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The economics of precast concrete panel production are a function of standardization of mould shape. Similarly, rationalization of panel size and the means of fixing are important for reducing the cost of transportation and assembly. There are many choices of materials of the mould. It is usually determined by the number of uses and also the matter of economics. Therefore, although mould can be made of steel, timber or GRP, there is a considerable cost differences between all these materials. The time taken to make the mould and the rate of output required to reach the erection stage are the factors for making choice of materials of mould. The shape and size of the unit to be cast are under consideration also.
Precast concrete offers a wide variety of shape, colours, textures and finishes. Each precast panel is independently supported to the building structure using an assemblage of building components and anchors. Sealant is used to fill in the joints around each of the precast panels to prevent water penetration to the wall cavity. Joints between panels must be able to accommodate thermal expansion and differential movement between panels.
Precast concrete cladding must designed to resist lateral loads such as wind and vertical loads which is its self weight. Other loads such as such as erection, impact, transportation, construction related loads must also taken into account in the design. The sealant in joints and protection system are required maintenance. The time frames of these are usually ranges from seven to 20 years.
The pipes should be laid in straight line from point to point with a fall. The excavation of trench should allow for the working space and bedding around the pipes. Any trench deeper than 1200mm (4 feet) must be properly shored up. It is depending on pipes material, there are two types of bedding are required to protect the pipes from ruptures or breakages. The pipes should be laid in straight lines to a steady gradient. There is a taut string line, sight rails or more commonly nowadays, a laser line is used to ensure accuracy in alignment and level. The bedding is prepared in advance, with a recess scooped out to accommodate sockets if necessary. The minimum gradient for surface water drainage is 1:100 and the minimum gradient for foul water drainage is 1:40. The fittings and access points must be installed at head of run, bend or change of direction, change in pipe diameter, and junction unless all runs connected to junction can be rodded from another access point.
The road pavement is a structure of superimposed layers of selected and processed materials that is placed on the basement soil or so-called subgrade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution. The road pavement is the actual surface on which the vehicles will travel. The purpose is to provide friction and to transfer normal stresses to the underlying soils.
There are some advantages of steel fibre reinforced concrete (FRC) compared with conventional concrete. For conventional concrete, the advantages are it can be cast in diverse shape but it also possesses high compressive strength, high water resistance, stiffness, low maintenance, long service life, low thermal and electrical conductivity, and low combustibility and toxicity. However, there are limitations of concrete included low tensile strength, low strain of fracture, formwork requirement, brittle and weak in tension.
For steel fibre reinforced concrete, it is different with conventional concrete by adding a small amount of fibres into the concrete to improve the structural properties, particularly tensile and flexural strength. It produced thinner and stronger elements, reduced weight and controlled cracking. When the loads imposed on conventional concrete, cracks will propagate. By adding fibres in concrete, it will provide a means of arresting the crack growth. The transformation from a brittle to a ductile type of material would increase substantially the energy absorption characteristics of the fibre composite and its ability to withstand repeatedly applied, shock or impact loading.
Besides that, short discontinuous fibres have the advantages of being uniformly mixed and dispersed throughout the concrete. Fibres are added to a concrete mix which normally contains cement, water, and fine and coarse aggregate. After fabrication, fibre-reinforced cement boards contain no course aggregate. The course aggregate is made by spraying mortar and chopped fibre simultaneously. The mortar with a high water and cement ratio is used to facilitate spraying. There are other application methods included simple casting, which is less versatile than spraying, and press moulding, which results in a lower effective water and cement ratio thus producing a stronger product.
The steel fibre reinforced concrete which has the composite properties. It can improve the toughness, the flexural strength, or both. However, it is chosen on the basis of their availability, cost and fibre properties. It can reduce creep strain which is defined as the time-dependent deformation of concrete under a constant stress. Ductility and post cracking strength, resistance to fatigue, spalling and wear and tear of steel fibre reinforced concrete are higher than in case of conventional reinforced concrete. The extent of improvement of mechanical properties achieve with steel fibre reinforced concrete depends on the shape, size, volume, percentage and distribution of fibres.