【作者】 张经双；

【导师】 马芹永；

【作者基本信息】 安徽理工大学 ， 采矿工程， 2014， 博士

【摘要】 矿山井巷喷射混凝土的人工现场拌料施工,存在原材料计量不准确、混凝土质量差、粉尘浓度大等问题。针对这一现状,提出了预拌干料和预拌料混凝土技术。预拌干料是指将水泥、砂子和石子等混凝土原材料,按照设计配合比拌合均匀、干燥贮存的散装混合料。预拌料混凝土是在预拌干料中加入水和外加剂,硬化后形成的一种混凝土。预拌料混凝土具有准确的配合比、良好的混凝土质量、较低的粉尘浓度等诸多优点。但预拌干料中的砂子含有的极少量水,与水泥发生水化反应,劣化了原材料性能,对预拌料混凝土性能产生影响。结合教育部博士点基金优先发展领域课题“预拌喷射补偿收缩混凝土微观结构与力学特性研究”,采用理论分析、室内试验和现场试验相结合的方法,对砂子含水率分别为0%、0.5%、1.0%、1.5%、2.0%和贮存期分别为0d、3d、7d、10d、15d、20d、30d的预拌干料和预拌料混凝土的微观结构进行分析,揭示微观结构对预拌料混凝土抗压强度、孔隙率等的影响机理。主要研究结论如下。(1)预拌干料和预拌料混凝土的微观分析表明,砂子含水率越高、贮存期越长,预拌干料中失效的水泥量越多,原材料性能劣化越严重,混凝土微观结构越疏松。当预拌干料的砂子含水率在1.0%以下、贮存期在15d以内时,预拌干料的水化产物和微观结构变化较小、材料性能劣化程度低,预拌料混凝土的微观结构密实：当预拌干料的砂子含水率在1.5%以上时,贮存期的增加导致预拌干料中失效的水泥数量增多、材料性能劣化加剧。(2)预拌料混凝土抗压强度试验表明,预拌干料的砂子含水率小于1.0%、贮存期在15d以内时,水胶比为0.45的预拌料混凝土强度损失率不超过8.64%,抗压强度达到42.3MPa,满足要求；当砂子含水率增加到1.5%以上时,贮存期对预拌料混凝土强度的影响较大。结果表明,砂子含水率为1.0%的预拌干料有效贮存期为15d。(3)建立了不同砂子含水率和贮存期条件下的预拌料混凝土抗压强度与孔隙率之间的定量关系。预拌干料的砂子含水率越小、贮存期越短,预拌料混凝土孔隙数量越少、孔径越小、微观结构越密实,预拌料混凝土的抗压强度越高。随预拌干料贮存期延长,砂子含水率在1.0%以下时,预拌料混凝土孔隙率增加较慢,对混凝土的强度影响较小；而砂子含水率为1.5%和2.0%时,预拌料混凝土孔隙率增加相对较快,对混凝土的强度影响较大。(4)通过分析,得出预拌干料的砂子含水率和贮存期对预拌料混凝土强度的影响机理。预拌干料的砂子含水率和贮存期对预拌干料的水化程度产生影响,水化程度高时,预拌干料水化消耗的水泥量多,导致后期混凝土中水泥数量减少,同时,密实的预拌干料水化产物包裹部分水泥颗粒,阻止或延缓了这部分水泥在混凝土中继续水化；水化程度低时,预拌干料中的水化产物疏松,这些疏松的微观结构在混凝土中很难水化密实,成为预拌料混凝土的薄弱环节。预拌干料的水泥水化程度越高,失效水泥量越多,预拌干料性能劣化越严重,预拌料混凝土强度降低越多。(5)工程应用表明,预拌料喷射混凝土具有良好的力学性能、较好的变形性能、较小的回弹率和较低的粉尘浓度。更多还原

【Abstract】 For the problems of artificial cast-in-situ shotcrete in coalmine roadway, such as inaccurate in raw material measurement, poor shotcrete quality, and large dust concentration, ready-mixed materials and ready-mixed concrete technology have been put forward to solve those problems. By mixing cement, sand and gravel uniformly in design proportion, the ready-mixed materials are formed and will be stored in some periods. When adding water and additives in ready-mixed materials, ready-mixed concrete is produced after hardening. Ready-mixed concrete gets many virtues, such as accurate mix proportion, good concrete quality, and low dust concentration. But the hydration reaction will occur between cement and a little moisture on sand in ready-mixed materials, which will deteriorate the performance of raw materials and affect the performance of ready-mixed concrete.Combining with the prior development project of doctoral fund of Ministry of Education, research on microstructure and mechanical characteristic of ready-mixed shrinkage-compensating shotcrete, the microstructure of ready-mixed materials and ready-mixed concrete are analyzed in moisture contents,0%,0.5%,1.0%,1.5%,2.0%, and storage periods,0d,3d,7d,10d,15d,20d,30d. Then the influence mechanism of microstructure on compressive strength and porosity of ready-mixed concrete is revealed. The main research contents and conclusions are shown as follows.(1) The microstructure analyses on ready-mixed materials and ready-mixed concrete show that larger sand moisture content and longer storage period lead to more amount of failure cement, more serious deterioration of raw materials, and more loosen microstructure of concrete. When sand moisture content is equal to or less than1.0%and storage period is within15d, there is little change of hydration production and microstructure in ready-mixed materials, therefore the degree of deterioration is low and the microstructure of ready-mixed concrete is dense. However, when sand moisture content is equal to or exceeds1.5%, the extending of storage period leads to the amount of failure cement increasing and the deterioration of raw materials intensifying.(2) The compressive strength tests of ready-mixed concrete show that when sand moisture content is equal to or less than1.0%and storage period is within15d, the strength loss rate of ready-mixed concrete with water-binder ratio of0.45is no more than8.64%and the compressive strength meets the requirements, reaching42.3MPa. When sand moisture content is equal to or exceeds1.5%, there is a big influence of sand moisture content on compressive strength. The results show that the valid storage period of ready-mixed materials in the condition of1.0%sand moisture content is15d.(3) The quantitative relation between compressive strength and porosity for ready-mixed concrete is established in various sand moisture contents and storage periods. Smaller sand moisture content and shorter storage period result in less pore number, smaller pore diameter, denser microstructure, and higher compressive strength of ready-mixed concrete. With storage period extending, the porosity increases slowly and shows little influence on concrete strength when sand moisture content is equal to or less than1.0%. While the porosity increases fast and presents large influence on concrete strength when sand moisture content is equal to1.5%or2.0%.(4) The influence mechanism of sand moisture content and storage period on compressive strength of ready-mixed concrete is obtained. The sand moisture content and storage period affect the hydration degree of ready-mixed materials. With high hydration degree, the hydration reaction consumes more cement leading to less cement in later concrete hardening, and some cement particles are packaged by dense hydration production which will stop or postpone the hydration reaction of cement. With low hydration degree, the hydration production of ready-mixed materials is loosen, and these loosen microstructures are much hard to hydrate densely which will become the weak parts of ready-mixed concrete. The higher the hydration degree, the more the amount of failure cement, the more serious the deterioration of ready-mixed materials, and the more the loss of concrete strength.(5) Engineering application indicates that ready-mixed shotcrete presents a better mechanical performance, better deformation performance, lower rebound rate and smaller dust concentration.更多还原