ICAR Technical Reports
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Browsing ICAR Technical Reports by Author "Fowler, David W."
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Item Aggregates in Self-Consolidating Concrete(2007-03) Koehler, Eric Patrick; Fowler, David W.Self-consolidating concrete (SCC) is an advanced type of concrete that can flow through intricate geometrical configurations under its own mass without vibration or segregation. A research project was conducted to investigate the role of aggregates in SCC. Although SCC can be proportioned with a wide range of aggregates, the selection of favorable aggregate characteristics can significantly enhance the economy and performance of SCC. The objectives of the research project were to evaluate the effects of specific aggregate characteristics and mixture proportions on the workability and hardened properties of SCC, to identify favorable aggregate characteristics for SCC, and to develop guidelines for proportioning SCC with any set of aggregates. 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. Target properties for SCC workability were defined as a function of the application and in terms of filling ability, passing ability, segregation resistance, and rheology. Seven workability test methods were evaluated extensively to provide sound, engineering justifications for their use and for the interpretation of their results. Specific tests for filling ability, passing ability, and segregation resistance were recommended. Based on the results of this research and well-established principles from the literature, a mixture proportioning procedure for SCC was developed.Item Alkali-Silica Reaction in Portland Cement Concrete: Testing Methods and Mitigation Alternatives(2001-07) Touma, Wissam; Fowler, David W.; Carrasquillo, Ramón L.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. Several tests have been developed for identifying aggregates subject to ASR, but each has its limitations. A three-year research study was initiated on January 1, 1998 at The University of Texas at Austin for investigating ASR in portland cement concrete. The scope of the study was essentially three fold: (1) investigate the predictive ability of ASTM C 1260 and C 1293, (2) develop more accurate and more efficient modifications of these procedures, and (3) investigate ASR mitigation alternatives. Aggregate samples from 14 sources from around the United States were acquired for the investigation. Aggregates were used in an extensive testing program during which guidelines for predicting the potential ASR of aggregates were developed and recommendations for minimizing concrete damage due to ASR were formulated. This report includes a review of the state-of-the-art of ASR, an evaluation of testing protocols and recommendations for dramatically shortening test time, test results, and mitigation options.Item Characterizing minus no. 200 fine aggregate for performance in concrete(2006-03) Stewart, Jane; Norwell, Justin; Juenger, Maria C. G.; Fowler, David W.ASTM C 33 limits the amount of microfine aggregate smaller than 75 µm (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.Item Determination of Aggregate Shape Properties Using X-ray Tomographic Methods and the Effect of Shape on Concrete Rheology(2005-08) Erdogan, Sinan Turhan; Fowler, David W.The shape of aggregate particles can significantly influence certain properties of concrete, both in its fresh and hardened states. Therefore, there is a need to be able to completely characterize the shape of aggregate particles, in three dimensions, in order to develop computational models that accurately predict properties. In the past, numerous methods have been suggested for this task. However, these methods are often only applicable to two-dimensional images of particles, they output a single or a few values, and fail to characterize the true shape of the particle. X-ray tomographic techniques allow the capturing of the true shape of particles and have been applied to concrete aggregates. Computed tomography has been used to characterize coarse and fine aggregate particles, while X-ray microtomography has been used to characterize particles passing the 75 m sieve. Sample preparation methods and scanning parameters applicable to concrete aggregates have been developed. The spherical harmonic method was used to efficiently store shape information, and to calculate useful parameters for individual particles, such as volume and surface area. Comparisons of the results to properties determined using other techniques were made and it was determined that the results of indirect or two-dimensional shape and size characterization methods can be misleading.Item Development of a Portable Rheometer for Fresh Portland Cement Concrete(2004-08) Koehler, Eric Patrick; Fowler, David W.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. Based on a literature search in which 61 existing workability test methods were identified and on feedback from government, industry, and academia, criteria for an improved workability test device were developed. It was determined that the best approach to measuring workability would be to develop a new portable rheometer. 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.Item The effects of the aggregates characteristics on the performance of Portland cement concrete(2003-12) Quiroga, Pedro Nel; Fowler, David W.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 tool suggested by Shilstone. The effect of different types and amounts of microfines was evaluated simultaneously as well as the impact of chemical 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.Item An Experimental Study on the Guidelines for Using Higher Contents of Aggregate Microfines in Portland Cement Concrete(2001-12) Fowler, David W.; Ahn, Nam-ShikThe use of manufactured fine aggregate (MFA) in portland cement concrete becomes more common as sources of natural sands are depleted. There is a great need to utilize MFA better, particularly the minus 75µm sizes. The development of specifications that aid aggregates producers, engineers, and specifying agencies in the utilization of MFA is of interest to many parties. Better utilization of crushed aggregates has both economic and environmental benefits for the construction and materials industry. 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.Item Federal Highway Administration Research Project, Task 3, Concrete Mixture Research Related to Pavements: Final Report(2008-10-15) Fowler, David W.Manufactured fine aggregate (MFA) can be used as a replacement for or in conjunction with natural sand in concrete mixtures. MFA does not exhibit ideal shape or texture for fine aggregate, and the production of MFA generates high percentages of microfines, particles that pass the No. 200 sieve. Microfines are washed from the aggregate due to specification limitations, resulting in wasted aggregate and a coarser fine aggregate grading. Three manufactured sands were incorporated into concrete mixtures to determine their effects on fresh and hardened concrete properties. It was found that greater proportions of manufactured sand caused the workability to decrease, the demand for high-range water-reducing admixture to increase, the compressive strength to increase, and the modulus of elasticity to decrease.Item Guidelines for Proportioning Optimized Concrete Mixtures with High Microfines(2004-08) Quiroga, Pedro Nel; Fowler, David W.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. One 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.Item ICAR Mixture Proportioning Procedure for Self-Consolidating Concrete(2007) Koehler, Eric Patrick; Fowler, David W.Self-consolidating concrete (SCC) is an advanced type of concrete that can flow under its own mass without vibration, pass through intricate geometrical configurations, and resist segregation. The use of SCC can result in increased construction productivity, improved jobsite safety, and improved concrete quality. To achieve SCC workability, the materials and mixture proportions must be carefully selected. The ICAR mixture proportioning procedure was developed as part of ICAR Research Project 108: Aggregates in Self-Consolidating Concrete. This research project evaluated the workability and hardened properties of SCC mixtures composed of a wide range of materials and mixture proportions. 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.Item The Prediction of Coarse Aggregate Performance by Micro-Deval and Soundness Related Aggregate Tests(2006-07) Fowler, David W.; Allen, John J.; Lange, Alexander; Range, Peter H.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.Item Qualification of Concrete Workability by Means of the Vibrating Slope Apparatus(2003-12) Bodenlos, Kainan David; Fowler, David W.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.Item Summary of Concrete Workability Test Methods(2003-08) Koehler, Eric Patrick; Fowler, David W.This document 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 scarcely used in the past, an examination of tests that have failed and tests that have been supplanted by better tests is instructive in recognizing trends in concrete workability research and in selecting key concepts for the development of a new test method. 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.Item Utilizing Aggregates Characteristics to Minimize Cement Content in Portland Cement Concrete(2009-02-06) Rached, Marc Manuel; De Moya, Michael; Fowler, David W.Aggregate, the main constituent of concrete, constitutes 60 to 80% of the total volume of concrete. Proper selection of the type and particle size distribution of the aggregates affects the workability and the hardened properties of the concrete. There are two main reasons for increasing the amount of aggregates in concrete. The first is that cement is more expensive than aggregate, so using more aggregate reduces the cost of producing concrete. The second is that most of the durability problems, e.g. shrinkage and freezing and thawing or hardened concrete, are caused by cement. Generally, concrete shrinkage increases with increase in cement content; aggregates, on the other hand, reduce shrinkage and provide more volume stability. Furthermore, cement production is a key source of carbon dioxide (CO2) emissions, and reducing its usage should be a goal for concrete production. Various projects have explored methods of minimizing cement in concrete; among the most common of those is replacing cement with cementitious and pozzolanic materials such as fly ash.