Precast concrete lining

Ecob, C.R., King, E.S., Rostam, S. and Vincentsen, L.J. (1995). Epoxy Coated Reinforcement Cages In Precast Concrete Segmental Tunnel Linings - Durability. Corrosion of Reinforcement, in Concrete. C.L. Page, K.W.J. Treadaway, P.B. Bamforth (eds), 1990 Published for the Society of Chemical Industry by Elsevier Applied Science, London and New York, pp 550-558. 

A. No. OSHA s fall protection standard for construction generally requires fall protection when there is a fall distance of six feet or more. In a few, very specific situations (low-slope roof work, some leading-edge work, precast concrete erection, and residential construction), because of feasibility limitations, the standard permits the use of a warning line, in combination with other measures, instead of conventional fall protection (guardrail systems, personal fall arrest systems or safety net systems) to keep employees away from an edge. 

Installation of HVAC equipment does not fall within the categories listed, i.e., leading-edge work, precast concrete erection, or residential construction. Therefore, the warning line at the six-foot option does not apply. 

Precast concrete liners have not yet found great use in the United States, except for the OTtouke block used in a number of tunnels in Detroit. They are not watertight and require a secondary lining. Precast concrete segments were designed for a test section of the Baltimore subway tunnels, but were not competitive with steel liners. 

A secondary lining is required if the primary lining consists of ribs and lagging or OHouke blocks, or if the tuimel interior needs a finish (as in highway tunnels). Rail tunnels with segmental metal or precast concrete usually do not receive a secondary lining. 

The latest vessel are provided with a wire winding system in which the wires are wound under tension into steel-lined channel either formed in the vessel walls or made of precast concrete. The band comprises of layers of wires anchored at both ends. In this way the maximum circumferential pressures are exerted with in a limited area. 

Cured concrete can be bonded to cured concrete, as in the installation of precast buttons to a highway surface. Steel bridge railings can also be bonded to the concrete surface of a bridge sidewalk. In the case of deteriorated concrete, the adhesive can be used to rebuild the structure to its former line and grade. Epoxy adhesives are also commonly used on other roadway materials, such as asphalt and brick however, the predominant application is concrete substrates. The most frequent combinations of substrates that are bonded with adhesives in this market segment are... 

As the reader will realize, this procedure will not be very satisfactory for a cover for a steel tank. If it is a fixed dome or conical cover, it may be lined with brick, but if the cover is to be removable, the cover may be steel, employing a high temperature membrane, or a precast polymer concrete or prefabricated FRP construction. 

Silicate polymer concrete (SPC) is used in the repair of foundations, for the manufacture of storage tanks for hot and cold acids, equipment lining, reservoirs, and building structures, and as the structural material in vessel heads, vaults, and diaphragms. SPC is of particular interest in precast structures in production of pickling baths for metallurgical plants. 

Applications of polymer mortars and polymer concretes include patching of Portland cement concrete, floor and pavement overlays, anti-corrosive linings, precast products, vaults, panels [8,11]. These indicate that there is no single polymer concrete that performs all of these tasks. Application and performance of polymer concrete depend on the binder used and the aggregate. Copolymerisation techniques allow the production of a wide range of binders with varying properties [11]. 

Precast Elements There are numerous applications of precast polymer concrete such as panels, pipes, drainage channels, tiles, bricks, linings, manhole structures, stair treads, electric insulators, etc. [11, 15]. 

PPCC applications include deck coverings, floors, pavements, precast units, anti-corrosive linings, adhesives, patching or repairing Portland cement concretes [11, 17]. 

---