General Contractor License Site Work and Concrete 5 — Questions and Answers
Question 1: The water-cement ratio in concrete directly affects which property?
- Color and finish of the surface
- Compressive strength and durability (Correct answer)
- Time required for formwork removal
- Aggregate gradation in the mix
Correct answer: Compressive strength and durability
A lower water-cement ratio produces higher compressive strength and better durability; excess water weakens the paste and increases porosity.
Question 2: What is the purpose of a geotextile fabric installed in a drainage aggregate layer?
- To provide waterproofing
- To separate soil from aggregate and prevent migration of fines (Correct answer)
- To increase load-bearing capacity of the aggregate
- To warm the soil in cold climates
Correct answer: To separate soil from aggregate and prevent migration of fines
Geotextile fabric acts as a filter that allows water to pass while preventing fine soil particles from migrating into and clogging the drainage layer.
Question 3: Cold weather concreting requires protecting fresh concrete because:
- Low temperatures increase the water-cement ratio
- Freezing before adequate strength gain permanently damages the concrete (Correct answer)
- Cold weather causes excessive bleeding and segregation
- Concrete shrinks too rapidly in cold conditions
Correct answer: Freezing before adequate strength gain permanently damages the concrete
If fresh concrete freezes before reaching approximately 500 psi, ice crystals permanently disrupt the cement paste matrix, causing irreversible strength loss.
Question 4: What does 'bench cut' excavation mean?
- Excavating with a backhoe on a flat bench
- Cutting stepped horizontal terraces into a slope to improve stability (Correct answer)
- Removing topsoil in a single horizontal pass
- Trenching along a building benchmark elevation
Correct answer: Cutting stepped horizontal terraces into a slope to improve stability
Bench cutting creates horizontal steps (benches) in a slope, reducing the effective height of each exposed face and improving overall slope stability.
Question 5: Concrete consolidation by mechanical vibration is done primarily to:
- Speed up the hydration process
- Eliminate air voids and ensure complete aggregate encapsulation (Correct answer)
- Increase the water-cement ratio for workability
- Create a smooth troweled surface finish
Correct answer: Eliminate air voids and ensure complete aggregate encapsulation
Internal vibration removes entrapped air pockets and ensures concrete flows around reinforcement and into form corners for a dense, uniform matrix.
Question 6: A 'benchmark' on a construction site is:
- A standard test for soil bearing capacity
- A fixed reference point of known elevation used for surveying (Correct answer)
- The minimum acceptable compaction density
- A legal boundary marker for the property
Correct answer: A fixed reference point of known elevation used for surveying
A benchmark is a permanent, precisely established reference point with a known elevation from which all site elevation measurements are taken.
Question 7: What does 'segregation' mean when it occurs in freshly mixed concrete?
- Premature hardening of the surface crust
- Separation of coarse aggregate from the cement paste and mortar (Correct answer)
- Cracking due to differential shrinkage rates
- Excessive air entrainment in the mix
Correct answer: Separation of coarse aggregate from the cement paste and mortar
Segregation occurs when coarse aggregate separates from the paste, resulting in non-uniform concrete with weakened zones and poor surface quality.
General Contractor License Site Work and Concrete 5
The water-cement ratio in concrete directly affects which property?