Which of the following methods reduces the drying shrinkage of concrete?

Detailed Explanation: Three Methods to Reduce Drying Shrinkage

Why D (All options) is correct: Drying shrinkage is primarily a cement paste phenomenon. Strategies to reduce it focus on reducing the amount and porosity of paste, reducing free water, and increasing aggregate restraint.

Methods to Reduce Shrinkage

Method	Mechanism	Effect on Shrinkage
A. Low w/c ratio	Less free water in the mix → less evaporable water → fewer capillary pores formed	Directly reduces drying shrinkage; also improves strength and durability
B. Less cement content	Paste = cement + water; less cement = less paste volume that shrinks. Aggregate does not shrink and restrains paste shrinkage	Reduces total shrinkage, but must maintain minimum cement content for durability (IS 456)
C. Proper mix design	Correct aggregate gradation minimises void space requiring paste; well-graded aggregate reduces paste demand for a given workability; stiffer aggregate (higher modulus) provides more restraint	Optimised aggregate/paste ratio minimises shrinkage

Additional Strategies to Reduce Shrinkage

Strategy	Why It Helps
Extended moist curing	Delays drying onset; allows more hydration products to fill pores → lower porosity → less evaporation
Shrinkage-reducing admixtures (SRAs)	Reduce capillary tension that drives shrinkage by lowering surface tension of pore water
Expansive cements	Chemically expand during hydration to offset later shrinkage
Minimize member thickness (slabs)	Thinner members dry faster but have less moisture gradient; use expansion joints for large areas

• Drying shrinkage reduced by: low w/c ratio, minimal cement content, and proper mix proportioning (all three together).
• Aggregate restrains paste shrinkage — maximising aggregate volume (within design limits) reduces shrinkage.
• Harder, stiffer aggregates (granite, quartzite) provide more restraint than softer aggregates.