Casting of Reinforced Concrete Beam: Project
Progress
1. INTRODUCTION
This project focuses on concrete structures in nuclear power plants (NPPs). Concrete structures are
grouped into the following four categories: (1) primary containment, (2) containment internal structures,
(3) secondary containment/reactor buildings, and (4) other structures such as used fuel pools, dry storage
casks, and cooling towers. These concrete structures are affected by a variety of chemical, physical, and
mechanical degradation mechanisms, such as the alkali-silica reaction (ASR), chloride penetration, sulfate
attack, carbonation, freeze-thaw cycles, shrinkage, and mechanical loading (Naus 2007). Age-related
deterioration of concrete results in evolving microstructural changes (e.g., slow hydration, crystallization
of amorphous constituents, and reactions between cement paste and aggregates). Therefore, it is important
that changes over long periods of time are measured and monitored, and their impacts on component
integrity are analyzed in order to best support long-term operations and maintenance decisions.
Vanderbilt University, in collaboration with Idaho National Laboratory and Oak Ridge National
Laboratory personnel, is developing a framework for health diagnosis and prognosis of aging concrete
structures in NPPs that are subject to physical, chemical, and mechanical degradation
(Mahadevan et al. 2014; Agarwal and Mahadevan 2014). The framework will allow researchers to assess
concrete structure degradation by integrating the following four technical elements: (1) monitoring,
(2) data analytics, (3) uncertainty quantification, and (4) prognosis. For details on each element of the
proposed framework, refer to Mahadevan et al. (2014).
A research activity is initiated between Idaho National Laboratory, Vanderbilt University, and
University of Nebraska - Lincoln to study the impact of reinforcement in concrete structures on
application of the VAM technique. To support this activity, University of Nebraska - Lincoln is casting
and curing four reinforced concrete samples that, at the end of the curing period, will be transferred to
Vanderbilt University to perform an experimental VAM study. Vanderbilt University and Idaho National
Laboratory will analyze the resulting data and enhance the developed structural health monitoring
framework.
This report presents a summary of the progress to date on casting and curing of reinforced concrete
samples at University of Nebraska – Lincoln.
2. TECHNICAL BACKGROUND
2.1 Concrete Structures Affected by Alkali-Silica Reaction
ASR is a reaction in concrete between alkali hydroxides (K+ and Na+) in the pore solution and
reactive non-crystalline (amorphous) silica (S2+) found in many common aggregates, given sufficient
moisture. This reaction occurs over time and causes expansion of the altered aggregate by the formation
of a swelling gel of calcium silicate hydrate (C-S-H). The primary sources of reactive silica are reactive
aggregates, while alkali is present in the cement clinker. ASR swelling results from the relative volume
increase between the product and reactant phases involved in the chemical reaction. First, the products
expand in pores and micro-cracks of the cementitious matrix. Once this free expansion space is filled, the
swelling is restrained and the product phases exert local pressure on the surrounding concrete skeleton
(Ulm 2000). Figure 1 depicts the mechanism of ASR (Kreitman 2011).
With the presence of water, the ASR gel increases in volume and exerts an expansive pressure inside
the material, causing spalling micro- to macro-cracks (due to nonhomogeneous swelling related to
non-uniform moisture distribution). As a result, ASR reduces stiffness and tensile strength of concrete -
properties that are particularly sensitive to micro-cracking. ASR can also cause serious cracking in