# An Insight into the Chemistry of Cement--A Review
## 6 Future Perspective in the Use of Recycled (Waste) Materials in Cementitious Matrices
The results show that CDW recycling leads to significant reductions in emissions, energy consumption, global warming potential, and conserves landfill space compared to the disposal of waste in landfills. [PERSON] et al. [99] summarize the key principles and best practices for CDW management across the entire construction value chain. Systematic implementation of these best practices could dramatically improve resource efficiency and reduce environmental impacts: reducing waste generation, minimizing transportation impacts and reuse/recycling, improving the quality of secondary materials, and optimizing the environmental performance of treatment methods. Lastly, [PERSON] et al. [100] studied the behavior of cementitious renderings incorporating very fine recycled aggregates from two types of CDW: recycled concrete aggregate (RCA, smaller one) and mixed recycled aggregate (MRA). Results pointed out that the modified mortars in most of the tests showed superior performance than the reference mortar (without CDW). An interesting and alternative use of recycled waste materials in concrete is reported by [PERSON] et al. [101], who propose a novel route for utilizing recycled coarse aggregate in high-quality recycled manufactured sand, and the use of such high-quality sand to prepare recycled mortar with good mechanical strength and durability, thus further increasing the value of recycling concrete waste. Furthermore, the use of alternative aggregates, besides those deriving from CDW, is another frequently discussed topic from the literature [102]. Among the possible recycled substrates, plastic waste that would be destined for landfills is attractive not only from the sustainability and economy viewpoint, but also for their very peculiar mechanical properties [103]. In this context, the literature proposes a multitude of different polymeric substrates to be exploited as aggregate fractions, fillers or fibers in the preparation of novel (green) functional concrete, such as polyethylene terephthalate (PET) [104, 105, 106, 107, 108, 109, 110, 111, 112], poly vinyl chloride (PVC) [113, 114], high density polyethylene (HDPE) [115], shredded and recycled plastic waste [116, 102, 117], expanded polystyrene foams (EPS) [118, 119], polycarbonate [120], or polyurethane foams [121; 122]. Even if the use of polymeric materials in concrete often leads to a decrease in the mechanical properties due to several factors, such as the poor adherence between the plastic aggregates and the cementitious matrix, and the granular characteristics of the polymeric waste (which in most cases is not sufficient to achieve the optimum packing leading to the minimum of porosity) [117], the use of plastic waste can also be properly exploited for the introduction of some specific properties, unconventional for ordinary concrete. Currently, there is a growing interest in the use of recycled rubber (mostly derived from tire waste) in concrete as a partial replacement of the aggregate fraction [16; 17; 123; 124]. In fact, the addition of rubber particles into concrete can introduce novel properties in cement, such as a limitation of the water absorption and a consequent improvement against corrosion, a reduction in noise propagation, and a further improvement in fire resistance [125]. Furthermore, in the literature, the use of rubber concrete in non-structural applications is also suggested [14; 126]. In this context, an important point that should be considered is that the introduction of rubber fragments as aggregate fraction in cementitious matrices significantly affects the final mechanical properties of the cement/concrete in a proportional way in respect to the rubber content [16; 17].