Development of natural fibre yarn-reinforced cement composites under enforced carbonation conditions
File(s)
Author(s)
Zhuge, Yixiu
Type
Thesis or dissertation
Abstract
Enforced carbonation can increase early-age strength and CO₂ uptake in cement-based materials, but its effectiveness is limited by restricted CO₂ transport into the interior. This thesis investigates whether placed natural fibre yarns can enhance CO₂ ingress, carbonation extent, and CO₂ uptake while maintaining acceptable mechanical performance.
A phenolphthalein-based image analysis method was developed to quantify heterogeneous carbonation at defined depths and linked to thermogravimetric measurements of CO₂ uptake. It was applied to single-yarn cement paste specimens containing different natural yarns, followed by mechanistic studies of jute yarns with controlled moisture states and surface treatments. The study was extended to multi-yarn paste and mortar systems containing yarn meshes, with compressive strength and sorptivity assessed under different post-curing regimes.
Under enforced carbonation (20 vol.% CO₂, 25 ± 0.5 °C, and 64 ± 2% RH), all natural yarns increased CO₂ uptake relative to fibre-free paste, with bast fibres producing the strongest effect. After seven days, hemp increased depth-averaged CO₂ uptake from 5.64 to 8.19 wt.% and enabled measurable uptake at 50 mm depth after one day. Carbonation was governed by moisture retention, pore connectivity, and interfacial transport. Pre-saturation increased carbonation, whereas epoxy sealing strongly reduced it. Across yarns and treatments, 24-hour water absorption was the strongest predictor of effective carbonation radius, typically 2–3 mm at 10 mm depth.
Bulk hydration was only marginally affected, confirming that enhanced carbonation arose mainly from yarn-assisted transport. Although increasing fibre content reduced compressive strength, a single-layer mesh with 5 mm spacing provided a practical balance. At mortar scale, saturated jute yarn meshes performed better than dispersed fibres at the same replacement level. Seven-day carbonation followed by air curing produced the highest strength. Overall, placed natural fibre yarns can form controlled internal transport networks that enhance carbonation and CO₂ uptake, although their long-term durability requires further study.
A phenolphthalein-based image analysis method was developed to quantify heterogeneous carbonation at defined depths and linked to thermogravimetric measurements of CO₂ uptake. It was applied to single-yarn cement paste specimens containing different natural yarns, followed by mechanistic studies of jute yarns with controlled moisture states and surface treatments. The study was extended to multi-yarn paste and mortar systems containing yarn meshes, with compressive strength and sorptivity assessed under different post-curing regimes.
Under enforced carbonation (20 vol.% CO₂, 25 ± 0.5 °C, and 64 ± 2% RH), all natural yarns increased CO₂ uptake relative to fibre-free paste, with bast fibres producing the strongest effect. After seven days, hemp increased depth-averaged CO₂ uptake from 5.64 to 8.19 wt.% and enabled measurable uptake at 50 mm depth after one day. Carbonation was governed by moisture retention, pore connectivity, and interfacial transport. Pre-saturation increased carbonation, whereas epoxy sealing strongly reduced it. Across yarns and treatments, 24-hour water absorption was the strongest predictor of effective carbonation radius, typically 2–3 mm at 10 mm depth.
Bulk hydration was only marginally affected, confirming that enhanced carbonation arose mainly from yarn-assisted transport. Although increasing fibre content reduced compressive strength, a single-layer mesh with 5 mm spacing provided a practical balance. At mortar scale, saturated jute yarn meshes performed better than dispersed fibres at the same replacement level. Seven-day carbonation followed by air curing produced the highest strength. Overall, placed natural fibre yarns can form controlled internal transport networks that enhance carbonation and CO₂ uptake, although their long-term durability requires further study.
Version
Open Access
Date Issued
2026-01-09
Date Awarded
2026-09-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Myers, Rupert
Wong, Hong
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/R010161/1
EP/R017727/1
EP/Y001370/1
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)