废弃混凝土再生利用的研究进展

废弃混凝土再生利用的研究进展摘要：废弃混凝土再生利用技术是发展绿色混凝土，实现建筑、资源、环境可持续发展的必然要求和主流趋势，是推动建筑垃圾资源化进程的有效途径。本文结合我国资源紧缺及环境污染严重的现状，从生态效益、经济效益、社会效益方面分析了废弃混凝土再生利用的必要性及可行性。通过查阅和研究大量文献，对国内外再生混凝土的研究动态与应用情况进行了深入剖析和对比，综述了再生混凝土基本力学性能、耐久性能及变形性能，对废弃混凝土再生利用技术前景进行了展望。 关键词：废弃混凝土;再生骨料;再生混凝土;力学性能;耐久性;变形性能前言： 随着我国城市化进程的加快和城市建设规模的扩大，建筑业迎来了一个新的快速发展期，每年产生大量的建筑垃圾，其中废弃混凝土约占建筑垃摄总量的30% - 40%。2004年，全国建筑垃圾排放总量60亿吨，其中废弃混凝土约18 - 24亿吨。废弃混凝土是指旧建(构)筑物拆除、市政工程动迁、路面返修、重大基础设施改造、工程施工等过程中产生的废混凝土块及商品混凝土厂和预制构件厂产生的不合格混凝土。废弃混凝土通常采用露天堆放或填埋方式处理，故需要占用大面积的耕地，处理费用与运费较高。废弃混凝土清运和堆放过程中易造成粉尘、灰砂飞扬，严重污染大气，形成二次污染。另外，混凝土生产需要花费大量砂石骨料，随着对天然砂石的不断开采，天然骨料资源渐趋枯竭，生态环境日益恶化。废弃混凝土循环再生利用可解决其导致的资源、能源、环境及相关社会问题，缓解骨料供求矛盾，具有显著的社会效益、经济效益和环境效益，是环境保护与可持续发展战略的迫切需求。 1再生混凝土的相关概念 再生骨料混凝土(Recycled Aggregate Concrete,RAC)是指利用废弃混凝土破碎加工而成的再生骨料，部分或全部代替天然骨料配制而成的新混凝土，简称再生混凝土(RecycledConcrete,RC)。再生骨料(Recycled Aggregate，RA)是指废弃混凝土经特定处理、破碎、分级并按一定的比例混合后，形成的以满足不同使用要求的粒径在40mm以下的骨料。其中粒径在0.5-5mm的骨料为再生细骨料(Recycled Fme Aggregate，RFA)，粒径在5-40mm的骨料为再生粗骨料(Recycled Coarse Aggregate， RCA)。RCA一般为表面包裹着部分水泥砂浆的石子，小部分是与砂浆完全脱离的石子，还有极少一部分为水泥石颗粒， RFA主要由砂浆体破碎后形成的表面附着水泥浆的砂粒、表面无水泥浆的砂粒、水泥石颗粒及少量破碎石块所组成。 2废弃混凝土再生利用在各国立法状况 废弃混凝土再生利用已受到许多国家的重视，有些国家采用立法形式来保证此项研究和应用的发展。澳大利亚联邦科学与产业研究组织(CSIRO)于1998年颁布了再生混凝土骨料配制非结构混凝土指南， 2002年颁布了再生混凝土与砌筑材料使用指南，推动了再生混凝土骨料的应用。日本早在上世纪七十年代初就已尝试利用废弃混凝土作为再生骨料配制再生混凝土，废弃混凝土再生利用工厂相继在各地建立，制定了多项法规以保证再生混凝土发展，为废弃混凝土资源化利用提供了法律和制度的保障。1977年日本颁布再生骨料和再生混凝土使用规范， 1991年颁布资源重新利用促进法，规定建筑施工过程中产生的渣土、混凝土块、沥青混凝土块、术材、金属等建筑垃圾，必须经“再资源化设施”进行处理。2001年颁布建筑材料再循环法，规定将C1、C2、C3三种 类型的再生粗骨料及F1、F2两种类型的再生细骨料应用于非结构构件。2001年颁布推进形成循环型社会基本法、促进废弃物处理指定设施配备和资源有效利用促进法。德国制定了在混凝土中采用再生骨料的应用指南，要求用作再生骨料的混凝土必须完全符合天然骨料混凝土的国家标准。3再生混凝土的研究及应用进展 3.1废弃混疑土破碎与再生骨料加工工艺 废弃混凝土块的回收、破碎和再生骨料生产工艺是废弃混凝土再生利用的前提。废弃混凝土经破碎加工后，骨料表面粗糙度加大，棱角效应增加，骨料表面包裹着相当数量水混砂浆，混凝土块解体过程中的损伤积累导致再生骨料内部形成大量微裂纹。上述因素使得再生骨料与天然骨料相比，压碎指标及孔隙率较高，密度较小，吸水性强，粘结力弱，骨料强度较低，所以再生骨料主要用来配制中低强度的混凝土，道路建设中用于路基、路面、路面砖、马牙砖等工程，建筑工程中用于基础垫层、底板、填充墙、非结构构件等部位。再生骨料的加工方法是将各种破碎设备、传送机械、筛分设备、清除杂质设备一体化，经破碎、筛分、去除杂质等工序，再得到符合质量要求的再生骨料。日本用加热碾磨法、螺旋精碎法、机械粉碎法、重力浮选法等先进工艺改善了再生骨料的品质，其性能与天然骨料相当，可用以配制高强度混凝土。加热碾磨法是指将废弃混凝土加热至约300，包裹于再生骨料表面硬化的旧水泥浆逐渐软化，然后通过碾磨工序将其与废弃混凝土分离，获得清洁的原生骨料。螺旋精碎法是指利用螺杆轴去除再生骨料表面的水泥浆。机械粉碎法的主要装置是以钢球为媒介物、内部设有隔板的转筒。它在转动时，铜球沿水平、坚直方向移动，混凝土块在转筒内旋转，相互碰撞、摩擦、碾磨，利用隔板去除附着于骨料表面的水泥浆和砂浆。重力浮选法是指当采用顿式粉碎机、冲击破碎机、改进式棒磨机对废弃混凝土进行处理后，粒径大于8mm的骨料被分为再生粗骨料与砂浆颗粒，粒径小于8mm的骨料被分为5mm及5-8mm的再生细骨料。然后采用温式重力浮选机进行分选，砂浆颗粒、木材等轻物质位于上面，骨料等重物质在下面。 3.2再生混凝土性能研究进展 3.2.1再生混凝土力学性能研究现状 对再生混凝土主要力学性能的研究，大多侧重于抗压性能和弹性模量。再生骨料来源不同，组成成分、性能、碳化程度、配合比、养护条件、试验条件和试验方法各异，导致再生混凝土抗压强度试验数据离散性较大。李镜、尹健等采用三因素、三水平的正交试验设计方法，探讨了水胶比、再生骨料掺量、超细粉煤灰掺量等试验因素对再生混凝土强度的影响规律和机理，采用多元回归分析方法，建立了再生混凝土强度与水胶比、再生骨料掺量、超细粉煤灰掺量的经验公式。结果表明：水胶比是影响再生混凝土强度的最主要因素，也是最显著因素；与同强度等级的高强混凝土相比，掺粉煤灰再生混凝土的拉压比较大，抗裂能力好；再生混凝土抗折强度与胶水比、再生骨料掺量以及超细粉煤灰掺量之间线性关系良好。研究表明，与天然骨料混凝土相比，部分再生骨料混凝土后期抗压强度较高。全部使用再生骨料的混凝土抗压强度比天然骨料混凝土下降约8%。掺加微细硅粉与高效减水剂后，再生骨料混凝土抗压强度及劈裂抗拉强度显著提高。肖建庄对再生混凝土棱柱体试件进行单轴直接拉伸试验，结果表明与普通混凝土相比，再生混凝土峰值拉应变较大，弹性模量较低。随再生骨料取代率的增加，再生混凝土抗拉强度逐渐减小，弹性模量逐渐降低。再生粗骨料取代率为100%时，与普通混凝土相比，其抗拉强度减小31%，原点切缉模量降低29%。相同应力水平下，再生混凝土变形较大。夏琴对再生混凝土与普通混凝土的单轴受压性能进行了对比试验，发现：在相同配合比条件下，再生混凝土弹性模量比普通混凝土降低8%15%；再生混凝土的破坏形态与普通混凝土类似，其单轴受压的应力应变曲线上升段形状与普通混凝土相似；再生混凝土单轴受压峰值应变比普通混凝土高约10%。邓旭华通过试验建立了再生混凝土配制强度公式fcu，i=0.37fce(C/W+0.0071)。石建光在水灰比0.55和水泥、细骨料、粗骨料的配合比为1 : 2 : 2.75时，测试了不同粗骨料级配情况下的再生混凝土工作性能和抗压强度，结果表明：(包裹骨料需要的水泥浆体积与混凝土中水泥浆总体积的比值)大于0.085时，混凝土工作性能较差，抗压强度低；小于0.085时，混凝土工作性能较好，抗压强度高。采用再生骨料自然级配制备的混凝土尽管值较小，但工作性能差，抗压强度低。再生骨料取代率分别 为50%、60%、100%时，调整粒径范围9.5-26.5 mm的骨料，使其级配接近，再生混凝土强度高于天然骨料的混凝土强度。孙成城通过试验发现相同配合比条件下，再生粗骨料二次搅拌工艺拌制的混凝土强度比一次搅拌工艺拌制的混凝土高约12%。邓旭华结合超声和回弹的测试方法，探讨了水灰比对再生混凝土抗压强度的影响，结果表明：当水灰比大于0.57时，再生混凝土的抗压强度随着水灰比的增大而减小；当水灰比小子0.57时，再生混凝土的抗压强度随着水灰比的增大而增大。基准混凝土和再生混凝土超声声速和回弹值随水灰比的变化规律与其实际抗压强度值的变化规律基本一致。王军强发现随着再生骨料取代率的提高，再生混凝土的7d和28d抗压强度总体呈下降趋势；再生骨料取代率为100%时，与普通混凝土相比，再生混凝土28d抗压强度下降约5%。再生混凝土的相对动弹性模量低于普通混凝土。 4结论 再生混凝土技术解决了大量混凝土废弃物处理困难和由此引发的对环境的负面影响等问题，节省了垃圾清运费用和处理费用;可以充分利用可再生资源，减少对天然砂石的开采，保护了自然资源和人类生存环境。再生混凝土技术是可持续发展战略的必然要求和主流趋势，是解决建筑垃圾问题最有效的途径。随着人类对废弃混凝土再生利用方面研究和开发的深入发展，再生混凝土的应用范围将逐渐拓展。作为一种极具发展潜力的环境友好材料，再生混凝土技术必将成为混凝土材料科学的一个发展方向，并推动混凝土生产最终走上良性发展之路。 Research of recycling of waste concreteAbstract: the technology of recycling of waste concrete is the necessary requirement and mainstream trends of developing green concrete,achieving in sustainable development of architecture, resources and environment, is an effective way to promote the process of construction waste resources.The artile analyses the necessity and feasibility of the recycling of waste concrete from the ecological, economic, social aspects faced with resource shortage and environmental pollution in our country.Through access and an abundance of literature on the domestic dynamics of recycled concrete and application of research conducted in-depth analysis and comparison,the article reviews the basic mechanical properties ,durability and deformation properties of recycled concrete,gives a outlook of prospect of technology of the waste concrete recycling.Key words:waste concrete; recycled aggregate; recycled concrete; mechanical properties;durability; deformation propertiesIntroduction:With the accelerated process of urbanization and the expansion of the scale of urban construction, the construction industry entered a new period of rapid development, large amount of construction waste generated each year, waste concrete accounts for 30% - 40% of total construction rubbish.In 2004, total construction waste is 6 billion tons,waste concrete is about 1.8 - 2.4 billion tons. Waste concrete is waste concrete blocks generated in the process of an old building (structures) demolition, relocation of municipal projects,road repair,reconstruction of major infrastructure, engineering construction and substandard concrete produced by precast concrete plants and concrete plants. Usually open dumping of waste concrete or landfill disposal, they need large areas of land occupied, and the disposal costs and freight costs is higher. Process of collection, transport and stacking of concrete could easily lead dust, gray sand flying, seriously pollute the atmosphere, make a secondary pollution. In addition, the production takes a lot of sand and gravel concrete aggregate, with the continuous exploitation of natural sand, natural aggregate resources become more depleted, the ecological environment is deteriorating. Recycling waste concrete can solve energy, environmental and related social issues, eases contradiction of aggregate supply and demand, makes a significant social, economic and environmental benefits, is the urgent need of environmental protection and sustainable development strategy.1.A related concept of recycled concreteRecycled aggregate concrete (Recycled Aggregate Concrete, RAC) is recycled concrete made by recycled aggregate crushing process, some or all of the place of natural aggregate prepared for the new concrete, referred to as recycled concrete (RecycledConcrete, RC). Recycled aggregate (Recycled Aggregate, RA) is the waste concrete by specific treatment, crushing, classification according to a certain percentage of mixed, formed to meet the requirements of different particle size used in the following aggregate 40mm. Aggregate of which diameter is 0.5-5mm is fine aggregate (Recycled Fme Aggregate, RFA), aggregate of which the size is 5-40mm is coarse aggregate (Recycled Coarse Aggregate, RCA). RCA are stones generally coated with some cement, a small part is completely out of stone, rarely part of which are cement particles, RFA mainly formed by the mortar broken body attached to the surface of the sand slurry surface without slurry of sand, cement particles and composed of small broken stones.2 Legislation of Recycling of waste concrete Recycling of waste concrete has been payed attention to by many countries, some countries have adopted legislation to ensure the development of research and application. In 1998 Commonwealth Scientific and Industrial Research Organisation of Australia(CSIRO) promulgated the preparation of recycled concrete aggregate non-structural concrete guidelines，in 2002 promulgated theuse of recycled concrete and masonry materials, guidelines, and promoted the application of recycled concrete aggregate . In the early seventies of last century Japan had tried to use waste concrete as recycled aggregate preparation of concrete, concrete waste recycling plant have set up in various places,formulated a number of laws and regulations to ensure the development of recycled concrete for the utilization of waste concrete to provide a legal and institutional protection. In1977, Japan issued the use of recycled aggregate and recycled concrete specifications,in1991, issued there-use of resources for law, in the course of construction, resulting muck, concrete block, asphalt concrete blocks, surgery material, metal and other construction waste must be approved by “Recycling facility” for processing. In 2001 issued the Building materials recycling law, provides that three types of recycled coarse aggregate including C1, C2, C3 and two types of fine aggregate including F1, F2 are used in non-structural components. In 2001, enacted law of promoting the formation of a recycling society, designated facilities for waste treatment equipment and effective use of resources in law Germany has developed the use of recycled aggregates in concrete application of guidelines, asked that recycled aggregate concrete must be fully consistent with national standards of natural aggregate concrete.3 Research and application of recycled concrete 3.1 Broken of waste concrete and processing of recycled aggregates The recycling, crushing of waste concrete block and recycled aggregate production process is the premise of using recycled concrete. Waste concrete once was treated by crushing process, the aggregate surface roughness increased, angular effects of increased aggregate coated with a considerable amount of water, mortar, concrete block disintegration during damage accumulation leading to recycled aggregate within the formation of large cracks. Because of these factors ,comparied with natural aggregate ,recycled aggregate has higher porosity, lower density, absorbent, weaker adhesive power and lower aggregate strength, so recycled aggregate is mainly used preparation of low-strength concrete,it is used in roadbed, road surface, road blocks, horse teeth bricks and other projects in road construction, during construction projects it is mainly used in basic bedding, floor, filling the wall, non-structural components and other parts. Recycled aggregate processing method is to all kinds of broken equipment, transmission machinery, screening equipment to remove impurities equipment integration, by crushing, screening, removal of impurities and other processes, in may meet the quality requirements of recycled aggregate. Heated milling method, spiral fine pieces, mechanical grinding, gravity flotation and other advanced technology are used in Japan to improve the quality of recycled aggregate,the performance is as same as natural aggregate,it can be used to prepare high-intensity concrete. Heating milling method is to heat waste concrete to about 300 , the old slurry gradually softened wrapped in recycled aggregate surface turn to soften, and then separate it with waste concrete by milling process, then get clean native aggregate. Spiral fine crushed France is to use screw shaft to remove water slurry of recycled aggregate surface. The main device of mechanical crushing method is a drum which the vehicle is a ball, the separator is set in internal.During the rotation, the copper ball along the horizontal, erect, move, concrete block in the switch barrel rotation, each collision, friction, grinding, using partitions to remove attached aggregate surface of the cementPaste and mortar. Gravity flotation means that when treating the recycled concrete by Dayton crusher, impact crusher, improved type rod mill, the aggregate whose diameter is greater than 8mm is divided into recycled coarse aggregate and mortar particles, aggregate whose diameter is lower than 8mm is divided into 5mm and 5-8mm recycled fine aggregate. Then sort them by temperature-type gravity flotation machine, mortar particles, wood and other light material are at the top, aggregate and other heavy material are below.3.2 Progress of performance of recycled concrete3.2.1 Research on mechanical properties of recycled concreteThe main research of mechanical properties of recycled concrete, mostly focused on the compressive properties and modulus of elasticity. Different sources of recycled aggregate, difference of composition, performance, carbonation level, mixing ratio, curing conditions, test conditions and test methods, resulting in greater dispersion of compressive strength test data. Li Jing,Yin Jian, etc explore the water cement ratio, recycled aggregate quantity, fine fly ash and other experimental factors on the strength of recycled concrete rules and mechanism by three factors, three level orthogonal experimental design, using multiple regression analysis,Established the strength of the recycled water-cement ratio, recycled aggregate quantity, ultra-fine fly ash in the empirical formula. The results showed that: water-cement ratio is the most important factor and the most significant factor to impact strength of recycled concrete,; comparied with the same strength grade of high strength concrete , tension and compression of fly ash recycled concrete are relatively larger, and crack resistance is better; recycled concrete bending strength and water binder ratio, recycled aggregate quantity and fine a good linear relationship between the fly ash. Summary of the study showed that compared with natural aggregate concrete, some of the recycled aggregate concrete has a higher post compressive strength. All use of recycled aggregateThan the natural aggregate concrete compressive strength of concrete decreased by about 8%. Mixed with fine silica fume and superplasticizer, the recycled aggregate concrete compressive strength and splitting tensile strength improved significantly. Recycled Concrete on the recycled concrete prism specimen uniaxial direct tension test results show that compared with ordinary concrete, recycled concrete higher peak tensile strain, elastic modulus is low. With the increase of recycled aggregate replacement ratio, gradually reduce the tensile strength of recycled concrete, the elastic modulus decreased. Recycled coarse aggregate rate of 100%, compared with ordinary concrete, the tensile strength decreased 31%, cut the origin Ji-modulus reduced by 29%. Under the ame tress level, deformation of recycled concrete. Xia Qin made a compared test between recycled concrete and ordinary concrete under uniaxial loading,found that: in the same mix proportions of recycled concrete elastic modulus lower than that of normal concrete 8% -15%; recycled concrete and common failure modes concrete is similar to the uniaxial compression stress-strain curves up section shape similar to ordinary concrete; recycled aggregate concrete under uniaxial compression of concrete higher than the average peak strain of about 10%. Deng Xuhua established by test preparation strength of recycled concrete formula fcu, i = 0.37fce (C / W +0.0071). Dan Jianguang 0.55 in water-cement ratio and cement, fine aggregate, coarse aggregateThe mixture ratio of 1: 2: 2.75 when tested with different coarse aggregate gradation in case of performance and compressive strength of recycled concrete, results showed that: (packages need to cement aggregate and concrete slurry volume of total volume ratio) is greater than 0.085, the poor performance of concrete, compressive strength, low; is less than 0.085, the better performance concrete, high compressive strength. Use of recycled aggregate concrete prepared with natural level value despite the smaller, but performance is poor, its compressive strength. Recycled aggregate replacement rates were 50%, 60%, 100%, adjust the size range of 9.5-26.5 mm of aggregate, gradation to close higher than the natural strength of the recycled aggregate concrete. Sun City into the same mix was found by experiment under the conditions of the second mixing process of recycled coarse aggregate concrete mixing intensity ratio of a mixing process to mix the concrete by around 12%. Deng Xuhua combination of ultrasound and the rebound of the test method, the water cement ratio of the impact on the compressive streng