1. Overview
Accurate volume calculations ensure correct material ordering and prevent costly mid-pour shortages. Concrete is ordered in cubic yards (US) or cubic meters (metric).
Equipment pads
Compressors, pumps
Reinforced pads for dynamic loads.
Tank foundations
Ring walls, full pads
Support storage tanks.
Pipe supports
Piers, pedestals
Drilled shafts for pipelines.
Building slabs
Control rooms
Floor slabs for structures.
Units and Conversions
Volume:
1 yd³ = 27 ft³ = 46,656 in³
1 m³ = 35.31 ft³ = 1.308 yd³
Density:
Normal weight concrete: 150 lb/ft³ (2,400 kg/m³)
Lightweight concrete: 110 lb/ft³ (1,760 kg/m³)
Ready-Mix Trucks:
Typical capacity: 10 yd³ per truck
Minimum order: 1–2 yd³ (short load fees apply)
Waste Factors
| Application | Factor | Reason |
|---|---|---|
| Formed walls | +5–10% | Precise forms |
| Slab on grade | +10–15% | Subgrade variation |
| Drilled piers | +15–20% | Over-drilling |
| Complex shapes | +15–20% | Irregular geometry |
Critical: Always order 5–10% extra. Running short creates cold joints that weaken the structure.
2. Volume Formulas
Break complex shapes into simple geometries, calculate each, then sum. Always convert to cubic yards for ordering.
Rectangular Slab
V = L × W × T
Example: 20 ft × 15 ft × 18 in slab
T = 18 ÷ 12 = 1.5 ft
V = 20 × 15 × 1.5 = 450 ft³
V = 450 ÷ 27 = 16.7 yd³
Order (10% waste): 19 yd³
Cylinder (Pier)
V = π × (D/2)² × h = 0.7854 × D² × h
Example: 24 in dia × 10 ft deep pier
D = 24 ÷ 12 = 2 ft
V = 0.7854 × 4 × 10 = 31.4 ft³ = 1.16 yd³/pier
12 piers with 20% waste:
12 × 1.16 × 1.20 = 16.7 yd³
Ring Wall (Hollow Cylinder)
V = π × (R_outer² − R_inner²) × h
Example: 40 ft OD, 38 ft ID, 3 ft tall
R_o = 20 ft, R_i = 19 ft
V = π × (400 − 361) × 3 = 367.6 ft³ = 13.6 yd³
Footing with Wall
V_total = V_base + V_wall
Example: 50 ft footing
Base: 3 ft × 1 ft, Wall: 1 ft × 2 ft
V_base = 50 × 3 × 1 = 150 ft³
V_wall = 50 × 1 × 2 = 100 ft³
V_total = 250 ft³ = 9.3 yd³
Formula Summary
| Shape | Formula |
|---|---|
| Rectangle | V = L × W × T |
| Cylinder | V = π r² h |
| Ring wall | V = π (R₁² − R₂²) h |
| Triangle prism | V = ½ b h L |
3. Equipment Foundations
Foundation size depends on equipment weight, soil capacity, and vibration requirements.
Sizing Criteria
Required Area:
A = W_total ÷ (q_allow × SF)
Typical Thicknesses:
Small pumps: 12–18 in
Compressors: 24–36 in
Reciprocating: 36–48 in (vibration mass)
Rule of thumb:
Foundation weight ≥ 2–3× equipment weight for vibrating equipment
Design Example
Compressor Foundation:
Equipment: 75,000 lb total
Soil: 2,000 psf, SF = 2.5
Foundation: 21 × 16 × 2.5 ft
Foundation wt: 21 × 16 × 2.5 × 150 = 126,000 lb
Total: 75,000 + 126,000 = 201,000 lb
Pressure: 201,000 ÷ 336 = 598 psf
SF check: 2,000 ÷ 598 = 3.3 ✓
Volume: 21 × 16 × 2.5 = 840 ft³ = 31.1 yd³
Order (10%): 35 yd³
Tank Foundations
| Tank Size | Foundation Type | Concrete |
|---|---|---|
| < 20 ft dia | Full pad, 6–12 in | 1–5 yd³ |
| 20–50 ft dia | Ring wall + fill | 5–20 yd³ |
| > 50 ft dia | Ring wall | 20–100 yd³ |
Pipe Support Piers
Typical Sizes:
4–12 in pipe: 12–18 in dia × 4–6 ft deep (0.3–1.0 yd³/pier)
16–36 in pipe: 24–36 in dia × 6–8 ft deep (1–4 yd³/pier)
Example:
20 in pipeline, 1,000 ft, 25 ft spacing
Piers: 1,000 ÷ 25 = 40 piers
Each: 24 in dia × 6 ft = 1.16 yd³
Total: 40 × 1.16 × 1.20 = 56 yd³
4. Reinforcement
Rebar provides tensile strength and crack control. Quantities estimated from steel ratios or bar schedules.
Reinforcement Ratios
Steel Ratios (% of concrete volume):
Light: 0.15–0.30%
Moderate: 0.50–1.0%
Heavy: 1.0–2.0%
ACI 318 minimum: ρ_min = 0.0018 (Grade 60)
Example:
Foundation: 30 × 20 × 2 ft = 1,200 ft³
Steel ratio: 1.0%
Steel volume: 12 ft³
Steel weight: 12 × 490 = 5,880 lb ≈ 3 tons
Rebar Sizes
| Bar | Dia (in) | Weight (lb/ft) | Area (in²) |
|---|---|---|---|
| #3 | 0.375 | 0.376 | 0.11 |
| #4 | 0.500 | 0.668 | 0.20 |
| #5 | 0.625 | 1.043 | 0.31 |
| #6 | 0.750 | 1.502 | 0.44 |
| #7 | 0.875 | 2.044 | 0.60 |
| #8 | 1.000 | 2.670 | 0.79 |
Concrete Mix Specifications
| Strength | Application |
|---|---|
| 3,000 psi | Light-duty, non-structural |
| 4,000 psi | Standard foundations |
| 5,000 psi | Heavy equipment, high loads |
| 6,000+ psi | Special applications |
Cover requirements: 3 in minimum for soil contact, 2 in for formed surfaces, 1.5 in for interior exposure.
5. Field Practices
Pre-Pour Checklist
- Verify formwork dimensions match drawings
- Check rebar size, spacing, cover, and lap splices
- Confirm anchor bolt locations and projections
- Ensure subgrade is compacted and not frozen
- Coordinate truck arrival schedule
Temperature Requirements
| Condition | Requirement |
|---|---|
| Cold weather (< 40°F) | Heat materials, insulate, maintain 50°F min for 3–7 days |
| Hot weather (> 85°F) | Cool mix, add retarder, max 90°F at placement |
| Normal | Begin curing immediately, maintain moist 7 days |
Common Issues
| Problem | Cause | Prevention |
|---|---|---|
| Cracking | Shrinkage, poor curing | Control joints, proper curing |
| Honeycomb | Poor vibration | Proper consolidation |
| Cold joints | Pour delay | Continuous placement |
| Scaling | Freeze-thaw | Air entrainment |
Curing: Concrete must stay moist for 7 days minimum to reach design strength. Use curing compound, wet burlap, or plastic sheeting. Equipment installation typically waits 7 days (70% strength) or 28 days (full strength).
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