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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.
In Phase I, the research team contacted each of 16 participating states to gather information about concrete and concrete material tests. A preliminary suite of tests to ensure long-term pavement performance was developed. The tests were selected to provide useful and easy-to-interpret results that can be performed reasonably and routinely in terms of time, expertise, training, and cost. The tests examine concrete pavement properties in five focal areas critical to the long life and durability of concrete pavements: (1) workability, (2) strength development, (3) air system, (4) permeability, and (5) shrinkage. The tests were relevant at three stages in the concrete paving process: mix design, preconstruction verification, and construction quality control. In Phase II, the research team conducted field testing in each participating state to evaluate the preliminary suite of tests and demonstrate the testing technologies and procedures using local materials.
The chemistry of today's concrete mixture designs is complicated by many variables, including multiple sources of aggregate and cements and a plethora of sometimes incompatible mineral and chemical admixtures. Adding to the complexity are construction variables such as weather, mix delivery times, finishing practices, and pavement opening schedules. Mixture materials, mix design, and pavement construction are not isolated steps in the concrete paving process. Each affects and is affected by the other in ways that determine overall pavement quality and long-term performance. Equipment and procedures commonly used to test concrete materials and concrete pavements have not changed in decades, leaving serious gaps in our ability to understand and control the factors that determine concrete durability. The concrete paving community needs tests that will adequately characterize the materials, predict interactions, and monitor the properties of the concrete. The overall objectives of this study are to evaluate conventional and new technologies and procedures for testing concrete and concrete materials to prevent material and construction problems that could lead to premature concrete pavement distress; and examine and refine a suite of tests used to more accurately evaluate concrete pavement properties. As part of Phase I, the MCO project research team contacted each participating state to gather information related to concrete and concrete material tests. A preliminary suite of tests to ensure long-term pavement performance was developed. The goal was to include tests that provide useful information and results that are easy to interpret, and that can be reasonably performed routinely in terms of time, expertise, training, and cost. The tests examine concrete pavement properties in five focal areas determined to be most critical to the long life and durability of concrete pavements: (1) workability, (2) strength development, (3) air system, (4) permeability, and (5) shrinkage. The tests were considered for relevance at three stages in the concrete paving process: mix design, preconstruction verification, and construction quality control. As part of Phase II, the research team is currently conducting field testing in each participating state to evaluate the preliminary suite of tests and demonstrate the testing technologies and procedures using local materials. A Mobile Concrete Research Lab has been designed and equipped to facilitate the demonstrations. This preliminary field testing report documents the results of the shadow construction project in Kansas. The results of the overall project to date are also being compiled in a user-friendly field manual of practical tests and troubleshooting guidance. Phase III will refine and finalize lab and field tests based on shadow project test data.
Construction of portland cement concrete pavements is a complex process. A small fraction of the concrete pavements constructed in the United States over the last few decades have either failed prematurely or exhibited moderate to severe distress. In an effort to prevent future premature failures, 17 state transportation agencies pooled their resources, and a pooled fund research project, Material and Construction Optimization for Prevention of Premature Pavement Distress in PCC Pavements, was undertaken in 2003. Its purpose was to evaluate existing quality control tests, and then select and advance the state-of-the-practice of those tests most useful for optimizing concrete pavements during mix design, mix verification, and construction. This testing guide is one product of that project. The guide provides three recommended testing schemes (Levels A, B, and C, depending on a pavement's design life and traffic volumes, etc.) that balance the costs of testing with the risk of failure for various project types. The recommended tests are all part of a comprehensive suite of tests described in detail in this guide.
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 objective of this research study was to develop guidelines for portland cement concrete (PCC) material inputs to the AASHTOWare Pavement ME Design program. The AASHTOWare Pavement ME Design is the software program used by the Mississippi Department of Transportation (MDOT) to develop pavement design alternatives based on the mechanistic-empirical pavement design guide (MEPDG) procedure originally developed under National Cooperative Highway Research Program (NCHRP) Projects 1-37A, 1-40D, and 20-07/Task 288 & 327. MDOT has conducted several research projects to support the implementation of the MEPDG and for increasing the accuracy of the distress prediction models calibrated for local conditions and material sources. The current project focuses on PCC material inputs that represent the mix designs, cementitious materials, and the aggregate sources that will be used in future paving projects. This report provides a summary of laboratory test results of 20 mix designs that include five different aggregate sources and four different options for supplementary cementitious materials (SCM) for partial cement replacement. The laboratory test results represent level 1 and 2 PCC material inputs and report the flexural strength, compressive strength, elastic modulus, poisson's ratio, coefficient of thermal expansion (CTE), and percent length change measurements. Strength and modulus data, are reported for 7, 14, 28, and 90 days as required by the MEPDG. The CTE measurements are reported at 28-days, while the shrinkage length change measurements are reported for ages of 7, 11, 14, 21, 35, 63, 119, and 231 days. Level 2 correlation equations were developed based on compressive strength and other index properties to estimate flexural strength and elastic modulus. In general, these models demonstrate a slight deviation for the default level 2 models used in the global calibration of the MEPDG. Level 2 equations were also developed for each aggregate type and it is recommended that future efforts by MDOT for the recalibration of the rigid pavement distress prediction models should examine the sensitivity of these level 2 correlation equations and provide recommendations in the MDOT Design Manual.
This report documents enhancement incorporated in the (HIgh PERformance PAVing) HIPERPAV(trademark) II software. Enhancements made within this project include the addition of two major modules: a module to predict the performance of Jointed Plain Concrete Pavement (JPCP) as affected by early-age factors and a module to predict the early-age behavior (first 72 hours) and early life (up to 1 year) of Continuously Reinforced Concrete Pavement (CRCP). Two additional Federal Highway Administration (FHWA) studies were also incorporated: one that predicts dowel bearing stresses as a function of environmental loading during the early age and a module for optimization of concrete paving mixes as a function of 3-day strength, 28-day strength, and cost. Additional functionality to the software also was incorporated by reviewing and prioritizing the feedback provided by users of the first generation of the software, HIPERPAV 1.
The installation of durable patches on jointed portland cement concrete pavement using several types of cast-in-place concrete, is described. The recommended procedures for pavement preparation and patch installation are given, and additional maintenance procedures as cleaning and sealing joints and assuring proper drainage are briefly discussed. The successful evaluation of proprietary products for repair concretes through a laboratory determination of concrete properties, field use of acceptable products, and the assessment of performance data during and after installation is discussed. Included in this study were some of the cements, admixtures, and other special products for repair concretes, from a list maintained by the Materials Division of the Virginia Department of Highways & Transportation to provide assistance in the selection of the proprietary products. A production chart is presented as an aid in estimating the number of patches that can be installed during typical lane closure periods. Concretes with short curing times increased potential production, however, the selection of a repair product is acknowledged to also be dependent on factors such as cost and availability of materials. A procedure for installing precast patches for partial-depth repairs is described however; the rate of pavement preparation is too slow to make this procedure a viable alternative to cast-in-place patching.