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

In 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.