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One of the main challenges of binder manufacturing industry is the reduction of its environmental impact. In this context, the key is the obtention of materials whose fabrication uses lower amount of natural resources and energy consumption. One of the the main strategies to achieve that goal is the incorporation of alkali activation processes to waste material or by-products. In this work, a SiMn slag has been alkali activated to prepare light mortars in which partial substitution of the aggregates by expanded polystyrene has been applied. An aggregate replacement up to 45% by volume has been used. In addition, also the SiMn has been used as aggregate in order to explore its valorization through that application. The following properties have been evaluated: fresh mortar workability, compressive strength, drying and autogenous shrinkage, water absorption by capillarity, apparent density and thermal conductivity. The intended application for this type of material would be as light cladding with improved isolation properties. Results have shown that the replacement up to 45% of natural aggregate by expanded polystyrene produces a decrease of the compressive strength up to 70%, a reduction of the density of 32%, an increase of the water absorption of 75% and a decrease of the thermal conductivity up to 87%.

Abstract

The aluminum and its alloys stand out thermal conductivity and good mechanical properties, which, combined with a low density, high environmental resistance and a reasonable cost, makes them very suitable for multiple applications. In spite of this, different applications, such as In the case of LED-based lighting systems, it is necessary to increase the thermal conductivity; while the transport sector demands to improve its mechanical properties, like rigidity and strength. To meet these requirements aluminum composite materials reinforced with unidirectional carbon fiber and woven have been developed, initially manufacturing pieces of simple geometry, but coming to manufacture complex elements, such as luminaires or clutch housings, with improved mechanical and thermal properties compared to those manufactured without reinforcement meeting the demands of this class of applications. The process used has been based on the injection of high pressure aluminum on the dry tissue giving rise to a very fast and efficient process in which the formation of fragile interfaces is avoided and there are no viscosity problems, such as those that occur in the manufacturing processes most commonly employed. In conclusion, through a process of high pressure injection of aluminum on carbon fibers, unidirectional or fabrics, pieces of metal matrix composite material that have superior thermal and mechanical properties with respect to uncoated aluminum alloys have been manufactured.

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In 2015, the European Commission adopted a Circular Economy Action Plan to stimulate the transition of European countries towards the circular economy. In the 2030 Agenda, which includes the 17 Sustainable Development Goals, the United Nations has also defined targets to be implemented by the construction sector based on circular economy concepts. In this context, the importance of directing the development of the construction sector towards sustainable solutions to address the challenges of energy consumption, climate change, resource reduction and waste production is undeniable. Waste incorporation in thermal mortars is already under study by several authors. Among the possibilities of producing sustainable mortars, the reduction of natural aggregates in their preparation, such as sand, or of binders, such as cement, stands out. The incorporation of residual materials in mortars is, therefore, a possible alternative to guarantee more sustainable solutions. The objective of this work was to evaluate the hygrothermal behaviour of non-traditional mortars and concretes, such as fibre-reinforced mortar (P1); sprayable thermal insulation mortar (P2); mortar with granulated cork (P3); concrete with expanded clay (P4); concrete with metallic fibres (P5); cement mortar with construction and demolition waste (P6). The thermal conductivity of these materials, with different moisture contents, from totally dry to saturated after 24 hours of total immersion was determined. The results showed that the thermal conductivity values of the dry materials were similar to those found in the literature. After the 24 hours of humidification, there was, as expected, an increase in mass, with a minimum of 2% for specimen P3 and a maximum of 51% for specimen P2. Regarding the thermal conductivity, there was also an increase in its value for higher moisture contents, being that increase more relevant in specimen P2, with a variation of 294%, and less relevant in specimen P5, with a variation of 18%.

Abstract

The increasing advances in the electronics industry, which operates with increasingly powerful systems and with greater performances, needs the development of new materials able to dissipate the high amount of heat they generate and that, over 50% of the occasions, is the source of catastrophic failures. The two major approaches in the design and manufacture of heat sinking materials lie in what are called active dissipators and passive dissipators. The last advances in passive dissipation come from Al/diamond composites, which exhibit high thermal properties that can be modulated through the manipulation of interfaces. On the other hand, interconnected pore metal foams have been widely studied because of their active dissipation properties and potentiality as electronic heat sinks. These foams can be designed and manufactured using the well-known replication method. This method produces a composite material consisting of a matrix and inclusions of such a nature that they can be subsequently eliminated by dissolution or chemical reaction. In the present work we propose the manufacture and characterization of materials formed by alternating layers of Al/Diamond and aluminium foam Recorded thermal conductivities reached 435W/Mk and are discussed by models that consider a semi-infinite alternating layered system of composite material and metal foam. In addition, power dissipation densities were recorded under working conditions and values up to 65% higher than conventional aluminium foams were registered.