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Keywords:

  • Raman microscopic imaging;
  • cement stone;
  • Roman cement;
  • blast furnace slag;
  • pigments

We present to our knowledge the first application of Raman microscopic imaging to cementitious materials. This technique yielded the composition and phase distribution (spatial resolution ≈ 500 nm) in samples of cement stone taken from façade elements of four Swiss buildings covering the period of 1892–1924. Raman maps of Roman cement, a predecessor of modern Portland cement, reveal the chemical heterogeneity of clinker remnants consisting of various crystalline, polymorphic, and amorphous phases and visualize different crystal orientations. Our findings include the observation of the γ-polymorph of Ca2SiO4 – previously, only detected in Portland cement – and Raman spectra of calcium aluminate (ferrite) interstitial phases in Roman cement showing significant differences to the corresponding phases in Portland cement clinker. Furthermore, calcite, vaterite, gypsum, and ettringite were identified in the rim of a nonhydrated residual nodule. Beyond binder remnants, aggregates in the form of spherical (≤500 µm diameter) slag and irregularly shaped pigment particles were analyzed. Here, we focused on the unambiguous identification of compounds in complex matrices by comparing sample spectra with database and own reference spectra. A Raman map collected on blast furnace slag in cement stone shows the spatial distribution of calcite, quartz glass and pyrite. Furthermore, several Fe-containing, Si-containing, and Pb-containing phases were identified. The analysis of pigments partly confirmed and partly contradicted the bequeathed historic recipe of a cement stone façade. These results have direct implications in the field of conservation and restoration and generally demonstrate the potential of Raman imaging to provide deeper understanding of (historic) building materials. Copyright © 2013 John Wiley & Sons, Ltd.