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DRY & GREEN

International Ltd.

Swinnenwijerweg 12
B-3600 Genk - Belgium
Tel: +32 (0)89 / 24 .80 .81
Fax: +32 (0)89 / 24 .80 .86
Email: info@dryandgreen.com

 


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JOINT DETERIORATION & CURLING

JOINT DETERIORATION

In the traffic-bearing areas of your floor you have two types of joints: construction and control joints. Construction joints are those joints at the ends of pour sequences.  Control (contraction) joints are joints within each pour designed to induce the anticipated cracks to crack in a straight line. Generally, you will find joints at intervals from perhaps 3m to 5 m grids.

Joints are affected by shrinkage.  Conventional concrete shrinks at a rate of approximately 3mm or more in each 6m.  This means that over the one-to-two year period during which concrete shrinks, your joints may open an additional 2mm tot 6 mm.  This can have a dramatic effect on any joint filler that is used.

Joints in traffic bearing surfaces should always be filled.  The function of a filler should be to protect (support) the joint edges from damage caused by hard wheel impact.  This damage is called 'spalling'. Once spalls occur they continually get wider and deeper.  Spalls damage vehicle wheels, result in bumps that material handling vehicles (MHV) drivers slow down for and eventually costs €€€ to repair. To be effective, the filler should be fairly stiff, like a very hard rubber. This means it will not expand as the joint opens. There are only two ways to overcome this dilemma: (1) install the filler late in the schedule to allow for as much of the shrinkage as possible; and (2) provide for repair or replacement of the filler after the shrinkage seems to have stabilized, usually after the first full heating season.

If you are experiencing joint filler separation (adhesive or cohesive), contact us for our  recommended corrective procedures.If you are already experiencing joint edge spalling, don't delay in reacting.  Identifying  the cause and taking the appropriate action before the spalls become too severe are the simplest and cheapest to correct.  The longer you wait, the more it will cost you - in more ways then one!

There are many causes of joint edge spalling for you to consider, including the following:

  1. Joints not filled or not filled correctly.
  2. Filler was too soft to support traffic.
  3. Filler was installed too early and separated badly as joints opened wider.
  4. Filler was installed too low in joint to protect edge.
  5. Filler was installed too shallow to support hard wheel load (filler should be full depth in saw cut joints, 5cm deep in construction joints).
  6. Filler was of poor quality, deteriorated with time.
  7. The concrete edge itself was weak.
  8. The joint was higher on one side, leaving it vulnerable to wheel impact. 

JOINT EDGE CURL

One type of a joint condition could be caused by a phenomena known as a 'curl'. Concrete shrinks at a faster rate on its top surface because it is exposed to the air. As shrinkage occurs the ends of each pour curl upward. (You can see the same effect by examining dried mud). To determine if you have a curled joint, simply lay a straightedge across the joint and see if it rocks. Another is to listen for a 'thump' as vehicles cross, or visually watch for slab deflection.

A curl can leave joint edges at different elevations, leaving the high one vulnerable to wheel impact. But a curl can cause even worse problems than that. As the top edge of a slab curls upward, the bottom of the slab may actually lift up off the ground. As MHV's cross, the two adjacent slab segments may actually "rock" as they deflect under load. This means that both slabs may be the exposed high point at given times in the vehicles progress. The rocking effect also causes any joint filler used to de-bond and become worthless. Generally, replacing the filler will not solve the problems of rocking. Curl is a natural phenomena that is almost impossible to avoid although, it can be minimized. The important questions for you, the owner, are:

  1. How severe is the curl with regard to joint edge elevation? Will it affect my operations?
  2. Do the slab ends "rock"? How much?
  3. Can the rocking be eliminated easily or are more sophisticated measures necessary?
  4. Is the rocking in my floor "normal" or did faulty design or construction practices contribute to the problem?