碱矿渣混凝土耐高温性能研究

发布时间：2018-03-30 15:22

本文选题：碱矿渣混凝土　切入点：高温　出处：《重庆大学》2014年博士论文

【摘要】：碱矿渣水泥生产工艺简单，生产能耗低，用其配制的碱矿渣混凝土具有优良的力学性能和耐久性能。对于该混凝土的耐高温性能，，不同学者有不尽一致的认识。一种观点认为，碱矿渣水泥水化产物中几乎不含在高温下易发生分解的Aft和Ca(OH)2，因此，碱矿渣混凝土具有较好的耐高温性能；另一种观点认为，碱矿渣水泥石高温下的收缩更大，浆体与集料间的热变形差异导致其耐高温性能较差。开展碱矿渣混凝土耐高温性能研究，揭示高温作用对其力学行为及微观结构的影响规律，并建立数值化模型，对丰富和发展碱矿渣混凝土理论研究，指导碱矿渣混凝土结构设计和应用具有重要意义。论文试验研究了升温制度、静置时间、强度等级、集料以及纤维对高温后碱矿渣混凝土试件外观、质量和强度的影响；采用综合热分析（TG-DSC）、X射线衍射(XRD)、傅立叶转换红外光谱(FTIR)、扫描电子显微镜（SEM）、氮吸附等测试手段分析了碱矿渣水泥石高温后产物和微观结构的变化。建立了高温下碱矿渣混凝土多物理场传输模型，推导了全耦合数值解法，并进行了算例分析。研究揭示的主要规律与取得的主要成果如下：碱矿渣混凝土强度及结构变化与受热温度有关。室温～200℃范围内，温度升高促进了碱矿渣水泥石水化反应，水泥石结构更加致密，混凝土抗压强度较常温有所增长；受热温度超过200℃后，水泥石与集料界面粘结强度下降，混凝土强度呈降低趋势；600℃～700℃，碱矿渣水泥石失去非蒸发水，混凝土强度大幅度降低；受热温度达到800℃后，水泥石发生固相反应，生成钙黄长石，混凝土中石灰石集料部分分解，质量损失率急剧增大，结构严重劣化。碱矿渣混凝土高温性能受强度等级的影响。低强度等级混凝土受高温影响较小。强度等级越高，结构越密实，高温条件下蒸汽压力和热应力对结构的损伤越大。碱矿渣水泥石具有比普通水泥石更大的热收缩，高温下水泥石与集料界面结构劣化产生的微裂纹不仅不会显著降低混凝土强度，而且可以有效缓解蒸汽压力对混凝土结构的破坏，避免爆裂现象的发生。与同强度等级普通混凝土相比，碱矿渣混凝土强度劣化温度提高100～200℃。碱矿渣混凝土高温性能受升温制度的影响。受热温度在400℃及以上温度条件下，升温速度越快，混凝土的损伤越严重；1h～6h范围内，持温时间越长，混凝土强度损失越大。空气冷却与水冷两种冷却方式作用下碱矿渣混凝土高温后性能相近。受热温度低于400℃，高温后再经标准条件养护，混凝土强度能够增长。经600℃及以上温度作用后的碱矿渣混凝土即使经标准条件养护，水泥石水化过程难以发展，强度损失无法恢复。碱矿渣混凝土高温性能受集料热物理性能的影响。玄武岩高温下体积变形小，与浆体界面结构稳定，蒸气难以散逸，导致蒸汽压力对混凝土损伤较大。石灰石在800℃左右发生分解，对以石灰石为集料的碱矿渣混凝土结构影响显著。页岩陶粒孔隙率大，高温作用下可以缓解蒸汽压力对混凝土结构的破坏，降低混凝土高温后的强度损失。比较而言，页岩陶粒配制的碱矿渣混凝土高温性能较好。碱矿渣混凝土高温性能受纤维影响较小。常温至600℃范围内，钢纤维对碱矿渣混凝土增强作用明显，受热温度达800℃时，镀铜钢纤维镀层严重氧化，纤维与浆体粘结强度降低，增强作用减小。碱矿渣混凝土界面结构劣化产生的微裂纹可有效降低孔压，聚丙烯纤维在碱矿渣混凝土高温性能中所起的作用不明显。碱矿渣混凝土高温条件下的结构变化符合多孔介质传热传质规律。将碱矿渣混凝土模型化为由固体骨架与孔隙组成的多孔介质，以多孔介质理论为基础，建立了碱矿渣混凝土高温过程中的湿热传输机制。在Bazant模型基础上考虑了固体骨架体积应变率和孔隙压力的全耦合效应以及全耦合效应下的弹性形变对湿热传输机制的影响，发展建立了碱矿渣混凝土高温条件下的热-孔隙-弹塑性全耦合数学模型。采用径向回归解法和Newton-Raphson向后欧拉法求解介质传输过程的应力增量。同时，为了保证求解过程二阶收敛，提出了用于热-孔隙-弹塑性全耦合过程求解的一致性切线模量刚度矩阵，建立非稳态有限元格式。结合对碱矿渣混凝土热物参数的研究，通过二次开发，采用ABAQUS软件进行了算例分析。算例分析表明模型计算结果与实测结果偏差较小，能够真实有效模拟高温环境下碱矿渣混凝土结构变化过程。
[Abstract]:Alkali slag cement has the advantages of simple production process, low production energy consumption, has excellent mechanical performance and durable performance for the preparation of alkali slag concrete. The concrete for high temperature performance, different scholars have different understanding. A view that the alkali slag cement hydration products almost does not contain easily decomposed Aft at high temperature and Ca (OH) 2, therefore, alkali slag concrete has good high-temperature performance; another view, alkali slag cement stone under high temperature shrinkage is larger, resulting in poor performance of high temperature slurry and aggregate the thermal deformation difference. To carry out high temperature performance of alkali slag concrete effect of high temperature, revealing the effect on microstructure and its mechanical behavior, and to establish a numerical model for the enrichment and development of alkali slag concrete theory, it has very important significance of alkali slag concrete structure design and application.
The experimental study of heating system, setting time, strength, and fiber on aggregate after high temperature alkali slag concrete appearance, affecting the quality and strength; the comprehensive thermal analysis (TG-DSC), X ray diffraction (XRD), Fu Liye (FTIR), infrared spectrum and scanning electron microscope (SEM). The nitrogen adsorption test method of alkali slag cement stone changes after high temperature products and microstructure analysis. A high temperature alkali slag concrete multi field transmission model, deduced numerical solution of coupling, and the example is analyzed. The main results of research and reveal the main rules are as follows:
The change of slag concrete strength and structural base related to heating temperature. At room temperature to 200 DEG C, elevated temperature promoted the alkali slag cement hydration reaction of cement stone, stone structure is more compact, the compressive strength of concrete is increased at room temperature; heating temperature more than 200 DEG C, cement and Aggregate Bond strength decreased, the strength of concrete decreased; 600 to 700 DEG C, alkali slag cement stone out of non evaporable water, the concrete strength is greatly reduced; the heating temperature reaches 800 degrees Celsius, cement solid state reaction, generating gehlenite material, partial decomposition of limestone set in concrete, the mass loss rate increases rapidly, the deterioration of the structure.
The high temperature performance of alkali slag concrete is affected by the strength of low strength concrete. The effect of high temperature low. Higher intensity, more dense structure, steam pressure and heat under the condition of high temperature stress on the structural damage is greater. Alkali slag cement has shrink more than ordinary cement, cement stone under high temperature with aggregate interface structure deterioration of micro cracks will not only reduce the strength of concrete, and can effectively alleviate the damage of steam pressure on the concrete structure, avoid bursting phenomenon. Compared with the same strength grade of concrete, alkali slag concrete strength degradation temperature increased by 100~200 degrees.
Effect of high temperature performance of alkali activated slag concrete heating system. The heating temperature at 400 degrees and over temperature, warming faster, more serious damage to the concrete; 1H ~ 6h range, holding time is long, the greater the loss of concrete strength. Effects of air cooling and water cooling mode of two kinds of alkali slag concrete high temperature performance is very similar. The heating temperature is lower than 400 DEG C high temperature after standard curing condition, the strength of concrete to increase. The alkali slag concrete temperature above 600 DEG C and after the action even after standard curing condition, the cement hydration process difficult to develop, strength loss cannot be recovered.
The high temperature performance of alkali slag concrete by the effect of aggregate thermal physical properties of basalt under high temperature. The volume deformation is small, and the interface structure of slurry stability, steam to escape of steam pressure caused great damage to the concrete. The limestone at about 800 DEG to decompose, the alkali slag concrete structure of limestone aggregate shale ceramsite significantly affected. The high porosity, under the action of high temperature steam pressure can reduce the damage of concrete structure, reduce the loss of strength of concrete after high temperature. In comparison, alkali slag concrete high temperature properties of shale ceramsite prepared better.
The high temperature performance of alkali slag concrete by the fiber is less affected. Room temperature to 600 DEG C, steel fiber on alkali slag concrete reinforcing effect, heating temperature up to 800 DEG, copper plated steel fiber coating serious oxidation, reduce the bond strength of fiber and paste, enhancement of micro cracks decreases. Alkali slag concrete deterioration of interface structure can effectively reduce the pore pressure, polypropylene fiber on performance of alkali activated slag concrete in high temperature is not obvious.
Changes in the structure of alkali slag concrete under high temperature with heat and mass transfer in porous media. The regularity of alkali slag concrete model of porous medium is composed of solid skeleton and pore, based on porous medium theory, established hot alkali slag concrete during high temperature transmission mechanism. Based on the Bazant model considering the influence of the elastic deformation of the whole the coupling effect of solid skeleton volumetric strain rate and pore pressure and the coupling effect on the heat transfer mechanism, developed conditions of alkali slag concrete under high temperature heat - pore elastic-plastic coupling mathematical model.
The incremental stress radial return method and Newton-Raphson medium transmission process solving backward Euler method. At the same time, in order to ensure the two order convergence of the solution process, for the consistent tangent modulus of thermal elastic-plastic coupled pore solving stiffness matrix is proposed, the establishment of non steady state finite element scheme. The combination of hot alkali slag concrete physical parameters, through the development of two times, is analyzed by ABAQUS software. The example analysis shows that the calculated results and test results of small deviation, can effectively simulate the real environment of high temperature alkali slag concrete structure change process.

【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528

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