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Research
Report ICAR 101-1 NOTE: This report is out-of-print. No copies available. The handling and disposal of fines produced as a result of the aggregate crushing and production process are some of the major problems facing the aggregate industry today, having both economic and environmental implications. This report describes a major effort undertaken to quantify and characterize these fines, their location , character, and sales. The focus of this project was to examine the methods and test procedures used in the past to characterize the properties of fines, and develop, on a preliminary basis, a framework to characterize and catalogue the properties of aggregate fines, propose new ones that would eventually complement a set of guidelines for the use of aggregate fines in portland cement concrete. Possible applications of aggregate fines, such as in high-performance concrete, controlled low strength materials, and insulated concrete forms are discussed as future directions of research. This report presents some of the effects of high fines on the properties of cement mortar and concrete. A total of 50 sands were used in this mortar study, 10 of which were included in the concrete research. A summary of aggregate characteristics that affect the properties of mortar and concrete are presented along with the correlations evaluated between these properties.
This project work consisted of developing technical data to justify, from the standpoint of material properties (of aggregate fines and HFC), construction efficiency, cost competitiveness, and energy performance, a basis for the use of high-fines concrete (HFC) inside ICF wall systems. Although several aspects of the study are listed above, the report primarily concentrates on the material aspects of a limited number of aggregate fines sources and their use in HFC reltive to strength development and placeability.
The optimization of aggregates is advantageous for economical and technical reasons; however, the availability of materials and construction operations can dictate the proportions of fine and coarse aggregates. Some general guidelines based on field experience, other investigations and the results of this investigation are presented. Two sets of guidelines were developed. On e is intended for users of the ACI 211 method who want to optimize aggregate proportions. The other is intended for eventual users of the Compressible Packing Model. CPM is more complex and requires more testing than ACI 211. As a result, it might not be the preferred procedure for some users. These guidelines are focused on the proportioning and optimization of aggregates; the determination of mixing water, water-to-cement ratio, and cement content is briefly mentioned. Aggregate shape, texture, and grading have a significant effect on the performance of fresh concrete. Aggregates blends with well-shaped, rounded, and smooth particles require less paste for a given slump than blends with flat, elongated, angular, and rough particles. At the same time, uniform gradings with proper amounts of each size result in aggregate blends with high packing and in concrete with low water demand. Optimized aggregate blends have high packing, requiring low amounts of paste. As a result, they are less expensive and will have less durability problems caused by the paste such as head generation, porosity, and drying shrinkage. The effect of shape, texture and grading of aggregates on fresh concrete was evaluated experimentally, quantified by means a proportioning method based on packing density concepts, the Compressible Packing Model (CPM), and analyzed by an empirical tood suggested by Shilstone. The effect of different types and amounts of microfines was evaluated simultaneously as well as the impact of hemical admixtures and some supplementary cementing materials can be used to improve the workability of concrete with high microfines without negatively affecting hardened concrete. Guidelines for portioning and optimizing aggregate blends were made based on Shilstone's Coarseness Chart and the 0.45 Power Chart and CPM equations and procedures.
This project describes 61 test methods for measuring concrete workability. Many more test methods have been developed for a single project or for a specific application and have been sparsely reported in the literature, if at all. Although many of the devices in this document will likely never be used in the future and have been scarecely used in the past, an examination of tests that have failed and tests that have been supplanted by better tests in instructive in recognizing trends in concrete workability research and in slecting key concepts for the development of a new test metod. This document first describes key principles and trends in the measurement of workability and then describes the 61 test methods. Based on the successes and failures of past test methods and the current needs of the concrete industry, requirements for new test methods are developed. A new device, the Vibrating Slope Apparatus (VSA), developed for qualifying concrete workability under vibration, was borrowed by the International Center for Aggregates Research (ICAR) Project 105 researchers for evaluation. Initial evaluation consisted of testing 24 different concretes that possessed a wide range of workability. The results indicate that the VSA is capable of differentiating between mixtures of similar workability and characterizing established trends. However, testing identified three problems inherent of the proposed test method. An excessive amount of time required to obtain results, the possibility of shear failure of a sample that skews results, and the possibility of an inverse relationship, if the minimum of two chute angles are tested. To solve these problems, the VSA was fitted with an accelerometer to monitor vibration displacement and frequency during testing. A new wedged-shape chute gate was also constructed. The data from the accelerometer were consolidated into one variable, energy, which was used to replace the chute angle from the initial test procedure. The new equipment and procedure were evaluated in a similar manner as before and promising results were obtained. The new procedure solved all three problems identified with the original procedure. A linear correlation between VSA and slump cone measurements for less then 3 inches was defined. This new method was able to characterize expected patterns and differentiate between mixtures of similar workability in an acceptable time, whereas a single-point test, the slump cone, was not. However, the size and complexity of the VSA limit implementation within the field.
The purpose of this research was to identify an effective field test method for measuring the workability of concrete in general and of high-microfines concrete in particular. The workability of fresh concrete has traditionally been measured with the slump test, which provides an inadequate indication of workability. For certain concrete mixtures—such as that containing fiber reinforcement, ground granulated blast furnace slag, or high contents of aggregate microfines—the slump test can provide inaccurate and misleading results. The need for a better test method for workability is well established within the concrete industry. The ICAR rheometer—a low-cost, fully portable test device for concrete—was developed and tested. A first generation prototype was built using off-the-shelf components. The ICAR rheometer is approximately the size of a drill and can be operated by hand or positioned above a standard container. It is capable of measuring a flow curve or performing a stress growth test and is appropriate for nearly the full range of concrete workability ranging from a slump of approximately 2 inches to self-consolidating concrete.
Experimental testing on a wide range of concrete mixtures indicated that the ICAR rheometer was able to detect changes in workability and rheology successfully. As a dynamic test that adds energy to concrete, it is well suited for measuring high-microfines concrete and other highly thixotropic concrete mixtures. Field testing confirmed the portability of the ICAR rheometer. The low cost and portable form factor of the ICAR rheometer can make the routine measurement of concrete rheology in the field an economically viable solution to characterizing concrete workability.
ASTM C 33 limits the amount of microfine aggregate smaller than 75 m m (No. 200 sieve) to be used in concrete. In the past, it was believed that this fraction was clay and, therefore, a poor performer. This is not necessarily the case with manufactured fine aggregates. While work continues toward altering ASTM C 33 to allow a higher percentage of microfine aggregates, there is need for a method of determining whether these microfines will have deleterious effects or not.
Fourteen aggregates were collected for evaluation in this study. Methods of characterizing the microfines to determine their effects on concrete properties were developed in this study. In addition to fully characterizing the aggregates using advanced techniques, simple tests for microfines that can be used as a criterion for their exclusion or inclusion were evaluated. For such a test to be meaningful there must be a strong correlation between its results and concrete performance. Mortar and concrete mixes incorporating microfines from fourteen different aggregates are tested in this project for a variety of performance criteria. This project fully characterizes microfines and evaluates simple tests for predicting performance in concrete.
The ICAR mixture proportioning procedure is based on a fundamental, rheology-based framework for concrete workability and is designed and written to be accessible and comprehensible. The procedure provides specific guidelines for each aspect of the mixture proportioning process but intentionally avoids long calculations or restrictive, discrete inputs. Instead, deliberate laboratory testing is conducted with actual job materials to establish final mixture proportions efficiently. All required testing is conducted with methods standardized by ASTM International. ICAR Research Report 108-2F, Aggregates In Self-Consolidating Concrete The effects of aggregate grading; maximum size; shape, angularity, and texture; clay content; and packing density were evaluated. Separately, the effects of mixture proportions, cementitious materials, and chemical admixtures were evaluated. In total, 12 fine aggregates, 7 coarse aggregates, and 6 microfines were tested. Tests were conducted on paste, mortar, and concrete. Paste measurements were conducted to evaluate the effects of cement, fly ash, microfines, high-range water-reducing admixture (HRWRA), and viscosity modifying admixture (VMA) on rheological properties. Mortar measurements were conducted to evaluate the effects of fine aggregates, microfines, and mixture proportions on workability and hardened properties. Concrete measurements were conducted to evaluate the effects of fine aggregates, coarse aggregates, microfines, and mixture proportions on workability and hardened properties. Based on the results of this research and well-established principles from the literature, a mixture proportioning procedure for SCC was developed. The procedure is based on a consistent, rheology-based framework and was designed and written to be accessible and comprehensible for routine use throughout the industry. In the procedure, SCC is represented as a suspension of aggregates in paste. In order to achieve SCC workability, the paste volume must be sufficient for the given aggregate blend and the paste rheology must be selected based on the aggregate blend and paste volume. The three-step procedure consists of selecting the aggregates, paste volume, and paste composition. Detailed recommendations are provided for each step. Aggregates are selected on the basis of grading, maximum size, and shape and angularity. The paste volume is set based on the aggregate characteristics. The paste composition is established to achieve workability and hardened properties. All required testing is conducted with methods standardized by ASTM International.
A comprehensive research program was conducted in three concurrent phases which examined the Superpave fine aggregate angularity (FAA) test, the restricted zone requirement, and the voids in the mineral (VMA) specification. As a result of these studies several reports were written. In this 201 series you will find the following reports: 201-1, “Evaluation of Superpave Fine Aggregate Angularity Specification,” Arif Chowdhury, Joe Button, Vipin Kohle and David Jahn. 201-2, “Effects of Superpave Restricted Zone on Permanent Deformation,” Arif Chowdhury, Joe Button, and Jose Grau. 201-3F, “Effects of Aggregate Gradation and Angularity on VMA and Rutting Resistance,” Dae-Wook Park , Arif Chowdhury, and Joe Button. This report documents the outcomes of the ICAR study on the Evaluation of Aggregate Characteristics Affecting HMA Concrete Performance. This study was conducted with support from the Federal Highway Administration (FHWA) program on Simulation, Imaging, and Mechanics of Asphalt Pavements at Texas A&M University. The first outcome includes assessment of HMA sensitivity to aggregate shape characteristics. Aggregate shape is characterized through detailed measurements of angularity, form, and texture using the Aggregate Imaging System (AIMS). The shape characteristics are presented in terms of the distribution of the property in an aggregate sample rather than an average index of this property.The second outcome of this study is the development of a viscoplastic model for permanent deformation. Research
Report ICAR 204 Research
Report ICAR 301-1F Identifying the susceptibility of an aggregate to alkali-silica reaction (ASR) before using it in concrete is one of the most efficient practices for preventing damage and failure. This paper provides a critical evaluation of the various methods available for testing the efficacy of measures for preventing expansion due to alkali-silica reaction (ASR) in concrete containing deleteriously reactive aggregate. The ideal test method should be rapid, reliable and capable of determining the influence of aggregate reactivity, alkali availability and exposure conditions. None of the currently available or commonly used methods meet all of these criteria. The shortcomings of the different test methods are discussed and suggestions are made for modifying the concrete prism test and accelerated mortar bar test to make these tests more acceptable.
This project was initiated specifically to investigate the potential for placing unbound aggregate base courses in thicker lifts to improve pavement performance, reduce costs, and increase the amount of aggregates used. Based on the results of this study, researchers recommend the new specifications be adopted to allow the placement of thicker lift bases. Those specifications are included in the ICAR 501-5F report. In this 501 series you will find the following reports: 501-2, “A Study on the Feasibility of Compacting Unbound Graded Aggregate Base Courses in Thicker Lifts than Presently Allowed by State Departments of Transportation,” Jaime L. Bueno, Kenneth H. Stokoe, II, and John J. Allen 501-3, “Prediction of Working Load Displacements Under Plate Loading Tests from Seismic Stiffness Measurements,” Michael L. Myers, Kenneth H. Stokoe, II, and John J. Allen 501-5F, “Increased Single-Lift Thicknesses for Unbound Aggregate Base Courses,” John J. Allen , Jaime L. Bueno, Michael E. Kalinski, Michael L. Myers, and Kenneth H. Stokoe, II Reports 501-1 and 501-4 were internal documentation only and were not published.
AASHTO is moving towards a mechanistic pavement design procedure for the Design Guide- 2002. This guide will establish the structural contribution of various materials used as pavement layers. It is essential that the structural contribution of unbound aggregate layers be accurately portrayed. This project developed laboratory test protocols, generated data, and defined materials models that support mechanistic design methods and accurately define the aggregate layers. This groundbreaking research provides an accurate structural model for predicting performance of unbound aggregate bases. Based on the results of this study, three reports were written. In this 502 series you will find the following reports: 502-1, “Structural Characteristics of Unbound Aggregate Bases to meet AASHTO 2002 Design Requirements: Interim Report,” Alex Adu-Osei, Dallas Little and Robert Lytton 502-2, “Field Validation of the cross-Anisotropic Behavior of Unbound Aggregate Bases,” Erol Tutumluer, Alex Adu-Osi, Dallas Little and Robert Lytton 502-3, “Characterization of Unbound Granular Layers in Flexible Pavements,” Alex Adu-Osei
The objective was to develop a test method that can operate in an automatic, continuous sampling mode. Current production methods are mechanical and time consuming. Most recent prior research was proprietary and had not made a significant advancement. The project evaluated current technology, proposed a promising solutions, build a prototype, and demonstrated the capability of the device, designed the "LASS" (laser-based aggregate scanning system). The LASS can rapidly acquire volumetric data on multiple particles in an aggregate sample. 503-1, “Evaluation of Potential Aggregate Grading Technologies,” Alan F. Rauch, Carl T. Hass, Hyoungkwan Kim, and Craig Browne 503-2, “An Evaluation of Automated Devices to Replace and Augment Manual Sieve Analyses in Determining Aggregate Gradation,” Alan F. Rauch, Carl T. Haas, Craig Browne, and Hyoungkwan Kim 503-3F, “Automation of Aggregate Characterization Using Laser Profiling and Digital Image Analysis,” Carl T. Haas, Alan F. Rauch, Hyoungkwan Kim, and Craig Browne
One of the objectives of this
study is to conduct a comparative analysis of flexible pavement response
using different models for unbound pavement layers: linear isotropic,
nonlinear isotropic, linear anisotropic and nonlinear anisotropic. Pavement
response is computed using a finite element program. The computations
from nonlinear isotropic and anisotropic models of unbound layers are
compared to the AASHO field experimental measurements. The second objective is to analyze the influence of using isotropic and anisotropic properties for the pavement layers on the performance of flexible pavements calculated using the AASHTO 2002 Models.
This research is intended to contribute toward the understanding, development, and implementation of a more fundamental design process for bituminous pavement materials, utilizing thermodynamic properties of the materials involved. The theory developed by van Oss, Chaudhury and Good forms the basis of this research. Optimization of techniques to characterize surface energy, as well as consideration and evaluation of additional factors that influence adhesion in the presence of water, are pursued. A synthesis of theories and mechanisms of bitumen-aggregate adhesion is presented, and existing and potential techniques for surface energy characterization are reviewed to establish firm background knowledge on this subject. The Wilhelmy plate technique was scrutinized and improved methodologies and analysis procedures are proposed. Inverse gas chromatography (IGC) is introduced as an alternative technique. A reasonable comparison of total surface energy values form these techniques with mechanical surface tension values were found. Results suggest that bitumen surface energies do not vary substantially. Inability of these techniques to detect the effect of a liquid additive is rationalized by the ‘potential' surface energy concept. Suggestions for a more realistic characterization of bitumen polar surface energy components are presented. A static gravimetric sorption technique was employed to characterize aggregate surface energies. Dynamic vapor sorption was identified as a candidate alternative technique for aggregate surface energy characterization. A study on the effect of pH on surface energy components of water revealed that this effect is practically negligible. Calculation of the free energy of electrostatic interaction ( D G EL ) indicated that this term contributes less than 1% to the total free energy of adhesion. Despite this finding, it is shown that D G EL alone is able to distinguish moisture sensitive mixtures. The significance of electrical phenomena at the interface is elucidated through another mechanism following the work of M.E. Labib. The relationship between pH and electron donor-acceptor properties of aggregate surfaces is presented. The Labib approach potentially offers the solution to quantify the effect of pH on adhesion. In addition, it should be possible to resolve issues with the acid-base scale proposed by the founders of the current theory, by replacing it with a more absolute donor-acceptor scale.
Physical and chemical properties of aggregates at the micro scale strongly impact the adhesive bond (strength and durability) between bitumen and aggregate. These properties include surface free energy, chemical interaction potential, and specific surface area. This report describes testing methods developed for the Universal Sorption Device (USD), the Wilhelmy Plate (WP), and the microcalorimeter (MC) to measure these surface properties of aggregates. Test results from five different asphalt binders and nine different aggregates are presented to demonstrate how these surface properties can be used to: (1) select combinations of bitumen and aggregates that are more resistant to moisture damage, (2) select additives that can be used to improve the performance of asphalt mixtures based on the physico-chemical nature of the bitumen and aggregate, and (3) predict the resistance of the mixture to moisture-induced damage.
This research project concentrated on determining whether or not a correlation existed between laboratory aggregate tests and observed aggregate field performance. For this purpose, aggregate samples were collected from the majority of the U.S. states as well as several Canadian provinces and subjected to a variety of strength, soundness, and intrinsic particle property tests. Additionally, performance data on the aggregates was obtained by contacting multiple DOTs where aggregates were in use in several categories – hot-mix asphalt, portland cement concrete, base course, and open-graded friction course. Numerical and qualitative analyses were performed to evaluate the success of separating good performers from fair and poor performers using the micro-Deval test alone as well as the micro-Deval test combined with another test. Special attention was paid to aggregate mineralogical composition. Furthermore, attempts were made to determine if a correlation exists between any two tests. |
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