The asphalt industry is constantly attempting to reduce its emissions as concerns are growing on global warming. This is done by decreasing the mixing and compaction temperatures of asphalt mixtures without affecting the properties of the mix which is possible through numerous available technologies in the industry. The production of asphalt mix is done by warm mix asphalt (WMA) technology at considerably lower temperatures (120°C or lower). Less energy consumption, lower mixing and compaction temperatures, early site opening, reduced ageing, fewer emissions, cool weather paving, better workability and, finally, an extended paving window could be mentioned as some of the benefits obtained by using the WMA. This paper presents the WMA techniques and technologies such as foaming techniques, wax and chemical additives techniques. Additionally, the performance of WMA popular technologies such as Sasobit®, WAM®-Foam, Evotherm®, Low energy asphalt, Rediset® WMX and REVIX™ are fully described.
Carbon footprint reduction of paving materials could be explored through recycling mining by-products into different applications, which will preserve natural resources and decrease environmental issues. One possible approach is to reuse quarry dust and mining ore waste as precursors in geopolymer applications. geopolymers are mineral polymers rich in aluminosilicates with an amorphous to a semi-crystalline three-dimensional structure. The current review aims to summarize the studies conducted during the past decade on geopolymers containing quarry dust and mine tailings. The first section discusses various precursors used for geopolymer cement production such as metakaolin, ground granulated blast furnace slag (GGBFS), fly ash, and quarry/mining ore wastes including silt, tungsten, vanadium, copper, gold, zinc, marble, iron, basalt, and lithium. Different calcination treatments and curing conditions have been summarized. In some cases, the precursors are required to be calcined to increase their reactivity. Both ambient temperature and elevated temperature curing conditions have been summarized. Less attention has been paid to room temperature curing, which is necessary for field and industrial implementations. Engineering properties such as compressive strength, density, durability and acid resistance, water absorption and abrasion of geopolymers containing mining waste were reviewed. One of the main barriers preventing the widespread use of waste powders, in addition to economic aspects, in geopolymers could be due to their unstable chemical structure. This was shown through extensive leachate of Na+ or K+ cations in geopolymer structures. The review of over 100 articles indicated the need for further research on different aspects of quarry waste geopolymer productions before its full industrial implementation.
This study aims to investigate the feasibility of including silt, a by-product of limestone aggregate production, as a filler in geopolymer cement. Two separate phases were planned: The first phase aimed to determine the optimum calcination conditions of the waste silt obtained from Società Azionaria Prodotti Asfaltico Bituminosi Affini (S.A.P.A.B.A. s.r.l.). A Design of Experiment (DOE) was produced, and raw silt was calcined accordingly. Geopolymer cement mixtures were made with sodium or potassium alkali solutions and were tested for compressive strength and leaching. Higher calcination temperatures showed better compressive strength, regardless of liquid type. By considering the compressive strength, leaching, and X-ray diffraction (XRD) analysis, the optimum calcination temperature and time was selected as 750 °C for 2 h. The second phase focused on determining the optimum amount of silt (%) that could be used in a geopolymer cement mixture. The results suggested that the addition of about 55% of silt (total solid weight) as filler can improve the compressive strength of geopolymers made with Na or K liquid activators. Based on the leaching test, the cumulative concentrations of the released trace elements from the geopolymer specimens into the leachant were lower than the thresholds for European standards.
The present research investigates the possibility to create a silt-waste reinforced composite through a NaOH-activated, metakaolin-based geopolymerization process. In this regard, we used thermal exo–endo analysis, X-ray diffraction (XRD), and oedometric mechanical tests to characterize the produced composites. In our experimental conditions, the tested material mixtures presented exothermic peaks with maximum temperatures of about 100 °C during the studied geopolymerization process. In general, the XRD analyses showed the formation of amorphous components and new mineral phases of hydrated sodalite, natrite, thermonatrite and trona. From oedometric tests, we observed a different behavior of vertical deformation related to pressure (at RT) for the various produced composites. The present work indicated that the proposed geopolymerization process to recycle silt-waste produced composite materials with various and extended mineralogy and chemical–physical properties, largely depending on both the precursors and the specific alkaline-activating solution. Thermal analysis, XRD, and oedometric mechanical tests proved to be fundamental to characterize and understand the behavior of the newly formed composite material.
Every year, up to 3 billion tons of non-renewable natural aggregates are demanded by the construction sector and approximately 623 million tons of waste (mining and quarrying) was produced in 2018. Global efforts have been made to reduce the number of virgin aggregates used for construction and infrastructure sectors. According to the revised waste framework directive in Europe, recycling at least 70% of construction and demolition waste materials by 2020 was obligatory for all member states. Nonetheless, quarries must work at full capacity to keep up with the demands, which has made quarry/mining waste management an important aspect during the past decades. Amongst the various recycling methods, quarry waste can be included in cement mortar mixtures. Thus, the current research focuses on producing cement mortars by partially substituting natural sand with the waste silt obtained from the limestone aggregate production in S.A.P.A.B.A. s.r.l. (Italy). A Design of Experiments (DOE) method is proposed to define the optimum mix design, aiming to include waste silt in cement mortar mixtures without affecting the final performance. Three cement mortar beams were produced and tested for each of the 49 randomized mixtures defined by the DOE method. The obtained results validate the design approach and suggest the possibility of substituting up to 20% of natural sand with waste silt in cement mortar mixtures.
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