This paper presents a review on fly ash as prime materials used for geopolymer. Due to its advantages of abundant resources, less in cost, great workability and high physical properties which lead to achieve high mechanical properties. Fly ash is considered as one of the largest generated industrial solid wastes or so-called industrial by products, around the world particularly in China, India and USA. The characteristics of fly ash allow it to be a geotechnical material to produce geopolymer cement or concrete as an alternative of Ordinary Portland cement. Many efforts are made in this direction to formulate a suitable mix design of fly ash based-geopolymer by focusing on fly ash as the main prime material. The physical properties, chemical compositions and chemical activation of fly ash are analysed and evaluated in this review paper. Reference has been made to different ASTM, ACI standards and other researches work in geopolymer area.
One of the major challenges faced in the optimization process of existing heating systems is the harnessing and integration of a higher share of renewable energy. Centralized integration at the thermic source leads to high investment costs at the first investment stage, and low values of conversion, transport, and storage efficiencies, due to high levels of heat loss from large-capacity entropic systems. This research paper presents a case study on the partially decentralized integration of thermal solar fields that are used for heat production in crowded urban areas within the optimization process of the existing heating system in the city of Oradea, Romania. A deterministic method was used as the method for the calculation of heat demand, in both stationary—hourly heat demand and dynamic regimes—annual heat demand, and the simulations within the configuration and the optimization process of the hybrid heating systems were carried out. In the case study, four representative urban areas with different thermal densities were analyzed within two working scenarios, which took into account the energy performances of the buildings inside the studied areas before thermal retrofitting, and after a usual thermal retrofit.
The rate of recycling and recovery of construction and demolition waste for the year 2020 is set at 70%. Currently in Romania, the waste recovery level is far below the set value, the collected waste is mostly disposed of by storage in landfills, without any other recovery or reuse. This paper presents practices in recycling of waste obtained from the construction of new buildings and demolition of existing buildings, with the potential of recovering large amounts of construction waste as filling material for road infrastructure or for heavy loaded industrial floors as well as possible other applications for using construction waste to substitute natural resources in concrete composition, obtaining material embedding waste with low energy consumption. The presented solutions might lead to an important increase of the recycling and recovery percentages, contributing to the fulfilment of the targeted and recycling, recovery and reuse rate. The viability of the possible applications is demonstrated with practical examples.
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