Masonry and Glass Flashcards
Define Masonry:
A built-up construction or combination of building units or materials of clay, shale, concrete, glass, gypsum, stone or other approved units bonded together with or without mortar or grout or other accepted method of joining.
Name advantages and disadvantages of masonry:
Advantages:
- Can use locally available stone/ clay to make bricks
- Tends to give high thermal mass.
- usually durable
- Usually high fire resistance
Disadvantages:
- Requires manual labour, hard to mechanise.
- Difficult to make tall structures
- heavy so needs thick foundations
- tensile/flexural strength is limited
- Compressive strength can also be a limitation.
- The main disadvantage is bad at shear in an earthquake.
Describe what Dry stone is:
Dry stone:
- the oldest form of construction
- durable
- interlocking stones
- skilled craftsmen
- filled with soil to block wind and insulate.
Describe what Brickwork is:
- Made from baked clay (900-1000 C)
- colour depends on firing temp
- Standard size differ
- Compressive strength up to 100 MPa but usually 20-40 MPa.
- Can’t build too high or bricks will crush
- Albi Cathedral tallest at 78m
- Monadnock (66m) has 1.8 m thick walls at the base
What is mortar and what is the standard thickness?
- mortar is a mixture of cement + sand + water and is used to bind the units together.
- standard thickness is 5-10 mm as the mortar is weaker than bricks.
Describe concrete blocks:
- often use fly ash as light and good thermal insulation
- Hollow-core with 20 MPa compressive strength
- larger than a brick
- Precast
How are bricks made?
- Fired clay
- Clay and sand mixed with water, pressed into moulds and heated to 900 - 1000 C
- Adding organic matter like straw accelerated the firing
- Dry pressing is more expensive but better quality
- Extruded bricks are cut by wire and are the cheaper and the most popular
What are the important brick properties?
- Compressive strength (higher the better)
- Water absorption (lower the better)
- Frost resistance (higher the better)
Name a common problem with masonry
Efflorescence:
- moisture travels through masonry and evaporates, depositing salt on the surface.
- to avoid this keep water out of the masonry (damp course)
Define glass:
Solid material lacking long-range chemical order, usually made by supercooling a liquid. Looks like a solid on observable timeframes
What is the ‘Glass transition’ temperature Tg?
- Actual physics of Tg is still a major unanswered question in the world of material science.
- Some properties do show distinct change at a given temp. (500-600 C for soda lime silicate glass/ 1200 C fo SiO2)
what is the most common glass used in structure and how is produced?
Soda-lime-silicate:
- common window glass and jars
- composition 70%SiO2, 15%NaO, 10%CaO, with minor components
Produced by float glass process:
- Glass floats in liquid tin
- liquid glass gives very flat surface.
Properties of glass:
- Extremely brittle: engineering glass isn’t 1% within its predicted strength. could be 14,000 MPa but actually 20-200 MPa
- Weak in tension
- Static fatigue - H2O attack on chemical bonds in cracks make it weaker under long term loading
Is there structural use of glass?
-People do use glass structurally but there are no existing global methodology.
What is toughened glass?
- it is glass that has been toughened. They heat a sheet of glass to above Tg, then quench the surface rapidly.
- this puts the surface into compression and centre in tension.
- to break the glass you need to crack through the surface region.
- fracture leaves cubic fragments due to tored energy
