A MULTIDIMENSIONAL INVESTIGATION USING X-RAY DIFFRACTION AND COMPUTED TOMOGRAPHY

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1 A MULTIDIMENSIONAL INVESTIGATION USING X-RAY DIFFRACTION AND COMPUTED TOMOGRAPHY Pöllmann, H., Meier, R.*, Blaj, G.*, Riedl, U.* University of Halle/Saale-Germany * Panalytical, Almelo, Netherlands ABSTRACT Phase analysis, density, microstructure and phase distribution were measured of two mortar samples to compare the variations in macro-, meso- and nanoscales to provide an evaluation of the properties especially the durability of mortars and concrete. INTRODUCTION Classical X-ray investigations of mortar and concrete bars in laboratory can show phases, phase distributions and even quantification of occurring phases. The new technique now provides the possibility of evaluation of microstructure by 3-dimensional imaging. For this purpose two different mortar bars according to DIN were fabricated. The first mortar bar was fabricated from mixtures of cement and norm sand at a ratio of 25 : 75 %, the second norm bar has a composition of 75 % norm sand, but the 25 % of cement were partially replaced by waste glass powder. The replacement of cement by reactive waste glass powder should result in a reduction of porosity in the norm bars and therefore increase the durability of these mixtures on a long term scale. An additional effect results in the CO 2 -reduction of this building material by a replacement of the total amount of used cement clinker in the samples. The used X-ray instrument equipped with different sample stages provides information on density, phase formation, microstructure and pore distribution. Combined with other methods like SEM and other technological measurements (physical tests like strength, tensile strength, expansion, shrinkage, permeability) an optimized information based on these materials can be obtained in laboratory. This provides knowledge for evaluation of the durability of materials. EXPERIMENTAL The X-ray experiments were performed on an Empyrean X-ray diffraction instrument equipped with a Pixcel 3D detector using Cu-Ká-radiation. Sample stages and optical lenses were optimized for phase determination, phase distribution and CT measurements. The X-ray data were treated using High score plus programs and VG Studio MAX 2.1 manufactured by Volume Graphics. The SEM investigations were performed using a LEO 1450 VP scanning electron microscope equipped with an EDAX detector system

2 Selection of samples The samples used were cut from norm bars 4cm x 4cm x 16cm in thick sections of about 4cm x 4cm x 2mm thickness. Macroscopically the samples with and without glass powder cannot be distinguished. But the reaction behaviour and the properties of these mortars are quite different. Figure 1 shows a typical concrete sample cut from a norm mortar bar. Fig.1.: Macroscopic view of a concrete sample 4cm x 4cm x 2mm thick. A more detailed view of the relevant phases was obtained by using SEM microscopy, showing the different formed phases on a ãm scale. Also some pore structures and micro cracks could be visualized. Figure 2 shows the different phases, pores and cracks measured by SEM-microscopy. The following components can be visualized : Sand grains Glass particle (amorphous) Pores Micro cracks Hydrated and carbonated cement

3 Glass grain Void caused by a ripped quartz grain Quartz grain void Fig.2: SEM micrograph of microstructure of mortar sample Determination of phases The main hydration products of the cement products are CSH phases, Portlandite, Calcite and quartz from norm sand. Small amounts of long elongated needles of ettringite can be seen also in the SEM images (figure 3) after longer times of hydration (several weeks). The amorphous amount of added glass contributes to the background of the X-ray diagrams.

4 Fig.3: Microstructure of a hydrated sample showing portlandite platelets, CSH-overgrowth and elongated ettringite needles A comparison of phase distribution of the samples with and without glass shows, that differences in the amounts of portlandite and calcite occur. In figures 4 and 5 the relevant X- ray diffraction parts are given. The sample bar containing glass powder shows a good content of portlandite which represents a dense structure and less carbonation effects, whereas the sample bar without added glass powder has decreased content of portlandite, but increased contents of calcite. This clearly shows, that the addition of glass leads to less carbonation of the investigated building material mixtures.

5 Counts cement 30 without Quartz Calcite 5000 Portlandite Position [ 2Theta] (Copper (Cu)) Fig.4 : X-ray diffractogram of concrete with added glass powder Counts cement 30 with new 5000 Portlandite Quartz Calcite Position [ 2Theta] (Copper (Cu)) Fig.5: X-ray diffractogram of concrete without glass powder The 3-dimensional relevant information was measured summarizing all the information from the intensity obtained by transmitting the sample. The density measurement is highly necessary to obtain direct correlations between physical properties like strength development and phase relations and porosity. The use of this non destructive technique provides an increased set of properties of the overall sample. Figures 6 and 7 show a comparison of both samples.

6 Fig.6: CT image of sample with lower density: sample without glass Fig.7: CT image of sample with higher density : sample containing glass Using this overall 3D-information, the complete microstructure and pore distribution can be obtained from the sample. Figure 8 show the CT-images of both cementitious concrete samples in comparison, to highlight the different densities.

7 Fig. 8: CT images of both concrete samples showing higher density on the right side and less density on left side The overall comparison of porosity analysis is given in figure 9 for comparison : With glass : ~ 3 % No glass : > 10% Fig.9: Determination of porosity of both sample bars A comparison of both samples shows clearly that by use of the CT image the pore volume can be quantified and shows lower porosity of glass containing bars which establish an increased stability of these mortars. Using the reverse mode it is even possible to show the porosity and the pore shape. The porosity is closely related to the water/solid ratio of the initial cementitious grouts and plays a very important role in the determination of the final quality and durability of the produced building material type. A summary of a pore distribution and pore size in inverted mode shows figure 10.

8 Fig.10: The image shows in an inverted mode the pores and their spatial distribution in a concrete sample SUMMARY AND CONCLUSION The usage of combinations of methods for determination of quality of cementitious materials enhances the chance of an optimized interpretation of the measured samples significantly. Besides SEM methods mainly the usage of CT data obtained with a commercial laboratory X- Ray diffractometer. The combination of density, phase formation, phase distribution and microstructural information from 1 laboratory X-ray tool is a powerful method for material analysis. X-ray experiments can now be used to understand phase evaluation, durability based on solids, but also based on pore distribution. The addition of glass in this experiment lowers the permeability and protects the material from further carbonation and lowers the ph-value. Embedded steel therefore is more and better protected. The new laboratory technique provides an excellent method to obtain in a short time data on solid material of the cementitious sample but also relevant data on porosity helping to understand and predict long term stability. ACKNOWLEDGEMENTS Thanks are due to the team of ZWL/Lauf (DR.J.Göske, Dipl.-Ing.S.Winter) for helping in acquiring the SEM-micrographs and Dipl.-Geol. M. Schmidt/Univ. Halle for providing the concrete bars.

9 REFERENCES Meier, R., Blai, G., Riedl, U., Pöllmann, H. (2011). 'A new strategy for X-ray Investigation of Materials - Ranging from 0 to 3 dimensional X-ray scattering techniques': AXXA conference, Abstract, Sydney, February 2011, in press Panalytical Application note (2010). Analysis of concrete A multi-dimensional investigation using X-ray diffraction and computed tomography Pöllmann, H., Maier,R., Riedl,U., Blaj,G. (2010). Multi-dimensional X-ray Investigation of Materials - Ranging from classical Bragg-Brentano type diffraction phase analysis to 3 dimensional CT microstructure analysis, Annual Denver X-ray conference, Abstracts, August 2010, Denver, Colorado Pöllmann,H., Meier,R., Blai,G., Bethke,K., Riedl,U. (2011). X-ray Investigation of Geo- Materials From Phase identification to 3 dimensional CT-measurements, AXXA conference, Abstract, Sydney, February 2011, in press Pöllmann,H., Meier,R., Riedl,U., Blai,G., Anderson,J. (2011).Multi-dimensional X-ray Investigation of Building Materials Powder Diffraction to Computed Tomography Analyses, Pittcon, Georgia, March, USA, in press Schmidt, M., Pöllmann, H., Egerdörfer, A., Göske, J. & Winter, S.(2010). Investigation on the pozzolanic reactivity of a special glass meal in a cementitious system Proc. 32 nd Int. Con. Cement Micr., 1-33, New Orleans, Louisiana, USA Wenda,R., Pöllmann,H., Meier, R., Blaj, G., Riedl, U., Schönbeck. T. (2010). A new method for X-ray Investigation of Materials Ranging from classical Bragg-Brentano type diffraction phase analysis to 3 dimensional CT microstructure analysis, DMG-meeting, Münster 2010, Abstract on CD