干湿循环下MgSO_4侵蚀对UHPC相组成及其微结构的影响机理
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摘要
UHPC在海洋工程建设中具有良好的应用前景,但海洋环境中存在的腐蚀性离子和干湿循环作用将会影响UHPC的微观结构,进而影响其耐久性能。通过XRD,SEM-EDS,~(29)Si和~(27)Al NMR等方法研究了干湿循环下MgSO4侵蚀和养护制度对UHPC微结构的影响。结果表明:干湿循环下MgSO_4侵蚀可促进UHPC浆体中AFt和Mg(OH)_2生成,降低C-S-H凝胶的Al[4]/Si和Ca/Si,并促进TAH和硅氧链上脱离的Al向AFt和AFm转化; 210℃-2 MPa压蒸养护过程可降低UHPC浆体中的Ca(OH)_2和SiO_2含量,提高UHPC浆体的水化程度和致密度,并形成Al[4]/Si较高且Ca/Si较低的C-S-H凝胶;压蒸养护可减少侵蚀作用下AFt和Mg(OH)_2的生成,有效削弱MgSO_4干湿循环侵蚀对UHPC浆体中C-S-H凝胶的脱铝和脱钙作用,并减少Al相转化程度。
UHPC has a good application prospect in marine engineering construction,but the corrosive ions and dry-wet cycles in the marine environment will affect the microstructure and durability of UHPC.The influence of dry-wet cycles combined MgSO_4 attack and curing-regime on the microstructure of UHPC were investigated by XRD,SEM-EDS,29 Si and27 Al NMR techniques. The results show that dry-wet cycles combined MgSO_4 attack promotes the formation of AFt and Mg( OH)_2 in UHPC paste,reduces Al[4]/Si and Ca/Si in C-S-H gel,and promotes the conversion of TAH and Al[4] to AFt and AFm.210 ℃-2 MPa autoclaved curing process reduces the content of Ca( OH)_2 and SiO_2,increases the hydration degree and density of the UHPC paste,and form C-S-H gel of higher Al[4]/Si and lower Ca/Si. Under dry-wet cycles combined MgSO_4 attack,autoclaved curing reduces the formation of AFt and Mg( OH)_2,effectively weakens the decalcification and dealuminization effect of the corrosion,and reduces the degree of Al phase conversion.
UHPC has a good application prospect in marine engineering construction,but the corrosive ions and dry-wet cycles in the marine environment will affect the microstructure and durability of UHPC.The influence of dry-wet cycles combined MgSO_4 attack and curing-regime on the microstructure of UHPC were investigated by XRD,SEM-EDS,29 Si and27 Al NMR techniques. The results show that dry-wet cycles combined MgSO_4 attack promotes the formation of AFt and Mg( OH)_2 in UHPC paste,reduces Al[4]/Si and Ca/Si in C-S-H gel,and promotes the conversion of TAH and Al[4] to AFt and AFm.210 ℃-2 MPa autoclaved curing process reduces the content of Ca( OH)_2 and SiO_2,increases the hydration degree and density of the UHPC paste,and form C-S-H gel of higher Al[4]/Si and lower Ca/Si. Under dry-wet cycles combined MgSO_4 attack,autoclaved curing reduces the formation of AFt and Mg( OH)_2,effectively weakens the decalcification and dealuminization effect of the corrosion,and reduces the degree of Al phase conversion.
引文
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[2] Rougeau P,Borys B. Ultra high performance concrete with ultrafine particles other than silica fume[C]. Proceedings of the International Symposium on Ultra High Performance Concrete,2004.
[3] Massidda L,Sanna U,Cocco E,et al. High pressure steam curing of reactive-powder mortars[J]. Special Publication,2001,200:447-464.
[4] Matte V,Moranville M. Durability of reactive powder composites:influence of silica fume on the leaching properties of very low water/binder pastes[J]. Cement and Concrete Composites,1999,21(1):1-9.
[5] Shao X,Zhan H,Lei W,et al. Conceptual design and preliminary experiment of super-long-span continuous box-girder bridge composed of oneway prestressed UHPC[J]. China Civil Engineering Journal,2013,46(8):83-89.
[6] Bruhwiler E,Denarie E. Rehabilitation and strengthening of concrete structures using ultra-high performance fibre reinforced concrete[J].Stucture Engineering International,2013,23(4):450-457.
[7] Müllauer W,Beddoe R E,Heinz D. Sulfate attack expansion mechanisms[J]. Cement and Concrete Research,2013,52:208-215.
[8] Ding Q,Hu C,Feng X,et al. Effect of curing regime on polymerization of C-S-H in hardened cement pastes[J]. Journal of Wuhan University of Technology(Materials Science Edition),2013,28(4):715-720.
[9] Li X. Study on the mechanism of magnesium sulfate to cement and C-S-H gel[J]. Advanced Materials Research,2011,243:4687-4690.
[10] Massiot D,Fayon F,Capron M,et al. Modelling one-and two-dimensional solid-state NMR spectra[J]. Magnetic Resonance in Chemistry,2002,40(1):70-76.
[11] Santhanam M,Cohen M D,Olek J. Mechanism of sulfate attack:a fresh look Part 1:summary of experimental results[J]. Cement and Concrete Research,2002,32(6):915-921.
[12] Zhang W,Zhang J,Ye J,et al. Influence of synthesis conditions on morphology of ettringite[J]. Journal of the Chinese Ceramic Society,2017,5:631-638.
[13] Yazici H,Yardimci M Y,Yi gˇiter H,et al. Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag[J]. Cement and Concrete Composites,2010,32(8):639-648.
[14] Tosun K,Baradan B. Effect of ettringite morphology on DEF-related expansion[J]. Cement and Concrete Composites,2010,32(4):271-280.
[15] Grimmer A R. Structural investigation of calcium silicates from29Si chemical shift measurements[J]. Application of NMR Spectroscopy to Cement Science,1994:113-151.
[16] Justnes H,Meland I,Bjorgum J O,et al. Nuclear magnetic resonance(NMR)-a powerful tool in cement and concrete research[J]. Advances in Cement Research,1990,3(11):105-110.
[17] Richardson I G. The nature of the hydration products in hardened cement pastes[J]. Cement and Concrete Composites,2000,22(2):97-113.
[18] Ding Q,Yang J,Zhang G,et al. Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend[J]. Journal of Wuhan University of Technology(Materials Science Edition),2018,33(1):108-116.
[19] Ding Q,Yang J,Hou D,et al. Insight on the mechanism of sulfate attacking on the cement paste with granulated blast furnace slag:an experimental and molecular dynamics study[J]. Construction and Building Materials,2018,169:601-611.
[20] Fernández-Jimenez A,Torre A G D L,Palomo A,et al. Quantitative determination of phases in the alkali activation of fly ash. Part I. Potential ash reactivity[J]. Fuel,2006,85(5):625-634.
[21] Andersen M D,Jakobsen H J,Skibsted J. A new aluminium-hydrate species in hydrated Portland cements characterized by27Al and29Si MAS NMR spectroscopy[J]. Cement and Concrete Research,2006,36(1):3-17.
[22] Sun G K,Young J F,Kirkpatrick R J. The role of Al in C-S-H NMR,XRD,and compositional results for precipitated samples[J]. Cement and Concrete Research,2006,36(1):18-29.
[23] Kunther W,Lothenbach B,Skibsted J. Influence of the Ca/Si ratio of the C-S-H phase on the interaction with sulfate ions and its impact on the ettringite crystallization pressure[J]. Cement and Concrete Research,2015,69:37-49.
[24] Zhang G,Zhang X,Ding Q,et al. Microstructural evolution mechanism of C-(A)-S-H Gel in portland cement pastes affected by sulfate ions[J]. Journal of Wuhan University of Technology(Materials Science Edition),2018,33(3):639-647.
[25] Andersen M D,And H J J,Skibsted J. Incorporation of aluminum in the calcium silicate hydrate(C-S-H)of hydrated portland cements:a highfield27Al and29Si MAS NMR investigation[J]. Inorganic Chemistry,2003,42(7):2280-2287.
[26] Richardson I G,Brough A R,Brydson R,et al. Location of aluminum in substituted calcium silicate hydrate(C-S-H)gels as determined by29Si and27Al NMR and EELS[J]. Journal of the American Ceramic Society,2010,76(9):2285-2288.
[27] Skibsted J,Jakobsen H J,Hall C. Quantitative aspects of27Al MAS NMR of calcium aluminoferrites[J]. Advanced Cement Based Materials,1998,7(2):57-59.