Drexel University

Yaghoob Farnam

Mohammad Balapour

Yick Grace Hsuan

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. The gaseous phase was generated by hematite reduction and anhydrite decomposition.

Lightweight aggregates produced from waste-coal combustion ash

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.

Growing community of inventors

Philadelphia, PA, United States of America

Yaghoob Farnam