Civil Engineering Materials: Concrete Mix Design, Admixtures, Metals, and Wood

Comprehensive vocabulary flashcards covering concrete mix proportioning, placement, curing, chemical and mineral admixtures, masonry, metallurgy, and timber technology.

Absolute volume method

A concrete mix proportioning design procedure based on the principle that the total volume of concrete equals the sum of the solid absolute volumes of all constituent materials, calculated by $\text{AV} = \frac{\text{Weight of material}}{(\text{Specific gravity of material})(\text{Unit weight of water})}$.

Specified compressive strength ($f'_c$)

The ultimate uniaxial compressive strength of concrete at 28 days specified by structural drawings and specifications, serving as the minimum design benchmark.

Required average compressive strength ($f'_{cr}$)

The higher average target compressive strength ($f'_{cr} > f'_c$) required in mix proportioning under ACI standards to ensure that the probability of strength tests falling below the specified strength $f'_c$ is statistically minimized.

Hauling time

The total elapsed duration from when concrete mixing begins at the batch plant (and water is added) to the time it arrives at the jobsite and is discharged, ideally within 30 to 60 minutes and not exceeding 90 minutes when a retardant is used.

Cold joint

A seam or structural plane of weakness formed when a layer of freshly poured concrete is placed against an underlying concrete layer that has already taken its initial set due to excessive placement delays.

Screeding (striking off)

The initial concrete finishing operation of striking off excess freshly placed concrete to bring the top surface to the proper grade and contour.

Bull floating

The finishing operation performed immediately after screeding to level ridges, fill surface voids, embed coarse aggregate slightly below the surface, and bring sufficient paste to the top.

Edging

The finishing operation of rounding off exposed concrete edges along forms with a radius tool to prevent corner spalling and chipping.

Concrete curing

The process of maintaining adequate moisture content and favorable temperatures in freshly placed concrete to foster continuous cement hydration and strength gain, without which concrete can lose over $50\%$ of its potential strength.

Air-entraining admixture

An admixture that intentionally introduces and stabilizes approximately 200 to 400 microscopic, well-spaced spherical air bubbles per cubic yard to alleviate internal hydrostatic pressure and dramatically increase freeze-thaw durability.

Scaling

The flaking, peeling, or loss of the hardened surface mortar layer on concrete pavements caused by repeated freeze-thaw cycles combined with chemical de-icing salts.

Water-reducing admixture (Type A)

A chemical admixture that imparts electrostatic repulsive charges onto cement grains to disperse lumps, releasing trapped water and reducing the required water-to-cement ratio without altering workability or compressive strength.

Retarding admixture (Type B)

A chemical admixture designed to delay the initial setting and rate of hydration of cement paste, commonly specified during hot weather concreting or extended transportation hauls.

Accelerating admixture (Type C)

A chemical admixture, commonly calcium chloride ($\text{CaCl}_2$ up to $2\%$ by weight of cement), added to speed up the rate of cement hydration and accelerate early compressive strength gain, especially in cold weather.

Materials of low reactivity

Ultra-fine powders such as micro-milled limestone or granite (around $3\,\mu\text{m}$) that physically pack into the transition zone between aggregate particles and cement paste to increase density and provide hydration nucleation sites.

Plastic shrinkage cracking (map cracking)

Cracks that form in unhardened concrete when the environmental rate of surface water evaporation exceeds the rate at which bleed water reaches the surface, exacerbated by high winds and high ambient temperatures.

Control joints (contraction joints)

Grooves sawed or formed into a fresh or curing slab to create predetermined planes of weakness, ensuring drying shrinkage cracking occurs neatly along the joint lines rather than randomly across the surface.

Expansion joints (isolation joints)

Through-thickness joints ranging from $1/4\,\text{inch}$ to $2\,\text{inches}$ that completely separate a concrete slab from adjoining walls, columns, or fixed pavements, providing room for thermal expansion and movement.

Construction joints

Stopping interfaces installed where one concrete pour ends and another begins later, typically detailed with embedded smooth dowels, tie bars, or keys to transfer loads across the cold boundary.

Adobe

Sun-dried, non-load-bearing masonry units manufactured from agitating wet clay in molds and drying it without kiln firing, typically exhibiting low compressive strengths of $150\text{--}200\,\text{psi}$.

Vitrification

The ceramic firing process in brick manufacturing where molded clay is heated to $400^\circ\text{F}$ to drive off free moisture, followed by heating to $1800^\circ\text{F}$ to fuse silicate molecules into an impermeable, high-strength structural unit.

Concrete masonry unit (CMU)

A modular hollow or solid structural block machine-cast under pressure and vibration from Portland cement, sand, and pea gravel using an ultra-low water-cement ratio of $0.25\text{--}0.8$.

Hydrated lime (in masonry mortar)

An ingredient added to Portland cement mortar to improve its workability, cohesiveness, water retention, and plastic board life during laying.

MSNOK classification

The standardized designating system for Portland cement-lime masonry mortars, ranked in descending order of compressive strength from Type M (highest strength) through S, N, O, to Type K (lowest strength).

Pig iron

The raw, high-carbon molten metallic intermediate extracted directly from a blast furnace by smelting iron ore, coke, and limestone.

Low carbon steel

Carbon steel containing $0.03\%\text{--}0.3\%$ carbon, characterized by exceptional ductility and toughness, widely used in hot-rolled structural shapes such as I, W, and C profiles.

Medium carbon steel

Carbon steel containing $0.35\%\text{--}0.55\%$ carbon, providing a balanced trade-off between higher tensile strength and adequate ductility, predominantly used for concrete reinforcing rebar.

High carbon steel

Carbon steel containing $0.6\%\text{--}1.5\%$ carbon, possessing very high hardness and strength with reduced ductility, commonly used for mechanical tools and wear parts.

Stainless steel

A corrosion-resistant alloy steel containing at least $12\%$ chromium, categorized into austenitic 300 series (containing nickel and non-magnetic) and ferritic/martensitic 400 series (magnetic).

Quenching

A heat-treating process where steel is heated above its upper critical temperature and rapidly cooled in a water or oil bath, transforming austenite into a hard, brittle crystalline phase known as martensite.

Annealing

A heat treatment process where metal is heated past its critical temperature and then cooled very slowly in a furnace to relieve internal residual stresses, refine grain structure, and enhance ductility.

Anisotropic material

A material whose mechanical, thermal, and physical properties vary significantly depending on the direction of measurement or applied force, such as the directional grain structure of timber.

Heartwood

The older, non-functioning, darker inner central core of a tree trunk containing resins and gums, providing high decay resistance and structural support.

Sapwood

The living, lighter-colored outer concentric growth rings of a tree surrounding the heartwood, responsible for sap and moisture transport between the roots and crown.

Lignin

The complex natural organic polymer in timber that acts as a structural adhesive binding together cellulose and hemicellulose fibers in wood cells.

Wood seasoning

The controlled drying of green lumber by air drying or kiln drying (at $160^\circ\text{F}\text{--}180^\circ\text{F}$) to lower moisture content to equilibrium, thereby increasing strength and preventing shrinkage or fungal attack.

Board foot

A volumetric unit of measurement for sawed lumber equal to the volume of a piece $12\,\text{inches}$ wide, $1\,\text{inch}$ thick, and $1\,\text{foot}$ ($12\,\text{inches}$) in length.