Concrete Properties and Durability

Properties of Hardened Concrete

• Strength influenced by several factors: water-cement ratio, aggregate-cement ratio, aggregate size and strength, compaction, mixing temperature, curing method, and age.
• Tensile strength is a vital property of concrete, essential for structural integrity.
• Compressive strength typically surpasses tensile strength in concrete; their relationship is key for structural design.
• Bond strength of concrete impacts adhesion between aggregate and cement paste, crucial for overall durability.

Durability of Concrete

• Permeability affects the absorption of water and chemicals, leading to potential damage.
• Sulphate attack can weaken concrete, especially in environments rich in sulphate salts.
• Attack by seawater poses risks due to chlorides and aggressive ions affecting the steel reinforcement.
• Acid attack can chemically erode concrete, diminishing its durability.
• Alkali-aggregate reaction may cause expansion and cracking, resulting from alkali-silica interactions.
• Corrosion of reinforcement can lead to structural failures due to loss of steel strength and integrity.

History and Evolution of Concrete

• Ancient uses dated back to 7000 BC in Israel; early forms of concrete were not hydraulic.
• Egyptian mortar (2690 BC) combined quicklime, gypsum, and sand, also not hydraulic.
• Romans advanced cement technology, introducing hydraulic cement using pozzolan, with the Pantheon dome (128 AD) as a major achievement.
• John Smeaton revived Roman cement knowledge in the 18th century, marking the start of modern concrete use in engineering.

Properties of Cement

• Cement is a powdered mix composed of lime and clay minerals, which develops binding properties through hydration.
• Portland cement is the most common hydraulic cement, consisting of calcium silicates.
• Gypsum is often added to regulate setting time.

Aggregates

• Aggregate constitutes approximately 75% of concrete volume, enhancing its stability and durability.
• Coarse aggregates have particle sizes larger than 4.75 mm, while fine aggregates are smaller than 4.75 mm.

Admixtures

• Admixtures are utilized to modify concrete properties; they can be added during mixing.
• Types include accelerators for early strength, set-retarders to delay setting times, water-reducers (superplasticizers) for improved workability, and mineral admixtures (pozzolans) that enhance strength and durability.

Production and Properties of Good Concrete

• Good concrete must exhibit consistency, cohesiveness, uniform strength, and absence of cracks.

Advantages of Concrete over Steel Structures

• Concrete offers superior maintenance (no corrosion), fire resistance, vibration damping, and thermal ductility.
• Cost-effective due to the abundance and low cost of materials; requires less skilled labor.
• Production of concrete saves energy compared to steel structures.

Types of Concrete

• Normal Weight Concrete has a density of approximately 2400 kg/m³ and uses natural aggregates.
• Light Weight Concrete is less than 1800 kg/m³, utilizing low-density aggregates.
• Heavy Weight Concrete exceeds 3200 kg/m³, applied for radiation shielding.

Explore the various properties of hardened concrete, including the factors that affect its strength such as water-cement ratio and aggregate-cement ratio. This quiz also discusses the durability of concrete, addressing issues like permeability and resistance to chemical attacks. Test your knowledge on these essential concepts in concrete technology!