Nonlinear finite element analysis of strength and durability of reinforced concrete and composite structures

The finite element method has emerged as the most powerful and versatile numerical method for solving a wide range of physical problems in science and engineering. Today a large number of commercial programs exist that can be used to solve diverse problems in structural and fluid mechanics, heat transfer and many other phenomena. However, certain critical problems related to durability of concrete structures, especially corrosion of reinforcement, cannot be readily solved using the available software. This paper presents two finite element formulations, developed by the writers, one dealing with the nonlinear analysis of composite concrete-steel bridges, and the other with the durability of concrete structures, with emphasis on the corrosion of reinforcement. The validity and accuracy of the proposed models are demonstrated by comparing their results with appropriate experimental data

Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor

The durability of in-place concrete is a high priority issue for concrete pavements and bridges. Several studies have been conducted by INDOT to use electrical resistivity as a measure of fluid transport properties. Resistivity is dependent on the chemistry of the cement and supplementary cementitious system used, as such it has been recommended that rather than specifying resistivity it may be more general to specify the formation factor. Samples were tested to establish the current levels of performance for concrete pavements in the state of Indiana. Temperature and moisture corrections are presented and acceptable accelerated aging procedure is presented. A standardized testing procedure was developed (AASHTO TP 119–Option A) resulting in part from this study that provides specific sample conditioning approaches to address pore solution composition, moisture conditioning, and testing procedures. An accelerated aging procedure is discussed to obtain later age properties (91 days) after only 28 days

Three-dimensional characterization of the steel-concrete interface by FIB-SEM nanotomography

While it is widely accepted that the steel-concrete interface (SCI) plays an important role in governing the long-term durability of reinforced concrete structures, understanding about the primary features of the SCI that influence corrosion degradation mechanisms has remained elusive. This lack of knowledge can be attributed, on the one hand, to the complex heterogeneous nature of the SCI, and, on the other hand, the absence of experimental techniques suitable for studying the relevant features of the SCI. Here, we use focused ion beam - scanning electron microscopy (FIB-SEM) nanotomography to obtain high resolution 3D tomograms of the steel-concrete interfacial zone. Five tomograms, spanning volumes ranging from 8,000 to 200,000 cubic micrometer, were acquired for situations representative of both non-corroded and corroded SCIs. The achieved voxel size falls within the range of 30-50 nm, thus providing a resolution clearly surpassing the capabilities of computed X-ray tomography. This resolution enables the 3D characterization of the microstructure at the capillary scale, which is the scale at which relevant corrosion and related mass transport processes occur. Thus, FIB-SEM nanotomography is capable of yielding datasets of the SCI that serve as basis for the generation of digital twins of the interfacial microstructure, thereby enabling future studies about durability and corrosion of reinforced concrete at the pore scale

Effects of neonatal gonadal steroids on adult CA3 pyramidal neuron dendritic morphology and spatial memory in rats

The hippocampus is implicated in spatial cognition, which is sexually dimorphic and developmentally sensitive to gonadal steroids. Previously we have shown a sex difference in CA3 pyramidal cell layer volume and neuronal soma size that was reversible with neonatal castration in males or prenatal treatment of females with either testosterone propionate (TP) or a nonaromatizable androgen, dihydrotestosterone propionate, but not estradiol benzoate, all of which correlated with adult water maze navigation. The present study further investigates developmental androgen sensitivity of CA3 pyramidal neurons by measuring dendritic morphology and its relation to adult spatial ability. Female rats were injected with TP on postnatal day (P) 3 and P5 or ovariectomized (OVX) on P2, and male rats were castrated on P2, with or without testosterone replacement (Cas+T). Sham surgery controls were also included. Animals were tested on a water maze in adulthood, sacrificed, and CA3 pyramidal neurons were Golgi-stained and reconstructed in three dimensions using a computer-interfaced morphometry system. High-androgen groups (control males, Cas+T, TP females) performed better in spatial navigation and exhibited CA3 neurons with longer dendrites, a larger number of dendritic branches, and volumes of influence compared to low-androgen groups (control females, castrated males, OVX). Collectively, these findings indicate that the critical time period for organizational effects of androgens on the CA3 pyramidal neurons includes both prenatal and postnatal life, during which time androgens regulate developmental events such as somal growth and neuronal differentiation, all of which significantly contribute to establishing the sex difference in adult spatial navigation. © 2003 Wiley Periodicals, Inc. J Neurobiol 55: 179–190, 2003Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34483/1/10200_ftp.pd

Transformation of 2-line ferrihydrite to goethite at alkaline pH

The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH >= 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life,t_1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 hours at pH = 14.0. Calculated first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log_10 k = log_10 k_0 + a*pH^E3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow re-dissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions

A Literature-based Dataset Containing Statistical Compositions and Reactivities of Commercial and Novel Supplementary Cementitious Materials

This dataset contains the chemical composition and reactivities of commercially used SCMs such as silica fume, Class-F and Class-C fly ashes, slags, and calcined clays. The dataset also includes the chemical composition and reactivity (where available) for several SCMs that are currently not specified in standard specifications by ASTM or AASHTO such as fly ashes not conforming to ASTM C618, bottom ashes, and pumices. This dataset can be used (i) for the classification of SCMs based on their statistics (in terms of composition and reactivity), (ii) as an input for predicting the performance of cementitious systems made with SCMs using thermodynamic modeling, (iii) generating realistic compositional and reactivity data for cementitious materials using techniques such as Monte-Carlo method, and (iv) for studying the feasibility of the use of novel SCMs in concrete based on the predicted performance of concrete made with these SCMs.Keywords: Portland cement, cement, ordinary Portland cement, OPC, supplementary cementitious materials, SCM, statistics, pozzolanic reactivity, reactivity, silica Fume, fly ash, slag, calcined clay, pumice, off-spec SC

Colocalization of estrogen β-receptor messenger RNA with orphanin FQ, vasopressin and oxytocin in the rat hypothalamic paraventricular and supraoptic nuclei

The functional significance of the novel estrogen receptor β in brain areas that exclusively contain the ERβ receptor subtype such as the paraventricular (PVN) and the supraoptic (SON) nuclei of the hypothalamus is not yet fully understood. The present study attempts to characterize the peptidergic nature of the ERβ-containing neuronal population in the PVN and the SON using the double in situ histochemistry method in the female rat. Using this method, the ERβ mRNA coexpressions with the novel opioid neuropeptide (orphanin FQ and its receptor ORL1) mRNA in addition to the previously reported neuropeptide (arginine vasopressin-AVP, oxytocin-OXY, corticotropin releasing hormone-CRH, enkephalin-ENK) mRNAs were assessed. In the PVN, roughly half of the ERβ expression was colocalized with the prepro-orphanin FQ mRNA, which was comparable to the colocalization observed between the ERβ and AVP mRNAs in the same region. In addition, there was 20% overlap between the ERβ and ORL1 receptor mRNAs, and 10% overlap between the ERβ and OXY mRNAs in the PVN. By contrast, the coexpression between the prepro-orphanin FQ and ERβ mRNAs was less striking in the SON. Potential interactions between the ERβ and the well-characterized AVP-OXY neurosecretory system as well as the novel OFQ-ORL1 opioid neuropeptide system may provide new leads for the functional significance of ERβ, specifically in stress/autonomic responses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42251/1/s00429-003-0314-9.pd

Developmental underpinnings of differences in rodent novelty‐seeking and emotional reactivity

Innate differences in human temperament strongly influence how individuals cope with stress and also predispose towards specific types of psychopathology. The present study examines the developing brain in an animal model of temperamental differences to examine how altered neurodevelopment may engender differences in emotional reactivity that are stable throughout the animal’s life. We utilize selectively‐bred High Responder (bHR) and Low Responder (bLR) rats that exhibit dramatic emotional behavior differences, with bHRs exhibiting exaggerated novelty‐exploration, aggression, impulsivity and drug self‐administration, and bLRs showing marked behavioral inhibition and exaggerated anxiety‐like and depressive‐like behavior. Using Affymetrix microarrays, we assessed bLR and bHR gene expression in the developing brain on postnatal days (P)7, 14 and 21, focusing on the hippocampus and nucleus accumbens, two regions related to emotionality and known to differ in adult bLR and bHR rats. We found dramatic gene expression differences between bLR and bHR in the P7 and P14 hippocampus, with minimal differences in the nucleus accumbens. Some of the most profound differences involved genes critical for neurodevelopment and synaptogenesis. Stereological studies evaluated hippocampal structure in developing bHR and bLR pups, revealing enhanced hippocampal volume and cell proliferation in bLR animals. Finally, behavioral studies showed that the characteristic bHR and bLR behavioral phenotypes emerge very early in life, with exploratory differences apparent at P16 and anxiety differences present by P25. Together these data point to specific brain regions and critical periods when the bHR and bLR phenotypes begin to diverge, which may eventually allow us to test possible therapeutic interventions to normalize extreme phenotypes (e.g. the anxiety‐prone nature of bLRs or drug addiction proclivity of bHRs).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87155/1/j.1460-9568.2011.07811.x.pd