CONCRETE - is a mixture of sand and, crushed rock or other aggregates

The Romans made significant advancements in concrete technology, creating a material known as "Roman concrete" or "opus caementicium."

The development of Portland cement in the early 19th century by Joseph Aspdin in England

 The introduction of the mixer truck in 1916 revolutionized the concrete industry by allowing for efficient transportation and delivery of ready-mix concrete.

CONCRETE CONSTITUENTS

Paste (30%-40%):

-PC : 7% - 11.5% by volume

-Water : 14% - 21% by volume

Aggregate (60%-70%):

-Coarse aggregate

-Fine aggregate

Admixture

COARSE VS FINE AGGREGATES

Coarse Aggregates -Larger in size, typically between 9.5mm and 37.5mm in diameter.

Comprise materials like crushed stone, gravel, or slag.Used primarily in the lower layers of concrete for structural strength.

Provide stability and support to the concrete mix.

Fine Aggregates -Smaller in size, typically less than 4.75mm in diameter.

Comprise materials like sand or fine crushed stone.

Used in the upper layers of concrete for a smoother finish.

Enhance workability and cohesiveness in the concrete mix.

COMMON AGGREGATES

-Crushed Stone, Sand, Gravel , Recycled Concrete Aggregate, Slag , Limestones, Expanded Clay Aggregate, Graded aggregate

PRINCIPLES OF PORTLAND CEMENT CONCRETE

Water-Cement Ratio and Strength -Strength depends on the water-cement ratio in the initial mix. Water is kept to a minimum for maximum hardness.

Workability and Cost Efficiency -Water increases workability, allowing the proportion of aggregate to cement to be increased, thereby reducing cost.

Coating Aggregate Particles -The ideal amount of cement is just enough to coat each aggregate particle completely.

Aggregate Size and Cost Impact -Fine aggregates require more coating material, and so the total cost of the concrete increases as the size of the aggregate decreases.

Shrinkage and Cement Proportion -is proportional to the amount of cement paste; the higher the proportion of cement, the more shrinkage.

STAGES OF CONCRETE

FRESH STATE -Concrete that has been recently mixed and is still in a fluid or plastic state, typically when it is being poured and shaped into forms. It has not yet hardened or fully set.

SOLID STATE -Concrete that has cured and hardened, reaching its full strength and rigidity. It is no longer in a fluid or plastic state and can support loads and perform its intended structural functions.

TYPES OF WORKABILITY

HIGH WORKABILITY -Highly fluid, suitable for intricate molds and thin sections.

NORMAL WORKABILITY -Balanced consistency for general construction.

LOW WORKABILITY -Stiff, maintains shape for vertical forms.

SELF CONSOLIDATING CONCRETE -Requires no vibration, flows into place.

PUMPABLE CONCRETE -Designed for pumping to remote sites.

RHEOPLATIC CONCRETE - Flows under stress, maintains shape at rest.

CONCRETE PRODUCTS

Ready-Mix Concrete - This is a commonly used type of concrete that is mixed at a concrete batching plant and delivered to the construction site in a ready-to-use form. It's convenient and ensures consistent quality.

High-Strength Concrete -This type of concrete has a higher compressive strength than regular concrete, making it suitable for structures that need to support heavy loads.

Self-Consolidating Concrete (SCC) -is designed to flow and fill formwork without the need for vibration or compaction. It's ideal for complex and congested structural elements.

Pervious Concrete -Also known as permeable or porous concrete, it allows water to pass through, reducing runoff and helping with stormwater management.

Lightweight Concrete -This type of concrete is made using lightweight aggregates, resulting in a lower density. It's used for applications where weight reduction is important, like in precast panels.

Shotcrete - is a method of applying concrete with high velocity using compressed air. It's often used for structural repairs, tunnels, and swimming pools.

Fiber-Reinforced Concrete -Fibers, such as steel, glass, or synthetic fibers, are added to the concrete mix to improve tensile strength and reduce cracking.

Rapid-Set Concrete -This concrete sets quickly, allowing for faster construction and repair projects. It's often used for road repairs and emergency repairs.

Colored Concrete -Pigments are added to the mix to achieve a wide range of colors for decorative purposes.

ADMIXTURES

Water Reducers -These admixtures, also known as plasticizers, improve workability by reducing the water content needed while maintaining the desired consistency. They are particularly useful in producing high-strength concrete mixes with lower water-cement ratios.

Retarders - slow down the setting time of concrete, which is useful when you need more time for transportation, placement, or finishing. They are especially handy in hot weather conditions.

Accelerators- speed up the setting time of concrete. They are used in cold weather to ensure that concrete gains strength quickly. Calcium chloride is a common accelerator.

Air-Entraining Agents-These admixtures create tiny air bubbles in the concrete, improving freeze-thaw resistance and reducing the risk of cracking due to temperature fluctuations. Air-entrained concrete is ideal for regions with harsh winters.

Superplasticizers- are highly effective water-reducing agents that can greatly improve the workability of concrete without increasing water content. They are often used in self-consolidating concrete (SCC) and high-performance concrete mixes.

Corrosion Inhibitors- inhibitors are added to concrete to protect embedded steel reinforcement from corrosion caused by exposure to aggressive environments or chloride ions.

Coloring Admixtures -Coloring admixtures are added to produce decorative concrete with various colors and textures. They are popular in architectural and decorative concrete applications.

Fiber Reinforcements-Fibers, such as steel, glass, or synthetic fibers, are added to concrete to improve its tensile strength and reduce cracking. They are often used in industrial floors and shotcrete applications.

Alkali-Silica Reactivity (ASR) Inhibitors -mitigate the risk of alkali-silica reaction, a chemical reaction that can cause expansion and cracking in concrete due to certain types of aggregates.

The 2 classifications of cement

Non-hydraulic (does not set and harden in water ex. plaster of paris)

Hydraulic (sets and hardens in water ex. Portland cement)

5 Types of Cement

Type I: Normal (portland cement for general construction)

Type II: Moderate Sulfate Resistance (near water bodies)

Type III: high early strength (cures faster (3-7 days) and gains earlier strength)

Type IV: low heat of hydration (used for massive concrete structures like dams)

Type V: High sulfate resistance (used where resistance to severe sulfate action is required; massive structures near water bodies)

Other uses for cement

Mortar: cement + sand + water

Plaster: cement + lime + sand + water; smoothens surfaces

Grout: cement + sand + a little water; tiles

PROPERTIES OF WOOD

hardness, strength, flexibility, durability