Effect of Portland cement concrete characteristics and constituents on thermal expansion

textThe coefficient of thermal expansion (CTE) is one of the major factors responsible for distresses in concrete pavements and structures. Continuously reinforced concrete pavements (CRCPs) in particular are highly susceptible to distresses caused by high CTE in concrete. CRCP is a popular choice across the U.S. and around the world for its long service life and minimal maintenance requirements. CRCP has been built in more than 35 states in the U.S., including Texas. In order to prevent CRCP distresses, the Texas Department of Transportation (TxDOT) has limited the CTE of CRCP concrete to a maximum of 5.5 x10-6 strain/oF (9.9 x10-6 strain/oC). Coarse aggregate sources that produce concrete with CTE higher than the allowable limit are no longer accepted in the TxDOT CRCP projects. Moreover, CTE is an important input in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Small deviations in input CTE can affect the pavement thickness significantly in MEPDG designs. Therefore, accurate determination of concrete CTE is important, as it allows for enhanced concrete structure and pavement design as well as accurate screening of CRCP coarse aggregates. Moreover, optimizing the CTE of concrete according to a structure’s needs can reduce that structure’s cracking potential. This will result in significant savings in repair and rehabilitation costs and will improve the durability and longevity of concrete structures. This study found that the CTEs determined from saturated concrete samples were affected by the internal water pressure. As a result, the TxDOT method yielded higher values than did the American Association of State Highway and Transportation Officials (AASHTO) method. To further investigate the effect of internal water pressure, an analytical model was developed based on the poroelastic phenomenon of concrete. According to the model, porosity, permeability, and the rate of temperature change are the major factors that influence the internal water pressure development. Increasing the permeability of concrete can reduce the internal water pressure development and can thus improve the consistency of measured CTE values. Preconditioning concrete samples by subjecting them to several heating and cooling cycles prior to CTE testing and reducing the rate of temperature change improved the consistency of the CTE test results. Concrete CTE can be reduced by blending low-CTE aggregates with high-CTE aggregates and reducing the cement paste volume. Based on these findings, a concrete CTE optimization technique was developed that provides guidelines for the selection of concrete constituents to achieve target concrete CTE. A concrete proportioning technique was also developed to meet the need for CTE optimization. This concrete proportioning technique can use aggregate from any sources, irrespective of gradation, shape, and texture. The proposed technique has the potential to reduce the cement requirement without sacrificing performance and provides guidelines for multiple coarse and fine aggregate blends.Civil, Architectural, and Environmental Engineerin

Nanotechnology Applied in the Design of the Next Generation of Canadian Concrete Pavement Surfaces

High friction response in pavement improves road safety, while reduced noise production from the tire-pavement interface benefits public health and the economy of a country. According to Transport Canada, highway crashes cost Canadians approximately $67 billion annually. The economic impact of noise is difficult to quantify; however, billions of dollars have been invested in noise barriers as noise mitigation alternatives. Roadway safety is related to many factors including the friction characteristics or skid resistance of pavements. Lack of sufficient friction at the tire-pavement interface is a significant contributing factor to vehicle crashes. Skid resistance of pavement is affected by both: the microtexture of the pavement as related to the fine and coarse aggregate properties in the mortar phase of the concrete mixture; and by the macrotexture, which is defined as the measurable grooves formed in the plastic concrete during the finishing operation, or created in the hardened pavement with cutting heads consisting of uniformly spaced circular diamond saw blades. Traffic noise is also a growing concern for public health and the country’s economy. Tire-pavement noise predominates over the other sources of roadway noise in many circumstances. Under accelerating conditions, the tire-pavement noise is dominant at speeds greater than 35 to 45 km/h for cars, and 45 to 55 km/h for trucks. Although the tire-pavement noise is generated through a variety of mechanisms at the tire-pavement contact patch, it is recognized that a proper design of Portland cement concrete (PCC) pavement surface may assist in reducing noise levels and thus has prompted the evaluation of new macrotextures. However, an optimization process must be carried out to achieve adequate friction while reducing noise generation through macrotexture because large macrotexture can increase friction and generate excessive noise due to an inadequate tire-pavement interaction. Next Generation Concrete Surface (NGCS) is the first new concrete pavement texture introduced in the United States in the last 20 to 30 years. NGCS also has the quietest texture developed for conventional concrete pavements, mainly through macrotexture modification. The construction process uses conventional diamond grinding equipment, but the blades have a different configuration in the drum. Currently, after the evaluations of long term pavement performance and noise characteristics of the NGCS, concerns have been reported regarding durability and increased noise level over time. In this research, a laboratory investigation examined how friction, noise absorption, and surface durability can be improved by modifying the concrete microtexture. The innovative approach of this research involved investigating those properties of concrete pavement through microtexture modification using nanotechnology. Nanotechnology involves manipulating materials at scales below 100 nm. Two different products were investigated: nanosilica applied in the cement paste, and a nano lotus leaf solution applied as a coating to mimic the lotus leaf effect. Several concrete mixes were prepared and tested in the laboratory. Results reveal that microtexture modification through the addition of nanosilica can change the properties of fresh concrete, hardened concrete, and concrete durability. In fresh concrete, the main findings indicate that nanosilica reduces the concrete slump and also reduces the air content for a given water cement ratio; however, the slump and air content can be adjusted using High Range Water Reduced and Air Entraining Admixtures. In hardened concrete, results reveal that a small amount of nanosilica can accelerate the hydration process and enhance the compressive strength and the friction response. Results also reveal that nanosilica cannot significantly modify the sound absorption coefficient. Scanning Electron Microscope (SEM) images in hardened concrete provide insight into the impact that the nanosilica has on the Interfacial Transition Zone (ITZ). Nanosilica can reduce ettringite crystal formation in voids and can also produce a denser and a more compact cement paste. Regarding durability, several abrasion tests using the rotating cutter method indicate that nanosilica can enhance the concrete’s abrasion response, resulting in better wear resistance and durability of PCC road surfaces. Freezing and thawing, and scaling resistance results show that nanoconcrete is able to reduce the external damage on the PCC surface. Regarding the coating mimicking the lotus leaf effect, several concrete mixes were prepared and tested in the laboratory. Visual inspections demonstrate that it is possible to create the lotus leaf effect on concrete surfaces. Laboratory results reveal that the coating is able to maintain the friction response of concrete surfaces; however, results also reveal that the sound absorption coefficient is not significantly affected by the coating. Further research must be done to determine the coating impact on the hydroplaning effect when a heavy rainfall is present

Intrinsic Properties and Fabric Anisotropy of Sands

The intrinsic properties and fabric anisotropy of sands significantly affect their macroscopic engineering behavior including packing densities, compressibility and strength. However, due to difficulties in reliably and rapidly determining them, intrinsic properties such as gradation, particle roundness and sphericity as well as the related fabric anisotropy of soils have not received their deserved attention and usage in practice. This dissertation introduces research that has facilitated rapid and precise quantification of soil properties and fabric anisotropy using various newly developed image analysis techniques. Extensive laboratory tests were performed on sands of various gradations, roundnesses, sphericities and geologic origins to develop relationships between their intrinsic properties and macroscopic mechanical behavior. A gradation-shape-fabric based Distinct Element Modeling technique was developed to simulate the properties and fabric anisotropy of soils. Besides geotechnical engineering, the technique can be used by engineers and scientists in various disciplines including material science, geology, mining, powder sciences, pavement engineering and agriculture to simulate more realistic material particle geometries and microstructures.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138645/1/junxing_1.pd

Energy-absorbing particles for enhanced mechanical performance of asphalt's aggregate skeleton

This paper evaluates the feasibility of using 3D-printed lattice metamaterials as an alternative to capsules containing rejuvenators to enhance the self-healing capability of asphalt. The original purpose of these capsules is to encapsulate a rejuvenator and ensure its gradual release under load. However, the cellular structure of the capsules, along with their inherent energy absorption properties, may have a non-negligible physical impact on the asphalt's aggregate skeleton, which is not well understood but could influence the asphalt performance. To address this, lattice structures with a wide range of stiffness, strength, and energy-absorption properties were firstly designed and 3D-printed. Subsequently, the mechanical behaviour of a composite granular medium composed of granite aggregates and either cellular capsules or 3D-printed lattices was investigated. Cyclic and monotonic experiments were conducted on this composite granular medium, which represents the aggregate skeleton of asphalt. Lastly, its mechanical response, plastic deformation of lattices and capsules, and the crushing behaviour of aggregates were measured. Through a comparative analysis of results obtained from lattices with significantly different mechanical and energy-absorption properties, it was found that: i) capsules do induce physical changes to the aggregate skeleton of asphalt; ii) despite design constraints, lattice metamaterials can be successfully 3D-printed and tailored to meet specific requirements; iii) Voronoi lattices emerge as a potential alternative to replace the capsules

Temperature Reduction Technologies Meet Asphalt Pavement: Green and Sustainability

This Special Issue, "Temperature Reduction Technologies Meet Asphalt Pavement: Green and Sustainability", covers various subjects related to advanced temperature reduction technologies in bituminous materials. It can help civil engineers and material scientists better identify underlying views for sustainable pavement constructions

Characterization and performance of eco and crack-free high-performance concrete for sustainable infrastructure

The main objective of this study is to develop, characterize, and validate the performance of a new class of environmentally friendly, economical, and crack-free high-performance concrete referred to as Eco and crack-free HPC that is proportioned with high content of recycle materials. Two classes of Eco-HPC are designed for: (I) pavement (Eco-Pave-Crete); and (II) bridge infrastructure (Eco-Bridge-Crete). Eco-HPC mixtures were designed to have relatively low binder content up to 350 kg/m3 and develop high resistance to shrinkage and superior durability. A stepwise mixture design methodology was proposed to: (i) optimize binder system and aggregate skeleton to optimize packing density and flow characteristics; (ii) evaluate synergy between shrinkage mitigating materials, fibers, and moist curing duration to reduce shrinkage and enhance cracking resistance; and (iii) validate performance of Eco HPCs. The composition-reaction-property correlations were developed to link the hydration kinetics of various binder systems to material performance in fresh state (rheological properties) and hardened state (strength gain and shrinkage cracking tendency). Results indicate that it is possible to design Eco-HPC with drying shrinkage lower than 300 µstrain after 250 days and no restrained shrinkage cracking even after 55 days. Reinforced concrete beams made with Eco-Bridge-Crete containing up to 60% replacement of cement with supplementary cementitious materials and recycled steel fibers developed significantly higher flexural toughness compared to the reference concrete used for bridge applications. In parallel, autogenous crack healing capability of concrete equivalent mortar mixtures was monitored using microwave reflectometry nondestructive testing technique. Research is in progress towards analyzing life cycle assessment of Eco-HPCs under field condition --Abstract, page iii

Example-Based Urban Modeling

The manual modeling of virtual cities or suburban regions is an extremely time-consuming task, which expects expert knowledge of different fields. Existing modeling tool-sets have a steep learning curve and may need special education skills to work with them productively. Existing automatic methods rely on rule sets and grammars to generate urban structures; however, their expressiveness is limited by the rule-sets. Expert skills are necessary to typeset rule sets successfully and, in many cases, new rule-sets need to be defined for every new building style or street network style. To enable non-expert users, the possibility to construct urban structures for individual experiments, this work proposes a portfolio of novel example-based synthesis algorithms and applications for the controlled generation of virtual urban environments. The notion example-based denotes here that new virtual urban environments are created by computer programs that re-use existing digitized real-world data serving as templates. The data, i.e., street networks, topography, layouts of building footprints, or even 3D building models, necessary to realize the envisioned task is already publicly available via online services. To enable the reuse of existing urban datasets, novel algorithms need to be developed by encapsulating expert knowledge and thus allow the controlled generation of virtual urban structures from sparse user input. The focus of this work is the automatic generation of three fundamental structures that are common in urban environments: road networks, city block, and individual buildings. In order to achieve this goal, the thesis proposes a portfolio of algorithms that are briefly summarized next. In a theoretical chapter, we propose a general optimization technique that allows formulating example-based synthesis as a general resource-constrained k-shortest path (RCKSP) problem. From an abstract problem specification and a database of exemplars carrying resource attributes, we construct an intermediate graph and employ a path-search optimization technique. This allows determining either the best or the k-best solutions. The resulting algorithm has a reduced complexity for the single constraint case when compared to other graph search-based techniques. For the generation of road networks, two different techniques are proposed. The first algorithm synthesizes a novel road network from user input, i.e., a desired arterial street skeleton, topography map, and a collection of hierarchical fragments extracted from real-world road networks. The algorithm recursively constructs a novel road network reusing these fragments. Candidate fragments are inserted into the current state of the road network, while shape differences will be compensated by warping. The second algorithm synthesizes road networks using generative adversarial networks (GANs), a recently introduced deep learning technique. A pre- and postprocessing pipeline allows using GANs for the generation of road networks. An in-depth evaluation shows that GANs faithfully learn the road structure present in the example network and that graph measures such as area, aspect ratio, and compactness, are maintained within the virtual road networks. To fill empty city blocks in road networks we propose two novel techniques. The first algorithm re-uses real-world city blocks and synthesizes building footprint layouts into empty city blocks by retrieving viable candidate blocks from a database. We evaluate the algorithm and synthesize a multitude of city block layouts reusing real-world building footprint arrangements from European and US-cities. In addition, we increase the realism of the synthesized layouts by performing example-based placement of 3D building models. This technique is evaluated by placing buildings onto challenging footprint layouts using different example building databases. The second algorithm computes a city block layout, resembling the style of a real-world city block. The original footprint layout is deformed to construct a textit{guidance map}, i.e., the original layout is transferred to a target city block using warping. This guidance map and the original footprints are used by an optimization technique that computes a novel footprint layout along the city block edges. We perform a detailed evaluation and show that using the guidance map allows transferring of the original layout, locally as well as globally, even when the source and target shapes drastically differ. To synthesize individual buildings, we use the general optimization technique described first and formulate the building generation process as a resource-constrained optimization problem. From an input database of annotated building parts, an abstract description of the building shape, and the specification of resource constraints such as length, area, or a number of architectural elements, a novel building is synthesized. We evaluate the technique by synthesizing a multitude of challenging buildings fulfilling several global and local resource constraints. Finally, we show how this technique can even be used to synthesize buildings having the shape of city blocks and might also be used to fill empty city blocks in virtual street networks. All algorithms presented in this work were developed to work with a small amount of user input. In most cases, simple sketches and the definition of constraints are enough to produce plausible results. Manual work is necessary to set up the building part databases and to download example data from mapping services available on the Internet

Discrete element methods for asphalt concrete : development and application of user-defined microstructural models and a viscoelastic micromechanical model

As an important Civil Engineering material, asphalt concrete (AC) is commonly used to build road surfaces, airports, and parking lots. With traditional laboratory tests and theoretical equations, it is a challenge to fully understand such a random composite material. Based on the discrete element method (DEM), this research seeks to develop and implement computer models as research approaches for improving understandings of AC microstructure-based mechanics. In this research, three categories of approaches were developed or employed to simulate microstructures of AC materials, namely the randomly-generated models, the idealized models, and image-based models. The image-based models were recommended for accurately predicting AC performance, while the other models were recommended as research tools to obtain deep insight into the AC microstructure-based mechanics. A viscoelastic micromechanical model was developed to capture viscoelastic interactions within the AC microstructure. Four types of constitutive models were built to address the four categories of interactions within an AC specimen. Each of the constitutive models consists of three parts which represent three different interaction behaviors: a stiffness model (force-displace relation), a bonding model (shear and tensile strengths), and a slip model (frictional property). Three techniques were developed to reduce the computational time for AC viscoelastic simulations. It was found that the computational time was significantly reduced to days or hours from years or months for typical three-dimensional models. Dynamic modulus and creep stiffness tests were simulated and methodologies were developed to determine the viscoelastic parameters. It was found that the DE models could successfully predict dynamic modulus, phase angles, and creep stiffness in a wide range of frequencies, temperatures, and time spans. Mineral aggregate morphology characteristics (sphericity, orientation, and angularity) were studied to investigate their impacts on AC creep stiffness. It was found that aggregate characteristics significantly impact creep stiffness. Pavement responses and pavement-vehicle interactions were investigated by simulating pavement sections under a rolling wheel. It was found that wheel acceleration, steadily moving, and deceleration significantly impact contact forces. Additionally, summary and recommendations were provided in the last chapter and part of computer programming codes wree provided in the appendixes