February 1991 Table of Contents

Features Electrochemical Process Stops Rebar Corrosion out of concrete while restoring alkalinity

A passivating oxide layer protects embedded steel reinforcement from corrosion. Over time, however, chloride and carbonation can cause the passivating oxide layer to deteriorate, leaving rebar open to corrosion. One way to rehabilitate concrete that has been corroded by carbonation is to remove the contaminated concrete and expose the corroded rebar so corrosion can be removed. Another newer option stops corrosion by drawing chloride ions out of contaminated concrete and restoring the high pH level. This process can restore concrete in 10 days to 10 weeks, according to its developer. Read more

Features Concrete Path Paver Eliminates the Need for Formwork

The increasing popularity of golf in this country could be big boost for the concrete paving industry. This is because many new golf courses are installing paved pathways for golf carts. To allow concrete contractors to take advantage of this market, a company recently developed a narrow-width slipform paver that reportedly reduces labor costs for concrete path installation by as much as 80 percent. Because of this cost reduction, contractors who use the paver can lower their bids and be more competitive with asphalt contractors. The paver also speeds up path installation. Depending on the slump of the concrete mixture used and the condition of the paving site, the machine can place 10 yards of concrete in less than 3 minutes, or up to 3,500 lineal feet per day. Read more

Features Vacuum Blasting Cleans Expansion Joints Without Dust

Diversified Concrete Cutting, Sparks, Nevada, found itself facing dust problems when it attempted to clean sawed joints along I-395, just north of Reno, using conventional abrasive blasting methods. Contract specifications originally called for sandblast cleaning of expansion joints before sealing. But workers soon found that it blew so much sand and dust into the air that it created a visibility hazard for motorists. So the contractor decided to try wet blasting. This method doesn't create dust because it uses a mixture of abrasive and water, which is then removed from the area by vacuum equipment. On this project, however, it was impossible to remove all water from the pavement surfaces and joint cuts without interfering with traffic. After water evaporated, cutting fines, abrasive, and dust that were suspended in the water remained in the cuts. Read more

Features Introducing Controlled Permeability Formwork

Controlled permeability formwork (CPF) can increase concrete durability in the critical cover zone, improve surface appearance, and reduce formwork pressures. The system is comprised of a filter, drain, and structural support. While the concrete is being compacted, air and some of the mix water escape through the form leaving the concrete in the cover zone with a reduced water-cement ratio and significantly increased durability. Site measurements carried out by the Cement and Concrete Association in the early 1980s revealed that pore water is responsible for about 90 percent of formwork pressures. This explains why CPF gives substantially lower formwork pressures. Read more

Features Abstract Form Cast in Concrete

Concrete sculpture may be done by carving, direct modeling, casting in a mold, or casting on a bed of sand. Brian Adddis has tried them all. The sculptor of "Abstract Form," a 15-foot-high creation standing on the grounds of the Portland Cement Institute of South Africa in Johannesburg, is devoted to concrete as a sculptor's medium. His devotion is due to the strength, low materials cost, and adaptability to almost any size and shape, as well as the variety of colors and textures available. Read more

Features Concrete Was Big in Seguin, Texas

In 1854, Frederick Law Olmstead, famed landscape architect of New York City's Central Park, passed through Seguin while traveling in Texas. He was surprised to find that a number of buildings were made of concrete. His surprise was justified because the use of concrete in common wall construction was less than 2 decades old. The city stands on a thick foundation of coarse gravels that was ideal for the concrete construction methods practiced in only a few places in the country at the time. Read more

Features Coat Concrete Floors Fast

A patented machine that can apply liquid coatings to concrete floors in a fraction of the time it takes to apply coatings manually is now available. This self-propelled machine has two 10-foot-long applicator blades, one at the front and one at the rear, that quickly and evenly spread coatings onto prepared concrete or asphalt surfaces. Power is supplied by a 5-hp gasoline engine. The machine is as easy to operate as a riding lawn mower. As the machine travels forward, the driver simply steers it around any obstacles by pushing levers that control the drive wheels. On straight paths with no obstacles, the floor coater doesn't even need a driver. It automatically travels in a straight track and follows the contour of the base being coated. Read more

Features Pattern Rolling Instead of Stamping?

The manufacturer of a new imprinting tool described the tool's speed and ease of use by saying it was as easy as broom finishing and twice as fast as pattern stamping. The tool consists of a hollow aluminum cylinder, having either a brick- or cobblestone-patterned relief, and a detachable bracket that can receive any standard bull float handle. To roll the cylinder across the slab surface, simply push it using the float handle. Using several float handles attached end-to-end allows rolling the cylinder across a wide slab without having to walk on fresh concrete. Read more

Problem Clinic Circular Cracks Probably Caused by Overloading

We moved into a 60,000-square-foot tilt-up concrete building 6 months ago. The building is 2 years old but we're the first tenant. The floor is 5 inches thick and contains 6x6--W2.9x2.9 welded wire mesh. Control joints are 20 to 25 feet apart. Before we b Read more

Problem Clinic Cap Cylinders Before Curing Them?

At our precasting plant we put sulfur caps on test cylinders the day after they're cast but before they're placed in the moist room. Is there anything wrong with doing this? Read more

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