2018 Graduate Student Showcase

Title of Submission

Study of Thermo-Chemo-Mechanics of ASR Expansions by Means of Micro-Structural Analysis

Degree Program

Civil Engineering, MS

Major Advisor Name

Yang Lu

Type of Submission

Scholarly Poster


Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and Portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates. This combination, or concrete mix, will react with each other to make a bond and output is a hard durable material termed as concrete with which we are all familiar. But, in concrete there may be many chemical components of aggregate & cement which are detrimental to concrete due to their chemical reaction. One of the major sources of this deterioration is the alkali-aggregate reaction. Though aggregates are more or less chemically inert, some aggregates react with the alkali hydroxides in concrete, which cause expansion of concrete and in turn cracking over a period of many years. This kind of alkali-aggregate reaction has two forms: alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). Alkali-silica reaction (ASR) is of more concern as aggregates commonly contain reactive silica materials. In ASR, aggregates containing silica will react with alkali hydroxide in concrete to form a gel which further swells when it absorbs water from surrounding cement paste or the environment. This swelling gel induce expansive pressure which is enough to crack concrete. In addition, creep and shrinkage are coupled with the ASR evolution. Environmental conditions, namely, temperature and humidity levels amplify ASR progression and evolution. Hence, the total mechanism can be define as thermo-chemo-mechanics of ASR expansion. Thus, ASR is an engineering-scale, mechanical process with a chemical origin. Despite decades of study, the chemistry of ASR remains poorly understood. My thesis project presents the results of a research study directed at developing a time-dependent model of the microstructure of concrete matrix and stochastic numerical method to study mechanical effects of ASR to assess the deterioration level and the stability of ASR-damaged concrete structures. Analysis is done considering two key steps: chemical ingress, and concrete cracking to predict the service life of concrete. The finite-element method (FEM) is employed to model the ingress of multiple chemical species into variably saturated concrete matrix. The proposed FEM model is yet to validate by using laboratory experiments.

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