廢棄混凝土再生利用的研究進(jìn)展

廢棄混凝土再生利用的研究進(jìn)展摘要：廢棄混凝土再生利用技術(shù)是發(fā)展綠色混凝土，實(shí)現(xiàn)建筑、資源、環(huán)境可持續(xù)發(fā)展的必然要求和主流趨勢(shì)，是推動(dòng)建筑垃圾資源化進(jìn)程的有效途徑。本文結(jié)合我國(guó)資源緊缺及環(huán)境污染嚴(yán)重的現(xiàn)狀，從生態(tài)效益、經(jīng)濟(jì)效益、社會(huì)效益方面分析了廢棄混凝土再生利用的必要性及可行性。通過(guò)查閱和研究大量文獻(xiàn)，對(duì)國(guó)內(nèi)外再生混凝土的研究動(dòng)態(tài)與應(yīng)用情況進(jìn)行了深入剖析和對(duì)比，綜述了再生混凝土基本力學(xué)性能、耐久性能及變形性能，對(duì)廢棄混凝土再生利用技術(shù)前景進(jìn)行了展望。 關(guān)鍵詞：廢棄混凝土;再生骨料;再生混凝土;力學(xué)性能;耐久性;變形性能前言： 隨著我國(guó)城市化進(jìn)程的加快和城市建設(shè)規(guī)模的擴(kuò)大，建筑業(yè)迎來(lái)了一個(gè)新的快速發(fā)展期，每年產(chǎn)生大量的建筑垃圾，其中廢棄混凝土約占建筑垃攝總量的30% - 40%。2004年，全國(guó)建筑垃圾排放總量60億噸，其中廢棄混凝土約18 - 24億噸。廢棄混凝土是指舊建(構(gòu))筑物拆除、市政工程動(dòng)遷、路面返修、重大基礎(chǔ)設(shè)施改造、工程施工等過(guò)程中產(chǎn)生的廢混凝土塊及商品混凝土廠(chǎng)和預(yù)制構(gòu)件廠(chǎng)產(chǎn)生的不合格混凝土。廢棄混凝土通常采用露天堆放或填埋方式處理，故需要占用大面積的耕地，處理費(fèi)用與運(yùn)費(fèi)較高。廢棄混凝土清運(yùn)和堆放過(guò)程中易造成粉塵、灰砂飛揚(yáng)，嚴(yán)重污染大氣，形成二次污染。另外，混凝土生產(chǎn)需要花費(fèi)大量砂石骨料，隨著對(duì)天然砂石的不斷開(kāi)采，天然骨料資源漸趨枯竭，生態(tài)環(huán)境日益惡化。廢棄混凝土循環(huán)再生利用可解決其導(dǎo)致的資源、能源、環(huán)境及相關(guān)社會(huì)問(wèn)題，緩解骨料供求矛盾，具有顯著的社會(huì)效益、經(jīng)濟(jì)效益和環(huán)境效益，是環(huán)境保護(hù)與可持續(xù)發(fā)展戰(zhàn)略的迫切需求。 1再生混凝土的相關(guān)概念 再生骨料混凝土(Recycled Aggregate Concrete,RAC)是指利用廢棄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，簡(jiǎn)稱(chēng)再生混凝土(RecycledConcrete,RC)。再生骨料(Recycled Aggregate，RA)是指廢棄混凝土經(jīng)特定處理、破碎、分級(jí)并按一定的比例混合后，形成的以滿(mǎn)足不同使用要求的粒徑在40mm以下的骨料。其中粒徑在0.5-5mm的骨料為再生細(xì)骨料(Recycled Fme Aggregate，RFA)，粒徑在5-40mm的骨料為再生粗骨料(Recycled Coarse Aggregate， RCA)。RCA一般為表面包裹著部分水泥砂漿的石子，小部分是與砂漿完全脫離的石子，還有極少一部分為水泥石顆粒， RFA主要由砂漿體破碎后形成的表面附著水泥漿的砂粒、表面無(wú)水泥漿的砂粒、水泥石顆粒及少量破碎石塊所組成。 2廢棄混凝土再生利用在各國(guó)立法狀況 廢棄混凝土再生利用已受到許多國(guó)家的重視，有些國(guó)家采用立法形式來(lái)保證此項(xiàng)研究和應(yīng)用的發(fā)展。澳大利亞聯(lián)邦科學(xué)與產(chǎn)業(yè)研究組織(CSIRO)于1998年頒布了再生混凝土骨料配制非結(jié)構(gòu)混凝土指南， 2002年頒布了再生混凝土與砌筑材料使用指南，推動(dòng)了再生混凝土骨料的應(yīng)用。日本早在上世紀(jì)七十年代初就已嘗試?yán)脧U棄混凝土作為再生骨料配制再生混凝土，廢棄混凝土再生利用工廠(chǎng)相繼在各地建立，制定了多項(xiàng)法規(guī)以保證再生混凝土發(fā)展，為廢棄混凝土資源化利用提供了法律和制度的保障。1977年日本頒布再生骨料和再生混凝土使用規(guī)范， 1991年頒布資源重新利用促進(jìn)法，規(guī)定建筑施工過(guò)程中產(chǎn)生的渣土、混凝土塊、瀝青混凝土塊、術(shù)材、金屬等建筑垃圾，必須經(jīng)“再資源化設(shè)施”進(jìn)行處理。2001年頒布建筑材料再循環(huán)法，規(guī)定將C1、C2、C3三種 類(lèi)型的再生粗骨料及F1、F2兩種類(lèi)型的再生細(xì)骨料應(yīng)用于非結(jié)構(gòu)構(gòu)件。2001年頒布推進(jìn)形成循環(huán)型社會(huì)基本法、促進(jìn)廢棄物處理指定設(shè)施配備和資源有效利用促進(jìn)法。德國(guó)制定了在混凝土中采用再生骨料的應(yīng)用指南，要求用作再生骨料的混凝土必須完全符合天然骨料混凝土的國(guó)家標(biāo)準(zhǔn)。3再生混凝土的研究及應(yīng)用進(jìn)展 3.1廢棄混疑土破碎與再生骨料加工工藝 廢棄混凝土塊的回收、破碎和再生骨料生產(chǎn)工藝是廢棄混凝土再生利用的前提。廢棄混凝土經(jīng)破碎加工后，骨料表面粗糙度加大，棱角效應(yīng)增加，骨料表面包裹著相當(dāng)數(shù)量水混砂漿，混凝土塊解體過(guò)程中的損傷積累導(dǎo)致再生骨料內(nèi)部形成大量微裂紋。上述因素使得再生骨料與天然骨料相比，壓碎指標(biāo)及孔隙率較高，密度較小，吸水性強(qiáng)，粘結(jié)力弱，骨料強(qiáng)度較低，所以再生骨料主要用來(lái)配制中低強(qiáng)度的混凝土，道路建設(shè)中用于路基、路面、路面磚、馬牙磚等工程，建筑工程中用于基礎(chǔ)墊層、底板、填充墻、非結(jié)構(gòu)構(gòu)件等部位。再生骨料的加工方法是將各種破碎設(shè)備、傳送機(jī)械、篩分設(shè)備、清除雜質(zhì)設(shè)備一體化，經(jīng)破碎、篩分、去除雜質(zhì)等工序，再得到符合質(zhì)量要求的再生骨料。日本用加熱碾磨法、螺旋精碎法、機(jī)械粉碎法、重力浮選法等先進(jìn)工藝改善了再生骨料的品質(zhì)，其性能與天然骨料相當(dāng)，可用以配制高強(qiáng)度混凝土。加熱碾磨法是指將廢棄混凝土加熱至約300，包裹于再生骨料表面硬化的舊水泥漿逐漸軟化，然后通過(guò)碾磨工序?qū)⑵渑c廢棄混凝土分離，獲得清潔的原生骨料。螺旋精碎法是指利用螺桿軸去除再生骨料表面的水泥漿。機(jī)械粉碎法的主要裝置是以鋼球?yàn)槊浇槲?、?nèi)部設(shè)有隔板的轉(zhuǎn)筒。它在轉(zhuǎn)動(dòng)時(shí)，銅球沿水平、堅(jiān)直方向移動(dòng)，混凝土塊在轉(zhuǎn)筒內(nèi)旋轉(zhuǎn)，相互碰撞、摩擦、碾磨，利用隔板去除附著于骨料表面的水泥漿和砂漿。重力浮選法是指當(dāng)采用頓式粉碎機(jī)、沖擊破碎機(jī)、改進(jìn)式棒磨機(jī)對(duì)廢棄混凝土進(jìn)行處理后，粒徑大于8mm的骨料被分為再生粗骨料與砂漿顆粒，粒徑小于8mm的骨料被分為5mm及5-8mm的再生細(xì)骨料。然后采用溫式重力浮選機(jī)進(jìn)行分選，砂漿顆粒、木材等輕物質(zhì)位于上面，骨料等重物質(zhì)在下面。 3.2再生混凝土性能研究進(jìn)展 3.2.1再生混凝土力學(xué)性能研究現(xiàn)狀 對(duì)再生混凝土主要力學(xué)性能的研究，大多側(cè)重于抗壓性能和彈性模量。再生骨料來(lái)源不同，組成成分、性能、碳化程度、配合比、養(yǎng)護(hù)條件、試驗(yàn)條件和試驗(yàn)方法各異，導(dǎo)致再生混凝土抗壓強(qiáng)度試驗(yàn)數(shù)據(jù)離散性較大。李鏡、尹健等采用三因素、三水平的正交試驗(yàn)設(shè)計(jì)方法，探討了水膠比、再生骨料摻量、超細(xì)粉煤灰摻量等試驗(yàn)因素對(duì)再生混凝土強(qiáng)度的影響規(guī)律和機(jī)理，采用多元回歸分析方法，建立了再生混凝土強(qiáng)度與水膠比、再生骨料摻量、超細(xì)粉煤灰摻量的經(jīng)驗(yàn)公式。結(jié)果表明：水膠比是影響再生混凝土強(qiáng)度的最主要因素，也是最顯著因素；與同強(qiáng)度等級(jí)的高強(qiáng)混凝土相比，摻粉煤灰再生混凝土的拉壓比較大，抗裂能力好；再生混凝土抗折強(qiáng)度與膠水比、再生骨料摻量以及超細(xì)粉煤灰摻量之間線(xiàn)性關(guān)系良好。研究表明，與天然骨料混凝土相比，部分再生骨料混凝土后期抗壓強(qiáng)度較高。全部使用再生骨料的混凝土抗壓強(qiáng)度比天然骨料混凝土下降約8%。摻加微細(xì)硅粉與高效減水劑后，再生骨料混凝土抗壓強(qiáng)度及劈裂抗拉強(qiáng)度顯著提高。肖建莊對(duì)再生混凝土棱柱體試件進(jìn)行單軸直接拉伸試驗(yàn)，結(jié)果表明與普通混凝土相比，再生混凝土峰值拉應(yīng)變較大，彈性模量較低。隨再生骨料取代率的增加，再生混凝土抗拉強(qiáng)度逐漸減小，彈性模量逐漸降低。再生粗骨料取代率為100%時(shí)，與普通混凝土相比，其抗拉強(qiáng)度減小31%，原點(diǎn)切緝模量降低29%。相同應(yīng)力水平下，再生混凝土變形較大。夏琴對(duì)再生混凝土與普通混凝土的單軸受壓性能進(jìn)行了對(duì)比試驗(yàn)，發(fā)現(xiàn)：在相同配合比條件下，再生混凝土彈性模量比普通混凝土降低8%15%；再生混凝土的破壞形態(tài)與普通混凝土類(lèi)似，其單軸受壓的應(yīng)力應(yīng)變曲線(xiàn)上升段形狀與普通混凝土相似；再生混凝土單軸受壓峰值應(yīng)變比普通混凝土高約10%。鄧旭華通過(guò)試驗(yàn)建立了再生混凝土配制強(qiáng)度公式fcu，i=0.37fce(C/W+0.0071)。石建光在水灰比0.55和水泥、細(xì)骨料、粗骨料的配合比為1 : 2 : 2.75時(shí)，測(cè)試了不同粗骨料級(jí)配情況下的再生混凝土工作性能和抗壓強(qiáng)度，結(jié)果表明：(包裹骨料需要的水泥漿體積與混凝土中水泥漿總體積的比值)大于0.085時(shí)，混凝土工作性能較差，抗壓強(qiáng)度低；小于0.085時(shí)，混凝土工作性能較好，抗壓強(qiáng)度高。采用再生骨料自然級(jí)配制備的混凝土盡管值較小，但工作性能差，抗壓強(qiáng)度低。再生骨料取代率分別 為50%、60%、100%時(shí)，調(diào)整粒徑范圍9.5-26.5 mm的骨料，使其級(jí)配接近，再生混凝土強(qiáng)度高于天然骨料的混凝土強(qiáng)度。孫成城通過(guò)試驗(yàn)發(fā)現(xiàn)相同配合比條件下，再生粗骨料二次攪拌工藝拌制的混凝土強(qiáng)度比一次攪拌工藝拌制的混凝土高約12%。鄧旭華結(jié)合超聲和回彈的測(cè)試方法，探討了水灰比對(duì)再生混凝土抗壓強(qiáng)度的影響，結(jié)果表明：當(dāng)水灰比大于0.57時(shí)，再生混凝土的抗壓強(qiáng)度隨著水灰比的增大而減??；當(dāng)水灰比小子0.57時(shí)，再生混凝土的抗壓強(qiáng)度隨著水灰比的增大而增大?；鶞?zhǔn)混凝土和再生混凝土超聲聲速和回彈值隨水灰比的變化規(guī)律與其實(shí)際抗壓強(qiáng)度值的變化規(guī)律基本一致。王軍強(qiáng)發(fā)現(xiàn)隨著再生骨料取代率的提高，再生混凝土的7d和28d抗壓強(qiáng)度總體呈下降趨勢(shì)；再生骨料取代率為100%時(shí)，與普通混凝土相比，再生混凝土28d抗壓強(qiáng)度下降約5%。再生混凝土的相對(duì)動(dòng)彈性模量低于普通混凝土。 4結(jié)論 再生混凝土技術(shù)解決了大量混凝土廢棄物處理困難和由此引發(fā)的對(duì)環(huán)境的負(fù)面影響等問(wèn)題，節(jié)省了垃圾清運(yùn)費(fèi)用和處理費(fèi)用;可以充分利用可再生資源，減少對(duì)天然砂石的開(kāi)采，保護(hù)了自然資源和人類(lèi)生存環(huán)境。再生混凝土技術(shù)是可持續(xù)發(fā)展戰(zhàn)略的必然要求和主流趨勢(shì)，是解決建筑垃圾問(wèn)題最有效的途徑。隨著人類(lèi)對(duì)廢棄混凝土再生利用方面研究和開(kāi)發(fā)的深入發(fā)展，再生混凝土的應(yīng)用范圍將逐漸拓展。作為一種極具發(fā)展?jié)摿Φ沫h(huán)境友好材料，再生混凝土技術(shù)必將成為混凝土材料科學(xué)的一個(gè)發(fā)展方向，并推動(dòng)混凝土生產(chǎn)最終走上良性發(fā)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