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The original non-conventional technique of preparing expanded bottle utilizing recycled bottle waste and a combination between glycerin in association with Na2SiO3 and Na2CO3, as liquid and respectively, solid expanding agents, was experimentally tested on an 800 W-electromagnetic wave oven and shown in this article. The work objective was obtaining a cellular glass with physio-mechanical and thermal features almost identical to those achieved by conventional techniques at industrial-scale. Thus, the heat conductivity was in the range of 0.060-0.072 W·m-1·K-1, while the compression resistance increased at 6.5-7.2 MPa. Also, the experimental results confirmed the remarkable power efficiency of the non-conventional process, the power use value being diminished to an extremely reduced measure (0.74-0.83 kWh·kg-1). In conclusion, the cellular product made by the unused technique worldwide proved to be suitable for application in special constructions.

The comparative analysis of the cellular glass products manufactured by the non-conventional microwave heating method compared to those made on a large scale by conventional methods is presented in this paper. Applying the non-conventional method was carried out in recent years by authors of the current article. Four different testing versions were selected by the composition of the material mixture including the expanding agent as well as the operational parameters. SiC, CaCO3, and Si3N4 separately constituted the expanding agents used in the analyzed experiments. Also, fly ash, red iron oxide, borax, and MnO2 were other additional materials included into the mixture, also separately. The specific energy consumption of producing processes were very low under the conditions of using a microwave equipment at very small-scale (0.8 kW), there being the possibility of improving this parameter by up to 25 % by applying the method on an industrial-scale.

Peculiarities of the modern cellular concrete manufacturing technique were borrowed in the expanding glass technique at ambient temperature presented in the work. Using aluminum dust in calcium hydroxide solution and adding carboxymethyl cellulose (CMC) as a froth fixer, cellular glass specimens with excellent insulating properties with minimal energy consumption could be experimentally obtained, as an alternative solution to conventional methods industrially used. The tests presented in this article intend to improve the mechanical resistance of the cellular product under the conditions of preserving existing insulating properties by adding to the starting mixture a very effective ultrafine powder (silica fume) contributing to the increase of strength and durability. Completing the manufacturing recipe with silica fume is the originality element compared to the previously applied solutions. The results confirmed the effectiveness of the new method, the compressive strength increasing up to 4.7 MPa under conditions of density below 0.35 g·cm-3 and heat conductivity below 0.079 W·m-1·K-1.

Porous material based on residual glass was non-conventionally made using anthracite as a pore-forming agent under the conditions of an oven with oxidizing atmosphere. Water glass as a protective agent for carbon particles avoiding their early oxidation and manganese dioxide (MnO2) as an oxygen-supplier contributed to obtaining cellular glass with excellent physical, thermal, mechanical, and morphological features. The best specimen made by microwave heating at 790 ℃ using 1 % anthracite, 11.5 % water glass, 1.8 % MnO2, and 5 % water allowed creating a product with excellent heat-insulating features (apparent density of 0.21 g·cm-3, heat conductivity of 0.039 W·m-1·K-1), and acceptable compressive resistance (2.3 MPa), the microstructural appearance being homogeneous with uniformly distributed pores with very low dimensions (0.1-0.4 mm).

This review presents polyurea (PU) synthesis, the structure–properties relationship, and characterization aspects for ballistic protection applications. The synthesis of polyurea entails step-growth polymerization through the reaction of an isocyanate monomer/prepolymer and a polyamine, each component possessing a functionality of at least two. A wide range of excellent properties such as durability and high resistance against atmospheric, chemical, and biological factors has made this polymer an outstanding option for ballistic applications. Polyureas are an extraordinary case because they contain both rigid segments, which are due to the diisocyanates used and the hydrogen points formed, and a flexible zone, which is due to the chemical structure of the polyamines. These characteristics motivate their application in ballistic protection systems. Polyurea-based coatings have also demonstrated their abilities as candidates for impulsive loading applications, affording a better response of the nanocomposite-coated metal sheet at the action of a shock wave or at the impact of a projectile, by suffering lower deformations than neat metallic plates.

Producing foamed bottle type with excellent heat-insulating features (denseness within the limits of 0.30-0.45 g·cm-3, heat conduction in the range of 0.064-0.093 W·m-1·K-1, and porousness within the limits of 78.6-85.7 %), and simultaneously high compression properties (6.3-8.2 MPa) was achieved in economical and environmentally friendly conditions using nonconventional method of preponderantly direct electromagnetic wave warming. The material mixture was composed of recycled residual coloured glass, CaCO3, borax, glycerin, water glass, and water adding. The sintering/expanding temperature had values between 829-845 ℃. Due to the high energy effectiveness of the warming technique designed by authors, the warming rate had excellent values (18.8-23.8 ℃/min) without affecting the quality of cellular bottle specimens and the electricity consumption was reduced (0.83-1.06 kWh/kg).

Cellular gravel based on alumino-silicate wastes including residual clay brick recovered from construction demolition and fly ash resulted from coal burning in energy industry was experimentally made. The expanding process made with glycerin as a liquid organic material together water glass was obtained by direct electromagnetic wave warming without affecting the structural integrity of the product. The special effectiveness of the direct irradiation of the material led to extremely low specific electricity consumption (0.53-0.64 kWh/kg). The optimal version had the following characteristics: bulk denseness of 0.21 g·cm-3, heat conductivity of 0.063 W·m-1·K-1, compression resistance of 3.9 MPa, flexural strength of 2.4 MPa, and cell dimension within the limits of 0.2-0.5 mm. The use of alumino-silicate wastes in association with direct microwave warming keeping the physical, thermal, mechanical and microstructural properties unchanged (almost similar to industrial products) constitutes the paper originality.

Cellular glass non-conventionally prepared from post-consumer drinking glass was made, silicon nitride (Si3N4) and manganese dioxide (MnO2) contributing to form the porous structure. The correlation between the physical-morphological properties (low denseness, high porousness, structural homogeneousness) of the expanded material and its strength features (high compression resistance) played an essential role. An optimal weight ratio between the two pore-forming additives was found at the value 1.0. The temperature of the sintering-expanding process was relatively reduced (823 ℃) and the warming rate reached very high values (27.7 ℃/min) due to the energy efficiency of the own preponderantly direct microwave warming method. The main features of the optimal cellular glass specimen were: denseness of 0.59 g·cm-3, heat conduction of 0.097 W·m-1·K-1, compression resistance of 6.6 MPa, and pore size between 0.1-0.4 mm.

The preparation at room temperature of cellular glass from recycled residual glass and fly ash was made adopting a manufacturing method recently applied in the case of geopolymer foam. Sodium perborate in aqueous solution as a blowing agent and detergent as a surfactant have been experimentally tested in several versions. The optimal cellular glass product was obtained by mixing 2.6 % sodium perborate, 0.2 % surfactant, and 7.6 % water addition. The characteristics of this expanded product were: density of 0.65 g·cm-3, heat conductivity of 0.134 W·m-1·K-1, and compression resistance of 1.2 MPa, being satisfactory for its application as heat insulating product in construction. The main advantage of this method was the product manufacture in satisfactory quality conditions without supplementary energy consumption and greenhouse gas emissions (CO2) into the atmosphere, like in the case of the usual manufacturing cellular products at high temperature.

New manufacturing recipe of glass waste-based foam glass gravel for special applications in construction was designed, tested, and presented in this paper. The work originality is the use of alumino-silicate materials in the form of waste (fly ash, blast furnace slag, alkaline earth alumino-silicate glass waste) as well as in the natural state (metakaolin) widely available in nature. Especially, in this work it was chosen the use of a waste of alumino-silicate glass recovered from halogen lamps, similar by chemical composition with the other materials adopted to constitute the material mixture. Three variants using a solid (SiC) and liquid (glycerin), respectively, blowing agent were tested, the mixtures being sintered and foamed at temperatures between 850-940 ºC. The heating was made by the economic and ecological technique of microwave irradiation. All tested versions led to obtaining cellular gravel types with characteristics suitable for special applications in construction, similar to industrially made foam glass gravel. Being more suitable for load-bearing properties, the variant made with alumino-silicate glass waste and glycerin associated with sodium silicate solution was chosen as the optimal alternative.

Ceramic foam prepared from steel slag particles in colloidal suspension was stabilized with propyl gallate and after drying was sintered by direct electromagnetic wave radiation at successive thermal regimes within the limits of 980-1200 ºC. The microwave heat treatment is the originality of the work. The heating rate reached very high values of up to 40 ºC/min without affecting the microstructural configuration of the foam. The peculiarities of ceramic foam include reduced heat conductivity (in the range of 0.060-0.085 W·m-1·K-1), high compression resistance (about 9.8 MPa) and extremely low pore size (between 20-160 μm).

An industrially manufacturing recipe of foam glass gravel (FGG) from glass waste by an unconventional heating technique, using simultaneously a liquid foaming agent (glycerol) and a solid one (calcium carbonate) was tested on a 10 kW-microwave oven. Using a ceramic crucible based on silicon carbide with large dimensions, placed in a horizontal position, inside which a metal mold containing the finely ground pressed raw material mixture was inserted, the conditions were created to experiment the manufacture of a much higher quantity and on a significantly extended surface of 725 cm2 of foamed product compared to previous tests performed on a 0.8 kW-microwave oven. In terms of quality, the results were appropriate, the characteristics of FGG samples manufactured by sintering at 834-840 ºC using the conversion of microwave power to heat being within the limits of values required for this type of thermal insulation material (bulk density of 0.20-0.25 g/cm3, thermal conductivity of 0.062-0.070 W/m•K, compressive strength of 7.1-7.4 MPa, water absorption below 3% and pore size between 0.10-0.65 mm).

The work presents the results of the experimental manufacturing process on a 10 kW-microwave oven of foam glass gravel (FGG) from glass waste (98 wt. %) and silicon carbide (2 wt. %), the sintering/foaming temperature being varied between 910-930 ºC. The paper originality is the significant increase (about 8 times) of the amount of glass-based raw material foamed by the unconventional heating compared to the previous experiments. The main features of the FGG experimental samples were: bulk density between 0.26-0.31 g·cm-3, compressive strength between 8.5-9.7 MPa and thermal conductivity between 0.068-0.077 W/mK, suitable for their use as thermal insulation material in several applications in construction.

Glass-ceramic foam was produced from residual glass (87.6-87.9 %), coal fly ash (8.5-10 %), silicon carbide (2-3 %), and kaolin (0.4-0.6 %) by sintering at 950-975 ºC. The heating technique was original, being used the preponderantly direct warming procedure using electromagnetic waves. The glass-ceramic foam had the following characteristics: apparent specific gravity between 0.22-0.28 g/cm3, porousness between 86.7-89.5 %, thermal conductance in the range 0.055-0.065 W/m·K, compression resistance between 1.8-2.5 MPa, water absorption below 1.2 vol. %, and pore dimension under 1 mm. The specific electricity consumption had very low values (between 0.75-0.83 kWh/kg). The application field of the product includes thermal insulation materials for construction, architectural components and other applications that do not require resistance to high mechanical stress.

An expanding agent (aluminum nitride) from the carbide and nitride group, less used in the cellular glass manufacturing process, was tested together with manganese dioxide in the experiment presented in the paper. The powder mixture of recycled residual glass and the two mentioned additives was thermally sintered and expanded by predominantly direct microwave irradiation at temperatures between 820-850 ºC. The remarkable energy efficiency of the original heating technique allowed obtaining very economic specific energy consumptions between 0.80-0.95 kWh/kg. The optimal products had the apparent density between 0.35-0.43 g cm-3, porosity between 79.5-83.3 %, heat conductivity between 0.080-0.094 W (mK)-1, and compression strength in the range 4.0-6.7 MPa. The cellular material has the characteristics required for its using as a thermal insulation material in the building sector.

A porous high-strength material having load-bearing thermal insulation properties suitable as light filling material for building foundation, drainage, road construction, underground insulation of heat pipes, etc. was experimentally made by sintering and foaming at 830-840 ºC applying the microwave irradiation to a pressed powder mixture composed of recycled post-consumer glass, glycerol, calcium carbonate, water glass and water. The manufacturing recipe adopted by authors is original by combining a liquid carbonaceous expanding agent (glycerol) with a solid agent (calcium carbonate) aiming at the increase of compressive strength at 6.5-7.6 MPa, the product bulk density being under 0.20 g cm-3. The nonconventional technique of predominantly direct microwave heating is also original and more economical compared to conventional methods applied both in industrial processes and in small-scale experiments.

The paper exposes testing results corresponding to the process of manufacture cellular glass from consumed drink glass packaging, a vegetable expanding agent (beech leaves) used for the world premiere, and borax as a flux agent. The process of sintering/expanding the powder material mixture was performed by microwave irradiation at 825-834 ºC, as a process improved by the authors of this paper and applied in previous experiments, unlike the conventional procedures used in processes of the same type. The nonconventional heating has allowed a higher energy efficiency of the process and reduced energy consumption (0.78 kWh/kg). The optimal version of the manufacturing process with 30 % beech leaves, 65 % consumed drink glass packaging, and 5 % borax led to obtaining a cellular glass with features adequate for its use as heat insulating material in civil engineering having density of 0.60 g/cm3, heat conductivity of 0.124 W/mK, compression resistance of 5.0 MPa, absorbing the water of 1.5 vol. %, and cells dimension between 0.7-1.0 mm.

The paper presents a new technique for making foam glass gravel by expanding at high temperature recycled glass waste with a liquid carbonic foaming agent (glycerol) in combination with sodium silicate (also called “water glass”). Unlike the conventional methods known worldwide in similar technological processes, the paper proposes a fast, economical and clean unconventional technique (microwave irradiation), applied to a very small extent in the industrial sector, although in the household it is a widely used process. The experiments carried out by the Daily Sourcing & Research Company on a 0.8 kW-microwave oven aimed at the manufacture of foam glass gravels with physical and mechanical characteristics almost similar to those industrially obtained by conventional methods, simultaneously demonstrating the superior energy efficiency of the technique of using microwave energy as an unconventional source. The products experimentally made had low thermal conductivity (between 0.057-0.063 W/ m·K), high compressive strength for this material type (up to 5.9 MPa) and very low pore size (below 0.9 mm). The specific energy consumption had values between 0.83-0.88 kWh/ kg comparable to those industrially achieved, but it should be considered that the use of a high power microwave equipment could improve the process efficiency by up to 25%.

The paper presents a recent application of the fast nonconventional microwave heating a fruit (honeydew melon) for removing the high moisture content (above 90 %) in order to preserving its qualities. The fruit was prepared as a paste in which a foaming agent (egg white) and a foam stabilizer (carboxymethyl cellulose) were inserted for obtaining an expanded product, facilitating the removal of water. By drying and fast heating the fruit, the required conditions for its preservation are achieved, keeping ß-carotene and C-vitamin unchanged. The microwave heating parameters were: product temperature between 190-250 ºC, heating and drying time between 1.50-2.41 min, heating rate between 95.4-113.3 ºC/min, water amount removed by vaporization between 14.8-15.3 g and energy consumption for the water vaporization between 4-6.2 W/min.

A high-strength porous aggregate for construction applications that require compression resistance and porosity has been experimentally made by direct microwave warming of residues from building demolition (clay brick and clear flat glass). Borax (4 wt. %) as a flux agent and silicon carbide (2 wt. %) as an expanding agent were incorporated into the starting mixture. Due to the high proportion of clay waste as an aluminum silicate material, the direct microwave warming was possible at very high warming rates (between 34-42.4 ºC/min) without affecting the structural homogeneity of the final product. The specific electricity consumption was extremely low (0.59-0.78 kWh/kg). The cellular glass features were: apparent specific gravity between 0.72-0.98 g/cm3, porosity between 50.3-65.7 %, heat conductivity in the range 0.161-0.197 W/m·K, compression resistance between 6.4-8.5 MPa, and pore size below 1.1 mm.

The paper presents experimental results obtained in the manufacturing process of porous high-strength glass foam for thermal insulation in buildings made of glass waste and kaolin clay as raw materials and dolomite as a foaming agent. The paper’s originality is the use of the unconventional microwave heating technique. The best product manufactured by this technique was that sintered at 1050 ºC using 18 wt.% kaolin clay and 3.5 wt.% dolomite. The product characteristics were: the apparent density of 0.66 g·cm-3, the thermal conductivity of 0.155 W/m·K, the compressive strength of 5.3 MPa and a microstructural homogeneity with pore size between 0.20-0.50 mm.

The paper presents an innovative technique for manufacturing glass foams from recycled glass waste at room temperature by using aluminum powder and an aqueous solution of calcium hydroxide. The physical, thermal, mechanical and morphological characteristics of the foamed products (porosity between 82.9-86.2%, thermal conductivity in the range 0.061-0.081 W/m·K and compressive strength between 1.15-1.28 MPa) were similar to those of the foams manufactured by sintering at high temperatures. Glass foams produced by this new technique are suitable for use as thermal insulation materials for buildings.

The first achieving in Romania of a self-aspirating burner using the nonconventional technique of burning in a porous inert media is presented in the paper. The originality of the work is the way of manufacturing the porous ceramic piece in the combustion zone of the burner by using the nonconventional method of producing a SiC ceramic foam by direct microwave heating. The main characteristics of the ceramic piece are: porosity of 36.8%, compressive strength of 58 MPa and operating temperature of 1430 ºC. The burner was made for operation with natural gas with a nominal thermal power of 20 kW. The concentration of pollutants emitted into the atmosphere is low: CO below 120 mg/m3N and NOx below 1.03 mg/m3N.

The paper presents results of the manufacturing process of a porous high-strength glass-ceramic foam using colorless glass waste (between 35.5-50.0%) and coal fly ash (between 24.6-35.5%) as raw materials, sodium borate (between 25.0-28.0%) as a fluxing agent and calcium carbonate (between 0.4-1.0%) as a foaming agent. The heating technique was based on the conversion of microwave energy into heat, the sintering/foaming temperature varying between 802-815 ºC. The characteristics of the glass-ceramic foam samples were: apparent density between 0.38-0.45 g/cm3, porosity between 78.6-81.9%, thermal conductivity in the range 0.049-0.064 W/m·K, compressive strength between 2.5-6.0 MPa and pore size below 0.60 mm. The specific energy consumption had very low values (0.72-0.82 kWh/kg) confirming the high energy efficiency of the predominantly direct microwave heating technique.

A glass foam with typical characteristics for a foam glass gravel usable as a thermal insulating material in difficult climatic conditions and with mechanical stress was made by sintering at 834 ºC a powder mixture composed of colorless glass waste (93.1 wt.%), glycerol (1.0 wt.%), sodium silicate (4.8 wt.%), calcium carbonate (0.8 wt.%), kaolin (0.2 wt.%) and water addition (14.5 wt.%). The physical, thermal, mechanical and morphological characteristics of the product were: apparent density of 0.28 g/cm3, porosity of 86.67%, thermal conductivity of 0.063 W/m·K, compressive strength of 7.3 MPa, water absorption of 4.3% and pore size between 0.10-0.35 mm. The specific energy consumption of the manufacturing process was 0.78 kWh/kg. The originality of the work is the use of a nonconventional heating technique based on the microwave energy.

The paper presents experimental results obtained in the manufacturing process of high-strength glass foam by combined use of two solid foaming agents (calcium carbonate and graphite) in variable weight ratios. The originality of the work is applying the unconventional microwave heating method, unlike the conventional techniques currently used in similar industrial processes. The optimal experimental variant, composed of 89.1 % glass waste, 0.9% calcium carbonate, 1 % graphite and other additives, was sintered at 828 ºC with a very low energy consumption (0.73 kWh/kg). The main characteristics of the optimal product were apparent density of 0.39 g/cm3, thermal conductivity of 0.088 W/m·K and compressive strength of 3.6 MPa, being usable in fields that requires resistance to mechanical stress and relatively difficult environmental conditions.

The paper presents experimental results obtained in the manufacture of glass foams from packaging bottle glass waste, using the microwave energy. The glass foam as insulating material for construction is an advantageous alternative to existing building materials (e. g. expanded polystyrene) due to its superior resistance to mechanical stress, fire and humidity. The results have shown that the manufacturing techniques of glass foams in microwave field lead to products with physical, mechanical and morphological characteristics similar to those of industrial products made by conventional methods (low apparent density and low thermal conductivity, acceptable mechanical strength, closed pores). The advantages of applying microwave energy are eliminating pollution as well as reducing the specific consumption of energy. The originality of research conducted in the Romanian company Daily Sourcing & Research consists in the use of microwaves as an unconventional source of energy, worldwide only conventional heating methods being currently applied.

Another experimental application of the nonconventional microwave heating technique in the manufacturing process of a porous glass foam with high mechanical strength confirmed the high energy efficiency of this procedure compared to the conventional techniques. The specific energy consumption of the manufacturing process was very low (0.72-0.73 kWh/kg). Due to its physical, thermal, mechanical and microstructural characteristics (apparent density of 0.23-0.27 g/cm3, porosity of 87.7-89.5%, thermal conductivity of 0.063-0.070 W/m·K, compressive strength of 6.4-6.8 MPa and pore size between 0.2-0.6 mm) the product can enter in the foam glass gravel category usable as a thermal insulating material in construction in application fields that require mechanical, chemical and thermal shock resistance.

The paper presents results of research in the manufacturing domain of some glass foams with thermal insulating characteristics (apparent density of 0.50 g/cm3, porosity of 76.2% and thermal conductivity of 0.149 W/m·K) and with a very high compressive strength (16.6 MPa). The product was achieved by sintering at 853 ºC of a pressed mixture composed from 78.2% container glass waste, 1.0% sodium carbonate, 2.0% glycerol, 7.8% sodium silicate and 11.0% water. The adopted heating technique was the predominantly direct microwave heating in a 0.8 kW-microwave oven, which allowed to obtain a low specific energy consumption of 1.10 kWh/kg.

The paper presents experimental results of manufacturing in microwave field of heat insulating plates by expanding a powder mixture of glass waste, coal ash, silicon carbide and water pressed into a mold with walls made of silicon carbide. The best variants corresponded to silicon carbide ratios of 2.9 and 3.0 wt.% and coal ash of 10 wt.%. The samples characteristics were almost similar to those industrially made by conventional methods: low apparent density (0.33-0.34 g/cm3), high compressive strength (1.7-1.9 MPa) and water absorption almost zero. The specific energy consumption had low values (1.01-1.04 kWh/kg), being comparable to that achieved by conventional techniques in the industrial production, although the conditions of small-scale experiments were obviously disadvantageous.

The paper presents experimental results obtained in the manufacturing process of a glass foam with good characteristics of insulating material (porosity of 90%, thermal conductivity of 0.042 W/m·K and compressive strength of 2.1 MPa) usable in construction. The basic raw material was recycled panel glass from cathode ray tube (CRT) waste. The heating technique was unconventional by using the microwave energy unlike the conventional techniques applied both in the industrial glass foam manufacture and in the numerous small-scale experiments known in the literature. The tests have shown an excellent energy efficiency, the specific energy consumption (0.72 kWh/kg) being more economical than that corresponding to the industrial manufacturing processes of glass foam.

The paper presents experimental results of the manufacture by a microwave heating technique of a fine porosity lightweight glass foam with high compression strength (up to 5.8 MPa) using a liquid carbonic foaming agent (glycerol) associated with "water glass" and water. The advantage of using the microwave irradiation was evidenced by the very low specific energy consumption (0.81-0.88 kWh/ kg) at the level of the lowest consumption obtained in industrial production by conventional techniques of similar products. Considering that a high power microwave equipment (industrial type) could have a higher energy efficiency (up to 25%) compared to the experimental oven, the superiority of the tested nonconventional method is theoretically obvious.

The paper presents recent achievements in the microwave use for manufacturing foam glass gravel from recycled glass waste and silicon carbide. The aim was to obtain a product with physical and mechanical characteristics almost similar to those of industrially manufactured materials by conventional heating techniques, but with a higher energy efficiency. A foam glass with the thermal conductivity of 0.075 W/m·K and the compressive strength of 7.5 MPa was experimentally obtained. The specific energy consumption was of 1.0 kWh/kg comparable with the industrial processes and it could reach values up to 25% lower by using a high power industrial microwave equipment.

The paper presents an unconventional technique for manufacturing foam glass gravel. The numerous experimental results obtained by the authors in the last year using various manufacturing recipes common in the world industrial production by conventional techniques were selected and subjected to a qualitative and energy efficiency comparative analysis, aiming to determine the best foam glass gravel manufacturing procedure under the conditions of the use of the microwave energy. The optimum recipe was composed of 83% glass waste, 1 % glycerol, 8 % sodium silicate and 8 % water. The maximum heating temperature reached 823 ºC with a very economical energy consumption of 0.88 kWh/kg. The sample characteristics were apparent density-0.24 g/cm3, porosity-89.1% with pore size between 0.3 - 0.6 mm, thermal conductivity-0.063 W/m·K and compressive strength - 5.9 MPa, almost similar to those industrially obtained.

The paper presents the results of the research for the production by a nonconventional method (using microwave irradiation) of a cellular glass with high mechanical strength from flat glass waste (86 – 95%), calcium carbonate (1%) as a foaming agent and an addition of sodium silicate also called “water glass” (4 – 13%). The cellular glass samples had the apparent density between 0.40 – 0.45 g/ cm3, the thermal conductivity in the range 0.076 – 0.081 W/ m·K and the compressive strength between 4.9 – 6.2 MPa, having the characteristics of a foam glass gravel industrially manufactured by conventional methods and used in construction as materials resistant to high mechanical loads. The morphological characteristic specific for the thermal insulating materials, i.e. a homogeneous distribution of the pores, have been fulfilled, even in case of using a raw material (flat glass waste) which is, generally, avoided because it causes structural inhomogeneity of the glass foam. The energy efficiency of the making process is remarkable, the specific energy consumption having low values between 1.13 – 1.19 kWh/ kg.

The paper presents results of the research of manufacturing silicon carbide ceramic foam applying the microwave energy as a power source for the heat treatment at very high temperature (up to 1610 ºC). On the other hand, aluminosilicate waste (clay recovered from recycled brick from building demolition as well as coal fly ash) as silica suppliers, has been used to replace some materials such as quartz or sand, with very high silica content. The obtained product had a very high compressive strength (up to 58 MPa), but the porosity had lower values than those obtained from the commonly used raw material. The most important characteristic of the ceramic foam obtained by the nonconventional method is the extremely low specific energy consumption (maximum 1.42 kWh / kg) required for sintering the raw material at very high temperature, with at least 50% lower than the values obtained by the conventional methods.

The results of the research in the field of microwave energy application in the process of manufacturing foam glass gravel from colored glass waste, calcium carbonate as a foaming agent, borax as a fluxing agent and sodium silicate solution as a binder are presented in the paper. The thermal process of sintering/ foaming the powder mixture was carried out in a 0.8 kW-domestic microwave oven adapted for high temperature operation. The foamed product at 845 ºC, with 1.5% calcium carbonate, 7% borax and 8% sodium silicate, reached the highest value of compressive strength (9.5 MPa), thermal conductivity 0.105 W/ m·k, apparent density 0.80 g/ cm3 and a homogeneous distribution of pores in the material structure with dimensions below 1 mm.

The paper presents the results of experimental research for manufacture a high mechanical strength thermal insulating material using the microwave energy. Clay brick waste (75 - 83 mass %) and coal ash (15 - 23 mass %) as raw material and silicon carbide (2%) as a foaming agent have been used as a powder mixture. The porous product obtained by a sintering/ foaming process at 1115 - 1145 ºC had relatively low density and thermal conductivity (0.50 - 0.68 g/cm3 and 0.078 - 0.095 W/mK, respectively) and high compressive strength (up to 7.5 MPa). This remarkable combination of some physical and mechanical characteristics of the insulating material allows its use in applications involving mechanical stress resistance.

The paper presents experimental results obtained in the process of making glass foam from glass waste using a cheap foaming agent (natural dolomite). The originality of the work is the application of the microwave energy, unlike the conventional techniques commonly used in the world. The main advantage highlighted by the experiments is the very low specific energy consumption (below 1.5 kWh/kg), due to the peculiarities of the microwave heating technique. The foamed product has physical, mechanical and morphological characteristics (density between 0.30-0.32 g/cm3, thermal conductivity between 0.064-0.067 W/m·K, compressive strength in the range 2.2-2.6 MPa), which are similar to those of foams made by conventional methods and are suitable for its use as insulating material in construction.

The paper presents an aluminum foam experimental technique using the microwave energy. The raw material was recycling aluminum waste processed by ecological melting and gas atomizing to obtain the fine powder required in the foaming process. The powder mixture was completed with dolomite as a foaming agent. The products had a fine and homogeneous porous structure (pore size between 0.4-0.9 mm). The density (1.17-1.19 g/cm3), the compressive strength (6.83-7.01 MPa) and the thermal conductivity (5.71-5.84 W/m·K) had values almost similar to the foams made by conventional methods.

The paper contains testing results of an intensification method of the remarkable microwave absorbing capacity of a silicon carbide crucible coated with a yttrium oxide layer, applied in the sintering/ foaming process of the glass waste. Using the same type of microwave oven and same composition of raw material and foaming agent as in previous tests, the functional parameters of the process were significantly enhanced without altering the characteristics of products made by known conventional and nonconventional techniques.

The use of microwaves as a nonconventional energy source in the manufacturing process of glass-ceramic foam is presented in the paper. The main raw materials, representing 88wt.% of the load, are bottle glass waste and old clay brick waste, available in very large quantities. The weight ratio of the two waste types was varied between 3/1 – 3/2, aiming the improvement of the glass-ceramic foam mechanical strength. Substituting 40% from the glass waste mass with clay waste, it was obtained a high compressive strength of 3.35 MPa, in conditions where the apparent density and the thermal conductivity had relative low values (0.78 g/ cm3 and 0.099 W/ m · K, respectively). Due to his physical, mechanical and morphological features, the foamed product is usable in construction as replacer of similar materials existing on the market.

The work refers to an innovative recycling solution of wastes from demolition and rehabilitation of buildings to produce more cost-effective lightweight aggregates. The adopted method is based on the use of microwave energy as a nonconventional source, replacing conventional energy sources and expanding the powder mixture of raw material with silicon carbide as a foaming agent. The final product has a porous structure and a high compressive strength (over 6 MPa), being suitable for use as a lightweight aggregate for concrete manufacture.

In the work experimental results on the manufacture of glass foam with high mechanical strength from glass waste are presented. By replacing the usual conventional energy source with a nonconventional energy (electromagnetic waves) the heating efficiency allows a fast and economical manufacturing process. Calcium carbonate as a foaming agent and an addition of sodium silicate (aqueous solution) as a binder were used. By their physico-mechanical and morphological features (0.40-0.66 g/ cm3 the apparent density, 0.054-0113 W/ m·K the thermal conductivity, 2.2-6.3 MPa the compressive strength, below 1.2 % the water absorption and under 2 mm the pore size), the foams are appropriate for their use as replacer of existing similar building materials on the market.

The paper presents experimental results of producing glass foam from borosilicate glass waste (laboratory ware) using the microwave energy. More variants of foaming agents (silicon carbide, calcium carbonate and activated carbon) and additives (coal ash and disodium phosphate) were tested in the Romanian company Daily Sourcing & Research. The glass foams have characteristics specific to those made of borosilicate glass waste by conventional heating, i. e. relatively low apparent density (0.34 – 0.47 g/ cm3), but higher than those resulting from soda-lime glass waste and compressive strength (1.5 – 2.5 MPa) higher than theirs. As glass foams mainly made of soda-lime glass waste, and those made of borosilicate glass waste are suitable for use as insulating material in construction.

The paper presents results of research conducted by the Romanian company Daily Sourcing & Research on the use of microwave energy in the manufacture process of glass foams. Compared to similar products manufactured by conventional heating techniques, the physical, mechanical and morphological features of the experimental samples are close and meet the requirements for materials used as thermal insulators. The apparent densities and thermal conductivities are low (0.16 – 0.24 g/ cm3 and respectively 0.037 – 0.043 W/ m · K) and the compressive strength has acceptable values (1.14 – 1.25 MPa). The manufacturing technique of glass foam in microwave field, in experimental stage in the Romanian company Daily Sourcing & Research, has already confirmed its effectiveness in numerous tests conducted in the last two years.

Results of the research conducted by the Romanian company Daily Sourcing & Research Bucharest to obtain glass foams from clear flat glass waste with good macrostructural homogeneity are presented in the paper. The favourable influence of the microwave heating was proved experimentally on a 0.8 kW-microwave oven. The most significant achievement was obtaining good macrostructural homogeneity, which is difficult to obtain under conditions of conventional heating methods. The pores of the samples are uniformly distributed and their size varies between 0.6 - 2 mm (foaming with calcium carbonate) and 0.9 - 3 mm (foaming with silicon carbide).

Experimental results obtained in the process of manufacturing dense glass foam using the microwave energy are presented in the work. The glass foam is produced from bottle glass waste, calcium carbonate as foaming agent and borax as fluxing agent. The high compressive strength (2.5 - 6.2 MPa) is the main mechanical feature of this product, which together with other physical and morphological features (apparent density 0.60 – 0.90 g/cm3, porosity 59.1 – 72.7%, thermal conductivity 0.081 – 0.105 W m K, water absorption 0.5 – 1.0%, pore size 0.5 – 3 mm), are appropriate for using as a substitute for similar building materials existing on the market.

The paper presents experimental results obtained by a team of researchers from the company Daily Sourcing & Research SRL Bucharest in the field of producing the foamed glass-ceramic from waste bottle glass, coal ash and silicon carbide as foaming agent. The originality of the experiments consists in the use of electricity or microwave energy, unlike all techniques known worldwide consumers of fossil fuel. The product, obtained with low energy consumptions and very low pollutants emissions, has physical and mechanical characteristics of an insulating material, i.e. high porosity, low thermal conductivity and an adequate compressive strength.