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ENGINEERING, CS 2025 HSC 25b

An engineer is deciding whether to use pre-tensioned concrete or post-tensioned concrete to make beams for a railway bridge.

Describe features of the manufacture of pre-tensioned and post-tensioned concrete that the engineer should consider.   (3 marks)

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  • Pre-tensioned concrete involves stressing the tendons before the concrete is poured, typically completed in a factory environment.
  • This method suits mass production and reduces on-site construction time.
  • Post-tensioned concrete involves stressing the tendons after the concrete has cured, allowing work to be completed on-site.
  • Post-tensioning offers greater flexibility for large or complex structures but requires more time, specialised equipment and higher cost.
Show Worked Solution
  • Pre-tensioned concrete involves stressing the tendons before the concrete is poured, typically completed in a factory environment.
  • This method suits mass production and reduces on-site construction time.
  • Post-tensioned concrete involves stressing the tendons after the concrete has cured, allowing work to be completed on-site.
  • Post-tensioning offers greater flexibility for large or complex structures but requires more time, specialised equipment and higher cost.

ENGINEERING, CS 2024 HSC 11 MC

Why are gap joints strategically placed in pedestrian footpaths?

  1. To improve visual appeal
  2. To improve wheelchair access
  3. To allow for contraction and movement
  4. To allow for movement of debris and water
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\(C\)

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  • Expansion joints or gaps in footpaths are necessary to prevent cracking by accommodating the natural expansion and contraction of concrete due to temperature changes and ground movement.

\(\Rightarrow C\)

ENGINEERING, CS 2023 HSC 9 MC

In the process of manufacturing a concrete slab, cables are placed in ducting. After the concrete is poured and cured, the cables are stretched, anchored and released.

What type of concrete slab is this?

  1. Meshed
  2. Reinforced
  3. Pre-tensioned
  4. Post-tensioned
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\(  D \)

Show Worked Solution
  • In a post-tensioned concrete slab, high-strength steel tendons are placed in the concrete before it sets, and then pulled tight afterwards to create a compressive force on the concrete.

\(\Rightarrow  D \)

ENGINEERING, CS 2016 HSC 21ai

The reinforced concrete modules shown are designed for public seating. A typical use would be as a bus shelter.
 

Outline benefits of using this type of modular seating system.   (3 marks)

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  • Reusable moulds can be used to manufacture the modules off-site and then delivered to the site.
  • The completed modules can then be delivered to the site, resulting in fewer site disruptions.
  • More modules can be added as required.
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  • Reusable moulds can be used to manufacture the modules off-site and then delivered to the site.
  • The completed modules can then be delivered to the site, resulting in fewer site disruptions.
  • More modules can be added as required.

Mean mark 54%.

ENGINEERING, CS 2016 HSC 21aii

The reinforced concrete modules shown are designed for public seating. A typical use would be as a bus shelter.

Steel-reinforced concrete is used in the seating module.

Explain why steel is suitable for reinforcing concrete.   (3 marks)

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Suitability of steel to reinforce concrete

  • Concrete and steel have similar coefficients of thermal expansion.
  • Compressive strength is provided to the composite by the concrete and tensile strength is added by the steel.
  • Complicated mould designs can be matched by bending steel into shape.
Show Worked Solution

Suitability of steel to reinforce concrete

  • Concrete and steel have similar coefficients of thermal expansion.
  • Compressive strength is provided to the composite by the concrete and tensile strength is added by the steel.
  • Complicated mould designs can be matched by bending steel into shape.

ENGINEERING, CS 2020 HSC 24a

A photograph of a cast concrete pad is shown.
 

Describe why concrete would have been selected for this situation.  (3 marks)

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  • Concrete was selected for this situation due to its high compressive strength and formability.
  • Irregular shapes such as the pad shown can be formed relatively easily onsite, or preformed offsite and transported.
  • This enables greater flexibility in the shape, design and construction of civil structures.
  • Concrete can also be reinforced if necessary, to increase tensile strength.
Show Worked Solution
  • Concrete was selected for this situation due to its high compressive strength and formability.
  • Irregular shapes such as the pad shown can be formed relatively easily onsite, or preformed offsite and transported.
  • This enables greater flexibility in the shape, design and construction of civil structures.
  • Concrete can also be reinforced if necessary, to increase tensile strength.

ENGINEERING, CS 2021 HSC 17 MC

Which of the following is a specialised test used to determine the compressive strength of cured concrete?

  1. Slump test
  2. Janka hardness test
  3. Shore hardness test
  4. Rebound hammer test
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`D`

Show Worked Solution

Considering each option:

  • Slump test – tests the workability and consistency of wet concrete.
  • Janka hardness test – tests hardwood flooring.
  • Shore hardness test – tests soft elastomers and other soft polymers.
  • Rebound hammer test – tests the compressive strength of cured concrete.

`=>D`

♦♦♦ Mean mark 19%.

ENGINEERING, CS 2021 HSC 21c

Reinforced concrete is a composite material.

In the box below sketch and label the components of the macrostructure of reinforced concrete.   (3 marks)

 

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Show Worked Solution

Image should include the following elements:

  • Bulk aggregate
  • Sand
  • Hydrated cement
  • Steel reinforcing bar

 

♦ Mean mark 45%.