Engineering Studies
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Suggested answers
Activity 1
With reference to Table 1 answer the following question. A brass pipe is to be soldered then submerged in salt water. Will the solder, or the brass become the anode? Explain why.
Referring to table 1 we can see solder is more anodic than brass. Therefore, the solder will become the anode.
Activity 2
With the aid of a diagram explain why galvanised steel does not rust, even if the zinc coating is scratched.
Zinc is anodic when compared to steel. When a groove is scratched in the zinc it will corrode in preference to the steel. The zinc also reacts with the environment to produce a resistant deposit in the scratch.
Activity 3
Discuss materials that could be used in lieu of carbon steel for use in concrete reinforcement, so that the concrete is less susceptible to concrete cancer?
Galvanised steel could be used as this would be resistant to corrosion if the reinforcing became exposed to the atmosphere. Likewise stainless steel could be used, but there may be cost issues with such a choice. Other materials like glass fibre or bamboo may be used, but not as effectively as galvanised steel.
Activity 4
Why does concrete cancer cause the concrete to spall (crack and break away)?
Because as the steel corrodes, it expands, taking up a greater volume than it previously occupied. As it expands it the concrete around it is placed in tension. As concrete is poor in tension it cracks away reducing the strength of the reinforced concrete structure.
Activity 5
The steel pier shown below is immersed in the water to support a jetty. Identify where the cathode and the anode will be on the pier. Explain your choices.
The cathode would be at, or just above, the water line, whilst the anode would be at the sea floor. This occurs because the sea floor will have less oxygen than the water at the water level. Hence the water line will become the cathode and the result will be an accumulation of rust at the water line.
Activity 6
An aluminium structure has been riveted unwittingly with Austenitic stainless steel rivets. The structure is then used at a salt water pool; determine what will happen to the structure in terms of corrosion.
The aluminium will become the anode and the stainless steel will be the cathode. This will mean the aluminium will degrade.
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