Abstract: Manufacturing lightweight aggregate (LWA) by a sintering technique requires a delicate balance among three conditions: forming sufficient amount of molten liquid phase during sintering; reaching an appropriate viscosity for solid-liquid suspension; and emitting sufficient amount of gas that can be entrapped by the liquid phase to form pores. LWAs were made from low-calcium and high-calcium Waste Coal Combustion Ash (W-CCA) including fly ash and bottom ash. A mass fraction of at least 40% liquid phase for fly ash and 50% for bottom ash is required for a successful entrapment of emitted gaseous phases during sintering. Larger pores were observed in the microstructure of LWA samples made using high-calcium W-CCA in comparison to low-calcium W-CCA. This result was mainly attributed to the high-calcium samples forming liquid phases with lower viscosity values and emitting higher amounts of gaseous phase during sintering than did the low-calcium samples.

Abstract: During lightweight aggregate (LWA) production through sintering process, formation of liquid phase captures emitted gas to form pores in the LWA and leads to successful bloating. As the LWA undergoes sintering in the kiln, the liquid phase starts to form on the LWA surface. Accordingly, in a rotary kiln where the LWA are continually rolling over each other, the touching surfaces of LWAs with liquid phase start to adhere together and form lumps of LWA exiting the furnace. This method prevents agglomeration of spherical LWA during sintering. The LWA can be produced from clay, slate, shale, and potentially other waste materials. This method results in production of discrete spherical LWA particles that can be coated with waste fly ash particles to form a thin layer on the surface of LWA that will not melt during sintering and will prevent touching surfaces of LWA particles from sticking together and forming lumps.

Abstract: Off-spec fly ash-based spherical lightweight aggregate (LWA), designated SPoRA, was manufactured and its engineering properties, including specific gravity, dry rodded unit weight, water absorption, mechanical performance, and pore structure, were evaluated. Using the characterized SPoRA, lightweight concrete (LWC) samples were made and properties of the LWC were assessed and compared with samples made using the traditional LWA. The results indicated that fine and coarse SPoRA had 72 h absorption capacities of 16.4% and 20.9%, respectively, which were higher than that of traditional LWA. SPoRA had a saturated surface dry (SSD) specific gravity higher than traditional LWA, which resulted in higher fresh density for the LWC prepared with SPoRA. Large spherical type pores were found for SPoRA similar to the traditional slate-based LWA. The pore size distribution of SPoRA, characterized using a dynamic vapor sorption analyzer, indicated that more than 97% of the pores had pore diameters greater than 50 nm.

Abstract: Manufacturing lightweight aggregate (LWA) by a sintering technique requires a delicate balance among three conditions: forming sufficient amount of molten liquid phase during sintering; reaching an appropriate viscosity for solid-liquid suspension; and emitting sufficient amount of gas that can be entrapped by the liquid phase to form pores. LWAs were made from low-calcium and high-calcium Waste Coal Combustion Ash (W-CCA) including fly ash and bottom ash. A mass fraction of at least 40% liquid phase for fly ash and 50% for bottom ash is required for a successful entrapment of emitted gaseous phases during sintering. Larger pores were observed in the microstructure of LWA samples made using high-calcium W-CCA in comparison to low-calcium W-CCA. This result was mainly attributed to the high-calcium samples forming liquid phases with lower viscosity values and emitting higher amounts of gaseous phase during sintering than did the low-calcium samples.

Abstract: Off-spec fly ash-based spherical lightweight aggregate (LWA), designated SPoRA, was manufactured and its engineering properties, including specific gravity, dry rodded unit weight, water absorption, mechanical performance, and pore structure, were evaluated. Using the characterized SPoRA, lightweight concrete (LWC) samples were made and properties of the LWC were assessed and compared with samples made using the traditional LWA. The results indicated that fine and coarse SPoRA had 72 h absorption capacities of 16.4% and 20.9%, respectively, which were higher than that of traditional LWA. SPoRA had a saturated surface dry (SSD) specific gravity higher than traditional LWA, which resulted in higher fresh density for the LWC prepared with SPoRA. Large spherical type pores were found for SPoRA similar to the traditional slate-based LWA. The pore size distribution of SPoRA, characterized using a dynamic vapor sorption analyzer, indicated that more than 97% of the pores had pore diameters greater than 50 nm.

Abstract: Manufacturing lightweight aggregate (LWA) by a sintering technique requires a delicate balance among three conditions: forming sufficient amount of molten liquid phase during sintering; reaching an appropriate viscosity for solid-liquid suspension; and emitting sufficient amount of gas that can be entrapped by the liquid phase to form pores. LWAs were made from low-calcium and high-calcium Waste Coal Combustion Ash (W-CCA) including fly ash and bottom ash. A mass fraction of at least 40% liquid phase for fly ash and 50% for bottom ash is required for a successful entrapment of emitted gaseous phases during sintering. Larger pores were observed in the microstructure of LWA samples made using high-calcium W-CCA in comparison to low-calcium W-CCA. This result was mainly attributed to the high-calcium samples forming liquid phases with lower viscosity values and emitting higher amounts of gaseous phase during sintering than did the low-calcium samples.

Abstract: Manufacturing lightweight aggregate (LWA) by a sintering technique requires a delicate balance among three conditions: forming sufficient amount of molten liquid phase during sintering; reaching an appropriate viscosity for solid-liquid suspension; and emitting sufficient amount of gas that can be entrapped by the liquid phase to form pores. LWAs were made from low-calcium and high-calcium Waste Coal Combustion Ash (W-CCA) including fly ash and bottom ash. A mass fraction of at least 40% liquid phase for fly ash and 50% for bottom ash is required for a successful entrapment of emitted gaseous phases during sintering. Larger pores were observed in the microstructure of LWA samples made using high-calcium W-CCA in comparison to low-calcium W-CCA. This result was mainly attributed to the high-calcium samples forming liquid phases with lower viscosity values and emitting higher amounts of gaseous phase during sintering than did the low-calcium samples.