--- title: "Creep phenomenon with time-dependent graph" subject: "Concrete Technology and Masonry Structure" chapter: 4 key: "semester_5/concrete_technology_and_masonry_structure:creep-phenomenon-graph" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/creep-phenomenon-graph site: BCT Engineering --- # Creep phenomenon with time-dependent graph Concrete Technology and Masonry Structure · Chapter 4: Properties of hardened concrete - Asked in: 2080 Bhadra, 6 marks; 2066 Jestha (old course), 1+4 marks (asked 2 times) - Video: [Creep Test | Creep Curve | Stages in Creep | Dr. Vasim A. Shaikh](https://www.youtube.com/watch?v=lNQ5hxFUZFI) — Prof. Dr. Vasim A. Shaikh - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/creep-phenomenon-graph - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-4 ## Question Define creep. Explain the phenomenon of creep in concrete with a time dependent graph during loading and unloading (elastic recovery, creep recovery and permanent deformation). ## Short answer Creep is time-dependent strain under sustained stress. On loading, instantaneous elastic strain occurs, followed by creep. On unloading, elastic recovery is immediate, then partial creep recovery, leaving permanent deformation. IS456 creep coefficient is1.1–2.2 depending on age at loading. ## Answer **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. ```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**. **Mechanism:** (i) seepage of adsorbed and gel water from the C-S-H under sustained stress, (ii) viscous slip of gel particles, (iii) microcracking at high stress and (iv) delayed elastic effect of aggregates. Specific creep is the creep strain per unit stress. **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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Creep in concrete is: A. the reduction in volume with time without any load B. the gradual increase in strain with time under a constant sustained stress, beyond the elastic strain C. the failure under repeated cyclic load D. the instantaneous strain on loading Answer: B. Creep needs a sustained load and appears as strain growth over and above the instantaneous elastic strain. (Key point: Definition of creep) 2. On unloading a crept concrete specimen, the sequence of behaviour is: A. instantaneous elastic recovery, then slow partial creep recovery, leaving a permanent deformation B. full recovery of all strain immediately C. no recovery at all because creep is plastic D. slow recovery first, then a sudden elastic recovery Answer: A. Elastic strain recovers at once, only part of the creep recovers slowly, and the rest is permanent. (Key point: Recovery after unloading) 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, 1.1 and 1.6 C. 1.6, 2.2 and 1.1 D. 2.2, 1.6 and 1.1 Answer: D. Earlier loading gives larger creep, so theta falls from 2.2 to 1.6 to 1.1 as loading age rises. 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