纳米压痕表征水泥基材料高温后微观力学性能
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摘要
为了考察水泥基材料经历高温后其微观各相的力学性能变化,采用三种典型水灰比(0. 2,0. 4,0. 6)的P·O 42. 5氢氧化钙水泥制备了水泥净浆试样并开展高温试验,采用纳米压痕试验和解卷积分析获取微观各相的弹模和硬度,对比分析了温度对各组分弹模和硬度的影响规律。结果表明:温度导致多孔复合相和水合硅酸钙(C-S-H)相的弹性模量、硬度降低,而氢氧化钙(CH)及未水化水泥矿物复合相则影响不显著。温度低于200℃时,C-S-H的弹性模量、硬度略微降低,此时水泥基材料中主要失去自由水和毛细孔水; 400℃时弹性模量、硬度显著降低,此时C-S-H中失去层间水和部分化学结合水,并造成C-S-H微观结构破坏;高于400℃后C-S-H的弹性模量、硬度不再显著降低。据此推算C-S-H微观破坏的临界温度在300～400℃。
In order to evaluate the changes in micro-mechanical properties for cementitious materials after being subjected to high temperature,typical cement paste specimens with three water-cement ratios( 0. 2,0. 4,0. 6) were tested by nanoindentation technology after being high temperature curing. The elastic modulus and hardness of main phases in cement pastes were obtained by nanoindentation test and deconvolution analysis,the effects of high temperature on micromechanical properties were investigated. The results showed that high temperature reduced the elastic modulus and hardness of porous composite phase and C-S-H phase,but had little effect on CH/unhydrated cement mineral composite phase. When the temperature was lower than 200 ℃,the elastic modulus and hardness of C-S-H decreased slightly due to the loss of free water and capillary water. When at 400 ℃,the elastic modulus and hardness of C-S-H decreased markedly since the microstructure of C-S-H was destroyed due to the loss of the interlayer water and some chemically bound water. When the temperature was higher than 400 ℃,the elastic modulus and hardness of C-S-H no longer decrease. Therefore,the critical temperature of C-S-H microcosmic damage could be deduced in the range of 300 ～ 400 ℃.
In order to evaluate the changes in micro-mechanical properties for cementitious materials after being subjected to high temperature,typical cement paste specimens with three water-cement ratios( 0. 2,0. 4,0. 6) were tested by nanoindentation technology after being high temperature curing. The elastic modulus and hardness of main phases in cement pastes were obtained by nanoindentation test and deconvolution analysis,the effects of high temperature on micromechanical properties were investigated. The results showed that high temperature reduced the elastic modulus and hardness of porous composite phase and C-S-H phase,but had little effect on CH/unhydrated cement mineral composite phase. When the temperature was lower than 200 ℃,the elastic modulus and hardness of C-S-H decreased slightly due to the loss of free water and capillary water. When at 400 ℃,the elastic modulus and hardness of C-S-H decreased markedly since the microstructure of C-S-H was destroyed due to the loss of the interlayer water and some chemically bound water. When the temperature was higher than 400 ℃,the elastic modulus and hardness of C-S-H no longer decrease. Therefore,the critical temperature of C-S-H microcosmic damage could be deduced in the range of 300 ～ 400 ℃.
引文
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[2] EHM C,SCHNEIDER U. The High Temperature Behaviour of Concrete Under Biaxial Conditions[J]. Cement and Concrete Research,1985,15(1):27-34.
[3] ULM F J,COUSSY O,BAZANT Z P. The‘Chunnel’Fire. I:Chemoplastic Softening in Rapidly Heated Concrete[J]. Journal of Engineering Mechanics,1999,125(3):272-282.
[4] ULM F J,ACKER P,LEVY M. The ‘Chunnel’ Fire. II:Analysis of Concrete Damage[J]. Journal of Engineering Mechanics,1999,125(3):283-289.
[5] KODUR V,SULTAN M A. Effect of Temperature on Thermal Properties of High-strength Concrete[J]. Journal of Materials in Civil Engineering,2003,15(2):101-107.
[6]钱在兹,吴慧.混凝土高温后的扫描电镜实验研究[J].福州大学学报(自然科学版),1996,24(9):34-38.
[7] KOKSAL F,GENCEL O,BROSTOW W,et al. Effect of High Temperature on Mechanical and Physical Properties of Lightweight Cement Based Refractory Including Expanded Vermiculite[J].Material Research Innovations,2012,16(1):7-13.
[8]冯竟竟,傅宇方,陈忠辉,等.高温对水泥基材料微观结构的影响[J].建筑材料学报,2009,12(3):318-322.
[9] KOMONEN J,PENTTALA V. Effects of High Temperature on the Pore Structure and Strength of Plain and Polypropylene Fiber Reinforced Cement Pastes[J]. Fire Technology,2003,39(1):23-34.
[10] PHARR G M. An Improved Technique for Determining Hardness and Elastic Modulus Using Load and Displacement Sensing Indentation Experiments[J]. J Mater Res,1992,7(6):1564-1583.
[11] OLIVER W C,PHARR G M. Measurement of Hardness and Elastic Modulus by Instrumented Indentation:Advances in Understanding and Refinements to Methodology[J]. Journal of Materials Research,2004,19(1):3-20.
[12] JENNINGS H M,THOMAS J J,GEVERNOV J S,et al. A Multi-Technique Investigation of the Nanoporosity of Cement Paste[J].Cement and Concrete Research,2007,37:329-336.
[13] CONSTANTINIDES G,ULM F J. The Nano-Granulae Nature of C-S-H[J]. Mechanics and Physics of Solids,2007,55:64-90.