Concrete Technology Lecture Notes

A comprehensive set of vocabulary flashcards covering the fundamentals of concrete technology, including materials, properties, types, admixtures, and testing methods.

Concrete

An artificially produced material formed by the hardening of a mixture of binding material (Cement, Lime), Aggregate (Sand and coarse aggregate), water, and an admixture.

Water-Cement (w/c) Ratio

The ratio of the weight of water to the weight of cement; it typically ranges from $0.45$ to $0.6$, with a minimum value of $0.4$ for hydration.

Hydration of Cement

The chemical reaction between cement and water; in a typical w/c ratio of $0.4$, approximately $0.23$ is used for hydration while $0.17$ remains in the voids.

Light weight concrete

Concrete with a specific weight between $3\,KN/m^3$ and $18.5\,KN/m^3$, made by including air or using light weight aggregates like pumice, diatomite, or scoria.

Medium weight concrete

Normally used concrete with a specific weight of $24\,KN/m^3$.

Heavy weight concrete

Concrete with a specific weight of $32\,KN/m^3$ made by adding heavy weight aggregates like Hematite, Limonite, or Magnetite, often used for nuclear plant shielding.

Plain Cement Concrete (PCC)

Concrete made from basic components including binding material, water, and aggregate without reinforcement.

Reinforced Cement Concrete (RCC)

Also called Ferro concrete, it is made by adding reinforcement, usually in the tensile zone, to increase structural strength.

Pre-stressed Concrete

Concrete in which initial compression is induced to resist tension with greater efficiency.

Polymer concrete composite

A type of concrete that uses polymers to replace lime-type cements as a binder or to fill voids and reduce porosity.

Vacuum concrete

Concrete where excess water used for workability is removed by a vacuum pump after placing to increase strength.

Fiber reinforced concrete (FRC)

Concrete containing short discrete fibers (steel, glass, synthetic, or natural) that are uniformly distributed to increase structural integrity and arrest cracks.

Ferro cement concrete

A system of reinforced concrete containing a thin layer of metal mesh, woven expanded-metal, or metal-fibers and closely spaced thin steel rods.

Sawdust concrete

Concrete where sawdust is used as a partial replacement for fine aggregates, generally used for panel walls and soundproofing.

Air-entrained concrete

Also called cellular or aerated concrete, it contains billions of microscopic air cells to improve frost resistance and workability.

Coarse aggregates

Aggregates larger than $4.75\,mm$ and smaller than $75\,mm$ according to the IS Sieve.

Fine aggregates

Aggregates larger than $75\,\mu m$ and smaller than $4.75\,mm$ according to the IS Sieve.

Flaky aggregate

An aggregate is classified as flaky if its smallest dimension is less than $0.6$ times the mean dimension.

Elongated aggregate

An aggregate is classified as elongated if its largest dimension is greater than $1.8$ times the mean dimension.

Gradation

The process of determining the percentage by mass occupied by various sizes of aggregate, typically done by sieve analysis.

Fineness Modulus (F.M.)

A numerical index used to measure the average particle size of aggregates; higher values indicate coarser particles.

Bulking of sand

The increase in volume of dry sand when water is added (maximum at $4\%$ moisture) due to a thin film of water forming around particles.

Aggregate Crushing Value

A measure of resistance to compressive loads; it is restricted to $30\%$ for concrete used in roads and pavements.

Los Angeles Abrasion Value

A measure of aggregate hardness and resistance to wear and tear determined by rotating aggregates in a cylindrical drum with steel spheres.

Aggregate Impact Value (AIV)

A measure of the toughness of an aggregate, determined by subjecting a sample to blows from a metal hammer.

Alkali-aggregate reaction

A chemical reaction between highly alkaline cement paste and non-crystalline silicon dioxide in aggregates that causes expansion and spalling.

Plasticizers (Water-reducing Admixtures)

Admixtures that reduce water content for a given workability by up to $15\%$ through induction of electrostatic repulsion and dispersion of cement grains.

Superplasticizers

High-range water reducers (e.g., SMF, SNF, PCE) that can reduce water content by up to $30\%$ and produce self-leveling concrete.

Accelerators

Admixtures like Calcium Chloride ($CaCl_2$) that increase the rate of hydration and shorten the setting time of concrete.

Retarders

Admixtures like Gypsum or sugar that increase the setting time of cement by suspending the action of $C_3A$ and $C_3S$.

Pozzolanic Admixture

Siliceous or aluminous materials like Fly Ash or Silica Fume that react with calcium hydroxide to form compounds with cementitious properties.

Fly Ash

A finely divided residue resulting from the combustion of ground or powdered coal, used to increase durability and hardness.

Silica Fume

A byproduct of the semiconductor industry containing over $90\%$ silicon dioxide in non-crystalline form, used to improve compressive and bond strength.

Rice Husk Ash

A bio-waste pozzolanic material that contributes to high strength and high impermeability in concrete.

Batching

The process of accurate measurement of all concrete materials (by weight or volume) to ensure uniform and desirable properties.

Bleeding

The appearance of water on the concrete surface due to excess water in the mix.

Segregation

The separation of particles from the concrete mixture, often due to excess water or excess vibration.

Laitance

A watery scum that forms on the surface of concrete due to excess vibration.

Honeycomb

The formation of cavities in concrete due to a lack of proper vibration, particularly in heavily reinforced sections.

Screeding

The process of removing humps and hollows from the concrete surface to produce a true and uniform plane.

Floating

The process of removing irregularities left on the concrete surface after screeding.

Troweling

The final stage of finishing that produces a smooth and dense concrete surface.

Target Strength ($f_t$)

The mean strength for which a mix is designed, calculated as $f_{f} = f_{ck} + KS$ where $S$ is the standard deviation.

Characteristic Strength ($f_{ck}$)

The 28-day strength of concrete below which not more than $5\%$ of test results are expected to fall.

Abrams Water/Cement Ratio Law

The principle stating that the strength of concrete is only dependent upon the water/cement ratio, provided the mix is workable.

Workability

A property of fresh concrete determined by the ease and homogeneity with which it can be mixed, placed, compacted, and finished.

Slump Test

A field test for workability using a standard cone ($100\,mm\times200\,mm\times300\,mm$) to measure the decrease in height of unsupported concrete.

Compacting Factor Test

A test that measures workability by comparing the density achieved by a standard free fall to the density of fully compacted concrete.

Vee Bee Consistometer Test

A test measuring the time (in seconds) required for concrete to be compacted by vibration; used for very dry or stiff mixes.

Powers Law (Gel Space Ratio)

A formula where strength is proportional to the cube of the gel space ratio ($Strength = 2400\,X^3\,Kgf/cm^2$).

Modulus of Rupture ($f_r$)

The flexural tensile strength of concrete, calculated by the formula $f_r = 0.7\times\sqrt{f_{ck}}$.

Shrinkage

The strain induced in concrete at zero stress, primarily caused by the withdrawal of moisture.

Creep

The additional strain that occurs in concrete under a prolonged constant stress.

Relaxation

The reduction in stress in a concrete member when it is held at a constant strain.

Secant Modulus

The slope of the line drawn from the origin to the point on the stress-strain curve corresponding to $40\%$ of the failure load.

Poisson’s ratio ($\mu$)

The ratio of lateral strain to linear strain; for concrete, it typically ranges between $0.11$ and $0.21$.

Schmidt Hammer (Rebound Hammer)

A non-destructive test device used to estimate surface hardness and correlate it with the compressive strength of concrete.

Ultrasonic pulse velocity method

A non-destructive test that measures the time of travel of an ultrasonic pulse through concrete to detect cracks or defects.

Pre-tensioning

A method of pre-stressing where tendons are tensioned against abutments before the concrete is placed.

Post-tensioning

A method of pre-stressing where tendons are tensioned in ducts after the concrete has hardened.

Buttering

The process of mixing some mortar in the mixer at the beginning of the first batch to coat the drum.