Erika Furlani

The present paper discusses experimental results obtained on several mortars prepared using a commercial type1 OPC cement, a commercial limestone aggregate with maximum particles dimension below 5 mm, superplasticizer and water. Different amounts of a waste silica sand, in form of loose powder, derived from the industrial production of refractory blocks, were added to the above basic components. Several additional samples were also prepared using same basic commercial components added by different amounts of a fine limestone filler. This latter set of compositions was used to prepare samples to be used as reference materials. Waste silica sand and fine limestone filler were used as received from their producer. During preparation, pastes containing silica sand showed better workability compared to all the other blended components. All hydrated materials displayed fair compressive strength and low water absorption after curing, but those containing silica sand showed the best mechanical performances due to their low residual porosity and to the pozzolanic reaction which could enable application for the production of structures in direct contact with water or aggressive environments such as sewers or tanks suitable for the containment of organic substances.

Several geopolymer-based materials were produced and characterized by mixing metakaolin, a commercial sodium silicate solution, a sodium hydroxide solution, and a loose waste olivine sand deriving from a metallurgical process devoted to the production of a high manganese steel. Olivine sand was added either in the as-received form or after a thermal treatment at 900 °C. Hardened materials containing different amounts of olivine sand were characterized and their behavior was compared to that of a blank geopolymeric matrix. Materials were examined by X-ray diffraction, Fourier Transform Infrared Radiation, and optical and scanning electron microscope investigation; mechanical compressive strength was discussed taking into account water absorption and microstructure. It has been observed that all compositions containing the as-received olivine sands badly perform, whereas those prepared using thermally treated olivine have higher compressive strength than the reference blank composition. In particular, samples with composition containing 100 g of metakaolin and 75 g of olivine displayed the best overall behavior. Graphical Abstract

In this work, different alternatives to conventional tertiary treatment of pulp and paper (P&P) wastewater (WW), i.e., physicochemical coagulation-flocculation, were investigated to enhance the environmental and economic sustainability of industrial wastewater treatment. In particular, following a preliminary characterization of secondary effluents, cloth filtration and adsorption were studied, the former by pilot-scale tests, while the latter at laboratory scale. An economic analysis was finally accomplished to verify the full-scale applicability of the most promising technologies. Cloth filtration showed excellent total suspended solids (TSS) removal efficiency (mean 81% removal) but a very limited influence on chemical oxygen demand (COD) (mean 10% removal) due to the prevalence of soluble COD on particulate COD. Adsorption, instead, led to a good COD removal efficiency (50% abatement at powdered activated carbon—PAC—dosage of 400 mg/L). The economic analysis proved that adsorption would be convenient only if a local low-cost (100 €/ton) adsorbent supply chain was established. Ultrafiltration was considered as well as a potential alternative: its huge capital cost (19 M€) could be recovered in a relatively short timeframe (pay-back time of 4.7 years) if the ultrafiltrated effluent could be sold to local industries.

Production and characterization of geopolymers prepared by mixing metakaolin, end-of-life dolomite refractories, sodium silicate solution, and sodium hydroxide solution have been performed. The as-received refractory was crumbled in order to obtain products having, respectively, 250 μm, 1 mm, and 2.5 mm maximum particles size. Each batch of powder was added in different proportions to a blank geopolymeric matrix. It has been observed that the addition of waste refractory reduces workability of the reference refractory-free slurry. After hardening, only the set of samples prepared with powders with maximum size of 250 μm maintain integrity while the others resulted affected by the presence of fractures caused by volumetric instabilities; samples with composition R100 showed the highest compressive strength, whereas higher refractory addition lowers strength. Specific surface area appears independent by materials composition; conversely pore volume slightly increases with the addition of dolomite refractory powder. During the thermodilatometric tests all compositions display a shrinkage of about 0.1% between 170 and 400 °C; however, sintering starts at higher temperature (above 600 °C) and samples melt in the range between 650 and 750 °C as a function of their composition, thus showing that the resulting materials loose refractoriness with respect to both the reference geopolymer and the dolomite refractory. Graphical Abstract

The present research deals with the production and characterisation of geopolymers prepared by mixing metakaolin (MK), a commercial sodium silicate solution, a sodium hydroxide solution and two types of industrial by-products: one olivine (OS) and one silica sand (SS) both of them in form of loose powders. Different specimens were prepared by mixing different quantities of OS or SS to the blank geopolymeric matrix. Specimens containing MK, a commercial sodium silicate solution and a sodium hydroxide solution were also prepared as blank composition for comparison. All specimens were characterised by their compressive strength, water absorption, pore size distribution, specific surface area and microstructure. The addition of olivine or silica powders improves the performances of the resulting materials in all the compositions examined, but those containing 50 wt% of added sand (relative to the amount of MK) displayed the best mechanical behaviour.

The paper describes the production, in single fast firing, of tiles containing 30 wt% of a natural red clay and a mixture of 42 wt% of paper mill sludge and 28 wt% of glass cullet which were coated with a commercial ‘matt white’ glaze. Fired materials have been characterized as a function of the top temperature (1090 or 1140 °C) reached at the top of the fast sintering process made by an industrial roller kiln. It has been observed that tiles fired at 1090 °C display the best overall performances because the matt glaze well covers the substrate, thus ensuring that the mechanical and physical properties of the tiles conform to the official standard.

This paper deals with the production of mortars prepared using a commercial CEMIIB-S 42.5N cement, a natural aggregate, steelmaking slag, a superplasticizer and water. The as-received unprocessed steel slag was milled by a hammer mill and then sieved to obtain batches with different maximum particle size. Each batch was used, together with the other components, in the production of mortars which were tested, by compression and water absorption, after different aging times in order to evaluate their long term stability. Several slag-free samples were also prepared as reference materials. All mortars were prepared with fixed aggregate/cement ratio (6/1), superplasticizer/cement ratio (s/c) and water/cement ratio (w/c). It has been demonstrated that an adequate protocol for the preparation and the use of slag containing particles with 2500 µm maximum size lead to the production of materials with mechanical properties suitable for civil engineering applications after aging for 28, 90 and 180 days. However, samples containing slag particles with size equal or greater than 1000 µm display a decay of mechanical properties after longer aging in water or after accelerated aging.

The paper reports on some experimental results obtained from the production of mortars prepared using a commercial cement, coarse steelmaking slag, superplasticizer, and water. The behaviour of this reference composition was compared to that of some others containing further additives in order to investigate materials compressive strength after long time ageing. It has been demonstrated that an optimized water/cement ratio coupled with slag particles of size lower than 2.5 mm and proper protocol of preparation leads to the production of materials with good mechanical properties after 28, 90, and 180 days of ageing. The resulting materials therefore appeared as good candidates for civil engineering applications. However, the present research also demonstrates that the mortar samples of all of the compositions prepared suffer from decay and compressive strength decrease after long time ageing in water. In the present paper the results are explained taking account of materials residual porosity and alkali silica reaction which occurs in the samples.