Concrete in the basement

The basement floor has concrete! Everyday the Kravis Center looks closer to what we’re used to seeing in a parking garage. In this blog, we’re going to learn about the work that goes into that concrete on the ground, known as “slab on grade” or S.O.G.

Once the underground electrical and plumbing work was completed, the sub-grade was prepped with 2” of sand and a 15 millimeters vapor barrier. This Stego Wrap is covered by another 2” of sand. In order to have electricity to the building, some electrical conduit is run from underground, through the sand, vapor barrier and concrete.

Once the sub-grade is done, rebar is laid. There is one layer of rebar which is designed in a cross pattern about 18” apart. The slab also has fiber mesh, which are strands of plastic mixed in the concrete at the batch plant. The rebar serves to strengthen the concrete, as we’ve mentioned in the blog before. The fiber mesh helps prevent cracking. The slab poured in our basement is 5” thick.

The first pour was 15,000 square feet (s.f.) and 330 cubic yards (c.y.); the second pour was 20,000 s.f. and 420 c.y. of concrete. The videos below show concrete being poured. You’ll see there is a self-propelled laser screed machine being used in the video. This is necessary to vibrate the concrete in order to ensure the concrete consolidates around the rebar. The screed also levels the concrete (you will see is moving across the surface of the poured concrete).

Finally, the slab was finished with a swirl pattern in order to provide traction to vehicles. Otherwise, if this weren’t done, it would become slippery when wet.

As you walk through a building, have you ever thought of exactly what you’re walking on? Have you ever given a thought to what’s beneath the carpet and concrete?

In the dirt lies plumbing and electrical work that is coordinated months in advance of digging trenches. BIM (Building Information Modeling) is the latest technology utilized to accomplish coordination among subcontractors. After all, there is only so much space for the plumber and electrician to lay their pipes or conduits. It takes time and careful planning to ensure all parties can put their materials in while meeting the quality specifications of the building.

This image, above, is a snapshot of the underground work, generated by NavisWorks (BIM software). We’re looking at it from below ground, up toward the dirt that covers it. The yellow indicates electrical conduit running into the main electrical room. The green and pink are plumbing pipes running underground.

The photo below shows 7 electrical conduits placed in a trench, running away from the main electrical room. This number of conduits in one trench is slightly higher at than average, due to the size of the project. It will take the electrician 20 days to complete all underground work. It’s surprising to see progress made so quickly every day. Trenches are dug, conduit placed and then trenches need to be back filled (put dirt or another mixture over them).

At this project, the rocky nature of the soil requires the use of a concrete-like mixture to take the place of dirt, as you can see in the photo below. A red caution tape is also placed on top to tell someone in the future to be cautious, since there are critical lines running beneath the mixture.

The Main Electrical Room houses switch gear, main panel boards, lighting control panels and transformers. As you can assume, these control and monitor the electrical elements of the building. Here is another image from NavisWorks, showing the various items (the yellow boxes) inside the electrical room. As you can see, there is a lot of equipment to fit into one room.

The Electrical Room also requires special conditions. For example, during operation, the room must be consistently kept at a moderate temperature level. The walls of the room must also be fire rated for one hour, per code. However, as mentioned in our previous blog, an advantage of using concrete is the slow spread of fire, so the walls around the Kravis Center’s Electrical Room are rated above an hour.