Showing papers in "Journal of Materials in Civil Engineering in 2009"

New Mixture Proportioning Method for Concrete Made with Coarse Recycled Concrete Aggregate

Abstract: New method of mixture proportioning is proposed for concrete made with coarse recycled concrete aggregates (RCA). The proposed method, dubbed the "equivalent mortar volume" method, is predicated on the fact that RCA is a two-phase material comprising mortar and natural aggregate; therefore, when proportioning a concrete mixture involving RCA, one must account for the quantity and quality of each phase and adjust both the coarse aggregate and fresh paste content of the mix accordingly to achieve the same total mortar volume as a companion mix with the same specified properties but made entirely with coarse natural aggregates of similar properties to the coarse natural aggregate contained in RCA. Using the proposed method and the conventional aggregate replacement method, a large number of mixes was made with RCA obtained from two demolition waste recycling plants. For each mix, its slump, fresh and hardened densities, compressive strength, and elastic moduli were measured. The results showed that using the proposed method, unlike the conventional method, yields concrete mixes with consistent, predictable, and comparable properties to those of similar mixes made with natural aggregates.

Characterization of Calcium Carbonate, Calcium Oxide, and Calcium Hydroxide as Starting Point to the Improvement of Lime for Their Use in Construction

Abstract: In this paper a complete characterization of lime cycle transitions is described. CaCO3 was collected from a Mexican mine and was processed to obtain Ca ( OH ) 2 through CaO. When the calcium hydroxide interacted with the CO2 in the air forming CaCO3 , the lime cycle was completed. Crystal structure and spectroscopy characterization was carried out to get the knowledge of lime cycle CaCO3 →CaO→Ca ( OH ) 2 → CaCO3 deeply. The changes in the crystalline structures were described using X-ray diffraction by powder to accomplish phase identification. Scanning electron microscopy was done to examine the morphology, topology, crystal structure, and crystalline growth habit. Dynamic light scattering was used to determine the particle-size distribution of Ca ( OH ) 2 . Fourier-transform infrared was done to identify molecules and atomic bonds. Finally, inductively coupled plasma-mass spectrometry was done to get quantitative analyses. These results are a contribution to the restoration and construction industry fi...

Utilizing Waste Recycled Glass as Sand/Cement Replacement in Concrete

Abstract: The potential use of waste recycled glass in concrete as recycled glass sand (RGS) and pozzolanic glass powder (PGP) was examined in this study. No major difference was found in compressive strength of concrete with the presence of RGS as sand replacement. While, the compressive strength of concrete reduced by 16 and 10.6% at 28 and 364 days respectively when 20% of Portland cement was replaced by PGP. The potential expansion of concrete due to alkali-silica reaction (ASR) was monitored according to the procedure of British Standard BS 812 Part 123:1999. As a siliceous material, the use of RGS as sand replacement in concrete possesses high risk of ASR expansion. Therefore, cracks were observed when RGS was used as sand replacement in concrete without any precautions to minimize this risk. Different materials were used as ASR suppressors to mitigate the potential risk of ASR, such as: ground granulated blastfurnace slag, metakaolin, PGP, and lithium nitrate (LiNO 3 ). The expansion associated with ASR was significantly reduced when the ASR suppressor was used in concrete.

Early-Age Properties of Cement-Based Materials. II: Influence of Water-to-Cement Ratio

Abstract: The influence of water-to-cement mass ratio (w/c) on early-age properties of cementbased materials is investigated using a variety of experimental techniques. Properties that are critical to the early-age performance of these materials are tested, including heat release, semiadiabatic temperature, setting time, autogenous deformation, and strength development. Measurements of these properties using a single cement are presented for four different w/c, ranging from 0.325 to 0.425. Some of the measured properties are observed to vary widely within this range of w/c ratios. The heat release and setting time behaviors of cement pastes are contrasted. While early-age heat release is relatively independent of w/c, the measured setting times vary by several hours between the four w/c investigated in this study, indicating the fundamental differences between a physical process such as setting and heat release which is purely a quantification of chemical reaction. While decreasing w/c certainly increases compressive strength at equivalent ages, it also significantly increases autogenous shrinkage and may increase semi-adiabatic temperature rise, both of which can increase the propensity for early-age cracking in cement-based materials.

Key Parameters for the Strength Control of Lime Stabilized Soils

Abstract: The addition of lime is an attractive technique when the project requires improvement of the local soil. The treatment of soils with lime finds an application, for instance, in the construction of pavement base layers, in slope protection of earth dams, and as a support layer for shallow foundations. However, there are no dosage methodologies based on rational criteria as exist in the case of the concrete, where the water/cement ratio plays a fundamental role in the assessment of the target strength, and in the case of soil-cement technology, where the voids/cement ratio is shown to be a good parameter for the estimation of unconfined compression strength. This study, therefore, aims to quantify the influence of the amount of lime, the porosity, and the moisture content on the strength of a lime-treated sandy lean clay soil, as well as to evaluate the use of a water/lime ratio and a voids/lime ratio to assess its unconfined compression strength. A number of unconfined compression tests and measurements of matric suction were carried out. The results show that the unconfined compression strength increased linearly with the increase in the lime content as well as with the reduction in porosity of the compacted mixture. The change in moisture content has not presented an obvious effect on the unconfined compression strength of mixtures compacted at the same dry density. It was shown that, for the soil-lime mixture in an unsaturated state which is usual for compacted fills, the water/lime ratio is not a good parameter for the assessment of unconfined compression strength. In contrast, the voids/lime ratio, defined as the ratio between the porosity of the compacted mixture and the volumetric lime content, is demonstrated to be the most appropriate parameter to assess the unconfined compression strength of the soi-lime mixture studied.

Accuracy of Predictive Models for Dynamic Modulus of Hot-Mix Asphalt

Abstract: Various models have been developed over the past several decades to predict the dynamic modulus ∣ E* ∣ of hot-mix asphalt (HMA) based on regression analysis of laboratory measurements. The models most widely used in the asphalt community today are the Witczak 1999 and 2006 predictive models. Although the overall predictive accuracies for these existing models as reported by their developers are quite high, the models generally tend to overemphasize the influence of temperature and understate the influence of other mixture characteristics. Model accuracy also tends to fall off at the low and high temperature extremes. Recently, researchers at Iowa State Univ. have developed a novel approach for predicting HMA ∣ E* ∣ using an artificial neural network (ANN) methodology. This paper discusses the accuracy and robustness of the various predictive models (Witczak 1999 and 2006 and ANN-based models) for estimating the HMA ∣ E* ∣ inputs needed for the new mechanistic-empirical pavement design guide. The ANN-based...

Workability Loss and Compressive Strength Development of Cementless Mortars Activated by Combination of Sodium Silicate and Sodium Hydroxide

Abstract: To explore the significance and shortcomings of an environment-friendly binder using powder typed activators, 16 alkali-activated (AA) cementless mortars and a control ordinary Portland cement (OPC) mortar were mixed, cured under room temperature, and tested. Both fly ash (FA) and ground granulated blast-furnace slag (GGBS) as the source material were activated by a combination of sodium silicate and sodium hydroxide powders. The main variables examined were the mixing ratio of sodium oxide ( Na2 O) of the activators to source material by weight, and the Blain fineness of the GGBS. The flow loss and compressive strength development of the mortars tested were examined according to the alkali quality coefficient explaining the silicon oxide-to-sodium oxide ratio (Si O2 ∕ Na2 O) in an alkaline activator, and the silicon oxide-to-aluminum oxide (Si O2 ∕ Al2 O3 ) ratio and calcium content in the source material. The hydration products and microstructural characteristics of the AA pastes sampled from AA mortars...

Prediction of Fatigue Life of Rubberized Asphalt Concrete Mixtures Containing Reclaimed Asphalt Pavement Using Artificial Neural Networks

Abstract: Accurate prediction of the fatigue life of asphalt mixtures is a difficult task due to the complex nature of materials behavior under various loading and environmental conditions. This study explores the utilization of an artificial neural network (ANN) in predicting the fatigue life of rubberized asphalt concrete mixtures containing reclaimed asphalt pavement (RAP). Over 190 fatigue beams were made with two different rubber types (ambient and cryogenic), two different RAP sources, four rubber contents (0, 5, 10, and 15%), and tested at two different testing temperatures of 5 and 20°C. The data were organized into nine or 10 independent variables covering the material engineering properties of the fatigue beams and one dependent variable, the ultimate fatigue life of the modified mixtures. The traditional statistical method was also used to predict the fatigue life of these mixtures. The results of this study showed that the ANN techniques are more effective in predicting the fatigue life of the modified mixtures tested in this study than the traditional statistical-based prediction models.

Compressive Strength and Rapid Chloride Permeability of Concretes with Ground Fly Ash and Slag

Abstract: Concretes with binary and ternary blends of portland cement, finely ground fly ash and finely ground granulated blast furnace slag were produced to investigate their effects on compressive strength and rapid chloride permeability. Portland cement was partially replaced by finely ground fly ash (Blaine specific surface: 604 m 2 /kg) and finely ground granulated blast furnace slag (Blaine specific surface: 600 m 2 /kg). Two series of concrete with water/binder ratios of 0.60 and 0.38 were produced and for both water/binder ratios, portland cement was replaced by: (i) 50% fly ash; (ii) 50% blast furnace slag; and (iii) 25% fly ash+25% blast furnace slag. At the high water/binder ratio, compressive strengths of the concretes with the pozzolans are lower compared to that of the portland cement concrete. At the low water/binder ratio, however, these strength reductions are less compared to the high water/binder ratio and compressive strength of the concrete produced with 50% slag was even higher than the portland cement concrete. The test results indicate the ground fly ash and ground granulated blast furnace slag greatly reduce the rapid chloride permeability of concrete. It was concluded that to reduce the chloride permeability of concrete, inclusion of pozzolans are more effective than decreasing the water/cement ratio.

Midrange Temperature Rheological Properties of Warm Asphalt Binders

Abstract: With increasing concerns of global warming and increasing emissions, the asphalt industry is making a constant effort to lower its emissions by reducing the mixing and compaction temperatures of the asphalt mixture without affecting the properties of the mix. Several proprietary chemicals are available in the industry that can help reduce the mixing and compaction temperatures. A significant reduction of required heat can be achieved in most cases. Several studies have been conducted evaluating the properties of the warm mix asphalt; however, properties of the binders containing these chemicals have not been studied in great detail. Warm asphalts were produced using two of the available processes utilizing five different asphalt binder sources, and some rheological tests were conducted (dynamic shear rheometer and viscosity). The results indicated that binders containing the inorganic additive Aspha-Min (Eurovia, France) underwent minor or no changes compared to the base binders in terms of flow properties, stiffness, and response to creep. However, the flow of binders with the additive Sasobit (Sasol Wax, Germany), which consists of aliphatic hydrocarbons, changed from Newtonian to shear thinning at 60°C, and the viscosity of the binder at 60°C increased. Sasobit also improved the stiffness and penetration resistance of the base binders, and binders with Sasobit had significantly lower permanent deformations after repeated creep-recovery tests compared to the base binders.

Research on Material Composition and Performance of Porous Asphalt Pavement

Abstract: With many advantages such as high skid resistance, low noise, and less splash and spray, porous asphalt pavement can significantly improve driving quality in wet weather condition and is used widely in Europe, the United States, and Japan. The early research in China on porous asphalt pavement was started in the 1980s. Due to the hot weather, overloaded traffic and poor material properties, the porous asphalt pavement paved in that time is not quite successful. This paper deals with the present research, especially the material composition and its impacts on the performance of porous asphalt pavement. In this study, the empirical equation of air void versus gradation was derived from uniform experimental analysis so that the target gradation could be achieved by using the formula. In addition, the quantitative relationship between air void and drainage efficiency is obtained by a series of experimental studies, and the performances of porous asphalt mixture with three types of bitumen are evaluated to analyze the influence of asphalt property on that of the asphalt mixture. Finally, the binder requirement of porous asphalt for China's weather and traffic condition is proposed.

Dynamic Modulus and Repeated Load Tests of Cold In-Place Recycling Mixtures Using Foamed Asphalt

Abstract: As part of the validation effort to evaluate the consistency of a new cold in-place recycling using foamed asphalt (CIR — foam) mix design process for the Iowa Department of Transportation, the dynamic modulus and repeated load tests were conducted to evaluate the performance characteristics of CIR — foam mixtures over a wide range of loading and temperature conditions. The main objective of this research is to study the impacts of the foamed asphalt contents and reclaimed asphalt pavement (RAP) material characteristics on dynamic modulus and flow number. Dynamic modulus and repeated load tests were conducted on CIR — foam mixtures with RAP materials collected from seven different CIR project sites located throughout Iowa. Dynamic modulus values of the RAP materials varied depending on the sources and foamed asphalt contents. Coarse RAP materials with a small amount of residual asphalt content exhibited a higher modulus value at 4.4°C but exhibited a lower dynamic modulus value at 37.8°C than fine RAP materials with a large amount of residual asphalt content. Flow numbers were varied significantly depending on their RAP sources and foamed asphalt contents. Fine RAP materials with a hard residual asphalt binder exhibited a higher flow number than coarse RAP materials with a soft residual binder. The relative rankings of RAP materials in terms of the flow number did not change when the foamed asphalt was increased from 1.0 to 3.0%, which supports the repeated load test being consistent in evaluating a rutting potential of RAP materials.

Carbonated Ladle Slag Fines for Carbon Uptake and Sand Substitute

Abstract: The possibility of using a carbonated ladle slag as a fine aggregate in concrete was investigated. The slag was treated with carbon dioxide to reduce the free lime content while binding gaseous CO2 into solid carbonates. The treatment took place with either a high concentration of CO2 at 500 kPa for 2 hours or with a low concentration of CO2 at atmospheric pressure for 56 days. It was found that CO2 uptake by the slag particles between 300 and 600 µm and by the slag particles smaller than 75 µm were about 4.2 and 15.6% of their mass, respectively. The extractable CaO contents were estimated by titration and were found to be significantly reduced by carbonation treatment. The carbonated ladle slag was used as a fine aggregate in zero-slump press-formed compact mortar samples and compared to similar samples containing a control river sand. The 28-day strengths of the mortars made with the carbonated slag sand were comparable to the strengths of the normal river sand mortars. The use of carbonated ladle slag as a fine aggregate in concrete is shown to be a novel way of sequestering CO2 in a beneficial manner.

Quantitative Comparison of Energy Methods to Characterize Fatigue in Asphalt Materials

Abstract: Different methods have been developed to assess fatigue cracking of asphalt mixtures based on dissipated energy. Most of these methods have been motivated by the need to develop a unified fatigue criterion that is independent of the mode of loading. This paper offers critical analyses of the energy methods based on their theoretical ability to: (1) unify the results from controlled-strain and controlled-stress modes of testing for the same material; and (2) accurately assess the fatigue cracking life of different materials. The efficacy of these methods is quantitatively compared using a common set of fatigue test data. The fatigue test data were obtained using the dynamic mechanical testing of three different mixtures that have been shown to exhibit different fatigue cracking resistance in the field.

Pore Structure Changes of Blended Cement Pastes Containing Fly Ash, Rice Husk Ash, and Palm Oil Fuel Ash Caused by Carbonation

Abstract: In this paper, the effects of carbonation on pore structure of blended pozzolan cement pastes were investigated. Ordinary Portland cement (OPC) was partially replaced with ground palm oil fuel ash (POA), ground rice husk ash (RHA) and classified fine fly ash (FA). The strength, total porosity, specific surface area, and pore size distribution were tested. In general, incorporation of pozzolans increased the total porosity of blended cement pastes in comparison to that of OPC paste. Carbonation of pastes under 5% CO2 and 50% relative humidity (RH) for 28 days resulted in filling of the pore voids and possible attack on calcium silicate hydrate (CSH) depending on the type of pozzolan used. After carbonation, total porosity decreased and specific surface areas of the blended pozzolan cement pastes reduced indicating the infilling of voids. Pore size distributions of POA and RHA pastes were different to those of FA pastes. Large pores of the POA and RHA pastes were increased indicating coarsening of pores owi...

Multiscale Prediction of Viscoelastic Properties of Asphalt Concrete

Abstract: The low viscosity of asphalt concrete at T>135°C is necessary for the construction and compaction process of high-quality asphalt concrete layers. Whereas the continuous increase of viscosity with decreasing temperature is desirable for the reduction of permanent deformations during warm periods, so-called top-down cracking may occur in the course of temperature drops during cold periods. In order to explain the complex viscoelastic properties of asphalt concrete, a multiscale model is proposed. Hereby, the viscoelastic behavior of bitumen serves as input and the effect of air voids and aggregates is investigated. The viscous properties of bitumen are identified, using the bending-beam rheometer and the dynamic-shear rheometer, providing access to the viscoelastic material response for different temperature and loading regimes. With the rheological properties of bitumen at hand, the viscoelastic properties of mastic, mortar, and asphalt concrete are determined using continuum micromechanics, employing the...

Shrinkage Behavior of Foam Concrete

Abstract: In the absence of coarse aggregate, the relative influence of factors affecting the shrinkage of foam concrete are likely to be different as compared to normal concrete. This paper presents the shrinkage behavior of preformed foam concrete for the influences of basic parameters, viz, density, moisture content, composition like filler-cement ratio, levels of replacement of sand with fly ash, and foam volume. Shrinkage of foam concrete is lower than the corresponding base mix. For a foam concrete with 50% foam volume, the shrinkage was observed to be about 36% lower than that of a base mix. The shrinkage of foam concrete is a function of foam volume and thus indirectly related to the amount and properties of shrinkable paste. Shrinkage increases greatly in the range of low moisture content. Even though removal of water from comparatively bigger artificial air pores will not contribute to shrinkage, artificial air voids may have, to some extent, an effect on volume stability indirectly by allowing some shrinkage; this effect was more at a higher foam volume.

Carbonation and pH in Mortars Manufactured with Supplementary Cementitious Materials

Abstract: An investigation of carbonation in mortars and methods of measuring the degree of carbonation and pH change is presented. The mortars were manufactured using ordinary portland cement, pulverized fuel ash, ground granulated blast-furnace slag, metakaolin, and microsilica. The mortars were exposed to a carbon dioxide-rich environment (5% CO 2 ) to accelerate carbonation. The resulting carbonation was measured using phenolphthalein indicator and thermogravimetric analysis. The pH of the pore fluid and a powdered sample, extracted from the mortar, was measured to give an accurate indication of the actual pH of the concrete. The pH of the extracted powder mortar sample was found to be similar to the pH of the pore fluid expressed from the mortars. The thermogravimetric analysis suggested two distinct regions of transport of CO 2 within mortar, a surface region where convection was prevalent and a deeper region where diffusion was dominant. The use of microsilica has been shown to decrease the rate of carbonation, while pulverized fuel ash and ground granulated blast-furnace slag have a detrimental effect on carbonation. Metakaolin has little effect on carbonation.

Mesoscale Simulation of Influence of Frost Damage on Mechanical Properties of Concrete

Abstract: Mesoscale constitutive models of frost-damaged concrete are developed in this study through numerical simulation using a two-dimensional rigid body spring model (RBSM). The aim of the simulation is to predict the macrobehavior of frost-damaged concrete subjected to mechanical loading. The models also clarify the difference in failure behavior of concrete with and without frost damage. Zero strength elements and the concept of mesoscale plastic tensile strain are introduced into the normal RBSM springs to consider the experimentally observed cracking and plastic deformation caused by frost damage. The difference in the effect of frost damage on compression and tension behavior as found in the experiments is clearly predicted. Finally, analysis of a notched beam subjected to bending after different degrees of frost damage is carried out. The resulting load-deflection curves agree well with those obtained in the experiments. These good correlations confirm the applicability of the mesoscale model for predict...

New Understanding of Cement Hydration Mechanism through Electrical Resistivity Measurement and Microstructure Investigations

Abstract: The new understanding for the hydration mechanism of cement has been achieved based on the noncontact electrical resistivity measurement. The cement hydration process is divided into dissolution, dynamic balance, setting, hardening, and hardening deceleration stages according to the characteristic points on the electrical resistivity development curve p(t)-t and the differential curve dp(t)/dt-t. The microstructure analysis corresponding to each hydration stage is conducted with scanning electron microscope, x-ray diffraction, differential thermal analysis, and Fourier transform infrared spectroscopy techniques. This study provides the theoretical foundation for understanding the relationship between setting behavior, hardening properties, and resistivity development.

Effects of Electrically Conductive Additives on Laboratory-Measured Properties of Asphalt Mixtures

Abstract: An asphalt mixture generally behaves as an insulator. The addition of electrically conductive additives may produce conductive asphalt mixtures. The present study investigated the effectiveness of several commonly used conductive additives to produce electrically conductive hot-mix asphalt (HMA). The effects of three conductive additives, a micron-scale steel fiber, a carbon fiber, and graphite, on some laboratory-measured properties of HMA mixtures were investigated through mixture performance testing. The results from this study indicated that the micron-scale steel fiber was the most effective additive to produce conductive HMA. The inclusion of steel and carbon fibers improved permanent deformation properties, maintained the indirect tensile cracking resistance, and slightly reduced the dynamic modulus of the conductive HMA. The inclusion of graphite as an electrically conductive additive significantly improved the rut resistance, increased the dynamic modulus, and significantly reduced the indirect tensile cracking resistance of the conductive HMA mixtures.

Corrosion of Glasses and Expansion Mechanism of Concrete Containing Waste Glasses as Aggregates

Abstract: Expansion and cracking of portland cement concrete containing glass aggregates have been known for decades. Traditional alkali-silica reaction and expansion mechanisms are being used to explain the reaction and expansion mechanisms of cement concrete containing glass aggregates. This paper reviews glass chemistry, alkali-silica reaction mechanism, expansion of concrete containing glass aggregates, and microstructure of the interfacial transitional zone between cement paste and glass particles. Analysis of these published results indicates that the formation of expansive sodium-calcium silicate hydrate (N-C-S-H) gel around glass particles in concrete results from the dissolution and precipitation of soda-lime glass in high pH environments and not from the reaction between glass particles and the alkalis in cement. The corrosion of soda-lime glass and formation of N-C-S-H can happen when the pH of the pore solution is greater than 12 regardless of the presence of alkali ions. Thus, the expansion of concrete containing glass aggregates is different from that caused by traditional alkali-silica reaction. The presence of moisture and high pH (>12) are the two necessary conditions for concrete containing glass aggregates to expand.

Evaluation of Pervious Concrete Workability Using Gyratory Compaction

Abstract: Portland cement pervious concrete (PCPC) is increasingly used across the United States, and this has prompted various entities to begin the process of developing standardized test techniques. A major issue with placing PCPC is the inconsistencies in concrete workability between mixtures developed in the laboratory and in the field. It is therefore urgent to properly determine workability of pervious concrete and to ensure that the designed concrete mixtures are suitable for particular compaction methods and field conditions. This paper describes a new test method for characterizing PCPC workability—the gyratory compaction test method. A modified Superpave gyratory compactor (SGC) is employed in the present study. Two PCPC workability parameters are defined from the gyration compaction curve: (1) workability energy index, which describes initial concrete workability and (2) compaction densification index, which describes the resistance of the tested mixture to further compaction. The effects of binder content and water-to-cement ratio as well as effect of concrete mixing time on PCPC workability are studied. Based on the test results, values of the workability parameters for concrete with various degrees of workability are specified.

Viscoelastic Analysis of Flexible Pavements and Its Effects on Top-Down Cracking

Abstract: When employing linear elastic layer analysis, which is widely used for the structural analysis of flexible pavements, it is commonly observed that most critical tensile strains occur at the bottom of an asphalt layer. It is well known that an asphalt mixture is a viscoelastic material, so its response is time and rate dependent; therefore, the results from the elastic assumption may not be borne out in the response of the asphalt layer. This study utilized viscoelastic analysis to identify critical tensile strains and their time-dependent responses. It was found that tensile strains occurred at the bottom and at the top of an asphalt layer and grew because of the rheological behavior of an asphalt mixture. As load repetitions continued, the strain at the top showed a higher strain value than the strain value at the bottom. A sensitivity analysis performed on various design parameters indicated that the development of strains at the top and at the bottom is a function of the structural characteristics of pavement structures. Expected trends were observed and findings compared favorably to results of field-calibrated top-down cracking model predictions.

Construction of an Embankment with a Fly and Bottom Ash Mixture: Field Performance Study

Abstract: Fly ash and bottom ash are coal combustion by-products (CCBPs) that are generated in large quantities throughout the world. It is often economical to dispose ash as mixtures rather than separately; that notwithstanding, only a few studies have been performed to investigate the behavior of fly and bottom ash mixtures, particularly those with high contents of fly ash. Also, there is very limited data available in the literature on the field performance of structures constructed using ash mixtures. This paper describes the construction and the instrumentation of a demonstration embankment built with an ash mixture (60:40 by weight of fly ash:bottom ash) on State Road 641, Terre Haute, Ind. Monitoring of the demonstration embankment was conducted for a period of 1 year from the start of construction of the embankment. The settlement of the embankment stabilized approximately 5 months after the end of its construction. According to horizontal inclinometer readings, the differential settlement at the top of the embankment is about 5 mm. Results from field quality control tests performed during construction of the demonstration embankment and monitoring data from vertical and horizontal inclinometers and settlement plates indicate that the ash mixture investigated can be considered an acceptable embankment construction material.

Application of microcalorimeter to characterize adhesion between asphalt binders and aggregates

Abstract: Adhesion between asphalt binder and aggregate in a dry state as well as in the presence of water is critical to the performance and durability of asphalt mixtures. According to the literature, distress mechanisms in asphalt mixtures such as rutting, fatigue cracking, and moisture-induced damage are correlated to the nature and quality of adhesion between asphalt binder and aggregate. Surface free energy components of aggregates and asphalt binders can be used to compute the work of adhesion between the two materials in a dry condition as well as the thermodynamic potential of water to displace the asphalt binder from the surface of the aggregate. This paper presents a methodology to estimate the surface free energy components of aggregates using the microcalorimeter. The microcalorimeter is a relatively fast and simple alternative tool to estimate surface free energy components of aggregates compared to other techniques such as the gas adsorption method. In addition to surface energy measurement, the application of the microcalorimeter to directly measure the total energy of adhesion between the asphalt binder and the aggregate at mixing temperatures and the hydrophilicity of different aggregates at ambient temperatures is also demonstrated. Both of these properties influence the performance of asphalt mixtures in dry conditions and in the presence of water.

Creep-Damage Coupled Effects: Experimental Investigation on Bending Beams with Various Sizes

Abstract: The serviceability of concrete structures is a problem in which creep and damage are coupled. In this paper, we present experimental investigations on concrete that involve tertiary creep. We consider residual capacity tests on notched bending beams and investigate the evolution of size effect due to basic creep. In these experiments, beams are first subjected to a constant load, at a given ratio of the maximum capacity during 90 days. They are then loaded up to failure and their residual capacity is obtained. During the creep phase, acoustic emission is analyzed and it shows that damage develops under creep. The comparison between the size effect test results with and without creep exhibits variations of the fracture properties of the material. The fracture energy and the size of the fracture process zone decrease when creep occurs prior to failure. These results, which include size effect fracture tests, may serve for the development and validation of coupled creep-damage models.

Quantitative Interpretation of Half-Cell Potential Measurements in Concrete Structures

Abstract: The interpretation of half-cell potential measurements in reinforced concrete structures can be a major challenge for civil engineers. The main reason for this is that half-cell potential mapping provides information to predict the probability of corrosion in concrete, but it does not give clear insight on the rate and the nature of corrosion. Although for general uniform corrosion, half-cell data can provide valuable information about the probability of corrosion. In the case of localized corrosion, the predictions of half-cell measurements can be misleading. The main objective of the present work is to provide practicing engineers a tool that they can use to better interpret the results of half-cell potential measurements. This tool quantitatively relates the potential readings on the surface of the concrete to the rate of probable localized reinforcement corrosion through concrete resistivity, cover thickness, and temperature, allowing the engineers to gain supplementary information from half-cell tests. Experimental comparisons presented in this paper demonstrate the potential benefits of the proposed approach when typical half-cell measurements may not be able to predict the localized corrosion mechanism.

Investigation of Layer Contributions to Asphalt Pavement Rutting

Abstract: As one of the main distresses that may occur in asphalt pavements, rutting affects pavement performance the most significantly. This paper presents the investigation of the contributions of the structural layers to the total rutting in the asphalt pavements with semirigid bases through in situ excavation of transverse trenches and cores taken in the selected typical pavements on a real-world expressway. The selected pavements exhibited different depths of rutting. Laboratory rut testing was conducted on the core samples. Statistical analysis was undertaken to evaluate the effects of the layer properties sensitive to the variations of temperature on the rutting. The results indicated that the high temperature stability of the asphalt intermediate course had the greatest effect on the rut development. This paper presents the regression relationship established between rut depth and dynamic stability for each structural layer in asphalt pavements. In addition, the criteria for the dynamic stability are provided for asphalt base courses on different longitudinal grades.

Relation between Strength Properties (Flexural and Compressive) and Abrasion Resistance of Fiber (Steel and Polypropylene)-Reinforced Fly Ash Concrete

Abstract: In this experimental study, the influence of using fly ash, polypropylene fiber, and steel fiber in concrete on abrasion resistance is presented. Seven concrete mixtures containing 0, 10, 15, 20, 25, 30, and 45% fly ash as cement replacement in mass basis were prepared. Another, seven fiber-reinforced portland cement concrete mixtures containing 0.25, 0.5, 1, and 1.5% steel fiber, and 0.05, 0.1, and 0.2% polypropylene fiber in volume basis were prepared. These seven fiber-reinforced Portland cement concrete mixtures were modified by replacing 15 and 30% fly ash with cement in mass basis, consequently, 14 fiber-reinforced fly ash concrete mixtures were prepared. Water-binder ratio was kept constant at 0.35 for all concrete mixtures. Bohme surface abrasions of the concrete mixtures were measured at 28 days. The results of the laboratory work showed that replacement of fly ash with cement reduced abrasion resistance of concrete; however, inclusion of the steel fiber improved the abrasion resistance of concrete. Using polypropylene fiber did not improve abrasion resistance of concrete made with or without fly ash. The comparison between the relation of abrasion to compressive strength and abrasion to flexural tensile strength, made in terms of R 2 of the linear regression on log scale, showed that a stronger relation existed between abrasion and flexural tensile strength than between abrasion and compressive strength of the concrete containing either fly ash or fibers, or both.