Abstract
The widespread adoption of Portland Limestone Cement (PLC) in U.S. concrete production has necessitated research into commercially available supplementary cementitious materials (SCMs) for formulating high-performance, low-carbon blended binders with PLC. This study investigated the influence of biochar (BC) in biochar-PLC composites (CBCs), focusing on hydration kinetics, microstructure, rheology, pore-solution chemistry, compressive strength, and the underlying mechanisms. Biochar was produced via downdraft gasification at 850 °C and incorporated into PLC at 5, 7, and 10% substitution by mass. Isothermal calorimetry and hydration data modeled using the Knudsen equation revealed that BC retarded early hydration but improved hydration degree and later-age heat evolution, as evidenced by increased end-of-induction periods (t0: 1.56, 2.29, 2.60, and 3.40 h) and heat flow rate at maximum acceleration (Q̇m: 3.12, 3.26, 3.33, and 3.43 mW/gcement) for PLC, CBC5, CBC7, and CBC10, respectively. Microstructural analyses (XRD, TGA/DTG, FTIR, SEM-EDS) demonstrated that BC promoted secondary reactions and enriched hydration products, resulting in a denser matrix in CBCs. Additionally, BC increased the static yield stress build-up rate (Athix) from 11.1 Pa/min in PLC to 17.0 Pa/min in CBC7 and slightly increased the apparent thixotropic index from 1.93±0.05 to 2.07±0.09. The 7% BC substitution (CBC7) was identified as the optimal dosage, increasing the 28-day compressive strength by 8.5%. The performance mechanisms of BC are mediated by modifications in hydration kinetics, filler effects, and later-age pozzolanic reactions. This work demonstrates the viability of a higher-level biochar (5–10%) replacement in PLC and provides a foundation for advancing its inclusion in sustainable SCM-PLC formulations.
Recommended Citation
U. Ewuzie et al., "Investigation of Portland Limestone Cement Blended With Biochar From Downdraft Gasification: Hydration Kinetics, Microstructure, Rheology, and Performance Mechanisms," Construction and Building Materials, vol. 526, article no. 146426, Elsevier, Jun 2026.
The definitive version is available at https://doi.org/10.1016/j.conbuildmat.2026.146426
Department(s)
Chemical and Biochemical Engineering
Publication Status
Full Text Access
Keywords and Phrases
Biochar; Higher biochar dosage; Hydration kinetics; Microstructure; Portland limestone cement; Rheology
International Standard Serial Number (ISSN)
0950-0618
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2026 Elsevier, All rights reserved.
Publication Date
06 Jun 2026
Included in
Chemical Engineering Commons, Civil and Environmental Engineering Commons, Materials Chemistry Commons, Materials Science and Engineering Commons
