Mississippi Marine Construction

Key Concepts

Fall protection (Subpart M) - Fall protection is required at 6 ft in residential construction; on scaffolds the trigger is 10 ft. - Low-slope roofs (slope ≤ 4 in 12) with unprotected sides and edges 6 feet or more above lower levels: guardrail systems, safety net systems, personal fall arrest systems, or a combination of warning line system and safety monitoring system — §1926.501(b)(10). Guardrails with toeboards are the steep-roof requirement under (b)(11). - Guardrail top rail: 39–45 inches (§1926.502). - Warning lines (§1926.502(f)): erected around all sides of the roof work area; not less than 6 ft from the roof edge when mechanical equipment is not used; not less than 6 ft (parallel) and not less than 10 ft (perpendicular) when it is; flagged at not more than 6-foot intervals; lowest point (including sag) no less than 34 inches and highest point no more than 39 inches from the surface; rope/wire/chain minimum tensile strength 500 pounds. - Safety monitoring (§1926.502(h)): a competent person monitors, must be on the same walking/working surface, within visual sighting distance, close enough to communicate orally, and shall not have other responsibilities that could take the monitor's attention from the monitoring function. Mechanical equipment shall not be used or stored where a safety monitoring system is protecting low-slope roofing work. Appendix A: a safety monitoring system alone is allowed only on low-sloped roofs 50 feet or less in width. - Subpart V: on poles, towers or similar structures, employees more than 1.2 meters (4 feet) above ground must use a personal fall arrest, work-positioning, or fall restraint system if no other subpart M protection is provided — §1926.954(b)(3)(iii)(B). - Covers (§1926.502(i)): twice the maximum axle load in roadways; all others twice the weight imposed; secured; marked "HOLE" or "COVER."

Key Concepts

Pile classification. On the basis of use there are two major classifications: (1) sheet and (2) load bearing. Sheet piles are used for earth retention and cofferdams and as temporary trench excavation support; major sheet pile materials are steel, prestressed concrete, and timber. Load-bearing piles are classified as timber (treated with a preservative / untreated), concrete (precast-prestressed, cast-in-place with shells, augered cast-in-place), steel (H section, steel pipe), and composite (concrete and steel, plastic with steel pipe core). (Ch. 17, PILE TYPES – CLASSIFICATIONS OF PILES)

Load transfer. If the load is transmitted to the soil through skin friction between the surface of the pile and the soil, the pile is a friction pile; if transmitted through the pile's lower tip, it is an end-bearing pile. Many piles depend on a combination of both. (Ch. 17, INTRODUCTION)

Timber piles. Treated piling lasts 50 years in northern marine waters and 20 years in southern marine waters; southern waters are defined as south of Cape Hatteras on the East Coast and below San Francisco on the West Coast. ASTM D 25–12 Standard Specification for Round Timber Piles establishes acceptance requirements for piles delivered to a project. Sound knots shall be no larger than one-sixth the circumference of the pile where the knot occurs. (Ch. 17, TIMBER PILES – Treated Timber Piles / Timber Pile Quality)

Precast-prestressed concrete (PPC) piles. May be removed from forms in as little as 24 hours, or as soon as the concrete has developed a compressive strength of 3,500 psi, using concrete with compressive strengths of 5,000 psi or greater under controlled curing. After form removal, piles are stored and cured 21 days or more before reaching driving strengths. Square and octagonal PPC piles are traditionally cast on beds 200 to 600 ft long so multiple piles can be cast and prestressed simultaneously. Plant-produced piles conform to PCI MNL-116–99. (Ch. 17, CONCRETE PILES – Precast-Prestressed)

Key Concepts

Cement types (Ch. 2 — Portland, Blended, and Other Hydraulic Cements) - Type V — high sulfate resistance for soils/groundwater high in sulfate; C₃A content not more than 5% (p. 26; 16th ed. p. 113). - Type II(MH) — generates heat more slowly by limiting the heat index (C₃S + 4.75 C₃A) to a maximum of 100 (p. 30; 16th ed. p. 112). - Type IV — for massive structures to minimize temperature rise; rarely manufactured in North America (p. 30; 16th ed. p. 113). - Type III — high early strength; used with heat curing by precast/prestressed producers for a 24-hour cycle (Ch. 22, p. 486; 16th ed. p. 69). - Air-entraining designations under ASTM C150: Types IA, IIA, II(MH)A, and IIIA (p. 27; 16th ed. pp. 113–114). - Flash set occurs when the proper amount/form of calcium sulfate is unavailable to control C₃A hydration; it cannot be dispelled by further mixing without adding water (p. 48; 16th ed. p. 134). - Above about w/c 0.40, water not needed for hydration remains in capillary pores or evaporates (p. 43; 16th ed. p. 131).

Aggregates (Ch. 5; Ch. 13) Nominal maximum size shall not exceed (ACI 318, Ch. 5 p. 103 / Ch. 13 p. 267): 1. ¾ the clear spacing between bars and between bars and forms; 2. one-fifth the narrowest dimension of a vertical member; 3. one-third the depth of slabs.

• Fine aggregate fineness modulus must be not less than 2.3 or more than 3.1 (ASTM C33); outside that range, reject unless proportions are adjusted (Ch. 5, p. 101).
• Recycled-concrete aggregate: lower specific gravity, higher absorption (3% to 10%) (Ch. 5, p. 97).
• Marine-dredged aggregate chlorides may alter set time, increase drying shrinkage, increase corrosion risk, and cause efflorescence; wash with fresh water (Ch. 5, p. 98).
• Particles with high porosity and medium-sized pores (0.1 to 5 µm) are most freeze-thaw vulnerable (Ch. 5, p. 109).
• 0.035% expansion in 350 or fewer freeze-thaw cycles is used by state highway departments to flag D-cracking susceptibility (Ch. 20, p. 427).

Mississippi Marine Construction — 4 questions (10% of exam) All content from Placing Reinforcing Bars, Recommended Practices (10th ed.), CRSI

Key Concepts

Concrete composition and strength (Chapter 3 — Concrete and Reinforced Concrete, Definitions) - Concrete = one part cement, about 1½ to 2½ parts fine aggregate (usually sand), about 3 to 5 parts coarse aggregate (gravel, crushed stone, or blast-furnace slag), and clean water. Strengths can be varied from about 3,000 to 10,000 psi, and higher. - Concrete sets up firm in hours (initial set), is self-supporting in a few days, and attains full rated strength in a specified length of time, usually 28 days. - High-early-strength cement produces about the same strength in about one-half or one-third of the time required with ordinary cement. Air-entraining cement creates tiny air voids for a more plastic, freeze-thaw-resistant mix. - Concrete is strong in compression but relatively weak in tension and shear; steel is strong in tension, compression and shear. - Bond: the adhesion of concrete to the bar surface plus the resistance of the deformations/ribs keeps bars from slipping and makes the two materials act as one.

Purpose and location of reinforcing steel (Chapter 6) - Compressive strength is verified with test cylinders 6 inches in diameter and 12 inches high, cured 7 to 28 days and crushed in a laboratory machine. - Longitudinal steel goes near the bottom of simple beams; continuous beams need bottom steel between supports and top steel over supports; cantilevers need top bars. Stirrups resist diagonal tension and are spaced closer near supports. Column ties and spirals restrain vertical bars from buckling. Temperature and shrinkage (T&S) steel is placed at right angles to the main steel.