Project Information

Link To Latest Report : Coming Soon

Background :

Biochar additions to concrete binder have shown great promise for enhancing the early-age performance of material for bridge applications, including its hardening rate and strength development. Biochar is a waste product of the pyrolysis of organic material (wood, rice husks, corn husks, manure, or other agricultural waste products) [Spokas 2020]. Depending on the source [Maljaee 2021], biochar is highly porous, with specific 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 may promote self-healing of the material via secondary mineralization involving 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).

Objective :

The objective is to advance the TRL of 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 secondary mineral formation 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. These ranges for the experimental variables are tentative and may be adjusted based on preliminary results to achieve the maximum amount of useable data. 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 Secondary Mineralization.

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. Secondary mineralization will be measured both by thermogravimetric analysis and by the standard phenolphthalein spray method.

Research Team:
Principal Investigator: Jeffrey W. Bullard, Ph.D.
Co-Principal Investigator: Yong-Rak Kim, Ph.D.