| Date | May 2019 | Marks available | 9 | Reference code | 19M.2.SL.TZ0.6 |
| Level | SL | Paper | 2 | Time zone | no time zone |
| Command term | Explain | Question number | 6 | Adapted from | N/A |
Question
Choosing the right material(s) for a product such as a bridge is a complex and difficult task as each one has different physical, aesthetic and mechanical properties. In addition, there may be environmental, social, cultural, moral and ethical issues associated with the choice of material(s).
The Anzac Bridge in Sydney, Australia is a cable-stayed bridge made of reinforced concrete and steel cable, see Figure 6. There is a patent on the cables.
In other cases, bridge designers have used traditional materials such as wood. Figure 7 shows a timber bridge in Canada.
Figure 7: A timber bridge
[Source: "File:Wood bridge Montmorency.jpg" by Cephas is marked with CC BY-SA 3.0. To view the terms, visit https://creativecommons.org/licenses/by-sa/3.0/?ref=openverse]
Outline why designers would register a patent.
Explain why the recycling of steel-reinforced concrete is problematic.
Discuss the conflict between form and function when designing a new bridge.
Explain why timber as a building material is influenced by its physical properties, aesthetic properties and environmental impact.
Markscheme
a patent is a legal agreement that gives someone the right to make or sell an invention (for a certain number of years) ✓
and protects the inventor from having their idea copied/imitated ✓
Award [1] for identifying why designers would register a patent and [1] for a brief explanation up to [2 max].
Do not award marks for answers referring to ‘copyright’ or ‘ownership’
Answer in brackets is not required to award the mark
steel-reinforced concrete is made up of two materials (steel and concrete) ✓
which are difficult/require a large amount of energy to separate ✓
the concrete must be crushed to allow the steel to be melted down/recycled ✓
steel-reinforced concrete is a composite material ✓
made from a variety of different materials (sand/gravel/water/cement with steel bars) ✓
which cannot be separated easily into each material category for recycling ✓
Award [1] for each of three distinct points in an explanation of why why the recycling of the steel reinforced concrete is problematic up to [3 max].
Answer in brackets is not required to award the mark
Do not award marks across clusters
Form:
relates to the shape and the aesthetic qualities of the bridge ✓
some bridges are designed to be recognisable/iconic ✓
should be in harmony with the surrounding environment ✓
the form of the bridge may be influenced by the intended load ✓
optimum materials/structure for the function may not compliment the form ✓
Function:
a bridge needs to function as a safe crossing between two land masses ✓
it is required to withstand forces/have tensile/compressive strength to fulfil its purpose ✓
needs to function under a specific/intended load (consider factor of safety) ✓
should withstand adverse environmental conditions (earthquakes/high winds etc.) ✓
form follows function/function is more important than form (in a safety-critical structure such as a bridge) ✓
Award [1] for each of six distinct points in a discussion of the conflict between form and function when designing a new bridge.
[3 max for each]
Answer in brackets is not required to award the mark
Do not award marks across clusters
Mark as [3] + [3].
Physical properties:
thermal expansion/contraction ✓
timber does not expand/contract readily ✓
retaining the structural integrity of buildings in different climates ✓
thermal conductivity/resistance ✓
timber does not conduct heat readily ✓
helping to insulate (warm/cool) the building ✓
mass/weight ✓
timbers vary in their density ✓
some buildings need to have lightweight features/high density for stability ✓
different timbers vary in their hardness ✓
consideration needs to be given to the selection of timber to reduce wear/resist impact/scratches ✓
to ensure its durability/longevity ✓
Aesthetic properties:
appearance/texture ✓
timber has a natural colour/grain ✓
and can be selected to suit various tastes/aesthetic/styles/environments ✓
smell ✓
certain species of timber have unique/distinctive smell ✓
that can enhance the user experience/create an emotional response/evoke memories ✓
finishes ✓
timber can be treated in a variety of ways ✓
such as painting/varnishing/oiling/staining/waxing ✓
Environmental impact:
Renewability ✓
timber can be harvested and regrown from sustainable sources ✓
minimising the depletion of finite resources ✓
deforestation ✓
involves clearing a wide area of trees ✓
causing a destruction of natural habitat/decrease in biodiversity ✓
recovery and disposal ✓
timber can be reused ✓
or used as biomass/creation of composite material ✓
biodegradable ✓
timber is a natural material ✓
that will degrade/return to the earth ✓
Award [1] for each of three distinct points in an explanation of why timber as a building material is influenced by its physical properties up to [3 max].
Award [1] for each of three distinct points in an explanation of why timber as a building material is influenced by its aesthetic properties up to [3 max].
Award [1] for each of three distinct points in an explanation of why timber as a building material is influenced by its environmental impact up to [3 max].
Answer in brackets is not required to award the mark
Do not award marks across clusters
Mark as [3] + [3] + [3].
Examiners report
Not many candidates obtained full marks. Patents have appeared before on past papers but in different contexts. This was open ended but confused some candidates who referenced their answers specifically to the bridge design.
This should have been fairly straightforward and the markscheme provided good opportunities for candidates who were familiar with steel reinforced concrete and composite materials. Although it is a good question, the issue may have been the concrete is a composite in its own right and then adding steel makes it another type of combination of composites. The question has added complexity by asking candidates to explain how recycling can be problematic in the context of the material. However, having said this, many candidates still were able to achieve 1-2 marks.
There were mixed responses here and better clarification is needed in the guide with regards to form/function. The markscheme was designed, however, to allow candidates to gain marks from both the 'form' and 'function' elements. The 'conflict' aspect made it a little harder for candidates to structure their responses coherently but many were still able to pick up between 2 and 4 marks.
A good question which should have allowed a good range of marks to be obtained. Candidates answered well from the environmental clusters with biodegradability and deforestation being the most popular responses. Aesthetics was generally well answered but there were many cross cluster responses here too. Almost no one considered thermal expansion of conductivity for physical properties. Many students wrongly identified stiffness and tensile strength as physical considerations, not making the distinction between physical and mechanical properties. A few mentioned weight and hardness but did not add further marks from these clusters.
