Drying shrinkage of concrete is affected by which of the following?

Detailed Explanation: Three Factors Affecting Drying Shrinkage

Why D (All options) is correct: Drying shrinkage occurs as free water evaporates from the capillary pores of hardened concrete. All three listed factors directly influence either the amount of water available to evaporate or the rate at which it evaporates.

Mechanism of Each Factor

Factor	Mechanism	Effect on Shrinkage
A. Relative humidity	At low RH, the vapour pressure gradient is high, driving rapid evaporation from capillary pores; at high RH, evaporation is suppressed	Lower RH → more/faster drying shrinkage; RH = 100% → zero drying shrinkage
B. Time	Drying is a time-dependent diffusion process; water evaporates progressively from the surface inward over months	Shrinkage increases with time, asymptoting to the ultimate value over years
C. Water-cement ratio	Higher w/c means more free (capillary) water in the mix; more evaporable water → more shrinkage on drying	Higher w/c → more porous paste → more drying shrinkage

Drying Shrinkage Over Time (Typical Pattern)

Time After Drying Begins	Approximate % of Ultimate Shrinkage Reached
28 days	≈ 14–34% (depends on w/c, humidity, member size)
3 months	≈ 40–70%
1 year	≈ 75–90%
Several years	Approaches 100% (ultimate)

IS 456:2000 Design Assumption: Total design shrinkage strain = 0.0003 (in absence of specific test data) This is a conservative but practical value for structural design.

• Drying shrinkage is affected by relative humidity, time, and w/c ratio (all three).
• At RH = 100%, no drying occurs and drying shrinkage is zero.
• Autogenous shrinkage (due to chemical contraction during hydration) is separate from drying shrinkage.