# Environmentally Friendly Smart Construction--Review of Recent Developments and Opportunities
### Use of Recycling Materials in Construction
#### 4.4.1 Rubberised Concrete  
There are several types of municipal solid waste, which can also be used in construction, namely recycled glass, waste tyres and recycled plastics [55]. The sources of recycled construction materials with the most potential are the waste tyres, which can be processed into rubber chips and steel and nylon wires. The steel can be utilised in the steel production, while the rubber particles can be added to concrete as a fine or coarse aggregate to produce the rubberised concrete (RuC).  
The possibility of recycling stockpiles of waste tyres and replacement of natural sand has been driving the research on RuC for the last two decades [57; 251; 252; 253]. The results of recent studies on the mechanical properties of RuC are systematically summarised in [55]. The inclusion of the rubber phase reduces compressive and tensile strength of RuC, its modulus of elasticity and density. Thermal insulation capacity, fracture resistance and electric resistivity of RuC, however, are superior over the conventional concrete [254; 255]. The freeze-thaw resistance is improved by the increased porosity of RuC, while the freezing resistance is degraded by the rubber particles [57]. The workability of RuC is degraded by the increased viscosity and decreased slump value [57]. The durability of RuC is on par with the conventional concrete [256]. It was shown using the standard test methods that RuC can provide a 50-year design life.  
Since the mechanical properties of concrete are dependent on the strain rate, the dynamic performance of RuC has attracted special attention [59; 60; 251; 257]. The dynamic increase factor for the dynamic strength and ultimate strain of RuC are higher than those of the conventional concrete. RuC is also able to absorb more impact energy than the conventional concrete. For example, [60] showed that even though the peak impact force is reduced by up to 40% for 30% rubber content, the impact energy absorption is increased by 63%, which indicated that a positive trade-off can be achieved. The damping ratio in RuC depends on the concrete and aggregate types. The greater increase in RuC damping is achieved using coarse rubber particles.  
Various applications of RuC in construction, which were discussed in the literature, include structural members for earthquake-resistance construction [258], hybrid structural beams with a top RuC layer and a conventional bottom one [259], steel tubes filled with RuC [61], RUC beams and columns [260] and RuC cladding for the protection of bridge piers [257]. On top of the ability to utilise the waste tyre, RuC provides a range of advantages and possible applications:  
* The lower thermal conductivity is important for the energy saving in buildings.
* The lower density is advantageous for the weight reduction in high-rise buildings.
* The recycled rubber can be naturally used in asphalt mixes as powder or large particulars (chips).
* Road pavements can benefit from the additional elasticity, which can improve the skid resistance.
* Enhanced impact resistance presents potential for the protective roadside barriers.