Concrete (C-8) · Lesson 3 of 7

Specified Strength and Air Entrainment by Exposure

"Specified Strength and Air Entrainment by Exposure" is lesson 3 of 7 in the Concrete (C-8) Learning Hub. It opens with "The Plans Name the Strength, the Code Sets the Floor" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. The Plans Name the Strength, the Code Sets the Floor
  2. Reading Table R402.2
  3. Air Entrainment
  4. Garage Floors, Deicers and Steel Troweling
  5. The Commercial Side: CBC 1904

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Interior slab on grade" through "Garage floor".

What you'll be able to do

  • Explain the main idea of "Specified Strength and Air Entrainment by Exposure" in plain language you can use on the exam.
  • Apply this step with confidence: "Air Entrainment".
  • Apply this step with confidence: "Garage Floors, Deicers and Steel Troweling".
  • Apply this step with confidence: "The Commercial Side: CBC 1904".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
F'C AND AIR BY EXPOSURE2025 CRC Table R402.2 and 2025 CBC 1904TABLE R402.2: SEVERE WEATHERINGminimum f'c in psi at 28 daysFoundations, not exposed to weather2,500Interior slab on grade (not garage)2,500Vertical work exposed to weather3,000Porch, carport, steps, garage floor3,500Moderate weathering: exposed walls 3,000 andporch/garage 3,000. Negligible: all 2,500.Weathering potential is set locally in Table R301.2AIR CONTENT, % BY VOLUMEair-entrained: 5% to 7% (note d)0%2%4%6%8%4.5% FAIL7.4% FAIL5.0% pass6.8% passSteel-troweled garage floor (note f):air may drop to 3% minimum only iff'c is raised to 4,000 psi or moreCBC 1904.2, nonstructural concrete:F0 2,500, F1 3,000, F2-F3 3,500Porch slab and steps, severe weathering: 3,500 psi, air 5% to 7%Loads at 5.0% and 6.8% pass; 4.5% and 7.4% are rejectedGarage floor: 3,500 psi with 5% to 7% air, or 4,000 psi with 3% minimum airSource: 2025 California Residential Code R402.2, Table R402.2 notes a-f; 2025 CBC 1904.1, 1904.2CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: The Plans Name the Strength, the Code Sets the Floor

The construction documents for structural concrete must state the specified compressive strength of the concrete for each element at the stated age (2025 CBC 1901.5, item 1). For houses, 2025 CRC R402.2 sets the minimum specified strength f'c in Table R402.2, and footnote a says the strength is measured at 28 days in psi. The table is read by location of the concrete and by weathering potential: negligible, moderate or severe, which the local jurisdiction lists in Table R301.2 (footnote b).

Step 2: Reading Table R402.2

Basement walls, foundations and other concrete not exposed to the weather: 2,500 psi in every weathering column. Basement slabs and interior slabs on grade except garage floors: 2,500 psi. Vertical work exposed to the weather (basement walls, foundation walls, exterior walls): 2,500 negligible, 3,000 moderate, 3,000 severe. Porches, carport slabs and steps exposed to the weather, and garage floor slabs: 2,500 negligible, 3,000 moderate, 3,500 severe.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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