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Content available remote Mechanical and durability properties of concretes incorporating natural zeolite
This paper investigates the application of natural zeolite as a substitute of cement in concrete. It studies the mechanical and durability properties of concretes containing 10% of natural zeolite and superplasticizer, as well as 10% of natural zeolite, superplasticizer and an air-entraining agent in comparison to concretes without natural zeolite. The study shows that fresh concrete mixture containing zeolite due to its high surface area demands a higher dosage of superplasticizer to achieve the targeted slump flow. While concretes containing natural zeolite characterize a lower compressive strength until 90 days of hardening, the compressive strength exceeds the strength of the concretes without zeolite after 180 days. The results also reveal the considerable effectiveness of using a superplasticizer and an air-entraining agent in zeolite incorporating concretes on water penetration, drying shrinkage and freeze–thaw resistance of concretes.
In this study, properties and peculiarities of hydration processes as well as paste microstructure of blended cements containing 10% by weight of natural zeolite were investigated. Free calcium hydroxide content, crystalline hydration products and microstructural architecture of hydrated cement pastes were examined by physical and chemical methods. It was found that the addition of natural zeolite provides formation of an extra amount of fine crystalline ettringite and tobermorite-like calcium hydrosilicates of CSH (B) type in the mineral non-clinker part of Portland cement resulting in strength synthesis of cement stone with high performance properties.
Content available remote Application of alternative fuels for cement production
A possibility of thermal utilization of alternative fuels in cement industry is presented. The replacement of natural fuels with secondary materials in the process of organized waste recycling is the most significant step in this direction. One should emphasize the concept of "organized recycling", i.e. executed consciously and above all with the earliest possible segregation of initial secondary materials. Such segregation must not only lead to separate of different materials, but should also be applied to secondary materials for the production of alternative fuels. Only then it will be efficient as regards both environmental protection and economics. The goal of lowering production costs is one of two main factors stimulating activities aimed at replacing the natural fuel used in the cement production process with alternative fuels obtained from combustible wastes. The second factor is environmental protection, for instead of undergoing potentially hazardous storage; wastes can be duly treated and rendered harmless in a useful way, with the total consumption of their energy. Cement kilns, in which combustion processes reach temperatures up to 2000°C, are one of the several industrial installations ensuring the effective and environmentally friendly combustion of alternative fuels.
Content available remote Composite cements for energy-saving concrete technologies
One of the most important problems of modern concrete technologies is the development of low energy containing composite cements. The reduction of raw materials and energy consumption in cement production is achieved by means of using fly ash and granulated blast furnace slag as an active mineral additives of composite cements and their sulphate-alkaline activation.
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