Concrete and Masonry Construction
Concrete
Mix design is governed by the water-cement ratio: lower w/c means higher strength and better durability. Slump (ASTM C143) is the field workability test. Air entrainment provides freeze-thaw resistance. Acceptance strength comes from cylinders tested at 28 days (ASTM C39); standard moist curing is 7 days for Type I cement. Consolidate with a vibrator without over-vibrating, which causes segregation. Form removal follows ACI 347 guidance based on member type and temperature.
Reinforcement
Bar sizes: #4 = 1/2 in diameter, 0.20 sq in; #5 = 5/8 in, 0.31 sq in; #6 = 3/4 in, 0.44 sq in. Typical clear cover: 3 in cast against earth, about 1.5-2 in exposed to weather, 3/4 in for interior slabs. Tension lap splices are commonly 40 bar diameters unless the drawings state otherwise. Chairs and bolsters maintain cover; cover is a durability and fire requirement, not a suggestion.
Masonry
Nominal versus actual: an 8x8x16 CMU measures 7-5/8 x 7-5/8 x 15-5/8; the 3/8 in mortar joint makes up the difference. Mortar types by strength: M (highest, below grade and severe exposure), S (general structural), N (above grade, moderate), O (low strength, nonstructural). Grout fills reinforced cores. Control joints accommodate movement; flashing and weep holes drain the cavity; efflorescence is a cosmetic salt deposit, not necessarily a leak.
Worked example
A 4 in slab over 1,000 sf: volume = 1,000 x (4/12) = 333 cf / 27 = 12.35 cy; add 5-10% waste and order about 13 cy. Dead load check: (4/12) x 150 pcf = 50 psf.
Traps: using nominal dimensions in quantity math, confusing mortar with grout, or assuming 7-day strength is the acceptance criterion.