The whereabouts of the overwhelming majority of plastic estimated to enter the environment is unknown. This study's aim was to combine information about the environmental occurrence and physicochemical properties of widespread polymers to predict the fate of aquatic plastic litter. Polyethylene and polypropylene are common in the surface layer and shorelines; polyester and cellulosic fibres in sewage treatment works, estuarine and deep-sea sediments. Overall, non-buoyant polymers are underrepresented on the ocean surface. Three main explanations are proposed for the missing plastic. The first is accumulation of both buoyant and non-buoyant polymers in sewage treatment works, river and estuarine sediments and along shorelines. The second is settling of non-buoyant polymers into the deep-sea. The third is fragmentation of both buoyant and non-buoyant polymers into particles smaller than captured by existing experimental methods. Some isolation techniques may overrepresent larger, buoyant particles; methodological improvements are needed to capture the full size-range of plastic litter. When microplastics fragment they become neutrally-buoyant, thus nanoplastics are potentially widely dispersed in aquatic systems, both horizontally and vertically. Ultimately, over decades or longer, plastics are potentially solubilized and subsequently biodegraded. The rates at which these processes apply to plastic litter in different environmental compartments remain largely unknown.

This research has investigated the properties of thermally insulating geopolymer composites that were prepared using waste expanded polystyrene as lightweight aggregate. The geopolymer matrix was synthetized using metakaolin and an alkaline activating solution. To improve its mechanical properties, this matrix was modified by the addition of an epoxy resin to form an organic-inorganic composite. Moreover, in order to reduce drying shrinkage marble powder was used as an inert filler. The materials obtained were characterized in terms of physico-mechanical properties, thermal performance and microstructure. The geopolymer expanded polystyrene composite have improved properties compared to Portland cement-based materials, with higher strengths and lower thermal conductivity. The research demonstrates the manufacture of sustainable lightweight thermally insulating geopolymer composites using waste expanded polystyrene.

The hydration of reactive periclase (MgO) in the presence of hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O) was investigated by a variety of physical and chemical techniques. Hydration of pure MgO-water mixtures gave very weak pastes of brucite (Mg(OH) 2 ), but hydration of MgO-hydromagnesite blends gave pastes which set quickly and gave compressive strengths of potential interest for construction applications. The strengths of the blends increased with hydration time at least up to 28days, and were not significantly decreased by increasing the hydromagnesite content up to 30%. Raman spectroscopy suggests that an amorphous phase, of composition between that of brucite, hydromagnesite and water, may form. Small amounts of calcite also form due to CaO in the MgO source. Thermodynamic calculations imply that the crystalline phase artinite (MgCO 3 ·Mg(OH) 2 ·3H 2 O) should be the stable product in this system, but it is not observed by either XRD or FTIR techniques, which suggests that its growth may be kinetically hindered

Clay is used as a raw material for the production of lightweight aggregates because it is readily processed into suitable granules and forms low-density but high strength aggregate particles when sintered at relatively low temperatures. The use of waste clay generated by major infrastructure development projects to make lightweight aggregate has a positive environmental impact and contributes towards a more circular economy. This paper reviews the manufacturing process used to produce lightweight aggregates from clay and the influence of processing conditions on properties. It also reviews secondary materials that have been incorporated into clays to produce lightweight aggregates. Additional research is required to improve understanding of the effects of composition and production parameters on the pore structure, density, water adsorption and strength of clay derived lightweight aggregates.

The influence of the addition of various types and various concentrations of expanded polystyrene foam (both commercial and recycled) on the durability of Portland cement mortars is studied. In particular, the microstructure is studied utilizing the following methods: Capillary absorption of water, mercury intrusion porosimetry, impedance spectroscopy and open porosity. In addition, the effects of heat cycles and freeze-thaw cycles on compressive strength are examined. Scanning electron microscopy is used as a complementary technique. An air-entraining agent, water retainer additive and superplasticizer additive are used to improve the workability of mortars. The resultsshow that the presence of expanded polystyrene in mortar results in a decrease in the capillary absorption coefficient. The mercury intrusion porosimetry technique and the equivalent circuits previously used by researchers to interpret impedance spectra of ordinary cementitious materials were found to be inadequate for interpreting the microstructure of mortars with expanded polystyrene. This is due to the polymeric nature as well as the internal porous structure of expanded polystyrene. A slight increase of compressive strength is observed in mortars with expanded polystyrene subjected to heat cycles. The compressive strength of mortars subjected to freeze-thaw cycles likely improves because expanded polystyrene particles absorb part of the pressure of ice crystallization. It is concluded that the durability of mortars improve with the presence of expanded polystyrene, making them viable for more sustainable usage in masonry, stucco and plaster mortars.