石灰岩质机制砂混凝土的长期变形性能研究

发布时间：2018-04-26 21:16

本文选题：石灰岩质机制砂 + 机制砂混凝土　；参考：《华中科技大学》2014年博士论文

【摘要】：当前,随着世界经济的发展,土木工程中包含混凝土骨料在内的建筑材料的需求也相应地急剧增加。天然砂作为一种常用的细集料,是一种短期内不可再生的资源而且储备量十分有限,我国许多地区的天然砂资源已经出现了严重的不足,因而,近年来世界上包括我国在内的许多国家,出于对环境的保护而限制天然砂的开采。机制砂作为最有潜力的天然砂替代品之一,随着对其物理力学性能研究上的深入,机制砂在桥梁、房屋建筑、水利工程等土木工程中的应用越来越广泛。机制砂与天然砂在外观、化学成分、颗粒形状、颗粒级配以及特细颗粒含量(75μm)等特性上有很大的不同,这些不同势必会导致机制砂混凝土物理力学特性上的差异。迄今为止,土木工程领域在有关机制砂混凝土常规的物理力学性能上,已经进行了相对广泛深入的研究,但有关机制砂混凝土收缩徐变性能上的研究却鲜见报道。为此,本文结合交通部及贵州省交通运输厅科技项目“北盘江特大桥关键技术研究”中的专题四,即：“石灰岩集料混凝土及北盘江特大桥长期性能研究”,通过试验研究和理论分析,对石灰岩质机制砂混凝土材料和构件的收缩徐变性能进行了相对全面的探究。主要研究内容及成果如下： (1)对北盘江特大桥所在的贵州黔西地区的石灰岩质机制砂的物理力学性能进行了系统的调查与试验研究,结果表明：该地区的石灰岩母岩饱和状态下的单轴抗压强度平均值达到114.5MPa,为致密石灰岩或灰泥石灰岩；采用该种岩石制成的机制砂不具有碱硅酸盐反应活性和碱碳酸盐反应活性；石灰岩质机制砂的质量受生产工艺的影响很大,该地区生产的石灰岩质机制砂石粉含量高,级配不连续、粗颗粒较多,所以,在实际工程应用中应在混凝土配合比设计、制备与施工过程中充分考虑石灰岩质机制砂的技术性能特点。 (2)按我国规范设计制作了C50石灰岩机制砂混凝土棱柱体标准试件,对其进行了标准环境条件下的收缩徐变试验,并与同配比的普通砂混凝土试验结果进行了对比。试验结果分析表明：石灰岩质机制砂混凝土的收缩徐变发展规律与普通砂混凝土的类似,而石灰岩质机制砂混凝土的收缩应变和徐变系数均比普通砂混凝土的大；常用的五种收缩徐变模型(即：CEB-FIP90模型、CEB MC90-99、ACI209模型、B3模型与GL2000模型)均过高的估计了石灰岩质机制砂混凝土的收缩和徐变；利用试验结果对ACI209的收缩与徐变模型分别进行修正,得出了石灰岩质机制砂混凝土收缩徐变的预测公式。 (3)设计制作了6根混凝土强度等级为C30的石灰岩质机制砂混凝土简支梁,其中,用于观测收缩的梁2根,观测徐变的梁4根,在自然环境条件下对其长期变形性能进行了试验观测和理论研究。试验结果表明：当环境的温度上升或者湿度下降时,梁的徐变挠度增加,但环境的湿度对徐变的影响有一定的滞后性；根据静力学理论,推导出由徐变系数计算简支梁跨中徐变挠度的公式；在此基础上,分别利用CEB-FIP90、ACI209及B3等收缩、徐变预测模型计算得到简支梁跨中徐变挠度,与试验梁跨中挠度的实测值比较表明,ACI-209模型的计算精度相对最好；由此,通过试验梁的实测徐变挠度,反推出自然环境条件下加载龄期为45天的C30石灰岩质机制砂混凝土的徐变系数计算公式。 (4)利用本文由试验得到的收缩徐变计算公式及我国现行桥规(JTG D62-2004)计算公式,采用MIDAS/Civil2012对北盘江特大桥成桥后的长期变形性能进行了数值建模与分析。计算结果表明：由混凝土收缩徐变导致的竖向位移增量在前期发展较快,后期发展较慢,且成桥30年后的下挠增量比较小,符合我国现规范要求,这也说明石灰岩质机制砂的应用,不会对北盘江特大桥的长期变形性能产生不良的影响,可以将其用于同类工程实践之中；同时,通过对三个模型的计算结果对比可以看出,采用桥规收缩徐变模型分析得到的位移增量最大,这表明按照我国桥规模型来预测石灰岩机制砂混凝土桥梁的长期变形性能是偏于安全的、且可行的。
[Abstract]:Currently , with the development of world economy , the demand of building materials including concrete aggregate in civil engineering has increased correspondingly . As a kind of commonly used fine aggregate , natural sand has been widely used as one of the most potential natural sand substitutes .

( 1 ) The physical and mechanical properties of limestone mechanism sand in Qianxi area of Guizhou province are investigated and studied . The results show that the average uniaxial compressive strength of limestone in this area reaches 114.5 MPa , which is compact limestone or lime mud limestone ;
the mechanism sand made of the rock has no alkali silicate reaction activity and alkali carbonate reaction activity ;
The quality of the limestone mechanism sand is influenced by the production process , the content of the limestone powder in the area is high , the gradation is discontinuous and the coarse particles are more . Therefore , the technical performance characteristics of the limestone mechanism sand should be fully considered in the practical engineering application in the concrete mix proportion design , preparation and construction process .

( 2 ) According to our country ' s standard design , we have made the standard test piece of sand concrete prism , and compared with the test result of common sand concrete with the same proportion . The results show that the shrinkage and creep rate of the stone mechanism sand concrete is similar to that of ordinary sand concrete , while the shrinkage strain and creep coefficient of the stone mechanism sand concrete are larger than that of ordinary sand concrete ;
The common five shrinkage creep models ( i.e . , CEB - FIP90 model , CEB MC90 - 99 , ACI209 model , B3 model and GL2000 model ) have been used to estimate the shrinkage and creep of sand concrete in limestone mechanism .
The shrinkage and creep model of ACI209 are corrected respectively by the test results , and the prediction formula of shrinkage creep of sand concrete in limestone mechanism is obtained .

( 3 ) Six concrete simply supported beams with concrete strength of C30 are designed and fabricated . The results show that the creep deflection of the beam increases when the temperature of the environment rises or the humidity decreases , but the humidity of the environment has a certain hysteresis effect on the creep .
According to the theory of statics , the formula for calculating creep deflection of simply supported beam from creep coefficient is derived .
On this basis , using the contraction and creep prediction model of CEB - FIP90 , ACI209 and B3 respectively , the creep deflection of simply supported beam is calculated and compared with the measured value of the deflection in the span of the test beam , and it is shown that the calculation accuracy of ACI - 209 model is relatively good ;
According to the measured creep deflection of the test beam , the calculation formula of creep coefficient of the C30 limestone sand concrete with the age of 45 days under the condition of natural environment is deduced .

( 4 ) Using the calculation formula of shrinkage and creep and the calculation formula of the existing bridge gauge ( JTG D62 - 2004 ) in our country , the numerical modeling and analysis of the long - term deformation performance of Beipan River Bridge are carried out by using MIDAS / Civil l2012 . The results show that the increment of vertical displacement caused by shrinkage and creep of concrete is relatively small in the early stage and the latter is slower in the later stage .
At the same time , by comparing the results of the three models , it can be seen that the displacement increment obtained by using the bridge gauge shrinkage creep model is the largest , which indicates that the long - term deformation performance of the sand concrete bridge of the limestone mechanism is predicted to be safe and feasible according to the bridge model of China .

【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528

【相似文献】