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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 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%.

Experimental results of manufacturing the cellular glass from container glass waste using an unconventional heat treatment technique (microwave energy) are presented in the paper. The cellular glass has physical, mechanical and morphological characteristics suitable for using as an insulating material in construction constituting an alternative for existing building materials. By comparison with these materials, the cellular glass has a higher resistance to mechanical stress, fire, humidity, attack of rodents, insects, bacteria, etc. The apparent density and thermal conductivity of the product are low (below 0.34 g/ cm3 and 0.062 W/ m·K, respectively), the compressive strength is acceptable (over 1.2 MPa) and the material structure is homogeneous with closed pores evenly distributed. The originality of the manufacturing technique of cellular glass presented in the paper is the use of microwave energy, unlike the conventional methods currently applied in the world. The advantages of the use of this unconventional technique are the low specific energy consumption (around 1 kWh / kg) and its non-polluting character.

The experimental results of the manufacturing process of foam glass gravel using recycled glass waste (in very high ratio) are presented in the paper. The technique used for heating at 815-837 ºC of the raw material, composed of a powder mixture of glass, calcium carbonate (between 3-5%) as a foaming agent and borax (between 4.5-5.3%) as a fluxing agent, is unconventional based on microwave irradiation. The main physical, mechanical and morphological characteristics of the glass foam (low thermal conductivity between 0.087-0.110 W/ m•K, very high compressive strength up to 6.3 MPa, practically zero water absorption, pore size between 0.7-1.7 mm), similar to those industrially manufactured by conventional methods, are suitable for load-bearing thermal insulation under foundations or floorings, for insulation around the perimeter of buildings, underground heating pipes, underground tanks, as well as a filling material in the structure of road and railway constructions.

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.