Repair of restraint cracks in parking rc slab exposed to weather.

[JacksPanic]

Hi,

I need your opinion on a repair method for the above situation. Do i simply ream the cracks a bit wider with an anglegrinder and apply a trafficable waterproofing paint? With the paint then being applied thicker in the areas of the cracks? Or do i injection grout the cracks and paint over it with aforementioned paint?

The idea was always to "waterproof the slab" with aforementioned paint, but now these cracks have appeared and i am concerned the paint wont bridge them if simply painted over.

I appreciate your advice and comments.

Thanks.

 

[BAretired]

Is the building located in a place where salt is added to the roads?

BA

 

[hokie66]

A bit of information about the structure would help. Tensioned or not, framing system, thickness of cracking elements, percentage reinforcement, etc. How wide are the cracks? What trafficable membrane is proposed?

 

[JacksPanic]

No salt is added to the roads. Warm summers, moderate rain during winters. never snows.

The structure consist of 3 office levels and 1 parking. Conventional reinforced concrete structure. Columns and shear walls. Slab is 280mm thick. Cracks are approx .2mm to .3mm and i was thinking of using basf monotop or similar as trafficable waterproofing paint.

 

[briancpotter]

That's a very thick concrete slab, what's the reinforcing in it? Were control joints properly placed during construction?

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[hokie66]

So this is a roof slab, used for carparking? What are the plan dimensions of the slab? How much reinforcement expressed as a percentage of Ag?

BASF and Sika would be my preferred manufacturers for traffficable membranes. You should have discussions with approved applicators in your area.

 

[JacksPanic]

Hi. The slab is actually 270 thick, sorry. Building size about 40x40 m. There is a slab on grade, then suspended parking slab which sits continuously supported on a retaining wall. This slab projects past the footprint of the office above. Some part of the slab will have paving and waterproofing, other part under the office, exposed concrete. I am interested to hear about crack repair method of cracks in this slab. Thanks for the help, ill speak to expert contractors and technical people at above mentioned companies. I realized this is not really "structural engineering" but wanted the opinions of the valued members here. Thanks again.

 

[JacksPanic]

I do not know what the rebar is, i have only seen the drawings and been to site.

 

[hokie66]

All those questions relate to the question of whether or not it is necessary to fill the cracks. Cracks are not always a problem, and sometimes filling them creates more problems than it solves.

As the slab is supported on a wall at the perimeter, the most likely reason for the cracking is restraint by the wall, resulting in tension in the slab as it shrinks. Are the cracks all the way through the slab? As you stated that "now these cracks have appeared", I take it that the crack widths are unexpected and perhaps recent. If they are direct tension cracks, they will continue to widen with time, so filling them early with a rigid material won't solve the problem.