Another mix option: portland cement substitute yields economic, environmental, and durability benefits - What's New - Product/Service Evaluation

Concrete Producer, The, Jan, 2004 by Tom Klemens

Dan Walker, president of Texas EMC Products, has an idea other producers may want to know about. Using a specially modified fly ash to replace at least half of the portland cement in concrete can reduce your material costs while also providing a more durable product. Also, recycling this waste product of coal combustion further strengthens the argument that concrete is environmentally friendly.

A new plant under construction in Texas will produce a more reactive fly ash using a patented technology developed in Sweden. Concrete producers can use the Energetically Modified Cement (EMC) material, called CemPozz, to replace up to 60% of the portland cement in a concrete mix while providing early set times and increased strength.

The new material is being introduced into the United States by Texas EMC Products Inc., a joint venture between Few Ready Mix Concrete Co., a Texas ready-mix producer, and EMC Cement BV, a Dutch corporation that is licensing the technology.

Walker says test pours using concrete where CemPozz replaced about half rile portland cement have offered improved workability, pumpability, and finishability compared to ordinary portland cement concrete. Shrinkage cracks and dusting and delaminating problems have been reduced. Early test results from the Texas Department of Transportation indicate concrete made with CemPozz shows very good sulfate resistance, Walker says.

Few Ready Mix Concrete, Jasper, Texas, poured a concrete slab containing 55% CemPozz for expanding its corporate office in May 2003. An industrial-sized pilot plant on site used the EMC technology to produce CemPozz for this trial, as well as several other test slabs in the area.

Benefits of use

CemPozz improves concrete's chemistry. Portland cement reacts with water to produce ordinary concrete. That chemical process, called hydration, forms two cementing compounds in the concrete--calcium silicate hydrate and calcium hydroxide.

The calcium silicate hydrate gives concrete its strength and dimensional stability. The calcium hydroxide, which makes up about 25% of ordinary concrete, is relatively weak and porous. As a continuing part of the hydration process, CemPozz consumes the calcium hydroxide, turning it into additional hardened concrete. This results in a denser, less permeable, and more durable concrete.

Texas EMC Products is initially suggesting replacing half of the portland cement in a given concrete mix with CemPozz to increase durability. The cost of total cementitious material in concrete will be significantly reduced using CemPozz, primarily because fly ash is a by-product of coal combustion that would otherwise be disposed of in a landfill.

CemPozz also offers environmental benefits. For example, every ton of portland cement replaced by CemPozz will result in 0.8 ton less of C[O.sub.2] emissions. Producing CemPozz also requires much less energy than producing portland cement.

Texas EMC Products has the exclusive license to use the EMC technology in Texas. Groundbreaking for the joint venture's first CemPozz production plant, 7 miles north of Jewett, occurred in November near Texas Genco's Limestone Power Plant. The power plant will supply the fly ash that makes up 90% to 95% of the CemPozz.

The balance of the material is portland cement and cement kiln dust. The plant's initial capacity is 150,000 tons per year. Commercial production is expected to begin in April 2004. It's conveniently located near the major markets of Austin, Dallas-Fort Worth, and Houston.

The technology

In the early 1990s, Dr. Vladimir Ronin, a guest researcher at Sweden's Lulea University of Technology, began using vibrating mills to experiment on the intergrinding of portland cement with various supplementary materials. The technology for EMC resulted.

The patented process involves the high energetic grinding of ordinary portland cement and pozzolans, such as fly ash, blast furnace slag, and other similar materials, to form a blended cement. The EMC process reduces the size of the particles and cracks open the porous structure to further activate the surface area. This improves the reactivity of the portland cement and the pozzolan in concrete mixes.

Because the pozzolan has been made to react more quickly, a higher percentage of pozzolan can be used without delaying set time and strength development. The grinding is carefully controlled to keep from destroying the spherical shape of the fly ash, preserving concrete workability.

A small-scale EMC grinding facility has operated in Sweden since 1994, primarily using quartz sand as the pozzolan, to produce materials for test placement and further development.

Other EMC products, including newly developed blended cements containing up to 70% fly ash, up to 50% fine quartz sand, and Lip to 80% blast furnace slag, have been successfully tested by independent testing facilities in Europe and the United States. Seventeen reference objects, including two bridges for the Swedish Road Administration, have been successfully built in Northern Sweden's severe climate over the last seven years using these products.