Zusammenfassung
Prüfinstitute spielen eine zentrale Rolle in der Qualitätssicherung und Werterhaltung von Bauwerken. Aldo Rancati, Leiter der akkreditierten Prüfstelle Tecnotest, gibt im Gespräch mit Johannes Lohner Einblicke in Kontrollprüfungen während der Bauphase und detaillierte Zustandsuntersuchungen bestehender Bauwerke. Dabei wird deutlich: Nur durch präzise Prüfmethoden lassen sich Fehlentscheidungen vermeiden und nachhaltige Instandsetzungskonzepte entwickeln.
Testing Institutes - for Structural Preservation
Testing institutes are essential for quality assurance and the preservation of concrete structures. In this discussion, Aldo Rancati, director of the accredited testing institute Technotest, shares insights into his company’s work. Technotest conducts both fresh concrete compliance tests and detailed assessments of existing structures for damage due to corrosion, frost, or chemical reactions. Infrastructure projects such as bridges, tunnels, and parking structures are particularly exposed to harsh conditions from moisture, chloride ingress, and heavy traffic loads. Aldo emphasizes that investing in precise diagnostics reduces long-term costs by preventing unnecessary repairs and enabling targeted interventions.
Quality Control Testing: Ensuring Compliance in Construction
Quality control testing is crucial to verify that construction materials are properly installed according to specifications. A common example is the replacement of hard concrete flooring in parking garages: Through tests on surface evenness, adhesion, and material properties, testing institutes ensure that the new surface meets required standards. Mistakes frequently arise when the substrate is not properly prepared—whether due to insufficient pre-wetting or improper compaction. This can lead to adhesion failure, cracks, or a reduced service life. Independent testing organizations like Tecnotest identify such defects early, providing clear guidance to property owners for necessary corrections.
Potential Field Measurement and Sustainable Maintenance: Accurately Identifying Corrosion
Potential field measurement is a key method for assessing the likelihood of reinforcement corrosion in concrete structures, but a reliable diagnosis requires additional tests. Using a copper-coppersulfate electrode, the electrical potential of the reinforcement is measured, helping to identify at-risk areas without removing the concrete cover. In practice, clear threshold values have been established: Potentials below -400 mV almost always indicate active corrosion, while values above -200 mV are generally uncritical. But there are examples where values of -100mV lead to strong corrosion. The results require further investigation, as moisture content and chloride exposure significantly influence corrosion risk.
A statistical evaluation of measurement results helps map potential distributions across a structure, guiding targeted sampling and supplementary tests, such as chloride profiling, carbonation depth analysis, and concrete strength assessments. Proper interpretation is crucial: A low potential alone does not necessarily indicate active corrosion, as high chloride concentrations in the concrete can also shift potential values without immediate reinforcement deterioration. This is particularly relevant in structures subjected to extreme exposure, such as bridge abutments and tunnel interiors, where chloride-laden mist from passing trucks accelerates damage. Combining potential field measurements with selective sampling and statistical analysis is therefore essential for developing effective and cost-efficient maintenance strategies.
AAR: The Overlooked Threat in Concrete
One of the growing challenges in structural preservation is alkali-aggregate reaction (AAR), which can cause severe damage. Initially thought to be a rare phenomenon, AAR has become increasingly prevalent in aging structures, particularly when exposed to persistent moisture or high chloride levels.
Aldo Rancati shares experiences of concrete that had to be demolished due to AAR. The reaction occurs when alkali-reactive aggregates in concrete interact with moisture, causing expansion and cracking. Bridges built in the 1970s, often using high-alkali cement, are particularly vulnerable. Pull-out tests on core samples and microscopic measurments can reveal AAR: Characteristic aggregate fractures confirm its presence. The crack patterns on the concrete surface may resemble shrinkage cracks, but detailed analysis is necessary to distinguish the cause.
In bridges affected by AAR, the damage can penetrate deep into the structure. If pull tests show intact material beyond a certain depth, a selective removal approach may be a cost-effective solution. However, if moisture ingress cannot be controlled, remediation becomes difficult. Hydrophobic treatments and protective coatings can slow deterioration, but in many cases, AAR remains one of the most complex challenges in structural maintenance.
BIM and Digital Diagnostics – Opportunities and Limitations
While Building Information Modeling (BIM) is increasingly used in new construction, its role in condition assessments remains limited. Tecnotest participated in a BIM pilot project and found that while potential field measurements and other test results can be visually embedded, proper interpretation of data remains critical. A digital model with color-coded overlays does not replace expertise—especially when analyzing complex diagnostics like potential measurements or AAR evaluations.
Furthermore, BIM integration requires significant additional effort, raising concerns about its economic feasibility for maintenance applications. However, BIM does offer advantages in documentation: By linking past test data to structural models, long-term deterioration trends can be tracked, improving future maintenance planning.
Conclusion: Testing Methods as the Key to Structural Preservation
Testing institutes play a crucial role in quality control, maintenance planning, and damage diagnostics. Methods such as potential field measurement, chloride profiling, and AAR testing help identify structural risks and enable targeted rehabilitation strategies. Without these detailed diagnostics, there is a risk of either unnecessary interventions or unexpected structural failures.
Aldo Rancati urges engineers and infrastructure owners to engage more deeply with lessons from past structural assessments. Many recurring failures could be prevented if previous insights were consistently applied. He emphasizes that for young engineers, understanding corrosion processes, chloride infiltration, and AAR is essential—as sustainable infrastructure maintenance begins with precise diagnostics.