MAT2600 - Non Metals

What is masonry?

Masonry is a built-up construction of building units bonded together with or without mortar or grout.

List some advantages of masonry

Can use locally available stones or local clay to make bricks.

Tends to give high thermal mass.

Usually durable and has high fire resistance.

List some disadvantages of masonry

Requires manual labor, hard to mechanize.

Difficult to make very tall structures.

Heavy – needs thick & strong foundations.

Tensile strength is very limited.

Compressive strength of bricks can be a limitation.

Major disadvantage is seismic resistance; unreinforced masonry has little resistance to shearing forces in an earthquake.

How are bricks made?

Bricks are made from baked clay at a temperature of 900-1000°C. Iron in clay gives the red color to most bricks, with the actual color depending on the firing temperature

What are the typical compressive strengths and water absorption rates of bricks?

Bricks have a compressive strength of 20-40 up to 100 MPa, and average bricks have about 20-30% water absorption (lower is better)

What is mortar made of and what is its crucial role?

Mortar is made of cement, sand, and water and is used to bind bricks. Adhesion of mortar onto brick faces is crucial, and it is often the weakest point under shear load.

Describe the general process of brick production, including different types of bricks.

Sand is used for dimensional stability, and some water is needed for effective molding. Organic matter and lime are also added to accelerate firing.
Soft mud bricks: Have more water (~25-30%).

• Dry press bricks: Have less water (~8%) and are more expensive but give a better quality product.

• Extruded bricks: (~12% water) are cut by wires from a column of clay and are becoming cheaper and more popular.

What is brickwork efflorescence?

Brickwork efflorescence occurs when moisture travels through masonry and evaporates, depositing salts on surfaces. It is generally an aesthetic issue rather than a structural problem.

What is glass?

Glass is a solid material lacking long-range chemical order, usually made by supercooling a liquid.

How does the cooling rate affect the formation of crystal versus glass from a silicate melt?

Very slow cooling (equilibrium) of a silicate melt leads to a crystal, while faster cooling (non-equilibrium) leads to glass.

What is the composition of the majority of glass used in structures?

The majority of glass used in structures is soda-lime-silicate (Na2O-CaO-SiO2), which is common window glass. Its composition is typically 70% SiO2, ~15% NaO, and 10% CaO, MgO.

Explain the "Float glass process

In the float glass process, molten glass floats on liquid tin. It is processed at 1050-1200°C, and the liquid bath gives a very flat surface.

Why is real engineering glass much weaker than theoretical flawless glass?

The strength of real engineering glass is governed by the size of the largest flaw, making it very weak in tension

What is static fatigue in glass?

Static fatigue is when water attacks chemical bonds in cracks, making glass weaker under long-term loading.

How is toughened (engineered) glass made, and what are its properties?

Toughened glass is made by heating a sheet of glass above its glass transition temperature, then rapidly quenching its surfaces. This puts the surfaces into compression and the center into tension, strengthening the surface. To break toughened glass, a crack needs to get through the surface region into the core. Fracture leaves cubic fragments due to stored strain energy.

What is laminated glass and how does it provide safety?

Laminated glass consists of a polymer film (most commonly polyvinyl-butyral) sandwiched between two glass sheets. The film is rolled on and heated to exclude air and bond to the glass. It protects surfaces and holds broken fragments if fracture occurs, resulting in a spider-pattern of cracks. It is used in car windscreens and other places where people might be exposed to breakages

What is bullet-proof glass?

Bullet-proof glass is a multilayer tempered glass/polycarbonate laminate, or multilayers of laminated glass, typically 20-75 mm thick. It requires careful matching of the optical properties of the two materials, and the polymer layers are much more elastic than glass.

Explain multiple glazed glass and its purpose.

Multiple glazed glass involves double or triple glazing with 2 or 3 sheets of glass in a sealed unit, with a gas layer (sometimes vacuum) in between. Desiccants are sometimes used in the gas space. Each interface provides resistance to heat transfer

What are some considerations for multiple glazed glass to prevent issues?

• Need very similar thickness glass inside & outside to prevent shearing.

• Temperature mismatch between inside and outside can cause cracking.

• Dimensional changes in units can break seals around unit edges, allowing moisture in and causing fog or mold.

What is Portland cement?

Portland cement is a material that binds solid bodies (aggregate) together by hardening from a plastic state.

It functions by forming a plastic paste when mixed with water, which then develops rigidity and steadily increases in compressive strength due to a chemical reaction with water.

What are the main raw materials for Portland cement production?

Clay (e.g., Al2O3, SiO2, Fe2O3) and limestone (CaCO3).

List the major clinker phases in Portland cement and their approximate percentages.

• Tricalcium silicate (alite), C3S: 50%

• Dicalcium silicate (belite), C2S: 25%

• Tricalcium aluminate, C3A: 12%

• Tetracalcium aluminoferrite, C4AF: 8%

• Gypsum, CaSO4.2H2O: 3.5%

Briefly describe the hydration process of C3S (Alite) and β-C2S (Belite).

Both C3S (Alite) and β-C2S (Belite) hydrate to form calcium silicate hydrate (C-S-H gel) and Portlandite (CH).

C3S hardens rapidly and develops high strength, while β-C2S hardens slowly and develops high strength.

C-S-H gel makes up ~70wt% of a fully hydrated paste and contributes to the majority of strength.

What is Portlandite (CH) and its role in hydrated cement paste?

Portlandite (CH, Ca(OH)2) is a byproduct of C3S and C2S hydration.

It makes up ~20wt% of a fully hydrated paste and does not contribute to strength directly, but forms large crystallites and keeps the internal pH high, which helps durability.

Explain the reaction of C3A (Aluminate) with water and the role of gypsum.

Direct reaction of C3A with water leads to a "flash set" (stiffening without strength development) by forming aluminate hydrates.

With the addition of gypsum (CaSO4.2H2O), C3A reacts moderately to form ettringite (AFt), which helps control initial setting.

What are Supplementary Cementitious Materials (SCMs)?

SCMs are mineral components added to improve performance or reduce cost.

They are blended with cement and react to alter the properties of the binder.

Aggregates and organic admixtures are not SCMs.

Many SCMs are pozzolans, and they are often waste materials, making them cheap and low in CO2.

What is a pozzolanic reaction and its impact on concrete properties?

In pozzolanic reactions, SiO2 components (with or without Al2O3) in SCMs react with CH (Portlandite) in hydrated cement to form more C-S-H.

This new C-S-H fills pore spaces at longer ages, refining pores and improving strength and durability.

Pozzolanic reactions are generally slower than cement hydration, so substituting cement with pozzolans usually reduces early strength, but blended cements give better long-term properties and improved chemical durability

Define cement paste, mortar, and concrete.

• Cement paste: Cement + water only (grout).

• Mortar: Cement + fine aggregate (<5 mm, usually sand) + water.

• Concrete: Cement + fine aggregate + course aggregate + water.

What is the role of aggregates in concrete strength and integrity?

Aggregates are inert additives bound together with cement. In terms of strength, concrete cannot be stronger than the aggregate, as it fails at its weakest point, hence good quality, clean, strong aggregates are needed. Clay contamination can have a negative effect.

For integrity, aggregates help reduce thermal cracking by diluting the cement.

What are the two main roles of water in concrete?

Water is required in cement hydration reactions and makes concrete flow (increased slump).

What are the negative effects of too much water in concrete?

Too much water delays setting/hardening, forms extra pores, and leads to a reduction in durability (more permeable) and strength.

What is plastic shrinkage cracking in concrete?

Plastic shrinkage cracking occurs when rapid water evaporation from the surface causes the paste to shrink, and water bleeds to the surface.

Evaporation later also causes drying shrinkage cracks. Aggregate particles stay in place and prevent the shrinkage that causes cracking/crazing.

What is plastic settlement in concrete?

Plastic settlement occurs when solid aggregate particles sink through the paste, leaving water pockets under aggregates and reinforcing bars, and cracks on the surface.

These cracks can extend to the reinforcing bars, which is detrimental to durability as the steel corrodes quickly.

How does the water-cement ratio affect concrete strength?

More water means more porosity, and more porosity results in less strength. Compressive strength decreases as the water-cement ratio increases. Normal water-cement ratios are around 0.5.

Describe Magnesium oxychloride cement as an alternative binder.

Magnesium oxychloride cement combines MgO with MgCl2 and H2O. Its main binder phase is 5Mg(OH)2+MgCl2+8H2O.

It has very high early strength (>70 MPa after 3-7 days) but is sensitive to water.

Describe Alkali-activated (geopolymer) cements as alternative binders.

Alkali-activated (geopolymer) cements use aluminosilicate materials + an alkaline solution ("activator").

They can utilize blast furnace slag or pozzolans and produce ~60-90% less CO2 emissions than Portland cement. The main drawback is the need for an alkaline solution.

What is Bitumen/Tar and how is it used in construction?

Bitumen/Tar is a mixture of heavy organic molecules, solid at room temperature, and can be produced in petroleum refineries.

It is used to bind stones/gravel together into a solid hardened material (asphalt/concrete), mostly for roads.

It is not technically a cement but a binder, and heat (or chemical solvents) are used to soften and make it flowable/workable.

Why is concrete reinforced with steel?

Concrete is strong in compression but weak in tension.

Steel is very good in tension and is used to reinforce concrete for structural applications. Almost all structural concrete is reinforced.

How does cement chemistry help prevent steel rusting in reinforced concrete?

The chemistry of cement usually stops steel rusting.

Mild steel is used, and its resistance to corrosion (passivation chemistry) works better for mild steel, relying on forming an oxide layer on the surface.

How is steel reinforcement typically integrated into concrete?

Steel reinforcing bars are ribbed for better bond to concrete and are used in either a mesh or cage structure.

Reinforcement is usually 3-5% of the cross-sectional area.

Concrete must flow through the gaps to properly compact.

Explain the concepts of pre-tensioning and post-tensioning in concrete.

• Pre-tensioned: Steel cables are stretched, and concrete is poured around them. The tension is then released, compressing the concrete. This relies on interfacial bond to steel.

• Post-tensioned: Concrete is poured with a duct, and then cables are inserted and tensioned after the concrete hardens. Post-tensioning can have severe problems if the steel corrodes and stress application is lost.

What is the main cause of concrete failure related to reinforcement?

The main cause of concrete failure is steel failure. When steel rusts, it expands and cracks the concrete. This is often due to the ingress of corrosive species into porous concrete.

How does passivation protect steel in concrete, and what can cause its breakdown?

Iron oxides form a passive film on the steel in concrete, protecting it from corrosion.

Breakdown of this film leads to iron corrosion.

Examples of breakdown include a drop in pH in the pore solution (e.g., carbonation) or expansion of the corrosion region (e.g., ingress of chloride ions).

How can corrosion be prevented in reinforced concrete?

Corrosion can be prevented by reducing permeability. Permeability depends on porosity, which in turn depends on water content.

Therefore, reducing the water/concrete ratio is key.

What is the difference between an extrinsic and intrinsic property? Provide examples.

• Extrinsic property: Dependent on sample size (e.g., mass, volume). Strength is an extrinsic property, thus specification is crucial.

• Intrinsic property: Independent of sample size (e.g., melting temperature, density).

How is mortar testing used to assess cement strength?

A hardened cement paste tends to give variable results in strength tests. To obtain cement strength information, a standard mortar is defined for use.

Mortar prisms (160x40x40mm) are broken in 3-point flexion, and then each end is tested as a pseudo-cube.

Why is concrete rarely tested in direct tension?

Concrete is very rarely tested in direct tension. More often, tensile or 3-point bending strengths are used.

These tests are sensitive to specimen geometry, size, and loading rate.

Bending tests give strengths ~40-80% higher than splitting tensile, so results cannot be compared directly.

How are mechanical properties of concrete often expressed to save on tests?

To save on the number of tests, mechanical properties are often expressed using the 28-day compressive strength, called fc or sc,28, or its mean value (fcm).

What is creep testing in concrete, and what causes it?

Creep testing involves stressing a material at a load well below failure for a long time, which will cause changes in size, more so at high temperatures.

Concrete creep is mainly caused by C-S-H nano-granules in the microstructure sliding over each other and becoming compressed/deformed under load.

What are non-destructive testing (NDT) methods in concrete? Provide examples.

Non-destructive testing does not require breaking a sample and is useful for structural components of a building in service

• Electrochemical testing

• Radiographic or radar-based methods (covermeter).

• Schmidt (rebound) hammer

• Windsor (penetration) probe

• Pullout test

• Ultrasonic pulse velocity

What is Electrochemical testing used for?

To check the condition of reinforcing steel (detect corrosion currents).

What is Radiographic or radar-based methods (covermeter) used for?

To identify the location of reinforcement, the condition of the cover concrete, or large cracks, and air or water permeability.

What is Schmidt (rebound) hammer used for

Measures how much a hammer bounces off the surface.

What is Windsor (penetration) probe used for

Measures how far a projectile can penetrate into the surface.

What is Pullout test used for

Measures how difficult it is to pull out a bolt screwed into a drilled hole.

What is Ultrasonic pulse velocity used for

Measures how well the microstructure of the material transmits ultrasound.

What is chloride attack, and how does it affect concrete service life?

Chloride attack involves chloride permeability, which is a key factor limiting concrete service life.

Chloride exposure does not directly affect the binder but causes steel to rust.

This is problematic in cold climates where salts are used for de-icing, and in marine conditions.

How can chloride attack be prevented in concrete?

Chloride attack can be prevented by reducing permeability through a dense binder, low water/cement ratio, lots of C-S-H, and a refined pore structure (small, tortuous pores).

Pozzolanic reactions also help in the long term by producing more C-S-H from portlandite and by extra AFm phases, which helps to fill pores and bind chlorides.

Describe the Ponding test for chloride permeability.

The ponding test involves placing a concrete cylinder or slab with a pool of NaCl on top and waiting for several months.

The distance the chloride has traveled through the concrete can then be used to calculate the diffusion coefficient.

It is simple and accurate but very slow and labor-intensive.

Describe the rapid chloride permeability test.

In the rapid chloride permeability test, a voltage is applied to a sample, and the current passing through it is correlated to chloride diffusion over 6 hours.

While fast, the charge passed depends on multiple factors (e.g., chloride ions and other dissolved ions in the pore solution), so it cannot be used to compare materials with different chemistry, but it is useful for quality control of one material.

Describe the hybrid method for chloride permeability testing.

The hybrid method uses electrical acceleration of chloride migration but involves splitting the sample and measuring the actual chloride depth at the end of the test.

This offers the advantage of a 24-hour testing time without dealing with the material's resistivity, allowing for comparison of different cement types and providing more reproducible results.

What are the two main reaction pathways for sulphate attacks on concrete?

• Internal sulphate attack: Sulphate present within the concrete causes phase evolution after a long period.

• External sulphate attack (more common): Sulphate from the environment enters the material and causes phase changes. AFm to AFt conversion is a key mechanism, and C-S-H can also be impacted.

What is Thaumasite sulphate attack, and what conditions are required for it?

Thaumasite sulphate attack requires cool (4-10 degrees), wet conditions with both carbonate and sulphate. In this attack, C-S-H is converted to thaumasite, which results in no strength at all, making the concrete soft and mushy.

How is sulphate resistance typically tested?

Sulphate resistance is tested by immersing concrete in a sulphate-rich solution (usually 5 wt.% Na2SO4) and regularly measuring the specimen length.

This tests for the conversion of AFm to AFt phases, which explains some expansion, though not all.

Crystallization of sulphate salts can also cause additional physical damage.

How can sulphate resistant cement be formulated?

Sulphate resistant cement typically has low C3A content or high slag content.

This favors the formation of C-S-H rather than AFm phases during hydration, thus preventing expansion.

High slag content also reduces permeability in the long term.

What is the alkali-aggregate reaction in concrete?

The alkali-aggregate reaction occurs when aggregate contains reactive components (e.g., glassy opal), which are attacked by the pore solution.

Portland cement contains small quantities of alkalis (Na and K) that stay in the pore solution, leading to the formation of an expansive white silicate gel product and characteristic map-cracking on the surface.

Describe the UK approach (BRE Digest 330) to alkali-aggregate testing.

The UK approach sets limits on the alkali content of concrete based on aggregate reactivity classification (low/normal/high).

If uncertain, a concrete prism test of 12 months duration can be used. Most cements sold in the UK are low-alkali; if not, the concrete alkali content needs to be calculated.

Blending with slag or pozzolans helps protect against damage.

What is the accelerated-aggregate testing method for alkali-aggregate reaction, and what are its pros and cons?

This method involves placing mortar bars in 40 g/L NaOH at 80°C and measuring expansion at 16 days.

The high alkali concentration means the alkalis in the cement are negligible.

While fast and widely used (advantages), it is well known to give false positives due to being an extremely aggressive test (disadvantages).

What is carbonation in concrete, and how does it affect the material?

Carbonation occurs when atmospheric CO2 acts as an acid, reacting with Ca(OH)2 to form CaCO3 and water (Ca(OH)2 + CO2 → CaCO3 + H2O).

This reduces the pH of the cement, which can induce corrosion of the steel reinforcing.

It happens fastest at intermediate humidity (~65%) or under wet-dry cycling.

It is the main limitation on concrete service life in warm climates without marine exposure.

In extreme cases, carbonation can also show damage (decalcification) in C-S-H phases.

How is carbonation measured, and what are the challenges in predicting performance?

Carbonation is measured by the depth of CO2 ingress after exposure to CO2 (often at an elevated concentration), which is then scaled to predict performance in natural conditions.

Ingress under natural conditions is slow (~mm/yr), so an accelerated test is used.

The color change of phenolphthalein corresponds well to danger levels for alkalinity in concrete leading to steel corrosion.

Obstacles to CO2 capture in concrete by carbonation include its slow rate and the fact that carbonation leads to degradation of reinforced concrete.

What is freeze-thaw damage in concrete, and what causes it?

Freeze-thaw damage is degradation based on the ingress of water. When water freezes, it expands ~9%, and salts worsen this (leading to larger volume changes).

How is freeze-thaw damage tested?

Freeze-thaw testing typically involves subjecting concrete cylinders or slabs to repeated freeze-thaw cycles (e.g., +4/-18°C every 4 hours, or +20/-18°C every 24 hours) for tens to hundreds of cycles.

Changes in elastic modulus, dimensions, and mass (material scaled from surface) are measured.

Sometimes, a visual rating of damage is given.

How can freeze-thaw damage be prevented in concrete?

Freeze-thaw damage can be prevented by air entrapment, which involves putting appropriately sized bubbles (<1 mm, a percentage by volume, well spaced) into the concrete.

These bubbles provide space for the water to expand into as it freezes.

What is the purpose of a standard?

A standard sets out an agreed way of doing something, whether making a product, following a process, delivering a service, or supplying materials.

Standards can cover a wide range of activities and come in many forms, including guides, codes of practice, specifications, and supporting documents.

Differentiate between prescriptive standards and performance-based standards.

• Prescriptive standards: Specify the allowable ingredients and recipes. If a material is made as specified, it is assumed to be acceptable for use, and safety margins are built in to be conservative.

• Performance-based standards: Define what a material needs to do (strength, durability, etc.), including how to test (setting criteria for pass/fail). They allow producers to design a material to meet these requirements (including conservative safety margins), offering more scope for innovation but requiring more work to prove sufficient performance.

Provide an example of a case study where strength is not the primary requirement for a material.

In the case of radioactive waste immobilization for the nuclear industry in the UK, only 0.7 MPa at 28 days is required for strength, but many other requirements are crucial, such as dissolution rate (e.g., for 137Cs).

What is ASTM C150?

ASTM C150 is a prescriptive standard for cement composition that defines clinker characteristics in detail. This contrasts with the BS EN approach, where clinker composition is barely described beyond it being Portland cement clinker.

What are the five main categories of cement under British & European Standard BS EN 197-1?

• CEM I Portland cement (>95% Portland clinker).

• CEM II Portland-composite cement (65-94% Portland + 1 pozz./limestone).

• CEM III Blastfurnace cement (5-64% Portland + slag).

• CEM IV Pozzolanic cement (45-89% Portland + 1 pozz.).

• CEM V Composite cement (20-64% Portland + slag + 1 other SCM)

What are the benefits of using fibers in concrete?

Using fibers (mineral, steel, polymer) in concrete instead of conventional reinforcement offers benefits such as crack bridging, reduced plastic shrinkage/cracking, and improved flexural strength.

What is Ultra High Performance Concrete (UHPC)?

UHPC has a compressive strength greater than 120 MPa (up to 800 MPa), high durability, and impermeability. It has an extremely low water/cement ratio (<0.2) and typically uses small aggregates, often with fiber reinforcement. It usually has a high SCM content and very high cementitious materials per m³ of concrete.

What is self-healing concrete?

Self-healing concrete uses bacteria or other methods to seal cracks with newly-formed CaCO3, capable of sealing cracks up to ~0.5 mm in width

How does the concrete industry contribute to recycling and waste valorization?

Both blended Portland cements and alternative cements utilize industrial by-products. The concrete industry is a net consumer of solid wastes (industrial and societal).