Diagnostic Reliability in the Assessment of Degradation in Precast Concrete Elements
Abstract
:1. Introduction
Research Aim
2. Concrete Bridge Failures and Collapses Due to Corrosion
3. Guidelines for Assessing the Concrete Degradation in Prestressed Elements
4. Causes of RC Structures Deterioration
4.1. Some Divergencies between Past and Present on RC Durability
4.2. Considerations on the Reliability of Nondestructive Techniques for Corrosion Measurement in Concrete-Embedded Steel Bars
5. Materials and Methods
5.1. Tested Elements
5.2. Site Environmental Conditions
5.3. Testing Methods
- visual inspection of the elements, with an appraisal of concrete cover depths;
- assessment of the deterioration of concrete and steel;
- extraction of concrete core samples, according to [43];
- visual inspection of the drilled surfaces;
- visual inspection of the core samples and possible oxidation evidence;
6. Tests and Results
6.1. Visual Inspections
6.2. Core Sampling
6.3. Mechanical Tests
6.4. Carbonation Tests
- −
- the storage area of the beams is located near the bank of the Volturno river and is a considerably humid site; therefore, since the higher the humidity, the slower the transport of gaseous CO2, due to the saturation of the pores by water [64], humidity may have slowed the penetration of CO2 through the concrete cover [65].
- −
- although beam B1 is younger, it could have been cast with a concrete composition that may have favored carbonation.
6.5. Corrosion Potential Mapping
7. Discussion
7.1. Reliability Hierarchy of Testing and Inspection Activities
7.2. Service Life: Past and Present
8. Conclusions
- −
- A close visual inspection of the structural elements showed what could be expected for prefabricated structures of twenty years of age. Only the steel surfaces directly exposed to the atmosphere showed generalized superficial corrosion. The same corrosion was detected in limited superficial regions with an insufficient thickness of concrete, or where cracks were present. As reported, a conservative upper bound of the percentage of surface extension of these degraded regions over the total area of the visible exposed surfaces can be reasonably set to 2%, while an upper bound of the thickness of the delaminated cover in these regions (see Figure 4b) can be set to 1.5 cm.
- −
- The concrete surfaces of the cores showed a well-sorted grain size distribution and adequate concrete compaction, demonstrating evidence of the good quality of the concrete manufacturing, coherent with the higher quality in prefabricated concretes.
- −
- No visually detectable corrosion was found in any of the sampled bar segments.
- −
- Altogether, the neutralization assays showed that the pH 9.2 threshold is far below the concrete cover thickness, so that the condition of pH lowering, deemed to be a necessary condition for bar corrosion, is not achieved. Such evidence is coherent with the big picture that came from the direct visual inspection of exposed concrete and bar surfaces.
- −
- The high compressive strength of the concrete can be considered indicative of an adequate design of the concrete mix and of the adoption of a sufficiently low water/cement ratio, capable of granting low porosity and, consequently, water tightness. For beam B2, the concrete compressive strengths were 21% lower than the design value that was retrievable from the available technical documentation. Even in this beam of presumably lower concrete quality, however, no evidence of oxidation was found across the sampled steel bars.
- −
- Half-cell measurements led to estimating the absence of interior zones where the corrosion process may be initiated. The measured potentials were affected by variations in the concrete cover thickness. The existence of some arbitrariness was recognized in interpreting these measures.
- −
- Neutralization assays of drilling powders have proven to be a much less invasive alternative when compared to neutralization assays performed on sampled cores. The importance of calibrating suitable corrective correlation factors, to avoid the overestimation of neutralization depths, was shown. Such a calibration was made possible by the availability of sampled cores.
- −
- Core sampling with a visual inspection of embedded bars can be assumed to be a diriment golden standard for the diagnosis of degradation in concrete and steel reinforcement. None of the non-destructive methods is reliable enough for corrosion estimation.
- −
- Altogether, the performed experimental research confirms a considerable amount of pre-1980 knowledge: adequate design and manufacturing of concrete cover and concrete mixture ordinarily lead to concrete infrastructures able to fulfill a design engineering service life conventionally established in 75 years.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Element Code | Element Description | Year of Casting | Design Rc (MPa) |
---|---|---|---|
C | Precast RC Column | 2000 | 45 |
B1 | Prestressed RC Omega beam | 2006 | 45 |
B2 | Prestressed RC T-beam | 2004 | 45 |
Specimen | ϕ mm | H mm | ρ kg/m3 | Breaking Load kN |
---|---|---|---|---|
C1 | 104 | 104 | 2275 | 326.49 |
C2 | 104 | 104 | 2259 | 386.50 |
B1_1 | 70 | 70 | 2487 | 150.87 |
B1_2 | 70 | 70 | 2613 | 179.01 |
B2_1 | 104 | 104 | 2279 | 302.10 |
B2_2 | 104 | 104 | 2257 | 253.75 |
Specimen | fcore | BS [53] | NTC [15] | ACI [54] | UNI EN [55] | CS [56] |
---|---|---|---|---|---|---|
C1 | 38.43 | 42.60 | 40.74 | 43.38 | 45.22 | 37.05 |
C2 | 45.50 | 50.43 | 48.23 | 51.53 | 53.53 | 43.85 |
B1_1 | 39.20 | 43.45 | 41.56 | 45.79 | 46.12 | 37.79 |
B1_2 | 46.52 | 51.56 | 49.31 | 54.52 | 54.72 | 44.83 |
B2_1 | 35.56 | 39.42 | 37.70 | 40.08 | 41.84 | 34.28 |
B2_2 | 29.87 | 33.11 | 31.66 | 33.58 | 35.14 | 28.79 |
Structural Element | Mean Cubic Strength from Cores MPa | Design Cubic Strength MPa | δ % |
---|---|---|---|
C | 45.65 | 45 | +1.44 |
B1 | 46.96 | 45 | +4.36 |
B2 | 35.56 | 45 | −20.98 |
Test Tube | |||||
---|---|---|---|---|---|
1 | 40 | 30 | 17 | 283% | 378% |
2 | 35 | 25 | 15 | 250% | 350% |
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Bossio, A.; Faella, G.; Frunzio, G.; Guadagnuolo, M.; Serpieri, R. Diagnostic Reliability in the Assessment of Degradation in Precast Concrete Elements. Infrastructures 2021, 6, 164. https://doi.org/10.3390/infrastructures6110164
Bossio A, Faella G, Frunzio G, Guadagnuolo M, Serpieri R. Diagnostic Reliability in the Assessment of Degradation in Precast Concrete Elements. Infrastructures. 2021; 6(11):164. https://doi.org/10.3390/infrastructures6110164
Chicago/Turabian StyleBossio, Antonio, Giuseppe Faella, Giorgio Frunzio, Mariateresa Guadagnuolo, and Roberto Serpieri. 2021. "Diagnostic Reliability in the Assessment of Degradation in Precast Concrete Elements" Infrastructures 6, no. 11: 164. https://doi.org/10.3390/infrastructures6110164