Hardscapes
What this domain covers
Hardscapes covers segmental paver systems and segmental retaining walls (SRWs): what happens below the surface. The exam asks you to sequence installation correctly - subgrade, separation, base, bedding, units, restraint, joint sand, and for walls, leveling pad, drainage column, and geogrid.
Core rules
- Paver standards: ASTM C936 covers solid interlocking concrete paving units; C902 covers units for pedestrian and light vehicular use; C1272 covers heavy vehicular units. Joint sand is typically ASTM C144 masonry sand.
- Base: compacted crushed aggregate placed in lifts of about 6–8 in. and compacted before the next lift. ICPI guidance commonly cites 98% of maximum density per ASTM D1557 (Modified Proctor); many SRW specifications cite 95% of ASTM D698 (Standard Proctor). Read which standard your specification invokes - the numbers are not interchangeable.
- Bedding course: about 1 in. of screeded concrete sand, never thicker than about 1-1/2 in., and never used to correct base errors. Joints run 1/8–3/16 in.
- Edge restraint is required on every unrestrained edge and is set on the compacted base, not on the sand.
- Drainage: minimum 2% slope (1/4 in. per ft) away from structures.
- SRW: compacted aggregate leveling pad; embedment of at least 6 in. for level grade, deeper (commonly 12 in.) with a sloping backslope; a 12 in. drainage aggregate column with filter fabric and perforated outlet pipe; geogrid laid level and tensioned, kept back from the face and extended beyond the calculated failure plane.
Worked example
Patio 20 × 15 ft = 300 sq ft, 6 in. compacted base, 1 in. sand. Compacted base = 300 × 0.5 = 150 cu ft. Loose-to-compacted bulking factor ~1.3 gives 195 cu ft, or 195 ÷ 27 ≈ 7.2 cu yd. Bedding sand = 300 × (1/12) = 25 cu ft ≈ 0.93 cu yd. At 2%, the 15 ft dimension falls 0.30 ft, about 3.6 in., across the slope.
Traps that cost marks
Thickening the sand to fix an uneven base; forgetting edge restraint; compacting base in one deep lift; setting restraint on the bedding; and skipping the drainage column behind an SRW, which is the most common cause of wall failure.