Material Processing and Property Modification

Introduction

A material’s performance is determined not only by its chemical composition but also by the way it is processed. Two components made from the same alloy, polymer, ceramic, or composite can exhibit very different strength, toughness, dimensional stability, durability, and appearance because their processing histories differ. Processing controls grain size, porosity, phase distribution, molecular orientation, fibre alignment, residual stress, moisture content, and interfacial bonding. These microstructural features, in turn, control macroscopic properties.

For construction technologists, this relationship is fundamental. Reinforcing steel is strengthened by controlled rolling and heat treatment; concrete develops strength through hydration and curing; bricks acquire their properties through drying and firing; polymer pipes are shaped by extrusion; and fibre-reinforced panels are produced by carefully controlling resin impregnation and consolidation. A sound understanding of processing helps professionals select materials, interpret failures, specify manufacturing requirements, and evaluate quality.

Learning Objectives

By the end of this chapter, the reader should be able to:

1. Explain how processing affects microstructure and engineering properties.
2. Describe the principles, advantages, and limitations of casting, forming, machining, sintering, and additive manufacturing.
3. Explain heat treatment of metals and curing of cementitious, polymeric, and composite materials.
4. Compare major polymer-processing and composite-fabrication methods.
5. Select suitable processes for construction products and identify likely defects.
6. Relate processing variables to strength, toughness, durability, dimensional accuracy, and sustainability.

1. The Processing–Structure–Property Relationship

Material engineering is often expressed as a chain:

Processing → microstructure → properties → performance

Processing includes heating, cooling, deformation, chemical reaction, mixing, consolidation, cutting, and surface treatment. Microstructure includes grain size, phase distribution, pores, cracks, inclusions, molecular orientation, fibre arrangement, and interfaces. Properties include density, yield strength, elastic modulus, thermal conductivity, permeability, hardness, fracture toughness, and resistance to weathering.

For example, rapid cooling of a steel may produce a fine-grained or martensitic structure and high hardness, but it may also generate distortion and cracking. Slow cooling may produce a softer, more ductile structure. In concrete, insufficient curing leaves unhydrated cement and connected capillary pores, reducing strength and increasing permeability. In a polymer, stretching during extrusion can orient molecules, increasing strength in one direction while reducing dimensional uniformity in another.

Important processing variables include:

• temperature and heating or cooling rate;
• pressure, strain, and strain rate;
• time and residence time;
• composition, moisture, and atmosphere;
• tool geometry and surface condition;
• mixing quality and material cleanliness; and
• post-processing such as curing, annealing, drying, or coating.

A process should therefore be specified by more than its name. “Heat-treated steel,” for example, is incomplete unless the heating temperature, holding time, cooling medium, and final condition are known.

2. Casting

Casting produces a component by pouring or injecting a liquid material into a mould, allowing it to solidify, and removing the mould or casting. It is suitable for complex shapes, large sections, and materials that are difficult to deform plastically. Cast iron drainage components, aluminium window fittings, steel machine bases, concrete units, and polymer products are common examples.

2.1 Solidification and microstructure

When a liquid cools below its equilibrium freezing temperature, nuclei form and grow into crystals. The resulting grains commonly have dendritic shapes. Cooling conditions strongly influence grain size and segregation. Rapid cooling generally produces finer grains, whereas slow cooling permits larger grains. Fine grains often improve strength and toughness, although the effect depends on alloy and phase structure.

As solidification proceeds, solute elements may be rejected into the remaining liquid. This can produce chemical segregation between dendrite arms or between the centre and surface of a casting. Segregation may cause local variation in hardness, corrosion resistance, or weldability.

Shrinkage occurs because most materials occupy less volume as they cool from liquid to solid and then to room temperature. Risers, feeders, directional solidification, and suitable mould design are used to compensate for this contraction. Gas porosity results when dissolved gases come out of solution or when air is trapped. Hot tears occur when a partly solidified casting is unable to contract freely.

2.2 Major casting processes

Sand casting uses expendable sand moulds and is economical for large or low-volume components. It offers broad material and size flexibility but usually gives a rougher surface and lower dimensional accuracy than permanent mould processes.

Die casting forces molten non-ferrous alloy into a metallic mould under pressure. It produces thin sections, good surface finish, and high production rates, but tooling costs are high and the process is generally unsuitable for very high-melting-point alloys.

Investment casting uses a disposable wax or polymer pattern surrounded by ceramic material. It can reproduce intricate geometry and fine detail, although preparation is relatively expensive.

Continuous casting produces long products such as slabs, billets, and blooms. Controlled cooling and withdrawal create a continuous solidification process used extensively in steel manufacture.

2.3 Casting quality control

Important controls include melt temperature, mould moisture, pouring rate, cleanliness, venting, feeding, and inspection. Radiography, ultrasonic testing, dye penetrant testing, and dimensional inspection may be used to identify internal or surface defects. Sound design avoids abrupt section changes, isolated heavy masses, and sharp internal corners because these promote hot spots and stress concentration.

3. Forming and Deformation Processing

Forming changes shape by applying stress, usually without removing material. Metal forming includes rolling, forging, extrusion, and drawing. Sheet forming includes bending, deep drawing, and stamping. Ceramic forming includes pressing and extrusion, while concrete products may be compacted by vibration or pressing.

3.1 Plastic deformation

A material deforms plastically when applied stress exceeds its yield condition. In crystalline metals, plasticity occurs mainly through dislocation motion. Cold working increases dislocation density, which makes further movement more difficult. This phenomenon, called strain hardening, raises strength and hardness but lowers ductility.

The engineering strain in a tensile operation is commonly written as:

where ε is engineering strain (dimensionless), L₀ is original gauge length, and L is final gauge length. This expression is appropriate for small-to-moderate deformation when engineering measures are being used. For very large deformation, true strain is more suitable:

Here ln denotes the natural logarithm. True strain is additive for successive deformation steps under uniform deformation.

3.2 Rolling, forging, extrusion, and drawing

Rolling passes material between rotating rolls to reduce thickness or produce a cross-sectional profile. It can refine grains and produce directional properties. Forging compresses material between dies. It often improves toughness because voids may close and the grain flow follows the component shape. Extrusion forces a billet through a die, producing constant cross-sections such as aluminium frames, polymer pipes, and metal channels. Drawing pulls material through a die, reducing cross-sectional area and increasing dimensional accuracy.

Cold forming provides excellent accuracy and surface finish but increases residual stress and work hardening. Hot forming reduces forming forces and permits large shape changes because recovery and recrystallization occur during processing. However, oxidation, scale formation, lower dimensional accuracy, and thermal gradients can be disadvantages.

3.3 Forming defects

Typical defects include folds, laps, surface cracking, internal bursts, wrinkling, springback, and uneven thickness. Springback occurs because elastic strain is released after the load is removed. It is controlled through die compensation, process calibration, and suitable material selection. Lubrication reduces friction, tool wear, and surface damage.

4. Machining and Surface Modification

Machining removes material with a cutting tool to achieve specified dimensions, tolerances, and surface finish. Turning, milling, drilling, sawing, grinding, and computer numerical control (CNC) machining are widely used for steel connections, formwork components, construction machinery, and precision fittings.

The cutting process generates a primary deformation zone in which the chip forms, a secondary zone at the tool–chip interface, and sometimes a tertiary zone at the finished surface. Heat is generated by plastic deformation and friction. Excessive temperature may soften the workpiece, damage coatings, accelerate tool wear, or produce residual tensile stress.

A simplified material-removal rate for a turning operation is:

where MRR is material-removal rate (mm³/min when dimensions are in mm and speed is in rev/min), D is workpiece diameter (mm), N is rotational speed (rev/min), and f is feed per revolution (mm/rev). This expression assumes a cylindrical turning operation and approximates the volume swept by the feed per revolution; it does not by itself account for cutting depth, tool geometry, interrupted cutting, or machine limitations.

Surface integrity includes roughness, residual stress, work hardening, microcracks, and altered metallurgical layers. Grinding can produce a fine finish but may cause grinding burns if heat is not controlled. Coolants can lower temperature and flush chips, but their environmental, health, and disposal impacts must be managed.

5. Sintering and Powder Processing

Powder processing is used for ceramics, cemented carbides, powdered metals, and some advanced construction products. The general sequence is powder production, blending, compaction, removal of binders where necessary, sintering, and finishing.

During sintering, particles bond by diffusion at a temperature below the material’s melting point. Neck regions grow between particles, pores shrink, and strength increases. Densification is affected by particle size, particle shape, packing, temperature, time, atmosphere, pressure, and additives.

The theoretical density of a material mixture can be compared with its measured bulk density using relative density:

where ρ_bulk and ρ_theoretical have the same units, commonly kg/m³. Porosity, expressed as a fraction when the solid and pore volumes are known, may be approximated by:

This relationship assumes that the theoretical density represents a fully dense material of the same composition and that open and closed pores are both reflected in the bulk-density measurement.

Sintering can produce near-net-shape components and controlled compositions, but shrinkage must be predicted. Non-uniform packing or temperature causes differential shrinkage, warping, or cracking. In ceramic tiles and refractory products, drying before firing is equally important because rapid moisture removal can generate internal pressure and cracks.

6. Heat Treatment of Metals

Heat treatment changes the phase constitution and microstructure of a metal by controlled heating, holding, and cooling. It is especially important for steels and aluminium alloys.

6.1 Annealing, normalizing, quenching, and tempering

Annealing generally involves heating and slow cooling. It reduces hardness, relieves residual stress, improves ductility, and may refine or homogenize microstructure. Normalizing involves heating steel above a transformation range followed by air cooling. It usually produces a finer structure and higher strength than full annealing.

Quenching rapidly cools a steel from an austenitic condition. In suitable compositions, carbon atoms become trapped and martensite forms. Martensite is hard but brittle and highly stressed. Tempering reheats quenched steel to a lower temperature and then cools it, allowing controlled decomposition of martensite. The result is usually a better balance of strength, toughness, and dimensional stability.

Precipitation hardening of aluminium and some other alloys involves solution treatment, quenching, and ageing. Fine precipitates obstruct dislocation motion and increase strength. Over-ageing causes precipitates to coarsen and strength to decline.

6.2 Thermal strain and residual stress

If a material is heated freely, its linear expansion is approximately:

where ΔL is change in length (m), α is the coefficient of linear thermal expansion (K⁻¹), L₀ is original length (m), and ΔT is temperature change (K or °C difference). The equation assumes a uniform temperature, small deformation, and approximately constant α over the temperature interval. If different regions heat or cool at different rates, restrained expansion produces residual stress and possible distortion.

Heat treatment must therefore consider component thickness, furnace uniformity, loading, atmosphere, quench severity, and dimensional tolerances. Decarburization, oxidation, quench cracking, distortion, and insufficient hardness are common problems.

7. Curing and Hydration-Based Processing

Curing is the controlled maintenance of moisture, temperature, and time needed for a material to develop its intended properties. It is essential for concrete, cement mortar, lime products, gypsum systems, coatings, adhesives, and some polymers.

In Portland-cement concrete, water reacts with cement minerals to form hydration products, especially calcium silicate hydrate, which provides much of the binding strength. Hydration is exothermic and depends on temperature and available water. If concrete dries prematurely, hydration stops in near-surface regions, capillary pores remain connected, and shrinkage cracking becomes more likely.

Curing methods include water curing, wet coverings, curing compounds, sealed curing, and controlled steam curing. Steam curing accelerates early strength development in precast products but must be controlled to avoid thermal gradients, delayed ettringite-related problems in susceptible systems, and excessive drying.

A lower water-to-cement ratio generally reduces capillary porosity and increases potential strength, provided the concrete can be properly compacted and cured. However, workability may decline, so water-reducing admixtures are often used instead of adding extra water. Curing is not simply a delay before use; it is a processing stage that determines pore structure, permeability, shrinkage, and durability.

8. Polymer Processing

Polymers are processed above or near their softening or melting range, or by chemical reaction from liquid or partially reacted constituents. Their behaviour depends on molecular weight, crystallinity, branching, cross-link density, plasticizers, fillers, temperature, and deformation rate.

8.1 Extrusion and injection moulding

Extrusion continuously forces polymer melt through a die. It is used for pipes, profiles, sheets, membranes, and insulation. Process variables include melt temperature, screw speed, die design, cooling rate, and draw-down. Excessive temperature can degrade the polymer; insufficient temperature causes poor fusion and high pressure.

Injection moulding fills a closed mould with polymer melt under pressure, followed by packing, cooling, and ejection. It is suitable for high-volume fittings, connectors, and complex components. Shrinkage, weld lines, sink marks, voids, and warpage are controlled through gate location, mould temperature, holding pressure, cooling design, and material drying.

Blow moulding produces hollow items such as tanks and bottles. Rotational moulding forms large hollow components by heating polymer powder in a rotating mould. Compression moulding is common for thermosetting compounds and fibre-reinforced sheet materials.

8.2 Thermoplastics, thermosets, and elastomers

Thermoplastics soften on heating and can generally be reheated and reshaped, although thermal degradation limits repeated processing. Thermosets form permanent cross-linked networks during curing and do not melt reversibly. Elastomers have lightly cross-linked networks that permit large recoverable deformation.

Orientation caused by flow can improve strength in the flow direction but produce anisotropy and shrinkage differences. Additives may improve ultraviolet resistance, flame performance, flexibility, colour, or processing stability. Selection must consider fire behaviour, ageing, chemical exposure, creep, and recycling.

9. Composite Fabrication

A composite combines two or more distinct constituents, usually a matrix and a reinforcement, to obtain a combination of properties not available from either constituent alone. In construction, examples include reinforced concrete, fibre-reinforced polymer bars, glass-fibre panels, carbon-fibre strengthening laminates, wood composites, and asphalt mixtures.

The matrix transfers load, protects the reinforcement, and determines environmental resistance. The reinforcement provides stiffness, strength, crack control, or thermal performance. The interface must transfer stress effectively; weak bonding causes debonding and premature failure.

Major fabrication methods include hand lay-up, spray-up, vacuum infusion, resin-transfer moulding, filament winding, pultrusion, compression moulding, and automated fibre placement. Pultrusion continuously pulls fibres through a resin bath and heated die to create constant cross-sections such as rods and profiles. Vacuum infusion uses pressure difference to draw resin through dry reinforcement, potentially reducing voids compared with uncontrolled hand lay-up.

Fibre orientation strongly affects properties. A unidirectional laminate may be very strong along the fibre direction but relatively weak transverse to it. Voids, resin-rich zones, fibre waviness, poor wet-out, insufficient cure, and delamination are important defects. Quality assurance includes control of fibre volume fraction, resin viscosity, temperature, pressure, cure cycle, and non-destructive inspection.

A simple rule-of-mixtures estimate for longitudinal elastic modulus of a continuous, aligned, well-bonded composite is:

where E_L is longitudinal modulus, V_f and V_m are fibre and matrix volume fractions, and E_f and E_m are their moduli. The volume fractions satisfy V_f + V_m = 1. This is an idealized upper-bound-type relation for loading parallel to continuous fibres; it is not reliable for transverse loading, discontinuous fibres, poor interfaces, or significant voids.

10. Additive Manufacturing

Additive manufacturing builds a component layer by layer from digital geometry. Processes include material extrusion, vat photopolymerization, powder-bed fusion, directed-energy deposition, binder jetting, and material jetting. Construction applications include printed concrete walls, polymer formwork, architectural components, repair material, and digitally fabricated reinforcement or connectors.

The process can reduce waste, enable complex geometry, and support mass customization. However, layer interfaces may be weaker than the bulk material, and properties can be anisotropic. In printed cementitious materials, open time, pumpability, buildability, interlayer bonding, nozzle speed, weather, and curing are critical. A mixture that is fluid enough to pump may be too weak to retain successive layers; a mixture that builds well may clog the nozzle or bond poorly.

Digital fabrication also introduces risks: design-file errors, inadequate process qualification, uncertain long-term durability, worker exposure to powders or chemicals, and unclear responsibility for inspection. Codes and standards are developing, so engineering judgement, traceability, and testing remain essential.

11. Applied Case: Processing a Precast Reinforced-Concrete Façade Panel

Background

A manufacturer produces thin precast reinforced-concrete façade panels containing steel reinforcement and architectural surface details. The panels must achieve dimensional accuracy, adequate early handling strength, low water penetration, and consistent appearance.

Problem

Early production batches show edge chipping, colour variation, small surface voids, and occasional cracking near lifting inserts. Investigation finds that the concrete is highly workable but is being placed with excessive water, vibrated inconsistently, and steam-cured immediately after casting.

Analysis

Extra water increases capillary porosity after evaporation. Poor vibration leaves entrapped air, while excessive vibration may cause segregation. Immediate steam curing creates temperature gradients between the panel surface and interior. The thin geometry also makes the panel sensitive to rapid moisture loss and thermal stress. At lifting points, local stress concentrations combine with insufficient early tensile strength.

Approach and solution

The manufacturer adopts a controlled mix with a lower water-to-cement ratio and a compatible high-range water reducer. Aggregate grading is adjusted to improve packing. Moulds are cleaned and coated consistently. Concrete is placed in measured batches and compacted using a defined vibration procedure. Steam curing begins only after an initial setting period, and the temperature rise and fall are limited to reduce thermal gradients. Lifting inserts are redesigned, and panels are released only after verified early-age strength is achieved.

Inspection includes slump or flow testing, temperature monitoring, dimensional checks, visual inspection, compressive-strength testing, and periodic permeability assessment. Defect records are linked to batch numbers and curing cycles.

Outcome

The revised process reduces voids and colour variation, improves edge quality, and decreases lifting cracks. Although the revised curing cycle lengthens production time slightly, fewer panels require repair and the total manufacturing cost decreases. The key improvement comes not from changing the cement alone but from controlling the entire processing–structure–property chain.

Learning points

1. Workability should be achieved through mix design and admixtures rather than uncontrolled water addition.
2. Compaction and curing are microstructure-forming operations.
3. Early-age strength must be related to the actual handling and lifting stresses.
4. Process records support traceability and continuous improvement.

12. Process Selection, Sustainability, and Professional Practice

Process selection should consider geometry, production volume, material behaviour, tolerance, surface finish, energy use, waste, repairability, and worker safety. Casting may minimize machining waste but require energy-intensive melting. Forming can improve material utilization but may require expensive dies. Additive manufacturing can reduce offcuts but may have high electricity consumption and limited throughput. Polymer and composite recycling is complicated by additives, contamination, and cross-linking.

Professionals should specify accepted materials and processes using recognized standards, inspection plans, and performance requirements. A specification may need to define heat-treatment condition, concrete curing regime, polymer grade, composite fibre orientation, surface preparation, allowable defects, and acceptance tests.

Health and safety controls include guarding of machinery, lockout procedures, ventilation for fumes and dust, safe handling of resins and solvents, protection from molten material, and management of noise and vibration. Environmental management includes responsible use of water, recovery of scrap, control of emissions, safe disposal of curing compounds and coolants, and life-cycle consideration of products.

Artificial intelligence and digital twins can assist process monitoring by identifying patterns in temperature, pressure, vibration, or image data. Such tools do not replace calibrated instruments, material testing, qualified personnel, or accountability. Data quality, cybersecurity, explainability, and validation are necessary before automated decisions influence structural products.

Challenges and Limitations

No processing method is universally superior. Increasing strength may reduce ductility; rapid production may reduce quality margin; lower porosity may increase shrinkage or cost; and highly automated systems may be less flexible for small projects. Laboratory results may not represent field conditions because scale, weather, handling, and operator practice differ. Processing-induced anisotropy and residual stress are often difficult to detect without specialized testing. Sustainable choices also require life-cycle analysis rather than judging a process solely by energy used during manufacture.

Best-Practice Checklist

• Define required performance before selecting a process.
• Identify the microstructural features that control that performance.
• Control temperature, time, pressure, moisture, and atmosphere.
• Design for manufacturability, inspection, repair, and safe handling.
• Validate the process using representative specimens or trial production.
• Record batch conditions and maintain traceability.
• Inspect both the product and the process, not only the final appearance.
• Consider durability, embodied energy, emissions, waste, and end-of-life recovery.

Chapter Summary

Processing is a principal means of modifying material structure and performance. Casting creates shapes through solidification but must control shrinkage, segregation, gas porosity, and feeding. Forming uses plastic deformation and can improve strength, grain flow, and material efficiency, although it may introduce work hardening, springback, and residual stress. Machining provides dimensional accuracy and surface finish but generates heat, waste, and possible surface damage. Powder processing and sintering consolidate particles through diffusion, with density and shrinkage controlled by powder characteristics and thermal cycles.

Heat treatment changes metal phases and residual stresses through controlled heating and cooling. Curing enables hydration, polymerization, or cross-linking and is essential for the development of concrete, coatings, adhesives, and composites. Polymer processing uses melting, flow, moulding, and cooling or chemical reaction; molecular orientation and shrinkage must be controlled. Composite fabrication depends on matrix–reinforcement bonding, fibre orientation, void content, and cure quality. Additive manufacturing offers geometric freedom and customization but raises issues of anisotropy, interlayer bonding, qualification, and regulation.

Effective construction technology links process variables to microstructure, properties, service performance, quality assurance, sustainability, and safety. The most reliable products result from controlled processing rather than composition alone.

Key Terms

Processing–structure–property relationship: The principle that manufacturing conditions create microstructure, which determines properties and performance.

Casting: Producing a component by solidifying liquid material in a mould.

Solidification: Transformation of a liquid into a solid through nucleation and crystal growth.

Segregation: Non-uniform distribution of chemical constituents during solidification.

Riser: A reservoir of liquid material that feeds shrinkage during casting.

Plastic deformation: Permanent deformation after stress exceeds the elastic limit.

Strain hardening: Increase in strength caused by plastic deformation and rising dislocation density.

Machining: Removal of material using a cutting tool.

Surface integrity: The condition of a machined surface, including roughness, residual stress, and altered layers.

Sintering: Bonding and densification of particles by heating below the melting point.

Porosity: The fraction or volume of voids within a material.

Heat treatment: Controlled heating and cooling used to modify a material’s microstructure.

Quenching: Rapid cooling, commonly used to form hard phases in steel.

Tempering: Reheating quenched steel to improve toughness and reduce brittleness.

Curing: Controlled treatment that allows hydration, drying, polymerization, or cross-linking to develop properties.

Thermoplastic: Polymer that softens on heating and can generally be reshaped.

Thermoset: Polymer that forms a permanent cross-linked network during curing.

Composite: Material made from a matrix and a distinct reinforcement.

Additive manufacturing: Layer-by-layer production from digital data.

Residual stress: Internal stress remaining after processing when external loads are removed.

Review Questions

Short Answer Questions

1. How does cooling rate influence the grain structure of a casting?
2. What is strain hardening, and how does it affect strength and ductility?
3. Why is curing essential in concrete production?
4. Distinguish between a thermoplastic and a thermoset.
5. Identify two common defects in composite fabrication and explain their causes.

Long Answer Questions

1. Explain the processing–structure–property relationship using examples from steel, concrete, and polymers.
2. Compare sand casting, die casting, and investment casting in terms of geometry, accuracy, cost, and applications.
3. Describe annealing, normalizing, quenching, and tempering, including the property changes expected from each treatment.
4. Explain the main stages of polymer processing and the causes of shrinkage, warpage, and weld lines.
5. Discuss the advantages, limitations, and quality-control requirements of additive manufacturing for construction products.

Analytical / Application Questions

1. A precast panel has high surface porosity despite having a fluid mix. Analyse the likely processing causes and propose a corrective action plan.
2. A cold-formed steel section meets its strength requirement but cracks during bending. Explain the microstructural and process-related reasons and recommend alternatives.
3. Select a suitable fabrication process for a continuous fibre-reinforced polymer construction profile. Justify your selection using geometry, production volume, fibre orientation, quality, and sustainability criteria.

Multiple Choice Questions with Answers

Question 1

Which processing change generally produces finer grains in a cast metal?

A. Slower cooling

B. Faster cooling

C. Adding uncontrolled water

D. Removing all mould vents

Correct Answer: B. Faster cooling

Question 2

What is the principal effect of cold working on a ductile metal?

A. Lower strength and higher ductility

B. Higher strength and lower ductility

C. Complete removal of residual stress

D. Conversion into a polymer

Correct Answer: B. Higher strength and lower ductility

Question 3

In the turning approximation MRR = πDNf, what does f represent?

A. Feed per revolution

B. Furnace temperature

C. Fracture energy

D. Fibre volume fraction

Correct Answer: A. Feed per revolution

Question 4

Sintering primarily bonds powder particles by:

A. Diffusion at elevated temperature

B. Freezing water inside the pores

C. Mechanical cutting

D. Elastic recovery

Correct Answer: A. Diffusion at elevated temperature

Question 5

Which treatment is normally applied after quenching steel to improve toughness?

A. Tempering

B. Casting

C. Cold drawing only

D. Blow moulding

Correct Answer: A. Tempering

Question 6

What is a major consequence of premature drying of concrete?

A. Reduced capillary porosity in all cases

B. Incomplete hydration and increased permeability

C. Automatic formation of martensite

D. Improved fibre alignment

Correct Answer: B. Incomplete hydration and increased permeability

Question 7

Which process continuously produces polymer pipes or constant-section profiles?

A. Extrusion

B. Investment casting

C. Deep drawing of steel

D. Quenching

Correct Answer: A. Extrusion

Question 8

In a fibre-reinforced composite, the matrix primarily:

A. Transfers load and protects the reinforcement

B. Always provides all of the tensile strength

C. Eliminates the need for an interface

D. Makes fibre orientation irrelevant

Correct Answer: A. Transfers load and protects the reinforcement

Question 9

A common limitation of layer-based additive manufacturing is:

A. Interlayer anisotropy or weak bonding

B. Inability to use digital geometry

C. Requirement that every product be machined from a billet

D. Guaranteed uniform properties in every direction

Correct Answer: A. Interlayer anisotropy or weak bonding

Question 10

If a material is heated freely and α is constant, which equation estimates its linear expansion?

A. ΔL = αL₀ΔT

B. ΔL = L₀/(αΔT)

C. ΔL = α/(L₀ΔT)

D. ΔL = α + L₀ + ΔT

Correct Answer: A. ΔL = αL₀ΔT