无机非金属材料毕业论文.pdf

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1、Effects of elevated temperature on compressive strength and weightloss of the light-weight concrete with silica fume and superplasticizerEmre Sancaka,Y.Dursun Sarib,*,Osman SimsekcaConstruction Department,Technical Education Faculty,University of Suleyman Demirel,Isparta,TurkeybDepartment of Civil E

2、ngineering,University of Atilim,Incek-Golbasi,06836 Ankara,TurkeycConstruction Department,Technical Education Faculty,University of Gazi,Besevler,Ankara,TurkeyReceived 21 June 2006;received in revised form 18 December 2007;accepted 11 January 2008Available online 20 January 2008AbstractIn this study

3、,structural light-weight concretes produced by Pumice(LWC)and concretes with normal-weight aggregate(NWC)wereinvestigated.Compressive strength and weight loss of the concretes were determined after being exposed to high temperatures(20,100,400,800,1000?C).To achieve these objectives,12 different typ

4、es of concrete mixtures were produced.In producing the mixtures,silicafume(SF)was used to replace the Portland cement in the ratios of 0%,5%and 10%by weight.Half of the mixtures were obtained byadding superplasticizers(SP)to the above mixtures in the ratio of 2%by weight.In conclusion;unit weight of

5、 LWC was 23%lower thanthat of NWC.The LWC containing 2%SP could retain 38%of the initial compressive strength.Rate of deterioration was higher in NWCwhen compared to LWC.The loss of compressive strengths increased depending on the ratio of using SF at about 800?C and over.?2008 Elsevier Ltd.All righ

6、ts reserved.Keywords:Light-weight concrete;Pumice;High temperature;Silica fume1.IntroductionIt is a well-known fact that coefficient of thermal expan-sion values of concrete ingredients(cement paste andaggregates)are different from each other.Therefore,tem-perature changes in concrete cause differen

7、tial volumechanges in the ingredients,and these results in crackingand lower durability.This concept is known as thethermal inconsistency of the ingredients”13.Neville 4 pointed out that at temperatures approxi-mately above 430?C,concretes with siliceous aggregatesshow significant strength loss when

8、 compared to those withlight-weight aggregates.At 600?C,concrete can loose halfof its strength.Above 800?C,loss of the bound water inthe hydrates may cause a strength loss of even 80%,whichmay lead to the failure of a structure.In this case,the dif-ference between the strength loss in normal-weight

9、con-cretes(NWC)and light-weight concretes(LWC)ceases.In another research 5,fire resistance of light-weightconcretes having 5001600 kg/m3unit weight was investi-gated and it was found that an increase in unit weightresulted in reductions in the fire resistance of the concretes.Previous studies showed

10、 that increasing moisture contentincreases the coefficient of thermal conductivity of con-cretes up to 100?C,but decreases it at higher temperatures.Turker et al.6 investigated the micro-structure andstrength of the concretes exposed to fire.In this study,mor-tars containing ordinary portland cement

11、 and three aggre-gate types were subjected to 100,250,500,700 and 850?Cfor 4 h.Unlike the mortars with quartz and limestone,athigh temperatures,cracking was observed in the aggregateitself for the mortars with pumice instead of crack propaga-tion at the interface.Therefore,it was concluded that thei

12、nterface was strong when pumice was used 6.Hammer 2 compared the data obtained from thehigh-strength light-weight and normal-weight concretescontaining 05%silica fume(SF)which were exposed to0958-9465/$-see front matter?2008 Elsevier Ltd.All rights reserved.doi:10.1016/j.cemconcomp.2008.01.004*Corre

13、sponding author.Tel.:+90 532 255 8775;fax:+90 312 586 8091.E-mail addresses:esancaktef.sdu.edu.tr(E.Sancak),ydsariatilim.edu.tr(Y.Dursun Sari) online at Cement&Concrete Composites 30(2008)71572120,100,200,300 and 450?C with the data of the concreteswhich were not exposed to high temperatures.It was

14、foundthatat450?C,NWC containing0%SFshowedthebestper-formance but the behavior of the others was similar to eachother.At 600?C,LWC with 5%SF and NWC without SFwere similar to each other and they showed the best perfor-mance by a strength loss of 48%relative to the control con-crete exposed to 20?C.Wh

15、en the concrete temperatureswere 200300?C,reductions in compressive strength were2535%.According to Kong et al.7 and Abeles and Bardhan-Roy 8,concretes containing light-weight aggregate pre-serve their strength up to nearly 500?C.It was stated thatthe residual strength of LWC after fire decreases li

16、nearlyfrom 100%to 40%as a result of increasing the temperaturefrom 500 to 800?C.Hammer 9 reported that during the hydrocarbon fires,light-weight aggregate concretes experience greater spallingwhen compared to normal-weight concretes.There arethree main reasons for this when the LWC and NWC arecompar

17、ed 10,11:?Permeability and vapor pressure depending on the mois-ture content.?Moisture in the capillary pores(glogging moisture).?Initial compressive strength of the spalling layer.In this study,the compressive strengths and weightlosses of the LWC containing pumice aggregate,SF andsuperplasticizer(

18、SP)at high temperatures were investigatedin comparison to NWC.2.Experimental study2.1.MaterialsNWC were produced with crushed aggregate fromAnkara-Elmadag(Turkey)district.Maximum aggregatesize was 16 mm.The density and water absorption capacityof the 04 mm aggregate groupwere 2570 kg/m3and2.73%,resp

19、ectively.These values were 2700 kg/m3and 0.55%for416 mm aggregate group.In concrete mix proportioning,aggregates were composed of 55%sand(04 mm)and45%gravel(416 mm).The light-weight aggregate(pumice)in LWC productionwas obtained from Isparta-Golcuk(Turkey)in threegroups:04,48 and 816 mm.The specific

20、 gravities ofthese sizes were 2.09,1.75 and 1.50,respectively.The pum-ice aggregate was graded to fit the limitations given inASTM C 330 12.The cement used was an ordinary portland cement(PC)with a specific gravity of 3.15,Blaine fineness of 3350 cm2/g,initial setting time of 150 min and final setti

21、ng time of196 min.The 7-day and 28-day compressive strengths ofPC were 41.3 and 51.2 MPa,respectively.SF used in the concrete production was obtained fromAntalya Etimine Electro-Ferrochrome Plant,Turkey.Chemical compositions of the pumice aggregate,PC andSF are shown in Table 1.Municipal tap water w

22、as used as mixing water.A TypeF superplasticizer(SP)conforming to ASTM C 494 wasused to improve the workability.2.2.Experimental programmeConcretes were produced with a 75 dm3capacity mixer.Mix proportioning of the LWC was made according toACI 211.2 13 standard.In naming the concrete mixes,the type

23、of the concrete(N for NWC and L for LWC)was followed by the SF incorporation amount(5 for 5%and 10 for 10%)and finally by the SP content(0 for 0%and 2 for 2%).For example,L-10-2 denotes the LWC with10%SF and 2%SP.To determine the effectsof high temperatures on concreteproperties,prismaticspecimens(1

24、00?100?500 mm)were produced.The specimens were cured in lime saturatedwater for 28 days 14,15.Then,they were stored in the lab-oratory at 20 2?C and 60 5%relative humidity until 90days.Core specimens with 50 mm diameter and 100 mmlength were drilled from the prismatic specimens and thedrilled specim

25、ens were exposed to 100,400,800 and1000?C by using a SFL Advanced High Temperature&Environmental Systems furnace having a heating capacityof 2000?C at a rate of 5?C/min.Five specimens were usedfor each temperature and they were allowed to cool with arate of 2?C/min to room temperature in a desiccato

26、r.Aftercooling,tests were performed to determine their masschanges and compressive strengths.Unit weight of the con-crete was also determined.The data obtained were com-pared with the results obtained for the control specimenswhich were stored at 20 2?C in the laboratory.To determine the weight chan

27、ges,the specimens wereweighed prior to heating(wi)and after cooling(ws)withan accuracy of 0.01 g.The changes(W)were expressed aspercentages of the initial weights by usingTable 1Chemical compositions of the PC,SF and pumice aggregateComposition(%)PCSFPumiceCaO63.980.444.60SiO220.6480.959.0Al2O35.060

28、.3416.6Fe2O33.140.554.80MgO1.205.231.80SO32.380.40K2O0.84.505.40Na2O0.310.355.20Cl0.0350.13Loss on ignition1.722.701.60Insoluble residue0.46C3Sa52.48C2Sa19.63C3Aa8.02C4AFa9.15aMain compounds of the PC were calculated according to Bougesequations.716E.Sancak et al./Cement&Concrete Composites 30(2008)

29、715721W wi?wswi?1001From the data obtained,mass changes of the NWC andLWC were investigated.3.Results and discussion3.1.Fresh concrete propertiesMix proportions and some fresh properties of the NWCare given in Table 2.The slump was tried to be kept con-stant at 7 2 cm.Since use of superplasticizer i

30、ncreasedthe slump by approximately 2 cm,water contents of themixes were reduced accordingly.As seen from the table,water/binder ratio of the NWC was between 0.42 and 0.58.Mix proportions and some fresh properties of the LWCare shown Table 3.As seen,water/binder ratio of the LWCwas between0.43 and 0.

31、47.Use of superplasticizerdecreased the slump by approximately 2 cm,water contentsof the mixes were reduced accordingly.The mix designs arebased upon an estimated active water demand.That por-tion absorbed by the aggregate is not considered for deter-mining yield since it has no volumetric effect.Du

32、e to theabsorbed condition this water is not available to affectthe cement paste.Therefore,as noted in ASTM C 125(Concrete and Concrete Aggregates),absorbed water isnot considered when calculating the watercement ratio.The considered water amount is net weight of water whichis the amount that is abs

33、orbed by the pumice subtractedfrom the total amount of water.Tables 2 and 3 show that water requirement of bothNWC and LWC increased when SF was used.Very finespherical SF particles improve the grading of the binderby filling the gaps between the relatively coarser cementparticles and increase the f

34、ree water amount.Despite thisbeneficial effect,the high surface area of SF particles to bewetted causes high water requirement and lower durabil-ity 16,17.In these cases,use of SP enabled to reachthe desired slump with much lower water contents,asseen from both Tables 2 and 3.Unit weights of bothNWC

35、 and LWC decreased slightly with the use ofadmixtures.3.2.Hardened concrete properties3.2.1.Physical propertiesSome of the physical properties of the hardened con-cretes after 28 days are given in Table 4.The concretes containing SP resulted in higher unitweights when compared to those without SP.Si

36、milar tothe results obtained for fresh states,use of SF slightlydecreased the unit weights.Therefore,highest unit weightswere obtained for the concretes containing 2%SP and noSF.When absorption capacities are considered,it is seenthat use of SP in NWC resulted in lower values when com-pared to contr

37、ol mix(N-0-0).On the other hand,for LWCmixes,the concretes containing SP and SF had generallyhigher absorption capacities when compared to controlmix.When SF content is kept constant,the absorptioncapacities of both NWC and LWC decreased by the useof SP.This can be attributed to the lower w/c when S

38、Pwas used.The comparison of the unit weights of NWC and LWCshow that even the heaviest LWC(1722 kg/m3)was 23%lighter than the lightest NWC(2248 kg/m3).Table 2Mix proportions(for 1/m3)and some fresh properties of the NWCConcreteCement(kg)Water(kg)Paste/aggregatew/bAggregate(kg)SP(kg)SF(kg)Slump(cm)Fr

39、esh unit weight(kg/m3)04 mm416 mmN-0-03862050.220.537889625.502367N-0-23861740.220.457889627.727.702385N-5-03672140.220.5578395719.3210.92347N-5-23671640.220.427889627.7219.309.802365N-10-03472240.220.5878295738.6710.22325N-10-23481640.220.427889627.7338.629.202342Table 3Mix proportions(for 1/m3)and

40、 some fresh properties of the LWCConcreteCement(kg)Water(kg)Paste/aggregatew/bAggregate(kg)SP(kg)SF(kg)Slump(cm)Fresh unit weight(kg/m3)04 mm48 mm816 mmL-0-04301990.320.46730550528.41809L-0-24301870.320.43730550528.66.41840L-5-0408.52020.320.477295495221.507.21792L-5-2408.51890.320.44729549528.621.5

41、17.11811L-10-03872020.320.4772954952436.81772L-10-23871880.320.44730550528.6436.21787E.Sancak et al./Cement&Concrete Composites 30(2008)7157217173.2.2.Weight loss after exposure to high temperaturesThe furnace used in this study to determine the proper-ties of the specimens exposed to high temperatu

42、res reached1000?C in 200 min.The weight losses(in percent)of theNWC and LWC with increasing temperatures are givenin Fig.1a and b,respectively.Highest weight losses were observed in N-10-0 for NWCand in L-5-2 for LWC.Similar to the results of a researchby Akoz et al.18 in which mortars with and with

43、out SFwere exposed to high temperatures,the concretes contain-ing SF showed higher weight losses when compared tothe control concretes.The comparison of Fig.1a and breveal that the weight losses for NWC were higher thanLWC.However,the most significant difference betweenthese figures was their shapes

44、:after 800?C,the weight lossof NWC increases with an increasing rate whereas theweight loss of LWC increases with a decreasing rate.Theseresults show that the performance of LWC were better thanNWC when weight loss is considered.The difference between the strength loss in normal-weightconcretes(NWC)

45、andlight-weightconcretes(LWC)was not observed until 100?C.The weight loss ofaggregates is different exposed to high temperatures.Attemperatures above 400?C,both of the concretes(NWCand LWC)show significant weight loss.From this temper-ature,behavior of NWC and LWC differs from each other.The rate of

46、 weight loss of NWC increases where as the rateof weight loss of LWC decreases until 1000?C,which leadsto the failure of specimen structure.This can be attributedto the mineral structure of the LWA.This is probablycaused by the fact that less evaporation of water in CSH structure of LWC.Less relativ

47、e weight loss of theLWC may be due to lower heat conductivity property ofthe pumice structure.The diffusion of heat into the LWCspecimen core is less than the NWC may also be the causeof less loss.Coefficient of thermal expansion of NWA ishigher than LWA.Use of silica fume in LWC increasedthe weight

48、 loss compared to LWC without additives.Thismay be due to reaction of Ca(OH)2with silica fume andby hydration CSH are built.The capillary pores andmicro-pores of LWA are filled and denser cement paste isformed.3.2.3.Change in strength after exposure to hightemperaturesStrengths of the NWC specimens

49、exposed to high tem-peratures are given in Table 5.Relative strengths in per-cent at a given temperature with respect to the strengthsof the same concrete at 20?C are also included in this table.Table 5 shows that at all temperatures,relative strengthswith respect to 20?C were highest in control con

50、cretes.Inother words,the strength losses of other concretes werevery close or higher when compared to control concrete.Maximum strength loss at 400?C was observed in N-0-2specimens and it was 42%.Nevertheless,the compressivestrength of this type of concrete(32.10 MPa)was stillhigher than that of con