# An Insight into the Chemistry of Cement--A Review
## 7 Conclusions  
Due to their remarkable mechanical properties, cementitious materials are among the most largely exploited substrates used by the construction industry for building cities, and linking them with highways, roads, and bridges. However, even if cement is a well-consolidated material, its chemistry remains very complex and not obvious. In order to try to improve the comprehension of the chemistry of cement, the present document has been organized into five parts.  
Part I (Paragraph 2) describes the manufacture process for obtaining ordinary Portland cement (OPC).  
Part II (Paragraph 3) provides information on the chemical composition of OPC, which is a mixture of different inorganic oxides (i.e., mainly CaO, SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\)), and deepens the understanding of the hydration mechanisms of every component forming the cement. Particular attention has been dedicated towards the evolution of the chemical composition in the cement system with time, after the reaction with water.  
Part III (Paragraph 4) is focused on the mechanism of setting, fundamental for improving structural integrity in the final material.  
Part IV (Paragraph 5) deals with the different types of porosities available in a cement. Additionally, a paragraph dedicated to the pivotal role of water in driving the pore formation has been provided.  
Part V (Paragraph 6) reports the recent findings of the alternative use of recycled (waste) materials in cementitious matrices, thus highlighting the future trends for the sustainable development of cementitious formulations.  
Based on the analysis of the literature, the following important statements can be delivered:  
1. Water plays a fundamental role in the evolution of the cement matrix. Since the hydration process consists of a series of different chemical reactions involving the main components of the cement powder with water, the reaction products deriving from the hydration mechanism strongly affect the final chemical composition of the cement.
2. During the setting time, there is a conversion from a plastic paste towards a set material, whereas the mechanical properties of the formulation are defined after the hardening step.
3. It is possible to distinguish between three different types of water: (i) chemically bound water, (ii) physically bound (gel) water, and (iii) free (evaporable) water.
4. Every type of water influences the porosity of the cement, and consequently the mechanical performance.
5. It is possible to use recycled (waste) materials and reuse them in cementitious matrices to form sustainable (advanced) cementitious composites.  
(6) The recent interest in smart inorganic materials for advanced technological applications opens the possibility of using cement as a matrix for novel nanoscopic composites with improved properties (e.g., self-healing and health-monitoring materials).  
Conceptualization, L.L. and R.N.; writing--original draft preparation, L.L.; writing--review and editing, L.L. and R.N. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Authors would like to thank [PERSON], and [PERSON] (Polytechnic of Torino, Italy) for fruitful discussions, and [PERSON], and [PERSON] for their precious help.  
The authors declare no conflict of interest.