LA-ICP-MS on hardened cement paste: laser-material interaction, signal formation and optimization of laser fluence

Abstract

AbstractIn almost all applications of concrete components, both the transport of substances such as chlorides, sulphates, acids, CO2, etc. through the pore structure into the concrete and the resulting local chemical and physical processes have a negative effect on the lifetime of the structure. Most data are actually obtained from layer-by-layer mechanical sampling of, for instance, bore dust, followed by chemical analysis. Several groups have previously demonstrated the enormous potential of LA-ICP-MS for monitoring these multi element processes both qualitatively and quantitatively and with high spatial resolution. However, there has been no fundamental investigation of laser-material interaction, aerosol particle formation, fractionation analysis or the effect of cement-specific parameters such as the water to cement (w/c) ratio on signal intensity. This paper presents the ablation mechanisms of a frequently used 213 nm quintupled Nd:YAG ns laser operating on the HCP (hardened cement paste) multi-phase system in comparison with amorphous and well-characterized NIST 612 glass. It includes energy-signal considerations, crater evaluations after multiple shots using different energy densities and aerosol structures captured on filters. The investigation determined a linear energy to signal behavior in a range of 2–6 J/cm2, while the ablation mechanism is different to common mechanisms obtained for glass or brass. The aerosol captured on the filter material displays cotton-like structures as well as defined spherical particles, which is comparable to observations made with NIST glass aerosols.