**Abstract**

The chapter describes the use of the Scanning Electron Microscope (SEM) in the Environmental Scanning Electron Microscope (ESEM) mode on building materials, whose capillarity is to be examined. The abbreviation SEM means Scanning Electron Microscope. The abbreviation ESEM means Environmental Scanning Electron Microscope. On the basis of condensation in the ESEM, the hydrophobicity of capillary building materials is demonstrated with the help of the contact angle method. In the chapter, the investigation in the ESEM is shown using capillary building materials that have been given subsequent injections. Due to the problem of rising masonry moisture on capillary masonry in the absence of a cross-section sealing, injection agents, which have a hydrophobic and pore-filling effect, subsequently are used in the borehole method. Such a subsequent masonry sealing must be checked for effectiveness. In addition to already existing macroscopic methods, a new microscopic detection method is presented. This detection method uses ESEM technology in the SEM to generate and detect in situ dew processes at samples taken from the injection level of the examined masonry. The output of the results is done by image or film. By means of the condensation with the medium of water, the contact angle measurement method on the dew drops can be used to make accurate statements about the water-repellent capabilities of the examined sample and thus about the sealing success. There are detectable correlations to the macroscopic detection methods. The contact angles measured in the ESEM during condensation are connected to the conventional macroscopic measurement methods. The method presented in this chapter offers the advantage to have very small samples and to be investigated in a short time with very precise results. The new detection method is suitable for practical use.

**Keywords:** SEM in the ESEM mode, capillary building materials, contact angle method, masonry moisture, capillary masonry, cross-section sealing, masonry injection, subsequent masonry sealing

## **1. Introduction**

In the refurbishment of old buildings, especially in the area of monuments [1, 2], capillary building materials, for example, consisting of brick masonry are found very often. Since the building materials of old buildings are often capillary-active materials [3–5], there is distinctive water absorption and release as well as water transport behaviour on this material. This process is called capillarity. Investigating the capillarity of old building materials can be of considerable relevance. The water absorption and release behaviour is, for example, crucially important for moisture transport and the moisture penetration of components.

The possibilities that result from examining the capillarity of a material in the Environmental Scanning Electron Microscope (ESEM) are explained in this abstract, using a subsequent sealing with injection agents on capillary masonry.

In many cases when renovating old buildings [6], sealing has to be carried out later because no sealing was installed when the object was built or the sealing is no longer adequately functional now. The proof of capillarity and the description of the moisture behaviour of the building materials play a major role here.

A good example is the construction of a subsequent cross-section sealing with injection agents. Although already known from antiquity, the regular use of functioning building waterproofing at capillary building materials began around 1890. Nevertheless, there were no uniform rules for the execution of structural waterproofing at that time. Only in the 1930s, structural waterproofing was normatively regulated. Although the cross-section sealing in massive walls had already a higher priority than other seals on buildings at the end of the nineteenth century, crosssection seals were regularly installed in masonry walls since 1930 onwards. In the old building area, there are very often buildings to find that have a cellar, even if the space requirements made this cellar unnecessary. This is related to the previous construction use, in which the basement was due to lack of sealing technology while permanently moist, but served as a 'buffer' to the upper floors, which thereby could be kept sufficiently dry. In this way, the buildings were built without a cross-sectional sealing. For these reasons, solid brick walls in cellars are often encountered in old building renovation and monument preservation, in which there is rising masonry moisture due to non-existent cross-sectional sealing. However, due to usage or conversion requirements of a value retention, there is a great need to permanently seal capillary masonry walls against increasing moisture in the wall cross section in the refurbishment in the renovation of historical monuments. A main group in the retrofitting of masonry cross-section seals is the masonry injection methods, which do not require static interventions [7, 8].

There are currently about 150 different injection agents [7] available for the subsequent cross-sectional sealing of capillary masonry. All injection agents have in common that they are applied by the production of borehole chains in the masonry. The injection agents react chemically. The sealant layer in the masonry is physically formed. There are pressurized and non-pressurized processes to apply the injection medium into the masonry.

However, all injection agents work in the same way: they change the capillarity of the building material and thus also the water transport properties of the material [9]. Therefore, the capillarity of a capillary-active substance that is changed by the injection agent can be used as a reference for the investigations in the Scanning Electron Microscope (SEM) in the ESEM mode. The investigations with the SEM in the ESEM mode can provide information about the efficiency of such a subsequent sealing by

*Investigation on Building Materials with the SEM in the ESEM Mode to Demonstrate… DOI: http://dx.doi.org/10.5772/intechopen.104292*

means of injection. In order to be able to monitor the injection procedure and to be able to demonstrate the effectiveness of the injection medium, it is therefore necessary to monitor the quality and quantity of the actually changed capillarity on the object [10].

The detection method presented here is based on the contact angle method in the Environmental Scanning Electron Microscope, ESEM. The ESEM is a modified version of a Scanning Electron Microscope, SEM [11, 12]. In contrast to the SEM, the ESEM can be used in low-vacuum mode. This circumstance allows the supply of a medium (here water steam) during the investigation. A cooling table in the chamber allows the sample to be refrigerated while the air in the chamber is at 100% relative humidity. Changing the chamber pressure causes condensation in the ESEM chamber [13]. During the investigation in the ESEM, condensation water droplets are formed on the sample. The contact angles can be determined on the formed drops of water [14]. When measuring the contact angle, one makes use of the interfacial tension of the water. Both static contact angles and dynamic contact angles can be measured in the ESEM. The contact angles provide information about the changed capillarity of the sample material on which the drops were formed. The contact angle can be measured directly in the ESEM or afterwards. The data obtained from this show a geometrically differentiated picture of the changed capillarity of the examined material. The method can provide information about the quality of the injection as well as about the geometric penetration with the injection agent.

### **2. The SEM in the ESEM mode**

The Environmental Scanning Electron Microscope (ESEM) is a special variant of the Scanning Electron Microscope (SEM). The main difference to a conventional Scanning Electron Microscope lies in the lower vacuum in the measuring chamber [15]. Moreover, a special detector is installed for the operation of the ESEM. Due to the lower vacuum (low vac mode), a medium can be supplied to the chamber in ESEM mode. For the examination of building materials, the supplied medium is usually water/water vapour. The gas pressure in the chamber of the ESEM is usually 130–1.300 pascals. In the same way as when using the SEM, the sample is scanned by a focused electron beam in the ESEM. The signal resulting from an interaction with the sample is picked up by the detector and used to generate the image. The ESEM uses the generation of low-energy secondary electrons (0–50 eV), which are emitted from the sample surface as slow electrons. For signal amplification, the ESEM uses the gas in the sample chamber, which generates an amplification cascade through ionization. This system also neutralizes charges on the samples. The most important difference between the ESEM and operation in high vacuum (= SEM) is that in low vacuum the water is not 'expelled' from the sample and condensation processes (droplet formation) and can thus be made visible. For this purpose, the detector of the ESEM is not sensitive to light or temperature. In order to be able to visualize the water wetting and drying processes in the ESEM, different aggregate states of the medium, here water, which are pressure- and temperature-dependent, are used.

For this purpose, a cooling table connected to a recirculating cooler is arranged in the chamber of the ESEM. The sample is glued to this cooling table with carbon or conductive silver to ensure optimal temperature conductivity. As part of the investigations in the ESEM, the temperature conditions of the cooling table are fixed while the chamber pressure is changed. This causes a change in the state of aggregation of

the medium in the chamber (from gaseous to liquid). If the dew point is reached on the sample, the water condenses out on the sample surface. This process is recorded with the help of pictures. In the ESEM, the forming contact angle of a drop can be measured in situ using the contact angle measurement method. Progressive, receding or static contact angles can be measured on ripe droplets. If a drying process is to be shown, the condensation water that has formed can be evaporated by reducing the chamber pressure, and the drying process is made visible. Technically, the ESEM is very well suited to show dynamic condensation in situ [16–20] (**Figure 1**).

The figure above shows the limit curves of the three phases: gaseous (water vapour), liquid (water) and solid (water-ice). These phase areas meet at the triple point. At this point, the three phases are in thermodynamic equilibrium. The formation of condensation is related to the dependence of the state of aggregation of the phases on temperature and pressure.

**Figure 1.** *Phase diagram of water, P. Körber.*

**Figure 2.** *Cooling table with circulation cooler, P. Körber.*

*Investigation on Building Materials with the SEM in the ESEM Mode to Demonstrate… DOI: http://dx.doi.org/10.5772/intechopen.104292*

**Figure 3.** *ESEM chamber: Cooling table with circulation cooler, P. Körber.*

Due to the change in the pressure conditions in the ESEM, the dew point inevitably occurs during the investigation in the ESEM, and the water that is gaseous in the medium becomes liquid in the form of droplets on the sample surface (**Figures 2** and **3**).
