A Concrete Education at Delta Middle School

Dec 21, 2018

Kissner GC, Inc.

Pioneer of modern architecture Ludwig Mies Van der Rohe said that “each material has its specific characteristics which we must understand if we want to use it. This is no less true of steel and concrete.”

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Bernhardt Construction, Inc. smooths the freshly poured concrete.

This week, KGCI subcontractor Bernhardt Construction, Inc. poured two more concrete slabs for the Delta Middle School addition project. That’s 60 yards of concrete last week, 30 yards earlier this week, and 44 yards today. Accordingly, it’s fitting to describe a few of those “specific characteristics” of concrete Mies referred to, particularly the process of pouring slabs.

STEP 1: Prepare the subbase, or the ground on which the concrete will be poured. 

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KGCI placed 2 feet of structural fill or 1-1/2 feet of structural base (subbase) over the top of compacted native material (subgrade).

Step 2: Set up a wood perimeter, or form, in which to pour the concrete.

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Wood forms keep the concrete in place when poured.

Step 3: Tie rebar mat for concrete slab.

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#4 rebar is first laid on center each way, in a 16″ grid pattern.
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Then the rebar is tied to form the grid pattern. It’s also “chaired up” to keep the rebar off the ground. The rebar will ultimately reinforce the concrete for structural integrity.

Step 4: Pour the concrete.

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Concrete is transferred from the concrete truck via a concrete pump.
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5″ of concrete are poured over the rebar.

Step 5: Smooth the concrete.

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After initially flattening out the concrete (or screeding), Bernhardt Construction uses a floating device to smooth out the aggregate.
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Concrete is smoothed with a hand float.
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The concrete power trowel ensures a smooth finish.

Step 6: Saw cut the concrete to create joints.

Saw cutting creates intentional cracks approximately every 15 feet in the concrete to allow the concrete to contract without breaking and shifting.