Civil Engineering Materials: Wood and Concrete

Vocabulary flashcards covering the structural characteristics of wood, processing methods of engineered timber, cement chemistry, hydration reactions, and concrete mix performance.

Technical report

A formal document characterized by sufficient detail and clarity such that it can be used to duplicate the work reported and obtain substantially the same results.

Abstract

The summary section placed directly after the title page in a technical report; it should be written last so that all conclusions are clear.

Principal elements of wood

Carbon, hydrogen, and oxygen, along with minor fractions of nitrogen and mineral ash.

Cellulose

The crystalline compound formed into long bands that provides the majority of strength within wood fibers.

Hemicellulose

The wood compound that bundles cellulose strands and acts as the structural link between cellulose and lignin.

Lignin

The natural stiffening glue located primarily in the middle lamella that provides a protective coating to seal wood microfibrils together.

Middle secondary wall ($\text{S}_2$)

The thickest cell wall layer containing the largest amount of microfibrils oriented parallel to the longitudinal direction, contributing the most to the strength of wood.

Sapwood

The exterior, actively living layer of wood that readily absorbs fluids, making it easier to treat with preservatives compared to heartwood.

Heartwood

The inner portion of wood containing extractives that dries out the tissue and makes preservative penetration difficult.

Latewood

Wood formed during the later part of the growing season that possesses smaller cells with thicker microfibrils oriented in a parallel direction, rendering it stronger and denser than earlywood.

Free water (in wood)

Liquid water contained inside the cell lumens of wood that affects only specimen weight, having no influence on volume or strength.

Hygroscopic water (in wood)

Water bound chemically within the wood cell walls whose removal causes wood shrinkage, warping, and an increase in strength.

Tangential shrinkage

The structural axis along which wood shrinks the most when dried, caused by the loss of moisture from the middle lamella cells and surrounding structure.

Longitudinal shrinkage

The structural axis along which normal wood shrinks the least, due to the parallel orientation of microfibrils having limited space to draw closer together.

Collapse (wood defect)

An abnormal flattening of cells caused by the rapid drying of green heartwood, where water exits faster than air can enter, drawing a vacuum inside the cell walls.

True slope of grain

A metric used to evaluate wood strength defined as the distance over which a one-inch deviation of the grain occurs from the longitudinal axis.

Compression wood

Reaction wood formed in softwoods featuring oblique, flat-spiral microfibrils, higher lignin content, abnormally high longitudinal shrinkage, and reduced tensile strength parallel to the grain.

Tension wood

Reaction wood formed in hardwoods characterized by lower lignin content, leading to easier microfibril movement and poor compressive strength parallel to the grain.

Parenchyma cells

Wood cells responsible for storing nutrients in the growing tree.

Case hardening

A seasoning defect occurring when rapid surface moisture loss causes the outer timber fibers to shrink and set in tension while the wet interior core is prevented from shrinking normally.

Particle board

A manufactured panel product made from wood chips, shavings, and sawdust combined with a synthetic resin or binder.

Oriented Strand Board (OSB)

An engineered wood panel produced by gluing and compressing randomized wood strands or chips measuring approximately $1\text{ in}$ to $6\text{ in}$ in length.

Plywood

An engineered panel assembled from thin sheets of wood (veneers) glued together with alternating, mutually perpendicular grain directions.

Glued-laminated timber (Glulam)

A structural timber element formed by bonding stress-graded lumber together with the grain of each parallel layer aligned in the same direction.

Cross-laminated timber (CLT)

A structural timber product fabricated by gluing layers of stress-graded lumber with the grain orientation alternating perpendicularly between adjacent layers.

Laminated Veneer Lumber (LVL)

A structural engineered wood product consisting of thin layers of wood veneers glued together with the grain of all plies oriented in the same direction.

Components of concrete

The five essential constituent materials: water, cement, fine aggregate, coarse aggregate, and air.

Saturated Surface Dry (SSD)

An aggregate moisture condition in which all interior permeable pores are filled with water, but no free moisture is present on the external surface, neither adding nor absorbing water from the concrete mix.

Bulking of sand

A temporary increase in volume of fine aggregate caused by surface tension from a thin water film holding particles apart at moisture contents between $4\%$ and $8\%$.

Tricalcium Silicate ($\text{C}_3\text{S}$)

The primary clinker compound responsible for early hydration and early strength development in Portland cement.

Dicalcium Silicate ($\text{C}_2\text{S}$)

A principal clinker compound that hydrates slowly and contributes significantly to the long-term ultimate strength of concrete.

Induction period

The early stage following cement wetting where hydration rates temporarily slow, keeping the cement paste plastic and workable for placement.

Flash set

The rapid, irreversible stiffening of cement paste caused by violent hydration of tricalcium aluminate ($\text{C}_3\text{A}$), releasing substantial heat; controlled by adding gypsum during grinding.

False set

A rapid stiffening of fresh cement paste that develops little heat or strength, distinguished by its ability to be completely reversed through remixing without additional water.

Type III Portland cement

High-early-strength Portland cement, ground finer and typically higher in $\text{C}_3\text{S}$ to rapidly develop compressive strength and produce high hydration heat.

Type IV Portland cement

A low-heat Portland cement manufactured with reduced proportions of $\text{C}_3\text{S}$ and $\text{C}_3\text{A}$ to hydrate slowly and minimize thermal cracking in mass concrete.

Type V Portland cement

High-sulfate-resistant Portland cement that limits tricalcium aluminate ($\text{C}_3\text{A}$) to less than about $5\%$ to mitigate destructive sulfate expansion.

Type IL cement

Portland-limestone blended cement containing between $5\%$ and $15\%$ ground limestone, compared to a maximum of $5\%$ in standard Type I Portland cement.

Pozzolan

A siliceous or aluminosilicate material that reacts chemically with calcium hydroxide ($\text{Ca(OH)}_2$) formed during cement hydration to produce additional calcium silicate hydrate ($\text{C-S-H}$).

Alkali-Silica Reaction (ASR)

A deleterious chemical reaction where alkali hydroxides attack reactive aggregate silica, generating a hygroscopic gel ($\text{N-S-H}$) that swells upon absorbing moisture, causing internal tensile cracking.

Pessimum percentage

The specific proportion of reactive silica in aggregate (around $5\%$) that generates maximum expansion and cracking in concrete suffering from alkali-silica reaction.

ASTM C1602

The standard specification governing non-potable water usage in concrete, requiring concrete or mortar mixes to attain at least $90\%$ of the 7-day strength of potable water controls and setting times within $1\text{ hour}$ earlier to $1.5\text{ hours}$ later.

Hourglass failure pattern

The characteristic compression fracture geometry of concrete cylinders caused by platen-end frictional restraint that establishes a state of triaxial compression at the ends, which fades toward the cylinder center.

Setting (concrete)

The onset of rigidity in fresh concrete paste representing the phase transition from a fluid/plastic state to a rigid solid, distinct from strength-gaining hardening.

Expansive cement

A specialized hydraulic cement engineered to expand slightly at early ages to produce compressive stresses that counterbalance drying shrinkage.

Fuller curve

A theoretical aggregate gradation curve optimized solely for maximum particle packing density, rarely utilized alone because it lacks sufficient fines for concrete workability and finishability.