--- title: "Shrinkage and creep of concrete" subject: "Concrete Technology and Masonry Structure" chapter: 4 key: "semester_5/concrete_technology_and_masonry_structure:shrinkage-and-creep" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/shrinkage-and-creep site: BCT Engineering --- # Shrinkage and creep of concrete Concrete Technology and Masonry Structure · Chapter 4: Properties of hardened concrete - Asked in: 2078 Kartik, 4+4 marks; 2073 Shrawan, 6 marks; 2072 Kartik, 6 marks; 2070 Chaitra, 2 marks; 2069 Chaitra, 4 marks; 2064 Jestha (old course) (asked 6 times) - Video: [Difference between Shrinkage and Creep](https://www.youtube.com/watch?v=xLUsS7XKgDk) — Civil Engineering - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/shrinkage-and-creep - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-4 ## Question Explain shrinkage and creep in concrete (describe the phenomena and their effect on concrete behaviour). ## Short answer Shrinkage is time-dependent volume reduction without load from moisture loss and chemical reactions, causing cracking, warping, and prestress loss. Creep is gradual strain increase under sustained stress, increasing deflection and prestress loss but relieving stress concentrations. Both depend on w/c ratio, curing, and aggregate stiffness. ## Answer #### Shrinkage **Shrinkage** is the time-dependent reduction in volume of concrete, without any applied load, caused by loss of moisture and by chemical reactions (hydration and carbonation). Typical long-term values are 0.0003 to 0.0008 (300 to 800 microstrain). **Types of shrinkage** | Type | Meaning | Remarks | |---|---|---| | Plastic shrinkage | Water lost from the surface of fresh concrete by evaporation, faster than bleeding can replace it | Occurs in the first few hours; causes surface cracks in hot, dry, windy weather | | Drying shrinkage | Loss of adsorbed and gel water from hardened concrete in dry air | Partly reversible; depends on W/C, paste content, aggregate stiffness, size of member, humidity | | Autogenous shrinkage | Volume reduction from the hydration reaction itself (self-desiccation) with no moisture exchange | Significant only at very low W/C (below about 0.4) | | Carbonation shrinkage | CO2 reacts with Ca(OH)2 and the paste shrinks | Highest at about 50% relative humidity | | Thermal shrinkage | Contraction when concrete cools after the heat of hydration | Important in mass concrete | **Effects:** surface and through cracks, warping of slabs, loss of prestress, and extra deflection. It is reduced by low W/C, low paste content, large well-graded aggregate, proper curing and joints. When no test data are available, IS 456 (Cl. 6.2.4.1) allows an approximate design shrinkage strain of 0.0003. #### Creep **Creep** is the gradual increase in strain of concrete with time under a constant sustained stress, over and above the instantaneous elastic strain. It is caused mainly by seepage of gel water out of the C-S-H layers and by slip of gel particles. Creep continues for years, with about 50% occurring in the first 3 months and 75 to 80% in the first year. **Creep coefficient and factors.** Creep coefficient $\theta = \varepsilon_{creep}/\varepsilon_{elastic}$. IS 456 (Cl. 6.2.5.1) gives $\theta$ = 2.2 (loaded at 7 days), 1.6 (28 days) and 1.1 (1 year). It increases with higher W/C and paste content, lower strength at loading, higher stress (up to about 40 to 50% of $f_c$), lower humidity, smaller members and lower-modulus aggregates. It decreases with later age of loading, good curing and stiff aggregates. **Effects:** increases deflection of beams and slabs, loss of prestress, redistribution of stress from concrete to steel in columns, but also relieves stress concentrations and reduces cracking due to shrinkage. ```text strain | | _________ | _..--'' | | _..--' creep | instantaneous | _..--'' | (elastic) recovery | .-'' | | | '. | | instantaneous '-._ | | elastic strain ''--.__ creep recovery | | ''--.__ (slow, partial) | | ''-------- permanent | | deformation +--------+------------------------------+---------------------------------- time 0 load applied load removed ``` - On loading, an **instantaneous elastic strain** appears. - Under sustained load, strain keeps rising with time (**creep**), fast at first, then slowly. - On unloading, an **instantaneous (elastic) recovery** occurs, nearly equal to the elastic strain on loading (slightly less because $E$ rises with age). - Then a slow **creep recovery** follows, which is only a part of the creep strain. - The remaining strain is the **permanent (irrecoverable) deformation**. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Shrinkage of concrete is: A. a time-dependent reduction in volume without applied load, due to moisture loss and chemical reaction B. an increase in strain with time under constant sustained load C. an instantaneous strain that disappears on unloading D. a loss of strength under repeated loading Answer: A. Shrinkage occurs with no load; the other options describe creep, elastic strain and fatigue. (Key point: Definition of shrinkage) 2. Which shrinkage occurs in the first few hours when surface water evaporates faster than bleeding can replace it? A. Drying shrinkage B. Autogenous shrinkage C. Plastic shrinkage D. Thermal shrinkage Answer: C. Plastic shrinkage is loss of surface water from fresh concrete, giving surface cracks in hot, dry, windy weather. (Key point: Plastic shrinkage) 3. Creep is caused mainly by: A. growth of ice crystals in capillary pores B. carbonation of Ca(OH)2 in the paste C. seepage of gel water out of the C-S-H layers and slip of gel particles D. expansion of aggregate under heat Answer: C. Gel water seepage and gel particle slip give the time-dependent strain; about 75 to 80% occurs in the first year. (Key point: Cause and time of creep) 4. IS 456 creep coefficient values for loading at 7 days, 28 days and 1 year are: A. 1.1, 1.6 and 2.2 B. 2.2, 1.6 and 1.1 C. 2.2, 1.1 and 1.6 D. 1.6, 2.2 and 1.1 Answer: B. Earlier loading gives larger creep, so theta falls from 2.2 to 1.6 to 1.1 as loading age rises. (Key point: Creep coefficient) 5. Which is an effect of creep in concrete structures? A. increase in modulus of elasticity of the beam B. reduced deflection under sustained load C. gain of prestress in tendons D. increased deflection of beams and slabs and loss of prestress Answer: D. Creep adds strain under sustained load, so deflection rises and prestress is lost. 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