concrete
- In art criticism, concrete
refers to things which are real, particular, tangible; as opposed
to abstract. The more general
use of the term refers to the concrete building material,
which is extremely heavy and durable when set. First employed
by the ancient Romans, it's made from a mixture of Portland cement, aggregate
(typically sand and gravel),
and water.
Concrete is typically poured into a form; very rarely modeled or carved. Slabs should be between four and eight inches thick, depending on their function. A basement floor: 4 inches; home garage floor or porch: 4-6; sidewalk: 5-6: driveway: 6-8. Concrete is sold by cubic volume. Calculate need as: slab thickness in feet x slab width in feet x slab length in feet = cubic feet of concrete. 27 cubic feet = 1 cubic yard. Large projects require steel reinforcing bars (called re-bar). The strength of concrete increases when the amount of cement in the mixture increases, the amount of water relative to cement decreases, the density of the concrete is higher, and the aggregate is coarser.
 hazardous to breathe. |
The most common problems encountered
in making concrete are adding too much water or sand, and poor
mixing.
The correct amount of water (by volume) should be about
half of the total mixture. The more trustworthy gauge,
however, is to add only as much water as makes the mixture workable.
For a pad or footings for outdoor sculpture, an excellent concrete mixture will be achieved at these ratios (by volume): 1 part cement, 1 part sand, 2 parts gravel; although 1:2:3 is suitable for most applications; and 1:2.5:4 is adequate for basic foundations.
Mixing the concrete is required in order to produce the strongest, most durable pour. When mixing concrete, mix the cement and sand first, then mix in the coarser aggregate.
Curing of concrete is necessary for the material
to harden properly. After the pour, the concrete must be kept
moist for a week, and the temperature
must not drop below 50°F.
