1. Intro Flashcards
(24 cards)
Why use concrete? (5)
Resistant to moisture
Compatible with any shape/mould
Cheap
Less energy input
Recycled materials as cement/aggregate
What does fresh concrete need to?
Form into required shape
Transport over long distances without segregation
Compacted to remove air
Ignoring good fresh concrete practices leads to?
Void formation
Poor bond between reinforcement
Segregation
What does hardened concrete need to?
Achieve strength
Curability
Desired surface appearance
Why do voids need to be minimised?
To improve strength and durability
Why do bonds need to be maximised?
To improve strength and durability
What is the function of cement?
Fill voids between aggregates
Lubrication and water tightness
Strength of hardened concrete
What is the function of aggregate?
Low cost filler
Resistance to loads, abrasion & percolation
Reduce volume change
What is W/C ration determined by?
Pozzolanic materials
Admixtures
Temp
Optimal particle sizes
What is cement paste quality based on?
W/C ratio
Cement type
Degree of compaction
Three sources of weakness in concrete
Pores
Interfaces
Structural defects
What is the definition of durability?
The ability of concrete to withstand the damaging effects of the environment and of its service conditions until it reaches a minimum level of performance.
Minimum acceptable level of performance.
What is design life?
Period of use intended by the designer
What is service life?
Period of use intended by the user
(Intended working life)
What are the factors of durability in concrete (4)
Structural design
Materials used
Workmanship/Execution
Curing
Causes of variability due to workmanship (6)
Non uniform supply of materials
Inaccurate batching
Excessive mixing
Segregation when placing
Over compaction or too little compaction (honeycombing)
Bad curing
Causes of variability due to materials
Aggregates - yield strength & durability
Cement and admixtures
Causes of variability due to properties (5)
Bleeding - loss of internal water for hydration
Heat of hydration - formation of thermal gradients/cracking
Degree of hydration
Moisture loss
Plastic shrinkage - cracks due to volume change.
Factors for permeability (3)
Environmental conditions
Capillary size and interconnectivity
Hydrate structure
What impacts capillary size and interconnectivity?
Aggregate size
W/C ratio
What law can be used to calculate permeability?
Darcy’s law
Factors for absorption (4)
Environmental conditions - moisture gradient
Capillary size
Hydraulic structure
Pore fluid content - degree of saturation
Factors for diffusion (4)
Environment - ionic concentration gradient
Capillary size
Hydrate chemistry
Pore fluid chemistry
Law for diffusion
Ficks First Law
