Reinforced Autoclaved Aerated Concrete: Structural Assessment and Retrofitting
Abstract
:1. Introduction
2. Structural Assessment and Retrofitting
2.1. Traditional Assessment
Residual Risk
2.2. Digitalised Assessment
3. RAAC Decision-Making Framework
- Cracking and spalling (CS);
- Inadequate reinforcement (IR);
- Moisture ingress (MI);
- Excessive deflection (ED).
3.1. Methodology
3.2. Analysis
3.3. Key Findings
- Defect IR in Quadrant IV:
- High Influence: IR has the highest column sum (C) value, indicating that it is significantly influenced by other defects;
- Impact Factor or Intertwined Receiver: IR’s high prominence but lower relation underscores its role as a major receiver of influences with significant weight in defect networks;
- Interdependencies: IR’s interdependence with MI and ED highlights the necessity of comprehensive reinforcement checks during construction and maintenance.
- Defect MI in Quadrant III:
- Central Role: Despite its lower prominence, MI’s higher relation indicates significant interactions with other defects;
- Independent Factor or Autonomous Receiver: MI’s influence on other defects, such as CS and inadequate reinforcement, IR, underscores its critical role in the defect propagation network.
- Defect CS in Quadrant III:
- Notable Influences: CS shows high row sum (R) values, indicating that it is a primary contributor to the deterioration of RAAC panels;
- Independent Factor or Autonomous Receiver: CS’s high relation hints at its dual role as a driver and receiver in the defect network, demonstrating the importance of early detection and repair to prevent further structural damage.
- Defect ED in Quadrant I:
- Secondary Nature: ED is prominently influenced by other defects, indicating its role as a secondary factor in the defect chain;
- Core Factor or Intertwined Giver: ED’s high prominence suggests that addressing deflection issues is crucial for managing overall RAAC panel conditions. For instance, ED issues directly instigate CS, triggering the subsequent defect network and further deteriorating the panel’s condition.
4. Conclusions and Future Directions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Degradation | Cause | Control |
---|---|---|
Shadow effect | AAC foaming process | Smaller-diameter rebar |
Rebar corrosion | High moisture content Rebar coating debonding | Protective waterproof membrane |
Excessive deflection | Poor reinforcement anchorage Thermal cycling Moisture movement | Sufficient bearing length ensured |
Property | Range | Reference |
---|---|---|
Compressive strength (MPa) | 2–5 | [4] |
Flexural strength (MPa) | 0.55–1.54 | [3] |
Elastic modulus (GPa) | 0.50–3.30 | [2] |
Risk Condition | Observation |
---|---|
Lack of transverse reinforcement | Peculiar panel geometry indicating cutting or modification |
Hangers supporting panels | |
Bearing length less than 75 mm | |
Deflection | Adjacent panels gap greater than 20 mm |
High span to depth deflections | |
Panel cracking/spalling | Major cracking or spalling |
Minor cracking or spalling within 500 mm of supports |
Case Study | Observation |
---|---|
1970s steel frame portal shed with RAAC roof panels | Inadequate tension reinforcement with diameter less than 6 mm |
Visible perimeter longitudinal bars | |
High span-to-depth ratio (S/D = 26) | |
1976 residential building with RAAC panels | Failure of longitudinal joints between slabs |
Large variation in cracking and deflection despite adequate performance tests on AAC properties | |
Irreversible moisture movement resulting in reduced elastic modulus and shorter slab | |
1981 complex with RAAC roof panels | Inadequate transverse reinforcement |
High moisture content (greater than 7%) | |
Corrosion of unprotected reinforcement, leading to rebar diameter reduction | |
High span-to-depth ratio (S/D = 30) leading to excessive deflection | |
Roof membrane stretching at supports and allowing water ponding | |
Damp roof soffits indicative of water damage | |
1991 and 1995 BRE experiments | Deflection and transverse cracking at soffits taken as evidence of long-term slippage between AAC and rebar as well as localised corrosion |
Overall Condition Score | Remediation |
---|---|
0–20 | Minor issues: routine maintenance |
21–35 | Moderate issues: targeted repairs |
36–50 | Significant issues: extensive repairs |
>50 | Severe issues: panel replacement |
Defect | Severity 1 | Severity 2 | Severity 3 | Severity 4 |
---|---|---|---|---|
CS | Minor cracks not close to supports | Minor cracks within 500 mm of supports | Major cracks without signs of spalling | Major cracks with spalling within 500 mm of supports, possibly accompanied with exposed reinforcement |
IR | Bearing >75 mm with transverse anchorage reinforcement | Bearing <75 mm with transverse anchorage reinforcement | Cut or modified panels supported on proprietary hangers | Bearing lacking transverse reinforcement |
ED | Span/250 or less | Span/200 to span/250 | Span/100 to span/200 | Span/100 or greater |
Defect | CS | MI | IR | ED |
---|---|---|---|---|
CS | 0 | 3 | 2 | 4 |
MI | 3 | 0 | 3 | 3 |
IR | 2 | 3 | 0 | 3 |
ED | 4 | 3 | 3 | 0 |
Defect | CS | MI | IR | ED |
---|---|---|---|---|
CS | 0.00 | 0.33 | 0.22 | 0.44 |
MI | 0.33 | 0 | 0.33 | 0.33 |
IR | 0.25 | 0.38 | 0 | 0.38 |
ED | 0.40 | 0.30 | 0.30 | 0 |
Defect | CS | MI | IR | ED |
---|---|---|---|---|
CS | 0.00 | 1.07 | 0.69 | 1.57 |
MI | 1.07 | 0.00 | 1.07 | 1.07 |
IR | 0.73 | 1.16 | 0.00 | 1.16 |
ED | 1.61 | 1.21 | 1.21 | 0.00 |
Defect | ||||
---|---|---|---|---|
CS | 3.33 | 3.41 | 6.74 | −0.08 |
MI | 3.21 | 3.44 | 6.65 | −0.23 |
IR | 3.05 | 3.97 | 7.02 | −0.92 |
ED | 4.03 | 2.80 | 6.83 | 1.23 |
Case Study | Defect Severity | Interdependency Scores (Si) | OCS | Remediation Decision |
---|---|---|---|---|
1981 complex with RAAC roof panels | CS: 3 MI: 4 IR: 4 ED: 4 | 51.15 | Panel Replacement |
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Di Sarno, L.; Albuhairi, D. Reinforced Autoclaved Aerated Concrete: Structural Assessment and Retrofitting. Buildings 2024, 14, 2570. https://doi.org/10.3390/buildings14082570
Di Sarno L, Albuhairi D. Reinforced Autoclaved Aerated Concrete: Structural Assessment and Retrofitting. Buildings. 2024; 14(8):2570. https://doi.org/10.3390/buildings14082570
Chicago/Turabian StyleDi Sarno, Luigi, and Danah Albuhairi. 2024. "Reinforced Autoclaved Aerated Concrete: Structural Assessment and Retrofitting" Buildings 14, no. 8: 2570. https://doi.org/10.3390/buildings14082570