Novel pyrolysis-gas chromatography/mass spectrometric techniques for the characterization of chemical additives in portland cement and concrete

Abstract

The application of pyrolysis gas chromatography mass spectrometry (py-GC/MS) has been improved for the determination of chemical additives that are either interground with cement clinker during the manufacture of Portland cement or admixed with a mixture of cement, sand, and stone, and water for the production of concrete. This technique has been found to be readily applicable for phenol-based cement grinding aids and naphthalene sulfonate formaldehyde condensate (NSFC)-based concrete admixtures. Furthermore, pyrolytic decomposition of a nitrite-based corrosion inhibitor incorporated into a concrete mixture was found to produce abundant dinitrogen oxide (N 2O), a unique indicator of the nitrite additive. Volatile methyl esters of fatty and rosin acid-based air entraining agents can be formed from the pyrolysis of powdered concrete treated with methanolic tetramethylammonium hydroxide (TMAH). Overall, the py-GC/MS analysis of cement and concrete has the potential to be far more specific and less tedious than the common extraction-spectroscopic based methods currently used. In-situ pyrolytic reactions can further expand the capability of py-GC/MS by volatilizing otherwise thermally stable or strongly adsorbed additives in cement and concrete.