G-1 Concrete types, materials, additives and treatments Flashcards
Plain concrete
contained no reinforcing or steel mesh
Reinforced concrete.
concrete is ten times stronger at compression then tension. when concrete needs to resist high levels of torsion steel mesh or cares are imbedded within concrete.
Three fundamental properties that permit concrete to steel
- thermal expansion is equal
- cement paste in concrete bonds strongly to steel
- concrete protects the steel from rust
Thermal expansion
concrete and steel expand at the same rate when they are heated and shrink at the same rate when they are cooled.
Bonding
the bonding between cement paste and reinforcing steel transfers loads from one steel reenforcing bar to the next. the steel bars are overlapped usually 24x the width of the bar
Corrosion
during hydration the cement paste bonds with the steel that protects it from corroding. in underwater concrete steel gets covered with epoxy
Pre stressed concrete
this is when the reinforcing members in the concrete are placed in a state of permanent tension before service loads are applied.
two types of pre stressed concrete
Pre-tension
post tension
Pre tension Concrete reinforcement
high strength steel cables are placed into the formwork for the member and tensioned before the concrete is placed
Post tensioning concrete reinforcement
high strength steel cables are placed in formwork but not tensioned until after the concrete is placed.
Pre-cast Concrete
pre made concrete parts used for construction beams walls stairs floor slabs girders
Concrete shells
a shell is a long continuous beam of curved cross section which combines advantages os trusses, purlins and wind bracing through the interaction of its parts.
common shapes include barrels, domes, hyperbolic paraboloids and folded plates
Concrete masonry
concrete masonry is applied to pre cast block and brick building units moulded of concrete and used in masonry construction.
products are made of materials that comply with local building codes.
Concrete pipes
used for irrigation, drainage , sewer , culverts water supply
Concrete paving
concrete is leading paving material. designed for specific loads of traffic and cost less than other materials that can carry same load.
Air Entrainment
the use of air entrainment helps concrete to resist the damage caused by numerous freeze thaw cycles.
- air bubbles provide tiny chambers where water can expand into as it freezes.
Soil-Cement
Soil cement is a simply highly compacted mixture of soil, Portland cement, and water. as the cement hydrates the mixture becomes more durable.
- used for paving roads, streets, airports. to complete the pavement a thin layer of sealing is placed over it.
Shot- Crete (Gunnite)
this is portland cement that is applied by a pneumatically operated gun.
Grout
Portland cement grout is placed under pressure and is used for
- stabilizing foundations
- making rock foundations under dams water tight
- filling cracks in concrete work
Mortar
mixture of cement water and sand, bonds masonry materials together in a strong water tight bond
fibre Reinforced concrete
concrete that is reinforced with class or metal fibres. these are mixed with the concrete at the time of batching.
Self leveling gypsum
normally used on woodframe apartment buildings and condos. reduces noise and acts as a fire block.
Previous Concrete
concrete mix that is used for specific purposes. most of its uses at present are slab on ground.
similar to regular concrete made with cement, aggregats and water. different because finished product is porous
Portland cement is hydraulic cement meaning
it sets and hardens by reacting with water. this reaction is called hydration
portland cement is a mixture of
Limestone, iron, silica alumina (LISA)
General Use hydraulic cement (GU)
for general use, normally referred to as portland cement. this is used in general construction
Moderate sulphate resistant hydraulic cement (MS)
this cement is used where precaution against moderate sulphate attack is important. if sulphates are a problem it can cause sailing cracking an expansion.
Moderate Heat of Hydration Hydraulic Cement (MH)
manufactured to generate less heat when curing. used in large pilers and this retaining walls a bulk foundations. MH reduces temperature rise and possible temperature related cracking.
High Early Strength Hydraulic Cement (HE)
HE cement provides high strength very quickly.
Low Heat of Hydration Hydraulic Cement (LH)
used when expansion caused by heat of hydration must be minimized. this develops strength at a much slower rate. (used in massive concrete structures)
High sulphate resistant hydraulic cement (HS)
HS cement is used in concrete exposed to severe sulphate action. it is used where soil or ground water has high sulphate content.
White cement
white portland cement cures to a white colour. used primarily for architectural purposes.
Masonry cement
mixture of portland and air entraining additional and supplement materials.
Air-entrained Portland cement
added to type 10 , 20 and 30 cements improve resistance to freeze thaw conditions and to scaling caused by chemicals
Oil-well cements
used to sealing oil and gas wells during drilling are made from portland cement or blended hydraulic . must be slow setting and able to resist high pressure and temperatures.
Water proofed cement
adding small amounts of stearate (calcium , aluminum, or other) to portland cement during final grinding will produce waterproof portland cement.
Plastic Cement
made by adding plasticizing agents up to 12%. often used for making mortar plaster and stucco
expansive cement
cement that expands during the early hardening period after setting. used for patching cracks and holes in existing concrete work.
Aggregates
occupy 60%-80% of concretes volume. the type size and quality of aggregates greatly influence the quality of concrete.
coarse aggregates
5mm and larger
fine aggregates
smaller then 5mm
Quality of aggregates
must be clean, hard and strong and durable and free of absorbed chemicals and clay coats.
Slump test
used to test the consistency of concrete mixture. remember cone video 3-4” slump is common for good quality cement.
water /cement ratio and strength
compressive strength is universal measure of concretes strength. the more water the less strength
water to cement ratio
is the weight of cement to the weight of water used in the mix.
Admixtures
for concrerte to modify properties
Air entrained admixtures
put microscopic bubbles into concrete. enhance ability to withstand freeze thaw cycles.
Water-reducing admixtures
added to concrete ti reduce amount of water required yet still maintaining required slump. by reducing amount of water needed the strength of concrete is increased.
Retarding admixtures
added to concrete to slow its setting rate. used in temperatures over 30degrees
Accelerating admixtures
added to increase rate of strength gain. needed to allow early stripping, protect concrete from freezing and to generally speed up construction process. calcium chloride is used to accelerate setting * do not use in concrete with steel reinforcements
Superplasticizers
added to concrete to increase the slump of mixture. active for short time no more then 60 min.
Damp-proofing and permeability-reducing agents
included when low cement content or a high water cement ratio is used.
Bonding agents
used when fresh concrete is to be applied to the face of an old existing concrete.
Gas fourming agents
expands grout a it cures. would be used in a grout designed to prevent water through wall cavities and cracks
Pozzolans
used in the mixture to reduce the cost o the finished concrete. possesses little or no cementing properties but when mixed with cement, it will hep to bond concrete together.
Metallic aggregates used in grout formulas because?
to allow grout to expand and offset the shrinkage.
Dry pack grouts
used where spaces are wide enough to pack grout into them.
Liquid grout
to fill small gaps
