Alabama Concrete Contractor

Key Concepts

Material Quantity Takeoff (Volume Calculations) - Concrete volume is calculated in cubic yards (CY). Convert cubic feet to CY by dividing by 27. - Slabs: Length × Width × Thickness (convert thickness to feet). Add 5–10% waste factor. - Walls: Length × Height × Thickness (in feet) ÷ 27. - Footings: Length × Width × Depth ÷ 27. For continuous footings, use total linear feet × cross-section area. - Always order 5–10% extra to account for over-excavation, waste, and uneven subgrades.

Mix Design vs. Mix Proportioning (per Design and Control of Concrete Mixtures, Ch. 15) - Mixture design defines performance parameters: strength (f'c), air content, slump, w/cm ratio, durability requirements. - Mixture proportioning translates those parameters into actual batch weights (lbs/yd³ or kg/m³). - These are not interchangeable terms — the exam may test this distinction. - Key fresh concrete parameters specified on drawings or specs: - w/cm ratio (water-to-cementitious materials): lower = stronger, more durable. Typical range: 0.40–0.50 for structural concrete. - Slump: Workability indicator, typically 3–5 inches for general placement; higher slump reduces strength. - Air content: 4–7% for freeze-thaw exposure; entrained air improves durability. - Compressive strength (f'c): Specified at 28 days; common values are 3,000–5,000 psi.

Key Concepts

Batter Boards & String Lines

Batter boards are temporary wooden frames set back from building corners (typically 4–6 ft) to preserve layout reference points during excavation. String lines are stretched between batter boards to establish building lines, elevation, and corner locations. A plumb bob is used to transfer string-line intersections to the ground. All layout must reference benchmark elevations from survey stakes.

Reading Plans & Survey Stakes

Survey stakes use abbreviations: TC (top of curb), FL (flow line), FG (finished grade), C (cut), F (fill). Cut/fill numbers indicate how much soil to remove or add. Construction plans show plan view, elevations, sections, and details — always cross-reference all views before excavating.

OSHA Excavation Safety — 29 CFR 1926 Subpart P

Key trigger: Any excavation 5 feet or deeper requires a protective system unless the excavation is in stable rock. Excavations 20 feet or deeper require a protective system designed by a Registered Professional Engineer (RPE).

A competent person must classify soil and inspect excavations daily and after any hazard-changing event (rain, freeze/thaw, vibration).

Key Concepts

Formwork Definition (§1926.700(b)(2)): Formwork is the total system — not just the form skin, but all shores, reshores, hardware, and braces supporting fresh or partially cured concrete.

General Design Requirements (§1926.703(a)(1)): Formwork must be designed, fabricated, erected, supported, braced, and maintained to support all vertical and lateral loads that may be applied without failure.

Lateral Pressure of Fresh Concrete on Vertical Forms: - Fresh concrete behaves like a fluid until it begins to set. Lateral pressure depends on rate of pour (R), concrete unit weight (~150 pcf), temperature, and concrete mix (admixtures, SCMs). - ACI 347 governs: slower pour rate and higher temperature = lower lateral pressure. Maximum pressure for columns and walls is capped but can approach full hydrostatic pressure at fast pour rates. - Columns generate higher lateral pressure than walls poured at the same rate due to smaller plan area and typically faster fill rates.

Vertical Loads on Formwork: - Dead load: Weight of fresh concrete (~150 pcf) + weight of formwork itself. - Live load: Workers, equipment, and material storage. ACI 347 minimum = 50 psf on deck forms, or 75 psf if motorized buggies are used. - Minimum design value: Total vertical load on slab forms shall not be less than 100 psf (dead + live combined) per ACI 347.

Key Concepts

ASTM Specifications & Grades

• A615: Deformed and plain carbon-steel bars. Most common. Grades 40, 60, 80. Grade 60 = 60,000 psi yield / 90,000 psi tensile minimum.
• A706: Low-alloy steel. Grade 60 yield = 60,000 psi min, 78,000 psi max (1.25× actual yield tensile minimum). Use when welding is required — A615 requires caution; A706 is the weldable choice.
• A955: Stainless steel reinforcing bars (corrosion-critical environments).
• A1035: High-strength, low-carbon chromium steel. Higher strength than A615; used in Grade 100 confinement applications.
• All welding must comply with AWS D1.4.

Bar Identification Markings

Deformed bars have rolled-in markings: 1. Line(s) = producing mill 2. Letter or symbol = bar size number 3. Letter = steel type (S = carbon/A615, W = low-alloy/A706, SS = stainless/A955, C = low-carbon chromium/A1035) 4. Grade mark: one line = Grade 40/60 (by number of lines), or the number 4, 6, 7, 8 rolled onto bar

Bar sizes are designated by number (#3 through #18); the number approximates bar diameter in eighths of an inch (e.g., #8 = 8/8 = 1 inch diameter).

Key Concepts

Mixture Proportioning & w/cm Ratio

• The water-cementitious materials ratio (w/cm) is the single most important factor controlling concrete strength and durability. Lower w/cm = higher strength and lower permeability.
• w/cm is calculated as: weight of water ÷ weight of cementitious materials (cement + SCMs).
• ACI 318 sets maximum w/cm limits by exposure condition (e.g., 0.40 for severe sulfate exposure, 0.45 for de-icing chemicals, 0.50 for moderate exposure).

Portland Cement Types

Supplementary Cementitious Materials (SCMs)

• Fly ash (Class C): Cementitious + pozzolanic; from lignite/sub-bituminous coal. Typical replacement: 15–40%.
• Fly ash (Class F): Pozzolanic only; from bituminous coal. Better sulfate resistance. Same replacement range.
• Slag cement (GGBFS): Latent hydraulic; improves durability, reduces heat. Typical replacement: 25–70%.
• Silica fume: Very fine pozzolan; dramatically reduces permeability; typical replacement: 5–10%. Requires water reducer due to high surface area.

Covers Subparts E, F, L, M, P, Q, AA, CC of 29 CFR 1926 | 6 questions, 10% of exam

Key Concepts

Fall Protection (Subpart M)

• 6-foot trigger height for all construction activities — if you're 6 feet or more above a lower level, fall protection is required.
• Three acceptable systems: guardrail systems, personal fall arrest systems (PFAS), or safety nets.
• Guardrail top rail: 42 inches (±3 inches) high; mid-rail at 21 inches; must withstand 200 lbs of force.
• PFAS must limit free fall to 6 feet and arrest forces to 1,800 lbs; anchor points rated at 5,000 lbs per worker.
• Safety nets deployed within 30 feet below work surface; must be drop-tested.
• Reinforcing steel: cover exposed rebar ends (impalement hazard) with caps or wooden troughs — this is Subpart Q, not just a fall issue.

Concrete & Masonry (Subpart Q – §1926.700–706)

• Formwork must be designed by a qualified engineer; shoring and reshoring drawings required before removal.
• Protruding rebar (impalement): must be guarded with caps, wooden planks, or equivalent — no exceptions.
• Concrete buckets: no workers allowed to ride; tag lines required to control swing.
• Post-tensioning: no workers behind the jack during stressing; warning signs required.
• Pumping systems: pipelines must be designed for max pump pressure; safety devices required on boom-type systems.
• Lift-slab operations: jacks must…