Asbestos-cement replacement

Some asbestos fibres, when inhaled, can constitute a health hazard leading to lung cancer. The health risks are greatest during the production process, but may be 

The asbestos fibre is unique in its properties. It permits control of the properties of the fresh mix, to make it processable by the efficient dewatering techniques, and, at the same time, it provides an excellent reinforcing efficiency in the hardened composite, due to its high strength, modulus of elasticity and bond. In addition, this fibre is stable in the alkaline cement environment, thus providing a composite of excellent durability. This combination of properties is difficult to match with any one type of fibre. There are fibres which can match the mechanical quality of asbestos, but they cannot, on the other hand, provide the processing characteristics. 

In the development of successful replacements, consideration was also be given to matrix modifications [33], to adjust its properties in order to accommodate fibres that are not ideally compatible with Portland cement. For example, fibres with some sensitivity to an alkaline environment might potentially be considered adequate if means are taken to reduce the alkalinity of the matrix. The use of inert and active fil lets, and control of the cement particle size distribution and the curing treatment provide additional means to a( ust for the processing properties as well as the characteristics of the hardened composite. 

Williden, A Guide to the Art of Asbestos Cement, J.E. Williden Publ., London, 1986. 

Hodgson, Chemistry and physics of asbestos , in L. Michaels and S.S. Chissick (eds) Asbestos, Chapter 3, John Wiley, New York, 1979, pp. 67-114. 

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Shotcreting Using a modification of normal shotcreting techniques, it has been found possible to produce steel and polypropylene fibre shotcretes, for use particularly for lining of tunnels, and for stabilization of rock slopes. With this method, too, relatively high volumes of fibres can be added to the mix. Pulp type processes For asbestos cement replacements (cellulose or other fibres are used as a replacement for the asbestos), the fibres are dispersed in a cement slurry, which is then dewatered to produce thin sheet materials. These can be built up to the required thickness by layering. This process yields fibre contents of typically from 9% to over 20% by volume. 

Earlier studies and publications addressed hybrid systems for applications in thin sheet composites, in particular for asbestos-cement replacements. In recent years the concept has been extended for high performance-high ductility FRC, which can be produced by simple mixing. 

Fiber-Reinforced Cementitious Material. Use of asbestos (qv) has been legally restricted in Europe and the United States as being ha2ardous to health. In asbestos cement, which had consumed 70—80% of total asbestos, PVA fiber has been used in large amount as a replacement for asbestos. PVA fiber has a strength of at least 0.88 N/tex (9 gf/dtex) and can therefore provide the necessary reinforcement for cement the fiber has excellent adhesiveness to cement (qv) and alkaU resistance, and is not a health ha2ard. 

It is explained that the remaining uses of white asbestos (asbestos cement, friction materials, seals and gaskets, textiles and composites) are likely to become prohibited in the UK in the near future. This article examines in detail the choices available for its replacement. 

Alternatively, industrial sites may have been granted a licence to bury waste materials on site and when pipework or plant was replaced, the insulation materials could have been crudely removed and disposed on site at a time when it was considered acceptable to carry out such practices. Often outbuildings and garages with asbestos cement roofs were demolished where they stood and all resulting materials used as hard standing for paths, roads or car parks etc. 

Carbon Fiber Cement as a Replacement for Asbestos Cement. 1024... 

Carbon fiber cement as a replacement for asbestos cement... 

Carbon fiber has made significant advances in replacing asbestos in asbestos cement products in two basic applications—structural covering and flues [215]. 

The imposed restrictions on the application of asbestos fibres in buildings as reinforcement of cement-based composites stimulated extensive research directed at other kinds of fibres. Because of the excellent mechanical properties, good durability and relatively low cost of asbestos cements, finding an appropriate replacement has been difficult. The research was mainly concerned with cellulose, polypropylene and carbon fibres and positive results have been achieved (Krenchel and Hejgaard 1975 Mai 1979 Krenchel and Shah 1985). The properties of asbestos cements are briefly described in Section 3.2.5. 

The water mains used to distribute drinking water have normally been constructed from cast-iron, ductile iron, asbestos cement and, more recently, from plastics (for example, MDPE medium density polyethylene). Leaching of lead from these materials does not normally occur. Very exceptionally, lead water mains have been used to distribute drinking water. The only known occurrences are in Ireland where their replacement has high priority (Devaney, 2009). 

Although Dr. Hinkebein s concept was promoted as an application of phosphate fibers, it should be useful with other fibers. It is believed that, with some additional research, a very satisfactory replacement for asbestos -cement pipe can... 

The final stage of the production process involves curing, which can be based on room temperature treatment in a tunnel in which moist conditions are maintained, or higher temperature steam curing to accelerate the hardening process. Autoclave curing is also common in the asbestos-cement industry, and in such instances part of the cement is replaced with finely ground silica. Replacement of part of the cement with low-cost inert fillers or fly ash is also sometimes used, for economic reasons. 

Figure 10.36 Stress-strain curves of asbestos cement and acrylic-cement composite produced to replace asbestos cement (after Gale [128]).

U.N. Sinha, S.N. Dutta, B.P. Chaliha and M.S. lyenger, Possibilities of replacing asbestos in asbestos cement sheets by cellulose pulp , Indian Conor. J. 49, 1975,... 

Continuous reinforcement of cementitious matrices is particularly attractive for fabrication of thin eiements, where cement paste or mortar is impregnated into a fabric. Eariier interest in this kind of reinforcement was driven by the need to develop new thin sheet components, that could serve as replacements for asbestos cement, or provide thin sheets with improved performance, especially with regard to toughness [1-20], New types of reinforcements were studied and developed for these purposes, and the mechanical properties of the composites as well as production technologies were explored. 

Chemical Resistance. Table 2 shows the chemical resistance of PVA fiber (40). The fiber exhibits markedly high resistance to organic solvents, oils, salts, and alkaU. In particular, the fiber has unique resistance to alkaU, and is hence widely used in the form of a paper principally comprising it and as reinforcing material for cement as a replacement of asbestos. 

Based on the technology developed for using PVA fiber as a replacement for asbestos in cement products, Kuraray has been developing thick fibers for reinforcing concrete (42). Super-thick fibers with a thickness of 39 tex (350 den) (200 p.m in diameter) to 444 tex (4000 den) (660 p.m in diameter) are now available the 39 tex material is used for reinforcing various mortar-based cement products and the 444 tex material for reinforcing concrete in civil engineering works such as tuimels, roads, harbors, and bays. 

PVA fibers have found wide spread industrial use in cement as replacement for asbestos in cement products, reinforcement of mbber material such as conveyor belts and hydraulic mbber hoses used in cars, ropes, fishing nets, etc. Only a small amount of fibers is used in the production of textiles. 

Considerable effort has been devoted to finding alternative fibers or minerals to replace asbestos fibers ia their appHcations. Such efforts have been motivated by various reasons, typically, avadabihty and cost, and more recendy, health concerns. During Wodd War I, some countries lost access to asbestos fiber suppHes and had to develop substitute materials. Also, ia the production of fiber reiaforced cement products, many developiug countries focused on alternatives to asbestos fibers, ia particular on cellulose fibers readily available locally at minimal cost. Siace the 1980s however, systematic research has been pursued ia several iudustrialized countries to replace asbestos fibers ia all of their current appHcations because of perceived health risks. 

Asbestos fibers are found worldwide in many products as reinforcement in cement water pipes and the inert and durable mesh material used in filtration processes of chemicals and petroleum, for example. However, asbestos is not the only inorganic fiber in use today. Synthetic inorganic fibers abound. Glass fibers have replaced copper wire in some intercontinental telephone cables. Fiberglas (a trade name) has become the insulation material of choice in construction. Carbon and graphite fiber composites are favored materials for tennis racket frames and golf clubs. Fibrous inorganic materials have become commonplace in our everyday lives. 

Mixing into pulp cement plate as filler material replacing asbestos... 

Some of the asbestos filler in hydraulic cements has been replaced by flbrlllated polypropylene. More than 500 thousand shell piles of this flbrlllated polypropylene-filled Portland cement, called "Carlcrete" are produced annually in England. —... 

Raincoats, sportswear Cement reinforcement, asbestos replacement, carbon and graphite fibers Light-fast outdoor fabrics, awnings, tents, car tops Knitted outerwear, cotton knits replacement... 

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