10Micro-Raman spectroscopy has been used to follow the reaction of free lime (CaO) exposed 11 for 24 hours to moist air at 80 °C under conditions of different relative humidities (10 -80 % 12 RH). X-ray diffraction and SEM imaging were applied as complementary techniques. The 13 conversion of lime to calcium hydroxide and its subsequent carbonation to various calcium 14 carbonate polymorphs was found to strongly depend on the relative humidity. At low RH (10 15 -20 %), only Raman spectroscopy revealed the formation of early amorphous CaCO 3 which 16 in the XRD patterns was detected only at ≥ 40 % RH. However, XRD analysis could identify 17 the crystalline polymorphs formed at higher relative humidities. Thus, between 20 and 18 60 % RH, all three CaCO 3 polymorphs (calcite, aragonite and vaterite) were observed via 19 XRD whereas at high relative humidity (80 %), calcite was the predominant reaction product. 20The results demonstrate the usefulness of Raman spectroscopy in the study of minor cement 21 constituents and their reaction products on air, especially of amorphous character. 22 23

The prehydration of industrial cements (CEM I 52?5 R and API Oilwell Class G) and pure cement clinker minerals (C 3 S, cubic C 3 A, orthorhombic C 3 A, C 4 AF) has been studied at 60 and 85% relative humidity using in situ X-ray diffraction (XRD), calorimetry, environmental scanning electron microscopy and X-ray photoelectron spectroscopy. This combination of techniques identifies the key components involved in the surface prehydration process. Prehydration of cement leads to dramatic retardation of hydration. In situ XRD shows the retardation of portlandite formation after prehydration, supporting the calorimetry results. X-ray photoelectron spectroscopy and ESEM investigations show surface modification after prehydration for C 3 S, C 3 A and doped C 3 A (4%Na 2 O). Prehydration of cement leads to modification of the surface area and surface charge, which can strongly influence the reactivity of bulk cements. This is relevant to the quality of cement during storage.

Prehydration -the reaction between anhydrous cement and water vapour -has deleterious effects on engineering properties such as compressive strength, workability and setting time. This study assessed changes in the engineering properties of CEM I Portland cement exposed to relative humidities (RHs) of 60% or 85% for 7 and 28 days. Thin layers (no more than 2 mm thick) of CEM I 42.5R cement were exposed to controlled RHs of 60% and 85%, followed by assessment of compressive strength, setting time and workability. These measurements were complemented by characterising the prehydrated anhydrous cement using isothermal calorimetry, scanning electron microscopy, X-ray diffraction and thermal gravimetric analysis. Following prehydration at 60% RH, conventional hydration resulted in a negligible reduction in strength development plus a decrease in workability and increase in setting time. At 85% RH, compressive strength was greatly reduced, particularly at early ages. There was also a greater loss of workability and increase in setting time.

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27The surface specific analytical method, x-ray photoelectron spectroscopy (XPS), has been 28 used to study the effects of water vapour and CO 2 on the cubic and orthorhombic polymorphs 29 of C 3 A. Significant differences between the two polymorphs were observed in the XPS 30 spectra. Upon exposure to water vapour, both polymorphs produced C 4 AH 13 on their surfaces. 31Additionally, the sodium-doped o-C 3 A developed NaOH and traces of C 3 AH 6 on its surface. 32Subsequent carbonation yielded mono carboaluminate on both polymorphs. Large amounts of 33 Na 2 CO 3 also formed on the surface of o-C 3 A as a result of carbonation of NaOH. 34Furthermore, the extent of carbonation was much more pronounced for o-C 3 A o than for c-35