Progress in building materials analysis (Part 1)

1 FE-SEM: Nova NanoSEM 230 installed at the SEM laboratory

2 ESEM-WET mode: a) OPC after 17 h hydration time – loss of surface information due to high V₀ = 30 kV; b) only by reducing V₀ to smaller than 1.5 kV it is possible to distinguish between C-S-H phases (they appear dark) and pore solution (shows a light color) image shows no confusion of structural overlap

3 Bundles of C-S-H phases in high resolution by means of ESEM-WET mode: a) before radiation damage (diameter of the individual fibers between 20 – 50 nm); b) after radiation damage. “Melting” of the nanofibres through exposure to an electron beam of 150 pA (charge density of
0.8 C/cm²)

4 Fracture surface of uncoated UHPC samples: a) ESEM-WET at V₀ = 30 kV low surface contrast; b) NanoSEM used as LV-SEM at V₀ = 2 kV optimization of surface contrast – structure details are now clearly visible

5 Hydrated C₃S with calcite rhombohedrons – the surface is sputtered with a 2 nm gold layer (V₀= 5 kV, right magnification 1000 000 x)

6 Silicon Drift Detector (SDD)-EDX-Detector Apollo 40 (40 mm²– SDD Chip) with a high collection efficiency installed at NanoSEM

7 EBSD camera with an integrated Forward Scatter Detector (FSD) installed at NanoSEM

8 EBSD and FSD detector within the sample chamber of the NanoSEM (on the right, tilted sample left)

9 EBSD-OIM (orientation imaging microscopy) measurements highlighting the grain size distribution and the grain boundaries

$10 EBSD pattern of the calcium carbonate modification calcite (crystal system triclinic) overlapped, solution; simulated diffraction pattern showing the indexed Kikuchi bands$

10 EBSD pattern of the calcium carbonate modification calcite (crystal system triclinic) overlapped, solution; simulated diffraction pattern showing the indexed Kikuchi bands

11 High Pressure Freezing Machine) – HPM 100

12 Loading Box with VCT 100 Shuttle, by means of HPM 100 frozen sample is loaded onto the sample holder

$13 MED 020 with docking station configured as freeze fracturing, etching and coating system combined with a light microscope$

13 MED 020 with docking station configured as freeze fracturing, etching and coating system combined with a light microscope

14 Docking station and VCT 100 Shuttle for the cryo-sample transfer to the cryo stage of the NanoSEM. The Shuttle can be removed from the microscope after completed transfer

Progress in building materials analysis

Summary: In this study two types of microscopes, a FEI XL-30 ESEM-FEG and a FEI Nova NanoSEM 230, were used which are capable of different high-resolution imaging techniques in order to characterize water containing and charging samples. In this field the environmental-SEM (ESEM) – technology in connection with high resolution electron microscopy is especially important, since water vapor can be used as gas in the sample chamber. Thus, water containing structures and phases can be investigated without sophisticated preparation i. e. in their native states. Part 1 of the article summarizes the experimental setup and the optimization measures, such as low voltage SEM. The newly developed NanoSEM combined with Helix detector, cryo-SEM, EDS and EBSD capabilities offers various advantages.

1 Introduction

The properties of cementitious binders such as workability, setting behavior, strength and durability depend directly on the hydration process. In order to understand the relations between material properties and material formation processes one has to understand the multiscale heterogeneous structure which is created. Water does not only play an important role in the hydration process but also with respect to the durability of cement-based and other building materials. Furthermore, water or pore solution are essential components within the microstructure of cementitious...