Journal of Materials in Civil Engineering

An algorithm for determining the rheological parameters of asphalt mixes in the creep test in the Nottingham Asphalt Tester (NAT) is presented. It was found that the smallest errors in identification of the rheological parameters are made for the third cycle of loading. The determined rheological parameters were verified by testing the mixes in the French Pavement Rutting Tester (FPRT), for which a rutting test model based on the finite-element method (FEM) was developed. Also the deformability of the asphalt mixes tested in the FPRT is analyzed. It is found that the viscosity coefficient ${\eta }_1$ and the delayed elasticity coefficient $E_2$ have a significant effect on rut depth in the rutting tester model. An analysis of the deformation sensitivity of the viscoelastic courses in a pavement structure model shows that the binder course’s rheological parameters, especially the viscosity coefficient ${\eta }_1$ , contribute most to rutting in the pavement. The deformation of this course is determined by the duration of the load. The deformation of the wearing course is influenced by the delayed elasticity modulus $E_2$ , and it depends mainly on the time between cycles of loading.

The transition from the uncracked to the cracked phase in lightly reinforced concrete beams was experimentally investigated by subjecting five full-scale beams to three-point bending. All beams had the same dimensions and the same percentage of flexural reinforcement, but varying diameters and number of reinforcing bars. By means of transducers, strain gauges, and geometric moiré, the crack profiles and the concrete strain field around the cracks were measured. In this way, it was possible to observe and to reproduce numerically the crack onset and its stable propagation up to the unstable behavior that follows the effective cracking moment. During the growth of the crack, the moment rotation diagrams, the values of tensile strains in concrete, and the shape of crack profiles demonstrate the dependence of the mechanical response on bar diameter. Consequently, to avoid brittle failure, the minimum reinforcement ratio for lightly reinforced concrete beams should likewise be a function of bar diameter.

In this study, a four-layer feed-forward neural network is constructed and applied to determine a mapping associating mix design and testing factors of asphalt concrete samples with their performance in conductance to flow or permeability. To generate data for the neural network model, a total of 100 field cores from 50 different mixes (two replicate cores per mix) are tested in the laboratory for permeability and mix volumetric properties. The significant factors that affect asphalt permeability are identified using simple and multiple regression analysis. The analyses results show that permeability of an asphalt concrete is affected mainly by five factors: (1) air void $\left(V_a\right)$ ; (2) the grain size through which 10% materials pass $\left(d_{10}\right)$ ; (3) the grain size through which 30% materials pass $\left(d_{30}\right)$ ; (4) saturation, or the CoreLok Infiltration Coefficient (CIC); and (5) effective asphalt to dust ratio $(P_{be}∕P_{0.075})$ . The significant factors are then used to define the domain of a neural network. Regardless of the significant factors included in defining the domain of such a mapping, a principle component analysis is performed to ascertain the most significant of these factors. The network is trained using the Levenberg-Marquardt algorithm. Using randomly generated synaptic weights to initialize the training algorithm, histograms are compiled and outputs are estimated. Excellent agreement is observed between simulation and laboratory data. It is believed that the developed NN model will be a useful tool in the study of asphalt pavement construction and maintenance.

The rheology behavior of fresh short fiber reinforced cementitious composite (SFRCC) for extrusion purpose was investigated through capillary extrusion. It was found that the classical capillary theory for single-phase fluid was not appropriate to interpret the flow behavior of fresh SFRCC due to the large pressure loss occurring at the capillary entrance and the significant slip effect happening in the capillaries. By using a set of capillaries with the same diameter but different lengths, the true shear stress was derived on the basis of Bagley’s end correction while the slip effect was calibrated through a series of capillary extrusion tests with different capillary diameters. It was found that the slip velocity could be determined by the Jastrzebski model. Further studies showed that the intrinsic rheology behavior of fresh SFRCC could be modeled by the Herschel–Bulkley equation and the associated parameters could be determined through the experimental and the data interpretation method described in this paper. The fresh SFRCC flow in capillary extrusion was dominated by slip, and the velocity profile could be determined through a superposition of an internal shear flow with a plug flow. The slip layer thickness developed in the capillaries was also estimated based on the calibrated theory and experimental data.

Approximately 30% of all vehicle related fatalities that occur each year are caused by a single vehicle leaving the road and striking a fixed object; the most common objects struck being trees, guardrails, and utility poles. In many cases, current crash cushion systems are too expensive to be installed on such hazards and may also require recurring maintenance. This makes the development of a less expensive crash cushion a necessity. The objective of this study was to evaluate the material properties of used tires and recycled tire-derived materials (TDMs) for use in low-cost, reusable crash cushions. The used tires and TDMs were tested statically and dynamically to evaluate their suitability as crash cushion materials. The test specimens were able to sustain high loads and proved to be durable, making them good candidates for use in a crash cushion.

In this paper, the influence of ultrafine fly ash on the early age property development, shrinkage, and shrinkage cracking potential of concrete is investigated. In addition, the performance of ultrafine fly ash as cement replacement is compared with that of silica fume. The mechanisms responsible for an increase of the early age stress due to restrained shrinkage were assessed; free shrinkage and elastic modulus were measured from an early age. In addition, the materials resistance to tensile fracture and increase in strength were also determined as a function of age. Results of the experimental study indicate that the increase in elastic modulus and fracture resistance with age are comparable for the control, ultrafine fly ash, and silica fume concretes. Autogenous shrinkage is shown to play a significant role in determining the age of cracking in restrained shrinkage tests. A significant reduction in the autogenous shrinkage and an increase in the age of restrained shrinkage cracking were observed in the ultrafine fly ash concrete when compared with the control and the silica fume concrete. Increasing the volume of ultrafine fly ash and decreasing the ratio of water-to-cementitous materials resulted in further increase in the age of restrained shrinkage cracking and a significant increase in the compressive strength.

In this paper, failure test results of brick masonry and concrete under biaxial stress state, and of concrete under triaxial stress state, are analyzed. In particular, in the biaxial compression stress state masonry is found to behave as an isotropic material. The pertinent failure interaction curve in terms of principal stress components can be expressed by an ellipse or a parabola. Because masonry can be conceived as a conglomerate material, as a concrete, formed by coarse aggregates (bricks) and cement paste (mortar joints), a generalized failure criterion in the form of an elliptical curve valid both for masonry and concrete in compression biaxial state is provided. In the case of the triaxial compression stress state, from an analysis performed on the test results available for concrete, a prediction of the hydrostatic compressive strength is derived, and a possible form of the limit surface in the principal stress space is hypothesized.

The degradation response of pultruded E-glass vinylester composites immersed in deionized water at 23, 40, 60, and $80°\mathrm{C}$ is characterized through mechanical testing (tension and short-beam-shear), moisture uptake, and dynamic mechanical thermal analysis (DMTA). Tests are conducted after periods of immersion and subsequently after a period of drying out to assess regain of performance due to reduction in sorbed moisture content. It is seen that, although the initial effect of immersion is just matrix plasticization, increased periods of immersion and/or use of elevated temperatures results in hydrolysis, interfacial debonding, microcracking, and even degradation of the fiber itself. Not only do these mechanisms of irreversible degradation result in significant drops in performance, but further, these decreases are increasingly irreversible. Both inductively coupled plasma and Fourier transform infrared studies indicate leaching of composite constituents.

Reliable implementation of transient temperature prediction models for asphalt pavements has been impeded by lack of reliable thermo–physical properties data. The existing methodology based on ASTM C177-85 is not conducive to asphalt concrete specimens due to the difficulty to meet the slab requirements of the standard. This paper discusses a new laboratory procedure for the determination of thermal properties of asphalt concrete specimens. The new device can accommodate small specimens derived from either laboratory compacted $150\mathrm{mm}$ diameter briquettes or cores from in-service pavements. The effect of compaction on thermal properties was tested by compacting the briquettes to 67, 99, 133, and 212 gyrations using the superpave gyratory compactor. Thermal conductivity $\left(\lambda \right)$ was determined after the experiment reached steady state, whereas thermal diffusivity $\left(\alpha \right)$ was determined during the transient state. Analytical curve fitting technique was applied to the test data to compute the thermal diffusivity. Thermal conductivity of laboratory compacted Superpave hot-mixed asphalt was observed to vary from $1.4\text{to}1.8\mathrm{W}∕\mathrm{m}\mathrm{K}$ for dense graded mixtures (corresponding to $\mathrm{2,295}–\mathrm{2,450}\mathrm{kg}∕{\mathrm{m}}^3$ bulk densities and 3–7% air voids). Thermal diffusivity was observed to range from $4.4\text{to}6.4\times {10}^{-7}{\mathrm{m}}^2∕\mathrm{s}$ . These values are much narrower and consistent than presented in the literature. The thermal properties were then examined for possible correlation with resilient modulus, Marshall stability and flow, and bulk density. It was found that there was no correlation between asphalt concrete thermal properties and physical properties.

Radial inhomogeneity is often observed in superpave gyratory compacted specimens because of the rotational movement of the gyratory and the boundary condition imposed by the gyratory mold. The effect of the inhomogeneity on mechanical properties of asphalt mixtures is not known. To study this effect, laboratory specimens of asphalt mixtures with known levels of aggregate inhomogeneity were fabricated. Nondestructive X-ray computed tomography was used to scan cross-sectional images of the specimens. A statistical index was developed to evaluate the scanned images for radial inhomogeneity. The results clearly show that the index can distinguish between levels of inhomogeneity. By means of frequency sweep at constant height (FSCH) test, the shear stiffness and the fatigue susceptibility at test temperature of $25°\mathrm{C}$ and the shear stiffness and rutting susceptibility at test temperature of $50°\mathrm{C}$ were evaluated. The resistance of the material to cumulative shear deformation was measured using the repeated shear at constant height (RSCH) test at $50°\mathrm{C}$ . The effects of radial inhomogeneity on the shear properties of the specimens were investigated at the two test temperatures. As indicated from the FSCH test, the shear modulus increases, the rutting susceptibility, and the fatigue susceptibility in thick layers decreases, and the fatigue susceptibility in thin layers increases with increasing radial inhomogeneity. The correlation between the shear properties from the FSCH test and the inhomogeneity index is greater at the test temperature of $25°\mathrm{C}$ than at the test temperature of $50°\mathrm{C}$ . Although the RSCH test is conducted at $50°\mathrm{C}$ , the permanent deformations resulted from the test shows the highest correlation with the level of inhomogeneity. The permanent strain decreases significantly with the increase in the level of inhomogeneity. The results of this study indicate that predicting the performance of the same material in the field based on the properties of laboratory-made specimens will lead to overprediction of the field performance and as a result underdesign of pavements.

The majority of U.S. departments of transportation (DOT) maintain quality assurance (QA) programs that require asphalt binder testing to verify grade compliance according to Superpave performance grade (PG) specifications. In Texas the binder is tested immediately after binder production, although the goal of QA is to ensure that the binder specified is used during construction. Between production and construction, the material is stored and transferred multiple times before it reaches the construction site or hot mix asphalt (HMA) plant. During this journey, binder properties may change due to many factors and these changes may have a negative impact on performance. To evaluate which factors are detrimental, a laboratory testing program was conducted to simulate the effects of storage time, storage temperature, contamination, and modification on the dynamic shear rheometer (DSR) performance parameter $G*∕\sin \delta$ after rolling thin film oven (RTFO) aging. A statistical analysis was performed, and the results indicated that all factors included in the simulation were significant. Results, conclusions, and general recommendations are provided to improve the current TxDOT QA program.

This paper investigates the adhesive properties of bitumen films. Tensile tests on bitumen butt joints and double cantilever beam specimens, over a wide range of test conditions, are described. The test results are treated using fracture mechanics and strength of materials approaches. It is found that the failure strain of bitumen is generally independent of equivalent strain rate, in both the brittle and ductile regimes, whereas the “normalized toughness,” $G∕2h$ is rate independent in the brittle regime and rate dependent in the ductile regime ( $G=\text{strain}$ energy release rate, $2h=\text{film}$ thickness). The toughness of a typical paving bitumen is quantified, both for brittle fracture and ductile failure, and a mechanism map classifying the failure mechanisms as a function of temperature and strain rate is presented.

To date, only linear elastic analyses have been used to explain the compression behavior of the concrete masonry prisms. In this study, nonlinear three-dimensional finite element analyses, based on both an elastoplastic approach and an isotropic damage model, have been applied to the compression behavior of hollow block and grouted concrete block prisms. Attention is particularly focused on the derivation of material parameters for concrete, grout, and mortar, and also on the improvement of existing code expressions for prism strength. This paper introduces adequate values for the cohesion and friction angle of the Drucker–Prager yield criterion and material damage parameters for the damage model for the constituent materials. The results of the nonlinear finite element analyses have been observed to be in good agreement with the experimental data in terms of failure mechanisms and ultimate load. Failure modes of grouted prisms are also investigated by evaluating the stress distributions at the outer face shell along the prism height. Finally, an analytical relation is proposed to predict the compressive strength of concrete masonry prisms, $f_m^{\prime }$ .