S F Johnson Consulting, LLC
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Division 03

Division 03

🧱 Division 03 — Concrete

Mixes • Reinforcement • Formwork • Placement • Finishing • Curing • Testing • Takeoff math. Verify project specs and ACI/ASTM requirements for your job.

🧭 Scope (What Div 03 Covers)

  • Cast-in-place, slab-on-grade, elevated slabs, beams/columns, foundations, walls.
  • Precast/prestressed (coord. with Div 05), grouts, non-shrink, toppings, overlays.
  • Reinforcing steel, welded wire reinforcement, fibers, accessories, vapor barriers.
  • Formwork & shoring, embedded items, joint devices (dowels, keyways, waterstops).

🔎 Plan Symbols & Notes

  • Concrete hatch (stipple); CMU cross-hatch in adjacent sections.
  • Rebar callouts: #5 @ 12" o.c. each way (ew); mats T/B; lap lengths noted.
  • Joints: CJ = contraction/control; CJ sawcut; SJ = construction; IJ = isolation.
  • Strength note: f’c (e.g., 4,000 psi @ 28 days); slump/air %, exposure class.

🧪 Mix Design (Typical Ranges)

  • Strength: 3,000–5,000 psi most building work (verify f’c).
  • Slump: 3–5" flatwork, 4–6" walls/columns (pump mixes vary).
  • Air: 4–7% for freeze-thaw exteriors; ~2% interiors (unless specified).
  • W/C: typically ≤0.45–0.50 (spec governs).
  • Admixtures: water reducer, HRWR, air-entraining, retarder/accelerator, shrinkage-reducing; SCMs (fly ash/slag/silica fume) per spec.

🧵 Reinforcement & Cover (Quick)

  • Bar sizes (lb/ft): #3 0.376 • #4 0.668 • #5 1.043 • #6 1.502 • #7 2.044 • #8 2.670.
  • Typical cover: 3" to earth; 2" to formed surfaces (exterior); 1½" interior (verify ACI/plan).
  • Tie wire/Chairs: maintain position; use supports matched to vapor barrier/hard finish.
  • Lap splices: per ACI/plan; rule-of-thumb tension laps ≈ 40d for #4–#8 Grade 60 (confirm).

📦 Formwork & Embedded Items

  • Oil/release agent applied uniformly; tight & true; chamfers at exposed corners.
  • Locate sleeves, blockouts, anchors, waterstops before pour (coord. with MEP).
  • Shoring/reshoring sequence per engineer; do not remove early.

🚚 Placement & Finishing

  • Prep: compact subbase, install vapor retarder (10–15 mil) if specified, set elevations.
  • Consolidate with internal vibrator; avoid over-vibration (segregation/honeycomb).
  • Strike-off/screed → bull float → wait for bleed → finish (trowel/broom/exposed).
  • Exterior air-entrained: avoid hard-trowel finishes.

✂️ Joints (Rules of Thumb)

  • Control joints: spacing ≈ 24–36 × slab thickness (inches); depth ≥ ¼ slab.
  • Sawcut window: when slab supports saw without raveling (≈ 4–12 hrs; weather-dependent).
  • Isolation joints: at columns, walls, footings; full-depth separation.
  • Construction joints: locate at low-moment areas; keyways/dowels per plan.

🌡️ Curing & Protection

  • Begin as soon as finish allows; keep surfaces moist 7 days (or per compound/spec).
  • Use wet cure, curing compound, coverings/blankets; protect from traffic early.
  • Hot weather: shade, cool mix, set retarders, fog mist, wind breaks.
  • Cold weather: heat enclosures, warm materials, insulated blankets; prevent freezing.

🧪 Field Testing (Common)

  • Slump (ASTM C143), Temp (C1064), Air (C231/C173), Unit Wt (C138).
  • Cylinders: make/store per C31; break per C39 (7-day & 28-day typical).
  • Acceptance: per spec/ACI — use average strengths & criteria in project docs.

🧮 Quick Math & Takeoff Shortcuts

Concrete Volume (CY)

CY = L × W × T(ft) ÷ 27. Add 5–10% waste.

6" = 0.5 ft • 8" = 0.667 ft • 12" = 1 ft

Beams/Columns

Rectangular: b × h × L ÷ 27 • Round: πr² × L ÷ 27.

Rebar Weight

Weight (lb) = bar lb/ft × length(ft) × qty.

#5 example: 1.043 lb/ft × 20' × 20 = 417 lb.

Bar Count @ Spacing

Count ≈ (clear width ÷ spacing) + 1.

Joint Spacing

CJ spacing ≈ 24–36 × slab thickness (in).

Cylinder Breaks

Common checks: 7-day (≈ 65–75% f’c), 28-day (100% design).

🦺 Safety & QA

  • Silica controls for cutting/sawing; PPE for caustic wet concrete.
  • Finish in proper window; avoid adding water at site (water-cement ratio!).
  • Protect embeds, anchor layouts, and vapor barriers from damage.
  • Document truck tickets, test results, placement logs, curing start/stop times.

📝 Self Test

  1. How many cubic yards for a 30' × 40' slab at 6" thick (add 5% waste)?
  2. You have twenty #5 bars at 20' each. Approximate total weight?
  3. Rule-of-thumb spacing for control joints in a 5" SOG?
  4. Typical curing period (days) for standard mixes?
  5. What’s a typical slump range for walls/columns vs flatwork?
  6. Minimum cover to earth for reinforcement?
  7. Quick rule-of-thumb lap splice for #6 Grade 60 in tension (confirm with plan)?
  8. Two hot-weather measures to reduce plastic shrinkage cracking?
  9. What tests are commonly taken at the truck/pour?
  10. When should sawcut control joints be made?

Answers: (1) 30×40×0.5 ÷ 27 ≈ 22.2 CY; +5% ≈ 23.3 CY. (2) 1.043×20×20 ≈ 417 lb. (3) 24–36 × 5" = 10–15 ft. (4) ~7 days (per spec/method). (5) Walls/cols ≈ 4–6"; flatwork ≈ 3–5". (6) 3". (7) ~40d (verify ACI/spec). (8) Cool mix/shade/wind breaks/fog mist/retarder/early curing. (9) Slump, temp, air, unit weight; cylinders. (10) Within the early window when it won’t ravel (≈ 4–12 hrs, weather-dependent).