huangyhg

5 to 8% air entrainment
if i am desiging a 100 feet long and 2 feet high retaining wall with 5 to 8% air entrained concrete for freezing and thawing, do i still need contraction joint?
the number of joints have nothing to do with air entrainment. it has to do with the amount of shrinkage and the amount of horizontal steel to resist the shrinkage forces.
with normal amounts of steel, i would recommend contraction joints at about 25 feet.
i agree with jike, but in my experience, cracks form about every 10 ft in low retaining walls if a footing is cast first, then the wall. if you want to control this cracking, space the joints at 10 ft centres.
joints (ftng. matching wall) at 10 ft spacing sounds great to control (appearance) the cracks. i would also include a few 3/4" expansion joints (dowels w/end cap) to give your ret. wall a little room to move.
i didn't mean joints in the footing at 10' centres. just in the wall. the footing doesn't shrink as much as the wall, but does it earlier. who cares about cracks in the footing, you can't see them.
i will mention an additional criteria that is for low walls only: the spacing of joints should not exceed about 3 times the height of the wall. this corresponds a little closer to hokie66 (for low walls).
thank you guys. what would i do with out you?
by the way if the contractor does not pour this whole 100 feet long wall in one pour and does it in the stages with construction joints so than we will not need any contraction joint as there isn't a large chunk of concrete setting at any given time?

i did not read your original post thoroughly. a wall only 2 feet high is like a curb. 10 foot spacing makes sense.
i would still insist on 10 foot spacing for contraction joints but the contractor may substitute a construction joint for any contraction joint. provide an expansion joint at 20 foot spacing.

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]