Concrete recycled

Keywords pitch-based high performance-type carbon continuous fiber reinforced plasUc, chemically resolvable resin, environment-conscious materials (ecomaterials) design, deformed rebar, hybrid structure, lighweight precast concrete, recycle, service life,... 

Keywords wood-chip concrete, recycling of used timber, special cement paste, injection method of cement paste, wood-chip packing ratio, strength, specific gravity, thermal conductivity... 

From an economics standpoint, the cement flour generated by the selective fragmentation of concrete is chemically and physically almost identical to raw cement flour, and hence can be used to replace the latter by approximately 50%. Accordingly, substantial savings of raw materials (limestone, clay) and energy, the preservation of the natural environment (disposal sites, resources), and the reduction of CO2 emissions will add to the benefits of intelligent concrete recycling. 

Constmction and dem olition (C D) debris is a potentiahy large source of recyclables. However, as of 1995, generation rates and ferrous scrap content were not weh estabUshed and estimates were highly variable. Eerrous materials in C D debris are typicahy reinforcing bars, wire mesh, and stmctural steel. Some of the scrap is sold for recycling once concrete is effectively removed and the scrap is sized to specification (17). 

A significant amount of waste composites is generated each year and the need for a recycling method is becoming a necessity. Environmental Technical Services has developed, with the support of the University of Missouri-St.Louis, a method for recovering valuable constituents from composite materials. The process converts the polymer matrix to lower chain hydrocarbons and fuel gas leaving behind fibres. Mechanical tests of BMC panels, reinforced concrete and compression moulded panels made with recovered fibres were carried out. 10 refs. USA... 

Extensive research has been conducted on the use of the following SWMs as highway C R materials (an alternative innovative way to recycle/reuse such wastes), soil stabilization material, roller compacted concrete, and road base stabilization materials. They include the following [1]. 

More than 2 billion tires are disposed of annually in the USA. Before being recycled and/or reused, scrap tires or crumb rubber are first processed to remove any loose steel and fibers and then finely ground. Research has been conducted on the use of crumb rubber in highway construction such as in lightweight fill, subgrade insulation, and channel slope protection, as well as an additive to Portland cement concrete pavement [66,67,259,260]. 

Short fibre (few millimetres or less) recyclates used to reinforce polymers or concrete. 

The process at Three Mile Island involved nuclear fission and subsequent reactor cooling using circulating water. The primary water was kept under pressure to prevent boiling. Heat was transferred to a secondary water system that supplied power to a steam generator. Upon completion of this step, steam condensate was recovered and recycled. All radioactive materials, including primary water, were enclosed in a lined concrete containment building to prevent their escape to the atmosphere. 

Addition of a new section on miscellaneous admixtures including shotcrete admixtures, corrosion inhibitors, and admixtures for recycling wash water and plastic concrete. 

Other applications for the stabilizer and the recycling system include hot-weather concreting, the transportation of ready-mixed concrete over long distances (particularly in the Middle East countries) or through city traffic where unexpected delays can be encoimtered. Higher dosage of the admixture can be used to obtain the desired set extension and the appropriate dosage of the activator (carried on the truck) can then be added at the destination. 

The characteristics of a soil determines the cost-effectiveness of the recycled product. Sandy, silty, and cobble soils are more suitable for recycling into asphalt concrete. 

Tons of spent abrasives result each year from the removal of old paint from bridges. Because the spent abrasives contain metals from the paint, some spent abrasives may be considered hazardous by the Toxicity Characteristic (TC) criteria. Incorporation of the spent blasting abrasives in nonstructural concrete offers an opportunity to recycle the spent abrasives while immobilizing potentially leachable metals. Solvents that are less aggressive will mean that abrasives will be necessary in some applications. Study results indicated that considerable quantities of these spent abrasives can be solidified/stabilized while reducing the leachability of cadmium, chromium, and lead and producing compressive strengths over 6895 kN/m2 (1000 psi) (Brabrand and Loehr, 1993). 

Saylak, D., Gallaway, . M., and Epps, J. A., "Recycling Old Asphalt Concrete Pavements", Proceedings of the 5th Mineral Waste Utilization Symposium, Chicago, 111., 13-14 April, 1976,... 

The recovery of valuable metals and metal alloys from hazardous metal sludges is technically and economically viable. Small quantities of excess slag are produced and this slag can be recycled into concrete blocks. The E.P. and TCLP leachate limits are met with the slag. 

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