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In the field, Schmidt rebound hammer testing showed that the internally cured concrete was neither consistently stronger nor weaker than the conventional concrete. On average, the internally cured concrete exhibited higher chloride concentrations than the conventional concrete. On average, the conventional concrete bridge decks had 4.6, 21.5, and 2.8 times more cracking than the internally cured concrete decks at 5 months, 8 months, and 1 year, respectively. At 1 year, very distinctive reflection cracks from the joints between the underlying pre-cast half-deck panels were observed on all of the decks.
Curing is one of those activities that every civil engineer and construction worker has heard of, but in reality does not worry about much. In practice, curing is often low on the list of priorities on the construction site, particularly when budgets and timelines are under pressure. Yet the increasing demands being placed on concrete mixtures also mean that they are less forgiving than in the past. Therefore, any activity that will help improve hydration and so performance, while reducing the risk of cracking, is becoming more important. Curing Concrete explains exactly why curing is so important and shows you how to best do it. The book covers: The fundamentals behind hydration How curing affects the properties of concrete, improving its long-term performance What curing technologies and techniques you can use for different applications How to effectively specify, provide, and measure curing in a project The author also gives numerous examples of how curing—or a lack of it—has affected concrete performance in real-world situations. These include examples from hot and cold climates, as well as examples related to high-performance concrete, performance parameters, and specifications and testing. Written for construction professionals who want to ensure the quality and longevity of their concrete structures, this book demonstrates that curing is well worth the effort and cost.
Maintenance, Safety, Risk, Management and Life-Cycle Performance of Bridges contains lectures and papers presented at the Ninth International Conference on Bridge Maintenance, Safety and Management (IABMAS 2018), held in Melbourne, Australia, 9-13 July 2018. This volume consists of a book of extended abstracts and a USB card containing the full papers of 393 contributions presented at IABMAS 2018, including the T.Y. Lin Lecture, 10 Keynote Lectures, and 382 technical papers from 40 countries. The contributions presented at IABMAS 2018 deal with the state of the art as well as emerging concepts and innovative applications related to the main aspects of bridge maintenance, safety, risk, management and life-cycle performance. Major topics include: new design methods, bridge codes, heavy vehicle and load models, bridge management systems, prediction of future traffic models, service life prediction, residual service life, sustainability and life-cycle assessments, maintenance strategies, bridge diagnostics, health monitoring, non-destructive testing, field testing, safety and serviceability, assessment and evaluation, damage identification, deterioration modelling, repair and retrofitting strategies, bridge reliability, fatigue and corrosion, extreme loads, advanced experimental simulations, and advanced computer simulations, among others. This volume provides both an up-to-date overview of the field of bridge engineering and significant contributions to the process of more rational decision-making on bridge maintenance, safety, risk, management and life-cycle performance of bridges for the purpose of enhancing the welfare of society. The Editors hope that these Proceedings will serve as a valuable reference to all concerned with bridge structure and infrastructure systems, including students, researchers and engineers from all areas of bridge engineering.
High performance concrete (HPC) provides a long lasting, durable concrete that is typically used in bridge decks due to its low permeability, high abrasion resistance, freeze-thaw resistance and strength. However, this type of concrete is highly susceptible to the deleterious effects of both autogenous and drying shrinkage. Both types of shrinkage occur when water leaves small pores, (
The Indiana Department of Transportation (INDOT) commissioned the construction of six bridge decks utilizing a new class of internally cured high performance concrete (IC HPC). The first four bridge decks were constructed in the summer of 2013, while the fifth was built in November of 2014 and the sixth is planned for the summer of 2015. These decks implement research findings presented in the FHWA/IN/JTRP-2010/10 report (Schlitter, Henkensiefken, et al. 2010) where internal curing was proposed as one method to reduce the potential for shrinkage cracking, leading to improved durability. In addition, the use of higher performance concrete mixtures and a new specification composed of prescriptive and performance based measures was implemented with the intention of extending the service life of the bridge decks. The objectives of this thesis are to provide documentation of the construction and performance of the IC HPC bridge decks cast in Indiana and provide a viable, practice-ready method for the assessment of the potential durability of these concretes. In fulfillment of these objectives, samples of the IC HPC used in construction were compared to a reference high performance concrete (HPC) which did not utilize internal curing and was made by the same producer with the same constituent materials. The samples collected in the field were transported to the laboratory where the mechanical performance, resistance to chloride ingress, and potential for shrinkage and cracking was assessed. Using experimental results and mixture proportions, the diffusion based service life of the bridge decks was able to be estimated. The construction process was documented for first four bridge decks made using internal cured high performance concrete (IC HPC). These concretes were able to be designed, batched, and placed and are now in service. While avoidable issues were observed during batching construction related to corrections of batching water, batching tolerances and fluctuations in air content (which apply to any concrete), the IC HPC was able to be batched and placed using slight modifications to conventional methods. The production of the IC HPC mixtures was implemented using a mixed specification using prescriptive and performance based measures representing an improvement on previous specifications which did not specifically have provisions that consider durability. To aid in the implementation of internal curing in the field, a new quality control technique for lightweight aggregate utilizing a centrifuge has been implemented is now standardized in Indiana Testing Method 222 (Miller, Barrett, et al. 2014). The results of laboratory testing indicate that the compressive strength, modulus of elasticity, and tensile strength of the IC HPC mixtures was not substantially different than the HPC mixtures and as such current codified equations are able to be used to predict the modulus of elasticity and tensile strength if the compressive strength is known. The diffusion of chlorides in these concretes was assessed, where it was shown that each of the mixtures tested had a charge passed in the rapid chloride permeability test of less than 1500 C at 91 days (AASHTO T277-07 2007); additional testing provided equivalent results when performing the Nordtest (NT Build 492 1999), Stadium migration test , or electrical resistivity test. Using experimental results which determined the chloride diffusion and permeability, the diffusion based service life of the IC HPC bridge decks was estimated to be between approximately 60 to 90 years, compared to approximately 18 years for the conventional class C bridge deck concrete used in Indiana. The susceptibility to early age shrinkage and cracking was evaluated where it was shown that IC HPC concretes exhibited a reduction in early age shrinkage of 70 to 90%, resulting in a reduction in residual stresses of 80% or more while reducing thermally induced stress by up to 55% when compared to HPC mixtures. Collectively, these results indicate that the IC HPC mixtures that were produced as a part of this study exhibit the potential of for substantially increased service life while markedly reducing the potential for early age cracking. The second phase of this thesis investigated the role of initial sample conditioning and the effect of changes in degree of saturation on the measured electrical resistivity, where a new function was developed to describe this relationship in air entrained concretes. The consistency and variability in the determination of the chloride diffusion coefficient was investigated through standardized testing methods, where it was shown that the coefficient of variation associated with the accelerated tests was approximately 15% or less and are dependent on the test. Chloride profile measurements made on cores taken from samples which were exposed with a known deicing solution and the temperature fluctuations of West Lafayette, Indiana indicated that on average, the coefficient of variation for determining the apparent chloride diffusion coefficient under is 30% or less. In addition, the use of resistivity measurements on sealed samples was used to evaluate the variability of the concrete produced throughout the construction of the fifth IC HPC bridge deck while comparisons of the samples from the first four bridge decks produced in the laboratory and in the field were also made. The results indicated that the coefficient of variation associated with the resistivity measurements made on the fifth bridge deck was less than 5%, while experimental results indicated that industrial production consistently results in lower performance as measured by the resistivity test when compared to laboratory production. In this study it was also shown that measurements of mechanical properties are not indicative of the potential durability of the concrete. The conclusions of this thesis and the findings presented in the FHWA/IN/JTRP-2010/10 report (Schlitter, Henkensiefken, et al. 2010) and the CDOT-2014-3 report (Jones et al. 2014) indicate that internal curing is a practice-ready, engineered solution that may lead to the production of higher performance concretes which have a reduced potential for cracking. To aid in the implementation of internal curing in practice, spreadsheets which automate calculations necessary for quality control for lightweight aggregates, mixture proportioning, and moisture adjustments have been developed by Miller (2014) and have been made available with the report documenting the construction of the first four bridge decks (Barrett et al. 2015). This thesis also provided the framework for a durability based design approach using sealed electrical resistivity measurements which may be implemented in practice. This method has been shown to be a viable way to rapidly evaluate the chloride diffusion coefficient of concrete and is appropriate for testing large numbers of samples during construction. It is recommended that the approach outlined in this work be implemented in performance based specifications in lieu of other accelerated testing methods which define the performance of the concrete based on the result of that test. Finally, it should be emphasized that the implementation of technologies such as those that are presented in this thesis alone does not guarantee higher performance, as the production of such concrete requires a degree of technical competence in design, production, and construction of concrete materials. As is the case with the production of any concrete, internally cured or not, performance will be directly tied to the careful accounting of water, be it on the surface of aggregates, in the mixing drum after washing, or elsewhere. Special attention should be paid to the proper operation of batching systems, while placement techniques should be reviewed to minimize unwanted effects, and proper finishing and curing techniques must always be practiced. Only after performing the basics of concrete production properly will the full benefits of internal curing be actualized.
Due to the relatively high cement content and low water-to-cement ratio (w/c) used, bridge deck concrete is prone to premature cracking. Internal curing has been found to greatly reduce the chance of premature cracking as well as concrete deterioration. This research developed internally cured bridge deck concrete based on a local mix design in Nebraska. Four different lightweight fine aggregate (LWFA) as internal curing agents were evaluated and their effects on fresh, mechanical, durability, and shrinkage properties of concrete were studied. The study focused on resolving two issues associated with fine aggregate replacement based on Bentz equation. To identify the most effective LWFA dosage for shrinkage reduction, different replacement rates of fine aggregates (50%, 100%, 125%, 150% and 175%) were adopted to account for the moisture loss during construction and drying period. Aggregate blends of internally cured mixes were also optimized to account for the disturbed aggregate gradations due to the introduced LWFA. Overall performance of internally cured concrete mixes with both non-optimized and optimized gradations were evaluated. The research demonstrated that effective internal curing concrete can be achieved with the optimized aggregate gradation.
As the need for durable, long lasting infrastructure increases, new methods and techniques are being explored to prolong the service life of roads and bridges. One method to reduce shrinkage and early age cracking in concrete is internal curing. Internal curing supplies water to concrete, using pre-wetted lightweight aggregate (LWA), as needed throughout the process of hydration to reduce self desiccation, which leads to cracking. This research project analyzed two types of coarse LWA, expanded clay and expanded shale. The mixtures were developed specifically for use in bridge decks and adhered to specifications of the Arkansas State Highway and Transportation Department (AHTD). The concrete mixtures contained LWA at rates of 0, 100, 200, and 300 lb/yd3. The research was divided into two phases. The first phase measured autogenous and drying shrinkage in both plastic and elastic states using embedded vibrating wire strain gages (VWSG) cast in concrete prisms. The expanded clay LWA mixtures, with the 300 lb. replacement rate yielding the best results, were most effective in reducing shrinkage. Compressive strength decreased as the amount of LWA included in the mixture increased. However, all mixtures surpassed the 28 day compressive strength specified by AHTD. The second phase of the research project measured plastic shrinkage cracking in thin concrete test slabs. Methods and materials were investigated to produce consistent plastic shrinkage surface cracks of the concrete slabs. The extent of plastic shrinkage that occurred was quantified by measuring the total crack area of the test slabs. Implementation of 300 lb. of expanded clay LWA did not reduce the crack lengths, but did reduce the average crack widths experienced by the test slabs due to plastic shrinkage.