Modulus of elasticity for service and accident conditions

Size: px

Start display at page:

Download "Modulus of elasticity for service and accident conditions"

Carol Dana Gardner
5 years ago
Views:

1 Materials and Strutu / Matériaux et Construtions, Vol. 37, Marh 2004, pp RILEM C 129-MH: est methods for mehanial properties of onrete at high temperatu Modulus of elastiity for servie and aident onditions he text pented hereafter is a draft for general onsideration. Comments should be sent to the C Chairman: Prof. Dr. Ulrih Shneider, University of ehnology Vienna, Institut für Baustofflehre, Bauphysik und Brandshutz, Karlplatz 13/206, A-1040 Vienna, Austria; el.: ; Fax: ; ulrih.shneider@tuwien.a.at, by 30 September C Membership Chairman: U. Shneider, Austria; Seretary: P. Shwesinger, Germany; Members: G. Debiki, Frane; U. Diederihs, Germany; R. Felietti, Italy; J.-M. Franssen, Belgium; U.-M. Jumppanen, Finland; G. A. Khoury, U.K.; A. Millard, Frane; W. A. Morris, U.K.; L. Phan, USA. 1. SCOPE his reommendation is valid for strutural appliations of onrete under servie and aident onditions. his doument pents test parameters (material and environmental), and test proedu for determining the modulus of elastiity of onrete ylinders at onstant temperature max after first heating or after ooling from max to ambient. he test temperatu range from 20 to 750 C or above. he modulus of elastiity an be determined for speimens heated with or without a onstant uniaxial ompsive externally applied load, see Ref SERVICE AND ACCIDEN CONDIIONS 2.1 Servie onditions Servie onditions normally involve long-term exposure to temperatu in the range 20 C-200 C and moisture states between the two boundary onditions: Boundary Condition d : Drying (unsealed) onrete Boundary Condition nd : Moisture saturated (sealed) onrete. In general, boundary ondition d applies to drying strutu in air with a maximum thikness < 400 mm, or strutu with no point whih is farther than 200 mm away from a surfae exposed to air. Boundary ondition nd is defined for the following wet strutu: Sealed strutu independent of their dimensions. Zones of strutu with a distane > 200 mm from the surfae exposed to air. Strutu under water. 2.2 Aident onditions Aident onditions normally involve short-term exposure to temperatu in the range 20 to 750 C or above and transient moisture states, i.e. the onrete is allowed to dry during heating. In this ase the moisture boundary ondition is the same as the ondition d mentioned above, see Ref. 2 Part DEFINIION 3.1 General he modulus of elastiity is defined here as seant modulus, desribed in Fig. 3. It an be determined either in the hot state, or at ambient temperature after heating and ooling. Properties determined at temperature max are heneforth desribed as hot. Properties determined after ooling from max are heneforth desribed as idual. Consequently, the modulus of elastiity of onrete is referred to as hot modulus of elastiity or idual modulus of elastiity he modulus of elastiity of onrete may be determined for sealed or unsealed speimens whih are loaded or nonloaded during the thermal exposure prior to testing /03 RILEM 139

2 RILEM C 129-MH Beause the sts level during heating influenes the modulus of elastiity of onrete, it is proposed to distinguish two ases: he hot or idual modulus of elastiity of speimens without load during the temperature exposure prior to testing is heneforth defined as unstsed. he hot or idual modulus of elastiity of speimens whih are loaded during the temperature exposure prior to testing is heneforth defined as stsed. 3.2 List of symbols and notations = strain = ((L - Li)/Li) = strain inrement = strain inrement of stsed speimen sts (onstant) relevant sts differene of the elasti strain inrement E = modulus of elastiity f = ompsive strength f = ompsive strength at temperature L = measured length (variable) L i = initial referene length at ambient temperature (onstant) r = radius of speimen R = onstant heating rate (d s /dt) RH = relative humidity t = time (variable) t i = time at initiation of test t max = time when reahes max = referene temperature (variable) a = temperature at entral axis of rotation of speimen (variable) max = maximum referene test temperature (onstant) s = temperature at the surfae of speimen (variable) = temperature differene s - a 0 = supersript index for zero sts ( = 0) = subsript index for ompsion a = subsript index for loation at entral axis of rotation of speimen d = supersript index for drying (unsealed onrete) el = subsript index for elasti i = subsript index for initial max = subsript index for maximum nd = supersript index for non-drying (sealed onrete) = idual s = subsript index for loation at surfae of speimen = supersript index for temperature th = subsript index for thermal 3.3 Non-drying onrete he hot modulus of elastiity of unstsed, sealed speimens is determined from the strain omponent orponding to the sts interval aording to Fig. 3, see setion nd (1) he hot modulus of elastiity of stsed, sealed speimens is determined aording to Equation (2): nd, (2) he orponding idual moduli of elastiity are referred nd nd to as or,. 3.4 Drying onrete he hot modulus of elastiity of unstsed, unsealed speimens is determined from the strain omponent orponding to the sts interval aording to Fig. 3, see setion 6.3 (3) he hot modulus of elastiity of stsed, unsealed speimens is determined aording to Equation (4). d, (4) he orponding idual moduli of elastiity are refered as or,. 4. MAERIAL 4.1 Material type his reommendation applies to all types of onrete used in onstrution inluding high performane onrete. 4.2 Mix proportions Mix proportions shall be determined aording to the onrete design in pratie with the following proviso: he maximum aggregate size should not be less than 8 mm. Note: he modulus of elastiity of onrete is sensitive to the aggregate ontent whih normally omprises 60-80% by volume. Varying the aggregate ontent may ult in variations of the modulus of elastiity. 5. SPECIMEN 5.1 Introdution he speimens referred to in this reommendation may be laboratory ast, field ast or taken as o and should onform to the reommendations given below. 5.2 Speimen shape and size he onrete speimens (see Fig. 1) shall be ylindrial with a length/diameter ratio between 3 and 4 (slenderness). 140

3 Materials and Strutu / Matériaux et Construtions, Vol. 37, Marh 2004 he speimen's minimum diameters shall be four times the maximum aggregate size for ored samples and five times for ast speimens. he reommended diameters of the test speimen are 150 mm, 100 mm, 80 mm, and 60 mm to be taken as standard. Other diameters, when used, should be desribed as non standard. 5.3 Moulds, asting, uring and storage Moulds Moulds shall be ylindrial and should meet the general reommendations of RILEM. he moulds should preferably be onstruted from suffiiently stiff, ylindrial or semi-ylindrial shells made of steel or polymer. he assembled moulds should be watertight so as to prevent leakage of the ement paste or water during asting. If polymer moulds are used, the polymer should not be water absorbent Casting Casting should be performed in two or three stages. he ompation of the onrete in the mould should be done preferably using a vibrating table Curing All speimens shall be stored during the first seven days after asting at a temperature of 20 2 C as follows: in their moulds - during the first 24 4 hours after asting under onditions - during the next 6 days without moisture exhange his an be ahieved by several means. he reommended method is to keep the speimens in their moulds adding a tight ap on the top. Other possibilities are the uring: in a room with a vapour saturated environment (relative humidity > 98%); in a plasti bag ontaining suffiient water to maintain 100% RH; wrapping the speimen in a metal foil, e.g. self-adhesive aluminium sheaths; under water (preferably water saturated with Ca(OH) 2 ) Storage he further storage onditions up to the beginning of testing shall be hosen to simulate the moisture onditions of the onrete in pratie. he following storage onditions are proposed: Moisture ondition d (drying onrete) storage in air at 20 2 C and RH of 50 5% Moisture ondition nd (non-drying onrete) storage within sealed bags or moulds or wrapped in water diffusion tight and non-orrosive foils at 20 2 C. In eah ase, the moisture loss of speimens over the storage period should be determined by weighing. For the ase of non-drying onrete, the weight loss should not exeed 0.2% of the initial onrete weight determined before storage in a surfae dry ondition, e.g. by dabbing the speimen in water absorbent paper until no traes of humidity appear on the paper. 5.4 Speimen preparation he length, diameter and weight of the speimen shall be measured before testing. he onrete speimen shall be prepared so that eah end is flat and orthogonal to its entral axis. his shall be done at an age of at least 28 days and not later than 2 months before testing. Speimens repenting non-drying onrete shall be sealed by polymer in, metal or polymer foils, or rigid enasement depending upon the maximum test temperature. he enasement shall not influene the deformation of the speimen or the ontat between the speimen and the strain measuring devie. he time for the preparation of sealed speimens under laboratory onditions should not exeed 4 hours. 5.5 Age at testing he speimen should be at least 90 days old before testing. 5.6 Standard and referene ompsive strength he standard ube or ylinder ompsive strength at ambient temperature shall be determined at 28 days, and at the time of testing, aording to national requirements. In addition the ompsive strength of the test speimen aording to setion 5.2 shall also be determined at 28 days. he ompsive strengths (ambient and hot or idual as appropriate (see Ref. 2, Part 3) of the speimens aording to setion 5.2 shall be determined at the time of testing. he ult shall be used as referene strength of the speimens. he related referene strength speimens shall ome from the same set of bathes and shall be tested under the same temperature and load ondition, see Ref. 2, Part ES MEHOD AND PARAMEERS 6.1 Introdution he following test parameters are reommended as standard to allow a onsistent generation and omparison of test ults. However, the test parameters may be altered to suit speifi appliations. his should be desribed as nonstandard and should be arefully detailed in the test report. 6.2 Measurements Length measurement Length is measured in the diretion of the entral axis of the ylindrial speimen, and shall be determined by measuring the distane between two ross-setions on the surfae of the speimen with at least two measuring points per ross-setion. he measuring points shall be symmetrially arranged on the ross setion. he rosssetions shall be perpendiular to the entral axis and at least one diameter away from eah flat end of the speimen (see Fig. 1). he initial referene length shall be at least one diameter. he initial referene length L i shall be measured at 20 2 C with a preision of at least 0.5%. 141

4 RILEM C 129-MH Changes in length relative to L i are measured in the diretion of the entral axis of the speimen. From the length measurements the strain inrements are derived. For strain inrements up to miro strain, the unertainty should be less than 10 miro strain. For strain inrements exeeding miro strain the unertainty should be less than 20 miro strain emperature measurement hermoouples or other types of temperature measuring devies may be used. In speial ases it may be neessary to protet the surfae thermoouples against radiation. emperature measurements shall be made during heating and, when required, during ooling at three points on the surfae of the speimen, at the entre and at the level of the two ross-setions as shown in Fig. 1. Fig. 1 - Cylindrial speimen showing the loation of three temperature measuring points. he preision of the temperature measurements should be at least 0.5 C or 1% of the measured values whihever is the greater. he mean surfae temperature is the simple average temperature of the three measurements taken on the surfae of the speimen. Load Measurement he load applied shall be measured with a preision of 1%. 6.3 est proedure he speimen shall not be removed from the uring environment more than two hours for unsealed speimens and four hours for sealed speimens before the ommenement of heating. he initial moisture ontent just before testing shall be determined using ontrol speimens (sealed or unsealed) from the same bath ured and stored under the same onditions as the test speimens. he evaporable moisture ontent is determined aording to setion he speimen shall be plaed in the testing mahine and entred with an auray of 1 % of the speimen s diameter. A small ompsive sts referred to as pre-load level, not exeeding 0.05 MPa shall be applied in the diretion of the speimen s entral axis prior to testing (see Fig. 2). Fig. 2 - Shemati illustration of speimen yling during installation at ambient temperature to verify the measurement of length hange. hen the speimen shall be subjeted to a load yle between the pre-load level (5%) and 15% or 5% and 15% of the referene strength, see Fig. 2. he loading and unloading should be performed at a rate of MPa s -1. he hold time at 5% and 15% load levels should be less than 60 s. At the end of the loading proess the hanges in length, as reorded at two or more loations on the surfae of the speimen, shall not exeed 20% of the mean value. If this differene exeeds 20%, then the following should be heked: strain measuring devie; entering of the speimen; flatness and orthogonality of the flat ends of the speimen. Appropriate adjustments should be made and the load yle repeated until the 20% riterion is met. If this is not possible within one hour, the speimen should be exluded from the test. For speimens whih are stsed during heating or heating and ooling a uniaxial ompsive load is applied ontinuously in the diretion of the entral axis of the speimen at a rate of MPa/s to the required onstant load level at 20 C immediately prior to heating. he load level must be kept onstant aording to setion he speimen shall be subjeted to heating at the appropriate onstant rate (see setion 6.4.1), ommening not later than min after reahing the required preload level or load level ( stsed speimen). After reahing the test temperature max as indiated by the mean surfae temperature, the temperature should be maintained for a period of 60 5 min. After the hold time period the speimen may be tested immediately or ooled down to ambient temperature at a speified rate aording to setion and tested at ambient. Before testing the pre-load of the stsed speimens shall be redued or adjusted to 0.05 MPa. Within 1 min after reahing this sts level the test should be ommened. he test proedure is illustrated on Fig. 3. he testing ommenes with a yling of the speimen aording to Fig. 3. he yling shall be performed with an upper level of sts of 0.3 f or 0.3 f, and a lower level of sts of 0.05 f or 0.05 f, (see Ref. 2, Part 3). he hold time at 0.05 or 0.3 of the appropriate referene 142

5 Materials and Strutu / Matériaux et Construtions, Vol. 37, Marh 2004 Fig. 3 - Shemati illustration of the test proedure showing how the referene, hot or idual modulus of elastiity is determined. strength level should be 30 s. he rate of loading and unloading shall be MPa s -1. he ompsive strength f or f, referred to shall be determined aording to Ref. 2, Part 3. he third asending branh of the test is being used to determine the strain inrement or, see setions 3.3 and 3.4. he strain inrement shall be determined in the sts interval from 0.15 to 0.3 of f or f,. 6.4 est parameters Heating and ooling onditions For normal weight onrete, the reommended heating and maximum ooling rates as well as the temperature reording intervals for servie and aident onditions are given in able 1. Note: For all types of onrete, the radial temperature differenes in the ylindrial part of the speimen should not exeed 20 C during heating or ooling. An approximation of this temperature differene during a heating or a ooling at a onstant rate an be made using the formula = Rr 2 /4D, where D = hermal diffusivity of the onrete, R = rate of heating, r=speimen radius. he thermal diffusivity D varies signifiantly with temperature and type of onrete. he heating of the onrete speimen should be able 1 - Reommended heating and maximum ooling rates and maximum temperature reording intervals at the surfae of the speimen on the referene length Maximum diameter of the ylindrial part (mm) Rate of heating or ooling ( C/min) emperature reording interval (min) performed in a way that a uniform temperature is ensured around the irumferene of the test speimen and axially along the referene length. Maximum axial temperature differenes between any of the three surfae temperature readings shall not exeed 1 C at 20 C, 5 C at 100 C and 20 C at 750 C. For intermediate values, the maximum axial temperature differenes permitted shall be alulated by linear interpolation between the two adjaent points. Note: Conrete an spall explosively when heated. Preautions should, therefore, be taken to avoid damage or injury Moisture ondition he moisture ontent just before testing shall be determined using a referene speimen ured and stored under the same onditions as the test speimen. he moisture ontent is the loss in weight related to the weight of a dried speimen. It is determined by drying at 105 C until onstant weight is ahieved (when the hange of weight due to moisture loss does not exeed 0.1% of the speimens weight over a period of 24 2 hours), and by measuring the maximum weight loss. During testing the drying speimens shall be heated in a heating devie where the moisture an freely esape from the speimen and the heating devie. Non-drying speimens shall be heated and tested with a total moisture loss during the test less than 0.5% by weight of a similar speimen dried at 105 C. Note. In the test temperature range from 20 C to 150 C the determination of moisture loss after the test is reommended in the ase of drying onrete speimens. his is beause during the hold time of 1 hour the evaporable moisture is unlikely to esape totally from the speimens, i.e., speimens with a boundary moisture ondition d may omprise different absolute values in this temperature range. At higher temperatu it an be assumed that more than 95 % of the moisture loss ours during heating within the hold time of one hour Number of tests A minimum of two repliate speimens shall be tested for any unique ombination of test and material parameters. he simple mean of two or more speimens should be determined. If the test ults differ more than 20% a third or more speimens should be tested. If the ult of a single speimen differs more than 20% from the mean value of all speimens it should be exluded from the evaluation. 7. APPARAUS he test apparatus normally omprises a heating devie, a loading devie, and instruments for measuring temperature, load and length hanges of the speimen. he test apparatus must be apable of fulfilling the reommendations given in setion 6 for the test parameters and the levels of preision. 8. EVALUAION AND REPORING OF RESULS 8.1 Evaluation of the referene temperature he referene temperature of the speimen is alulated from the mean surfae temperatu using: 143

6 RILEM C 129-MH = ( )/3 (5) where 1, 2 and 3 are the measured surfae temperatu. 8.2 Evaluation of strain ults Non-drying onrete and drying onrete he strain differene or of a eah onrete speimen is evaluated, as the arithmeti mean of two or more of the reorded strain values, in aordane with the proedu given in setion 6. If the differene of the mean value and a single value measured exeeds 20 % the ult for this speimen has to be exluded Average modulus of elastiity he modulus of elastiity of the onrete is the simple average evaluated as the arithmeti mean of the values of two or more aepted speimens (see setion 6.4.3). 8.3 est report General he method of evaluating the modulus of elastiity of the onrete shall be desribed inluding any deviation from the standard. he valid ult of eah speimen tested shall be reported together with the mean modulus of elastiity as follows: nd nd unstsed speimens: or and or stsed speimens: nd, or, nd, or E., and he report shall inlude the items highlighted by underlining below. he other items listed below should be reported when available Mix proportions Cement type and soure, ement replaements, additives, ement ontent, water/ement ratio, maximum aggregate size, aggregate/ement ratio, aggregate grading, mineralogial type of aggregate, aggregate ontent by volume of onrete Fh onrete Air ontent, bulk density, slump (or equivalent) Hardened onrete and speimen details Curing regime, age at testing, initial moisture ontent of referene speimen, assumed thermal diffusivity D, standard ube strength or ylinder strength, referene ompsive strength, referene modulus of elastiity at ambient, diameter and length of speimen, mode of preparation of the flat surfaes of the speimen, method of sealing (if appliable), weight before and after testing (exluding the weight of items suh as thermoouples) est apparatus he apparatus used shall be desribed unless it is in aordane with a published standard, in whih ase the standard should be referened est parameters ime between removal of speimen from the uring environment and initiation of heating. ime between end of loading and start of heating. Initial referene length. Level of the training load (if appliable). he following should be reported as funtions of time during heating: individual temperature measurements, mean surfae temperature, mean entre temperature, referene temperature, rate of heating, axial and radial temperature differenes, and hanges in the measured length (inluding any adjustments made for movements of any or all omponents of the length measuring devie). Any deviation from the reommended test parameters (e.g. heating rate, loading rate, load level during heating) shall also be reported separately as "non-standard" Strain during initial load yling Strains during initial two load yles measured for eah loation at ambient temperature (setion 6.3) Modulus of elastiity ults he modulus of elastiity ults for non drying onrete nd nd, nd,, nd and, or drying onrete,,, and, of every speimen shall be reported in tabular form as funtion of the referene temperature. he average modulus of elastiity (see setion 8.2.2) shall also be reported Plae, date, operator Country, ity and institution where the experiment was arried out. he dates of the experiment and report. Name of the operator. REFERENCES [1] Shneider, U. and Shwesinger, P. (Ed.), Mehanial testing of onrete at high temperatu, RILEM ransation 1, February 1990, ISBN: X, Kassel, [2] RILEM C 129-MH Committee, est methods for mehanial properties of onrete at high temperatu, he Committee is in the proess of preparing the following douments: Part 1: Introdution Part 2: Sts-strain relation Part 3: Compsive strength (published, 1995) Part 4: ensile strength (published, 2000) Part 5: Modulus of elastiity Part 6: hermal strain (published, 1997) Part 7: ransient reep for servie and aident onditions (published, 1998) Part 8: Steady-state reep and reep reovery (published, 2000) Part 9: Shrinkage (published, 2000) Part 10: Restraint Part 11: Relaxation 144

Part 9: Shrinkage for service and accident conditions

Part 9: Shrinkage for service and accident conditions Materials and Structures/Matériaux et Constructions, Vol. 33, May 2000, pp 224-228 RILEM TECHNICAL COMMITTEES RILEM TC 129-MHT: Test methods for mechanical properties of concrete at high temperatures Recommendations