Optimization of conditions for spectral determination of chlorine content in cement-based materials

Abstract

A combination laser/electrospark method is used for fast determination of chlorine in cement-based materials. Excitation of the spectra is carried out both directly in an ablation plume and when a pulsed electric discharge is applied to it. In both cases, we obtain calibration curves that are linear for the major concentration range of practical importance for the analyte element, up to 1.5%. The chlorine detection limit for the combination discharge approach is 0.05%. We consider the basic steps and characteristic features of the proposed experimental procedures. Introduction and Background.Local chloride corrosion of the metal is the major reason for accidental damage to concrete structures due to cracking and breaking of the high-strength steel reinforcement [1][2][3]. In this case, elevated and accelerated corrosion of the reinforcement is generally connected specifically with the presence in the concrete matrix of chlorides at a concentration greater than the standard 2 wt.%. As we known, additives are widely used routinely in concrete work to accelerate hardening of the concrete: CaCl 2 , NaCl, FeCl 3 , HCl, etc., often without strict limits. Furthermore, the technology for adding more significant amounts (up to 20 wt.%) of chloride salts, with the aim of obtaining cement mortars that do not freeze at negative temperatures, clearly has negative long-term consequences due to rapid corrosion of the reinforcement and weakening of the concrete matrix as a whole. An especially acute problem is the long-term stability of concrete roadway surfacing, bridge structures etc. that are exposed to the weather, artificial irrigation, and snow-cover reduction by application of salt mine tailings. Ultimately, the additional accumulation of chlorides leads to an increasing effect of the chlorides on the quality of the structures. So development of methods for monitoring the initial content and accumulation of chlorides in objects of the construction industry is an important problem in the national economy.Until the last decade, determination of chlorine in construction materials and structures based on cement was done by relatively labor-intensive chemical methods involving mechanical sampling, preparation of the sample as required, and dissolution of the analyte material. When appropriate equipment is available, the analytical procedures might be carried out using reliably developed variants of spectral analysis, although chlorine is an element that is difficult to determine by spectrometry.Sporadic work has been done to date on determination of chlorine in lime/cement mortar and concrete by laser-induced breakdown spectroscopy (LIBS) [4][5][6]. Incidentally, determination of chlorine and other halogens (fluorine, bromine) by the LIBS method has been tested on solid organic compounds, which makes it possible to identify these materials [7]. In [8], the prospects are noted for using LIBS for environmental monitoring of air composition for fluorine, chlorine, sulfur, and carbon content. Along with providing sensitivity of th...

Laser ablation molecular isotopic spectrometry (LAMIS): current state of the art

“…The secondary excitation coupled to LIBS has a long history and has been shown as an effective means to boost sensitivity of the analysis. Examples include microwave, [32][33][34] glow discharge, 35,36 radiofrequency torch, 37 spark [38][39][40][41][42][43][44] and arc 45 as the sources of the secondary excitation. Relative to the singlepulse ablation, a longer sustained plasma at lower temperature ought to be productive in the enhanced formation of molecules in their excited emitting states.…”