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Title:Understanding effects of pre-soaked lightweight aggregate on volume stability of mortar and concrete mixtures
Author(s):Ardeshirilajimi, Ardavan
Director of Research:Mondal, Paramita
Doctoral Committee Chair(s):Mondal, Paramita
Doctoral Committee Member(s):Lange, David A.; Popovics, John S.; Roesler, Jeffery R.
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(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.
Issue Date:2018-11-30
Rights Information:Copyright 2018 Ardavan Ardeshirilajimi
Date Available in IDEALS:2019-02-06
Date Deposited:2018-12

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