Optimization of Mixture Proportions for Concrete Pavements—Influence of Supplementary Cementitious Materials, Paste Content and Aggregate Gradation

The ultimate goals of this study included investigation of the optimal ranges for paste content, amount of cementations materials and aggregate gradation for concrete paving mixtures. In general, the optimum concrete mixtures developed in this study contained low paste content (below 23%), and were characterized by low scaling and sorptivity. In addition, it was also possible to achieve high cement replacement levels for these mixtures. Finally, for optimized fly ash mixtures, the selection of well graded aggregate gradation with high packing density increased the most desired paste content for those mixtures, thus indicating that combined aggregate gradation has strong influence on concrete performance. Lastly, concrete mixtures developed with optimum ranges of variables studied in this research contained low cement content. The overall scope of the research was divided into three distinctive phases, each of which is described briefly below: PHASE I: This phase consisted of statistical optimization of the proportions of concrete binder. The Central Composite Design methodology (CCD) was used to design the experiment for the optimization of binder in three types of concrete mixtures: a) cement + fly ash, b) cement + GGBFS, and c) cement + fly ash + GGBFS. The variables studied in each of these systems included: paste content (from 21 to 25 % by mixture volume) and total content of supplementary cementitious material (SCM) in the mixture. This was expressed as weight percent of total binder, and varied depending on the binder system used. PHASE II: The main goal of this phase was to investigate the effect of different aggregate gradations on the fresh and hardened properties of optimized concrete mixtures developed in PHASE I, as well as to identify the most desired aggregate gradations for paving mixtures. Different aggregate gradations were prepared by blending of 2, 3 or 4 different sizes of aggregates based on concept of Shilstone’s Coarseness Factor Chart. PHASE III: The concept of air-free paste–aggregate void saturation ratio (k”) introduced in PHASE II seemed to fairly accurate link the properties of concrete mixtures with their paste content. Thus, it was decided to further investigate this concept in connection with aggregate packing density (Φ). In addition, it was believed that defining optimum values of “k” will allow for revising the paste content ranges developed in PHASE I for different systems, and thus define more general optimum paste ranges for paving mixtures

Music Intervention and its Effect on State Anxiety: An Integrative Literature Review

Approximately 5 million patients are admitted to Intensive Care Units (ICU) in the United States for acute or life-threatening medical problems or injuries annually. The ICU patient experience has been described in the literature as dehumanizing, stressful, and anxiety provoking. Given the adverse physiological and psychological effects of sustained state anxiety, it is important anxiety is effectively managed in the ICU environment. Standard care for management of anxiety often relies heavily upon sedative medications and are correlated with poor outcomes when used in high doses and over a long duration. The SCCM recommends nonpharmacologic adjunctive measures to decrease the occurrence of post intensive care unit syndrome (PICS). The purpose of this integrative literature review was to identify evidence whether the use of an adjuvant therapy, music intervention, can reduce state anxiety for ICU patients. A review of the literature spanning the years 2011-2021 was performed based on the concept of music intervention implemented in the critically ill adult population and its effect on state anxiety. Several systematic reviews and many randomized control trials were identified for this inquiry; Evidence found was not homogenous in intervention and application and various factors were identified by researchers. Despite this, state anxiety, as measured by various scoring tools across the literature, was reduced after music interventions regardless of the implementation process. Irrespective of study design, no adverse effects were noted with music intervention

Analyzing Carbohydrate-Based Regenerative Fuel Cells as a Power Source for Unmanned Aerial Vehicles

Based on current capabilities, we examine the feasibility of creating a carbohydrate-based regenerative fuel cell (CRFC) as the primary power source for unmanned aerial vehicles (UAV) for long endurance missions where station keeping is required. A CRFC power system is based on a closed-loop construct where carbohydrates are generated from zooxanthellae, algae that create excess carbohydrates during photosynthesis. The carbohydrates are then fed to a carbohydrate fuel cell where electric power is generated for the UAV’s propulsion, flight control, payload, and accessory systems. The waste products from the fuel cell are used by the zooxanthellae to create more carbohydrates, therefore mass is conserved in the process of power generation. The overall goal of this research is to determine if CRFCs should be explored further as a viable power source. Through simulations, a UAV is sized to determine if greater than 24 hour endurance flight is possible and these results are compared to UAVs using more traditional photocell based power systems. The initial results suggest that more research should be done in the development of CRFCs as a power system for long endurance UAVs. The final outcome of this research is to identify the most important areas for more detailed follow-on work in designing a production-ready CRFC power system for long endurance UAVs

Investigation of Premature Distress Around Joints in PCC Pavements: Parts I & II

Some of the Indiana concrete pavements constructed within the last 10-20 years have shown signs of premature deterioration, especially in the areas adjacent to the longitudinal and transverse joints. This deterioration typically manifested itself as cracking and spalling of concrete combined with the loss of material in the direct vicinity of the joint. In addition, in some cases “bulb-shaped” damage zones were also observed under the sealed parts of the joints. The objective of this study was to investigate possible causes of this premature deterioration. To reach this objective, the characteristics of the concrete in and near the deteriorated joints were compared and contrasted to the concrete characteristics in the non-deteriorated sections of pavement. The study was conducted in two different phases (Phase I and Phase II), and the findings are presented as a two-part report. The investigation started with a detailed inventory of selected areas of affected pavements in order to identify and classify the existing types of distresses and select locations for collection of the cores. During the Phase I of the study a total of 36 concrete cores were extracted from 5 different pavements.. During Phase II of the study a total of 18 cores were retrieved from five different pavement sections and subject to examination. The cores were subjected to eighth different tests: air-void system determination, Scanning Electronic Microscopy (SEM) analysis, X-ray diffraction (XRD) analysis, sorptivity test, freeze-thaw & resonance frequency test, resistance to chloride ion penetration (RCP) test and chloride profile (concentration) determination. The test results identified several cases of in-filling of the air voids (especially smaller air bubbles) with secondary deposits. These deposits were most likely the result of the repetitive saturation of air voids with water and substantially reduced the effectiveness of the air voids system with respect to providing an adequate level of freeze-thaw protection. Specifically, it was observed that the existing air void system in the concrete from panels near the deteriorated longitudinal joint had neither spacing factors nor specific surface values within the range recommended for freeze-thaw durability. Contrary to this, nearly all the concrete in lanes without damage had an adequate air void system at the time of sampling. In addition, the affected concrete often displayed an extensive network of microcracks, had higher rates of absorption and reduced ability to resist chloride ions penetration. From the observation of the drains performed using the remote camera it was obvious that not all the drains were functioning properly and some were entirely blocked. However, more precise or direct correlations could not be made between the conditions of the drains and observed pavement performance

Carbon nanotube composites : mechanical, electrical, and optical properties

In the frame of this thesis novel concepts for the functionalization of nanotubes and fabrication of optimized, homogeneous MWNT/polymer heterostructures are presented. The effects of various dispersion states and morphologies of carbon nanotubes on mechanical, rheological, and electrical properties of the CNT-based nanocomposites were investigated. Additionally, a new approach for the fabrication of CNT/quantum-dots heterostructures for potential photoelectric and optical applications is shown. The tensile strength and elastic modulus of polymeric systems are shown to be significantly improved (even by more than 1500 %) after introducing the MWNT-filler by using the layer-by-layer assembly technique. However, nanoindentation experiments reveal that the presence of MWNTs within the polymeric host material do not have any impact on the hardness of such composites. Furthermore, shear oscillatory tests show that the viscosity of MWNT/polymer composites increases together with the concentration of the nanotubes in polymer. The rheological percolation threshold is shown to be as low as 0.5 wt% of MWNTs. Investigations of electrical properties of MWNT/polymer heterostructures show a significant increase of electrical conductivity with the increase of the MWNTs’ content. The conductivity of the sample with only 8 wt% MWNTs load is as high as 10-2 S/cm which is four orders of magnitude higher than that of the neat polymer. The electrical percolation threshold is reached at 1.48 wt%. Investigation of MWNT/quantum dots heterostructures reveal a complete quenching of the PL-bands, presumably through an electron transfer between QDs and MWNTs. The deposition of a silica shell (with thicknesses >20nm) around the CNTs preserves the fluorescence properties by insulating the QD from the surface of the CNT. It is shown that carbon nanotubes as components of various nanocomposites have a significant effect on the mechanical, electrical, and optical properties of these hybrid materials. The results of this thesis indicate the potential of utilizing CNT-based nanocomposites towards mechanical, electrical, sensing, optical, and actuating applications

Compatibility of Cementitious Materials and Admixtures

Growing demand for creating more sustainable and durable concretes lead to the increased usage of various cementitious materials and chemical admixtures in the mixtures. However, the increased usage of these components resulted in more complex mixtures that sometimes cause unexpected incompatibility problems. This report summarizes the results of the investigation of the parameters that may lead to workability problems, early age hydration irregularities and difficulties in achieving quality air void system in both plain and fly ash cementitious mixtures. The present research work was performed in three major phases and the statistical modeling was used to aid in interpretation. Phase I involved evaluation of more than 100 different paste and mortar mixtures with respect to potential slump loss and hydration irregularities. The results showed that cements with high C3A and low SO3 content were more prone to incompatibility problems. It was also observed that mixes with lignin based water reducing agent (WRA) had higher tendency for rapid stiffening than mixes with polycarboxylate type superplasticizer (PCSP). Increased replacement of cement by class C ashes resulted in the development of abnormal secondary peaks in semi-adiabatic calorimetry curves and accelerated the setting behavior. The focus of phase II was on identifying material combinations that can result in problems related to air void generation and stability. The experiments were conducted on 18 different systems and included determination of foam drainage and foam index parameters. The results show that the amount of air entrainers required to obtain target air percentage, increased with the increase in the fly ash content in the mixture. Lignin based WRA had, in general, a higher air entraining effect than the super-plasticizer when used in combination with air entrainers. Also, five out of the six mixtures with most unstable air void system, identified using the foam drainage experiments, contained the PCSP. The third (and final) phase of the study involved production of 10 concrete mixtures to verify the incompatibility findings from the paste and mortar experiments performed in phases I and II. The observations from the concrete testing were in agreement with the findings from the paste and mortar testing. Statistical modeling (performed using the material properties and results from phase I) identified the total C3A, SO3 and Na2Oequ contents of the binder system along with dosage of PCSP (if present in the mixture) as statistically significant in predicting the initial set time and area of spread (measured using the mini-slump test)

Updating Physical and Chemical Characteristics of Fly Ash for Use in Concrete

When incorporated in concrete mixtures, fly ashes are known to influence both its fresh and hardened properties. An accurate and quick technique to predict the extent of this influence based on the characteristics of fly ash would be highly beneficial in terms of field applications. The current study was an attempt to quantify the effects of fly ashes on the properties of pastes as a function of: (a) the mean particle size of the fly ash particles, (b) their fineness and (c) their chemical composition. In addition, since the type and the amount of glass present in the fly ash significantly affect its reactivity, this property was also included in the investigation. Twenty different fly ashes (both, ASTM Class C and Class F), obtained from power plants in and around Indiana, were characterized during the Phase 1 of the study. The information collected included: physical characteristics, chemical composition and the amount and type of glass present. Phase 2 of the study consisted of evaluation of various properties of binary paste systems (portland cement with 20% of cement of fly replacement). The evaluated properties included: the set time, the heat of hydration, the strength activity index, the non-evaporable water content and the amount of calcium hydroxide formed at different ages. These results obtained from both phases of the study were used to build statistical models for prediction of previously evaluated properties for any hypothetical fly ash with similar characteristics. The models included only the most significant variables, i.e., those which were found to most strongly affect any specific property. The variables to be included in the model were selected based on the adjusted R2 values. As a result of the modeling process, it was found that the sets of statistically significant variables affecting the properties consisted of both physical and chemical characteristics of the fly ash and that the combination of these variables was unique for each property evaluated. When applied to a set of results from two additional (not previously used) fly ashes, the models provided the following residuals of predicted properties: (a) Initial set time – 100 minutes for Class F ashes and over 300 minutes for Class C ashes (b) Peak heat of hydration – 0.7 W/kg (c) Time of peak heat – 375 minutes (d) Total heat of hydration – 96 J/kg (e) Calcium hydroxide content at various ages – 0.25% for early ages (1 and 3 days) and 0.5% for later ages (7 and 28 days) (f) Non-evaporable water content – 0.7% for early ages (1 and 3 days) and 5% for later ages (28 days) (g) Strength activity index – range of 1% in Class C ashes and 1% to 2% in Class F ashes (from 7 days to 28 days) Phase 3 of the study consisted of evaluating the same set of properties but using ternary paste systems (cement and two different fly ashes). The goal for this study was to ascertain the applicability of the weighted sum of the models chosen for the binary paste systems to predict the properties of ternary binder systems. In addition, the analysis as to which of the chosen variables has the maximum effect on the properties was performed. It was found that the properties of the ternary binder systems were not additive in nature, except for strength activity index at 28 days. Lastly, the percent influence of each of the chosen independent variables, which affect the mentioned properties, was calculated along with the unexplained variation (error percentage). The error percentages varied for each of the properties, with set time having the maximum error (almost 50%)