Showing papers in "Journal of Materials in Civil Engineering in 2003"

Influence of Recycled Aggregate on Interfacial Transition Zone, Strength, Chloride Penetration and Carbonation of Concrete

Abstract: This study is conducted (1) to examine the influence of recycled aggregate on interfacial transition zone (ITZ), strength, chloride penetration, and carbonation of concrete, and (2) to propose a method for improving strength, chloride penetration, and carbonation resistances of concrete using recycled aggregates Five types of recycled aggregate, and four levels of water-binder ratio are used in this study The recycled aggregate concrete is evaluated according to compressive strength, tensile strength, chloride penetration depth, and carbonation depth The characteristics of ITZs in recycled aggregate concrete are also measured and used to explain the influence of recycled aggregate on the mentioned properties Additionally, the double-mixing method for improving strength, chloride penetration, and carbonation resistances of recycled aggregate concrete is evaluated in this study

Effectiveness of Impressed Current Technique to Simulate Corrosion of Steel Reinforcement in Concrete

Abstract: Accelerated corrosion by means of the impressed current technique is widely used in concrete durability tests. In this study, the influence of varying the impressed current density level between 100 and 500 mA/cm 2 on the actual degree of steel reinforcing bar corrosion as well as on the concrete strain behavior due to expansive corrosion products was experimentally investigated. Twelve reinforced-concrete prisms ~15032503300 mm! were used. The prisms were reinforced by two No. 10 reinforcing bars. Corrosion was induced by means of impressed current using electric power supplies. To depassify the steel reinforcement, 5% NaCl by weight of cement was added to the concrete mix. The strain response due to the expansion of corrosion products was measured at each face of the prisms. At the end of the corrosion phase, all the corroded reinforcing bars were removed, cleaned according to the ASTM G1-90 standard, and weighed to get the actual degree of mass loss. The results showed that, up to 7.27% mass loss, accelerated corrosion using the impressed current technique was effective in inducing corrosion of the steel reinforcement in concrete. With respect to Faraday's law, the use of different current densities has no effect on the percentage of mass loss. However, increasing the level of current density above 200 mA/ cm 2 results in a significant increase in the strain response and crack width due to corrosion of the steel reinforcement.

Assessing Damage of Reinforced Concrete Beam using b -value Analysis of Acoustic Emission Signals

Abstract: Concrete bridges in the United Kingdom represent a major legacy that is starting to show signs of distress. Therefore, the need for monitoring them is an urgent task. The acoustic emission ~AE! technique was proposed as a valid method for monitoring these bridges but more study is needed to develop methods of analyzing the data recorded during the monitoring. The writers would like to propose a b-value analysis as a possible way to process AE data obtained during a local monitoring. The b-value is defined as the log-linear slope of the frequency-magnitude distribution of acoustic emissions. This paper presents the results of a b-value analysis carried out on data recorded during a laboratory test on a reinforced concrete beam designed as representative of a bridge beam. During the experiment, the specimen was loaded cyclically and it was continuously monitored with an AE system. The data obtained were processed and a b-value analysis was carried out. The b-value was compared with the applied load, with a damage parameter, and with the cracks appearing on the beam. The damage parameter represents the cumulative damage in terms of total sum of acoustic emissions. The results showed a good agreement with the development of the fracture process of the concrete. From a study of the b-value calculated for a whole loading cycle and for each channel, some quantitative conclusions were also drawn. Further development work is needed to make the b-value technique suitable for practical use on a real bridge.

Fatigue and healing characterization of asphalt mixtures

Abstract: This paper investigates the effect of the processes on fatigue fracture and fracture healing during controlled-strain, dynamic mechanical analysis (DMA) testing. Sand asphalt samples were fabricated with two SHRP-classified binders: AAD-1 and AAM-1. DMA testing was performed at 25°C and at 10 Hz. The mechanical response during DMA testing was monitored using three different damage indicators: (1) change in dynamic modulus; (2) change in pseudo stiffness; and (3) change in dissipated strain energy. When either of these parameters are plotted versus the number of load cycles, two inflection points are apparent that define a significant change in sample behavior due to damage. The second inflection point is a reasonable definition of failure, as it is strongly correlated with the peak of the plot of phase angle versus load repetitions. Furthermore, the phase angle drops precipitously at the second inflection point. By performing controlled-strain torsional fatigue tests at three different strain levels, each great enough to induce damage, a reproducible fatigue relationship (number of load cycles as a function of stress level) is developed. The introduction of several rest periods during testing lengthened fatigue life. Successful development of this testing method is suggested as a potential specification-type test method because of its efficiency, reproducibility, and reliability.

Effect of temperature on thermal properties of high-strength concrete

Abstract: For use in fire resistance calculations, the relevant thermal properties of high-strength concrete (HSC) were determined as a function of temperature. These properties included the thermal conductivity, specific heat, thermal expansion, and mass loss of plain and steel fibre-reinforced concrete made of siliceous and carbonate aggregate. The thermal properties are presented in equations that express the values of these properties as a function of temperature in the temperature range between 0 and 1,000°C. The effect of temperature on thermal conductivity, thermal expansion, specific heat, and mass loss of HSC is discussed. Test data indicate that the type of aggregate has a significant influence on the thermal properties of HSC, while the presence of steel fiber reinforcement has very little influence on the thermal properties of HSC.

Modeling of damage in cement-based materials subjected to external sulfate attack. I: Formulation

Abstract: A chemomechanical mathematical model is presented to simulate the response of concrete exposed to external sulfate solutions. The model is based on the diffusion-reaction approach, and several mechanisms for the reaction of calcium aluminates with sulfates to form expansive ettringite are considered. Fick’s second law is assumed for diffusion of the sulfate ions. A second-order chemical reaction between reacting calcium aluminates and ingressing sulfates depletes the sulfate concentration. The products of the second-order reaction between the aluminates and sulfates are chosen among several competing mechanisms, and a rule-of-mixtures approach is used to relate the expansive nature of the products with the prescribed specific gravity of the compounds. It is furthermore assumed that the crystallization pressure of products of reaction results in a bulk expansion of the solid. The constitutive response of the matrix and the expansive stresses are calculated from the imposed volumetric strain. Microcracks are initiated when the strength of the matrix is reached, leading to changes in the diffusivity and a reduction in the elastic properties of the matrix. The variation of diffusivity is linked to the scalar damage parameter due to cracking of the matrix. Due to the changes in the diffusivity, the problem is treated as a moving boundary problem, and a methodology is proposed to adapt the solution of the 1D case to the 2D problem of a prismatic specimen. Theoretical expansion-time responses are obtained and compared with a variety of data available in the literature.

Ultrasonic Imaging of Concrete Elements Using Reconstruction by Synthetic Aperture Focusing Technique

Abstract: Ultrasonic reconstruction by the synthetic aperture focusing technique (SAFT) has a great potential to image concrete elements and detect embedded objects. Its algorithm focuses ultrasonic signals received at many aperture points by coherent superposition, yielding a high-resolution image of the region of interest. Using this approach, several problems caused by the strongly inhomogeneous structure of concrete are diminished, where scattering of transmitted pulses leads to disturbing phenomena such as attenuation and structural noise. This contribution is intended to review the work of the writers on the application of SAFT reconstruction to concrete testing. First, consequences of scattering of ultrasonic waves in concrete are qualitatively explained. Then the use of SAFT is discussed in comparison to traditional A-scan and B-scan techniques. Different reconstruction algorithms and implementations are presented for one-, two-, and three-dimensional SAFT. Pulse-echo measurement systems are described, which are able to acquire large sets of data on linear and planar apertures employing single transducer, transducer array, and scanning laser Doppler vibrometer arrangements. To illustrate the application of the SAFT techniques, examples from laboratory and field experiments are described comprising imaging of back walls, tendon ducts containing faults, layers, and reinforcement in concrete elements.

Development of Bottom Ash as Pozzolanic Material

Abstract: This research studies the potential of using bottom ash from the Mae Moh power plant in Thailand as a pozzolanic material. Bottom ash, which was rarely used in concrete due to its inactive pozzolanic reaction, improved its quality by grinding until the particle size retained on Sieve 325 was less than 5% by weight. Bottom ashes before and after being ground were investigated and compared for their physical and chemical properties. The bottom ashes were used to replace portland cement type I in mortar and concrete mixtures. The results indicated that the particle of bottom ash was large, porous, and irregular shapes. The grinding process reduced the particle size as well as porosity of the bottom ash. Compressive strengths of mortar containing 20–30% of bottom ash as cement replacement were much less than that of cement mortar at all ages, but the use of ground bottom ash produced higher compressive strength than the cement mortar after 60 days. When ground bottom ash was used at a 20% replacement of cemen...

Chloride Penetration in Nonsaturated Concrete

Abstract: The two governing equations that describe the diffusion of chloride ions into nonsaturated concrete are established. Material models for the four material parameters involved in the governing equations are developed, including chloride binding capacity, chloride diffusion coefficient, moisture capacity, and moisture diffusion coefficient. The planned attempt is to establish material models based on analytical results first, and if this is not possible, to develop empirical models based on dominant physical or chemical mechanism(s) at different scale levels and calibrate the individual model by related test data. The alternating-direction implicit (ADI) finite-difference method was employed for solving coupled two-dimensional moisture diffusion and chloride penetration equations. The numerical solutions are compared with the experimental results obtained by the 90-day ponding test (AASHTO T259-80). The numerical prediction agrees very well with the test data. Free chloride concentration profiles at different depths and different ages of concrete slab are presented. Two limiting cases for different initial relative humidity levels are analyzed in detail to study the dependence of the chloride diffusion on the moisture diffusion in nonsaturated concrete.

Carbonation of Concrete Containing Mineral Admixtures

Abstract: This study deals with the carbonation of concrete incorporating ground granulated blast-furnace slag (GGBS), fly ash (FA), and silica fume (SF). It is observed that a decreased water-to-binder ratio and replacement level of GGBS, FA, or SF, or an increase in GGBS fineness and curing age in water, led to better carbonation resistance. However, compared to a plain concrete, the concrete incorporating mineral admixtures (except GGBS with higher fineness and SF) generally showed lower resistance to carbonation, possibly due to the dominating effect of the reduction in calcium hydroxide over pore refinement. Hence, adequate curing is recommended for enhancing the resistance of concrete containing GGBS, FA, and SF to carbonation. It is also found that both the carbonation coefficient and compressive strength served as good indicators for the carbonation rate of concrete with and without mineral admixtures.

Tension Stiffening and Cracking of Steel Fiber-Reinforced Concrete

Abstract: Fiber-reinforced concrete used in structural applications requires characteristic material properties that can be easily incorporated into existing design procedures. This paper investigates the postcracking response of reinforced concrete tension members made with both plain and steel fiber-reinforced concrete (SFRC). Loading was either monotonic or cyclic, and shrinkage effects are included in analysis of the member response. Tension-stiffening results are used to determine the average tensile response of concrete after cracking, and an expression is developed to predict this smeared behavior as a material property for cracked SFRC, as well as to estimate crack spacings. Specimens with steel fibers exhibited increased tension stiffening and smaller crack spacings, which both contributed to a reduction in crack widths. The postcracking tensile strength of fiber concrete at the cracks is the determining factor affecting behavior and is a fundamental material property used to predict tension stiffening and crack behavior for conventionally reinforced SFRC. The uniaxial strength of SFRC immediately after cracking governs serviceability behavior, while the postcracking strength at larger deformations governs strength design and is responsible for tension stiffening after yielding of the reinforcement. Cyclic loading did not have a significant effect on either tension stiffening or crack width control for the specimens tested.

High-Volume Fly Ash Concrete with High Strength and Low Drying Shrinkage

Abstract: In this work, a laboratory investigation was carried out to evaluate the strength and particularly the shrinkage properties of concrete containing high volumes of fly ash. The concrete mixtures made with 50 and 70% replacement (by mass) of ordinary portland cement (OPC) with fly ash were prepared. Water-cementitious material ratios ranged from 0.28 to 0.34. Some concrete mixtures were also made with superplasticizer. The strength and shrinkage properties of the concrete mixtures cured at 20°C temperature with 65% relative humidity are reported. The laboratory test results show that high-volume fly ash (HVFA) concrete attained satisfactory compressive and tensile strength at 1 day of age. It also showed that 50% replacement HVFA concrete developed higher strength than OPC concrete at 28 days and beyond. The inclusion of high volumes of fly ash in concrete with a low water-cementitious material ratio resulted in a reduction in the shrinkage values of up to 30% when compared to OPC concrete. The concrete mixtures made with superplasticizer showed higher shrinkage values of up to 50% when compared to the concrete made with no superplasticizer.

Nondestructive Evaluation of Concrete Infrastructure with Ground Penetrating Radar

Abstract: In recent years the use of ground penetrating radar (GPR) at frequencies from 500 MHz to 2.5 GHz has yielded very good results for inspection of concrete structures. The possibility of performing nondestructive measurements quickly and with convenient recording of the measurement results is particularly beneficial. The technique is well-suited for locating tendon ducts at depths down to 50 cm, detecting voids and detachments, and measuring thickness of structures that are only accessible from one side. This paper presents the basics of GPR, its limits, and the results of laboratory investigations and case studies. It also shows that GPR can be used for regular inspection, searching for the cause of damage, and quality assessment of civil engineering structures.

Ultrasonic guided waves for inspection of grouted tendons and bolts

Abstract: There is currently a need to improve the nondestructive testing techniques that are used to inspect grouted steel reinforcing tendons, anchors, and rock bolts for corrosion and fracture. A method of inspection using guided ultrasonic waves has been proposed, which uses a pulse-echo technique carried out from the free end of the structure. The maximum inspection range is determined by the amount of attenuation that the wave experiences as a result of leakage into the embedding material and material losses. However, previous work has identified high frequency modes that have low attenuation and so increase the inspection range. Research has been carried out with a focus on the inspection of the posttensioning tendons used to reinforce concrete. The research presented in this paper uses experimental techniques to measure the attenuation in short lengths of grouted tendons, to evaluate the reflection coefficient of the modes from different geometry breaks, and to assess the impact of tendon curvature. The outcome of this research shows that the inspection range for tendons is limited, but the outlook for the inspection of the larger diameter grouted bolts and rebars that are used in the construction industry is promising. Considerable success has already been achieved in the testing of epoxy bonded rock bolts using this method.

Stress measurement and defect detection in steel strands by guided stress waves

Abstract: Health monitoring of steel strands is the subject of much research in the nondestructive evaluation and civil engineering communities. This paper deals with a guided stress wave method for stress monitoring and defect detection in seven-wire strands. A simplified acoustoelastic formulation of the Pochhammer-Chree vibrations in cylindrical waveguides is derived in the framework of the partial wave representation for guided waves. Magnetostrictive transducers are used to excite and detect the waves in the experiments. Results from acoustoelastic measurements on single wires and on strands are presented, showing the feasibility of the method for stress measurement, although an anomalous behavior of the strands at low stress levels remains the subject of current investigation. Improvements to the inherently low sensitivity of acoustoelastic stress measurements are suggested by adding the effect of strand elongation. The role of the strand anchorages is also examined in the context of wave attenuation. Finally, the suitability of the guided wave method for the detection of indentations and broken wires in the strands is demonstrated, including the possibility of inspecting the critical anchored regions.

Modeling of Damage in Cement-Based Materials Subjected to External Sulfate Attack. II: Comparison with Experiments

Abstract: A study is presented to predict the degradation of cement-based materials due to external sulfate attack. Parameters of the model are chosen based on the mix design parameters, degree of hydration, and exposure conditions of concrete. A solution of the diffusion equation with a term for a second-order chemical reaction is proposed to determine the sulfate concentration and calcium aluminate profile as a function of time and space. The crystallization pressure of hydration products such as ettringite can lead to internal stresses. Using the volumetric information, the model predicts the generation of internal stresses, evolution of damage, reduction in stiffness, and thus expansion of a matrix phase. The theoretical expansion-time responses are obtained and compared with a variety of available data in the literature. The most important parameters are the w/c ratio, internal porosity, diffusivity of the cracked and uncracked material, and available calcium aluminates. The importance of controlling the pH of the test solution is clearly observed. Model simulations indicate a reasonable agreement with experimental expansion-time data available in the literature.

Application of FTIR-ATR to Characterization of Bitumen Rejuvenator Diffusion

Abstract: Fourier transform infrared spectroscopy by attenuated total reflectance (FTIR-ATR) has been applied to laboratory studies of bitumen rejuvenator diffusion. Previous studies have given more indications rather than a real understanding of the mechanisms involved. FTIR-ATR can be performed in a relatively easy manner to provide diffusion measurements. In this study, parameters such as temperature, binder film thickness, type of bitumen, and, to some extent, chemical properties of the binders have been investigated. The results show a major influence of temperature on the diffusion rate. The study also shows that the diffusion process can be described using Fick's law. The need for a paper on this topic emanates from the lack of knowledge regarding the diffusion process by which new and old binders are mixed during asphalt recycling. If the process is incomplete, the properties of the final recycled asphalt will be influenced negatively. Further research is required to better understand the process of diffusion in bituminous binders. This can be accomplished by testing other combinations of binders, aged and unaged, as well as by studying the diffusion of selected chemical substances (markers) into bitumen.

Recent Research in Nondestructive Evaluation of Civil Infrastructures

Abstract: Assessing the condition of a structure is necessary to determine its safety and reliability. Ideally, structural health monitoring should be similar to medical health monitoring of the body. In medical health monitoring, the life signs such as pulse and blood pressure give an overall indication of the overall health of the body. This is analogous to global structural health monitoring, in which damage to the structure can be identified by measuring changes in the global properties of the structure. Once the body signs show an anomaly, we do a battery of tests to determine the cause of the anomaly. Analogously in structural health monitoring, nondestructive evaluation (NDE) can be used to determine the nature of the damage. NDE methods to determine local damage are also becoming more accepted in practice. This paper describes some of the recent and current National Science Foundation projects in this area of research. Promising areas for NDE are identified.

Residual Life of Corroding Reinforced Concrete Structures in Marine Environment

Abstract: Investigations have been conducted during the last three decades regarding chloride penetration and prediction of corrosion initiation. However, few investigations have dealt with corrosion propagation and/or residual life predictions, which are also needed for durability forecasting. Therefore, the aim of this investigation is to discuss, based on experimental information from previous investigations, the possibility of linking the degree of degradation (from a load-capacity reduction point of view) to the surface distress (for example, crack width opening) of a corroding reinforced concrete element in a marine environment. An empirical relationship between the residual load capacity of a reinforced-concrete element and the degree of reinforcement radius loss by corrosion was estimated, and a second empirical relationship between the surface crack width and the reinforcement radius loss was established based on available experimental data. Finally, data between the average corrosion penetration and the maximum pit depth were used to propose an empirical relationship that may be applicable to the performance of corroding prestressed-concrete elements.

Dielectric Properties of Asphalt Pavement

Abstract: This paper describes dielectric properties of asphalt pavement that were studied in the process of developing a roller mountable microwave asphalt pavement density sensor as part of the National Cooperative Highway Research Program IDEA project. This new sensor involves simultaneously measuring reflected microwave signals from the asphalt pavement in front of and behind the vibratory roller. As the reflected signal and penetration depth of microwaves depend on the dielectric properties of asphalt pavement, temperature, and frequency dependencies of the permittivity and loss of asphalt, samples of different densities were studied in the frequency range from 100 Hz to 12 GHz. Results show that (1) permittivity and loss depend on frequency and temperature; (ii) the higher the pavement density, the higher the permittivity; (iii) permittivity slightly increases with temperature; (iv) moisture strongly increases permittivity and loss at low frequencies and only slightly at microwave frequencies; and (v) the penetration depth of microwaves in asphalt pavement is about 1214 cm at 8 GHz and only about 4 cm at 30 GHz.

Atmospheric corrosion resistance of structural steels

Abstract: The main objective of this paper is to provide engineers with data on thickness loss of structural steel members resulting from corrosion. To this end, the writers have collected atmospheric exposure data from many research reports and journal papers. The data are presented in graphs of thickness loss versus exposure that demonstrate the effects of types of environment and steel. The environments include rural, industrial, and marine, becoming increasingly severe in that order. The steels under consideration are A242, A588, copper, and carbon steels, with their corrosion resistance decreasing in that order. Comparisons of the data with the medium corrosivity bands for weathering and carbon steels help to determine the severity of environments and the corrosion resistance of steel compositions. For bare exposed structures, a corrosion allowance should be added to all member thicknesses arrived at by stress calculations can be estimated by extrapolating an applicable thickness loss curve to the end of the s...

Cementing Material from Calcium Carbide Residue-Rice Husk Ash

Abstract: This paper proposes a new cementitious material from a mixture of calcium carbide residue and rice husk ash. Calcium carbide residue and rice husk ash consist mainly of Ca(OH)2 and SiO2, respective...

Hydration Mechanisms, Microstructure, and Mechanical Properties of Mortars Prepared with Mixed Binder Cement Slurry-Asphalt Emulsion

Abstract: Nowadays, deep cold recycling techniques are increasingly considered an effective method for the preventive and corrective maintenance of existing pavements. Not only are these techniques quickly performed and cost effective, but they also allow one to recycle in-place materials, thus limiting the cost of transportation. Various binders can be used for the cold recycling process, including asphalt emulsion, asphalt foam, hydraulic binders, or mixed binders. Of the latter, asphalt emulsion is most often used with the addition of a small quantity of cement (less than 2% with respect to the total mass of aggregates) to accelerate the breaking of the emulsion. This paper aims at understanding the hydration process, the microstructure, and the mechanical properties of mortars prepared with a new mixed binder made of a cement slurry and a small quantity of asphalt emulsion (SS-1 and CSS-1). Conduction calorimetry data reveal that the cement hydration process is nominally influenced by the presence of a small quantity of emulsion. Scanning electron microscope observations show the good dispersion of the asphalt droplets inside the hydrated cement paste. A cationic emulsion tends to entrain less air than anionic emulsion. Test results also indicate that the introduction of asphalt droplets inside a cement mortar matrix leads to a significant reduction in compressive strength and elastic modulus as well as a slight decrease in flexural strength. Mortars made with the cationic emulsion (CSS-1) show higher strengths and elastic modulus than mortars made with anionic emulsion (SS-1).

Signal-Based Acoustic Emission Techniques in Civil Engineering

Abstract: The acoustic emission (AE) technique can be a useful method for the investigation of local damage in materials. One of the advantages compared to other techniques is the recording of the damage process during the entire load history without any disturbance to the specimen. Differences between the traditional parameter-based and newer signal-based techniques are described along with some examples of measurements to study the steel-concrete interaction in reinforced-concrete cubes. Signal-based procedures, such as accurate 3D localization of damage sources, solutions for fault plane orientation, and moment tensor inversion, are described with respect to applications in civil engineering. The more quantitative analysis of the signals is based on a 3D localization of AE sources (hypocenters) and the recordings obtained from a sensor network. Using moment tensor inversion methods, the radiation pattern of acoustic emission sources and the seismic moment (as an equivalent to the emitted energy), as well as the type (Mode I, Mode II, and mixed modes) and orientation of the cracks, can be determined.

Preliminary Thermography Studies for Quality Control of Concrete Structures Strengthened with Fiber-Reinforced Polymer Composites

Abstract: Fiber-reinforced polymer (FRP) composites, in the form of pultruded laminates or built-up woven fabrics, are being used widely to strengthen existing concrete and masonry structures. The success of these materials in performing their intended functions depends, to a large extent, on how well they are bonded to themselves and to the substrate. There is a need for an efficient and reliable method to detect and characterize defects at the substrate interface and within multi-ply systems. Infrared thermography is well suited for this purpose because it is inherently sensitive to the presence of near-surface defects and can interrogate large areas efficiently. Before infrared thermography can be developed into a standard methodology, however, an understanding is needed of the effects of testing parameters and different types of defects. A multiyear study is under way to develop this understanding through the use of controlled-flaw experiments and finite-element modeling. This paper reports on the initial phases of this study. An experimental setup is described for measuring the emissivity of a carbon FRP composite and for obtaining a well-defined heat pulse. Good agreement was found between experimental thermal response parameters and those calculated from finite-element models of controlled-flaw specimens. This agreement provides assurance of the validity of parametric studies based on numerical simulations.

Resistance Changes during Compression of Carbon Fiber Cement Composites

Abstract: The incorporation of a small volume of carbon fibers into a concrete mixture produces a strong and durable concrete and at the same time lends the product a smart material property. This intrinsic capability can be tapped by using simple electrical resistance techniques. There is the potential for these techniques to be used as nondestructive testing methods to assess the integrity of the composite. The results of some fundamental investigations on the bulk electrical properties of carbon fiber cement composites under compressive loading are presented. Well-defined patterns are exhibited in the electrical resistance behavior which can be correlated with the stress-strain behavior. The resistance behavior was evaluated for various fiber volume contents for both mature and early-age specimens. The response under cyclic compressive loading was studied. The effect of taking measurements both parallel and perpendicular to the axis of loading was also investigated.

Evaluation of FWD Data for Determination of Layer Moduli of Pavements

Abstract: Falling weight deflectometer (FWD) testing has been done extensively in the past to assess structural condition and determine the moduli of pavement layers. The set of modulus values for pavement layers obtained from the backcalculation process may not be accurate even though the computed and measured deflection basin may match within tolerable limits. Extensive interpretation is involved in obtaining the layer moduli of these pavements. Guidelines and tools are provided for calculating layer moduli for flexible pavements. FWD interpretation has become increasingly challenging because more and more of our roads have experienced multiple milling operations and overlays. The characteristics of the structure such as damaged layers, thickness variation, and temperature changes can overwhelm the deflection data, having a far more significant effect than those induced by structural layer stiffness. This study emphasizes that proper interpretation of FWD data involves a complete evaluation of all available data, including core data, roadway data, and section-specific distress information. Evaluating multiple FWD measurements along the sections allows for the evaluation of consistency and assures reasonableness of interpretation.

Properties of Field Manufactured Cast-Concrete Products Utilizing Recycled Materials

Abstract: This investigation was performed to develop technology for manufacturing cast-concrete products using Class F fly ash, coal-combustion bottom ash, and used foundry sand. A total of 18 mixture proportions with and without the by-products was developed for manufacture of bricks, blocks, and paving stones. Replacement rates, by mass, for sand with either bottom ash or used foundry sand were 25 and 35%. Replacement rates, by mass, for portland cement with fly ash were 25 and 35% for bricks and blocks, and 15 and 25% for paving stones. Analysis of test data revealed that bricks with up to 25% replacement of cement and blocks with up to 25% replacement of cement and sand with recycled materials are suitable for use in both cold and warm climates. Other bricks and blocks were appropriate for building interior walls in cold regions and both interior and exterior walls in warm regions. Paving stones with 15% replacement of cement with fly ash showed higher strength, freezing and thawing resistance, and abrasion resistance than the control specimens.

Carbonation-Porosity-Strength Model for Fly Ash Concrete

Abstract: The potential of a concrete for carbonation can be assessed effectively by measuring its carbonation depth using an accelerated carbonation testing. This paper reports the findings of a laboratory study including compressive strength, accelerated carbonation depth, and porosity properties of concrete mixtures made with fly ash and normal portland cement. The study involves two replacement ratios of fly ash, various water-to-cement ratios, use of superplasticizer, two curing conditions, and four concrete ages. Statistical models that relate accelerated carbonation depth to strength and porosity are presented.