University of Illinois Urbana-Champaign

Understanding effects of pre-soaked lightweight aggregate on volume stability of mortar and concrete mixtures

Ardeshirilajimi, Ardavan

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ARDESHIRILAJIMI-DISSERTATION-2018.pdf

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https://hdl.handle.net/2142/102447

Description

Title
Understanding effects of pre-soaked lightweight aggregate on volume stability of mortar and concrete mixtures
Author(s)
Ardeshirilajimi, Ardavan
Issue Date
2018-11-30
Director of Research (if dissertation) or Advisor (if thesis)
Mondal, Paramita
Doctoral Committee Chair(s)
Mondal, Paramita
Committee Member(s)
  • Lange, David A.
  • Popovics, John S.
  • Roesler, Jeffery R.
Department of Study
Civil & Environmental Eng
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2019-02-06T19:36:07Z
Keyword(s)
Lightweight Aggregate, Shrinkage Cracking, Concrete, Internal Curing
Abstract
Shrinkage cracking is a predominant deterioration mechanism greatly affecting the durability and integrity of concrete structures. This is especially the case for concrete bridge decks due to the large surface-to-volume ratio of these types of structures, which results in a high rate of moisture loss from the exposed surface. An extensive body of literature suggests that pre-soaked lightweight aggregate (LWA) is greatly beneficial for curing concrete internally and reducing autogenous shrinkage by providing additional water reservoirs for the mixture. However, the literature on the effect of LWA on drying shrinkage is limited. Therefore, the main objective of this work is to improve our understanding of the influence of LWA on microstructure development and shrinkage of mortar and concrete mixtures in an unsealed condition. The effect of LWA on drying shrinkage under different boundary conditions is examined. By varying the number of faces exposed to the surrounding unsaturated environment, the severity of drying condition is altered and its effect on drying shrinkage of internally cured mixtures is studied. The efficiency of LWA in reducing drying shrinkage is shown to be significantly dependent upon the severity of the drying condition, and the duration and type (sealed versus moist) of external curing. The effect of sample size on the efficiency of LWA in reducing drying shrinkage is also studied. It is shown that incorporation of LWA to internally cure concrete may be an inadequate shrinkage compensating strategy, particularly in a severe drying condition. Nonetheless, internally cured mixtures exhibited a denser microstructure which can be advantageous in terms of durability. An attempt was made to design a low-shrinkage internally cured mixture using expansive cement. The expansive nature of Calcium Sulfoaluminate (CSA)–based cements can be used to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. It is shown that combining CSA with internal curing is mutually beneficial; ordinary Portland cement (OPC)–CSA mixtures show increased hydration of CSA and a denser microstructure when LWA is added to the mixture. Furthermore, the addition of CSA to the mixtures with LWA results in a positive deformation even in an unsealed condition. Moreover, moisture movement in internally cured cement-based materials is modeled using diffusion equation to better understand the characteristics of LWA that influence its effectiveness. A two-dimensional diffusion equation in Cartesian coordinates is used to model moisture movement inside cement-based materials. After defining the governing equation and verifying its various components, the model is solved analytically. The output of the model is compared with experimental measurements of moisture loss and local moisture content to ensure the accuracy of the model. Influence of absorption and desorption characteristics of LWA on its effectiveness in resaturating the emptied pores is then studied using the model.
Graduation Semester
2018-12
Type of Resource
text
Permalink
http://hdl.handle.net/2142/102447
Copyright and License Information
Copyright 2018 Ardavan Ardeshirilajimi

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