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Browsing by Author "Fang, Yi"

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    Bio-Based Admixture (Black Tea Extraction) for Better Performance of Metakaolin Blended Cement Mortars
    (MDPI, 2022) Fang, Yi; Wang, Jialai; Wang, Xiaodong; Do Amaral, Monica Lages; Kniffin, Hannah; Reed, Miranda; Wang, Liang; Qian, Xin; University of Alabama Tuscaloosa; Anhui University of Science & Technology; Tongji University
    With high pozzolanic reactivity, metakaolin (MK) is a popular supplementary cementitious material (SCM), which can be used to partially replace Portland cement in concretes. Due to its small particle size, however, MK can agglomerate, resulting in a nonuniform matrix and underperformance of the produced concrete. To address this issue, this paper exploits a low-cost, bio-based admixture-black tea extract (BTE)-to replace the traditional petroleum-based chemical admixture to enhance the dispersion and workability of MK blended cement mortars. Major biomolecules in the BTE such as caffeine, catechin, theanine, and theaflavin are rich in polyphenol, hydroxyl, and carboxylic acid groups, which can interact with cement particles and have profound effects on the hydration process and microstructure of the hydration products. Experimental studies showed that BTE does improve the workability of the MK blended cement mortar. More importantly, the BTE introduces significant change on the microstructure of the hardened pastes. Both the pores with size less than 50 nm and the total porosity of the hardened paste were significantly reduced, leading to a significant improvement in the micro- and macro-mechanical properties of the hardened paste. Experimental results suggest that up to 35% greater improvement in the compressive strength at 28 days was achieved using the proposed bio-admixture. Economic and environmental advantages of using the BTE as a renewable admixture were also illustrated through analyzing the cost-benefit, embodied carbon, and eco-efficiency of the MK blended mortars.
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    Low-cost, ubiquitous biomolecule as next generation, sustainable admixture to enhance the performance of ordinary portland cement-based concretes
    (University of Alabama Libraries, 2021) Fang, Yi; Wang, Jialai; University of Alabama Tuscaloosa
    The production of ordinary Portland cement (OPC) is highly energy-intensive and responsible for approximately 6% of anthropogenic greenhouse gas emissions. To reduce the carbon footprint of OPC based concrete, this research proposes to use a low-cost, ubiquitous, naturally occurring compound, tannic acid (TA) as a small-dose additive to significantly enhance the strength of OPC based concrete.This study is inspired by biosystems’ protein-based materials, which generally exhibit superior strength and toughness owing to their hierarchical structures via hydrogen-bonding assembly. With abundant reactive terminal phenolic hydroxyl groups, TA has an ability to complex or cross-link macromolecules sites through multiple interactions. Thus, TA can be used to complex or cross-link hydration products of cement at multi-binding sites so that the strength and durability of concrete can be significantly improved. A comprehensive research plan has been carried out to evaluate the potential of TA on performance enhancement of OPC-based concrete, understand how TA modifies the hydration of cement, mitigate the retardation of TA on cement’s hydration, and evaluate application potentials in concretes with SCMs. Experimental studies show that TA can strongly retard the hydration of cement and alite due to its ability to bind to various particles and chelate with calcium ions, causing less calcium hydroxide produced by the hydration. The strong interaction between the TA and hydration products leads to morphology change of the hydration products and generates nanoparticles at early age. Furthermore, addition of TA can significantly densify the nanostructure of cement pastes. Particularly, capillary pores smaller than 70nm are drastically reduced by TA. This finding is not only explaining why TA can enhance the micromechanical properties of concrete, but also opening a new approach to tune the nanoscale pores in concrete. Besides, a pre-hydration method is proposed and verified to mitigate the retarding effect of TA for widely adopted in practical application. Significant strength improvement at late age can be achieved by pre-hydration with TA without losing of strength at early age. TA is also successfully used in mortars with silica fume to achieve over 30% strength improvement, suggesting its huge potential to reduce the carbon footprint of concrete.