Engineering properties and pore structure of lightweight aggregates produced from off-spec fly ash

Published

September 19, 2022

Author(s)

Edward Garboczi, Mohammad Balapour, Thiha Thway, Grace Hsuan, Yaghoob Farnam, Newell Moser

Abstract

This study characterizes the engineering properties of lightweight aggregate (LWA) manufactured from low calcium (F-FA) and high calcium (C-FA) waste fly ash that were designed using a previously-developed thermodynamics-guided process. LWA properties that were characterized include specific gravity, vacuum absorption, water absorption over time, water desorption, porosity, pore size distribution, and permeability. The LWA studied had a low oven dry specific gravity ranging from 1.22 to 1.45. The vacuum absorption and total open porosity of F-FA LWA decreased as the fluxing agent (NaOH) concentration increased while the values for C-FA LWA exhibited some random variations with increasing amounts of fluxing agent. All LWA passed the ASTM C1761 requirements for application to the internal curing of concrete, which are: greater than 5 % water absorption (by mass) over 72 h and release of more than 85 % (by mass) of the absorbed water at 94 % relative humidity. X-ray computed tomography (XCT) and dynamic vapor sorption analyzer (DVSA) techniques were used to characterize the LWA pore structure. It was found that for F-FA LWA the normalized porosity, counting only pores smaller than 50 nm (gelpores + mesopores), ranged from 4 % to 11.5 %, while for C-FA LWA, this same pore size range had porosity ranging from 1.7 % to 2.8 %. Pore size distribution measurements of F-FA LWA using XCT showed that the pores became larger and the predicted permeability coefficient increased as the fluxing agent concentration increased. For C-FA LWA, the predicted permeability increased with increasing NaOH concentration. Since the pore size distribution had random variations and did not follow a specific increasing trend, the increase in C-FA permeability could only be due to an increase in pore connectivity.

Citation

Construction and Building Materials

Volume

348

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.conbuildmat.2022.128645

Local Download

Keywords

Waste fly ash, lightweight aggregate, sorption properties, pore size distribution, X-ray computed tomography

Citation

Garboczi, E. , Balapour, M. , Thway, T. , Hsuan, G. , Farnam, Y. and Moser, N. (2022), Engineering properties and pore structure of lightweight aggregates produced from off-spec fly ash, Construction and Building Materials, [online], https://doi.org/10.1016/j.conbuildmat.2022.128645, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933015 (Accessed October 8, 2025)