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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 ( ). 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.
The main objective of this study was to evaluate the effect of aggregate particle packing optimization and cement reduction on Nebraska slip-form pavement concrete performance. A literature review was conducted to examine different aggregate optimization tools, quality control tests, and historical data of Nebraska Department of Transportation (NDOT) mixtures. It was found that the Modified Toufar Model has good potential in optimizing particle packing and predicting packing degrees. The combined void content test was found to be useful to experimentally justify optimized aggregate gradations. Two specific pavement concrete workability tests, i.e., the Box Test and the VKelly Test, were used to evaluate the effect of cement reduction and optimized aggregate gradation on pavement concrete workability. The Box Test ranking was modified to provide a more detailed and objective evaluation. Analysis of different aggregate combinations has shown that experimental packing from the combined void content test has a high correlation with estimated packing from the Modified Toufar Model. Results showed that when the optimized aggregate gradation is used, cement content can be effectively reduced by up to 1.0 sack (94 lb/yd3) without compromising the fresh properties, mechanical properties, and permeability. Based on the results of free and restrained shrinkage, it was justified that shrinkage and cracking potential can be reduced in optimized concrete mixtures. Freeze/thaw resistance can be slightly improved with optimized mixtures. A mix design improvement procedure considering both theoretical and experimental packing and the minimum excess paste-to-aggregate ratio can be used to design concrete with an optimum cement content.The main objective of this study was to evaluate the effect of aggregate particle packing optimization and cement reduction on Nebraska slip-form pavement concrete performance. A literature review was conducted to examine different aggregate optimization tools, quality control tests, and historical data of Nebraska Department of Transportation (NDOT) mixtures. It was found that the Modified Toufar Model has good potential in optimizing particle packing and predicting packing degrees. The combined void content test was found to be useful to experimentally justify optimized aggregate gradations. Two specific pavement concrete workability tests, i.e., the Box Test and the VKelly Test, were used to evaluate the effect of cement reduction and optimized aggregate gradation on pavement concrete workability. The Box Test ranking was modified to provide a more detailed and objective evaluation. Considering one of the goals of the study was to maximize the use of local materials, locally available cementitious materials and aggregates from East and West Nebraska were selected. Analysis of different aggregate combinations has shown that experimental packing from the combined void content test has a high correlation with estimated packing from the Modified Toufar Model. Results also demonstrated that the current aggregate combination is not the optimum gradation and can be improved. The experimental program included in this study consisted of three Phases. Phase 1 focused on obtaining promising aggregate blends by maintaining the standard cement content (564 lb/yd3, 335 kg/m3). Fresh concrete properties were the main criteria to select promising blends. Phase 2 included an evaluation of performance of pavement concrete with cement content reduced by 0.5 sack (47 lb/yd3, 28 kg/m3) steps for other reference and optimized aggregate blends. Results justified that when optimum gradation is used, cement could be reduced up to 94 lb/yd3 (56 kg/m3). Phase 3 is the performance evaluation phase, which included evaluating the reference mix and selected promising mixes for setting time, modulus of elasticity, free shrinkage, restrained shrinkage, and freeze/thaw resistance. Mixtures with reduced cement and optimized aggregate gradation have shown improved freeze/thaw resistance and lower shrinkage rate. Finally, a mix design improvement procedure incorporating theoretical and experimental particle packing and using excess paste-to-aggregates ratio as the control parameter was proposed. To sum up, the study has justified that the Modified Toufar Model and the combined void content test can be useful tools in aggregate gradation optimization. In order to evaluate workability of pavement concrete more accurately, the Box Test ranking was modified based on image analysis of surface and edge quality. It was also proved that mixtures with reduced cement content and optimized aggregate gradation perform better in terms of freeze/thaw resistance and shrinkage.
Ultra-Thin Continuously Reinforced Concrete Pavement (UTCRCP) is an innovative pavement type that has the potential to fulfil South Africa’s pavement repair strategy requirements. It consists of a thin high strength concrete layer reinforced with steel mesh. Premature pavement failure occurs in UTCRCP and has been linked to the formation of cracks wide enough to allow water ingress into the supporting layers. Crack formation is influenced by environmental conditions and concrete mixture proportions of which the mixture proportions is the only factor that can be controlled by the manufacturers. To ensure that UTCRCP reaches its potential the effect of mixture proportions on the properties of High Strength Concrete (HSC) must be investigated with the aim of preventing excessive crack formation. A literature study had revealed that fly ash, silica fume, superplasticizers and high paste contents are commonly used in HSC. The influence of these mixture constituents was investigated in three sets of experiments. In the first set the effect of fly ash and silica fume was tested using mortars. A ternary cement blend was also selected to be used in the second set of experiments where the effect of paste content and superplasticizers on HSC was determined using multivariable analysis. The effect of a wider range of paste content on the properties of HSC was investigated in the third set of experiments. Results confirm that fly ash and silica fume are complimentary when used in ternary blends and these two supplementary cementitious materials may increase the total early-age deformation in mortars. The multivariable analysis revealed that within the parameter range tested paste content and superplasticizer dosage influenced the early-age properties but not the long-term properties of HSC. Through variation of the paste content over a wider range, from 25% to 60%, it was found that paste content does influence both the early-age and long-term properties of HSC.
The purpose of this study was to investigate the effect of cement paste quality on the concrete performance, particularly fresh properties, by changing the water-to-cementitious materials ratio (w/cm), type and dosage of supplementary cementitious materials (SCM), and airvoid system in binary and ternary mixtures. In this experimental program, a total matrix of 54 mixtures with w/cm of 0.40 and 0.45; target air content of 2%, 4%, and 8%; a fixed cementitious content of 600 pounds per cubic yard (pcy), and the incorporation of three types of SCMs at different dosages was prepared. The fine aggregate-to- total aggregate ratio was fixed at 0.42. Workability, rheology, air-void system, setting time, strength, Wenner Probe surface resistivity, and shrinkage were determined. The effects of paste variables on workability are more marked at the higher w/cm. The compressive strength is strongly influenced by the paste quality, dominated by w/cm and air content. Surface resistivity is improved by inclusion of Class F fly ash and slag cement, especially at later ages. Ternary mixtures performed in accordance with their ingredients. The data collected will be used to develop models that will be part of an innovative mix proportioning procedure.
This research project investigated important variables that impact the homogeneity and rheology of concrete mixtures. The project consisted of a field study and a laboratory study. The field study collected information from six different projects in Iowa. The information that was collected during the field study documented cementitious material properties, plastic concrete properties, and hardened concrete properties. The laboratory study was used to develop baseline mixture variability information for the field study. It also investigated plastic concrete properties using various new devices to evaluate rheology and mixing efficiency. In addition, the lab study evaluated a strategy for the optimization of mortar and concrete mixtures containing supplementary cementitious materials.
Portland Cement Association reference, dealing with fundamentals, cold weather concreting, curing, admixtures, aggregates, mixing, and much more.
Manual of integrated material and construction practices for concrete pavements.
By optimizing the packing of the combined aggregate gradations, the cement paste content needed to make concrete can be reduced, improving sustainability, cost, performance, durability, and workability. Optimization can be achieved using theoretical and empirical techniques, or waste concrete material as an intermediate size fraction. However, the potential for improvement is currently limited by prescriptive grading specifications that require meeting individual requirements for fine and coarse aggregates.From this study, using various optimization techniques, it was found that by inclusion of an intermediate sized aggregate material, a reduction in cement paste up to 16% is possible for 35 MPa and 50 MPa mix designs typically used in Ontario bridge decks. The aggregate materials used were a natural sand, and two crushed limestones of 19.0 mm and 6.7 mm maximum size. From these findings, recommendations are made for improving the current Ontario Provincial Standard Specification (OPSS) 1002 used for concrete aggregates.
This dissertation, "Effects of Water Content, Packing Density and Solid Surface Area on Cement Paste Rheology" by Hin-cheong, Henry, Wong, 黃憲昌, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled EFFECTS OF WATER CONTENT, PACKING DENSITY AND SOLID SURFACE AREA ON CEMENT PASTE RHEOLOGY submitted by Wong Hin Cheong Henry for the degree of Doctor of Philosophy at The University of Hong Kong in September 2007 High-performance concrete (HPC) has become increasingly popular in recent years. To produce HPC, addition of supplementary cementitious materials is virtually an essence. The use of these materials renders numerous possible mix combinations, making it difficult to optimize HPC mixes and limiting the usage of conventional mix design methods on HPC. In this regard, a comprehensive study aiming at developing a scientific mix design method for HPC has been launched. This thesis presents the findings on the first part of the study, which focuses on studying the scientific parameters governing the cement paste rheology. Due to the lack of a generally accepted method for measuring the packing density of cementitious materials, the postulation that the packing density has considerable influence on cement paste rheology has not yet been verified experimentally. Herein, a new wet packing method, which directly obtains the packing density by measuring the apparent density and voids content of cement paste, is developed. Using this method, the packing characteristics of pure ordinary Portland cement (OPC) and several blended cementitious materials measured under different conditions were acquired and compared with those obtained indirectly from consistence test. Based on the comparison, it is advocated that the packing density and water demand should be measured directly using the new wet packing method rather than other indirect methods. By using the wet packing method, the packing densities of cementitious materials containing OPC, pulverized fuel ash (PFA) and condensed silica fume (CSF) were measured. Results showed that the packing densities of pure cementitious materials could be improved by double blending and further increased by triple blending at appropriate proportions. The results also proved experimentally the postulation that packing density of cementitious materials could be improved by blending. Using the results, a ternary packing density diagram for determining the mix proportions for maximum packing density has been produced. Apart from experimental method, three existing packing models were also examined for their applicability on predicting the packing density of cementitious materials. By comparing the measured and predicted packing densities, together with some additional test results, it was found that in the presence of a third-generation superplasticizer the packing density of CSF is dependent on the lime content. When the effect of lime on the packing density of CSF is taken into accounted, very good agreement between the measured and predicted packing densities has been achieved, which verified the applicability of the models on cementitious materials. Although it is known that water content, packing density and solid surface area are the important parameters governing cement paste rheology, little progress has been made in evaluating the combined effect of these parameters on the rheology. In this thesis a new parameter called the excess water to solid surface area ratio is proposed to quantify the combined effect. A number of cement paste samples con