CLA CLA Hardscape & Materials 2 — Questions and Answers
Question 1: What does 'compressive strength' measured in PSI indicate for a hardscape material like concrete?
- The maximum tensile force before cracking
- The force per unit area the material can withstand under compression before failure (Correct answer)
- The freeze-thaw resistance rating
- The slip resistance value for pedestrian surfaces
Correct answer: The force per unit area the material can withstand under compression before failure
Compressive strength (PSI) is the maximum compressive load per square inch a material can sustain; concrete for walkways is typically specified at 3,000–4,000 PSI.
Question 2: Which surface treatment for concrete improves slip resistance for pedestrian areas?
- Burnished finish
- Exposed aggregate or broom finish (Correct answer)
- Polished epoxy coating
- Sealed smooth trowel finish
Correct answer: Exposed aggregate or broom finish
Broom finishing or exposed aggregate creates surface texture that increases friction coefficients and reduces slip hazard, especially when wet.
Question 3: What is the purpose of 'control joints' (contraction joints) in a concrete slab?
- Provide structural reinforcement at slab edges
- Create weakened planes that guide crack formation to controlled locations (Correct answer)
- Allow thermal expansion to occur
- Connect two separate concrete pours
Correct answer: Create weakened planes that guide crack formation to controlled locations
Control joints are saw-cut or tooled grooves that create planes of weakness, directing inevitable shrinkage cracks to predictable, aesthetically acceptable locations.
Question 4: What is the typical recommended base depth for a permeable interlocking concrete pavement (PICP) system designed for stormwater infiltration?
- 1–2 inches of sand only
- 6–12+ inches of open-graded aggregate (Correct answer)
- 4 inches of compacted dense-graded base
- 2 inches of asphalt leveling course
Correct answer: 6–12+ inches of open-graded aggregate
PICP requires a deep open-graded aggregate reservoir (often 6–18 inches) to store and infiltrate stormwater, unlike traditional pavements that simply convey runoff.
Question 5: What is 'efflorescence' in masonry and concrete hardscape materials?
- A decorative acid-stain color effect
- White salt deposits that leach to the surface as water migrates through the material (Correct answer)
- A polymer admixture for crack resistance
- Surface pitting from freeze-thaw cycles
Correct answer: White salt deposits that leach to the surface as water migrates through the material
Efflorescence is the migration of soluble salts to a masonry or concrete surface where they crystallize as white deposits when water evaporates.
Question 6: Which hardscape material is valued for its high thermal mass, durability, and natural variation in color and texture in landscape design?
- Pressure-treated lumber
- Asphalt
- Natural cut stone (granite, limestone, bluestone) (Correct answer)
- Recycled rubber pavers
Correct answer: Natural cut stone (granite, limestone, bluestone)
Natural cut stone offers exceptional durability, natural beauty, and color variation that improves with age, making it a premium landscape paving choice.
CLA CLA Hardscape & Materials 2
What does 'compressive strength' measured in PSI indicate for a hardscape material like concrete?