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利用加速试验中的短期数据预测混凝土梁中GFRP的耐久性能

Durability Prediction for GFRP Reinforcing Bars

Using Short-Term Data of Accelerated

Aging Tests

Yi Chen1;Julio F.Davalos2;and Indrajit Ray3

Abstract:This paper presents a procedure based on the Arrhenius relation to predict the long-term behavior of glass?ber-reinforced polymer?GFRP?bars in concrete structures,based on short-term data from accelerated aging tests.GFRP reinforcing bars were exposed to simulated concrete pore solutions at20,40,and60°C.The tensile strengths of the bars determined before and after exposure were considered a measure of the durability performance of the specimens.Based on the short-term data,a detailed procedure is developed and veri?ed to predict the long-term durability performance of GFRP bars.A modi?ed Arrhenius analysis is included in the procedure to evaluate the validity of accelerated aging tests before the prediction is made.The accelerated test and prediction procedure used in this study can be a reliable method to evaluate the durability performance of FRP composites exposed to solutions or in contact with concrete.

DOI:10.1061/?ASCE?1090-0268?2006?10:4?279?

CE Database subject headings:Durability;Aging;Fiber reinforced polymers;Glass?ber;Predictions;Reinforcement;Bars.

Introduction

Corrosion of steel reinforcement is a major cause of deterioration of reinforced concrete structures.Fiber-reinforced polymer?FRP?reinforcing bars are being increasingly used in concrete structures due to their resistance to corrosion,high strength-to-weight ratio, good fatigue properties,and ease of handling?Uomoto et al. 2002?.But among the various FRP products,glass?ber-reinforced polymer?GFRP?bars,which are extensively used in civil engineering structures due to their signi?cantly low cost,are readily attacked by concrete pore solutions having pH values of 12.4to13.7?Diamond1981;Anderson et al.1989;Bank and Gentry1995?.

Glass?bers are known to be susceptible to attack by water and acidic and alkaline solutions?Bank and Gentry1995?.The most severe degradation is observed in alkaline solutions.The main attack mechanisms include etching,leaching,and embrittlement. The matrices of FRP bars are intended to protect the?bers from harmful agents,but hydrolysis,plasticization,and swelling due to alkaline solution may lead to degradation of the matrix itself?Karbhari and Chu2005?.The?ber/matrix interphase,an inhomogeneous region,may also degrade easily due to matrix osmotic cracking and interfacial debonding and delamination ?Bradshaw and Brinson1997?.

Though numerous studies have been conducted on the durabil-ity of composites used for aerospace or naval applications,long-term performance data for GFRP bars in civil engineering appli-cations are still not available?Micelli and Nanni2004?.Design guidelines for FRP-reinforced concrete structures recommend strength reduction factors to account for environmental effects and sustained stress?ACI2001;JSCE1997?.However,these fac-tors are offered without support by signi?cant experimental data ?Greenwood2002;Nkurunziza et al.2005?.This necessitates de-velopment of critical test methods by which long-term durability performance of GFRP bars in a concrete environment can be as-sessed,in order to establish a50-to75-year life-cycle perfor-mance of GFRP-reinforced structures.

To obtain durability results of GFRP reinforcing bars within a reasonable time,accelerated test methods have generally been adopted by researchers by immersing bare GFRP bars in simu-lated solutions at elevated temperatures.Since degradation of GFRP bars in solutions mainly depends on diffusion and chemical reactions?Micelli and Nanni2004?,both of these factors can be accelerated by raising temperatures;thus elevated temperatures were used as an accelerating factor by several researchers?Micelli and Nanni2004;Porter and Barnes1998;Dejke2001?.Sustained loading during environmental exposure was also used by other researchers such as Benmokrane et al.?2002?and Sen et al.?2002?,while a combination of elevated temperatures and sus-tained loading was used as an accelerating factor by Rahman et al.?1998?and Nkurunziza et al.?2003?.

In recent studies?Mukherjee and Arwikar2005,Almusallam and Al-Salloum2006?,GFRP bars were embedded in concrete beams under sustained load in solutions at elevated temperatures. ASTM E632?ASTM2000?provided a general approach for conducting accelerated tests of construction materials.Recently, ACI Committee440?ACI2004?proposed an accelerated test

1Doctoral Student and Research Assistant,Dept.of Civil and

Environmental Engineering,West Virginia Univ.,Morgantown,WV

26506-6103.E-mail:sjtuchenyi@https://www.wendangku.net/doc/948287447.html,

2Benedum Distinguished Teaching Professor,Dept.of Civil and

Environmental Engineering,West Virginia Univ.,Morgantown,WV

26506-6103?corresponding author?.E-mail:Julio.Davalos@mail.

https://www.wendangku.net/doc/948287447.html,

3Research Assistant Professor,Dept.of Civil and Environmental

Engineering,West Virginia Univ.,Morgantown,WV26506-6103.

Note.Discussion open until January1,2007.Separate discussions

must be submitted for individual papers.To extend the closing date by

one month,a written request must be?led with the ASCE Managing

Editor.The manuscript for this paper was submitted for review and pos-

sible publication on August29,2005;approved on November16,2005.

This paper is part of the Journal of Composites for Construction,V ol.

10,No.4,August1,2006.?ASCE,ISSN1090-0268/2006/4-279–286/

$25.00.

JOURNAL OF COMPOSITES FOR CONSTRUCTION?ASCE/JULY/AUGUST2006/279

method for evaluating alkali resistance of FRP bars.The test consists of subjecting FRP bars to alkali environments with or without stress at a temperature of60°C.But questions still remain on procedures,magnitude of sustained loads to be applied to the specimens,types of simulated alkaline environment to be used, and duration of exposures.

Following accelerated tests,analyses were often carried out on the short-term data,and predictions for long-term behavior were made based on various models.Following the procedure used by Litherland et al.?1981?,prediction equations were suggested for GFRP bars by Porter and Barnes?1998?,but the approach successfully used in GRC?glass?ber-reinforced concrete?in Litherland et al.?1981?may not be applicable to GFRP bars, since the?bers are embedded in polymers.

Recently,Caceres et al.?2000?adopted the time-temperature superposition method to analyze the short-term data from accel-erated testing of FRP composites used in naval waterfront infra-structures,but details of how to superimpose the accelerated data sets were not provided.Dejke?2001?suggested a time shift factor based on the Arrhenius relation to correlate strength retentions of concrete-encased GFRP bars exposed to solutions at20and60°C. Since data from only two different exposure temperatures were used to calculate the activation energy,the time shift factor may not be generally applicable.Bank et al.?2003?provided a proto-

col for predicting long-term property values of FRP composites subjected to accelerated aging based on the Arrhenius relation. However,a recent study by Gonenc?2003?showed that this method cannot be directly applied to GFRP bars.

Diffusion models based on Fick’s law were also used to cor-relate the losses in tensile strength with the moisture absorption of FRP bars by Katsuki and Uomoto?1995?and Tannous and Saadatmanesh?1998?.But the main assumption of this approach, that the matrix and?bers within the depth of the damaged zone ?the area with diffused chemicals?were completely degraded, may not be accurate,as shown by Aguí?iga et al.?2004?.This approach cannot be applied to specimens exposed to water since the concentration of solution is required in the analysis.Also, high-quality matrices typically used currently may not allow dif-fusion of ions in measurable quantities?Dejke2001?.

From the literature review,one can conclude that no consensus was reached on using a particular accelerated test method or pre-diction model.Also,no correlation between accelerated test results and real-life aging was suggested by the relevant ACI committee report?ACI2004?.Prediction models based on the Arrhenius relation have often been used in the published litera-ture,such as Litherland et al.?1981?and Phani and Bose?1987?, but concern remains about the implicit assumption that the elevated temperature will only increase the rate of degradation without in?uencing the degradation mechanism or introducing other degradation mechanisms for FRP bars.

A comprehensive study on the durability of FRP bars subjected to environmental agents such as water,seawater,alkaline solu-tions,wetting and drying cycles,and freezing and thawing cycles was recently reported by Chen et al.?2006?.Based on that study, the most signi?cant degradation was found to occur for GFRP bars exposed to alkaline solutions.In the present study,critical short-term data on the durability of GFRP bars are obtained through accelerated aging tests by exposing specimens to simu-lated concrete pore solutions at different temperatures.Based on these short-term data,a detailed procedure is developed and veri?ed to predict the long-term behavior of GFRP bars in simu-

lated concrete pore solutions.This procedure includes a modi?ed

Arrhenius analysis to evaluate the validity of accelerated tests

before the prediction is made.

Experimental Program

Materials

In this study,GFRP bars made of E-glass?bers and vinyl ester

resin were selected due to their wide application in civil engineer-

ing infrastructure.For the purpose of developing and verifying

the proposed prediction procedure,two types of GFRP bars with

a9.53mm diameter?No.3?were used.The bars were produced

using the same resin but different types of E-glass?bers.Both

GFRP1and GFRP2bars were helically wrapped and slightly sand

coated?Fig.1?and were manufactured by a commercial pultru-

sion process.The glass?ber contents of both GFRP bars were

above70%by weight.Both types of bars were provided by the

same manufacturer,and GFRP2bar is a commercially available

product.

Testing Plan

Tensile strengths of specimens were measured before and after

the exposures,since changes in tensile strength values can reli-

ably be used as indicators of the durability performance.The

tensile test was conducted in accordance with ASTM D3916-94?ASTM2000?with some modi?cations.The overall length of the specimens was1.02m.The end grip used in this study was a

200-mm long steel pipe cut lengthwise into two halves.After

being coated with epoxy in their inner surface,the split pipes

were bonded on each end of the bar.The length-to-diameter ratio

of the test specimens was64.The tests were carried out on a

Baldwin machine,and the duration of the loading was2to4min

for each

specimen.

Fig.1.GFRP bars

280/JOURNAL OF COMPOSITES FOR CONSTRUCTION?ASCE/JULY/AUGUST2006

In this study,groups of GFRP bars were tested before and after immersion in simulated pore solutions at different temperatures for different exposure times.Two types of alkaline solutions were made to simulate the pore solutions of normal concrete ?NC ?and high-performance concrete ?HPC ?,respectively.Due to the increasing use of HPC in civil infrastructure,a simulated HPC pore solution was included in this study.Solutions 1and 2were both made with combined sodium hydroxide ?NaOH ?,potassium hydroxide ?KOH ?,and calcium hydroxide ?Ca ?OH ?2?,according to Shi et al.?1998?and Gowripalan and Mohamed ?1998?.Solution 1,with a pH value of about 13.6,was intended to simu-late the pore solution of NC,and Solution 2,with a pH value of about 12.7and different proportions of hydroxides compared to Solution 1,was made to simulate the pore solution of HPC.The compositions of Solutions 1and 2are listed in Table 1.

Elevated temperatures of 40and 60°C were adopted to accel-erate the attack of simulated environments on specimens.These temperatures were well below the glass transition temperature of selected GFRP bars.Temperature-controlled tanks ?Fig.2?were custom designed for specimens exposed to solutions at tempera-tures of 40and 60°C.For exposure of specimens in solutions at room temperature ?RT,about 20°C ?,polypropylene heavy-wall tanks were used.

For illustrative purpose to develop and verify the proposed prediction procedure,GFRP1bars were immersed in Solution 1

and GFRP2bars in Solution 2.The justi?cation for exposing a particular type of GFRP bars in a speci?c type of solution is based on previous ?ndings by Chen et al.?2006?of a comprehensive study on interactions of GFRP bars and various simulated solu-tions.In that study,it was observed that in terms of durability,GFRP2bars performed better than GFRP1bars,and in terms of its reactivity with GFRP bars,Solution 2was less aggressive than Solution 1.

Since the objective of the current paper is to develop a proce-dure to evaluate the durability of GFRP bars,it is necessary to verify the validity of the procedure through at least two distinct conditions in terms of the reactivity between a ?ber-resin system of GFRP bars and solutions.Considering this objective,two dis-tinct conditions are formulated,in which GFRP1bars exposed in Solution 1are regarded as a high-reactivity condition,and GFRP2bars exposed in Solution 2are considered as a relatively low-reactivity condition.The applicability of the model when includ-ing these two distinct conditions will enable evaluation of its accuracy for predicting durability from critical short-term data of accelerated tests.

The environmental exposure plan for specimens is summa-rized in Table 2.After each exposure,usually three to six GFRP bars were removed from solutions and tested for tensile strength retention compared to baseline specimens.

Test Results and Discussion

During the tensile test of dry specimens,both types of GFRP bars showed an approximately linear behavior up to failure and failed through the rupture of ?bers.The failure of both types of GFRP bars was accompanied by the separation of ?bers and the rupture of spiral bundles on the deformed surface of bars,as shown in

Table https://www.wendangku.net/doc/948287447.html,positions of Simulated Concrete Pore Solutions

Quantities ?g/L ?

Solution type NaOH KOH Ca ?OH ?21 2.419.622

0.6

1.4

0.037

Fig.2.Temperature-controlled tank:?a ?digital temperature control;?b ?Te?on-coated immersion heater

Fig.3.Similar but less catastrophic failure was observed for con-ditioned specimens,and similar tensile failure modes of GFRP bars were also observed by Micelli and Nanni ?2004?.

The tensile test results of unconditioned and conditioned specimens are summarized in Figs.4–6?the overbar represents a standard deviation ?.Each data represents an average of three to six test results.As shown in Figs.4?a and b ?the tensile strengths for pristine GFRP1and GFRP2bars were 925and 771MPa,respectively.Note that the tensile strength of GFRP1bars reduced to 352MPa after only 120days exposure to Solution 1at 60°C,and the tensile strength of GFRP 2bars reduced to 455after 120days exposure to Solution 2at 60°C.

Figs.5and 6show that the tensile strength decreased with an increase in exposure time for both GFRP bars at all temperatures,and degradation was more severe for specimens in solutions at higher temperatures.A comparison of GFRP bar and solution interaction con?rms the previous ?nding of greater reactivity of the GFRP1–Solution 1combination.One can also observe that the degradation was signi?cant for both GFRP bars in such short exposure times compared to their expected service life.The rapid degradation may be due to the direct exposure of specimens to strong alkaline solutions.The degradation of the bars was made visibly apparent by white blisters on the surface,as described in Chen et al.?2006?.The blisters may be the manifestation of osmosis in the surface of bars.

Predictions of Long-Term Behavior of GFRP Bars The basis for the proposed prediction is the Arrhenius relation,which is introduced ?rst.Then a detailed procedure is carried out on the short-term data to predict the long-term behavior of GFRP bars.A modi?ed Arrhenius analysis is included in the procedure to determine the validity of the accelerated test.Then,based on the results of this study,comments and discussions are given on both the present prediction procedure and those proposed by other researchers.

Arrhenius Relation

In the Arrhenius relation,the degradation rate is expressed as follows ?Nelson 1990?:

k =A exp

??E a RT

?1?

where k ?degradation rate ?1/time ?;A ?constant of the material and degradation process;E a ?activation energy;R ?universal gas constant;and T ?Kelvin temperature.The primary assumption of this model is that the single dominant degradation mechanism of the material will not change with time and temperature during the exposure,but the rate of degradation will be accelerated with the increase in temperature.Eq.?1?can be transformed into

1k =1A exp ?E a RT ?

?2?

?1k ?

E a R 1

?ln ?A ??3?

From Eq.?2?,the degradation rate k can be expressed as the

inverse of time needed for a material property to reach a given value.From Eq.?3?one can further observe that the logarithm of time needed for a material property to reach a given value is a linear function of 1/T with the slope of E a /R .Prediction Procedure

For the ?rst step,the relationship between tensile strength reten-tion ?the percentage of residual strength over original tensile strength ?of GFRP bars and exposure time for the accelerated test was de?ned as

Y =100exp ??

t ?

?4?

where Y ?tensile strength retention value ?%?;t ?exposure time;and ??1/k ,as expressed in Eq.?2?.The form of this equation was modi?ed from a study by Phani and Bose ?1987?by assuming that GFRP bars degraded completely at in?nite exposure time.The data of Figs.5and 6were used in Eq.?4?in order to obtain the coef?cient ?by regression analysis.Corresponding ?values and correlation coef?cients ?r ?are summarized in Table 3,with all regression lines having a correlation coef?cient above 0.93.Thus,the time to reach a given tensile strength retention at different temperatures can be approximately calculated through Eq.?4?.In the second step,the Arrhenius relationships were obtained by plotting the natural log of time to reach 50,60,70,and 80%tensile strength of GFRP bars versus 1/T ?the inverse of exposure temperature ?in Figs.7and 8.Straight lines were ?tted to the data

Table 2.Environmental Exposure Plan of GFRP Bars

Bar type Solution type Temperature

?°C ?

Exposure time

?days ??days ??days ??days ?GFRP1

606090120240406090120240206090120240GFRP22

606070901204060709012020

120

Fig.3.Typical failure mode of GFRP bars

with the assumption that the degradation rate was a function of

temperature as expressed in Eq.?3?.Eq.?2?was also ?tted to the data of Table 3to obtain E a /R .From the analysis,the regression coef?cients ?E a /R ?and correlation coef?cients ?r ?are listed in Table 4.The correlation coef?cients for all regression lines were close to 1,and straight lines in Arrhenius plots for different strength retentions were nearly parallel to each other ?the slopes of straight lines are E a /R ?.This implies that the Arrhenius rela-tion can be used to describe the degradation rate of GFRP bars,as the degradation mechanism may not change with temperature and time during exposure in the range tested.Moreover,Eq.?4?can be used to de?ne the time and temperature dependence of tensile strength for GFRP bars exposed to alkaline solutions.

For the third step,the acceleration factor ?AF ?for the same solution at two different temperatures can be obtained from pre-vious Arrhenius plots.The AF can be expressed as AF =t 0t 1=c /k 0c /k 1=k 1k 0=A exp

??E a

RT 1?

A exp

??E a RT 0

=exp ?E a R ?1

T 0?

1T 1

?5?

where AF ?acceleration factor;t 1and t 0?times required for some property to reach a given value at temperatures of T 1and T 0,respectively;c ?constant;and k 1and k 0?degradation rates at temperatures of T 1and T 0,respectively,as expressed in Eq.?1?.For example,for 70%retention of tensile strength of GFRP2bars ?as shown in Fig.8?,the AF for Solution 2at 60°C in relation to 20°C can be calculated,AF ?7.5.Since the ?tted lines are parallel to each other ?Figs.7and 8?,the acceleration factor remains constant for all strength retention values,such as those shown from 50to 80%,at each speci?ed temperature level,either 40or 60°C.The AF values with reference temperature T 0?20°C are listed in Table 5.Therefore,Eq.?5?can be ?tted to data in Table 5to obtain the AF values for other temperatures based on the reference temperature of 20°C.

For the fourth step,once the AF values for 60and 40°C were obtained,Figs.5and 6were transformed into Figs.9and 10by multiplying exposure times at 60and 40°C with corresponding AF values.Master curves for tensile strength retention versus exposure time at 20°C were obtained by ?tting Eq.?4?to data in Figs.9and 10.As listed in Table 6,these data have correlation coef?cients of 0.92and 0.99,respectively.Interestingly,the val-ues for ?correspond exactly to those at 20°C given in Table 3;this close correlation also con?rms the validity of this procedure.Finally,Eq.?4?with the values for ?listed in Table 6could be used to predict the tensile strength retention at any exposure time.

Table 3.Coef?cients of Regression Equations for GFRP Tensile Strength Retention

Temperature ?°C ?

GFRP1bars in Solution 1

GFRP2bars in Solution 2

?r ?r 601430.932220.99402000.987140.9620

256

0.96

1,667

0.94

Fig.4.Tensile strength of GFRP bars:?a ?tensile strength of GFRP1bars in Solution 1after 120days exposure;?b ?tensile strength of GFRP2bars in Solution 2after 120days

exposure

Fig. 5.Tensile strength retention of GFRP1bars exposed to Solution 1at 20,40,and

60°C

Fig. 6.Tensile strength retention of GFRP2bars exposed to Solution 2at 20,40,and 60°C

For example,from the master curves,after only 178-day exposure in Solution 1at 20°C,the tensile strength retention of GFRP1bars will drop to 50%.For GFRP2bars exposed to Solution 2at 20°C,the tensile strength retention will be 50%at 1,156days.

Discussions

The Arrhenius analysis ?the ?rst and second steps in the above prediction procedure ?was also used to determine the validity of the accelerated tests.If the ?tted straight lines in Arrhenius plots had a low correlation coef?cient ?e.g.,r ?0.8?and/or were not parallel to each other,one would infer that the degradation mechanism would have changed with temperature and time,indi-cating that the accelerated tests are not valid and the procedure could not be used to predict long-term behavior.

Note that the slope ?E a /R ?of Arrhenius plots for GFRP1bars is about 1,420,which was much lower than about 4,890for GFRP2bars,revealing that the activation energy ?E a ?for degra-dations of GFRP1bars in Solution 1is much lower than for GFRP2bars in Solution 2,resulting in different degradation rates and probably mechanisms.In a recent study ?Dejke 2001?,an E a /R value of 6,300was obtained for GFRP bars embedded in moisture concrete,and therefore the degradation of different GFRP bars in different alkaline environments will be different.

So it is worth noting that if the master curve for prediction is developed for one type of GFRP bars in a speci?c exposure condition,it may not be applicable to other types of GFRP bars used in different environments.

From the obtained master curve,the degradation was signi?-cant for both GFRP bars in such short exposure times compared to their expected service life.Based on a diffusion model,a simi-lar trend was also predicted for GFRP bars directly exposed to alkaline solution by Sen et al.?2002?.The predicted service life for a speci?c E-glass/vinyl ester reinforcement used by the U.S.Navy was only between 1.6and 4.6years.

Prediction procedures proposed by other researchers were also used to analyze the data from this study.In the model proposed by Bank et al.?2003?,the relationship between strength retention and log of exposure time was assumed linear.The Arrhenius plots were directly used to predict the service life of different strength retentions,and second group of Arrhenius plots was also obtained and used to predict the strength retentions at different exposure periods.Following the procedure proposed by Bank et al.?2003?,straight lines of Arrhenius plots obtained using their approach were found not to be parallel to each other,which invalidates the procedure based on the assumption that the degradation mechanism will not change with time.The same situation was also found in a recent study ?Gonenc 2001?when the procedure given in Bank et al.?2003?was applied to GFRP rods.The pro-cedure proposed by Caceres et al.?2000?was also applied to the present data.Since no details were given on how to super-impose the accelerated test data for different temperatures,results were signi?cantly in?uenced by the superposition method used.Moreover,as stated in Caceres et al.?2000?,extrapolation of the master curve obtained using their procedure may lead to unreal-istic predictions.

Compared to the procedures proposed by other researchers,the procedure in this study can be used for short-term data for GFRP bars successfully and ef?ciently.The proposed procedure can be easily carried out by de?ning simple plots and performing regression analysis.The results indicate that increasing the num-ber of exposure temperatures and using longer exposure durations in accelerated tests can lead to more precise predictions.This procedure may also be used for FRP materials exposed to other

Tensile strength retention ?%?

GFRP1bars in Solution 1GFRP2bars in Solution 2E a /R

E a /R r 501,4200.994,8910.99601,4230.994,8920.99701,4200.994,8910.99801,4200.99

4,8920.99Eq.?2?

1,4150.994,899

0.99

For Eq.?2?based on data in Table 3.

Table 5.Values for Acceleration Factors Temperature ?°C ?

GFRP1in Solution 1

GFRP2in Solution 2

60 1.807.5040 1.28 2.3320 1.00 1.00

Fig.7.Arrhenius plots of tensile strength degradation for GFRP1bars exposed to Solution

Fig.8.Arrhenius plots of tensile strength degradation for GFRP2bars exposed to Solution 2

solutions or even embedded in moist concrete.Due to the com-plexity of the degradation mechanism,no degradation model has been proposed to simulate exactly the degradation of GFRP bars in alkaline media.The accelerated test method and prediction procedure used in this study may be good options to assess the long-term durability performance of GFRP bars.

Conclusions and Recommendations

This study is part of an ongoing durability research program on FRP reinforcing bars for concrete.From the short-term data and prediction procedure presented in this paper,the following con-cluding remarks and recommendations can be made.

Possibly due to lower alkalinity,HPC pore solutions may be less aggressive to GFRP bars than those of NC in spite of having different ionic proportions.Simulated pore solutions with differ-ent compositions may result in different degradation mechanisms for various kinds of GFRP bars.Thus,the guidelines in ACI 440.3R2-04?ACI 2004?,in which one kind of alkaline solution is used to represent different pore solutions of various kinds of con-crete,would have to be revised.

There is a dominant degradation mechanism for GFRP bars in alkaline solutions that does not appear to change with temperature or time.Elevated temperature can be used to accelerate the degradation of GFRP bars in alkaline solutions.Further,the

temperature dependence of the degradation rate can be described by the Arrhenius equation.Eqs.?1?and ?4?can be used to predict the relation between tensile strength retention of GFRP bars with exposure time and temperature.The method presented in this study can probably be used to evaluate the durability performance of FRP composites,while the Arrhenius analysis in this procedure can be used to determine the validity of the accelerated test using elevated temperatures.

From the master curves of this study,the tensile strength retention of GFRP1bars drops to 50%after only a half-year exposure in Solution 1at 20°C,and for GFRP 2bars exposed to Solution 2at 20°C,the tensile strength retention is 50%after about 3years.But in a recent study ?Mufti et al.?2005?,much less degradation was found for GFRP bars in ?eld concrete structures.Since in the present study bare GFRP specimens were directly exposed to simulated pore solutions,the reported short-term results and the predicted tensile strength retention should be considered conservative.Note also that the master curves in this paper are only applicable to the GFRP bars tested and exposed to the speci?c simulated pore solutions in this study.

To investigate the durability of GFRP bars in concrete,specimens embedded in concrete should be tested.To predict long-term behaviors of GFRP bars based on the short-term data,the correlation between degradations of GFRP bars in accelerated tests and real applications needs to be investigated.Long-term data,including those in real applications,should be collected to validate accelerated tests and prediction models.Moreover,coupling effects of sustained load and environmental exposures should also be included in future studies to simulate real-life conditions.

Acknowledgments

We appreciate the ?nancial support from the Korea Institute of Construction Technology ?KICT ?,Republic of Korea.The fund-ing provided by the college dean,Eugene Cilento,and department chair,David Martinelli,at West Virginia University is also grate-fully acknowledged.We thank Doug Gremel of Hughes Brothers,Inc.for supplying FRP bars and for his valuable technical suggestions.

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浅谈混凝土结构耐久性问题

④ XXXXXXX（XX）现代远程教育毕业设计（论文）题目：浅谈混凝土结构耐久性问题学习中心：XXXXXX 年级专业：函授XXX 专升本学生姓名：XXX 学号：XXXXXXXXX 指导教师：X X X职称：副教授导师单位：威海职业学院中国石油大学（华东）远程与继续教育学院论文完成时间：2012 年 6 月30 日

XXXXXXX（XX）现代远程教育毕业设计（论文）任务书发给学员xxx 1．设计(论文)题目：浅谈混凝土结构耐久性问题 2．学生完成设计(论文)期限：2012 年 1 月30 日至2012 年6 月30 日3．设计(论文)课题要求： 1）、重点论述提高我国中小型出口企业国际竞争力的对策 2）、论文字数不少于6000字。 3）、论文要求结构完整，思路清晰，论据缺凿，论点明确，有说服力。 4）、要从安全角度分析，从各个方面去论述。 5)、针对论文所重点阐述的内容，广泛查阅相关资料，为论文的写作奠定坚实的基础，提供有力的证据。 4．实验（上机、调研）部分要求内容：如果条件具备，可深入企业进行实际调研，写出调研报告，为论文写作提供充分的素材 5．文献查阅要求：广泛查阅与本文相关的文献材料，为论文写作奠定坚实的基础，通知注意文献材料的真实性。 6．发出日期：2012 年 1 月30 日 7．学员完成日期：2012 年 6 月30 日指导教师签名：学生签名：

摘要混凝土耐久性是指结构在规定的使用年限内,在各种环境条件作用下,不需要额外的费用加固处理而保持其安全性、正常使用和可接受的外观能力。影响混凝土结构耐久性的因素有很多，本文通过从混凝土的渗透破坏、冻融破坏、侵蚀性介质的腐蚀、碱骨料反应、碳化和钢筋锈蚀六个方面论述了混凝土发生耐久性失效的原因及影响因素，对混凝土耐久性问题进行了研究。最终提出从混凝土材料的选择、结构设计和质量的生产控制三方面进行提高混土耐久性的处理措施。混凝土结构以其整体性好、耐久性好、可塑性强、维修费用少等优点广泛使用，随着混凝土结构应用领域越来越广泛，大量的混凝土结构由于各种各样的原因而提前失效，达不到预定的服役年限，混凝土耐久性发生失效现象日趋严重。关键词：混凝土；耐久性；影响因素；措施

混凝土结构耐久性浅谈

网络教育学院本科生毕业论文（设计）题目：混凝土结构耐久性浅谈学习中心：层次：专科起点本科专业：土木工程年级：学号：学生：指导教师：完成日期：2013 年11 月14 日

混凝土结构耐久性浅谈内容摘要混凝土由于其具有经济、耐久、节能等众多优点, 而成为重要的建筑材料, 其应用范围十分广泛。作为目前世界最大宗的人造建筑材料, 其在给人类带来巨大文明进步的同时 , 也面临由此造成的严峻的资源、能源和环境问题。传统意义上的混凝土由于自身结构材料和使用环境的特点, 还存在着严重的耐久性问题, 已不能满足混凝土行业的绿色可持续发展的要求。因此, 提高混凝土的耐久性是实现混凝土环保化、节约化的积极有效措施。本文综述了耐久性对混凝土的重要意义, 并着重分析了影响混凝土耐久性的主要因素。最后介绍了目前世界上提高混凝土的耐久性的研究结果以及目前国际上对混凝土的耐久性设计要求。关键词：耐久性；混凝土；影响因素

混凝土结构耐久性浅谈目录内容摘要 .................................................. ..................................................... ....................I 引言......................................... ......................................... ......................................... . 1 1 绪论......................................... ......................................... ......................................... . 2 1.1 混凝土耐久性问题的提出................................................... (2) 1.2 混凝土耐久性的概念 .................................... ........................................ (2) 2 混凝土结构耐久性问题的分析 ........................................... (3) 2.1 混凝土冻融破坏 .................................... ........................................ (3) 2.1.1 破坏机理 .......................... ............................. ............................. (3) 2.1.2 影响因素 .......................... ............................. ............................. (4) 2.2 混凝土渗透破坏 .................................... ........................................ (4) 2.2.1 破坏原因 .......................... ............................. ............................. (4) 2.2.2 影响因素 .......................... ............................. ............................. (5) 2.3 碱骨料反应 ..................................... ........................................ (5) 2.3.1 破坏原因 .......................... ............................. ............................. (5) 2.3.2 影响因素 .......................... ............................. ............................. (6) 2.4 混凝土的碳化 .................................... ........................................ (6) 2.4.1 破坏原因 .......................... ............................. ............................. (6) 2.4.2 影响因素 .......................... ............................. ............................. (7) 2.5 钢筋锈蚀 ..................................... ........................................ (7) 2.5.1 破坏原因 .......................... ............................. ............................. (7) 影响因素 ..........................

试论混凝土结构的耐久性检测

试论混凝土结构的耐久性及其检测摘要：混凝土结构是目前应用最广泛的工程结构，因此对现有混凝土结构及正在建设的混凝土结构进行的耐久性检测与评估就显得十分重要。本文结合作者的工作实际对混凝土结构的耐久性检测与评估过程进行讨论。 1、前言混凝土结构在土木工程中得到应用以来，它的诸多优点已经得到充分体现，因此混凝土结构是目前应用最广泛的结构。虽然混凝土结构具有寿命长和较长时间无需维护的特点，但任何结构在长期的自然环境和使用环境的双重作用下，其功能将逐步衰减，这是一个不可逆的客观规律。混凝土结构在外部因素及其自身内在因素作用下，其安全性和使用功能都将有所下降。在这种情况下，混凝土结构耐久性问题就日益突出。从混凝土应用于土木工程至今，大量的钢筋混凝土结构由于各种各样的原因而提前失效，达不到预定的服役年限；这其中有的是由于结构设计的抗力不足造成的，有的是由于使用荷载的不利变化引起的，但更多的是由于结构的耐久性不足导致的；特别是沿海及近海地区的混凝土结构，由于海洋环境对混凝土的腐蚀，导致钢筋锈蚀而使结构发生早期损坏，丧失了结构的耐久性能，已成为实际工程中的重要问题。早期损坏的结构需要花费大量的财力进行维修补强，甚至造成停工停产的巨大经济损失。所谓混凝土结构耐久性，是指混凝土结构在自然环境、使用环境及材料内部因素的作用下，在设计要求的目标使用期内，不需要花费大量资金加固处理而保持其安全、使用功能和外观要求的能力。国内外经验表明，混凝土对环境作用的抗力不够只是一个方面，施工质量差则是混凝土结构耐久性不良的主要原因之一。多种环境侵蚀会损害混凝土耐久性，但其中最主要的是钢筋锈蚀应起的混凝土开裂、剥落，钢筋断面减小，粘结力丧失，最终导致混凝土结构破坏，缩短使用寿命。在施工、设计、维护等都会影响混凝土耐久性。常见的施工问题如混凝土质量不合格、钢筋保护层厚度不足都有可能导致钢筋提前锈蚀。另外，在混凝土结构的使用过程中，由于没有合理的维护而造成结构耐久性的降低也是不容忽视的，如对结构的碰撞、磨损以及使用环境的劣化，都会使混凝土结构无法达到预定的使用年限。一位美国学者通过调查研究得出工程质量风险管理费用的“五倍定律”：对新建项目在钢筋防护方面在五个不同阶段的投资，每推迟一个阶段进行防护，其投入的资金分别是上一阶段的五倍。这四个阶段是建设阶段，始锈阶段，涨裂阶段，破坏阶段。所以对混凝土结构的耐久性检测与评估就显示出其重要性与必要性。我们国家现在正是进入大规模建设的阶段，在建设阶段投入必要的资金对混凝土结构进行必要的耐久性设计与施工控制，将大大减少后期对建筑维护的投资，真正做到使用寿命设计。 2、影响混凝土材料耐久性的机理

钢与混凝土组合梁

第四章钢与混凝土组合梁思考题： 1．组合梁是由哪几部分组成的？钢梁与混凝土板之间能够共同工作的条件是什么？ 2．组合梁的设计计算理论有哪两种？一般各在什么情况下应用？ 3．组合梁按塑性理论计算时，钢梁截面应满足哪些要求？为什么？ 4．完全剪切连接组合梁按塑性理论计算时采用了哪些基本假定？ 5．连续组合梁在受力性能和设计计算方面有什么特点？ 6．连续组合梁按照弹性理论计算的原则和方法是什么？ 7．连续组合梁按塑性理论计算时应满足哪些要求？ 8．组合梁中的钢梁在哪些情况下可不进行整体稳定性验算？ 9．什么是部分剪切连接？一般在什么条件下，采用部分剪切连接的设计方法？ 10．在简支组合梁的变形计算中为什么采用折减刚度，而不直接采用换算截面刚度？习题： 1．某平台次梁采用钢与混凝土简支组合梁，梁的跨度为6m ，梁间距为2m ，梁的截面尺寸见题图4.1。施工阶段和使用阶段的活荷载标准值分别为1.5kN/m 2和6kN/m 2，使用阶段活荷载的准永久值系数5.0=q ψ。平台上有30mm 厚水泥砂浆面层，钢梁与混凝土之间无温差。混凝土的强度等级为C25（2N/mm 9.11=c f ，24N/mm 1080.2?=c E ），钢材采用Q235钢(2N/mm 215=f ,2N/mm 125=v f ,25N/mm 1006.2?=s E )。钢梁与混凝土板之间采用栓钉连接件，以承受交界面上全部的纵向剪力.试按弹性理论进行以下内容的验算：施工阶段：(1) 钢梁的受弯承载力；(2) 钢梁的受剪承载力；(3) 钢梁的挠度；使用阶段：(1)组合梁的受弯承载力；(2) 组合梁的受剪承载力；(3) 组合梁的挠度；(4) 钢梁腹板的局部稳定性；(5) 剪切连接件设计。

2016继续教育-混凝土力学性能检测

千分表的精度不低于（）mm A.0.01 B.0.001 C.0.0001 D.0.1 答案:B 您的答案：B 题目分数：9 此题得分：9.0 批注：第2题加荷至基准应力为0.5MPa对应的初始荷载值F0，保持恒载60s并在以后的()s内记录两侧变形量测仪的读数ε左0，ε右0。 A.20 B.30 C.40 D.60 答案:B 您的答案：B 题目分数：9 此题得分：9.0 批注：第3题由1kN起以()kN／s～（）kN／s的速度加荷3kN刻度处稳压，保持约30s A.0.15～0.25 B.0.15～0.30 C.0.15～0.35 D.0.25～0.35 答案:A 您的答案：A 题目分数：9 此题得分：9.0 批注：第4题结果计算精确至（）MPa。 A.0.1 B.1 C.10 D.100

您的答案：D 题目分数：9 此题得分：9.0 批注：第5题下面关于抗压弹性模量试验说法正确的是哪几个选项 A.试验应在23℃±2℃条件下进行 B.水泥混凝土的受压弹性模量取轴心抗压强度1/3时对应的弹性模量 C.在试件长向中部l／3区段内表面不得有直径超过5mm、深度超过1mm的孔洞 D.结果计算精确至100MPa。 E.以三根试件试验结果的算术平均值作为测定值。如果其循环后任一根与循环前轴心抗压与之差超过后者的10%，则弹性模量值按另两根试件试验结果的算术平均值计算，如有两根试件试验结果超出上述规定，则试验结果无效。答案:B,D 您的答案：B,D 题目分数：12 此题得分：12.0 批注：第6题下面关于混凝土抗弯拉弹性模量试验说法正确的是哪几个选项 A.试验应在23℃±2℃条件下进行 B.每组6根同龄期同条件制作的试件，3根用于测定抗弯拉强度，3根则用作抗弯拉弹性模量试验。 C.在试件长向中部l／3区段内表面不得有直径超过5mm、深度超过2mm的孔洞 D.结果计算精确至100MPa。 E.将试件安放在抗弯拉试验装置中，使成型时的侧面朝上，压头及支座线垂直于试件中线且无偏心加载情况，而后缓缓加上约1kN压力，停机检查支座等各接缝处有无空隙(必要时需加木垫片) 答案:B,C,D 您的答案：B,C,D 题目分数：13 此题得分：13.0 批注：第7题对中状态下，读数应和它们的平均值相差在20%以内，否则应重新对中试件后重复6.6中的步骤。如果无法使差值降到20%以内，则此次试验无效。答案:正确您的答案：正确

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混凝土结构耐久性研究

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