huangyhg

diamond dowel in slab-on-grade
does anyone have any credible testing/verification data or documentation regarding the use of diamond dowel (plate) systems for shear transfer in slab-on-grade construction joints? typically, we would use smooth dowels for shear transfer, however, on a particular job the diamond dowel system has been presented as a "quick and dirty" alternative.
having no prior experience with this system, i'd like to get some opinions on advantages/disadvantages from those who have utilized both methods. at first glance, i would be concerned about break-out of the concrete above the exposed side of the diamond plate, since the larger surface area (as opposed to intermittent smooth dowels) presents a slippage plane in the slab.
also, the embedded side of the plate is cast in with the plastic form. i'm not familiar with how plastic would perform through temperature variation, although i believe it has a much lower thermal coefficient than both steel or concrete. would this have any undesired effect when considering expansion or shrinkage of the slab?
i hadn't used diamond dowel systems until i came to new zealand, but have found them to be quite common (and reliable) since my arrival. your concerns are much the same as my own when i first was shown the system, however they do not seem to pan out. i've yet to see anything go wrong with a set of diamond dowels installed as per manufacturer's written specs and have found them quick, easy and contractor friendly. when you aren't compromising the end product for the client those aren't bad things at all...
one caveat: i have heard of (but not personally seen) some very bad failures caused by installing the plates too high on poorly compacted sungrade. that said, i wouldn't think round bar dowels would do much better when abused by the installer.
good luck and please post to let us know how it turns out!
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
you should not look on diamond plate dowels as a "quick and dirty" solution. rather, they are designed to let the slab shrink in both directions without restraint from dowels. round dowels restrain the second pour parallel to the joint, and also perpendicular to the joint if they are not straight. the supplier of the dowels should supply you with the data you require: if not, don't use them. the only issue i am aware of is if the diamond dowels are used in thin slabs and the concrete is not well consolidated.
doesnt anyone know how to google these days...

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