Properties of Civil Engineering Materials – Lecture Review

Vocabulary flashcards covering key terms and concepts from the lecture on civil engineering materials, including concrete, steel, timber, masonry, and plastics.

Composite action (reinforced concrete)

The combined behaviour of concrete and steel whereby tensile forces are carried by steel and compressive forces by concrete, made possible through adequate bond at their interface.

Bond failure

Loss of adhesion between reinforcing bar and surrounding concrete, causing the bar to slip and eliminating composite action.

Tensile strength of concrete

Approximately 10 % of its compressive strength; so concrete is generally assumed to carry no tensile stress in design.

Compatibility of strain

Design assumption that strain in reinforcement equals strain in adjacent concrete, ensuring perfect bond across the section.

Stress–strain curve of concrete (compression)

Starts almost linear-elastic, then becomes nonlinear and plastic; unloading in the plastic range leaves permanent (residual) strain.

Residual strain

Permanent deformation remaining in concrete after a load applied into the plastic range is removed.

Creep (concrete)

Time-dependent increase in strain under sustained stress, leading to long-term deformations several times the short-term elastic strain.

Thermal shrinkage control procedures

Five measures: use low-cement mix; avoid rapid-hardening, finely ground cement; keep aggregates and water cool; cool steel shuttering with water; strike formwork early to dissipate heat.

Yield point (mild steel)

Stress level where mild steel shows a sudden increase in strain with no increase in load, marking transition from elastic to plastic behaviour.

Stress–strain curve of mild steel

Linear up to yield, then plateaus, followed by rapid strain increase to ultimate stress, showing ductile plastic behaviour.

High-yield steel behaviour

Exhibits a smoother transition without a distinct yield plateau; higher proof stress and smaller plastic deformation than mild steel.

Strain hardening (work hardening)

Increase in steel’s proportional limit and stiffness upon reloading after plastic deformation, as illustrated by the offset unloading–reloading curve.

Manual stress grading (timber)

Process where trained inspectors visually assess defects like knots and splits and stamp pieces as General Structural or Special Structural grades.

Machine stress grading (timber)

Automated method measuring bending stiffness of each piece; machine assigns a strength class (e.g., C14–C30) and stamps accordingly.

Strength class (timber)

Categorisation (e.g., C16, C24, C30) indicating ultimate bending stress in N/mm² for structural design.

Orthotropic material (wood)

Material whose mechanical properties differ along three mutually perpendicular directions: longitudinal, radial, and tangential.

Longitudinal direction (wood)

Axis parallel to grain and tree stem; strongest and stiffest orientation in timber.

Radial direction (wood)

Axis perpendicular to growth rings, from the centre of the tree outward; intermediate mechanical properties.

Tangential direction (wood)

Axis tangent to growth rings; generally weakest and most dimensionally unstable direction in wood.

Advantages of reinforced concrete

Can be cast into any shape, uses widely available materials, offers durability, water-tightness, low maintenance, fire resistance, design flexibility, and strength increases with age.

Disadvantages of reinforced concrete

Members cannot easily be altered once cast, require strict quality control, and have high self-weight compared with steel or timber.

Durability factors for reinforced concrete

Four key influences: exposure conditions, concrete quality, cover to reinforcement, and width of cracks.

Exposure conditions

Environmental actions (soil, seawater, chemicals, atmosphere) that determine concrete type and minimum cover needed for durability.

Cover to reinforcement

Thickness of concrete between steel and surface; essential barrier preventing corrosive agents reaching steel through cracks or pores.

Characteristics of creep

(1) Final deformation ≈3–4 × elastic strain; (2) roughly proportional to stress and inversely to concrete strength; (3) only elastic part recovers upon unloading; (4) causes internal stress redistribution between concrete and steel.

Creep rate

Slope of the time–deformation curve representing the speed at which creep strain accumulates under constant stress.

Quality properties of plastics

Include abrasion resistance, adhesiveness, dimensional stability, ductility, high impact strength, low moisture uptake, chemical and weather resistance, toughness, transparency, lightness, formability, and corrosion resistance.

Abrasion resistance (plastics)

Ability of a plastic material to withstand surface wear caused by friction or rubbing without significant loss of mass or appearance.