Browse Forums Paving & Concreting 1 Apr 04, 2011 10:13 am Here are some fancy pics Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Here are some catch words (in blue) For dowels to be effective they must be aligned properly. Dowels must be perpendicular to the joint both horizontally and vertically or joint deterioration can occur. construction joints are just one way to help minimize random cracking in concrete floors “Doweled joints are recommended when positive load transfer is required" when dowels are used, the slab designer should consider the properties of the dowel system specified, which include its geometry, installation tolerances, and bond-breaking material, along with the cost of the dowel system. If only one of these properties are compromised, then severe and costly problems could occur: Like ⋅ 1 comment ⋅ Pin to Ideaboard ⋅ Joints are one of the weakest areas in PCC pavement. There is a discontinuity in concrete at saw cut joints and wheel loads are not transferred 100 % from one slab to the next, resulting in higher wheel load stress. When incompressible materials get into the joints, expansion of concrete slabs due to high ambient temperatures will squeeze the incompressible materials and high localized stresses will develop in the concrete. Localized high concrete stresses can cause spalling in the joints. Also, if a good joint seal is not maintained, water and de-icing compounds can get into the joint and cause corrosion problems in dowel bars as shown in Figure 1: dowel bars are used to improve load transfer efficiency For dowel bars to perform as they are intended, their alignment should be parallel to the direction of concrete movement, both horizontally and vertically. If dowel bars are mis-aligned, high stress concentration and cracking will result in the concrete slab. special attention for proper concrete consolidation under the longitudinal steel. If proper consolidation is not provided at these transverse joints, delamination and distress can result as shown in Figure 3: I am confused as to why sometimes a new slab is not dowelled into the old slab. I noticed that sometimes a very large concrete "paving" area is dowelled into the house or garage slab, but at other times they just use a flexible sponge between the old and the new slab EVEN when building a patio slab next to the house. Is there any logic in this and what is better ??? My signature is distracting people from my wise posts ... Re: Dowelling in concrete 2Apr 04, 2011 12:25 pm If levels are critical Dowel, if not don't. If you dowel into an existing slab and the ground consolidates under the new slab you cause cracking of the new slab, and stress the existing slab. An example is my driveway is dowelled to the front of the garage slab as i don't want a step to form. The concrete hardstanding at the side of the garage is dowelled into the driveway but not dowelled into the side of the garage slab as it doesn't matter if this drops a little. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Dowelling in concrete 3Apr 04, 2011 4:10 pm bashworth If levels are critical Dowel, if not don't. What about 2 slabs moving away from each other / rotating / warping/curling, and all the other "charming" stuff that they do!? Can a small new slab really move that much?? Even if it's supported on piers? My signature is distracting people from my wise posts ... Re: Dowelling in concrete 4Apr 04, 2011 5:27 pm For small slabs most of the problems are related to the material the slab stands on not being compacted enough so that it settles after construction. If the material is compacted well at the edges and not at the middle then thats when the curl happens. Some of those illustrations are much emphasised to get the point across. In very big concrete areas (Im talking runways and freeways) expansion is probably the next biggest problem The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Dowelling in concrete 5Apr 04, 2011 6:59 pm bashworth For small slabs most of the problems are related to the material the slab stands on not being compacted enough so that it settles after construction. If the material is compacted well at the edges and not at the middle then thats when the curl happens. My signature is distracting people from my wise posts ... Re: Dowelling in concrete 6Apr 04, 2011 9:54 pm You can design for anything but probably the best thing is to do the proper compaction. That is go back to undisturbed ground and bring surface up in 150mm layers of gravel compacting each layer with a vibrating plate. This is a lot different to what usually happens. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Dowelling in concrete 7Apr 04, 2011 9:59 pm What about a slab that would be suspended (eve though it started out as slab on ground)? In case that the ground subsides, can the slab still support itself and how? BTW, we noticed that same thing happened to our house slab over the sewage trench . Hope it's not going to give way and collapse into the trench?! My signature is distracting people from my wise posts ... Re: Dowelling in concrete 8Apr 04, 2011 10:31 pm Slabs resist the effect of trench subsidence by shear strength. The issue with subsidence is that you never know whether you will have to deal with the slab acting as a beam between two points or cantilevering out over a hard spot on the centre. When I worked in airports the common wisdom was that reinforcement was only provided to hold the broken bits together as it was uneconomic to provide enough steel to prevent any cracking due to bending. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Dowelling in concrete 9Oct 30, 2019 2:00 am Hello forum. What can I use as a joint filler material To my understanding early saw cuts are to control shrinkage cracks, so doing them now would be pointless. Control joints may reduce ugly cracking during periods of soil… 3 9862 Hi all I need a guidance on how far I need to space expansion joints in the concrete driveway and its type (keyway/foam.) Contraction joints are at 3m max for a 125 slab. Thanks 0 10940 |