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• Cement-replacing with tailings is one of the practical management approaches. • The use of tailings in the concrete matrix reduced the leaching rate of heavy metals. • Mechanical activation of LZTs without addittive causes the formation of new phases. • Mechanical activation increases the LZTs reacitivty for concrete construction. • Concrete containing activated LZTs represented a more uniform elements distribution. Use of mine tailings as a replacement for cement in concrete construction is a highly efficient method to reduce the environmental pollution of tailings' accumulation including toxic elements, acid mine drainage, and dust emission. Thus, safe management and accurate reuse of tailings is necessary. In this research, lead–zinc mine tailings (LZTs) were used and their reactivity were improved through mechanical activation. The compressive strength, mercury intrusion porosimetry (MIP), and toxicity characteristic leaching procedure (TCLP) tests were performed on the concrete samples. The TCLP test revealed that an increase in curing days led to a significant reduction in heavy metal leaching rate (cobalt, zinc, lead, nickel, copper, arsenic, cadmium and chromium) to a permissible limit. This indicates that the application of LZTs in concrete construction would lessen environmental concerns. The MIP test indicated that mercury intrusion volume in the activated sample with 20 % cement-replacement (T A20) was lower than that of the raw sample with 20 % cement-replacement (T R20) and control (C 100) samples. The results from X-ray diffraction (XRD) analysis showed that upon activating and increasing the curing time, the hatrurite converted to scawtite in samples containing activated tailings. The compressive strength results after 28 and 90 curing days revealed a rise in the strength from 16.9 MPa to 19.8 MPa for concrete samples T R20. However, upon prolonging the curing time from 28 up to 90 days, the compressive strength of the concrete samples T A20 grew from 28.35 MPa to 45.5 MPa. This indicates that the mechanical activation enhanced the hydration process and the cohesion of samples. The results of scanning electron microscopy (SEM) revealed that hydration products were also observed in concrete samples containing activated tailings. Overall, the results showed that mechanically activated LZTs, up to 40 % (by weight), can be a suitable substitute for cement in concrete production. [ABSTRACT FROM AUTHOR]

A large amount of mine wastes is generated every year through mining and mineral processing operation. The management of mine tailings is an attractive topic for researchers from both environmental and economic aspects. Mine tailings have shown a capacity as a raw material for the construction industry or a substitution for previous materials to produce the cement. It is applied in some specific environments such as offshores or massive projects like large bridges and tunnels. However, the cement industry has caused a variety of environmental issues. The production of Portland cement on an industrial scale increases the greenhouse effects and generates acidic rains. It releases greenhouse gases by the generation of carbon dioxide. In recent years, strict environmental regulations led to more efforts from mining industries to manage their tailings. A new approach to decrease the environmental issues, improve cement technology and obtain economic benefits is the use of mine tailings for cement production. Mine tailings in the cement mixtures decrease the initial hydration, retard the setting time, and lower the product mechanical strength. These problems can be fixed by the use of additives. Additives as chemical compounds are added to a cemented paste to change its properties and improve its performance. Therefore, the additives in cemented paste tailings can increase the pump-ability, reduce the water-to-cement ratio, increase density, or even adjust setting time and hydration according to the desired purposes. However, the amount of additives in the cemented paste tailings changes based on the type of additive. It should be optimized to cause a positive effect on the cement properties. Furthermore, the additives and their adaptation to the physical and chemical characteristics in cement and tailings is an important issue that should be investigated. In this paper, the usage of several chemical additives was studied, which can strengthen the properties of cemented paste tailings during backfilling operation. It can cause a better condition to decrease the environmental problems for the cement industry and mine tailings. A review of previous works is presented with an explanation of the gaps in previous studies. [Display omitted] • Mineral tailings can be used as a partial alternative to cement. • Additives in cement paste can improve the efficiency and strength of cement paste. • Water reducer and accelerator are the main additives in cement paste tailings. • The use of mine tailings in cement paste reduces costs. [ABSTRACT FROM AUTHOR]

Over the past few decades, as demand for minerals and metals has increased, the amount and volume of wastes and tailings has also increased dramatically. The management and reuse of mineral wastes and tailings not only help protect the environment but also are properly associated with economic benefits. As a result, mineral processing wastes disposal and storage has become a global issue. Along with the use of cemented paste as a backfill in underground spaces, the use of mineral processing wastes in the construction industry or as a substitute for cement is one of the new approaches to mineral tailings management. It is worth noting that the cement industry is facing crucial environmental issues. Portland cement production in industries increases the greenhouse effect and creates acidic rain. In fact, it generates greenhouse gases directly through carbon dioxide emission during clinker production as well as through energy consumption. In addition, the increasing stringency of environmental regulations has forced the mining industries to make efforts in order to manage tailings. One of the new and attractive techniques to reduce environmental problems and to obtain economic and technological benefits is to increase the use of tailings, for example, the use of mineral tailings as a substitute for cement. It is important to note that mineral tailings are not normally cemented and are accompanied by reduced strength of cement and concrete mortars; thus, there is a need for methods to increase their cementitious properties. Activation is one of the methods improving cementitious/pozzolanic properties of mineral tailings. Therefore, the present review study aimed to investigate the activation methods to improve the properties of tailings resulted from minerals processing in order to be used as a replacement for cement, to reduce the pollution caused by cement production, as well as to reduce the volume of unused mineral tailings. Different physical, chemical, and thermal activation methods were examined, and criticisms and research gaps of previous studies were presented. Image 1 • A comprehensive critical review about mine tailings reuse in concrete industry was conducted. • The activation processes could be enhanced the application of tailings as cement in concrete. • The risk of release of toxic elements from tailings could be greatly decreased in concrete matrix. [ABSTRACT FROM AUTHOR]

Nanotechnology plays a significant role in construction industry. The construction industry has been employed nanomaterials to improve the performance of construction components and the safety of the structure and to reduce the energy consuming and the cost of maintenance. In other words, nanotechnology has a substantial impact on the construction industry. Therefore, it is necessary to identify and evaluate the critical factors of the application of nanotechnology in construction in order to concentrate on the most critical factors. However, several techniques have been developed to prioritize the evaluation criteria. Analytical network process (ANP) technique, a branch of multi criteria decision making (MCDM) methods, is a powerful tool to rank a limited number of criteria. This technique takes into account both tangible and intangible criteria in the process of formulation of a decision making problem. This method is capable of handling all types of independence and dependence relationships. On the other hand, intuitionistic fuzzy set (IFS) is a well-known technique in considering the inherent uncertainty involved in the process of modelling a decision making problem. In this paper, a new model based on the IFS and ANP technique is proposed to evaluate the critical factors of the application of nanotechnology in the construction industry. The results demonstrate that the proposed model has a high potential for taking into account the uncertainty in the form of a three dimension function, including membership, non-membership, and non-determinacy. [ABSTRACT FROM AUTHOR]