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**Civil Engineering Materials**

Department of Civil, Structural and Environmental Engineering Trinity College Dublin Roger P. West (TCD) Peter Flynn (Arup)

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**Section A: Concrete A1 Basic Materials: A2 Fresh Concrete Properties:**

A3 Hardened Concrete Properties: A4 Concrete Mix Design: A5 Reinforced Concrete: A6 Pre-stressed Concrete:

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**Section A.3 Hardened Concrete Properties**

1. Curing 2. Strength Development 3. Durability 4. Cube/Cylinder Manufacture & Testing 5. Cube Failures 6. Young’s Modulus & Poisson’s Ratio

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**Section A.3 Hardened Concrete Properties**

7. Drying Shrinkage 8. Creep 9. Thermal Expansion

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**Section A.3 Hardened Concrete Properties**

1. Curing

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**Section A.3 Hardened Concrete Properties: Curing:**

Moisture: Water/Cement Ratio Free Water Loss of Water Retention of Water Temperature Standard Temperature – 20oC Ambient Temperature – 5oC to 30oC Loss of heat Heat Differential Temperature of Concrete Time Early Age Stripping of Formwork Continuation of Work

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**Section A.3 Hardened Concrete Properties**

1. Curing

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**Section A.3 Hardened Concrete Properties**

2. Strength Development Characteristic Compressive Strength: Test cube or cylinder samples in compression Strength below which not more than 5% of test results fall. Generally referred to as 28 day strength Flexural & Indirect Tensile Strength: Generally taken to be around 10% of its uni-axial compressive strength

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**Section A.3 Hardened Concrete Properties**

2. Strength Development

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**Section A.3 Hardened Concrete Properties**

2. Strength Development

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**Section A.3 Hardened Concrete Properties**

2. Strength Development Grade Characteristic Strength (28day) 7day Strength 2month 3month 6month 12month C20 20.0 13.5 22.0 23.0 24.0 25.0 C25 16.5 27.5 29.0 30.0 31.0 C30 33.0 35.0 36.0 37.0 C40 40.0 28.0 44.0 45.5 47.5 50.0 C50 54.0 55.5 57.5 60

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**Section A.3 Hardened Concrete Properties**

2. Strength Development

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**Section A.3 Hardened Concrete Properties**

2. Strength Development Constituents: Water Cement Aggregates Admixtures

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**Section A.3 Hardened Concrete Properties**

2. Strength Development Methods of Preparation: Batching Mixing Placing Compaction

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**Section A.3 Hardened Concrete Properties**

2. Strength Development Test Conditions for compressive strength testing: Specimen Shape & Size Specimen Moisture Content Specimen Temperature Bearing Surface Conditions Method of Loading

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**Section A.3 Hardened Concrete Properties**

3. Durability Durability of concrete is its resistance to weathering, chemical attack, abrasion, frost and fire. Permeability should be as low as possible and is improved by; Full compaction Proper curing Low water content High cement content

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**Section A.3 Hardened Concrete Properties**

3. Durability Carbonation Reinforcement is protected by highly alkaline pore water in the hardened concrete Carbon dioxide in the air neutralises the free lime. If the reaction reaches the reinforcement corrosion will occur. Very slow process dependent on permeability

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**Section A.3 Hardened Concrete Properties**

3. Durability Chloride Attack Slow process dependent on permeability Attacks steel quickly if chloride ions can permeate concrete cover Sources are sea water and de-icing salts predominantly Keep surface permeability as high as possible through compaction, curing and using alternative cement materials

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**Section A.3 Hardened Concrete Properties**

3. Durability Frost Resistance Depends on permeability Improved by the use of air-entraining agent Chemical Attack OPC is subject to attack by acids including organic acids and acid fumes Also attacked by sulphates in the ground and ground water Resisted by; Appropriate cement Correct concrete mix design Dense & well compacted

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**Section A.3 Hardened Concrete Properties**

3. Durability Alkali-silica Reaction A reactive form of silica is present in the aggregate Pore solution contains sodium, potassium & hydroxyl ions and has a high alkalinity (released during hydration) Water is available

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**Section A.3 Hardened Concrete Properties**

3. Durability Fire Resistance Concrete is non-flammable Low thermal conductivity

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**Section A.3 Hardened Concrete Properties**

4. Cube/Cylinder Manufacture & Testing

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**Section A.3 Hardened Concrete Properties**

4. Cube/Cylinder Manufacture & Testing

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**Section A.3 Hardened Concrete Properties**

Cube Failures

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**Section A.3 Hardened Concrete Properties**

Cube Failures

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**Section A.3 Hardened Concrete Properties**

6. Young’s Modulus & Poisson’s Ratio E is influenced by; Elastic properties of the aggregates Conditions of curing Age of concrete Mix proportions Type of cement For concrete Young’s modulus is taken as approx 28kN/mm2 (GPa)

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**Section A.3 Hardened Concrete Properties**

6. Young’s Modulus & Poisson’s Ratio

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**Section A.3 Hardened Concrete Properties**

6. Young’s Modulus & Poisson’s Ratio

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**Section A.3 Hardened Concrete Properties**

6. Young’s Modulus & Poisson’s Ratio

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**Section A.3 Hardened Concrete Properties**

6. Young’s Modulus & Poisson’s Ratio n = - etrans / elongitudinal For Concrete Poisson’s Ratio is taken as The phenomenon explains why cubes fail in compression.

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**Section A.3 Hardened Concrete Properties**

7. Drying Shrinkage Dependent on; Humidity Temperature of surrounding air Rate of air flow over surface Ratio of surface area to the volume of concrete Water & cement contents Curing

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**Section A.3 Hardened Concrete Properties**

7. Drying Shrinkage 50% of all shrinkage between 1month to 1 year depending on mass May be controlled by reinforcement details

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**Section A.3 Hardened Concrete Properties**

7. Drying Shrinkage

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**Section A.3 Hardened Concrete Properties**

8. Creep Dependent on; Humidity Temperature of surrounding air Cement Content Water/cement ratio Type of cement & aggregate

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**Section A.3 Hardened Concrete Properties**

8. Creep

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**Section A.3 Hardened Concrete Properties**

8. Creep Takes place over many months Elastic Recovery Restrained by Reinforcement

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**Section A.3 Hardened Concrete Properties**

8. Creep

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**Section A.3 Hardened Concrete Properties**

9. Thermal Expansion Influenced by; Types of Aggregates Water content Mix Proportions Varies from 0.5 to 1.2 x 10-5 / oC

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