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Investigations into the effects of biochar on the strength development of cementitious systems
Hylton, Julia
Hylton, Julia
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2025
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2026-05-11
Abstract
Mitigating the embodied carbon in concrete is an urgent task with few options that can meet the scale of the industry. Biochar, a renewable and carbon-negative material, is emerging as a promising additive in cementitious systems. However, large-scale adoption requires fundamental understanding of how biochar influences compressive strength development. This thesis provides critical insights into these mechanisms, paving the way for optimized biochar use in cementitious materials.
By characterizing the physical and chemical properties of 16 distinct biochars, this research identifies three key factors—initial saturation, oxygen-to-carbon atomic ratio, and soluble silicon content—that account for over 75% of the variation in mortar compressive strength. These findings provide a pathway to strategically engineering biochar for enhanced performance, enabling greater cement replacement and directly mitigating CO2 emissions from cement production.
A novel analytical method using hyphenated TG-IR was developed to quantify the progression of the cement hydration reaction in the presence of biochar. This technique surpasses conventional TGA-only methods by accurately deconvoluting gas evolution, distinguishing the decomposition of organics from the decomposition of hydration products. By offering a precise method to track hydration in complex cement systems, this innovation equips researchers with the tools needed to keep pace with emerging cement additives.
Finally, this work demonstrates that biochar significantly reduces interparticle spacing in fresh cement mixes, increasing shear forces on cement grains and accelerating hydration. When biochar is pre-saturated with a portion of the mix water, these effects are amplified, leading to higher early-age strength without compromising long-term hydration.
By establishing the link between biochar properties, cement hydration, and strength development, this thesis advances the scientific foundation for biochar’s integration into concrete, bringing the industry closer to scalable, carbon-neutral construction materials.
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