XRD和FTIR的掺硅酸钠富水材料强度演化机制

doi:10.3964/j.issn.1000-0593(2019)10-3199-06

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Abstract Portland cement (PC) and calcium aluminate cement (CAC) are sorts of inorganic materials applied widely. Gel materials, with short setting time and high strengths, can be prepared by blending PC and CAC. Under rich-water conditions (water-cement ratio>1), the PC-CAC-based rich-water materials can be obtained by adding appropriate amount of gypsum into Portland cement-calcium aluminate cement binary system. However, the long-term strength of the rich-water materials tended to decrease. To improve the strength properties of the PC-CAC-based rich-water materials, certain amount of sodium silicate was blended into the PC-CAC-gypsum ternary system. Herein, RMT-150 mechanical experimental system was applied to test the strengths of the PC-CAC-based water-rich materials with different additions of sodium silicate, thus the strength evolution properties and the impact of sodium silicate on the strength can be illuminated. Then, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were adopted to characterize the micro-structures of the corresponding materials, aiming to analyze the development of micro-morphologies and hydrated phases, further to illuminate the strength evolution mechanism of the PC-CAC-based rich-water materials. Strength test results show that the early strength of the rich-water material was low, and its long-term strength would be reduced; however, by adding the sodium silicate, the early strength of the PC-CAC-based rich-water materials can be improved, and the long-term strength retrogression can be reduced partly. When the addition of the sodium silicate was more than 3%, the long-term strength retrogression of the rich-water material could be controlled effectively. The results of SEM, XRD and FT-IR indicate that without addition of sodium silicate and hydrated for 14 days, the CAH₁₀ and C₂AH₈ with hexagonal structures changed to be C₃AH₆ with cubic structures, and this crystal transformation caused the long-term strength attenuation of the PC-CAC based water-rich material. When the sodium silicate addition was 1%, on the 3th day for hydration, more calcium silicate hydrate (C-S-H) gel formed compared with the rich-water material without sodium silicate, which brought benefits to the increase of the early strength of the PC-CAC-based rich-water material. After 14 days of hydration, XRD presented the diffraction peaks of C₂ASH₈ at d=11.75 and 6.24 Å. And the diffraction intensity of C₃AH₆ was detected on the 28th day, and was lower than that in the material without sodium silicate, which was confirmed by the vibration bond caused by C₃AH₆ and appeared at 3 643 cm^-1 in FT-IR. This indicates that the addition of sodium silicate can inhibit the formation of C₃AH₆ by promoting transformation of CAH₁₀ and C₂AH₈ to C₂ASH₈. However, the crystal conversion could not be inhibited completely by the sodium silicate addition of 1%, thus the long-term strength still decreased. When the sodium silicate addition rose to 4%, the formation of C₂ASH₈ had an obvious increase, besides, C₃AH₆ could not be detected on the 28th day, which indicates that the crystal transformation has been inhibited completely. Therefore, the long-term strength retrogression of the rich-water material was controlled effectively.

Key words：Rich-water material; Sodium silicate; Strength evolution; X-ray diffraction; Fourier transform infrared spectroscopy

Received: 2018-09-03 Accepted: 2019-01-15

ZTFLH:

TQ172.78

Corresponding Authors: SUN Yu-ning E-mail: sunyn639@126.com

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http://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)10-3199-06 OR http://www.gpxygpfx.com/EN/Y2019/V39/I10/3199