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What is the difference among cement plaster, cement render and cement screed? Under what situations should each of the above be used?

The purpose of plastering, rendering and screeding is to create a smooth, flat surface to receive finishes like paint, wallpaper etc.

Plastering is the intermediately coating of building materials to be applied on the internal facade of concrete walls or blockwalls. Rendering is the intermediate coating for external walls only. Screeding is the coating laid on floors to receive finishes like tiles, carpet, and marble.

Hence, these terms differ basically from the locations at which they are applied. Due to different locations of application of plasterwork, the proportion of material component for plaster and render is different. For example:

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(i) Cement plaster
Undercoat- cement:lime:sand (by volume) = 1:4:16
Finishing coat – cement:lime:sand = 1:12:30

(ii) Cement render

Undercoat- cement:lime:sand (by volume) = 1:2:6
Finishing coat – cement:lime:sand = 1:3:6

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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In pumping stations one of the choices for the material of water tanks is fibre-reinforced plastic (FRP). What are the advantages associated with this kind of material?

There are two main advantages for FRP water tanks:

(i) It possesses high strength to weight ratio and this leads to the ease of site handling.

(ii) It is highly resistant to corrosion and thus it is more durable than steel water tank.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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What are the components of a waterproofing system in the roof of a typical pumping station?

In the design of a waterproofing system at the roof of a pumping station, normally the following components are:

(i) Above the structural finish level of the concrete roof, a screed of uniform thickness is applied to provide a smooth surface for the application of waterproofing membrane. (Screed of varying thickness can also be designed on the roof to create a slope for drainage.) The screed used for providing a surface for membrane should be thin and possess good adhesion to the substrate. Moreover, the screed aids in the thermal insulation of the roof.

(ii) Above the screed, waterproofing membrane is provided to ensure watertightness of the roof.

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(iii) An insulation board may be placed on top of waterproof membrane for thermal insulation. In cold weather condition where the loss of heat at the roof is significant, the insulation board helps to reduce these losses. On the contrary, in summer the roof is heated up by direct sunlight and the insulation layer reduces the temperature rise inside the pumping station.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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In selecting screw pumps in polder scheme projects, what are the factors that affect the design capacity of screw pumps?

The commonly used angles of inclination for screw pumps are 30o, 35o and 38o. For screw pumps of relatively high lifting head, like over 6.5m, angle of inclination of 38o is normally used. However, for relatively lower head and high discharge requirement, angle of inclination of 30o shall be selected. In general, for a given capacity and lifting head, the screw pump diameter is smaller and its length is longer for a screw pump of 30o inclination when compared with a screw pump of 38o inclination.

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To increase the discharge capacity of screw pumps, a larger number of flights should be selected. In fact, screw pumps with 2 flights are more economical that that with 3 flights in terms of efficiency and manufacturing cost. Moreover, the discharge capacity is also determined by the screw pump diameter and sizes of 300mm to 5000mm are available in current market.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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What is the minimum volume of sump volume for pumps?

Maximum pumping rate = Qp

Volume of sump= V

Inflow Rate= Qi

Cycle Time Tc = t1+t2

t1= V/[Qp-Qi]

t2= V/Qi

Tc= Minimum cycle time

minimum volume of sump volume for pumps

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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