Link To Latest Report : Coming Soon.
Background :
Two main strategies have emerged toward low-carbon concrete. One of these is a “back-end” loading of concrete with CO2, either absorbed passively from the environment during its service live or actively injected from stored CO2. Either way, the absorbed CO2 is eventually locked chemically within the concrete in the form of carbonate minerals such as calcite, or magnesite, or hydrotalcite. The second strategy focuses on the “front end” of concrete production by replacing as portion of portland cement with pozzolanic waste material from other industrial or societal activities.Biochar additions bridge both these approaches. It is a waste product of combustion of organic material (wood, rice husks, corn husks, manure, or other agricultural waste products) [Spokas 2020]. Depending on the source [Tan 2021; Maljaee 2021; Gupta 2017], biochar is highly porous, with CO2-accessible surface areas of ~300 m2/g, porosities up to 50 %, and pore sizes down to several nanometers. With high ash content biochar is pozzolanically active. It also efficiently absorbs CO2 and thereby promotes carbonate mineralization with dissolved alkali earths such as calcium. In cement, milled fast-pyrolysis char has been used at up to 32 % replacement by mass with improved compressive strengths due to its role as an internal curing source and nucleating agent for calcium silicate hydrate gel (C-S-H) [Tan 2021; Pecha 2022].
Objective :
The objective is to advance the TRL of low-carbon biochar-infused concrete materials for implementation in bridge construction and repair. The approach to achieve that objective will be to determine the robustness of the material by investigating a wider range of w/c ratios, biochar dosages, and curing conditions for their effects on several important concrete properties, including the initial and final setting times, compressive strengths at 7 d, 28 d, and 90 d, and the carbon sequestration extent at 7 d, 28 d, and 90 d.
Scope :
Task 1 – Determine Range of Experimental Variables.
The most promising biochar from Cycle 1 research, in terms of its influence on strength and setting time, will be selected for this project. This high-silica biochar has already been characterized to obtain its chemical composition, porosity, absorption capacity, specific surface area and particle size distribution. The other materials for this project will be a Type I ordinary portland cement and a common silica sand for the fine aggregate. We intend to examine water-cement mass ratios (w/c) of 0.35 and 0.45, which covers that used for most normal-strength concrete applications. Biochar dosages will be 5 % by mass (used in Cycle 1 research), 10 % by mass, and 20 % by mass replacement for portland cement. The mixtures will be prepared by standard mixing methods using either dry or pre-saturated biochar— keeping the total water content constant—and will be cured under saturated or moisture-sealed conditions. In each case, three replicates will be cured in ambient air and three will be cured in air with 5 % CO2 by mass (so-called carbon curing). These ranges for the experimental variables are tentative and may be adjusted based on preliminary results to achieve the maximum amount of useable data.
Task 2 – Determine Influence of Experimental Variables on Setting Time, Compressive Strength, and carbonation.
. The standard test method for initial and final setting times by the Vicat apparatus (ASTM C191) will be employed on each of the mixtures. The compressive strengths of mortars made from the biochar-infused mortar cubes will be measured according to the ASTM C109 standard test method. Strength measurements will be made at 7 d, 28 d, and 90 d for a total of 75 strength measurements. Carbonation extent will be measured both by thermogravimetric analysis and by the standard phenolphthalein spray measurement to determine carbonation depth.
Research Team:
Principal Investigator: Jeffrey W. Bullard, Ph.D.
Co-Principal Investigator: Yong-Rak Kim