Case 5 – old
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Good Practices
Concrete
Design
An understanding of the environment /atmospheric conditions should be taken into consideration during the design stage.
| Environment | Exposure conditions |
| Mild | Concrete surfaces protected against weather or aggressive conditions |
| Moderate | Exposed concrete surfaces but sheltered from severe rain or severe traffic Concrete surfaces continuously under non-aggressive water Concrete in contact with non-aggressive soil Concrete subject to condensation |
| Severe | Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing or severe condensation Concrete surfaces occasionally exposed to light traffic |
| Very severe | Concrete surfaces occasionally exposed to seawater spray (directly or indirectly) Concrete surfaces exposed to corrosive fumes and heavy traffic |
| Most severe | Concrete surfaces frequently exposed to seawater spray (directly or indirectly) and heavy traffic |
| Abrasive | Concrete surfaces exposed to abrasive action |
Table 1: Classification of exposure conditions [6]
Material
Cement should comply with SS EN 197 series while coarse and fine aggregates used should comply with SS EN 12620. All aggregates shall be stored in clean places [7]. Table 2 shows the various concrete grade to be achieved.
| Concrete Grade | 30 | 35 | 40 | 45 | 50 |
| Minimum cement content (kg per m3) | 275 | 300 | 325 | 350 | 400 |
| Maximum cement content (kg per m3) | 550 | 550 | 550 | 550 | 550 |
| Maximum % of Fine Aggregate to Total Aggregate | 50 | 50 | 50 | 50 | 50 |
| Maximum water to cement ratio | 0.55 | 0.50 | 0.45 | 0.40 | 0.40 |
Table 2: Designed mix of concrete [7]
Construction
Ready mix concrete is preferred over site mixed concrete to achieve consistency.
Check for quality of concrete before placing [8]. e.g. water cement ratio, slump test, etc.
Place the concrete carefully. If concrete is placed directly from a truck or concrete pump, place concrete vertically into position. Do not allow the concrete to fall more than 1 to 1.5 metres.
Ensure thorough compaction of the concrete during placement.
Quality control
Avoid following during concreting to minimize cracks:
- Avoid excessive manipulation of the surface, which can depress the coarse aggregate, increase the cement paste at the surface, or increase the water-cement ratio at the surface.
- DO NOT finish the concrete before it has completed bleeding.
- Do not dust any cement onto the surface to absorb bleed water.
- Do not sprinkle water on the surface while finishing.
Reinforcement
Design
Sufficient concrete cover should be provided to prevent corrosion of reinforcement.
| Condition of exposure | Nominal cover | ||||
| Mild | 25 | 20 | 20 | 20 | 20 |
| Moderate | – | 35 | 30 | 25 | 20 |
| Severe | – | – | 40 | 30 | 25 |
| Very severe | – | – | 50 | 40 | 30 |
| Most severe | – | – | – | – | 50 |
| Abrasive | – | – | – | see note 3 | see note 3 |
| Maximum free water/cement ratio | 0.65 | 0.60 | 0.55 | 0.5 | 0.45 |
| Minimum cement content (kg/m3) | 275 | 300 | 325 | 350 | 400 |
| Lowest grade of concrete | C30 | C35 | C40 | C45 | C50 |
| 1) This table relates to normal-weight aggregate of 20mm nominal size. Adjustments to minimum cement contents for aggregates other than 20 mm nominal maximum size are detailed in BS EN 206+A2. | |||||
Table 3: Limiting values of the nominal cover of normal weight aggregate concrete [6]
Material
All high yield reinforcement bars should comply with SS 2 and welded steel fabric should comply with SS 32 [7]
Reinforcement can be protected further by using following methods:
- removal of rust and mill scale before embedment
- use of non-metallic coatings such as epoxy resins and solvent containing acrylic resins [9]
- use of metallic coatings such as zinc and nickel
- Cathodic protection
- use of corrosion inhibitors
- use of corrosion resistance reinforcement (eg. stainless steel)
- use of low permeability concrete, with improved resistance to chloride ion ingress
Standards
British Standards
Concrete
BS 4550 Part 6 Methods of testing cement. Standard sand for mortar cubes
BS EN 934 Part 6 Admixtures for concrete, mortar and grout. Sampling, conformity control and evaluation of conformity
BS EN 12504 Part 2 Testing concrete in structures. Non-destructive testing. Determination of rebound number
BS EN 13139 Aggregates for mortar
American Society for Testing and Materials
Concrete
ASTM C33 / C33M Standard Specification for Concrete Aggregates
ASTM C94 / C94M Standard Specification for Ready-Mixed Concrete
ASTM C136 / C136M Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates
ASTM C150 / C150M Standard Specification for Portland Cement
ASTM C387 / C387M Standard Specification for Packaged, Dry, Combined Materials for Concrete and High Strength Mortar
ASTM C597 Standard Test Method for Pulse Velocity Through Concrete
ASTM C642 Standard Test Method for Density, Absorption, and Voids in Hardened Concrete
ASTM C805 / C805M Standard Test Method for Rebound Number of Hardened Concrete
ASTM C1077 Standard Practice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency Evaluation
Reinforcement
ASTM A1022 / A1022M Standard Specification for Deformed and Plain Stainless Steel Wire and Welded Wire for Concrete Reinforcement
ASTM A1064 / A1064M Standard Specification for Carbon-Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete
Australian Standards
Concrete
AS 1012 Methods of testing concrete
- Method 1 – Sampling of concrete
- Method 2 – Preparing concrete mixes in the laboratory
- Method 3.1 – Determination of properties related to the consistency of concrete – Slump test
- Method 3.2 – Determination of properties related to the consistency of concrete – Compacting factor test
- Method 8.4 – Method for making and curing concrete – Drying shrinkage specimens prepared in the field or in the laboratory
- Method 11 – Determination of the modulus of rupture
- Method 13 – Determination of the drying shrinkage of concrete for samples prepared in the field or in the laboratory
- Method 21 – Determination of water absorption and apparent volume of permeable voids in hardened concrete
AS 1478 Part 1 Chemical admixtures for concrete, mortar and grout – Admixtures for concrete
AS 2758 Part 1 Aggregates and rock for engineering purposes – Concrete aggregates
AS 3600 Concrete structures
CIA Z9 CIA Curing of Concrete
SA HB 84 Guide to Concrete Repair Protection
Reinforcement
AS/NZS 4671 Steel reinforcing materials
Singapore Standards
Concrete
SS 509 Code of practice for cleaning and surface repair of buildings
- Part 1: Cleaning of natural stone, brick, terracotta, concrete and rendered finishes
- Part 2: Surface repair of natural stones, brick, terracotta and rendered finishes
SS EN 197 Cement
- Part 1: Composition, specifications and conformity criteria for common cement
- Part 2: Conformity evaluation
SS EN 12620 Specification for aggregates for concrete
CP 65 Part 1 Code of practice for structural use of concrete – Design and construction
International Organization for Standardization
Concrete
ISO 20290 Aggregates for concrete — Test methods for mechanical and physical properties
- Part 1: Determination of bulk density, particle density, particle mass-per-volume and water absorption
- Part 2: Method for determination of resistance to fragmentation by Los Angeles Test (LA-Test)
- Part 3: Determination of aggregate crushing value (ACV)