The Chemistry Laboratory

The Chemistry Lab

The classical, mostly wet chemical tests for the characterization of building materials are carried out in the chemistry laboratory of the WiB. In addition to the usual durability tests (chloride determination, capillary water absorption, porosity, water absorption, carbonation), non-standard tests and investigations can also be carried out and developed. Furthermore, the sample preparation for various tests takes place here. Samples are, for example, cast in epoxy resin and prepared, ground or dried for (scanning electron) microscopic investigations. Furthermore, various experimental setups, test rigs and methods are tested, validated and optimized here. Chloride penetration, diffusion experiments, chemical resistance or preparation of special solutions and material composition are only a small part of the wide range of tasks in the WiB chemistry laboratory.

Our laboratory equipment:

More detailed information on a selection of the experimental possibilities in our chemistry laboratory can be found here.

High temperature furnace

Ion chromatograph

Zeta potential analyser

Rapid Chloride Migration Test

Sample preparation

Further tests

High-temperature furnace

Model:

RWF 1100 and RHF 1600 Carbolite Gero

Brief Description:

The two chamber furnaces from Carbolite Gero are used for various experiments to determine thermal properties or to initiate processes through thermal energy. Both furnaces have control options for ramp, set point and process timer functions to run special heating programs. Short heat-up times (RWF 1100 can be heated to 1100°C within 10 minutes, RHF 1600 can be heated to 1600°C within 40 minutes) and large volumes (RWF 1100 23 liters; RHF 1600 15 liters) coupled with effective heating elements allow the installation of larger samples and guarantee uniform temperature distribution within the firing chamber.

RWF 1100:

  • Maximum temperature: 1100°C
  • Chamber volume: 23 Liter
  • Short heat-up time
  • Fast heating and cooling rates
  • Controllable for ramp, set point and process timer function

RHF 1600:

  • Maximum temperature: 1600°C
  • Chamber volume: 15 Liter
  • Short heat-up time
  • Fast heating and cooling rates
  • Controllable for ramp, set point and process timer function

Ion chromatograph

Model:

881 Compact IC pro from Metrohm (Cation)

Short description:

Ion chromatography can be used to identify and quantify chemical complexes, anions and cations in aqueous systems. At WiB the device is set up for cation investigations. For this purpose, a sample is taken from a prepared aqueous solution with the aid of an autosampler and passed over a column. The respective ion is retained in this column as a function of its mass. In this way, the duration of the run time (column start to detection) can be used to determine which substance is involved.

In our laboratory, different eluates, e.g. from experiments on chemical attacks, can be analyzed. This helps to understand the reaction and can provide information about dissolved ions.

Pore solutions can also be examined, which in turn can provide information about alkalinity and, in turn, about durability in special environments.

Zeta potential analyzer

Modell:

Zeta potential analyzer (DT-310, 3P-instruments.com)

Brief Description:

Every particle possesses a surface charge. In a suspension or emulsion, ions of the surrounding medium accumulate on the particle surface, leading to a charge balance. A Helmholtz double layer and a loosely bound diffuse layer are formed. When the particle moves, shearing occurs in the loosely bound layer so that the particle is no longer electrically neutral. It has a potential at this shear boundary, which is called the zeta potential.

The zeta potential is a relative measure of the surface potential (i.e., charge) of a particle.

The zeta potential is determined by measuring the velocity of the particle through an applied electric field.

The zeta potential plays an important role in the analysis of finely dispersed substances in a dispersing medium. Thus, among other things, optimized dosages, targeted phase separation processes (precipitation mechanisms) or bacteriostatic effects can be determined.

Rapid Chloride Migration (RCM)

Test:

Chloride penetration using Rapid Chloride Migration test according to NT Build 492

Brief description:

With the so-called Rapid Chloride Migration (RCM) test according to NT Build 492, the chloride penetration coefficient of a sample can be determined within a relatively short test period. This coefficient describes how fast the chloride ions can penetrate through the pore system of the concrete or cement paste.

The test is carried out with slices from drill cores. These are saturated with a calcium hydroxide solution (Ca(OH)2) under vacuum.

For the actual test, each specimen is placed in a separate “migration cell”. These cells do not allow any liquid contact between the surface of the specimen and the test liquid except for the frontal surfaces.

First, an initial voltage is applied. By measuring the current flowing through the test specimens, a correction to the voltage is made using tabulated values and the test duration is determined.

The specimens are split longitudinally and the cross-section is sprayed with a silver nitrate solution. Chloride penetration can be detected and measured by color indication.

By measuring several points, a diffusion coefficient can be determined for calculating the corrosion risk.

This method can be used to model long-term behavior. This can be used in the context of expert reports or to determine the chloride penetration resistance of building materials.

Sample preparation

Models:

CitoVac by Struers, LaboForce 100 by Struers, RM 200 Retsch

Brief Description:

Sample preparation is where the process of examination begins. Errors made here can lead to incorrect test results.

To minimize this error, we have protocols for sample preparation and handling.

For effective sample preparation, we have a vacuum impregnator (CitoVac from Struers) for embedding samples for further tests and examinations, as well as a matching polisher (LaboForce 100 from Struers). Especially for optical examinations (light microscopy, scanning electron microscopy) well treated surfaces are an absolute necessity.

However, we can also prepare experiments with special geometric requirements using our preparation.

Many tests are performed with powdered materials. In order to be able to examine also the hardened binders or to homogenize samples, we own a mortar grinder RM 200 from Retsch. With this we can generate reproducible results, wet and dry grinding (closed, dust-tight grinding chamber with viewing window) and have no problems grinding hard materials due to the high hardness of the mortar and pestle material (agate).

Further tests

Model:

785 DMP Titrino by Metrohm

Short description:

Determination of the concentration of chloride ions in concrete is particularly important for reinforced concrete. Above a critical chloride concentration, there is a risk of corrosion to the steel reinforcement and, as a consequence, of an increase in volume, cracks, spalling and, ultimately, component failure.

At the WiB chemistry laboratory, chloride contents can be determined with a titration according to Mohr using a 785 DMP Titrino.

Experiment:

Determination of capillary water absorption according to DIN 52617.

Brief description:

Capillary suction takes place in a pore size range between 0.1 µm and 1 mm diameter.

As a rule, water absorption in a building material (usually concrete or mortar) is not desirable. Water can both introduce pollutants or cause stress cracking or even freeze-thaw damage due to temperature changes.

Experiment:

Phenolphthalein test for the determination of carbonation

Brief description:

In cementitious systems, calcium hydroxide (Ca(OH)2) is formed during the hydration process. Its high solubility leads to an alkaline pore solution with a pH of about 12.5. In steel-reinforced concrete, an alkaline milieu protects the reinforcement from corrosion damage by a so called passivation layer. Over time, limestone (CaCO3) is formed from the dissolved Ca(OH)2 in combination with water and carbon dioxide (CO2) from the air. This leads to a reduction of the pH value in the pore solution. If the pH value is below 9, the reinforcement is no longer protected.

Decisive influences on the depth of carbonation are moisture, porosity and concrete age.

Phenolphthalein is sprayed onto a fresh fracture surface. If the area turns purple (pH > 8.2), there is no carbonation.

Experiment:

Water absorption testing of aggregates (RC aggregate, lightweight aggregate, conventional aggregate), mortar and concrete test specimens.

Brief Description:

The water absorption of aggregate plays a major role in the production of concrete and mortar. In order to determine the water demand, to identify particularly highly absorbent aggregates or to carry out a full-scale investigation of an RC aggregate, various standard tests for water absorption can be carried out at the WiB chemistry laboratory.

Likewise, water absorption plays a major role in manufactured building materials. In addition to possible damage processes and accelerated aging, water absorption affects the thermal insulation properties. Also in this respect we have various possibilities to test according to standards.

We are also able to carry out modified tests and develop test rigs that simulate special cases or are adapted to the respective test objects.

Experiment:

Chemical attack on building materials

Brief Description:

The durability of hardened concretes and mortars depends largely on their resistance to external chemical agents. Aggressive substances can lead to a dissolving or driving attack. Solvent attack is triggered by acids, exchangeable salts, soft water and organic fats and oils. In this case, the calcium-containing components in particular are converted into water-soluble reaction products and thus lead to dissolution of the hardened cement paste. Driving attacks can occur, among others, through reactions with sulfates, alkali-silica reaction, free lime and free magnesium.

At the chemistry laboratory of the WiB it is possible to carry out standard tests (e.g. DIN EN 196-2, DIN 4030-2, DIN EN ISO 7980) as well as to create own, adapted tests. For this purpose, test rigs and test programs can be designed specifically for the desired requirements.

We also carry out tests on acid resistance with alternative binders and, with our laboratory equipment in the micro laboratory, we can specifically clarify further process questions and coordinate corresponding tests and investigations.