Browsing by Author "Qian, Xin"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    In-situ production of calcium carbonate nanoparticles in fresh concrete using pre-carbonation method
    (University of Alabama Libraries, 2017) Qian, Xin; Wang, Jialai; University of Alabama Tuscaloosa
    To reduce the carbon footprint of ordinary Portland cement (OPC)-based concrete, a novel technique, pre-carbonation process, has been developed to produce CaCO3 nanoparticles in fresh concrete. In this technique, gaseous CO2 is first absorbed into a slurry of calcium-rich minerals which is then blended with other ingredients to produce mortar/concrete. The objective of this work is to obtain an in-depth understanding of the underlying scientific mechanisms associated with the enhancement of strength and durability of the concrete induced by the new method. A comprehensive research plan has been carried out to study the carbonated slaked lime slurry and the effect of carbonated slaked lime slurry on the performance of OPC-based concrete, and to evaluate the potentials of the pre-carbonation method. Experimental studies show that carbonating the calcium-rich mineral slurry with CO2 can produce CaCO3 nanoparticles and Ca(HCO3)2 in the slurry, and these carbonation products were dictated by four parameters of the pre-carbonation method: the duration and temperature of the carbonation, the concentration of the calcium source slurry, and the stirring method of the calcium source slurry during the carbonation. The mechanical properties and durability of the mortar/concrete made with the carbonated slurry were significantly improved, which can be attributed to major mechanisms induced by the pre-carbonation method: promoted hydration of the cement and denser microstructure of the mortar/concrete. Calorimetry testing showed that the hydration of OPC was greatly improved by the pre-carbonation because of the extra heterogenous nucleation sites provided by the CaCO3 nanoparticles. XRD and TGA results revealed that more ettringite was produced in the mortar/concrete with pre-carbonated slaked lime slurry. The overall volume of the hydration products of the cement was increased by the pre-carbonation, leading to denser microstructure of the mortar/concrete. It has been found that the pre-carbonation can be used to the OPC-supplementary cementitious materials (SCMs) blended cement mortar/concrete, as evidenced by the improved mechanical properties achieved by these mortars produced by using the pre-carbonation method. A preliminary study was also conducted to examine whether other calcium-rich minerals, such as Class C fly ash and limestone, can be used as calcium source in the pre-carbonation method.
  • Thumbnail Image
    Item
    Pioglitazone Improved Insulin Sensitivity and First Phase Insulin Secretion Among Obese and Lean People with Diabetes: A Multicenter Clamp Study
    (Springer, 2018) Qian, Xin; Wang, Hui; Yang, Gangyi; Gao, Zhengnan; Luo, Yong; Dong, Aimei; Zhang, Fang; Xu, Mingtong; Liu, Shiping; Yang, Xin; Chen, Yanyan; Li, Guangwei; Chinese Academy of Medical Sciences - Peking Union Medical College; Fu Wai Hospital - CAMS; Chongqing Medical University; Peking University; Sun Yat Sen University; Central South University; University of Alabama Tuscaloosa
    Introduction: To investigate the effects of pioglitazone (PIO) on insulin resistance and first phase insulin secretion among obese and lean Chinese people with type 2 diabetes mellitus (T2DM). Methods: Sixty-eight drug-naive patients with T2DM were treated with PIO for 16 weeks. Before and after the treatment, insulin sensitivity was evaluated by the euglycemic hyper-insulinemic clamp test. Plasma insulin levels at 0, 3, 5, 7, and 10 min during intravenous glucose tolerance test were determined to calculate the first phase insulin secretion and pancreatic beta-cell function. Circulating adiponectin levels were quantified. Results: In both the lean and the obese patients with T2DM, the reduction of HbA(1c) following the PIO treatment was more than 1% (P < 0.001) and glucose infusion rate, acute insulin response, glucose disposal index, and beta-cell glucose sensitivity increased significantly (P < 0.001). A multiple linear regression analysis showed that the improvements of first phase insulin secretion and insulin sensitivity were independently associated with the changes of HbA(1c), but the change of first phase insulin secretion exhibited a higher correlation coefficient (R-2 = 0.20, P = 0.001) than the change of insulin sensitivity did (R-2 = 0.07, P = 0.040). The PIO treatment led to a significant increase in adiponectin levels only in the obese group (P < 0.05). Conclusion: A 16-week treatment of PIO significantly increased insulin sensitivity and beta-cell function in the lean group as well as in the obese group among Chinese T2DM patients, demonstrating that both lean and obese diabetic adults would profit from PIO.