Masonry

Question 1

What is masonry?

Answer 1

• Any structure made by stacking, piling, bonding discrete pieces to form a whole

Question 2

Bricks and Blocks 1 = Fired Clay

Answer 2

• Made from moist clay
• Pressed into shape
• Fired at 850-1300 degrees C

Question 3

Bricks and Blocks 2 = Calcium Silicate

Answer 3

• Lime, silica sand and water
• Cured in high pressure steam room for hours
• Lime reacts with sand to bind together - makes precise and smooth bricks

Question 4

Bricks and Blocks 3 = Concrete

Answer 4

• Same ingredients as normal concrete
• Mix compacted in mould by pressing, before moulds instantly removed
• Needs to support own weight almost instantly after casting
• Less water, cement and fine aggregate than normal mix
• Steam curing accelerates strength gain

Question 5

Bricks and Blocks 4 = Natural Stone

Answer 5

• Rough irregular shapes
• Considered good for environment but only is if local stone

Question 6

Durability Affectors

Answer 6

• Staining (efflorescence, iron and bio)
• Chemical attack (rain, carbonation, sulphate and corrosion)
• Erosion (frost, crypto-efflorescence and abrasion)

Question 7

Staining 1 = Efflorescence

Answer 7

• Soluble salts disolved by water and crystalize on brick surface
• Salts in clay, ground water and mortar
• White stain on brickwork

Question 8

Staining 2 = Iron

Answer 8

• Orange/brown stains
• Iron in bricks and mortar (if well distributed won’t cause a problem)

Question 9

Staining 3 = Biological

Answer 9

• Growth of moss or fungi
• ONLY in wet conditions

Question 10

Chemical Attack 1 = Rainwater

Answer 10

• Pure water has no effect but Co2 in rainwater means it is slightly acidic so it reacts with calicum carbonate present in brickworks
• Acid rain near high pollution areas increases rate

Question 11

Chemical Attack 2 = Carbonation

Answer 11

• Calcium hydroxide from lime or cement combines with Co2 in air to make cal carb
• Carbonated mortar isn’t an alkaline now and has less protection

Question 12

Chemical Attack 3 = Sulphate

Answer 12

• Diffuse into concrete and reacts with concrete’s calcium
• Can cause expansion, cracking and loss of strength
• From sea water, soils or interal sulphates
• To resist = lower cal content, low WC ration (more cement) or cement replacement materials

Question 13

Chemical Attack 4 = Corrosion

Answer 13

• Other processes accelerate it
• Calcium hydroxide reacts with CO2 over time - carbonation reduced pH to near 9 - passivity of steel is destroyed (protection is destroyed)
• Protect steel to avoid corrosion

Question 14

Erosion 1 = Frost

Answer 14

• Bricks and mortar are affected
• Due to expansion when water freezes

Question 15

Erosion 2 = Crypto-efflorescence

Answer 15

• Same process as efflorescence
• Under some temps/humidity salts crystalise below brick surface

Question 16

Mortar used to bond masonry

Answer 16

• Cement, sand and water
• Bricks can absorb water and this depends on the amount of water that is needed in morta

Question 17

Modern masonry

Answer 17

• Single skin of bricks in stretcher bond pattern with inner skin of concrete blocks to provide reinforcement

Question 18

Compressive loading (top/bottom)

Answer 18

• Strongest resistance (load baring walls, tunnels)
• Test individual units
• Cracks form in mortar joins
• Depends more on masonry strenght not the mortar

Question 19

Compressive loading (sides)

Answer 19

• Lower resistance as in line with the mortar

Question 20

Sheer loading

Answer 20

• One side pushing top, other at bottom
• Caused by wind/impact

Question 21

Flexural loading (either side and middle)

Answer 21

• Aka bending
• Either snaps straight through mortar and bricks or zig zags down through mortar