Concrete Test 1 Flashcards
Concrete is like a sponge in that…
Spaces absorb moisture
In freezing conditions water in pours could…
Freeze, increasing in volume and causing cracks
Greater connectivity of pours usually gives
Less durability
Only _____ pours affect durability
Open
Definition of porosity
Overall volume of pours (open and closed)
Definition of permeability
Measure of ease with which water / gas can flow through a material
More permeable / porous concretes are used in places like
Roads, runways, motorways to allow water to drain
Permeability is not the same as porosity, give exmaple…
You could have a high porosity (with closed pours) and low permeability
Usually with concrete the permeability will be…
Relative to the porosity
Definition of absorption
Ability to draw water into voids (open pours only)
Usually porosity is ____________________ to absorption (_____________________)
Not equal to
Due to closed pours not absorbing water
There are how many forms of density - give names
Two
Bulk density
Relative density
Definition of bulk density
Measure of compaction - tells how closely particles are packed - is defined as dry mass of unit volume
Definition of relative density
Same definition as bulk density only volume is only the volume of the solids, no spaces (pours)
Bulk density will have….
A greater volume
Relative density will have
Smaller volume due to solids being crushed
Definition of moisture content
Mass of water in concrete related to its dry mass
When determining mass, concrete samples will be…
Put in an oven to dry / remove moisture then weighed
In highly porous concrete relative density will always be __________ than bulk
Greater
Two types of porosity are
Open porosity
Closed porosity
In most cases, the higher the porosity…
The higher the permeability
Bulk density formula
P = mass / volume (solids + voids)
Relative density formula
P = mass / volume (solids only)
total water absorption is the…
Maximum value moisture content
Moisture content cannot exceed…
The total water absorption
Concrete is composed of (5)
1) cement
2) crushed rock or gravel
3) sand
4) water
5) sometimes chemical admixtures and other materials
Cement + water =
Cement paste
Cement + sand + water =
Cement mortar
Cement + sand + gravel + water =
Concrete
More water used = ______ pores & _________ concrete
More
Weaker