Damage and deterioration mechanism and curing technique of concrete structure in main coal cleaning Damage and deterioration mechanism and curing technique of concrete structure in main coal cleaning

Damage and deterioration mechanism and curing technique of concrete structure in main coal cleaning

  • 期刊名字:矿业科学技术(英文版)
  • 文件大小:196kb
  • 论文作者:LV Heng-lin,ZHAO Cheng-ming,SO
  • 作者单位:School of Architecture and Civil Engineering,State Key Laboratory for Geomechanics and Deep Underground Engineering,Wuha
  • 更新时间:2020-06-12
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论文简介

Availableonlineatwww.sciencedirect.comMINING. Science DirectSCIENCE ANDTECHNOLOGYELSEVIERMining Science and Technology 19(2009)0750-0755www.elsevier.com/locate/jcumtDamage and deterioration mechanism and curing technique ofconcrete structure in main coal cleaning plantsLV Heng-lin", ZHAO Cheng-ming, SONG Lei, MA Ying, XU Chun-huaSchool of Architecture and Civil Engineering, China University of Mining Technology, Xuzhou, Jiangsu 221116, China2State Key Laboratory for Geomechanics and Deep Underground Engineering, Xuzhou, Jiangsu 221008, chinaWuhan Design& Research Institute of Sinocoal International Engineering Group, Wuhan, Hubei 430064, ChinaAbstract: Concrete structures in main coal cleaning plants have been rebuilt and reinforced in the coal mines of the Shanghai Da-nun Energy Sources Co. Ltd, the first colliery of the Pingdingshan Coal Co. Ltd. and the Sanhejian mine of the Xuzhou MiningGroup Co. Ltd. In these projects, the operating environment and reliability of concrete structures in the main plants of the threeompanies were investigated and the safety of the structures inspected. Qualitative and quantitative analyses were made on the spe-cial natural, technological and mechanical environments around the structures. On the basis of these analyses, we discuss thelong-term, combined actions of the harsh natural (corrosive gases, liquids and solids) and mechanical environments on concretestructures and further investigated the damage and deteriorating mechanisms and curing techniques of concrete structures in thmain coal cleaning plants. Our study can provide a theoretical basis for ensuring the reliability of concrete structures in main coalcleaning plantsKeywords: main coal cleaning plants; concrete structure; operating environment; reliability detection and inspection; damage anddeteriorating mechanisms; curing technique1 Introductioncontent have improved or modified some large-scalevibration equipment in the main plants of the threeThe main coal cleaning plants of the Shanghai Da- companies, where partial members needed to be re-n Energy Sources Co. Ltd, the first coal mine of built. To ensure that the plants can meet their re-the Pingdingshan Coal Co. Ltd. and the Sanhejian quirements in terms of function and durability aftercoal mine of the Xuzhou Mining Group Co. Ltd, the improvements, we have carried out a comprehenbuilt during the 1980s have served for more than 20 sive study of the natural environments, the technolyears( Fig. I). The special uses and processes of main ogy used and the mechanical environment and thecleaning plants worsen their intemal environment. reliability of reinforced concrete members in threeThey result in increases in the amounts of corrosive main plants between 2005 to 2008. Based onases and liquids and solids accumulate on member these studies and assessments, structures were redes-surfaces with the frequent alternation of wetting and igned for checking the safety of relevant membersdrying( Fig. 2). Simultaneously, vibration loads from and overall structures. Further improvements for re-power equipment have serious consequences. Thus pair, reinforcement and maintenance were designedmost reinforced concrete members exhibit serious separately. The damage and deteriorating mechanismdamage and deterioration phenomena, such as con- of concrete structures in the main plants, which showcrete spalling, clouds of micro-cracks, crack propaga- the worst natural and special mechanical environ-tion, exposed steel corrosion etc( Fig. 3). Many hid- ments were studied and effective reinforcement andden dangers already exist in normal production and maintenance techniquesdiscussedthe safety of concrete members.structures which had been damaged or allowed toIn order to meet the requirements of transforming deteriorate. Thus the long-term safety and durabilitycoal prepararation processes, recent improvements in of the structures can now be ensuredthe yield and quality of coal and reductions in slime中国煤化工Received 1I February 2009: accepted 26 May 2009CNMHGProject BK2008128 supported by the Natural Science Foundation of Jiangsu ProvinceCorrespondingauthor.Tel:+86-516-83590601;E-mailaddress:henglinlv@cumt.edu.cnFig. I Picture of main coal cleaning plantFig 2 Accumulation of corrosive media in main coal cleaning plantFig 3 Serious damage and deterioration of reinforced concrete membersTable 1 Results of gases discovered in the environmentLocation00141Outside Sanhejian main plant00191Inside Datun main plant00181Outside Datun main pla00152021130.05620.0824Table 2 Results of liquids discovered in the environmentLocationSO4H valueInside Sanhejian main plant1319Outside Sanhejian main plantOutside Pingdingshan main plant16233Inside Datun main plant2 Major results and analyses of operating structures of the main coal cleaning plants are locatedenvironmentsis the worst. The levels of many corrosive gaseousmedia such as H,S, HCl, SO, Cl and others areCompared with more general buildings, the main dozens to hundreds times higher than under normalcoal cleaning plants have a unique operating envi- conditions. According to the Code for Anticorrosionronment which entail the worst natural. as well as花- nd judging by thecomplex technological and mechanical environments. corro中国煤lbers, the levelsThe results discovered and analyses of the operating of theCNMHGnsidered moderateenvironments are as followsI)The gaseous environment in which the concrete2)The liquid environment of the main plants752Mining Science and TechnologVol 19 No 6rather severe Levels of some corrosive ions such as1)Honeycombs and bug holes are universalCl, NO3, SO4, F and so on are several, hundreds many reinforced concrete members with manyor even thousands of times higher than under normal anomalous microscopic cracks and corroding expanconditions. According to the Code for Anticorrosion sion cracks along steel bars with a maximum width ofDesign of Industrial Constructions, the levels of cor- 5 mm( Fig. 3). On the surface of partial members,rosion are moderate as well (Table 2concrete has become loose and flaked off.3)The types and amounts of elements deposited on 2) The average depth of concrete carbonation isreinforced concrete member surfaces were examined. between 25 and 45 mm. The average carbonizationOur results discovered many corrosive media suchspeed is 1.8-2.7 times as fast as that in more commonS, CI and others which seriously corrode the rein- environmentsforced concrete members under their combined envi-3)The compression strength of concrete basicallyronment actionsatisfies the requirement of the original designs, But4)The ambient temperature in the main plants their values are too variable and partly much lowermainly changes along with the local climate and is than the allowable limits. moreover, the concretepartially affected by movement of equipment and the performance itself deteriorates continuously, so thateating system. Changes in humidity have a great internal lesion accumulates, brittleness increases anddeal to do with the movement of equipment which permeability becomes highrequires a lot of water when they move, with humid4)As well, the diameter and distribution ofity above 80%. But the humidity is between 60% and bars in members basically satisfy the requirements of75% when the movement of the equipment stops. The the original designs. But due to poor conditions anddeterioration of reinforced concrete members speeds levels of construction, the average thickness of cov-up as a result of frequent alternating between wetting ering layers is approximately 25 mm. Covering layersand drying. 31.of partial members are too thin. We discovered mod-erate corrosion with a rate of corrosion of steel barsbetween 5% and 15%. Steel ductility reduces withoutobvious necking stage( Fig. 5)Fig 4 Complex technological and mechanicalnvironment5)Because of the requirement of coal preparationtechnology, main plants have special split levels andFig 5 Results of mechanical tests of corroded steel barsopenings. Main plants have a number of large-scalepieces of vibration equipment, whose deadweights5)The concrete surface of members has been af-are between several tons to several dozen tons with fected by extraneous factors over long periods. Afterhigh vibration frequency, with ancillary equipment hydration, carbonization and mineral decomposition,such as chutes, pipelines, bunkers and basins posi-many new materials are produced, such as Cacotioned among them. All these form a complex tech- and Fe2 O3, in our samples. It shows that carbonize-nological and mechanical environment in main plants tion is serious and there are different degrees of rust,Fg.4)corroding steel bars. Some samples contain high levels of the element S which inosculate with the high3 Major results and analyses of reliability levels of SO2, H2S in the environment1of reinforced concrete members6)Given the large-scale vibration equipment, rein-forced concrete members are subject to forced vibra-We have investigated reinforced concrete memberstion at low cycles and high frequency, where the vi-in the main plants of the three companies[I-3. The bration amplitude is quite wide. Our study resultsparameters involved were apparent characteristicsindicated that the strain increment reached 95 ue incarbonized depth, compression strength of concrete, the n中国煤化工 beams, caused bythe rate of corrosion of steel bars, dynamic force per- vibra-lent. Fatigue damformance, the reaction of members and so on. The ageTYHCNMH Gand continuouslyresults of our major discoveries and conclusions are aggravatedas followLV Heng-lin et alDamage and deterioration mechanism and curing technique of4 Mechanism of damage and deteriorationthe latest load distribution was designed, computedPKPM software(FigsMoreover,of reinforced concrete material and special simulated dynamic calculations for the vibra-tion loads of equipment were carried out.) The three main coal cleaning plants were built inthe 1980s. Limited by design techniques and con-struction at that time the raw material of concretewere not graded accurately and the water-cement ra-tio was high and concrete strength low. The coveringlayer was thin, the quality of steel bars poor and thequality of construction less than adequate. Honeycombs and bug holes were widespread in manymembers. These are the major intrinsic factors, af-fecting the reliability of reinforced concrete materialand members2)The gaseous and liquid environments in themain plants, where the reinforced concrete membersFig 6 Entire model of the main coal cleaning plant in theare located, contain levels of harmful media up toFirst Coal Mine of Pingdingshan Coal Co. Ltdthousands of times greater than when compared withthose under normal conditions. Slime and corrosivesolids, attached to members have a rather large corro-sive effect on concrete and some members are quitefrequently exposed to conditions of alternating between wetting and drying. These are part of the extrinsic factors that affect the reliability of reinforced oconcrete material and members. these extrinsic fac-tors affect each other. then combined with the intrin-c factors, result in a series of problems on the reli-ability of reinforced concrete members, such as cor-roding steel bars, cracking of concrete, decrease inbearing capacity, etc(6.3)The layout of the structure and special techno-logical and mechanical environment in main plantsare complex. Thus the local and even the overallAs well, given our findings, particularly those ofmembers of the construction are suffering from natural conditions, the technological and mechanicalforced vibration, under conditions of very complex environments, corroding media, fatigue loads, dete-stresses. Long-term forced vibration aggravates the riorating concrete and corroding steel bars, we as-expansion of micro-cracks in concrete and deforma- sumed the concrete compression strength to betion of members. Coupled with conditions of consid- 0.85-0.95 of its assessed value. During the inspectionerably worse natural environments, the vibrations will process, the area of steel should be multiplied bycause increased deterioration and corrosion, which 0.8-0.9. a reduction coefficient for the effective steelfinally results in a decrease of the bearing capacity of area. Then we compared the analytical results of ourreinforced concrete members, seriously reducing the computation with the practical situation after reducreliability and service life of structurestion and obtained the interrelated balance data7Based on our results and the differences in cor5 Redesign method for inspecting the safe- tations, according to related stipulations in the Tech-ty of concrete structuresnical Code for quality Test and Reliability evaluationof Existing Buildings and Technical Code for ReliGiven our projects, the operating environment of ability Appraisal of Factory Building, we divided thethe main coal cleaning plants and the reliability of main structural members into four grades, i.e,A,Breinforced concrete materials and members were in-C and D and provided a basis for further designvestigated and a number of analyses of our results repair, reinforcement and maintenancewere made. On the basis of these analyses, the struc-tures of the main plants from single members to the 6 o中国煤化工ete structuresoverall structure were redesigned. By considering theCNMHGplace and size of each structural member, includinglon Ineunuas or reinforcement andnew members added after rebuilding, a model with rebuilding largely include such efforts as enlargingMining Science and TechnologyVol 19 No 6the section, gluing carbon fiber material, chemical first, weed out bad concrete, clean out floating dust,grouting, steel cladding by direct reinforcement then paint a three-ply permeable corrosion inhibitormethods and steel cladding without cementation, of 0.3 to 0.5 kg per m after cleaning the surface andadding pivoting techniques from indirect reinforce- finally plastering two layers of cement mortar, 20 mmment methodsthickGluing carbon fiber material to reinforce concrete We should adhere strictly to the prevailing stan-structures has many advantages that other reinforcement methods do not have for instance, itslards and pay close attention to cleaning membercorrosionsurfaces, leveling and rounding work when gluingproof performance and durability are good, its carbon fiber material. Moreover, we must ensure thatanti-fatigue ability is better, its structural appearance the cohesive force is strong enough between carbonand size neither changes obviously, nor does it cause fiber material and the original concrete and surfacedamage to the original structure. Reinforcement is maintenance layereffective, maintenance and repair costs are lower, theconstruction period is short and the engineering tech-7Conclusionsniques are comparatively mature. Considering par-larly the natural conditions, the technological and 1)Today in China, most main coal cleaning plantsmechanical environments in the main plants, we sug- have already served for a long time Reinforced con-gest using gluing carbon fiber material to enhance crete members have congenital interior defects andtheir bearing capacity when designing reinforcements are limited by design and construction techniques.to reinforced concrete members that are assessed as C, This is the major internal factor which affects theD grades in the main plants of the three companies reliability of reinforced concrete material and mem-(Fig 8)8-9). For some members for which this cannot bersbe used, other ways, such as enlarging the section,2) The combined actions of a complex operatingmay be considered(Fig 9)nvironment are the main extermal factors affectingthe reliability of reinforced concrete material andmembers. Both the corrosive matter in three states(solid, liquid and gas)and the frequent alternationbetween wetting and drying are harmful to concretestructures. Furthermore, the long-term actions of acomplex mechanical environment degrade the per-formance of structures3)Under the coupling action of internal and external factors. reinforced concrete material in main coal④cleaning plants badly deteriorates over time. As theFig 8 Construction drawing of gluing CFRP on ainterior microcracks grow, concrete structures in-reinforced concrete beam in the main cleaning placrease their penetrability, neutralization and brittle-of the first Pingdingshan collieryness, while steel bars decrease their ductility andstrength because of corrosion. Over time cracks1425along steel bars expand, the concrete surface peelsdamage from fatigue accumulates and the adhesiveforce between concrete and steel bars declines. Con-sequently, damage and deterioration of reinforcedconcrete members accelerate and deformation in-OriginalsectIoncreases. Thus the structural reliability of concrete中8@150structures continually drops and the service life of theoriginal design can hardly be guaranteed.4)When inspecting the reliability of concretestructures of main coal cleaning plants, we must em-phasize the long-term coupling action of a harshFig. 9 Construction drawing of enlarging a section ofnatural environment andtionsa reinforced concrete beam in the main cleaning plantBased on the results of our investigations and analyof the first Pingdingshan collieryses, the reliability of inspections and calculations canbe ensured by discounting related parametersIn order to meet the requirements in terms of dura-bility and extending their service life all C and d al中国煤化工 aning plants,grade members after reinforcement and b grade accCNMHGd equal attentionmembers should be provided with maintenance si- should Dereinforcement and long-term main-multaneously. The suggested plan is as follows: at tenance. Priority should be given to reinforcingHeng-lin et almethods of gluing carbon fiber material and enlargingProceedings of the Second International Forum on Ad-sections. Simultaneously, the long-term cohesivevances in Structural Engineering. Dalian: China Archi-orce and compatibility between reinforcing materialtecture Building Press, 2008: 816-823. (In Chineand original structures and surface maintenance layer[4]Jin X Y, Jin N G Tian Y Study on the behavior and dura-bility of reinforced concrete in boric acid environment.must be ensuredKey Engineering Materials, 2009(400-402): 441-446.le D. Identification of damage inAcknowledgementsforced concrete beams subjected to corrosion. ACI Struc-re Journal,2000,97(6:902-9091 Financial support for this study, provided by the [6] Lv H L, Zhou S C, wu Y Z. Study on deteriorationural Science Foundation ofmechanism and prevention and cure technology of RCProvincestructures in coal mining surface industrial environment.( BK2008128), is gratefully acknowledged.In: 2007 /Cross-Strait Concrete Technology WorkshopConference Proceedings. Keelung, 2007. (In Chinese)References[7 Wu Q, Yuan Y S, Li J Y Research on structural behav-iors deterioration of corroded reinforced concrete beams[I] Lv H L, Song L, Zhao C m. Reliability detection andunder man-made climate. Journal of China University ofssessment of the RC major structure in the washery mainMining Technology, 2007, 36(4):441-445(In Chi-plant of some colliery. In: Proceedings of ICDCS 2008Hangzhou: Zhejiang University Press, 2008: 1003-1007[8] Yin H G Li B N. Ductility analysis of concrete beam[2] Zhou S C, Wu Y Z, Liu w, Zhao C M. Safety assessmentstrengthened by extermally bonding carbon fiber rein-and countermeasures on RC structure after reinforcementforced polymer. Journal of China University of Mining &eand reconstruction in a washery main plant. In: ProceeTechnolog, 2004, 33(6): 712-716(In Chinese)[9] Cui S Q, Wang J S, Pei Z Z, Liu Z.Test analysis for RCngs of ICDCS 2008. Hangzhou: Zhejiang UniversityPres,2008:1045-1050.beams strengthened with extermally bonded prestressed3] ZhaoC M, Lv T F, Zhou S C Reliability detection andCFRP laminates. Key Engineering Materials, 2008(385.387):41-4assessment and reinforcement and maintenance measuresof the rC structure in a certain washery main plant. in中国煤化工CNMHG

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