Year 9 have concluded their topic on ‘materials’ with an investigation into composite materials. In a composite material the properties of two or more materials are combined to produce an improved material. A recent innovation has been the use of plastic waste as the reinforcing medium in reinforced concrete rather than the more traditional use of steel rods. An understanding of how plastics are produced was first required and students modelled the process with ‘molymods’ making the small monomers and joining them together to form the longer chain polymer (see above), a process known as polymerization.
Our attention then turned to the concrete. Concrete is itself a composite material being made from cement, sand, aggregate and water. Cement is formed by the heating of limestone (calcium carbonate) and clay (aluminium and silicon oxides). During heating the limestone undergoes thermal decomposition (breakdown) to form calcium oxide (lime). As ‘lime’ is produced it starts to glow with a bright white light. In 1816 Thomas Drummond used this reaction in his theatre to light the front and center of the stage, hence, the phrase to be ‘in the limelight’.
With an understanding of how cement was produced we then started to investigate how the proportions of cement, sand, and water affect the strength of the concrete (more correctly, mortar). Different proportions were cast into discs and then tested to destruction! Two methods were used: dropping a weight from an increasing height until the disc cracked or crushing the sample in a vice. The amount of cement present was identified as the critical variable.
Ian Richardson, Head of Chemistry