Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

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

Published

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

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 April 19, 2024)
Created September 19, 2022, Updated February 8, 2023