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Thymolphthalein as alternative to phenolphthaleine in concrete carbonation testing


Phenolphthalein is used in carbonation test of concrete. It is however a recognized carcinogen. Thymolphthalein has been used as an alternative with good results.

Substituted substance(s)

  1. Phenolphthalein

    CAS No. 77-09-8 EC No. 201-004-7 Index No. 604-076-00-1

Alternative substance(s)

  1. 3,3-Bis(4-hydroxy-5-isopropyl-o-tolyl)phthalide

    CAS No. 125-20-2 EC No. 204-729-7 Index No. 

Other type of alternative

Reliability of information

Internet information: data are from an internet document and only a basic and partial evaluation could be performed

Hazard assessment

Thymolphthalein is not included in the harmonized EU classification and is not on the lists with substances currently known to fulfill  SUBSPORT screening criteria for hazards of high concern.
See also Further reading.

» Check the Substance Database according to SUBSPORT Screening Criteria (SDSC)

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Substitution description

Carbonation process causes the pH of concrete to drop and affects the passivity of the reinforcing steel, posing a threat  to constructions, especially those exposed to environment.
The carbonation is generally tested with phenolphtaleine which gives a colour change indication.
The study consider that phenolphthalein has a reliability problem regarding test results. It is also a carcinogen chemical.
It was find that thymolphthalein was the best substitute for phenolphthalein.

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Case/substitution evaluation

The substitution  of phenolphthalein  for concrete carbonation determination is easy to implement. Costs of alternative reagent are a bit higher, yet comparable.

For determining the very early carbonation of concrete  (before concterte setting), a mixture that still contains phenolphtalein is needed.

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Other solutions

Further information

MSDS Thymolphtaleine from Sigma Aldich is here

ECHA C&L inventory ( retrieved on 25 February 2012)

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Who provided the information

Type of information supplier


Publication source

Yu, Myoung-Youl Yu, Lee, Jae-Yong ,Chung, Chul-Woo ,The Application of Various Indicators for the Estimation of Carbonation and pH of Cement Based Materials, SEDL / Journals / Journal of Testing and Evaluation (JTE) ,Volume 38, Issue 5 (September 2010)

Type of publication and availability 

scientific publication

Original document: click here
Archived copy: click here

Comments from SUBSPORT users

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Publication or last update: 27.02.2012