High-Volume Carbon Sequestration for Controlled Low- Strength Materials

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Title: High-Volume Carbon Sequestration for Controlled Low- Strength Materials

Author(s): Wei Cheng, John R. Elliott, and Kenneth C. Hover

Publication: Materials Journal

Volume: 116

Issue: 4

Appears on pages(s): 235-244

Keywords: biochar; carbon sequestration; controlled low-strength materials; lightweight fine aggregate; mortar; sustainability

Date: 7/1/2019

Abstract:
Crushed charcoal (biochar) was introduced into mortar as lightweight, high-carbon fine aggregate, at eight levels of sand replacement varying from 0 to 100% and up to 275% of cement content by mass. Carbon encapsulated in hardened mortar offset the carbon footprint of cement production and reduced demand for natural sand. Water content was increased to accommodate 125% biochar absorption and maintain workability. Mixture proportions affected water-cement ratio (w/c), fresh density, and compressive and splitting tensile strength of hardened mortar, with significantly diminished strength at increased biochar content. A net carbon benefit accrued when biochar content exceeded approximately 10% of the total aggregate mass or one-third of the cement mass. At this level, compressive strength is less than typically associated with structural concrete, but net sequestration of 800 kg carbon per m3 (1350 lb/yd3) could be realized at strength levels associated with controlled low-strength materials (CLSM). Multiple environmentally effective applications are suggested.