Concrete Products

The use of waste rubber and other polymers such as polyethylene terephthalate (PET, from bottles) to modify concrete is an active area of research. One of the attractions of this recycling is the potential to use up large amounts of waste material. A recent paper [45] by 

Pacheco-Torgal and co-workers reviewed the research carried out in this area, and discussed the influence that the size of the ruhher particles and the total amount of waste rubber or PET have on the properties of both wet and hardened concrete. 

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When it is used in concrete, rubber crumb is either a partial or total replacement for conventional aggregates. A complete replacement of the aggregate by crumb gives a product that is regarded as plain rubberised concrete and this can be typically used for non-structural 

The products produced in Phase III were subjected to a full range of tests carried out at Brand C Rae and at an approved laboratory. The results showed that there was some reduction in the strength of the blocks (1.25 N/mm ) compared to the control product that did not contain any rubber, but that the presence of the rubber did improve the thermal conductivity, reduced the level of water absorption, and increased the density by 105 kg/m, yielding an improvement in noise attenuation. 

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Concrete Products. Limestone aggregate is used competitively with other aggregate in the manufacture of molded, reinforced, and prestressed concrete products in the form of block, brick, pipe, panels, beams, etc. 

Type I (Normal). This is the general purpose Pordand cement used for all appHcations where special properties are not needed. Common appHcations include concretes for paving, building doors, roof decks, reinforced concrete buildings, pipes, tanks, bridges, and other precast concrete products. In 1989 Type I and Type II accounted for over 92% of the Pordand cement produced in U.S. plants. Exact data are not available that separate Type I and Type II Pordand cement, but it can be assumed that Type I production was much greater than Type II. 

Calcium Silicates. Cements aie hydiated at elevated tempeiatuies foi the commercial manufacture of concrete products. Using low pressure steam curing or hydrothermal treatment above 100°C at pressures above atmospheric, the products formed from calcium siUcates are often the same as the hydrates formed from their oxide constituents. Hence lime and siUca ate ftequendy used in various proportions with or without Portland cement in the manufacture of calcium siUcate hydrate products. Some of these compounds are Hsted in Table 6. 

In the past 30 years, the ready-mixed concrete industry became the primary customer for cement manufacturers. In 1990 more than 72% of the cement shipped was sold to the ready-mixed concrete industry, compared with 63% in 1975. The other primary uses are in building materials, concrete products, and highway constmction. 

Figure 4. Structural specifications for a modified precast manhole structure as revised and redrawn from Iowa Concrete Products Co. SK-83-61.

POLYETHYLENE FOAM WASTE UTILISATION FOR LIGHTWEIGHT CONCRETE PRODUCTION... 

This type of dampproofing admixture is widely used in the concrete products industry, in particular the calcium and aluminium stearates. The calcium stearates can be produced by grinding stearic acid with lime or cement to produce a material containing 10-30% calcium stearate. 

It was explained earlier that materials of this type are added to concrete products to reduce the ingress of rain and ground water for aesthetic and damp-proofing reasons, rather than to prolong the structural capabilities of the construction. The improvements in aesthetic qualities are not short lived, and results [15] for a stearate-based composition over a 10-year period are given in Table 4.8. 

Anon (1983). Metering of Inorganic Pigments in the Manufacture of Coloured Concrete Products Technical Information Leaflet, Mobay Chemical Corporation, Pittsburg, PA, USA, 6. 

The long range objectives of the joint program are the investigation and development of a concrete-polymer composite as a new construction material. The program includes the development of techniques for preparing concrete-polymer material, measurement of the physical and chemical properties, preparation of full-scale concrete products, and the conceptual design and evaluation of various specific applications. 

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