Abstract
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.
Highlights
As concrete is a widely used material for the construction of bridges, roads, houses, water pipes and sewers, etc. an essential factor is that they have a long lifetime
The size and shape of the particles entering the ICP are defined by the interaction of the laser with the material, showing that the ablation mechanism is a major source of fractionation
As hardened cement paste (HCP) has a specific microstructure of needles and crystals that have grown together and pores of various sizes, a detailed knowledge of general laser parameters, and in particular of working fluence and ablation behaviors is of great importance, so as to avoid fractionation of this multi-phase system
Summary
As concrete is a widely used material for the construction of bridges, roads, houses, water pipes and sewers, etc. an essential factor is that they have a long lifetime. The size and shape of the particles entering the ICP are defined by the interaction of the laser with the material, showing that the ablation mechanism is a major source of fractionation. Kuhn et al observed different particle shapes resulting from the two different ablation mechanisms In their experiment, particles from 100 ablation pulses were collected on filters to determine the overall size and shape of the aerosol from two different laser wavelengths. As HCP has a specific microstructure of needles and crystals that have grown together and pores of various sizes, a detailed knowledge of general laser parameters, and in particular of working fluence and ablation behaviors is of great importance, so as to avoid fractionation of this multi-phase system. 144 Page 4 of 19 obtain knowledge of ablation and aerosol structure for use in potential in-house standards
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