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Showing 4 results for Drying Shrinkage

R. Abbasnia, M. Kanzadi, M. Shekarchi Zadeh, J. Ahmadi,
Volume 7, Issue 2 (6-2009)

Drying shrinkage in concrete, which is caused by drying and the associated decrease in moisture content, is one of the most important parameters which affects the performance of concrete structures. Therefore, it is necessary to develop experimental and mathematical models that describe the mechanisms of drying shrinkage and damage build up in concrete. The main objective of this research is the development of a computational model and an experimental method for evaluation of concrete free shrinkage strain based on the internal moisture changes. For this purpose and for modeling of moisture losses in concrete members a computational program based on finite element approach and the modified version of Fick's second law in which the process of diffusion and convection due to water movement are taken into account, is developed. Also the modified SDB moisture meter was used to measure the internal moisture changes in concrete. Based on the obtained results, calculated humidity is in good agreement with measured data when modified Fick's second law with diffusion coefficient from Bazant method were used, and are very reasonable for determining the moisture gradient. Also, the predicted value of shrinkage strain from the proposed method is in good agreement with measured data and also the established relationship can be used for determine the distribution of shrinkage strains in concrete members.
A. Allahverdi, B. Shaverdi, E. Najafi Kani,
Volume 8, Issue 4 (12-2010)

:The aim of this work is to investigate the influence of sodium oxide on properties of fresh and hardened paste of alkali-activated blast furnace slag from Isfahan steel plant. The silica modulus (SiO2/Na2O) of activator was adjusted at 0.6 and a number of mixes were designed in such a way to contain different levels of sodium oxide including 1, 2, 3, 4, 5, and 6% by weight of dry slag. The most important physico-mechanical properties of the pastes including workability, initial and final setting times, 28-day compressive strength and efflorescence severity were measured. Suitable mixes were chosen for more studies including compressive strength at different ages, 90-day autogenous and drying shrinkages. According to the results, increasing the sodium oxide content of the mixes results in increased workability, reduced setting times, and higher compressive strength. The results confirm the possibility of achieving 28-day compressive strengths up to 27.5, 50.0 and 70.0 MPa for mixes with sodium oxide content of 1, 2 and 3 wt% respectively. The measured values for autogenous shrinkage were all less than 0.1% and SEM studies showed a significant decrease in pore sizes with increasing sodium oxide concentration from 1 to 2%.

H. Famili, M. Khodadad Saryazdi, T. Parhizkar,
Volume 10, Issue 3 (9-2012)

Self-desiccation is the major source of autogenous shrinkage and crack formation in low water-binder ratio (w/b) concretes

which can be reduced by internal curing. In this paper performance of high strength self consolidating concrete (HS-SCC) with

w/b of 0.28 and 0.33 including autogenous shrinkage, drying shrinkage, compressive strength, and resistance to freezing-thawing

was investigated. Then, for the purpose of internal curing, 25% of normal weight coarse aggregate volume was replaced with

saturated lightweight aggregate (LWA) of the same size and its effects on the material properties was studied. Two modes of

external curing, moist and sealed, were applied to test specimens after demoulding. Autogenous shrinkage from 30 minutes to 24

hours after mixing was monitored continuously by a laser system. The initial and final setting time were manifested as a change

of the slope of the obtained deformation curves. Shrinkage after initial setting was 860 and 685 microstrain (&mu&epsilon) for 0.28 and 0.33

w/b mixtures, respectively. The saturated LWA reduced these values to 80 and 295 &mu&epsilon, respectively. By LWA Substitution the 28-

day compressive strength of 0.28 w/b mixture was reduced from 108 to 89 and 98 to 87 MPa for moist and sealed cured specimen,

respectively. The corresponding values for 0.33 w/b mixture was 84 to 80 and 82 to 70 MPa. Shrinkage of 0.28 w/b mixture

without LWA after moist and sealed cured specimen dried for 3 weeks was about 400 &mu&epsilon. Shrinkage of moist and sealed cured

specimen containing LWA was reduced 9% and 25%, respectively. On the contrary for 0.33 w/b mixture an increase was noticed.

Freezing-thawing resistance was improved by sealed curing, decreasing w/b and substituting LWA.

M. S. Lee, T. S. Seo,
Volume 12, Issue 1 (3-2014)

Because thin plate reinforced concrete members such as walls and slabs are greatly influenced by the drying shrinkage, cracks can occur in these members due to the restraint of the volume change caused by drying shrinkage. Therefore, the control of cracking due to drying shrinkage is very important in building construction that the thin plate members are frequently used. However, few researches of estimating shrinkage cracking in RC walls have been executed, and the cracking control design of RC walls has been conducted based on the experience rather than the quantitative design method. In this study, the practical cracking prediction method using equivalent bond-loss length Lb was proposed for the quantitative drying shrinkage crack control of RC wall. The calculated values using proposed method were compared with the experimental results from uniaxial restrained shrinkage cracking specimens and the investigative values from the field study. In general, the results of this method were close to those of the experiment and the field study.

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