土木建筑毕业设计外文翻译--混凝土受持续高温影响的强度的研究

1、外文资料STUDIES ON IMPACT STRENGTH OF CONCRETE SUBJECTED TO SUSTAINEDELEVATED TEMPERATURESuresh NARAYANConcrete has a remarkable fire resisting properties. Damage in concrete due to fire depends on a great extent on the intensity and duration of fire. Spalling cracking during heating are common concrete

2、 behaviour observed in the investigation of the fire affected structures. Plenty of literature is available on the studies of concrete based on time temperature cures. In power, oil sectorsand nuclear reactors concrete is exposed to high temperature for considerable period of time. These effects can

3、 be reckoned as exposure to sustained elevated temperature. The sustained elevated temperature may be varying from a few hours to a number of years depending upon practical condition of exposures. The knowledge on properties under such conditions is also of prime importance apart from the structures

4、 subjected to high intensity fire. Impact studies of structure subjected to sustained elevated temperature becomes more important as it involves sensitive structures which is more prone to attacks and accidents. In this paper impact studies on concrete subjected to sustained elevated temperature has

5、 been discussed. Experiments have been conducted on 180 specimens along with 180 companion cube specimens. The temperatures of 100C, 200C and 300C for a duration of exposure of 2 hours 4 hours and 6 hours has been considered in the experiments. The results are logically analyzed and concluded.1. INT

6、RODUCTIONThe remarkable property of concrete to resist the fire reduces the damage in a concrete structure whenever there is an accidental fire. In most of the cases the concrete remains intact with minor damages only. The reason being low thermal conductivity of concrete at higher temperatures and

7、hence limiting the depth of penetration of fire damage. But when the concrete is subjected to high temperature for long duration the deterioration of concrete takes place. Hence it is essential to understand the strength and deformation characteristics of concrete subjected to temperature for long d

8、uration. In this paper an attempt has been made to study the variation in Impact Strength of concrete when subjected to a temperature range 100oC, 200oC and 300oC sustained for a period of 2 hrs, 4 hrs and 6 hrs.The review of the literature shows that a lot of research work 1 3 has taken place on th

9、e effect of elevated temperature on concrete. All these studies are based on time temperature curves. Hence an attempt has been made to study the effect of sustained elevated temperature on impact strength of concrete and the results are compared with the compressive strength. The experimental progr

10、amme has been planned for unstressed residual strength test based on the available facilities. Residual strength is the strength of heated and subsequently cooled concrete specimens expressed as percentage of the strength of unheated specimens.2. EXPERIMENTAL INVESTIGATION2.1. TEST SPECIMEN AND MATE

11、RIALSA total of 180 specimens were tested in the present study along with 180 companion cubes. An electric oven capable of reaching a maximum temperature of 300oC has been used for investigation. Fine and coarse aggregates conforming to IS383 has been used to prepare the specimen with mix proportion

12、s M1 = 1:2.1:3.95 w/c = 0.58, M2 = 1:1.15:3.56 w/c = 0.53, M3 = 1:0.8:2.4 w/c = 0.4.2.2 TEST VARIABLESThe effects of the following variables were studied.2.2.1 SizesSize of Impact Strength Test Specimen was 150 mm dial and 64 mm thickness and size of companion cube 150 x 150 x 150 mm.2.2.2 Maximum T

13、emperatureIn addition to room temperature, the effect of three different temperatures (100oC, 200oC and 300oC) on the compressive strength was investigated.2.2.3 Exposure Time at Maximum TemperatureThree different exposure times were used to investigate the influence of heat on compressive strength;

14、 they are 2 hrs, 4 hrs and 6 hrs.2.2.4 Cooling MethodSpecimens were cooled in air to room temperature.3. TEST PROCEDUREAll the specimens were cast in steel moulds as per IS516 and each layer was compacted. Specimens were then kept in their moulds for 24 hours after which they were decoupled and plac

15、ed into a curing tank until 28 days. After which the specimens were removed and were allowed to dry in room temperature. These specimens were kept in the oven and the required target temperature was set. Depending on the number of specimen kept inside the oven the time taken to reach the steady stat

16、e was found to vary. After the steady state was reached the specimens were subjected to predetermined steady duration at the end of which the specimens are cooled to room temperature and tested.ACI drop weight impact strength test was adopted. This is the simplest method for evaluating impact resist

17、ance of concrete. The size of the specimen is 150 mm dial and 64 mm thickness. The disc specimens were prepared using steel moulds cured and heated and cooled as. This consists of a standard manually operated 4.54 kg hammer with 457 mm drop. A 64 mm hardened steel ball and a flat base plate with pos

18、itioning bracket and lugs. The specimen is placed between the four guides pieces (lugs) located 4.8 mm away from the sample. A frame (positioning bracket) is then built in order to target the steel ball at the centre of concrete disc. The disc is coated at the bottom with a thin layer of petroleum j

19、elly or heavy grease to reduce the friction between the specimen and base plate. The bottom part of the hammer unit was placed with its base upon the steel ball and the load was applied by dropping weight repeatedly. The loading was continued until the disc failed and opened up such that it touched

20、three of the four positioning lugs. The number of blows that caused this condition is recorded as the failure strength. The companion cubes were tested for cube compression strength (fake).4. ANALYSIS AND RESULTS4.1 RESIDUAL COMPRESSIVE STRENGTH VS. TEMPERATUREFrom Table 1, at 100C sustained elevate

21、d temperature it is seen that the residual strength of air cooled specimens of mixes M1, M2 and M3 has increased in strength 114% for M1 mix, 109% for M2 mix and 111% for M3 mix for 6 hours duration of exposure. When the sustained elevated temperature is to 200C for air cooled specimens there is a d

22、ecrease in strength up to 910% approximately for M1 mix for a duration of 6 hours, but in case of M2 mix it is 82% and for M3 mix it is 63% maximum for 6 hours duration of exposure. When the concrete mixes M1, M2 and M3 are exposed to 300C sustained temperature there is a reduction in strength up to

23、 78% for M1 mix for 6 hour duration of exposure.4.2 RESIDUAL COMPRESSIVE STRENGTH VS DURATION OF EXPOSUREFrom Table 1, result shows that heating up to 100C for 2 hours and 4 hours, the residual strength of mix M1 has decreased where as the residual strength of mix M2 and M3 has increased. The residu

24、al strength is further increased for 6 hours duration of exposure in all the three mixes M1, M2 and M3 even beyond the strength at room temperature. When the specimens of mixes M1, M2 and M3 are exposed to 200C for 2,4 and 6 hours of duration, it is observed that the residual strength has decreased

25、below the room temperature and has reached 92% for M1 mix, 82 and 73% for M2 and M3 mix respectively. Concrete cubes of mixes M1, M2 and M3 when subjected to 300C temperature for 2,4 and 6 hours the residual strength for mix M1 reduces to 92% for 2 hours up to 78% for six hours duration of exposure,

26、 for M2 mix 90% for 2 hours duration of exposure up to 76% for six hour duration of exposure, for M3 mix 88% up to 68% between 2 and 6 hours of duration of exposure.5. IMPACT STRENGTH OF CONCRETE5.1 RESIDUAL IMPACT STRENGTH VS TEMPERATUREFrom the table 1, it can be observed that for the sustained el

27、evated temperature of 100C the residual impact strength of all the specimens reduces and vary between 20 and 50% for mix M1, 15 to 40% for mix M2 and M3. When the sustained elevated temperature is 200C the residual impact strength of all the mixes further decreases. The reduction is around 60-70% fo

28、r mix M1, 55 to 65% for M2 and M3 mix. When the sustained elevated temperature is 300C it is observed that the residual impact strength reduces further and vary between 85 and 70% for mix M1 and 85 to 90% for mix M2 and mix M3.5.2 RESIDUAL IMPACT STRENGTH VS DURATION OF EXPOSUREFrom the Table 1 and

29、Figures 1 to 3, it can be observed that there is a reduction in impact strength when the sustained elevated temperature is 100C for 2 hrs, 4 hrs and 6 hrs, and its range is 15 to 50% for all the mixes M1, M2 and M3. The influence of duration of exposure is higher for mix M1 which decreases more rapi

30、dly as compared to mix M2 and mix M3 for the same duration of exposure. When the specimens are subjected to sustained elevated temperature of 200C for 2,4 and 6 hour of duration, further reduction in residual impact strength is observed as compared to at 100C. The reduction is in the range of 55-70%

31、 for all the mixes. The six hour duration of exposure has a greater influence on the residual impact strength of concrete. When the sustained elevated temperature is 300C for 2,4 and 6 hours duration of exposure the residual impact strength reduces. It can be seen that both temperature and duration

32、of exposure have a very high influence on the residual impact strength of concrete which shows a reduction up to 90% approximately for all the mixes.Table 1. Residual impact strength and residual compressive strengthTemperatureDurati on of exposueResidual impactStrength at failureResidual compressiv

33、e strength in N/mm2% variation in residual impact strength% variation in residual compressive strengt CHoursI1I2I3M1M2M3ri1ri2ri3M1M2M3041.34966334460100100100100100100100C24633.62419.3433629545260353836505251646867815846877559827960107114109109115113106112111200C2461713.713.3181513.3241816302927403

34、937514845413332363027362723908681888581847975300C24612.396.79.38.78.78.36.3627252340363252444030211619131213998175698678718573656. CONCLUSIONThe compressive strength of concrete increases at 100oC when exposed to sustained elevated temperature. The compressive strength of concrete decreases when exp

35、osed to 200C and 300C from 10 to 30% for 6 hours of exposure. Residual impact strength reduces irrespective of temperature and duration. Residual impact strength decreases at a higher rate of 20% to 85% as compared to compressive strength between 15% and 30 % when subjected to sustained elevated tem

36、perature. The impact strength reduces at a higher rate as compared to compressive strength when subjected to sustained elevated temperature.混凝土受持续高温影响的强度的研究苏雷什纳拉延混凝土具有显着的耐火性能。在电力，石油部门核反应堆和混凝土接触在高温环境相当一段时间，因混凝土对火的强度和持续时间很大程度上取决于温度和时间。这些持续高温的影响不容忽视。根据多年的研究数据显示，持续升高温度可从几个小时不同的实际情况解释，在这种情况下混凝土的性能最重要的因素还

37、是它的结构承受高强度火。持续受到结构的影响研究高温下变得更加重要，因为它涉及到敏感的结构，这是更容易袭击和意外事故。本文对混凝土的影响研究受到持续升高温度已经讨论过。实验已进行了180份标本，沿180同伴立方体试样。试验中一直以温度100，200和300的接触时间2小时，4小时和6小时为参照，结果是在理论和实践上进行分析和总结。在众多火灾案例中, 建筑结构严重破坏甚至倒塌的情况屡有发生, 火灾对建筑结构的危害已受到人们的广泛关注。目前, 国内外对混凝土高温后力学性能的研究进行了大量研究工作并取得了一定成果:研究了加热速度、达到的最高温度、在最高温度下的接触时间对混凝土强度的影响;进行了混凝土升

38、温、冷却速率对剩余强度的试验;本文正是基于这种情况, 通过试验研究了骨料类型、冷却方式、强度等级、静置时间等因素对混凝土高温后抗压强度的影响, 为高温(火灾)后进行结构的安全评估和鉴定、加固提供依据。1引言随着温度升高, 混凝土的不同力学性能均有不同幅度的下降; 在相同温度作用下, 随着恒温时间的增加,混凝土的各项力学 性能降幅逐渐增大; 混凝土骨料及冷却方式、冷却速度对火灾 后混凝土的力学性能有较大影响。 第一，火灾后混凝土的抗压强度：（1）随温度升高,火灾后混凝土抗压强度逐渐降低；（2）相同温度作用后, 喷水冷却比自然冷却混凝土的强度损失大, 快速冷却比慢速冷却混凝土的强度损失大；（3）相

39、同温度作用后, 硅质骨料比钙质骨料混凝土的强度损失大；（4）相同温度作用后, 最高温度持续时间越长,混凝土的强度损失越大。第二，火灾后混凝土的抗拉强度：（1)火灾后 混凝土抗拉强度随温度升高逐渐降低；（2）混凝土抗拉强度的降幅高于抗压强度；（3）相同温度作用后, 最高温度持续时间越长,混凝土的强度 损失越大。因此，有必要了解混凝土的强度和变形特性持续受温度的时间长。本文尝试研究混凝土强度时，受到温度范围100，200和300持续影响期间2小时，4小时和6小时发生的变化，文献回顾显示，已对混凝土的温度升高得到的效果进行了大量研究工作，所有这些研究都是基于时间温度曲线。因此对持续高温的影响，冲击强

40、度研究抗压强度与混凝土和结果进行了比较。2实验研究2.1试样和材料在本研究中，随着180的同伴立方体，共有180份标本进行了测试。已被用于调查的电烤箱能够达到的最高温度300。已用于符合以IS383的粗骨料配比试样准备M1=1:2.1:3.95 W / C =0.58，混合比M2=1:1.15:3.56 W / C =0.53，M3=1:0.8:2.4 W / C= 0.4。2.2测试变量对以下变量的影响进行了研究。2.2.1尺寸冲击强度试样尺寸是直径150毫米和64毫米的厚度和大小同伴的150150150毫米的立方体。2.2.2最高温度除了到室温，三个不同温度（100，200和300）的效果

41、对抗压强度进行了调查。2.2.3在最高温度的接触时间三种不同的接触时间被用来研究热的影响，对抗压强度，他们分别是是2小时，4小时和6小时。2.2.4冷却方法标本在空气中冷却至室温。3测试程序所有标本共投中钢模具为IS516和每一层被压缩。标本然后保持24小时后，他们将固化脱模和放置在他们的模具坦克，直到28天后的标本，并允许在室温干燥温度。这些标本保存在烤箱和温度设定所需的目标。根据标本数量保持箱内，以达到稳定状态的时间被发现有所不同。而后达到稳定状态的标本到预定稳定的时间，其中的试样冷却至室温和测试结束。通过ACI落锤冲击强度测试，这是最简单的方法评估影响混凝土电阻。试样的尺寸为直径150毫

42、米和64毫米的厚度。光盘标本准备使用钢模具固化和加热和冷却。这包括一个手动操作标准457毫米下降4.54公斤锤。64毫米的淬硬钢球和平面226底板与定位支架。试样放置之间的四个导向件（耳）位于远离样品的4.8毫米。一个框架（支架定位），然后建立以目标在混凝土光盘中心的钢球。光盘被涂上一层薄薄的凡士林底部或沉重的油脂，以减少标本和底板之间的摩擦。底部的一部分其基地后，钢球锤单位和被丢弃的重量反复负载应用。继续加载，直到光盘失败，开辟了这样，它触及的三个四个定位耳。破坏强度的打击，造成这种情况的数量记录。同伴立方体抗压强度（FCK）进行了测试。4分析和结果4.1残余抗压强度VS温度从表1可以看出，

43、在100C持续高温，残余强度的空气冷却混合M1，M2和M3的标本增加M1混合强度至114，109，M2与M3的组合至111，混合到6个小时的接触时间，当持续高温是200C的空气冷却，标本有一个下降强度高达910，大约为M1组合的6个小时的时间，但在M2的组合的情况下，它是82和M3的组合，它是63，最高为6个小时的接触时间。当混凝土混合的量M1，M2和M3接触于100C持续高温是减少在比量M1组合为6小时的接触时间高达78的强度。4.2残余抗压强度VS接触时间从表1结果表明，加热到达100，2小时和4小时后，混合残余强度M1有所下降，其中作为混合M2和M3的残余强度增加。残余强度进一步增加为6个小时的接触时间，在所有的三个M1，M2和M3的混合比量，甚至超越了在室温下的强度。当混合比量M1，M2和M3的标本接触在2，4和6小时的时间