外文翻译废弃混凝土再生新技术探索

1、废弃混凝土再生新技术探索【摘 要】 本文对目前废弃混凝土再生技术的研究做了论述 ，并指出了其 中存在的一些问题。结合混凝土各组成部分的结构特点 ，提出了通过低温煅烧对 废弃混凝土综合利用的新方法。在 750C温度条件下煅烧1h,可以实现水泥浆与 骨料的分离。脱水后的水泥浆可以重新获得水化活性。 得到的混凝土骨料可以满 足使用要求。【关键词】废弃混凝土 ；再生技术;煅烧;水化活性;压碎指标【中图分类号】TU352 8【文献标识码】A【文章编号】1001-6864(2009)09-0004-02国家“十五计划”纲要指出：“坚持资源开发与节约并举，把节约放在首位, 法保护和合理使用资源，提高资源利用

2、率，实现永续利用。推进资源综合利用技术 研究开发，加强废旧物资回收利用，加快废弃物处理的产业化，促进废弃物转化为 可用资源。”保护环境、节约能源、减少废料、以持续的方式使用可再生资源是 可持续发展战略的重要内容。建材工业是典型的基础原料工业，在国民经济发展中具有重要作用。建材工业又是典型的资源、能源消耗型工业，在其快速发展的同时，面临着资源、能源的过度消耗和环境的严重污染。建筑和建材行业的根本 出路就是走可持续发展的道路1。起初，我国对混凝土的利用仅是简单的破碎充 当再生粗骨料，这种生产的再生骨料性能与天然粗骨料的性能存在一定差异，主要 表现在密度低、吸水率高、压碎指标大，表明再生骨料的空隙率

3、高，强度低,这主要 是由于其表面附着有大量水泥砂浆及在破碎过程中引入一定量的微裂纹的缘故2,生成的混凝土性能低，耐久性、抗冻融、抗腐蚀能力差。研究者根据再生骨料 再利用过程中存在的问题，对再生骨料进行了物理、化学改性以及整形改性。如 朱崇绩等通过整形除去再生骨料表面的砂浆，使颗粒变得光滑，需水量降低，使所 配制的混凝土收缩降低，但仍高于天然骨料混凝土 3。没有解决再生骨料中微裂 纹带来的弊端。目前有研究者对废弃混凝土进行了综合利用研究，通过筛分获得砌筑砂浆或进步筛分生产具有水化活性的再生水泥。如孙荣光等4对旧水泥浆高温处理后的再水化胶凝特性研究，得出再生水泥具有再水化的能力，同时生成 C-S-

4、H凝胶、Aft和CH等物质，说明水化产物结构相同，但由于大量脱水相的存在 使水化速度快。余睿等5通过对水泥浆的研究得出石膏和粉煤灰组成改性剂能 延长活化水泥浆的初凝时间，增强其抗压强度，但不能减少活化水泥浆的标准稠度 需水量。由于易水化的水泥石脱水需要时间，所以煅烧时间和脱水温度对再生水 泥性能不容忽视。1 .废弃混凝土裂解温度确定混凝土是由水泥、粗细集料、矿物掺合料等加水拌合，经水化硬化而形成的一种微观不均匀，宏观均匀的人造石。废弃混凝土在低温煅烧时的温度由水泥脱 水温度与石灰石分解温度共同决定。1 1水泥水化产物脱水温度文献认为,含水矿物中普通吸附水的脱水温度一般为100110°

5、C ,存在于层状硅酸盐结构中的层间水或胶体矿物中的胶体水多数要在200300C以内脱水，个别要在400C以内脱水；架状结构的硅酸盐结构水则要在 400C左右才大量脱出。 结晶水在不同结构中的矿物中结合程度不同，其脱水温度也不同。结构水是矿物 中结合最牢的水，脱水温度较高，一般要在450C以上才脱水 。为了确定废弃混凝土的低温煅烧温度，保证在该温度条件下骨料和水泥浆能够充分分离，水泥石完 全脱水,本课题对水泥浆进行了热重分析 （TGA）,热失重曲线及（TG）及差热曲线 （DTG）如图1所示。-7.5-&0-9.0-9,5-10,0温度/毛-7.08*5图I水泥浆的熔重分析曲线从图1可以看

6、出，水泥浆在100C前后分别有一个明显的失重过程，理论上应 当是失去自由水和弱吸附水所形成的过程。在500r以前又有一个明显的失重过程，该失重过程温度范围较窄，但失重速度较快，从水泥石的组成看应当是Ca（OH）2 失水形成的。另一个水泥石脱水过程发生在682775°C之间,脱水的峰值速率发生 在740C。这一过程脱水过程剧烈，持续时间较长，这一失水过程使C-S-H凝胶分 解，重新生成为具有潜在水化活性的胶凝材料。温度继续升高，直至1000C再无明显的吸热峰出现。另外，温度再渡升高可能影响混凝土骨料的结构。因此，混凝土分解温度确定为750C。经过高温处理的水泥浆因脱水而重新获得水化活性

7、，这一 性能已在实验中得到证实。1 2碎石分解温度粗骨料（碎石）的成分主要由 CaCO3和在少量的MgCO3组成，其中MgCO3 的分解温度较低,600C就开始剧烈反应,CaCO3剧烈分解温度则更高达到 900C 左右但其开始分解温度较低,在650C就开始分解。所以在550900C范围内煅烧 混凝土时，随着温度的升高，骨料发生分解的量增大，使骨料的强度降低。过渡区是 混凝土的薄弱环节，一方面搅拌时在骨料表面被水膜覆盖,妨碍了水泥粒子与骨料 表面接触，骨料周边水灰比变大，另一方面，水化反应溶出的迁移性大的Ca2+、AI3+、SO4-3离子为使浓度平衡向骨料表面扩散。在骨料表面附近，六角板状结 晶

8、的氢氧化钙和针状结晶的钙钒石的析出比较显著，形成大且连续的空隙构造8。使过渡区的水分也几乎以层间水及自由水的形式存在，所以在较低的煅烧温度就可实现骨料与水泥砂浆的分离，理论上在300C以上即可实现分离。为了探究 煅烧温度对骨料强度的影响，本试验分别对600、700、800C煅烧温度时所得到的 粗骨料压碎值进行了研究，并与天然碎石和直接破碎的混凝土进行了比较，实验结 果如图所示。800天然骨料破碎混艇土o on64 2600T 700图2碎石的压碎脂标从图2可知在燃烧温度600C时，碎石的压碎指标略高于天然碎石，而随燃烧 温度的提高，压碎指标明显增大，标志着骨料强度降低。但在 800r所得到的骨

9、料 强度仍高于混凝土直接破碎得到的骨料强度，所以在混凝土煅烧温度不超过800 C时是可行的。2结语根据混凝土各组分的结构特点，采取煅烧的方法把骨料和水泥浆分离是可行 的。经分解后的粗骨料可以在新拌混凝土中应用，其强度高于混凝土直接破碎得到的再生骨料。经分离得到的水泥浆重新获得了再次水化的活性。为废弃混凝土的回收以及骨料和水泥浆的再生和利用开辟了一条新的途径。参考文献1 水中和，曹禧禧,万惠文废弃混凝土再生利用技术及其发展前景J 资源节约 与综合利用，2006,(3):8-11 2 王耀新.混合应用天然与再生骨料混凝土的基本性能J 混凝 土 ,2005,(8):49-53 3 朱崇绩，李秋义,李

10、云霞.颗粒整形对再生骨料混凝土耐久性的影响J 水泥与 混凝土 ,2007,(3):6-10 4 孙荣光，余睿，玄东兴,水中和.旧水泥浆高温处理后的再水化胶凝特性研究J. 武汉理工大学学报，2007,(9):115-1185 余睿，水中和,玄东兴.再生水泥浆的改性研究J 2009,(4):104-1076 SidneyMindess 混凝土(原著第二版)M.吴科如，等译北京：化学工业出版 社,2005 - 1 7 王培铭许乾慰.材料研究方法M.北京:科学出版社,2005,236-2498 徐新生，徐卫生.混凝土过渡区对混凝土物质渗透性影响J 山东建 材,1999,(3):10-13 EXPLOR

11、ATION ON REC YCLING TECHNOLOG Y OF WASTE CONCRETEMA Xi n-weil,ZHANG Do ng-qi ng2, YINWei-fe ng2,LI Ning2(1 epartme nt of Civil Engin eeri ng, Harbi n In stitute ofTech no logy at Weihai, Sha ndo ng Weihai 264209, Chi na;2School ofMaterials Scie nee and En gi neeri ng, Harbi n In stitute ofTech no lo

12、gy, Harbi n 150001, Chi na)Abstract:The curre nt research situati on on the recycli ng tech no logy ofwaste con crete and existi ng problems in applicati on was summarized on sideri ngthe - structural characteristics of ceme nt paste and aggregate, a new recycli ng tech no logy through calc in ati o

13、n is prese ntedThe cement paste and aggregates could be separated at 750°C for one hour - The dehydrated cement paste can have reactivity again, and the aggregates can meet the requireme nt of applicati onKey words:waste con crete;recycl yin gte;ch no logy;calc in ati on; reactivity;crushi ng i

14、ndexNational "tenth five-year plan" outline pointed out: "insists resource developme nt and save the save itself, in the first place, protect and rati on ally use method of resources, and improve the resource utilizatio n rate, to achieve susta in able use. Push tech no logy research

15、and developme nt resources comprehe nsive utilizati on of waste materials, strengthen recycling, accelerate the industrialization, promote waste disposal of waste into usable resources." Protect the environment and save energy, reducing waste, with continuous way, using renewable resource is th

16、e importa nt content of strategy of susta in able developme nt. The buildi ng materials industry is typical of basic raw materials industry in the national economy development, plays an important role. The building materials industry is typical resources, energy consumption industries in its rapid d

17、evelopment, at the same time, facing the excessive con sumpti on of resources, en ergy and en vir onmen tal polluti on. Con structio n and buildi ng materials in dustry is the fun dame ntal way to walk the path of susta in able developme nt 1.At first, the use of con crete in the crushi ng only a si

18、mple as recycled coarse aggregate, the production of natural regeneration aggregate performanee and the performa nee of coarse aggregate, mai n show there is some differe nee in den sity low, bibulous rate is high, crush in dex is big, show the gap rege nerati on aggregate rate high, low intensity,

19、and it is mainly becausethe surface adhesion has large cement mortar and crushi ng process in certa in micro cracks of in troduci ng the sake 2 and gen erated con crete performa nee low, durability, freez in g-thaw ing resisti ng, corrosi on resista nee is poor. The researchers based on ren ewable a

20、ggregate reuse the problems existing in the processof recycled aggregate, carried on the physical and chemical modificati on and plastic modificati on. As such ZhuCh ong performa nee by plastic toremove the mortar, ren ewable aggregate surface water that particles, smooth, prepared by reducing shrin

21、kage of concrete lower, but still higher than the natural aggregate con crete 3. Not solve the rege nerati on aggregate micro cracks in the malpractices. Currently have researchers of the waste comprehensive utilization of concrete research, through the scree ning get bonding mortar or progress scre

22、e ning product ion of renewable cement hydration activity with. If SunRongGuang etc 4 to the old cement. after high temperature treatment of slurry rehydration characteristics study gel, it is con cluded that ren ewable ceme nt with a rehydrati on ability, while gen erat ing C - S - H gel, Aft and C

23、H that hydrati on products such material, but same structure dehydrated phases because of the existe nee of hydratio n speed to. YuRui etc 5 for water mud through the research that fly ash and compositi on modifier gypsum slurry can exte nd the in itial sett ing activatio n time and stre ngthe n the

24、 compressive stre ngth, however does not reduce activation of standard slurry water viscosity. Due to easy hydrati on of ceme nt stone dehydrati on n eed time, so calc ining time and dehydrati on temperature of recycled ceme nt performa nee cannot be igno red.1. Determi ne the decompositi on tempera

25、ture of waste con creteConcrete is made of cement, thick aggregate, such as mineral admixture, the water hydrati on sclerosis regardi ng mix-proporti on formed a microscopic un eve n, macro un iform man-made stone. Aba ndoned the con crete in low temperature calci nati on temperature by ceme nt dehy

26、drati on temperature decompositi on temperatures decided together with limest one.1 1 ceme nt hydratio n products dehydrati on temperatureLiterature in mi nerals that water cut the dehydrati on temperature ordinary adsorpti on water for 100 110 °C com mon ly, exists in layer silicate structure

27、between layers of the colloid water or colloid mineral water in 200 300 much C in with in dehydrati on, in dividual C 400 with in dehydrati on; Frame shape structure of silicate structure in 400 C water is only around large emerge. The minerals in differe nt structure gesso comb in ati on of differe

28、 nt degree, the dehydratio n temperature is differe nt. Structure comb in ati on of water is min eral water, the most jail dehydrati on temperature is higher, typically in 450 C above just dehydration 5. In order to determ ine the low temperature calc ining temperature waste con crete, guara ntee th

29、e temperature con diti ons in slurry aggregates, and can be fully separati on, ceme nt stone completely dehydration, this topic to the slurry thermogravimetric analysis (TGA), thermo-gravimetric curve and (TG) and differe ntial thermal curve (DTG) as show n in figure 1 below.From figure 1 in 100

30、76;C , water slurry before an obvious weightlessness, respectivelyn theory should be losing process of free water and weak adsorption water by the formation of the process. In 500 C ago and have an obvious of weightless ness process, this weightless ness process temperature range is n arrower, but w

31、eightless ness faster, the compositi on of the ceme nt paste.the watch from shall be the Ca (OH) 2 water loss formatio n. Ano ther ceme nt stone an hydrati on process occurs in 682 775 C between, dehydration rate occurred in 740 C peak. This process a severe dehydrati on process, continues for a lon

32、g time, the water loss process makes C -S - H gel decomposition, born again into a potential hydration activity of cementitious material. Temperature continues to rise again until 1000 C , has no obvious heat-s ink peak appeari ng. In additi on, temperature rise aga in cross ing may in flue nee the

33、structure of con crete aggregate. Therefore, con crete decompositi on temperature determined for 750 C . The slurry high-temperature processing for dehydrati on and rega in hydrati on activity, this performa nee has bee n con firmed in the experime nt.1 2 gravel decompositi on temperatureThe coarse

34、aggregate (gravel) main ly by the in gredie nts in a small amount of CaCO3 and MgCO3 compositi on, which MgCO3 decompositi on temperature is lower, 600 C began to react vigorously CaCO3 decomposition temperatures,severe C is high reached 900 around, but its start decomposing temperature is lower, at

35、 650 C bega n to decompose. So in 550 900C scope whe n calc ined con crete, with the rise of temperature, aggregate ratio in creases occurred decompositi on, aggregate stre ngth decreased. Tran siti on al z one is the con crete and the weak link in aggregate, on one hand, mixing the surface is water

36、 film covering, hampered cement particles and aggregate surface con tact, aggregate peripheral water-ceme nt ratio cha nge, on the other hand, the transference of hydration reaction dissloution Ca2 +, big Al3 +, SO4-3 ion to make to the aggregate bala nce of surface concen trati on of diffuse. In ag

37、gregate, hexagonal near the surface plate crystallization of calcium hydroxide and needle crystal stone precipitati on of calcium van adium, formi ng a no table large andcontinuous space structure 8. Make the moisture in the transition between layers also almost free water and water exists in the fo

38、rm of lower, so in the calcining temperature can achieve aggregate and ceme nt mortar in the separati on of more than 300 °C, the theory can be realized separation. In order to explore calcining temperature effect on the stre ngth of aggregate respectively, and the test of 600, 700, 800 C calci

39、 ning temperature get the coarse aggregate crush values are studied, and directly with n atural gravel and broke n con crete were compared, and the experime nt results as show n.600700800 Natural aggregate broken concreteFrom graph 2 600 C in combustion temperature that when the crush index, gravel,

40、 and slightly higher than the natural macadam with combustion temperature rise, crush in dex in creased, marked the aggregate stre ngth decreased. But in 800C obtained aggregate strength is still higher than the aggregate concrete crushing get directly in the concrete intensity, so no more than 800

41、C calcination temperature is feasible.2 .EpilogueAccord ing to the structure characteristics of various comp onents of the con crete methods of, take the aggregate and pellets slurry separation is feasible. After the decomposition of coarse aggregate in concrete in new mix, its strength of concrete application of crushing get di