Lawrence Sutter

Mineral carbonation for carbon sequestration in cement kiln dust from waste piles

Alkaline earth metals, such as calcium and magnesium oxides, readily react with carbon dioxide (CO(2)) to produce stable carbonate minerals. Carbon sequestration through the formation of carbonate minerals is a potential means to reduce CO(2) emissions. Calcium-rich, industrial solid wastes and residues provide a potential source of highly reactive oxides, without the need for pre-processing. This paper presents the first study examining the feasibility of carbon sequestration in cement kiln dust (CKD), a byproduct generated during the manufacturing of cement. A series of column experiments were conducted on segments of intact core taken from landfilled CKD. Based on stoichiometry and measured consumption of CO(2) during the experiments, degrees of carbonation greater than 70% of the materials potential theoretical extent were achieved under ambient temperature and pressure conditions. The overall extent of carbonation/sequestration was greater in columns with lower water contents. The major sequestration product appears to be calcite; however, more detailed material characterization is need on pre- and post-carbonated samples to better elucidate carbonation pathways and products.

Long-Term Effects of Magnesium Chloride and Other Concentrated Salt Solutions on Pavement and Structural Portland Cement Concrete: Phase I Results

Many state highway agencies use various chemicals to deice or anti-ice pavement and bridge surfaces. Most often these are aqueous solutions of various chlorides (e.g., magnesium chloride, sodium chloride, and calcium chloride) or other chemicals such as calcium magnesium acetate, urea, or others. Possible detrimental effects to concrete caused by these chemicals have not been fully examined and documented. Mortar specimens of three different water-to-cement ratios (0.4, 0.5, and 0.6) were immersed in concentrated solutions of various chemical deicers and held above freezing at a constant temperature of 40°F up to 84 days. Considerable expansion and cracking were noted in specimens immersed in the MgCl2 and CaCl2 solutions. Petrographic analysis and quantitative microanalysis were used to positively identify the presence of Mg(OH)2 (brucite) formation in the outer layers of the specimens. Furthermore, the results presented clear evidence of calcium oxychloride formation in the specimens analyzed. Further r...

Hardened Concrete Air Void Analysis with a Flatbed Scanner

Digital images collected from a polished concrete surface with a flatbed scanner are used to quantify air void characteristics. The surface is scanned a total of three times. Between the first and second scans, the surface is stained with phenolphthalein to color the cement paste pink. Between the second and third scans, the surface is painted black, and white powder is pressed into depressions left by air voids. The images collected from the three scans are aligned and input into a classification scheme to yield an output image. Each pixel in the output image is categorized as air void, cement paste, or aggregate. By digitally applying a grid of points and a series of lines to the output image, a modified point count is automatically performed according to ASTM C457, Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete. A comparison is made between results obtained by an automatic analysis of the digital output image and results obtained by a manual analysis of the surface with an optical microscope.

The Practical Application of a Flatbed Scanner for Air-Void Characterization of Hardened Concrete

Over the past 30 years, with the advent of computers and digital imaging, many automated systems have been introduced for the purpose of air-void characterization. The majority of the systems employs a contrast-enhancement procedure where a polished cross-section of concrete is darkened with paint, and white powder is forced into the depressions left by air-voids. The system described here follows the same approach and uses a flatbed scanner to collect a single digital image of the entire sample. For all of the systems based on contrast enhancement, the first step is to select a threshold level. Image pixels brighter than the threshold level represent air and image pixels darker than the threshold level represent non-air (i.e., paste or aggregate). Further digital processing steps may be employed but the initial selection of threshold level exerts a strong influence on whether a pixel in the final data set is classified as air or non-air. A systematic approach for threshold determination has been proposed based on an iterative procedure that compares automatically determined air-void parameters to manually determined air-void parameters from a set of training specimens. The calibration procedure finds a single optimum threshold level for the automated system that is to be used for all subsequent analyses. The approach was tested on a population of 88 specimens with manually determined air-void parameters, with the goal of determining an appropriate value for the number of training specimens.

Methods for Evaluating Fly Ash for Use in Highway Concrete

This report presents recommended changes to coal fly ash specifications and test protocols contained in AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing (AASHTO M 295). These changes include modifications to the test methods currently specified for evaluating acceptability of fly ash for use in highway concrete as well as the introduction of new test methods for enhancing such evaluations. The modified specifications and test protocols will guide materials engineers and fly ash producers in evaluating fly ash and assuring that highway concrete is enhanced, and not deleteriously affected, by replacing a portion of the cement in the concrete mixture with fly ash. The information contained in the report will be of immediate interest to state materials engineers and others involved in specifying and evaluating concrete mixtures for use in highway pavements and structures.

Effect of Sample Preparation on Chemical Composition and Morphology of Alkali-Silica Reaction Products

The chemical composition and morphology of alkali–silica reaction (ASR) products is of great importance in studying the reaction mechanism and assessing the effectiveness of mitigation techniques. Epoxy-impregnated, polished thin sections were prepared from an in-service concrete pavement to examine ASR products that originate from chert particles in the fine aggregate. Both hydrous and anhydrous thin-section preparation techniques were used to investigate the influence of sample preparation on the results. Two distinct morphologies of ASR products were observed in the voids adjacent to the chert particles: a bladed crystalline type and a glassy amorphous type. The chemical compositions of the reaction products were determined with a scanning electron microscope via quantitative X-ray energy dispersive spectrometry. Both the chemical composition and morphology were influenced by sample preparation, with hydrous preparation resulting in leaching and degradation. It is recommended that, when conducting studies to assess the ASR mechanism and the effectiveness of mitigation techniques, anhydrous sample preparation be used.

Field Study of Air Content Stability in the Slipform Paving Process

This study evaluated the impacts of construction on the air content and air void system structure of portland cement concrete pavements. The primary intent was to quantify the air content of fresh concrete before and after it had gone through the slipform paver. The air void system parameters of hardened concrete were then assessed with cast cylinders and extracted core specimens. The results of the air content testing on fresh concrete and the concrete cylinder specimens cast in the field suggested that some loss of air (approximately 1%) occurred as the concrete passed through the paver. Laboratory testing performed on cores extracted from the pavement did not provide conclusive evidence that entrained air was lost during the slipform paving process. In fact, many extracted cores had measured air content values that were much higher than those measured in the fresh concrete and even higher than the specification requirement. If excessive, such values could result in increased permeability and low-strength-related issues. The results suggested that the air content testing on fresh concrete did not capture the true air content of the concrete as it was placed with a slipform paver. The fresh concrete air content in general was lower than was the air content measured in the cores.

Fly Ash Iodine Number for Measuring Adsorption Capacity of Coal Fly Ash

Fly ash is used as partial replacement of cement in concrete. The residual carbon in fly ash adsorbs some of the organic concrete admixtures, altering the concrete properties. The use of fly ash in concrete is limited by the lack of adequate fly ash adsorption capacity quantification tools. This paper presents the fly ash iodine number test for the direct measurement of the adsorption capacity of coal fly ash. This test can be used to determine suitability of fly ash for concrete. The developed test was evaluated by comparing the results obtained with the loss on ignition (LOI) and foam index test results for the same fly ash samples. Results show that the fly ash iodine number test can replace current qualitative indicators of adsorption capacity and can be directly used for the characterization and specification of fly ash for the use in concrete.

EVALUATION OF PREMATURE DETERIORATION OF CONCRETE BRIDGE BARRIERS BY PETROGRAPHIC EXAMINATION

Many of the current-generation concrete bridge barriers used in Michigan have deteriorated at a rate greater than expected. For an assessment of the possible causes of this premature distress with the objective of alleviating future occurrences, sixteen core specimens from eight sites constructed between 1983 and 2001 were evaluated. The evaluation included visual inspection, stereo and petrographic optical microscopy, and scanning electron microscopy. The major observations revealed through this analysis were that poor consolidation, marginal air-void systems, alkali-silica reaction associated with chert and siltstone in the fine aggregate, corrosion of reinforcing steel, and possibly frost susceptibility of fine siltstone aggregates were responsible for the deterioration. These results provide the basis for improving the quality of such barriers in future construction.

Deterioration in Concrete Pavements Constructed with Slag Coarse Aggregate

In Michigan, sections of an Interstate-type pavement are suffering extensive cracking and joint deterioration after 10 years of service, having been constructed in 1992. An adjacent section constructed in 1993 with comparable design features and materials remains in good condition, with little visual sign of distress. A study was conducted to determine, if possible, the cause of the observed distress in the highway built in 1992. In all, cores from nine different projects were evaluated, all of which were made with iron blast-furnace-slag coarse aggregate and natural fine aggregate containing chert constituents. The analyses conducted included stereo and petrographic microscopy and chemical extractions to determine levels of exchangeable and soluble potassium and sodium, as well as sulfates. The findings indicate that, in distressed pavement sections, the chert constituents in the fine aggregate are deleteriously alkali–silica reactive (ASR), whereas these same constituents are not deleterious in the sections rated as fair. Further, the distressed sections all had sulfate levels significantly higher than predicted by the mixture design. It is hypothesized that, in addition to the ASR in the fine aggregate, dissolution of the calcium sulfide dendrites in the slag coarse aggregate is providing excess internal sulfates, resulting in in-filling of the air-void system with ettringite and potentially sulfate attack. The exact nature of the deterioration mechanisms is not fully understood, but it seems clear that some type of interaction exists between the ASR and excess sulfates.