Concrete, Masonry, and Metals
Concrete questions center on mix design, placement, curing, and strength. Know that water-cement ratio controls strength and durability - more water means lower strength and more shrinkage. Understand slump as a workability measure, air entrainment for freeze-thaw resistance, and curing (moist curing, typically 7 days for normal cement). Know that concrete reaches design strength at 28 days; a common rule is that strength gain slows significantly after that.
Understand reinforcement: rebar sizes (#3 = 3/8 in, #8 = 1 in diameter), cover requirements, and the purpose of stirrups and ties. Know control joints (planned cracks) versus expansion joints (allow movement).
For masonry, understand mortar types (Type S for structural, Type N for general veneer), flashing, weeps, and wall ties. Know the difference between brick, block (CMU), and stone and the role of the bond pattern. For metals, understand structural steel shapes (W, S, C, L), bolted vs. welded connections, and fireproofing requirements for structural steel.
Worked example: A slab specified at f'c = 3,000 psi with a 0.50 water-cement ratio. If the mix uses 500 lb of cement per cubic yard, maximum water = 0.50 × 500 = 250 lb (about 30 gallons). Adding water on site to boost workability lowers strength - a classic trap.
Traps: adding water at the site; confusing control and expansion joints; wrong mortar type; forgetting steel fireproofing.