Implementation of natural and artificial materials in Portland cement
For the preparation of modern cement and concrete, supplementary cementitious materials (SCM) have become essential ingredients. The technical, economic and environmental advantages of using SCM have become unquestionable. The main technical reasons for their use are the improvement of the workability of fresh concrete and durability of hardened concrete. Actually, SCM affect almost all concrete properties, while environmental and economic reasons may be more significant than technical reasons.
... technical reasons. These ingredients can reduce the amount of Portland cement used in cement composites, resulting in economic and environmental benefits. In addition, many of the SCM are industrial by-products, which can otherwise be considered as waste. This paper presents a literature review of the present knowledge on the impact of natural zeolite, waste construction brick and waste container glass on physical, chemical and mechanical properties of Portland cement as the most commonly used cement in the world. Hem. Ind. 74 (0) 000-000 (2020) 3 2. Additives with partial hydraulic properties, but also pozzolanic properties. This group includes fly ashes with high contents of CaO >10 % by weight. 3. Additives with high pozzolanic activity. This group includes filter SiO2 dust from ferrosilicon production or silica fume and rice husk ash. 4. Additives classified as natural pozzolans. 5. Different mineral additives, such as slow-cooled slag and poorly reactive rice husk ash. The main impacts of the use of pozzolanic materials in cement and concrete are: reduction of the cement content in cement composites, which contributes to lowering costs, reducing heat of hydration, improving the workability of cement composites, achieving projected strength after 28 days of hydration and improving resistance of the cement composite to sulfate action [37-39]. 1. NATURAL ZEOLITE AS A SCM Natural zeolites are a kind of natural pozzolans that has been widely used in construction since ancient times. Natural pozzolans in general largely differ regarding chemical composition, but silicon, aluminum and iron oxides prevail. According to most standards, if a pozzolan contains silica, aluminum and iron oxide amounts above 70 % by weight, it is regarded suitable for use in cement and concrete  . Natural zeolites are microporous crystalline hydrated aluminosilicates accommodating alkaline earth metal cations. The zeolite structure consists of a three-dimensional network of (SiO4) 4and (AlO4) 5tetrahedra connected by oxygen atoms  . Neutralization of the negative charge in (AlO4) 5tetrahedra is achieved by incorporating highly mobile hydrated alkali and alkaline earth cations (Na + , K + , Ca 2+ , Mg 2+ ) in cavities and channels in the zeolite structure. The existence of cavities interconnected by channels of a particular shape and size is the main structural feature that distinguishes zeolites from other aluminosilicates and other crystalline materials. The geometry of free space in dehydrated zeolites is important in determining physical and chemical properties       . The chemical composition and the XRD image of clinoptilolite as one of the most abundant and used natural zeolites are shown in Table 1 and Figure 1 , respectively [48, 49] .