. It allows engineers to reduce the mass of columns, bridge spans or beams. It’s being used extensively in pre-cast construction. When used to build a 50-story building, it can reduce the floor height by 1' per story because floor beams are smaller. The smaller size means you could add four more stories in the same building height. It all becomes an economic question of the benefit of reducing column and beam size vs. the cost of the concrete to get more usable space in the building,” Collins says.

To get even greater strength from high-strength concrete, steel or synthetic fibers are sometimes added to the mix. Commonly called reactive powder concrete, it is an extreme variation of high strength/high performance concrete. “These powders can produce concrete strength of 25,000 to 30,000 psi,” he says.

There is some controversy over the use of fibers vs. steel reinforcement. “Some in the fiber industry propose that fiber can replace steel, but I don’t believe that is so. The two provide different functions in concrete. Fibers can control plastic shrink and improve impact resistance, but it can’t control crack width like steel can. Steel also helps to provide load transfer from slab to slab,” he says.

Super-plasticizers are also being used to reduce the amount of water in the mix for greater strength. These compounds affect the particle charge of the cement, so less water is needed to lubricate the mix, easing placement and finishing, but may increase shrinkage. “In general, it is good for slab work because it can reduce finish time. It’s also used extensively in tilt-up applications. Judicious use can improve the water-cement ratio and reduce cost because less cement is used. However, it takes time and knowledge to use these correctly.”

Pervious concrete gains attention
In warmer climates, pervious concrete is gaining acceptance. “This is a no-sand concrete that allows water to percolate through it. It is attractive in areas where storm water runoff is a big issue. It should be used with caution in colder climates because freeze-thawing action would rip the concrete apart if water ponds on the body of the pavement,” he says.

Perhaps the most glamorous trend in concrete is the decorative market. “Staining, etching and stamping concrete is very high-profit but also very high risk,” Collins says. “We find that inexperienced contractors do a poor job of explaining the limitations brought on by ambient conditions and materials to customers. It’s important to produce test panels to establish the appropriate aesthetic goals and then use the test panels as a guide for acceptance of the work to be completed. Customers must understand it can’t be reproduced with 100 percent accuracy,” he says.

On the supply side of concrete production, Collins predicts that quality aggregate will be harder to find and be more expensive.

“It’s becoming a challenge to find high-quality aggregate. Siting and permitting aggregate production facilities is a growing issue. It is more difficult to locate them without objections from the community,” Collins concludes.

 

Concrete cutting tips Using a concrete-cutting chain saw isn’t as daunting as it first appears. Joe Taccogna, marketing manager at ICS Blount International, offers some helpful cutting tips to make the job even easier: 1. Keep steady, firm pressure on the saw as the chain cuts. This helps prevents chain bounce and chattering and helps extend diamond life. 2. For the straightest cuts, use the “step cut” method. After outlining the cut, score the cut line approximately 1/2" deep using the nose of the bar. Next, deepen cut by about 2", then plunge through and complete the cut using the Wallwalker attachment available with ICS saws as a lever. 3. Plunge cut instead of starting on top of the wall. Use the “step cut” method and begin with a plunge cut several inches from the top of the wall. 4. Always operate a chainsaw at full throttle. Apply enough feed force so speed drops between 20 and 30 percent when cutting. If too much feed force is applied, the engine will lug causing the engine to overheat. The chain will also not have enough speed to cut effectively. If too little feed force is applied, the diamonds will skid and not cut well. 5. When cutting heavy rebar, slowly rock the saw over the rebar. This keeps you cutting concrete as well as steel and helps keep diamond exposed. Expect shorter chain life when cutting heavy rebar. 6. A properly tensioned chain optimizes cutting performance. A good rule of thumb: The chain should be tight but can be pulled around the bar by hand. 7. If the saw begins to cut consistently crooked, turn the guide bar over and use the other side. If problem persists, dress worn rails with belt grinder. The normal life of a guide bar is two to three chains; heavy rebar can shorten bar life. 8. With a new chain, increase cutting speed to “open up the diamonds”. Do this by making a few cuts in an abrasive material such as a cinder block.

Published in the January/February 2005 issue of Contractor Tools and Supplies magazine.

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