Contents of Materials Performance - MAR 2012

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

Page 20 of 84

MATERIAL MATTERS Continued from page 17
Q\ ZMÆMK\[ The pH and chloride sensors rely on
ÅJMZ WX\QK[ \W \ZIV[UQ\ \PMQZ UMI[]ZM- UMV\ LI\I J]\ \PMa LW VW\ ][M .*/ technology to physically sense changes QV X0 WZ KPTWZQLM TM^MT[ VW\M[ ;]V 1V- stead, these sensors use a chemical re- sponse instead of a physical response to UMI[]ZM MV^QZWVUMV\IT KPIVOM[ Shown is the polymer-based chloride sensor probe, which is mechanically attached to the end of a fiber-optic cable. Photo courtesy of Tong Sun, City University London.
environment changes the optical signal generated by the sensor, which is re- turned to the interrogator through the [IUM ÅJMZ .WZ \PM KWZZW[QWV [MV[WZ[ developed by the research team, the LMOZMM WN KPIVOM QV MQ\PMZ \PM ZMÆMK\ML wavelength or the signal generated by the sensor is an indicator of the degree of the environment's corrosiveness, [Ia[ ;]V oped by the research team to measure temperature and humidity (two impor-
18 MATERIALS PERFORMANCE March 2012
\IV\ NIK\WZ[ \PI\ QVÆ]MVKM I\UW[XPMZQK KWZZW[QWV ]\QTQbM I ÅJMZ *ZIOO OZI\QVO .*/ I[ \PM [MV[QVO MTMUMV\ is sensitive to changes in temperature and [\ZIQV available in the marketplace, the re- searchers' goal was to develop durable IVL [][\IQVIJTM QV [Q\] ÅJMZ WX\QK [MV[WZ probes that could detect high pH values (12 and above) and respond to changes in the chloride concentrations in con- crete, as well as survive in concrete's PQOPTa ITSITQVM MV^QZWVUMV\ [Ia[ ;]V She notes the pH probes, in addition to measuring high pH values, will help in- dicate the presence and depth of carbon- ation when they are placed at different LMX\P[ QV \PM KWVKZM\M ?PMV KWVKZM\M comes into contact with carbonic acid (H2
CO3 ) resulting from hydrated cement
compounds reacting with atmospheric carbon dioxide (CO2
), the ensuing car-
bonation leads to a reduction of the concrete's alkalinity—to a pH value as TW_ I[
¸IVL KI][M[ I OMVMZIT JZMIS-
down in passivity of the steel rebar that UISM[ Q\ [][KMX\QJTM \W KWZZW[QWV
NACE International, Vol. 51, No. 3