See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/333378907 'TM-Ring Test' - A quality control test for TMT (or QST) steel reinforcing bars used in reinforced concrete systems Article in Indian Concrete Journal · April 2017 CITATIONS 2 READS 5,417 2 authors: Some of the authors of this publication are also working on these related projects: Cold Weather Concreting View project Bond performance of pre-tensioned concrete system View project Sooraj Kumar A O Nair Arizona State University 14 PUBLICATIONS 78 CITATIONS SEE PROFILE Radhakrishna Pillai Indian Institute of Technology Madras 145 PUBLICATIONS 747 CITATIONS SEE PROFILE All content following this page was uploaded by Radhakrishna Pillai on 25 May 2019. The user has requested enhancement of the downloaded file.
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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/333378907
'TM-Ring Test' - A quality control test for TMT (or QST) steel reinforcing bars
used in reinforced concrete systems
Article in Indian Concrete Journal · April 2017
CITATIONS
2READS
5,417
2 authors:
Some of the authors of this publication are also working on these related projects:
Cold Weather Concreting View project
Bond performance of pre-tensioned concrete system View project
Sooraj Kumar A O Nair
Arizona State University
14 PUBLICATIONS 78 CITATIONS
SEE PROFILE
Radhakrishna Pillai
Indian Institute of Technology Madras
145 PUBLICATIONS 747 CITATIONS
SEE PROFILE
All content following this page was uploaded by Radhakrishna Pillai on 25 May 2019.
The user has requested enhancement of the downloaded file.
Sometimes it becomes necessary to determine if aparticular reinforcing bar/wire, or lot, has undergoneproper heat treatment or is only a mild steel deformedbar. Because the two cannot be distinguished visually,the following field test may be used for purposes ofidentification. A small piece (about 12 nun long)-canbe cut and the transverse face lightly ground flat onprogressively fmer emery papers up to '0' size. Thesample can be macroetched with nital (5 percent nitricacid in alcohol) at ambienttemperature for a fewsecondswhich should then reveal a darker annular regioncorresponding to martensitelbainite microstructure anda lighter core region. However, this test is not to beregarded as a criterion for rejection. The materialconforming to the requirements of this standard forchemical and physical properties shall be consideredacceptable.
The core of the heat treated reinforcing bars/wiresconsist of ferrite and perlite - more ductile but lessstrong than the martensite. Computerized processcontrol is used to dynamically adjust the many rapidlychanging parameters depending on the chemicalcomposition of the steel, the desired grade and size ofthe reinforcing bar/wire etc. For the larger diameters,small addition of microalloys is usual.
in during the sudden quenching of the red-hot steel incold water. The resulting tempered-martensite showsimproved deformability compared to the as-quenchedmartensite.
A-I The processing of reinforcing steel is usuallythrough one or combination of processes which mayinclude hot rolling after micro alloying, hot rollingfollowed by controlled cooling (TMT process) and hotrolling followed by cold work.
Heat treatment is a thermal process undergone by thesteel in the solid state. The most common practice isfinishingonline heat treatment while rolling, commonlyknown as thermomechanical treatment (TMT) process.After leaving the last stand of the rolling mill, the barsare quenched (rapidly cooled) in water from a finalrolling temperature of about 950°C. The quenching ispartial, only until a surface layer has been transformedfrom austenite (a steel phase stable only at very hightemperatures) to martensite (stable at temperaturesbelow 350°C). This controlled quenching is achievedin one or more online water cooling devices throughwhich the steel passes at a very high speed beforereaching t~e cooling bed=
Because, the quenching is .only partial, a part of theoriginal heat remains in the core of the steel and, on thecooling bed, this heat migrates towards the surface,Thisresults in an automatic self-tempering process wherethe surface layer of martensite is tempered; this'tempering temperature' (or equalization temperature)refers to the maximum temperature attained by the barsurface after quenching. Tempering enables a partialdiffusionof carbon out of the extremelybrittle but strongmartensite, thus relieving the inherent stresses locked
ANNEXA(Foreword)
INFORMATION ON CONTROLLED COOLING PROCESS
IS 1786 : 2008
(ii) After etching(i) Before etching
Cold Set
(ii) Side view(i) Front view
LEVEL 2 (L2) ACCEPTANCE CRITERIANo. Observations mmm1 Diameter of rebar, D2 Measured thickness of TM, tTM
No. Question Answer(circle one)
1 Is tTM~ 0.07 D ? Yes INo2 Is tTM::;0.10 D ? Yes INo
DecisionIf all the answers are 'Yes', then accept the rebar lotIf anyone or more answers are 'No', then reject the rebar lot
LEVEL 1 (Ll)ACCEPTANCE CRITERIA
No. Question Answer(circle one)
1 Is a dark grey peripheral region and light grey core seen? Yes INo2 Does the dark grey peripheral region form a continuous outer ring? Yes I No3 Are the dark grey peripheral region and light grey core concentric? Yes INo4 Is the thickness of the dark grey peripheral region uniform? Yes INo
DecisionIf all the answers are 'Yes', then accept the rebar lotIf anyone or more answers are 'No', then reject the rebar lot
