Concrete Types, Components and History

• Concrete is an artificial stonelike building material.
• It consists of cement, mineral aggregates, and water.

Types of Concrete

• Plain Concrete: Contains no reinforcement except for shrinkage or thermal stress reduction.
• Reinforced Concrete: Steel reinforcement is embedded to help resist forces, with the two materials working together.

Components of Concrete

• Binder: A binding agent that forms materials into a structurally stable, cohesive whole.
• Aggregate: Hard, inert mineral materials (sand, gravel) added to cement paste to create concrete or mortar.
• Cement Paste: The mixture of cement and water.
• Cement Mortar: Cement, water, and sand.
• Masonry Mortar: Cement, water, sand, and lime.
• Concrete: Cement, water, sand, and coarse aggregates.

Historical Developments

• Pozzolan: A siliceous material like fly ash that reacts with slaked lime.
• 1824: Joseph Aspdin patented Portland Cement.
• 1890: E.L. Ransome built Leland Stanford Jr. Museum.

Typical Sources of Portland Cement Raw Materials

• Limestone
• Iron
• Silica
• Alumina
• Calcium Sulfate
• Seashells
• Shale
• Slag
• Lime

Advantages of Concrete

• Readily available ingredients.
• Free from defects and flaws unlike natural stones.
• High durability.
• Can be cast into any desired shape.
• Economical casting can be done on-site.
• Low maintenance cost.
• Non-combustible nature makes it fire-safe.
• Resistant to wind and water.

Disadvantages of Concrete

• Relatively low tensile strength compared to other binding materials.
• Less ductile.
• High weight compared to its strength.
• May contain soluble salts that cause efflorescence.

Cement Defined

• A calcined, finely pulverized mixture of clay and limestone used as an ingredient in concrete and mortar.

Pyro-processing

• Materials are subjected to high temperatures, typically over 800°C, to cause chemical or physical changes.

Two Types of Cement

• Hydraulic Cement: Capable of setting and hardening through a reaction with water.
• Portland Cement: A hydraulic cement made by burning a mixture of clay and limestone in a rotary kiln, then pulverizing the clinker.

Types of Portland Cement

• Type I (Normal): Used for general construction.
• Type II (Moderate): Reduced tricalcium aluminate makes it sulfate-resistant; used in large piers and retaining walls.
• Type III (High Early Strength): Very finely ground with increased tricalcium silicate, for faster curing in cold weather.
• Type IV (Low Heat): Reduced tricalcium silicate and increased dicalcium silicate for massive concrete structures like gravity dams.

Cement Terminologies

• Entrained Air: Microscopic, spherical air bubbles (0.004 to 0.04 in diameter) intentionally dispersed in concrete or mortar to increase workability.

• Air-Entrained Cement: Hydraulic cement with an air-entraining agent to entrain air in mortar.

• Sulfate Action: Expansive reaction when cement matrix of concrete or mortar contacts sulfates in groundwater or soil.

• Chemical Attack: Chemical reactions in concrete and its reinforcements leading to cracking.

• Hydration: A process where a substance combines chemically with water

• Natural Pozzolans: Volcanic ash, Diatomaceous earth, Calcined clay, Metakaolin clay, Rice hull ash, etc.

• By-Product Material (Class F or Class C)

• Fly Ash: Finely divided residue from the combustion of grounded or powdered coal

• Ground Granulated Blast-Furnace Slag: Obtained by quenching molten iron slag from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.

• Expansive Cement: Increases in volume after setting when mixed with water.

• Special types of cement:

  • White Cement: Hydrates to a white paste; made of low-iron raw materials. -Water-Repellent: Hydraulic binding material made from finely ground cement clinker, gypsum, and additives -Masonry Cement: Mix of Portland cement, hydrated lime, plasticizers, air entraining agents, gypsum, with sand and water -Mortar Cement Plastic mixture of lime or cement or combination of both, with sand and water as bonding agent

  -Oil-Well Utilized for cementing work in the boring of oil wells where they are liable to high temperatures -Plastic (Poly Cement) It is used to secure various materials together, be it wood, plastic, ceramic or metal -Rapid-Setting – Cement characterized by a rapid increase in strength during initial hardening period -Regulated Set Hydraulic cement containing fluorine-substituted calcium aluminate, capable of very rapid setting -Calcium Aluminate Cements containing hydraulic calcium aluminates, used in small scale specialized applications -Asphalt Cement Strong, versatile, weather and chemical resistant binding material for surface for roads, streets and airport runways -Bituminous Cement – Made with bituminous material as binder for sand and gravel -Bulk Cement – Cement transported and delivered in bulk (in specially constructed vehicles) instead of in bags -High Fineness Cement a hydraulic cement of substantially higher specific surface and substantially smaller mean particle diameter than typical -Hot Cement Newly manufactured cement that has not had an opportunity to cool after grinding of clinker -Hydrophobic Cement contains admixtures which decrease the wetting ability of cement grains. Obtained by grinding Portland cement clinker with a film forming substance -Keene’s Cement A hard plaster formulation, primarily used for ornamental work -Low-Alkali Portland cements with a total content of alkalies not above 0.6% -Modified Cement Energetically modified cements (EMC) class of cementitious materials made from pozzolans (e.g. fly ash, volcanic ash, pozzolana), silica sand, blast furnace slag or Portland cement -Natural Cement Naturally occurring clayey limestone that, when calcined and finely pulverized, produces a hydraulic cement -Non-staining Cement Cement that prevents passage of moisture and staining matter -Ordinary Portland Cement – is the most widely used type of cement, which is suitable for all general concrete construction. -Roman Cement is a substance developed by James Parker in the 1780s, being patented in 1796. -Sticky Cement -finished cement that develops low or zero flowability during or after storage in silos or after transportation in bulk containers or hopper-bottom cars -Super sulfated cement Is produced with blast furnace slag, gypsum, and Portland cement clinker to produce a fine cement, which is resistant to sulphate attack. -Roman Concrete Ancient Roman concrete consisted of volcanic ash (Pozzolana), lime, and water for mortar, mixed with aggregate. -Sticky Concrete - A richer concrete mixture that contains less water and the conventional one. -High Volume Fly Ash (HVFA) Concrete - Fly ash is the cement of the future

Aggregates Defined

• Inert mineral materials (sand, gravel) added to cement paste to create concrete or mortar.
• Types of Aggregates:
• Normal Weight Aggregate - Used for most concretes, naturally occurring gravels -Boulders – Large naturally rounded rock -Cobbles Smaller than boulders and larger then pebbles -Coarse Aggregate – Crushed stone, gravel, blast furnace slag, larger than ¼ in (6.4mm) -Fine Aggregate – Sand, smaller than ¼ in (6.4mm) -Mineral Filler – Finely pulverized inert material or rock
• Heavy Weight Aggregate Possess high density, 2,400 kg/m3 and higher -Magnetite One of the oxides of iron, most magnetic of naturally-occurring minerals -Barite Smaller than boulders and larger than pebbles -Limonite Iron ore used as pigment in the manufacture of paints, coloring weathered surface of rock -Ferro phosphorous Crude alloy of iron and phosphorous -Steel Shot/ Punchings
• Light Weight Aggregate Artificially produced aggregate of low density -Expanded clay strong, contained by exfoliation of clay or shale -Shale Fine-grained, clastic, sedimentary rock -Slate Finest grained foliated metamorphic rock -Blast furnace slag

Admixtures Defined

• Substances, other than cement, water, or aggregate, added to concrete or mortar to alter properties:
• Air Entraining Agent An admixture that disperses entrained air in a concrete or mortar mix to increase workability -Water Reducing Agent For reducing the amount of mixing water required for the desired workability of a concrete/mortar mix -High-Range Water-Reducing Admixture/Superplasticizer Organic compounds that transform a stiff concrete mix into one that flows freely into forms -Accelerator Admixture that hastens the setting and strength development of a concrete mortar or plaster mix -Workability Agent Improve the plasticity of wet concrete to make it easier to place in forms and finish
• Water-Cement Ratio Ratio of mixing water to cement in a unit volume of concrete or mortar mix -Sack Measure of Portland Cement: 94 lb, 50 kg. Also bag
• Shrinkage-Reducing Admixtures Reduce drying shrinkage and the cracking that results therefrom
• Corrosion Inhibitors Used to reduce rusting of reinforcing steel in structures exposed to road deicing salts
• Freeze Protection Admixtures Allow concrete to cure satisfactorily at temperatures as low as 20°F (7°C)
• Retarder – Slows the setting of a concrete, mortar or plaster mix in order to allow more time for placing and working the mix
• Coloring Agent Pigment or dye added to concrete mix to alter its color

Mix Design

• Most economical selection and proportioning of cement and water in a volume of concrete or mortar.

Slump Test

• Determines the consistency and workability of freshly mixed concrete by measuring the slump of a tested specimen. -Consistency Relative ability of freshly mixed concrete or mortar to flow -Workability Relative ease with which freshly mixed concrete or mortar can be handled