Dr Moslemi said the business has changed quite a bit since the first of the series of meetings convened in 1988. He declared: "In North America, fibre-cement seems to be quite successful in some segments, but cement-bonded particleboard is not having the same success." He continued: "The fibre-cement business began in 1988 with virtually no production in the US. Now it is well exceeding one billion ft² annually and is well recognised in North America. Wood-plastic composites are having some success in recycled as well as virgin material." Dr Yasuo Kuroki, Nichiya Corp, Nagoya, Japan, announced that cement siding represents 70% of the exterior walls in Japanese housing construction compared with1983’s 18% of the market. Last year 118.8 million m2 of cement exterior siding was sold, although the Japanese housing industry has not grown recently.
He described research combining particle orientation with carbon dioxide for curing. He explained that the gas accelerates cement’s hydration reaction. The internal bond of a single-layer formed board was lower than that of a three-layer formed board. The experiments used pure carbon dioxide gas but the scientists believe that boiler exhausts could provide a 15% content with the side benefit of air quality control. Horst G Goessele, fibre-cement plant engineering division manager, Händle GmbH, Mühlacker, Germany, praised the advantages of extruding fibre-reinforced concrete products.
He said the matrix can be made up of a combination of different materials: cement, limestone powder, fly ash, fibres (glass, cellulose and other natural or man-made fibres), silica, mica, water, and additives. He summarised the benefits:
* Quick installation, use of standard tools and techniques
* Light because of hollow core profile, easy handling on site
* High loadbearing capacity and tensile strength combined with non combustibility
* Reduced building costs due to low material costs, minimum waste, and speedier construction with fewer trades
* Panel installation is virtually dry with no need for surface rendering along with precise cut-to-length from factory
* Minimum noise, dust, and construction waste
Michael P Wolcott, Washington State University, Pullman, Washington, reported that composite production from wood and thermoplastic resins has tripled over the last 10 years and predicted annual 60% increases over the next five years. Dr Wolcott said wood dispersion throughout the thermoplastic melt is a major processing step influencing product quality. He said melt-blending wood and thermoplastics is facilitated through high shear forces. Wood flour is generally easy to disperse in a matrix, but fibres and larger particles require longer times and higher mixing intensity. Twin screw extruders provide simultaneous mixing with extrusion or injection moulding.
Ashish Dubey, USG Corporation, Libertyville, Illinois, US, declared that mesh-reinforced cement boards are lightweight, easily installed, weather durable, dimensionally stable, mould and mildew resistant, and non-combustible. Mr Dubey listed one of the advantages as the board’s score-and-snap property: one surface of the board can be scored, using a knife to cut through the reinforcing mesh. The board is then snapped and the scrim on the reverse surface is cut to part the board. This simplifies construction as fewer power tools are required. Manfred Börger, University of Erlangen-Nürnberg, Erlangen, Germany praised glass fibre- reinforced concrete as a well-established material for producing corrugated roofing sheets and flat tile backer boards. In the product’s production, a slurry containing cement paste, aggregates, and additives is spread on a moving line. Chopped glass fibres are sprayed onto the board’s surface and mechanically pushed into the matrix in a random orientation. In corrugated boards additional glass fibre rovings oriented to the corrugations are incorporated. Special moulds form the corrugations.
No excess water is used and no dewatering is required. The water is entirely consumed by cement hydration. A problem is ageing degradation, particularly in a wet environment, caused by chemical attack of the glass fibre reinforcement by the alkaline cement; however microsilica (silica fume) can help this problem. Dr Börger explained that the Wellcrete process uses a blend of blast furnace cement, CEM III/B and microsilica, along with AR-glass reinforcement. It seems to show a good long-term durability with the addition of 20% silica fume or 30% trass. Katie Wierman-Kuder, Center for Advanced Cement-Based Materials, Northwestern University, Evanston, Illinois, US, confirmed the US growth of fibre-reinforced cement board as the fastest of the 1990s. She said the product might make up more than one quarter of the siding market by 2005.
She said fibres are added to the cement to increase the product’s crack-arresting ability. It is subject to freeze-thaw deterioration because of its high porosity, the organic cellulose fibres that reinforce it, and the laminated structure of the material. She continues experimenting with product pressing to improve properties. Henning M Thygesen, Elkem ASA Materials, Kristiansand, Norway, outlined handling methods for microsilica, or silica fume. Microsilica was virtually a waste byproduct of manufacturing silicon or ferrosilicon. It is a mineral composed of ultrafine amorphous spheres of silicon dioxide produced in manufacturing. However, it has become one of the most used and valuable additives for fibre cement products. The powder is 100 times finer than ordinary cement, generating transportation, storage and dispensing considerations. It is available in undensified, densified, slurry and, rarely, in micro-pellets.
Mr Thygesen’s colleague, Harold Schreiner, R&D project manager, declared good dispersion of microsilica slurry as the key factor in gaining its maximum benefits. He said bending strength increases with increased microsilica content and porosity and water absorption of the sheets decreases. Freeze-thaw resistance is also improved. Bill Johnson, 2KF Company, Minneapolis, Minnesota, US, advocated using power plant residues in producing cement fibre products. He said: "The cost of inorganic cementitious materials continues to rise as feedstocks, energy, and transportation all become more expensive. As these costs rise, users are turning to lower cost materials as replacements for some or all of the cementitious components. Power plant residues, mostly fly ash scrubber solids, but also bottom ash and cenospheres are a major replacement source."
He continued: "New technologies using these residues are providing much higher quality in the finished materials. What was once a waste product stored in unsightly landfills is now a strong component of the construction industry." He said that such materials as coal fly ash can replace clay, sand, limestone and gravel, saving the energy costs of mining the materials. All this means not only lowering material cost, but there is the advantage of lower weight and reduced shipping costs. Another advantage is greater material strength, allowing products to be designed with less material. Steven Booz, marketing director for fibre cement products for CertainTeed Corporation, Valley Forge, Pennsylvania, US, reported that the North American fibre cement market has consolidated significantly over the past few years.
Remaining producers are CertainTeed, James Hardie and Maxi Tile in siding, Nichiha-USA in brick and stone, and Re-Con in roofing. Hardie is by far the market leader with perhaps 90% of the business. Mr Booz said that 75% of the North American fibre cement market is in exterior cladding, followed by underlayment and backer board. He sees market changes afoot, with thoughts of others entering the market. "One thing is certain," he concluded, "the industry will look very different five years from now." George Carter of George Carter & Affiliates, Hillsdale, New Jersey, US, has intensely studied fibre cement siding markets. He said the rate of change in residential siding markets seems to be increasing. His studies show that, generally speaking, siding producers improved their customer satisfaction performance between 1994 and 2002, however, apparently prices and long-term durability are not adequate.
Dr Klaus Bohnemann, president, Wehrhahn Group, Delmenhorst, Germany, said corrugated fibre cement roofing has some acceptance problems caused by changing design fashions and the lack of practical insulation systems for industrial buildings. He reported that modern designs have increased the market for dry wall and wall cladding. He said that fibre cement remains a quite versatile building material. Max Fischel, vice-president, E A Euroamerica SA, San Jose, Cost Rica, was unable to attend the conference, but he sent a description of his firm’s gypsum board operations. The plant produces five million m² of board annually in sizes of 2ft x 2ft up to 4ft x 10ft. The calcining plant is BMH. Cellulose fibre consists of recycled newspapers, magazines, and telephone directories. Calcined gypsum powder and cellulose fibre are formed into a mat. Water is added as it enters the Siempelkamp roll press. The board proceeds down the line through trimming and cutting to length and then to the Dornier four-deck dryer heated by diesel oil.
J Patrick Lancaster, product development chemist at Wacker Silicones , Adrian, Michigan, US, is a strong proponent of preventing water damage to building materials. He said: "History has shown that for every 100 buildings, 24 are damaged in the first year, 15 in the second year and that over a five-year period, 55% of newly constructed buildings are damaged." He concluded: "The use of silanes, siloxanes, silicone resins, and silocanates at relatively low levels can help prevent the loss of durability, aesthetics, and performance in a variety of building materials." Durable coatings are necessary for fibre cement. Michael E Bowe, Rohm & Haas Company, Spring House, Pennsylvania, US, declared: "The exterior durability of a coating is determined not only by paint composition, but by application method. The highest quality paint requires a polymeric binder that is resistant to both water and ultraviolet light, a property which acrylics bring."
He said that a durable paint also requires proper formulation by someone who understands the contribution and interaction among the main ingredients in a water-borne paint. He added that a high quality paint can only provide its maximum performance if it is applied to a properly prepared substrate and dried to give the best film formation. Continuing on the coating theme, David O’Callaghan, plant manager CertainTeed SPG, Fiber Cement, White City, Oregon, US, commented: "The heterogeneous nature of uncoated fibre cement is permeable to water via voids, capillaries, pores, fissures and capillary action. Although the end-user is expected to apply a high quality paint following installation, a factory-applied sealer ensures a minimum standard of water resistance and uniformly covers the fibre cement edges. Edges are known to be overlooked during installation painting." Julie Rapoport, Center for Advanced Cement-Based Materials, Northwestern University, Evanston, Illinois, US, said cellulose fibres are inexpensive reinforcement for cement-based materials. She is studying their use for cast-in-place concrete. Her results indicate that cellulose fibre volumes as low as 0.14% in mortar significantly reduces shrinkage cracking; crack widths are reduced by approximately 37%.
Reinhard Kalbskopf, Redco SA, Kapelle-op-den-Bos, Belgium, outlined advantages of PVA (polyvinylacetate) fibres to prevent cracks in fibre cement roofing products. He said air-cured matrix strength increases during natural exposure. He expects a total service lifetime of air-cured roofing products comparable to that of clay tiles or natural slates.
