Using Theoretical And Experimental Particle Packing For Aggregate Gradation Optimization To Reduce Cement Content In Pavement Concrete 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. Advisor: Jiong H

DESIGN STUDENT RESIDENCE BUILDING USING AERATED CONCRETE/BLOCK IN NAZARBAYEV UNIVERSITY, ASTANA, KAZAKHSTAN

This project is focused on the design of a student residence building using aerated concrete in Nazarbayev University, Astana, Kazakhstan. The shortage of residential places on the campus is one of the primary problems of the university. Thus, the design of the residence building for master students by DC Group is studied in this paper. Major part of the worldwide energy is consumed by residential and commercial buildings. Because of low thermal conductivity and light weight compared to normal concrete, aerated concrete is proposed in order to provide proper thermal insulation and prevent significant heat loss. Moreover, the project includes obtaining own mixture design through laboratory experiments, where aerated concrete blocks will be casted and tested for both mechanical and thermal properties

Using Theoretical And Experimental Particle Packing For Aggregate Gradation Optimization To Reduce Cement Content In Pavement Concrete 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. Advisor: Jiong H

A Comprehensive Analysis of Recycled Concrete Aggregate (RCA) Characteristics and Effective Use of RCA Characteristics in Concrete Mixture Design

Concrete waste contributes to the majority of 230-530 million tons of Construction and Demolition wastes produced in the US each year, yet only a small proportion of which is recycled. Recycling waste concrete and producing recycled concrete aggregate (RCA) is one of the crucial topics in civil engineering as it promotes sustainability through reducing the demand for the natural resources and consumption of landfill space, and lowering the production costs. Major obstacles that hinder the use of RCA in concrete construction are the lack of specifications and procedures for qualifying an RCA source and the unclear impact of RCA on concrete performance. A more comprehensive study focused on RCA characterization and its use in concrete mixture design is needed. Most of the current practices and standard specifications use only gradation, specific gravity, and absorption to characterize and classify RCA, as they are easily accessible and generally considered to be related to the strength and residual mortar content of RCA. However, it is unclear if these parameters can sufficiently characterize RCA for concrete applications. The proposed study considers and evaluates various parameters that can be used to describe the physical, mechanical, and durability characteristics of RCA. Besides, with the more effective characterization, a more rational mixture design of concrete that is incorporating RCA has been developed. There is a misconception that the properties of concrete are definitely compromised with the incorporation of RCA. However, the study showed that with an effective characterization of the geometrical and physical properties of RCA, and particle packing-based mixture design approach, concrete with workability and mechanical properties comparable to normal concrete could be achieved. This study provides a concrete mixture design method that incorporates key RCA characteristics, focusing on pavement concrete. Finally, the effect of RCA mechanical properties on mechanical properties and cracking behavior of concrete was studied, which will provide insights into the role of RCA in the mechanical properties of concrete

Evaluation of Reducing Cement Content in NDOR Class R Combined Aggregate Gradations

The main objective of this research project was to achieve a cement reduction on Nebraska slip-form pavement concrete through aggregate particle packing optimization. A literature review was conducted to examine different aggregate optimization tools, quality control tests, and historical data of Nebraska Department of Transportation (NDOT) pavement mixtures. It was found that the Modified Toufar Model has good potential in optimizing particle packing and predicting packing degrees. The combined aggregate void content test was found to be useful to experimentally justify optimized aggregate gradations. The Box Test with a modified index and image analysis tool for surface void estimation was used to evaluate the effect of cement reduction and optimized aggregate gradation on pavement concrete workability. Considering one of the goals of the study was to maximize the use of local materials, locally available aggregates from both 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 NDOT standard 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). Phase 2 included an evaluation of the 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) with satisfactory key fresh and hardened concrete properties. Phase 3 is the performance evaluation phase, which included evaluating the reference mix and selected promising mixes for slump, air content, setting time, compressive strength, modulus of rupture, modulus of elasticity, surface and bulk resistivity, free shrinkage, restrained shrinkage, and freeze/thaw resistance. 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. Results from the study demonstrated that with the optimized aggregate gradation, cement content can be reduced without compromising key fresh, mechanical, and durability properties