Concrete and Masonry
What is tested
Concrete and masonry questions test mix design, placement, curing, reinforcement, joints, CMU assembly, mortar, grout, and water management.
Core rules
- Water-cement ratio controls strength and durability; lower w/c generally means higher strength. Do not add water to regain slump without approval; use plasticizers.
- ACI 318 governs structural concrete; cover, lap splices, and formwork are design-critical. Curing time and temperature matter; cold and hot weather require protection.
- Control joints are planned cracks; construction joints are planned stops. Consolidate with a vibrator without segregating the mix.
- Masonry: mortar types M, S, N, and O vary in strength; Type S is common for structural and exterior work. Grout fills reinforced cells. Flashing, weep holes, and an air space drain water.
- CMU is nominal; actual face dimensions are smaller, such as 8×8×16 nominal block being about 7⅝×7⅝×15⅝.
Worked example
A mix has 600 lb of cement and a specified w/c of 0.45. Maximum water = 600 × 0.45 = 270 lb. Water weighs 8.34 lb/gal, so 270 ÷ 8.34 = 32.4 gal. If the batch already has 30 gal, only 2.4 gal may be added, assuming no other water sources. Reasoning: w/c is a mass ratio, not a volume ratio.
Traps
Adding water for slump; confusing mortar types; omitting flashing or weeps; assuming nominal CMU dimensions; ignoring curing temperature.