Journal of Materials in Civil Engineering

The ingress of chloride ions in a harsh chloride environment leads to the corrosion of reinforcing steel bars and reduction in the service life of concrete structures. Prediction of the service life of chloride-exposed concrete structures is strongly dependent on chloride diffusion coefficient, which in turn is influenced by several factors including materials and environmental parameters, binding of chloride ions to the solid phase of concrete, and the stresses caused by external load acting on the structure. The diffusion of chloride in concrete is increased significantly by damage associated with load-induced stress, which, if not taken into account, can lead to erroneous prediction of the service life. This paper investigates the impact of compressive stress-induced damage on chloride transport in concrete. An experimental investigation involving non-steady-state migration test as per NT BUILD 492 was carried out on unloaded concrete specimens damaged under axial compressive load. Numerical simulation of the rapid chloride-migration test using multiphysics finite element software is presented in which a phenomenological damage model and a chloride-binding isotherm coupled with Nernst-Planck equation is used to evaluate chloride migration in the damaged concrete specimens.

Because of the large grainsizes typical of railroad ballast, large triaxial samples are required to assess the reactions of these materials. The parallel gradation modeling technique was originally developed by John Lowe in 1964 to allow assessment of large grain-size geomaterial properties in smaller, more typical testing facilities. Emphasis has focused on monotonic loading, in which the material is progressively loaded to failure. Cyclic testing of this model has been absent. This paper presents an investigation of the possibility of using the parallel gradation modeling technique in a cyclic triaxial testing framework. Three separate gradations of ballast material were used in this research. The largest gradation contains a top particle size of 63.5 mm (2.5 in.) and is marketed as #3 modified railroad ballast. The second two gradations contained a top size of 38 mm (1.5 in.) and 19 mm ($3/4\mathrm{in}$.), respectively. Up to 10,000 load cycles were applied for each test. Resilient modulus, permanent axial, volumetric strain, and particle shape were determined from the test results. It is concluded that applying parallel gradation technique to cyclic behavior characterization should be cautious. If particle shape is not consistent throughout the particle sizes used in the parallel gradation model, the model is invalid in the cyclic triaxial framework.

The objectives of this research are to modify an asphalt mixture with two materials—nanoclay and carbon microfiber—and to investigate the interactions of chloride deicer solutions with nano- and/or micromodified and unmodified asphalt mixtures in terms of indirect tensile strength (ITS) and fracture energy. Artificial neural networks (ANNs) were used in this study to establish predictive models and quantify the complex cause-and-effect relationships between the nano- or micromodification and conditioning of asphalt mixtures and the resulting mechanical properties. Four influential variables (nanoclay content, microfiber content, deicer type, and deicer dilution ratio) were collectively examined to predict the ITS and fracture energy of asphalt mixtures, and a back-propagation neural network of three layers with seven or nine hidden nodes was employed respectively. The established ANN models were then successfully used for numerical investigations on the parameters affecting the asphalt properties. The addition of polysiloxane-modified montmorillonite and/or carbon microfiber (both at less than 2% by weight of asphalt binder) can enhance the tensile strength fracture energy of asphalt concrete mixtures and reduce their moisture susceptibility and cracking risk, and such benefits are especially significant when the asphalt concrete is conditioned in water or chloride-based deicer solutions. This evaluation makes it possible to design asphalt mixtures for a desired level of ITS or fracture energy in the absence or presence of common chloride-based deicer solutions.

In this study, the effect of incorporating wollastonite microfibers in ultrahigh performance concrete (UHPC) on its early-age properties was investigated. Wollastonite microfibers were added at 0, 4, 8, and 12% as partial volume replacement for cement. Results show that the early-age properties of UHPC mixtures incorporating wollastonite microfibers are highly affected by the microfiber content and aspect ratio. Increasing the wollastonite microfiber content resulted in a compressive strength comparable to or higher than that of the control mixture without microfibers. Wollastonite microfibers reduced shrinkage strains and increased cracking resistance compared to that of the control mixture. However, no significant improvement in the flexural behavior was achieved with the addition of wollastonite microfibers because of a sudden rupture of microfibers within the matrix. Wollastonite microfibers can act as an internal restraint for shrinkage, reinforcing the microstructure at the microcrack level, and leading to an enhancement of the early-age engineering properties of UHPC matrix. Partially replacing cement with natural wollastonite microfibers leads to a reduction in the cement factor, which represents economic and environmental benefits.

The mechanical properties of adhesive materials change over time, especially when they are subjected to long-term loadings. The significance of this is often overlooked at the design stage. When adhesives are subjected to a constant load, they may deform continuously, depending on temperature, humidity, and cross-link density. This progressive deformation is called creep. It is imperative that reliable accelerated tests be developed to determine the long-term time-dependent performance of adhesives under different environmental conditions. The long-term creep behavior of thixotropic and room temperature cure epoxy-based adhesives reinforced with nano particles were investigated. The adhesives in this investigation are formulated with the target of application for in situ bonding of pultruded rod into timber for the repair and strengthening of timber structures. In this study, two epoxy-based adhesives with added nano particles (silica fume and rubber) were subjected to bending creep tests in accelerated environments. Experimental data showed that the adhesives reinforced with nano rubber particles exhibited less creep deformation than the unreinforced ones.

The characterization of viscoelastic properties of the aged field asphalt mixtures has been a challenge for pavement engineers. Instead of characterizing full mixtures from the field cores, only the binder was extracted from the mixture and was evaluated for its aging properties. Because the binder is only one component of the mixture, the properties of the aged binder may not clearly indicate the properties of the aged field mixtures. This study presents a novel method to calculate the complex stiffness gradient of a field-aged specimen using a direct tension test. Because the field asphalt mixtures are not aged uniformly with the pavement depth, there is a modulus gradient through the thickness of the asphalt layer. The asphalt mixture is stiffer at the surface. As a result, rectangular specimens cut from field cores when tested in a direct tension test in electrohydraulic servo machines with feedback frequency tend to oscillate. An analytical method has been developed to analyze the oscillating behavior of the specimen and to produce the stiffness gradient function as it varies with loading frequency and position relative to the pavement surface. Furthermore, a finite-element simulation of the test is conducted to verify the validity and robustness of the proposed method. This method was successfully used to characterize aged viscoelastic properties of field cores obtained from different roads in Texas.

Permanent deformation of asphalt mixture under repeated load can be divided into three phases: decelerating phase, stationary phase, and accelerating flow phase. Most of the existing models cannot fully describe deformation characteristics during the three phases. In this paper, the characteristics of three-phase permanent deformation are considered as the results of a competition between damage and hardening, in which a damage variable and a hardening variable are introduced to modify Burger’s model. First, the series-wound dashpot of the Burger’s model is modified by Usan’s hardening variable, and the undamaged viscoelastic properties are derived from rheological theory. Secondly, Kachanov’s equation for damage evolution is adopted to establish the constitutive model by using Lemaitre’s effective stress principle. Then a repeated load consisting of a haversine loading period and rest period is employed to simulate the actual vehicle loading on the asphalt pavement. Third, a viscoelastic-damage mechanical model is proposed to characterize the permanent deformation of asphalt mixture under repeated load. The proposed model is validated by conducting uniaxial permanent deformation tests on four kinds of asphalt mixtures. The model parameters are obtained by using the principle of least square. The proposed model is capable of describing the whole three-phase permanent deformation of the asphalt mixtures. The proportion of residual viscoelastic strain to permanent strain decreases very quickly as load cycle increases and only accounts for $2\sim 3\%$ during most of the loading period. It is indicated that residual viscoelastic strain is significantly less than the permanent strain, thus the residual viscoelastic strain can be ignored and the proposed model could be simplified to a concise format.

This research was conducted to establish the effects of fly ash and used foundry sand on strength and durability of concrete. Two series (Series 1 and Series 2) of experiments were performed. All concrete mixtures were produced for and at the production plant of an architectural precast concrete products producer. Concrete mixtures produced were used in manufacture of precast concrete panels. Tests were performed with normal and air-entrained fly ash concrete. Concrete test specimens were evaluated for compressive strength, abrasion resistance, salt-scaling resistance, freezing and thawing resistance, and chloride-ion penetration resistance. On the basis of strength and durability evaluations, it was concluded that both nonair and air-entrained concrete mixtures developed in this investigation are appropriate for manufacture of high-quality, high-durability architectural precast concrete using used foundry sand and fly ash.

The objective of this investigation was to develop rules for automatic assessment of concrete quality by using selected artificial intelligence methods based on machine learning. The range of tested materials included concrete containing nonstandard waste material—the solid residue from coal combustion in circulating fluidized bed combustion boilers (CFBC ash) used as an additive. Performed experimental tests on the surface scaling resistance provided data for learning and verification of rules discovered by machine learning techniques. It has been found that machine learning is a tool that can be applied to classify concrete durability. The rules generated by computer programs AQ21 and WEKA by using the J48 algorithm provided a means for adequate categorization of plain concrete and concrete modified with CFBC fly ash as materials resistant or not resistant to the surface scaling.

This paper examines the effect of organic matter content and the curing conditions on the one-dimensional compressibility of Portuguese soft soil stabilized with binders, with a special emphasis on creep behavior. Consolidation and creep oedometer tests were carried out on remolded and stabilized soil samples to study the effects of these factors. The increase of the organic matter content induces the increment of compressibility characteristics, including creep. Curing conditions also affect the one-dimensional compression behavior of the stabilized soil because the underwater curing, the increase of the vertical stress applied on the sample, and the increase of the curing time improve the compressibility characteristics, inducing the reduction of creep deformations.

High lateral pressure exerted on formwork systems by self-consolidating concrete (SCC) is one of the hindrances for using such highly flowable concrete in cast-in-place applications. Self-consolidating concrete is a complex system that can be made using a wide range of mixture proportioning and often incorporated various chemical admixtures and supplementary cementitious materials. The investigation of the effect of each material ingredient independently on lateral pressure of SCC is not a simple task. In this study, thixotropy is rather used to assess the effect of various mixture parameters on formwork pressure. Thixotropy is determined by the evaluation of the structural buildup at rest using a concrete rheometer and two field-oriented test methods (inclined plane and portable vane). Sherbrooke pressure device is employed to evaluate the maximum lateral pressure of SCC. The device receives 0.5 m of fresh concrete and pressurized with air to simulate 13 m of concrete casting at the required casting rate. A parametric study and full-factorial design approaches were employed to evaluate the effect of concrete consistency level, coarse aggregate content, sand-to-total aggregate ratio, paste volume, and nominal maximum size of aggregate on SCC thixotropy and formwork pressure. The investigation resulted in proposing statistical models to determine the effect of each of the modeled mixture parameters and their interaction on thixotropy and lateral pressure. Contour diagrams were established to compare the trade-off between the effects of the different mixture parameters on thixotropy and formwork pressure characteristics.

With increasing interest in the use of warm mix asphalt (WMA) in the paving industry, more studies in this field for improvement of WMA properties seem to be necessary. In past decade, several studies focusing on use of Sasobit and asphamin as warm additives in asphalt mixtures have been conducted; however, the effects of these additives on moisture susceptibility of asphalt mixture are still not fully understood. In this study, the moisture susceptibility of WMA evaluated with and without a new nanotechnology material as antistrip additive (namely Zycosoil) by determining the micromechanisms that affect the adhesion bond between the aggregate and asphalt binder and the cohesion strength of the asphalt binder using the surface free energy (SFE) concept and laboratory testing analysis. Indeed, the primary goal of this research was to decrease the moisture damage in WMA. Two types of aggregates, limestone and granite, and two types of WMA additives, namely Sasobit and aspha-min, in addition to as Zycosoil as an antistrip additive were evaluated in this study. Moisture sensitivity index, which is the percentage of the aggregate surface exposed to water ($P$) as calculated by using the measured SFE and dynamic modulus results, was considered an index for the moisture susceptibility of mixtures. The findings suggest that WMA additives cause an increase in the acid component and a reduction in the SFE base components of asphalt binder. This causes decreased adhesion between acidic aggregate that is more moisture damange and asphalt binder. Moreover, Zycosoil additives cause an increase in the adhesion SFE between asphalt binder, modified with WMA additives and aggregates in the presence of water. A dynamic modulus test of Zycosoil performance yielded similar results, suggesting that using this material causes the ratio of the dynamic modulus values for wet/dry condition to increase significantly in samples made with WMA additives. For these reasons, the percentage of aggregate surface area wetted by water, index $P$, decreased when Zycosoil was used in all samples.

Permanent deformation and fracture may develop simultaneously when an asphalt mixture is subjected to a compressive load. The objective of this research is to separate viscoplasticity and viscofracture from viscoelasticity so that the permanent deformation and fracture of the asphalt mixtures can be individually and accurately characterized without the influence of viscoelasticity. The undamaged properties of 16 asphalt mixtures that have two binder types, two air void contents, and two aging conditions are first obtained by conducting nondestructive creep tests and nondestructive dynamic modulus tests. Testing results are analyzed by using the linear viscoelastic theory in which the creep compliance and the relaxation modulus are modeled by the Prony model. The dynamic modulus and phase angle of the undamaged asphalt mixtures remained constant with the load cycles. The undamaged asphalt mixtures are then used to perform the destructive dynamic modulus tests in which the dynamic modulus and phase angle of the damaged asphalt mixtures vary with load cycles. This indicates plastic evolution and crack propagation. The growth of cracks is signaled principally by the increase of the phase angle, which occurs only in the tertiary stage. The measured total strain is successfully decomposed into elastic strain, viscoelastic strain, plastic strain, viscoplastic strain, and viscofracture strain by employing the pseudostrain concept and the extended elastic-viscoelastic correspondence principle. The separated viscoplastic strain uses a predictive model to characterize the permanent deformation. The separated viscofracture strain uses a fracture strain model to characterize the fracture of the asphalt mixtures in which the flow number is determined and a crack speed index is proposed. Comparisons of the 16 samples show that aged asphalt mixtures with a low air void content have a better performance, resisting permanent deformation and fracture.

The natural stone veneer used to clad sandwich panels needs to be less than 1 cm thick to ensure a lightweight structure. However, diminishing the thickness reduces slab strength, which is important when the stone is to be rough finished. Thus, traditional techniques such as bush-hammering and flaming are unfeasible for these veneers. The main aim of this study was to investigate the possibility of using high pressure waterjet technology for stone veneer finishing. First, the characteristics of the stone were determined (origin, petrography chemistry, strength). Suitable combinations of waterjet operating parameters (pressure, traverse speed, distance between successive passes) were then tested to determine optimal results in terms of both performance and aesthetics. The investigation demonstrated the success of this technique for processing large slabs ($100\mathrm{cm}\times 200\mathrm{cm}$), with thickness of just 3 mm, thus also overcoming the problems involved in maneuvering heavy slabs with thickness of more than 2 cm. Surface roughness analysis of the treated stone showed it to compare favorably with competing technologies, with the advantage that waterjet maintains the natural color of the rock. Finally, some economic considerations are discussed.

Fatigue cracking is considered to be the primary failure mechanism that occurs at ambient temperatures in an asphalt pavement. The bituminous binder plays an important role in this failure mechanism, because fatigue cracking tends to take place predominately within the binder itself. Oscillatory tests using a dynamic shear rheometer (DSR) and wheel tracking fatigue tests were carried out on a wide range of bitumen-filler mastics and on asphalt mixtures containing the corresponding mastics to investigate their fatigue relationships. The addition of the mineral filler to bitumen was found to have a significant influence on the fatigue life of mastic owing to the stiffening effect and the filler particles interrupting the crack growth in the mastic. The results of stiffening ratio showed that the 65% mastics were in the concentrated suspension region, whereas the 35% mastics were in the dilute suspension region. In terms of shear stress, the fatigue order was $40/60$ pen bitumen followed by 35% mastic, with 65% mastic having the highest fatigue performance. In terms of shear strain, the fatigue order was the reverse of the fatigue relationships versus stress, but the $40/60$ pen bitumen had the greatest slope compared with the bitumen-filler mastics. No loading mode dependency occurred with results undertaken on the dilute suspension mastics, whereas testing mode had an influence on fatigue life for the mastics with concentrated suspension. In addition, the fatigue performance of asphalt mixtures seemed to be more sensitive to the wheel load rather than the concentration and nature of bitumen-filler mastics. The slope of the fatigue line for the mixtures was synonymous with that of the fatigue line for the mastics with concentrated suspension when subjected to wheel tracking testing rather than DSR oscillatory shear testing.

This paper presents the findings of an extensive laboratory investigation on the geotechnical properties of waste excavation rock in pavement subbases. The waste excavation rock used in this study originated from “basalt floaters,” or surface excavation basalt rock (basalt). Traditionally, this material would have been disposed as waste, often into landfill. The engineering properties of the crushed basaltic waste rock were compared with the local road authority specifications to assess its performance as a pavement subbase material. The experimental program was extensive and included tests such as particle size distribution, modified Proctor compaction, particle density, water absorption, California bearing ratio, Los Angeles abrasion loss, pH, organic content, static triaxial, and repeated load triaxial tests. The Los Angeles abrasion loss value obtained indicated that the crushed basaltic waste rock is durable. California bearing ratio values were found to satisfy the local state road authority requirements for a subbase material. Repeated load triaxial testing established that the crushed basaltic waste rock would perform satisfactorily as a pavement subbase material in the field. The results of the laboratory testing undertaken in this research indicated that crushed basaltic waste excavation rock satisfied the criteria for use in pavement subbase applications.

Bridges are a vital link to the nation’s mobility and prosperity, and those bridges with inadequacies will need to be repaired or replaced as soon as possible. High-performance concrete (HPC) could be the most economical solution. What typically distinguishes HPC from conventional concrete (CC) is the wide variety of cements, supplementary cementitious materials, aggregates, chemical admixtures, and fibers in use. The purpose of this research project was to demonstrate the use of HPC in bridge decks in Oklahoma. HPC mixtures were designed with an optimum blend of three aggregates. With less voids between aggregate particles, the HPC mixtures contained less cement paste, approximately 24% by volume. Examined more than one year after construction, crack densities were less on HPC bridge decks than CC bridge decks. HPC mixtures with fly ash exhibited the best potential durability with crack densities less than $0.1\mathrm{m}/{\mathrm{m}}^2$. The addition of fibers did not have an effect on crack density.

Several factors affect the behavior of concrete used in structural elements such as columns or beams. One of the primary factors that affects the behavior of concrete is the characteristic properties of the aggregates used in the mix proportion. The main purpose of this study is to investigate and compare the behavior of lightweight and ordinary concrete produced with lightweight and ordinary aggregates in selected reinforced concrete beams. In the first part of the study, brief information is given about the use of lightweight concrete in structures. In the second part of the study, properties of materials used in the production of beams selected for this study are discussed. In the third part of the study, the production stage of selected lightweight and ordinary reinforced concrete beams is explained. Some conclusions drawn from this study are presented in the final section. The results of this study show that the use of lightweight concrete in reinforced concrete beams is more suitable than the use of ordinary concrete.

In this study, influence of the textural properties, e.g., grain size and its boundaries, of granite on the cutting performance of abrasive waterjet (AWJ) was experimentally investigated. In the experiments, predimensioned granite samples were cut by an abrasive waterjet. Following the cutting process, the cut depth, surface roughness, and kerf angle of the granites were evaluated. As a result, it was disclosed that the cut depths and surface roughness increased when the grain size of the granites decreased. Contrary to the behavior of the cut depths and surface roughness of the granites, the kerf angle of the granites increased with an increase of the grain size. Conversely, it was concluded that the high number of the grain boundaries led to an obtainment of higher cut depths and surface roughness, whereas it caused a lower kerf angle. Additionally, it was found that the grains horizontally lying through the cutting line resulted in lower surface roughness and cut depths, whereas the grains vertically allocated through the cutting line resulted in higher cut depths and surface roughness.

Qualitative as well as quantitative effect of oxygen on the corrosion of reinforced concrete structures under various environments and compositions has been successfully obtained through extensive multivariable laboratory experimentation in this research for which the previous research data is limited and has difference of opinion. The experiment results of this research showed that the diffusion of oxygen is not an influential factor for corrosion inhibition as long as the reinforced concrete is not placed completely under water even in very high humidity environmental conditions as much as 95% relative humidity. The only exception is when the diffusion path of oxygen from the surface of concrete to the depth of steel reinforcement is extended and made slender enough by using a thick concrete cover and low water/cement ratio to make the coefficient of oxygen comparable to that of submerged condition which is not a normal practice. In all cases of relative humidity less than one hundred percent, the diffusivity of concrete is never less enough to make the system oxygen diffusion controlled. This finding is also quantified in this research in terms of concrete cover depth and water/cement ratio in relation to half-cell potential and corrosion rate by using a variety of material and environmental variables. The extensive results of this research can also be used for detailed calibration of underwater half-cell potential measurements which were observed as not the true representative values of corrosion progress showing extremely negative half-cell potential values due to underwater reduced resistivity of concrete.