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what does the term subgrade refer to?
the ground or base that is directly under and supporting to the concrete slab
what 2 parts may be included in the base for the concrete slab?
the prepoaration of the___is just as important as the slab.
what are the properties of problem soils?
clay and organic soils that are highly expansive or compressive and do not provide uniform support
what is non uniformity?
when the soil contains both hard and soft spots in close proximity
what can occur when the soil is non uniform?
point loading- different compression causes a bridging effect creating cracks
what precautions must be taken when a trench is back filled in a prepare base?
it must be compressed back to its original density
what is a sub base and under what conditions is it used?
thin layer of granular material is helpful when it is not possible to level and compact the existing ground to a uniform height and density
what are acceptable materials for a sub base?
stone, gravel, sand, or a mixture of these
where are slab thickening used?
for the purpose of carrying greater loads, masonry block work, bearing walls, heavy machinery, and support wall loads
where should reinforcement be placed in the slab?
lower portions of the slab
under what conditions should a vapour barrier be placed under the slab?
where water or water vapour may be a problem
where is air-entrained concrete used?
should be used anywhere it would be subject to freeze thaw cycles (driveways, sidewalks, etc..)
what method can be used to ensure that slab corners are square?
what 2 forces must edge forms be able to resist?
- 1. buckling- pressure of concrete
- 2. downward pressure of screeding
list and describe 3 basic types of joints.
- 1. isolation joints- allow both vertical and horizontal movement between joints
- 2. control joints- used to control the location of cracking
- 3. construction joints- used where the pour has been intentionally stopped and will be continued
on what 5 conditions does the spacing of control joints depend?
- 1. slab thickness
- 2. shrinkage potential
- 3. sub-grade friction
- 4. environment
- 5. pressure or lack of reinforcement
what is done to the sub-base when no vapour barrier is used?
surface should be dampened with water to reduce loss of water from concrete to sub-base
what is the most important factor in the screeding and striking off process?
that it is completed before excess bleed water collects on the surface
what does a low tolerance mean in relation to slab placement quality?
that higher variations in the slab are allowed
what type of trowel must not be used on air-entrained concrete?
do not use a steel trowel
what are the 3 goals of the curing process?
- 1.protect from rapid drying
- 2. " "temperature extremes
- 3. " "damage from use