【作者】 李九苏；

【导师】 肖汉宁；

【作者基本信息】 湖南大学 ， 材料学， 2009， 博士

【摘要】 混凝土的再生利用是21世纪水泥混凝土领域可持续发展的热点问题之一。再生混凝土技术因具有出色的环境效益、经济效益和社会效益而受到广泛关注。但是,再生混凝土强度较低,干缩变形较大,常常成为制约其应用于结构混凝土的瓶颈。目前的生产工艺难以制备出经济性好而且品质优良的再生骨料,因此在今后较长一段时期内,如何利用压碎值和吸水率较高的再生骨料来制备可以作为结构混凝土使用的较高强度并具有较低干缩变形的再生混凝土,是混凝土再生利用亟需解决的问题。此外,再生骨料虽然强度不高,但与水泥浆体基质界面结合较好,用于开发具有某些特定功能的再生混凝土,如透水性再生混凝土,也成为当前再生混凝土技术新的研究方向。本文在对再生骨料和再生混凝土基本性质进行深入分析的基础上,提出了再生骨料的分级方法和适用范围。根据Andersen方程,对二元、三元、四元水泥-活性粉末体系进行级配优化,确定了活性粉末的最佳掺量,并用可压缩堆积理论计算了体系的实际堆积密实度,对优化的级配进行了验证。用原生混凝土强度等级为C40的Ⅱ级再生骨料,通过再生骨料预处理、采用活性粉末裹石工艺等技术措施,成功制备出干缩性小的活性粉末高强再生混凝土。根据体积指标确定透水性再生混凝土配合比设计的主要参数,提出了一种新的透水性再生混凝土的配合比设计方法,并利用硅灰对透水性再生混凝土的增强作用,研制出强度较高、透水性能优良的再生混凝土。本文的主要研究工作和结果如下:1.建立了掺或不掺活性粉末的再生混凝土抗压强度数据库,对影响普通再生混凝土、高强再生混凝土、活性粉末高强再生混凝土抗压强度的诸因素进行了系统深入的分析,提出了再生骨料的分级指标体系。结合文献和试验数据,建立了以表观密度、表观密度变异系数、吸水率、砂浆含量（或洛杉矶磨耗损失）和压碎值为指标的再生骨料的质量评价方法和分级体系,确定了不同品质再生骨料的适用范围:Ⅰ级再生骨料可直接应用于制备各强度等级的再生混凝土（RC15^RC60）;Ⅱ级再生骨料能直接应用于生产中等强度的再生混凝土（RC40以下）;Ⅲ级再生骨料只宜应用于生产等级较低的再生混凝土（RC30以下）。2.提出了制备活性粉末再生混凝土时水泥及活性粉末的选择原则和技术要求。通过优化再生骨料级配、活性粉末体系级配、采用粉末裹石工艺,可以改善再生混凝土过渡区结构,从而提高其强度。综合运用再生骨料预处理技术和活性粉末裹石工艺,并采用高强度水泥来进一步提高基体强度,成功制备出28d抗压强度达71.21MPa,抗折强度达7.98MPa的高强再生混凝土。其干缩性能也得到大幅改善,90d干缩率降低至29%。活性粉末高强再生混凝土的XRD、IR和SEM分析结果表明,水化产物中的Ca（OH）2数量减少、水化产物更为均匀密实、过渡区结构更为致密。3.借鉴沥青路面中沥青碎石玛蹄脂（Stone matrix asphalt,SMA）和开级配磨耗层（Open Graded Asphalt Friction Course ,OGFC）的配合比设计方法,提出了基于体积参数指标的透水性混凝土（或透水性再生混凝土）配合比设计方法。用这种设计方法研制得到了空隙率达19.29%、透水系数为8.3mm/s、28d抗压强度达19.03MPa的透水性再生混凝土。4.指出活性粉末材料与再生骨料粘结点的数量对透水性再生混凝土的强度起关键作用。在粉煤灰、硅灰和矿渣中,硅灰是最佳的增强活性粉末。比较了硅灰单掺、有机聚合物增粘剂（HEMC）单掺、硅灰和增粘剂（HEMC）双掺以及高强度水泥对再生混凝土的增强效果。结果表明,单掺硅灰的效果最好:掺入4%的硅灰,获得了28d抗压强度达26.37MPa,抗折强度为3.37MPa,透水系数为7.8mm/s的透水性再生混凝土。界面显微结构和红外光谱分析结果表明,硅灰的掺入能促进Ca（OH）₂继续水化,生成大量的水化硅酸钙（C-S-H）凝胶,提高了浆体的密实程度,从而提高了透水性再生混凝土的强度。5.将新老混凝土界面结构由渗透层、反应层和渐变层所构成的假设引入到透水性再生混凝土界面结构的研究中,并通过试验结果验证了反应层的存在。新的水泥浆体和再生骨料上粘附的旧砂浆通过反应层进行复杂的离子交换,活性粉末掺入使新浆体水化产物的尺寸变小,增强了离子的穿透能力,使反应层的离子交换活动增多,从而有利于提高界面的粘结强度。6.建立了二维平面的圆形颗粒和多边形颗粒有限元模型,用ANSYS软件对透水性再生混凝土的受压和受弯拉破坏进行了数值分析,模拟了受压破坏和受弯拉破坏的起始部位。结果表明,受压破坏主要发生在新的水泥浆体中,而受弯拉破坏既可发生在新浆体中,也可发生在旧砂浆中（当旧砂浆抗拉强度较小时）。分析了影响透水性再生混凝土抗压、抗折强度的因素,计算了活性粉末透水性再生混凝土的理论强度。理论计算和试验结果表明,用原生混凝土强度等级为C40的再生骨料制备的活性粉末透水性再生混凝土的抗压强度和抗折强度分别达到理论强度的90.3%和94.9%。更多还原

【Abstract】 Recycling of concrete is one of the hot spot issues for sustainable development of concrete in 21st century. Technology of recycled aggregate concrete (RAC) has attracted widely attention due to its distinguished environmental benefits, economic advantage and social returns. Relatively low strength and high dry shrinkage of RAC, however, often limit the extensive application to structural occasions. It is difficult to produce both cheap and quality-satisfying recycled aggregate (RA) by current crushing technology. As such, utilization of inferior or moderate RA (characterized by high crushing value and high water absorptive behavior) for structural concrete, where relatively high strength and low dry shrinkage are commonly required has become a pressing issue. In addition, character of low strength but good bonding between RA and the cement paste matrix makes it possible to develop functional recycled concrete, e.g., pervious recycled aggregate concrete, has become a new research orientation related to concrete recycling.Based on a deep investigation on basic properties of RA and RAC was completed. Grading method of RA and its recommended applications were then proposed. Gradation of binary, ternary and quaternary system of reactive powder (RP) and ordinary Portland cement (PO) was optimized according to Andersen formula. The proportion of RP was determined and verified by actual packing density calculated by compressible packing model (CPM). By pretreatment of ordinary RA (gradeⅡ,manufactured from C40 cement concrete),adoption of stone-enveloped with RP , etc., high strength and low dry shrinkage of RP reinforced high strength RAC(RP-HSRAC) was achieved. A novel proportioning design method mainly governed by volumetric parameters for pervious concrete was established. By utilization of silica fume, both high strength and excellent permeability of pervious concrete were achieved.The main research components and conclusions of this dissertation are summarized as follows.1. Database of RAC mainly related to compressive strength with or without active powder was established. Factors influencing compressive strength of RAC, high strength RAC(HSRAC) and reactive powder reinforced HSRAC(RP-HSRAC) were analyzed and summarized. Combining the experimental data and references, grading indexes of RA including apparent density, variation coefficient of apparent density, water absorption ratio, old mortar content (or Los Angeles loss) and crushing value were then put forward. Applicable scope of RA was determined: gradeⅠcan be used for RC15~RC60;gradeⅡis capable of production of RAC with a moderate strength (lower than 40MPa);gradeⅢis limited to lower strength concrete(lower than RC30).2. Principles and requirements for selection of RP and cement were determined. By optimizing gradation of RA and RP and adoption of stone-enveloped with reactive powder (SERP) results in modification of interfacial transition zone (ITZ) that leads to the improvement of the strength. By pretreatment of RA, SERP technology and utilization of high strength cement to strengthen the cement mortar matrix of RAC, high strength of RAC with 28d compressive strength of 71.2MPa, flexural strength of 7.9MPa was successfully manufactured in laboratory. Besides, 29% reduction of the dry shrinkage at 90 days’age was observed. XRD, IR and SEM analysis results reveals that less Ca(OH)2 in hydrates were produced in RP-HSRAC. Uniform and dense structure of both hydrates and ITZ can be observed.3. Enlightened by proportioning mix method for stone matrix asphalt (SMA) and open graded friction course (OGFC), a novel proportioning design method mainly governed by volumetric parameters for both no-fines pervious concrete and no-fines pervious recycled concrete(NPRC) was established. NPRC with 28d compressive strength of 19.03MPa, void volume of 19.29% and 8.3mm/s permeability coefficient was produced by the new method.4. It is pointed out that bonding points between RP and RA vital for the strength NPRC, and hence, silica fume is a type of ideal powder for improving strength when compared with fly ash(FA),blast slag(BS). Compared with polymer, addition of polymer and SF, use of high strength cement, SF proved effective for improvement of strength: recycled pervious concrete with 28d compressive strength of 26.37MPa , flexural strength of 3.37MPa and permeability coefficient of 7.8mm/s was manufactured when an optimum dosage of 4% silica fume was added into the mixture. SEM and IR analysis results indicate that addition of SF benefits to further hydration, which results in much more C-S-H and improves the density. Thus improves the strength of NPRC.5. The interfacial structure of new and old concrete was assumed consisting of permeable layer, reactive layer and transitional layer, which was introduced to investigate the interfacial structure of NPRC. The experimental results verified the existence of reactive layer. New paste exchanges icons through the reactive layer with the attached old mortar. Reactive powder contributes to uniform and small hydrates that help to enhance the permeability of icons. Thus, increases the exchange of icons and results in better bonding in the interfacial zone.6. Finite element model of plane circular particle and polygon particle was established, respectively. Analysis and simulation was conducted on compression and flexion state of pervious concrete. Original failure position was simulated for both compression and flexion test. The result shows that new mortar tends to fail first in compression. However, the new mortar or the old mortar can fail when the specimen is bending. Factors influencing compressive and flexural strength of NPRC were simulated and the theoretical strength of NPRC was calculated. The experimental and calculating results indicate that 90.3% and 94.9% of maximum theoretical compressive strength and flexural strength can be achieved, respectively.更多还原