draft maturity meter procedure-mndot concrete manual

8/15/2019 DRAFT Maturity Meter Procedure-MnDOT Concrete Manual

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August 2015 - DRAFT CONCRETE MANUAL 5-694.560

5-694.560 DEVELOPING STRENGTH-MATURITY RELATIONSHIP

The maturity method utilizes the principle that directly relates the strength ofconcrete to the cumulative temperature history of the concrete. Using this principle,the Engineer and Contractor can quickly and reliably estimate the field strength ofconcrete based on the maturity index (equivalent age or timetemperature factor!

rather than by beam or cylinder tests in the field or the laboratory. The maturity asapplied to a concrete mi" is specific to that particular mi". #hen the mi" design ischanged, the Contractor may need to develop a ne$ maturity relationship, ormaturity curve in accordance $ith %n&'T tandard pecification )*+.

The development of a maturitystrength relationship requires three steps. Theseinclude-

! &eveloping the maturitystrength curve in the laboratory or in the field,)! Estimating the inplace strength in the field, and! /erifying the strengthmaturity relationship in the field.

This procedure utilizes the 0urseaul method for developing strengthmaturitycurves, as described in 1T% C 23*. The 0urseaul method uses a specificdatum temperature (usually 24C, but may be determined e"perimentally! tocalculate the timetemperature factor (TT5! and to relate this to the measuredconcrete fle"ural or compressive strength at the particular TT5 value. The generalform of the 0urseaul method is sho$n in Equation .

∑ ∆−= t T T TTF a

)( 0

$hereTT5 6 the timetemperature factor at age t, degreedays or degreehours,7t 6 time interval, days or hours,Ta 6 average concrete temperature during time interval, 7t, 4C, andT2 6 datum temperature, 24C.

This test method describes the procedure for developing maturitystrengthrelationships to estimate concrete strength using the maturity method. This methoduses either beams for fle"ural strength or cylinders for compressive strength. #hilethe ma8ority of this procedure uses dual units, measure and record all temperatures

relating to the computation of maturity in degrees centigrade (4C!.

A. DEFINITIONS

1. Temper!"re Se#$%r The device on a maturity meter or data logger that is inserted into the concreteand provides a measure of temperature.

Equation




&. D! L%''er 1 commercially available device that record temperature measurements from atemperature sensor at various intervals.

(. M!"r)!* Me!er 1 commercially available device that includes a temperature sensor, data logger,and conducts maturity calculations automatically.

4. M!"r)!* I#+e,The cumulative area under the timetemperature curve developed as concretecures. The units of maturity inde" are in degreehours (Chr!. 5or the purposesof this procedure, the maturity inde" called the timetemperature factor (TT5!.

5. M!"r)!* "reThe relationship bet$een the timetemperature factor and the strength of theconcrete.

6. Ver)/)!)%# Te$!

1t various intervals during construction, the maturity curve is verified by castingadditional specimens and comparing the TT5strength relationship $ith theoriginal maturity curve for a particular mi".

. APPARATUS

1. M!"r)!* Me!er %r Temper!"re Se#$%r #+ D! L%''er 1 maturity meter, for the sole purpose of recording concrete maturity, or atemperature sensor and data logger combination, accurate to 94C, and capableof recording data at a time interval of hour or less. 5or highearly strength oraccelerated opening mi"es, provide a device capable of recording data at a time

interval of : minutes or less.

Calibrate maturity meters yearly to ensure proper operation and temperaturesensing.

/erify proper operation of maturity meters and temperature sensors every 2days during normal plant production. ;erform verification by comparing thetemperature recorded by the maturity meter or temperature sensor to a kno$ntemperature, as provided by a calibrated thermometer. Use at least threetemperature points (e.g. *245, 3:45, and 245 <:4C, ):4C and *:4C=! in thesensor verification.

&. em Spe)me# M%2+$&eveloping a maturity relationship $ith beams, a minimum of : beam specimenmolds are required. Use beam molds + in " + in (:2 mm " :2 mm! in crosssection, and $ith an overall length allo$ing for a span length in the testingapparatus of at least times the depth.




(. *2)#+er Spe)me# M%2+$&eveloping a maturity relationship $ith cylinders, a minimum of 3 cylindersspecimen molds are required. Use cylinder molds * in " > in (22 " )22 mm!. ?fthe aggregate has a ma"imum size greater than @ in (.: mm!, use + in " )in (:2 " 22 mm! molds.

4. F2e,"r2 S!re#'!3 Te$! Appr!"$

The apparatus for testing beam strength in fle"ure shall conform to therequirements in ection :+A*.:)) (Testing Beams for 5le"ural trength! of the%n&'T Concrete %anual.

5. %mpre$$)e S!re#'!3 Te$! Appr!"$The apparatus for testing compressive strength shall conform to therequirements in ection :+A*.:2 (Compressive trength Tests! of the %n&'TConcrete %anual and 11T' T)) (Compressive trength of CylindricalConcrete pecimens!.

. PREPARATION OF SPEIMENS

1. ;repare specimens according to ection :+A*.: (cylinders! or ection :+A*.:) (beams!. The preferred method is to cast, cure, store, and testspecimens in the field at the beginning of the construction pro8ect. Ensure thatconcrete temperatures in the specimens do not drop belo$ :245 (24C!. ?f airtemperatures are e"pected to drop belo$ *245 (*4C!, place the specimens onfoam board or ply$ood to insulate them from the cold ground. ;lace insulationon and around the specimens.

?f prepared in the laboratory, ensure that concrete used in making the specimensis identical in mi"ture proportions, quantities and material manufacturers to those

specified on the 1pproved %i" &esign.

B. Test and record air content, temperature, and slump of the fresh concrete on theConcrete Maturity-Strength Development form. ee 5igure 1 for an e"ample of acompleted form using 5le"ural Beam trength. ee 5igure B for an e"ample of acompleted form using Compressive trength.

C. 5or beams, prepare : specimens according to the appropriate standard listed inection B.) above. Use a minimum of cubic yards of concrete. Embedtemperature sensors in at least t$o of the specimens. ;lace all sensors so thatthey are appro"imately in. (3: mm! from any surface and in one of the outside

thirds (i.e. $ithin + in. (:2 mm! from the end of the beam!. ave the specimens$ith the temperature sensors for testing last.

5or cylinders, prepare 3 specimens according to the appropriate standard listedin ection B. above. Use a minimum of cubic yard of concrete. Embedtemperature sensors in the center of t$o of the specimens, record the data anddo not test for strength.




&. ;rotect the concrete specimens according to ection :+A*.: (cylinders! orection :+A*.:) (beams!.

D. PROEDURE

1. Dee2%p S!re#'!3-M!"r)!* Re2!)%#$3)p

;erform strength tests according to ection :+A*.:)) (beams! or 11T' T))(compressive! for the type of concrete at the ages specified in the table belo$.

3r%#%2%')2 Te$!)#' A'e$ %/ S!re#'!3 Spe)me#$

T*pe %/ %#re!e Te$!)#' A'e$

Concrete pavement as defined in )2 &etermined by the Contractor‖

0ormal trength Concrete as defined in )*+ , ), , 3 and )> days

ighEarly (E! Concrete as defined in )*+ ) hours, , ), 3 and )> days

Ultra ighEarly (UE! Concrete as defined in)2)

, * and > hours, and * days

D The Contractor may ad8ust the testing ages if approved by the Engineer, incon8unction $ith the Concrete Engineer.

Test at least t$o ()! sets of strength specimens before the anticipated opening‖strength.

Test three specimens at each age and compute the average strength.

?f a lo$ test is the result of an obviously defective specimen, discard the resultfrom the average but record its value and the reason for discarding it in the dataentry form.

1t each test age, determine the average maturity inde" (TT5! at the time thespecimens are tested, by averaging the values obtained from the t$o maturitymeters or data loggers. ?f using a maturity meter, read the maturity inde" directlyfrom the meter. ?f using a temperature sensor and data logger, calculate thematurity inde" using the timetemperature history from the logger, and Equation in ection of this procedure. 1verage the t$o maturity inde" values and reportthis in the appropriate location on the Concrete Maturity-Strength Development form.

The Concrete Maturity-Strength Development form is a %icrosoft E"cel

spreadsheet that plots the average fle"ural strength vs. the average maturityinde" for each test age, and determines the bestfit logarithmic curve using theform.

α

τ

−

= TTF

ueS S

#here-

Equation 2




6 fle"ural strength (modulus of rupture! or compressive strength, psiTT5 6 the timetemperature factor at age t, degreedays or degreehours,u 6 ultimate e"pected fle"ural strength, psi

, F 6 time and shape coefficients.

Use the resulting fitted curve maturitystrength relationship for estimating the inplace strength of concrete cured under any conditions including those in the lab

or in the field.

'btain the Concrete Maturity-Strength Development form for these calculationsfrom the Concrete Engineering $ebsitehttp-GG$$$.dot.state.mn.usGmaterialsGconcrete.html.

5or pavements, determine the opening strength criteria for concrete pavementsin accordance $ith )2..', H'pening ;avement to Traffic.I

5or pavement repairs, determine the opening strength criteria for concretepavements in accordance $ith )2)..B.*, H'pening to Construction Equipment

and Traffic.I

5or structures, determine the strength criteria for form removal or loading inaccordance $ith )*2..J, HConcrete Curing and ;rotection.I

Enter all collected and recorded data in the Concrete Maturity-StrengthDevelopment form.

&. E$!)m!e I#-P2e %#re!e S!re#'!3

To estimate the inplace concrete strength in the field, place a temperature

sensor in the concrete at a rate specified in %n&'T tandard pecification )*+.

Kecord the identification number(s! of the maturity meters or data loggers on theMaturity - Field Data form. ee 5igure C for an e"ample of a completed form.

;rotect any protruding $ires from construction equipment. ?nitiate data collectionand recording according to the manufacturerLs instructions. Use a datumtemperature value of 24C.

1t regular intervals, check the recorded maturity inde" (or temperature historyand compute the maturity inde"!.Kecord the temperature readings and calculate

the maturity values on the Maturity - Field Data form to estimate the strength ofthe inplace concrete.

(. Ver)/* S!re#'!3-M!"r)!* Re2!)%#$3)p

1t intervals specified in tandard pecification )*+, cast and cure threespecimens and insert a temperature sensor in at least one of them. ?f usingcylinders, cast an additional cylinder for inserting the temperature sensor only.




Test all three specimens as described in this standard as close to the maturityinde" (TT5! for the opening, loading or form removal strength criteria as possible.Compute the average strength as described in ection &. using the ConcreteMaturity-Strength Verification form. ee 5igure & for an e"ample of a completedform using 5le"ural Beam trength. ee 5igure E for an e"ample of a completedform using Compressive trength.

;lot the average strength and maturity inde" on the Concrete Maturity-StrengthVerification form and check that it falls on or near the curve. Take appropriateactions according to tandard pecification )*+.

Keport the results of the validation testing on the Concrete Maturity-StrengthVerification form and submit the form to the Engineer in the field.




F)'"re A




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F)'"re D




F)'"re E

draft maturity meter procedure-mndot concrete manual

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