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Effect and mechanism analysis of hydroxylated nano‑boron nitride on workability and multi‑scale mechanical properties of cement paste

Liu Jianglin, Li Yue, Jin Caiyun, Lin Hui, Li Hongwen

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 3

art. no. e122

Nano-boron nitride (h-BN) has excellent physical and mechanical properties. Due to its stable chemical performance, the improvement effect on the properties of cement-based materials was limited. Therefore, the chemical modification method was used to prepare functional h-BN to improve its application potential in cement-based materials in this paper. The hydroxylated nano-boron nitride (h-BN-OH) was prepared by modified pristine h-BN with saturated sodium hydroxide (NaOH). The effects of h-BN-OH after ultrasonic dispersion for 10 min, 20 min, 30 min and 40 min on the setting time, fluidity, resistivity, mascroscopic strength and microscopic Young’s modulus of hydration products of ordinary Portland cement were investigated. Fourier transform infrared spectroscopy (FTIR) test results showed that h-BN-OH had obvious hydroxyl infrared characteristic peaks. After adding h-BN-OH into cement paste, the initial and final setting time of cement paste was shortened 6.44-15.34% and 5.05-13.00%, respectively; the fluidity was reduced 9.86-22.79%, and the resistivity was increased 7.14-25.96%. Meanwhile, the compressive strength of cement paste and the microscopic Young’s modulus of hydration products were significantly improved 10.82-40.85% and 9.90-31.01%, respectively. The main reasons were as follows: (1) The dispersion effect and stability of h-BN-OH in cement pore solution were better than that of pristine h-BN, and the hydroxyl group grafted on the h-BN-OH provided nucleation sites for the growth of calcium-silicate hydrate (C-S-H) gel. (2) The hydroxyl groups grafted on the h-BN-OH can absorb Ca2+, resulting the polymerization degree (nc) and medium chain length (MCL) of C-S-H gel increased. The formation of C-S-H gel network structure was accelerated by the increasing proportion of Q3. (3) The pore structure of cement hydration products was significantly optimized.

Effect of multi-walled carbon nanotubes on the damping property of cement mortar and mechanism analysis

Li Yue, Li Hongwen, Jin Caiyun

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 3

289--302

The effect of the type and content of multi-wall carbon nanotubes (MWCNTs) on the damping performance of cement mortar is studied in this paper. The pristine MWCNTs (P-CNT) and the functionalized MWCNTs (F-CNT) grafted with COOH were used in the experiment. The content of MWCNTs was 0.05wt% and 0.1wt% of cement. The flexural/compressive strength and loss factor of CNT-mortar composites were measured. The experimental results show that MWCNTs can significantly enhance the flexural strength and loss factor, and the values increased with the increase of CNTs content. The effect F-CNT was better than P-CNT when the MWCNTs content was the same due to the presence of COOH. The mechanism of MWCNTs reinforced mortar damping performance was analyzed by a variety of micro test techniques. The test results of X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermogravimetry showed that MWCNTs did not change the compositions of mortar, but improved the polymerization degree of gel and the degree of hydration of cement. The results of mercury intrusion porosimetry, N2 adsorption and backscattered scanning electron microscopy showed that MWCNTs effectively reduced the porosity and interfacial transition zone thickness of mortar. Transmission electron microscope results showed that the energy dissipation capacity of mortar is increased due to the bridging effect of MWCNTs.