At here, I would like to discuss about precast concrete cladding and metal cladding (steel and aluminiun cladding)
Precast concrete cladding is a common form of precast cladding. This cladding is usually made of pre-cast concrete with a texture face in a storey height or under sill panel format. It is used for both head bearing and non-load bearing purposes. It is commonly used because of it is non combustible material, have good strength to weight ratio, its mobility, speed of erection, freedom from shuttering support on site, and a better quality and variety of surface finish because panels are manufactured in factory. The use of precast concrete cladding will improves the buildability, as it is a dry construction and will not affected by the problem of lack of labours. The characteristic of concrete is durable, non combustible, and long life span. Precast concrete cladding can help to reduced cost of construction, because the precast concrete cladding is need less number of labour during construction and maintainance due to is durability. The cost is mainly due to transportation cost. The quaility control of the precast concrete cladding and construction process of the cladding is independent of weather.
In comparison between precast concrete cladding and in situ cladding, the main advantages of using precast cladding are speed of erection, economical, cost of construction freedom from shuttering on site and better quality. Cranes are used to hoist the concrete panels into position and bolted and/or welded onto anchorages. The joints between precast concrete panels are sealed with either one-stage or two-stage joints. One-stage joints are those which are simply sealed against water penetration by the use of a sealant near the outer surface. Two-stage joints are those which have a sealant near the outer surface and an air-seal usually close to the inner face of the panels. Between the two is a chamber which must be vented and drained to the outside. Although dimensional inaccuracies in manufacturing are small (±3 mm), those arising during assembly due to the deviations in the frame and erection deviation on the panels (possibly ± 25mm) and movement deviations (usually in the order of 1mm per 3m) necessitate the allowance of the tolerance in the method of fixing and in the clearance between the panels and the structure.
Precast concrete cladding can fulfill the functional requirement of cladding. Strength of precast concrete can be improved with adding reinforcement. So that the cladding can support more tension force and support itself between the joints. Precast cladding also proposed strength to sustain the wind load pressure. Precast concrete also have less expansion and contraction due to the weather. Precast concrete is high durability, so this kind of cladding needs a low frequency of work of maintenance. Precast cladding also provides fire resistance, thermal insulation, and sound insulation due to mass of precast concrete. Sound insulation also can be provided with resilient pad. Consideration of choosing a precast concrete panel is depend on column or beam spacing, lifting capacities of plant available, jointing method, exposure conditions, and any special planning requirement as to finish or texture.
For metal cladding, the most common material is steel and aluminiun. Steel cladding is normally use pre-galvanized and pre-painted steel. During the galvanizing process the steel is dipped into molten composition metals like zinc or alloy. Hard and durable outer layer is formed by metallic coating. The thickness of the steel can be varied and usually is expressed in weight. Steel is harder, so is more resistant to impact and resistant to expand due to temperature. Aluminium is naturally more corrosion resistant and lighter in weight.
There are few types of metal cladding. The most commonly used is profiled metal sheeting cladding. This has been in use for many years. Steel or aluminum profiled cladding is widely use; they can be applied to roof and walls cladding although the performance requirements is different. Profiled metal cladding offer a wide variety of sharper profiles, or vertically with patent bending processes available. It is lighter and easy in handling but very expensive. Profiled metal cladding will be exposed to large amount of heat, therefore, steel with high thermal insulation is choose so that to control internal temperature. The steel and aluminum surface are reflective, they can reflect partial of heat and light from the building. The reflective surface also has aesthetic value.
Profiled metal cladding can fulfill the functional requirement of cladding. Metal surface is strong and can to resistance impaction. The metal is sufficiently stable to receive wind load pressure. The metal is not very heavy metal like aluminium, they can support themselves in between the point of jointing. Metal is corrosive especially exposed to raining, the steel and aluminum profiled cladding will need some rain screen substance. Steel and aluminum high durability, but need some maintenance work, because oxidation and faded will appear on the surface of the metal, it affect its aesthetic value and durability. The shiny metal, steel and aluminium can reflect the light and heat, its help to control internal temperature. Steel and aluminium also provides fire resistance and their melting point is high. Sound insulation metal cladding can be provided with resilient pad. The thermal insulation of metal cladding is help with some core material. The metal is reinforce with core material to improve its thermal insulation properties.
Thickness (mm) for a U value of 0.45W/m2K
Glass or mineral fibre
Thermal performance of core insulation (source: The Metal Cladding and Roofing Manufacturers Association)
1b) Describe two types of sub surface drainage system for domestic usage
There are two types of sub surface drainage system. That are foul water system which the system usually only deals with foul water and combine system which the foul water system is combining with surface water. Foul water is the waste water like kitchen waste, waste water from toilet and bath room, and any industrial process water. Surface water are the rain water, usually collected from rainwater pickup, yard or road gullies, and linear drains. Sub surface drainage system consist of underground pipe line and manhole or inspection chamber.
Underground pipie line consist of drainage and sewer pipes. Drainage and sewer pipes are made from a range of different materials for domestic application including vitrified clay, uPVC, concrete, iron and asbestos. Other materials used for drainage pipes included ductile and cast iron (CI), glass fibre reinforced plastics (GRP), high density polyethylene(HDPE), concrete, asbestos and pitch fibre. For jointing of pipes, the plain ended pipes are those that have identical ends and are joined by means of a coupling. The socketed pipes have identifible 'male' and 'female' ends, and must be laid with the 'female' end pointing upstream. The pipes is laid in straight line from point to point with a fall, the fall for different system is different. If the pipe is laid deeper than 1200mm (4 feet), the pipes have to be shored up properly. Different types of material of pipes will required different bedding. In a pipes system, 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 fron another access point.
Manhole and inspection chamber are some kind of access chamber that providing access to drainage or sewer. Access chamber are intended to provide simple access for cursory inspection and access for drain rods or other maintenance equipment. Generally not more than 600mm deep. Inspection chamber are larger than access chamber, typically a minimum 450mm diameter. It provide an access for maintenance equipment, but tend to have more branches or spurs feeding into them and are often up to 1000mm deep. Manholes are the largest chambers providing access to a sewer or drain for maintenance equipment. The minimum internal dimensions of a manhole are 600x900mm and they can be of any depth. At least 1 metre deep with inspection chambers used for shallower depths.
There is no big different of the two system. Materials of pipe, jointing of pipes, bedding, and fittings and access points can be the same. All these depend on how the drainage system is constructed, how long the system. The different is the gradient of the drainage. Foul water system need 1 : 40 as minimum for its drainage, then combine system can have lower gradient like 1: 50 as minimum. This is because the mix with rain water can help the foul water to flow more smoothly. The choose of chamber or manhole for both system is almost the same. They are depend on area and the usage at the area. Combine system will have a porblem is foul water will overflow to storm water over flow outlet during the rainy seasons. So, to overcome this probem, a separate storm water tank need to be constructed or add in the system.
1c) Briefly describe the function of road and pavement
The surface of road and its associated construction is known as pavement. Pavement is the surface which is intend for traffic and soil is protected by an overlay of imported or treated material with the objective to limit the stress in the ground. Normally, the pavement construction is carried out after completion of all drainage system, service ,and ducts. But the road for temporary access to site can be constructed earlier up to the road base layer. The general function of road pavement is to provide a flat surface for a comfortable journey, transfer and distribute transportation load onto ground, and prevent the ground surface being damage from weather effects. Pavement are divide into two types, that are flexible pavement which is stone bace with surfacing of tar macadam and rigid pavement which is concrete road slab.
The uppermost layer of a flexible pavement is called the surfacing. The primary function of this layer is to provide a safe, smooth, stable riding surface. When a surfacing is composed of bituminious materials it may comprise a single homogeneous layer or course; more ussually, however, with heavily-trafficked roads, two distinct sublayers known as a wearing course and a basecourse are lai in separate operations.
The wearing course forms the uniform carriageway surface upon which vehicles run. Factors of choosing wearing course are it should offer good skid resistance, allow for rapid drainage of surface water, minimize traffice noise, resist cracking and rutting, withstand traffic turning and braking forces, protect the underlying road structure, require minimal maintainance, be capable recycled or overlaid, and be durable and give value for money. The basecourse is a structural platform which regulates the top of the underlying roadbase, thereby ensuring that the wearing course has a good riding quality when built; it also helps to distribute the applied traffic loads
The roadbase, which provides the platform for the surfacing, is the main structural layer in flexible pavement. As the stresses induced in a flexible pavement by the applied wheel loads decrease with depth, the main function of the roadbase is to distribute the loads transmitted to it so that the strength capacities of the weaker subbase and subgrade are not exceed. Roadbases in flexible pavements are normally designed to be very dense and highly stable, and to resist fatigue cracking and structural deformation.
A subbase is very often present in a flexible pavement as a separate layer beneath the road base. Subbase is further distributes the applied wheel loads to the weaker subgrade below. It must be able to resist the stresses transmitted to it via the roadbase and it must always be stronger than the subgrade soil. Another major function of the subbase is to act as a working platform for , and protect the subgrade from, site and construction vehicles as a pavement is being built.
When the subgrade soil is weak a capping layer may be created to provide a working platform for equipmemt used to lay the subbase. This is most commonly done by improving the top of the subgrade. The interface between the subbase and the subgrade is normally shaped to reflect the cross slope of the carriageway, to assit in the lateral drainage of water that might accumulate within the pavement.
1d) Cellular concrete roofing units, pavement overlays, bridge decks airport runways, pressure vessels, blast-resistance structures, tunnel linings and ship-hull construction are some application of a particular fibre reinforcement concrete. Specify the type of fibre with characteristics comparison with the conventional concrete
The fibre reinforcement concrete for cellular concrete roofing units, pavement overlays, bridge decks airport runways, pressure vessels, blast-resistance structures, tunnel linings and ship-hull construction are some steel fibre reinforcement concrete. Its has been used for pavement overlays roads, and bridge decks. The diameter of the steel fibres is from o.25 to 0.75mm
Steel fibre reinforcement concrete mainly improve the toughness, the flexural strength, tensional strength, impact and fatigue strength of concrete. It also can reduce creep strain, which is define as the time dependent deformation of concrete under a constant stress. It help to increased performance of concrete, for example, it help in increasing bending resistance of slab, so the thinner slabs can perform better and used. But steel fibre reinforcement increased the cost of typically between 50 to 100% per cubic metre.
Conventional concrete have high compressive strength, this is the factors that conventional concrete was use for many years. But conventional concrete is week in tensional strength. This so the conventional concrete is brittle and break easily when tension force is apply to it. Steel fibre reinforce concrete also have high compressive strength, and it also help to improve the tensional strength of the concrete. This reinforcement also help to improve the toughness of the concrete, this reinforce concrete can produce thinner slab, can perform like thicker slab, can withstand more load. The shear strength of the concrete also increase.
Conventional concrete always have the problem of cracking. The concrete is not very durable. The quality control of the concrete is not very good as theoritical because of conventional. Steel fibre reinforce concrete will have a better quality and more durable. This will increase the resistance of cracking.
Fatigue and impact resistance:-
Conventional concrete is weaker compared to steel fibre reinforce concrete. The conventional concrete will have high mixture of volume of water. The friction force inside of the concrete is only between sand and aggregate,or steel bar. The impact and fatigue resistance is not very strong enough. Not like steel fibre reinforce concrete, it has addition of steel fibre and less volemu of water mixture in a cubic metre of concrete. It increases the force of the concrete, make the concrete harder, so fatigue and impact resistance is increase.
Time of construction:-
Conventional concrete need a longer time. Because the concrete is prepared on site. The process of is long and time consuming. The process need curing, test and etc. Steel fibre reinforce concrete is a type of precast concrete, lighter and more easy in handling. It can improve the time of construction and is a dry construction.
Cost of construction:-
Conventional concrete need more material and labours during consrtruction period. Conventional concrete need a large number of labours to prepare to concrete and consruction. It need many steel bar and wire mesh for reinforcement. Steel fibre reinforce concrete need less amount of worker, because it is precast and high workability. It can save material usage like the steel bar and wire mesh.
The are some similarities characteristics between conventional concrete and steel fibre reinforce concrete. They are non flamable material, high fire and electricity resistance, and non toxicity.
In conclusion, the steel fibre reinforce concrete has a lot of advantage compared to conventional concrete. It cn be said that steel fibre reinforce concrete is a new technology or material in construction industry. It bring a lot benefits to construction industry. However, it is not very common in used because of it cost. It cost increase is in between 50 to 100% per cubic meter. It can be consider as a expensive maaterial.
Steel fibre reinforce concrete
Fatigue and impact reistance