QCAA Engineering Civil engineering materials
1 sample question with marking guides and sample answers · Avg. score: 81.5%
Analyse the information in the table to determine whether polyvinyl chloride (PVC) or polyethylene is the most suitable material for wastewater pipes in the home. Justify your response with four properties from the table.
| Properties | PVC | Polyethylene |
|---|---|---|
| Mechanical | resistant to abrasion, impact and weathering rigid — limited flexibility, can withstand high pressure | resistant to cracking, impact and environmental stress; strong; durable malleable — highly flexible |
| Young’s modulus | 2.41–4.14 GPa | 1.08 GPa |
| Yield strength | 40.7–44.8 MPa | 26.2–33.1 MPa |
| Tensile strength | 40.7–51.7 MPa | 22.1–31.0 MPa |
| Chemical | excellent chemical resistance (including corrosive chemicals) | good chemical resistance |
| Thermal | good heat resistance | very good heat resistance |
| Manufacturing cost | low | high |
Reveal Answer
PVC is resistant to corrosive chemicals, making it more suitable for use in wastewater pipes in the home where it is likely to come into contact with corrosive chemicals, such as bleach or drain cleaner.
Although polyethylene has greater heat resistance than PVC, the pipes won't be exposed to anything hotter than boiling water in the home so PVC will be good enough.
PVC has a higher Young's modulus than polyethylene, which means it will be more rigid/less flexible, making it suitable for long lengths of pipe under the sink, floor or ground.
PVC is cheaper than polyethylene as the manufacturing cost is lower.
The combination of these properties makes PVC a more suitable material for use in the home.
| Descriptor | Marks |
|---|---|
Describes that PVC has greater chemical resistance than polyethylene | 1 |
Describes that polyethylene has better thermal properties so is more heat resistant than PVC, but this is not an important property for this application | 1 |
Describes that PVC is more rigid or less flexible than polyethylene | 1 |
Describes that PVC is cheaper than polyethylene | 1 |
Determines that PVC would be most suitable for wastewater pipes in the home | 1 |