Journal of Materials in Civil Engineering

A holistic electrochemical-mechanistic model of the corrosion of steel reinforcing bars inside concrete that accounts for the diffusion of oxygen and moisture into the concrete and rust layers, the densification of rust due to confinement, the flow of rust into the concrete pores, the development of internal pressure due to rust buildup, and cracking of the concrete cover is presented. The relationship between the corrosion current and the pressure buildup due to the corrosion products for different concrete cover thicknesses and concrete quality was calibrated through experiments using an accelerated corrosion test with an applied current. Results from finite-element analysis with an inelastic smeared crack concrete model were used to calibrate a simple analytical model of the critical internal pressure required to cause cracking of the concrete cover. The various submodels are linked together to predict the time for cracking of the concrete cover from the time of corrosion initiation. Results of parametric studies using the model indicate that the main factors that control the corrosion current and the time to cracking are the boundary condition, water-cement ratio, and concrete cover.

The purpose of this study is to investigate the effects of water-to-binder ratio (w/b), air content, and type of cementitious material on the fresh and hardened properties of binary and ternary blended concrete mixtures in pavements. This experimental program prepared a total matrix of 54 mixtures with w/b of 0.40 and 0.45; nominal air content of 2, 4, and 8%; and three types of supplementary cementitious materials and one ordinary portland cement in different combinations. Binder systems included ordinary portland cement, binary mixtures with slag cement, Classes F and C fly ash, and ternary mixtures containing a combination of slag cement and one type of fly ash. Workability, total air content, air void system parameters (i.e., spacing factor and specific surface) in fresh concrete, setting time, compressive strength, surface resistivity, and shrinkage were determined. Test results showed that ternary mixtures followed the trends of their constituent materials. Binary and ternary mixtures containing Class C fly ash and slag cement exhibited higher compressive strength than the control mixture. The surface resistivity and shrinkage results of binary and ternary mixtures were equal to or improved over the control mixture.

The investigation presented herein was intended to study the influence of combined transportation time and hot and cold temperatures on the flow properties of self-consolidating concretes (SCC). Seven different temperatures (43, 36, 28, 21, 14, 7, and $-0.5°\mathrm{C}$) and five transportation times (10, 20, 40, 60, and 80 min) were adopted. Transportation time of 10 min and temperature of 21°C were used as the control conditions. Polycarboxylate-based high range water-reducing admixture (HRWRA) and viscosity modifying admixture (VMA) were used to produce different matrices that met the target unconfined slump flow of 635 and 711 mm and dynamic stability of stable to highly stable conditions. In general, the selected self-consolidating concrete produced and transported in extreme temperatures experienced slump flow losses in hot conditions and slump flow gains in cold environments when compared to those of the equivalent concretes produced under the control condition. Significant losses in unconfined flow rate ($T_{50}$) were observed at the evaluated temperatures when transportation time exceeded 40 min.

In structural analysis, because of its anisotropic behavior, wood requires an appropriate constitutive law covering different behavior modes, such as ductile compressive behavior and brittle character in shear and tension. In this study, nonlinear material models were proposed to describe the behavior of timber in a finite-element method (FEM) model. An anisotropic elastoplastic constitutive law with hardening according to Hill yield criterion was used to describe the compressive behavior. Brittle behavior in tension and shear were modeled by using the progressive failure analysis approach, which is based on a failure criterion representing the evolution of damage in timber by a reduction of the elastic modulus. The wood material model was implemented in a three-dimensional FEM model to simulate the nonlinear behavior of timber joints with various types of loadings. The numerical model reliably predicted the stiffness and failure load of the joints. Furthermore, the failure index provided by the numerical model was used to evaluate the potential brittle failure position. Moreover, the initiation of damage and growth in timber members was modeled by using the element removal controlled by stress checking on the basis of the failure criterion. Good agreement was observed between numerical simulations and experimental measurements of failure modes.

The dynamic characterization of cement-based materials under high strain rates is fundamental to understand the material behavior in case of heavy earthquakes and dynamic events. Abram’s law, which was originally formulated for cement-based materials under static loading, is not directly applicable to the dynamic loading condition. In this paper, a modified relationship has been proposed to evaluate the tensile strength of cement mortar. An extensive experiment was carried out to determine the effect of strain rate and water-to-cement ($w/c$) ratio on tensile strength of cement mortar. The dynamic characterization of tensile strength has been carried out by the split Hopkinson pressure bar at high strain rates. The results of the tests show a significant strain rate–sensitive behavior, exhibiting dynamic tensile strength of cement mortar increases with an increase in strain rate. The influence of $w/c$ ratio on dynamic increase factor is minor.

The use of recycled concrete represents an environmentally friendly solution for minimizing the impact of construction and demolition wastes. In many countries, the incorporation of recycled coarse aggregate (RCA) is a common practice because the maximum contents of RCA are usually limited to approximately 25% of the total coarse aggregate content. The incorporation of higher volumes of RCA is a field of discussion, primarily regarding the durable behavior of concrete. This study analyzes different transport properties of concretes with compressive strength of 20–50 MPa prepared with variable contents of RCA (0, 25, and 75%). Eight types of RCA were obtained from concretes incorporating four different natural coarse aggregates: granitic, basaltic, quartzitic crushed stones, and siliceous river gravel. Capillary absorption, water penetration, and chloride diffusion tests were conducted. The variation of transport properties with concrete compressive strength and the effect of RCA content on the variability of transport properties were analyzed. According to the results, the durable behavior of recycled concretes is different according to the transport mechanisms to which they are exposed and this behavior can match that of concretes made with natural coarse aggregates.

A research attempt was made to design a controlled low-strength material (CLSM) mix that can be used as bedding and haunch material for a pipeline by using the native soil as fine aggregate. Several CLSM mix designs were attempted using native high-plasticity clay as fine aggregate material. Comprehensive material characterization studies including flowability to strength tests were performed. These results were analyzed to address the applicability of each mix to serve as pipe bedding/backfilling zones in a pipeline construction. Both flowability and density test results are first evaluated, and as a result, several mixes are formulated. These mixes were further subjected to engineering characterization-related studies, and this paper presents these test results. Setting time, strength, and stiffness results as well as excavatability evaluations of these mixtures are covered as a part of these studies. These results indicate that the CLSMs can be produced using native high-plasticity soils with strength properties always matching specified requirements. Certain relaxation on setting time periods could further help in developing economical mix designs. CLSMs that meet project specifications are recommended for field implementation.

The aim of the research reported in this paper is to assess the mechanical performance of concrete containing different percentages of fine aggregates produced from waste generated by the marble quarrying industry (0, 20, 50, and 100% of the total volume of aggregates). More specifically, the workability and bulk density of fresh concrete were measured and the compressive strength, splitting tensile strength, modulus of elasticity, and abrasion resistance of hardened concrete were determined. In general, concrete containing secondary fine aggregates proved to have worse mechanical properties than conventional concrete made with primary siliceous sand, basalt, and granite fine aggregates. This poorer performance was more noticeable when the replacement percentage was higher. However, the reduction in mechanical performance is acceptable and does not compromise use of these secondary aggregates in structural concrete.

To determine the mechanical properties of cement asphalt mortar (CAM) in the field, this contribution first presents a model to elaborate the relationship of strength to ultrasonic pulse velocity (UPV). Next, a mechanical test (compressive, flexural strength, and static modulus) and a UPV test are conducted on CAM at different ages to calibrate the proposed model. Finally, three fitted formulas are established based on the proposed model and verified with additional test results. Results suggest that a UPV test is a helpful method for estimating the mechanical properties of CAM in the field and can reach a high precision.

Areas affected by dryland salinity in Australia are predicted to more than double over the next 40 years as a result of land use and climatic changes. This presents a significant risk to road asset managers because the concentration of salts within road pavements has been shown to cause damage to pavements and surfacings. The present study explores the impact of dryland salinity on road pavements by assessing the effect of naturally occurring salts on the tensile and shear strength of a sealed granular pavement. Microstructure analysis techniques using scanning electron microscopy and mercury intrusion porosimetry were employed to analyze tested specimens to explain the physical mechanisms that occur as a result of salt concentration. The presence of natural salts was found to have a positive effect on granular pavements but a negative impact on bituminous surfacings. While in solution, salts were found to have a very small positive effect on the tensile strength of the pavement material, which is likely related to clay chemistry interactions. Upon crystallization, salts were observed to form bonds within the pores of the pavement material, which led to a significant increase in tensile strength and a moderate increase in shear strength. However, at the interface between the surfacing and the pavement material, whisker-shaped crystals were observed to grow from the bitumen. Interestingly, the chemical composition of the two types of crystals observed was found to be completely different, despite occurring within the same specimens, under the same conditions. The implications of these findings for road pavements in high-saline areas are also discussed.

In recent years, a new group of technologies has been introduced in the United States that allow producing asphalt mixtures at temperatures 30 to 100°F (16.7–55.6°C) lower than what is used in traditional hot-mix asphalt (HMA). These technologies are commonly referred to as warm-mix asphalt (WMA). From among these technologies, foamed WMA produced by water injection has gained increased attention from the asphalt paving industry in Ohio since it does not require using costly additives. This type of asphalt mixture is advertised to have better workability than traditional HMA mixtures. However, limited research has been conducted to validate this claim. In this study, a new device was designed and fabricated to evaluate the workability of foamed WMA mixtures and compare it to that of HMA mixtures. Two asphalt binders (PG 70-22 and PG 64-28), two aggregate types (limestone and crushed gravel), and two nominal maximum aggregate sizes (12.5 and 19.0 mm) were used in this study. The test results showed that foamed WMA mixtures are more workable than HMA mixtures, which was attributed to the lower asphalt binder absorption observed for the foamed WMA mixtures. Another factor that might have contributed to the improvement in workability for the foamed WMA mixtures is the presence of vapor pockets entrapped within the foamed asphalt binder that keeps the binder slightly expanded and reduces its viscosity. For both foamed WMA and HMA mixtures, better workability was obtained for PG 64-28 than for PG 70-22, and for the 12.5-mm nominal maximum aggregate size than for the 19.0-mm nominal maximum aggregate size. HMA mixtures prepared using crushed gravel had better workability than those prepared using limestone aggregates. However, foamed WMA mixtures prepared using limestone aggregates had better workability than those prepared using crushed gravel, which indicates that aggregate type affects foamed WMA mixtures differently than HMA mixtures.

This paper presents the results of an experimental investigation on the effect of load on chloride diffusion in concrete members in tidal zone and salt spray zone which were simulated by using a self-designed tidal circulation device and a salt spray chamber. The concrete members were loaded by using self anchoring at both ends. The load conditions were 0, 0.3, and 0.5 times of the member’s flexural strength ($f_f$). Chloride concentration profiles in concretes were determined after 35, 70, 120, and 180 days of exposure, respectively. Regression analysis of the experimental data was carried out by applying Fick’s law of diffusion to determine the diffusion coefficient ($D_c$) and chloride concentration on the surface ($C_s$). The results show that chloride diffusion has a big difference between the two zones; diffusion coefficient ($D_c$) is time dependent and gradually reduces over time; loads have a certain impact on diffusion; and tensile stress promotes chloride diffusion whereas compressive stress inhibits chloride diffusion. Based on the results obtained, analytical expressions of chloride concentration considering loads and time in marine concrete are given.

A series of spectral analyses of surface waves (SASW) tests were conducted on a cement concrete pavement by dropping steel balls of four different values of diameter ($D$) varying between 25.4 and 76.2 mm. These tests were performed (1) by using different combinations of source to nearest receiver distance ($S$) and receiver spacing ($X$), and (2) for two different heights ($H$) of fall, namely, 0.25 and 0.50 m. The values of the maximum wavelength (${\lambda }_{\max }$) and minimum wavelength (${\lambda }_{\min }$) associated with the combined dispersion curve, corresponding to a particular combination of $D$ and $H$, were noted to increase almost linearly with an increase in the magnitude of the input source energy ($E$). A continuous increase in strength and duration of the signals was noted to occur with an increase in the magnitude of $D$. Based on statistical analysis, two regression equations have been proposed to determine ${\lambda }_{\max }$ and ${\lambda }_{\min }$ for different values of source energy. It is concluded that the SASW technique is capable of producing nearly a unique dispersion curve irrespective of (1) diameters and heights of fall of the dropping masses used for producing the vibration, and (2) the spacing between different receivers. The results presented in this paper can be used to provide guidelines for deciding about the input source energy based on the required exploration zone of the pavement.

Low-plasticity silt is known to have a potential to liquefy during earthquakes. The compressibility characteristics could change before and after a dynamic event that produces liquefaction. This research investigates the liquefaction resistance and postliquefaction reconsolidation characteristics of Mississippi River Valley (MRV) silt using laboratory cyclic triaxial compression testing. The MRV silt experienced initial liquefaction under cyclic loading, and the results are presented as cyclic stress ratio versus loading cycle curve. After cyclic loading, the liquefied specimens were reconsolidated. Permeability did not change significantly as a result of liquefaction. The reconsolidation curves are more parallel to the compression line than the recompression line in $e\text{-}\log {\sigma }_3^{\prime }$ space, suggesting reconsolidation behaved more like preliquefaction compression. The postliquefaction compression and recompression indexes show less compressibility when compared with preliquefaction conditions. These characteristics of MRV silt suggest that reconsolidation after liquefaction should be a consideration during design of civil infrastructure.

This paper deals with the influences of phenol formaldehyde resin on the rheological properties of petroleum bitumen. Different amounts of phenol formaldehyde were doped into the bitumen of $50/70$ penetration grade and variations in viscosity as a function of temperature and additive concentration were determined. The effects of the phenol formaldehyde additive were examined by conventional and Superpave test methods. Adhesion and stability of bitumen aggregate mixtures prepared using pure and modified bitumen were compared using Nicholson stripping and Marshall tests. The appropriate dosage of the additive yielding the best rheological and performance properties in hot climates was found to be 2% (w/w). Appreciable decreases in the formation of rutting, bleeding, stripping, and cracking in bitumen may be obtained through phenol formaldehyde addition.

A statistical design of experiments method was applied to optimize the mixture proportions of high-strength self-consolidating concrete (SCC) incorporating metakaolin (MK). The optimization involved varying three mixture factors (variables) at five different levels. These factors included total binder content, percentage of MK in the mixture, and water-to-binder ratio. The statistical analysis was exploited to determine the most significant factors affecting the properties of SCC and the optimum level of each variable. A total of 27 mixtures were tested at both the fresh and hardened states to obtain the best SCC mixture containing MK and to compare its results with SCC mixtures containing other supplementary cementing materials. The fresh properties tests included slump flow, V-funnel, L-box, J-ring, and air content tests. On the other hand, at 28 days, the compressive strength of SCC samples under two curing regimes was evaluated. The results showed that the optimized high-strength SCC mixture had a superior performance in the fresh and hardened states compared with the SCC mixtures containing silica fume, fly ash, or slag. The results of the numerical optimization for SCC mixture containing MK showed optimum levels of total binder content of $490\mathrm{kg}/{\mathrm{m}}^3$, water-to-binder ratio of 0.39, and replacement of cement by MK of 19.9%. The results also showed that MK replacement proved to be the most significant factor affecting the 28-day compressive strength of all tested mixtures regardless of curing techniques.

The present study investigates the mechanisms of moisture transport in porous materials. For partially saturated porous materials, moisture transport relies on both the Darcian flow by capillary pressure gradient and the Fickian flow by gas concentration gradient. Taking into account the capillary curves that are associated intimately with the pore structure and play crucial roles on both drying and wetting processes, a uniform model that only depends on one variable, the saturation degree, is established. The isothermal adsorption/desorption method and the Kelvin equation are used to evaluate the capillary curve that obeys the van Genuchten form equation. The established model is applied to characterize the moisture distribution in four (near) coastal regions of China (Guangzhou, Hangzhou, Jinan, and Shenyan). Wetting time is shown to be a dominant factor influencing the stable saturation degree and the influence depth.

The biaxial compressive behavior of concrete has been widely studied in the literature, and the biaxial envelope has always been reported for a particular uniaxial compressive strength. However, there is no theoretical or experimental evidence that concrete with similar strength exhibits similar biaxial behavior. In this study, several kinds of concrete with different maximum aggregate sizes were tested for their biaxial compressive strength under several load ratios. To ensure a uniform stress state in the cubic specimens, four layers of plastic membrane separated by three layers of butter were inserted between the steel loading platens and concrete surfaces to reduce the end friction during the test. In addition to biaxial strength, the uniaxial compressive strength, fracture energy, and characteristic length of each concrete mix were also determined. It was found that the biaxial compressive strength of concrete was dependent on both the uniaxial strength and the fracture energy (or characteristic length). Biaxial tests on concrete should therefore be conducted together with fracture tests to enable the proper comparison of biaxial behavior among different kinds of concrete. While further testing is required, this finding casts new light on concrete behavior under biaxial loading.

Limitations on the joint orientations for which a joint is free to fail exclusively by sliding (without the need for rupture of intact material), for a given specimen height-to-diameter ratio ($L/D$), can influence the results obtained from uniaxial compressive strength (UCS) testing of jointed rock. For example, a jointed specimen with $L/D=2$ can only possibly fail exclusively by sliding for joint angles up to $\sim 63°$ from the plane perpendicular to the axial direction. For joints greater than $\sim 63°$, intact material rupture is required to accommodate failure and UCS is likely to be overestimated. Experimental work was performed to determine the UCS of jointed rock containing various joint orientations, for sample sets with $L/D=2$ and 4. Only joint orientations that allowed joint formats for which failure could occur by sliding on the joint for the $L/D=4$ sample set (i.e., up to 75°) were considered. For joint orientations greater than $\sim 63°$, the $L/D=2$ sample set produced significantly higher UCS values than the $L/D=4$ sample set. Additionally, specimens with joint orientations in excess of 63° displayed failure mechanisms involving intact-material rupture for the $L/D=2$ sample set. Only sliding failure was observed for the same tests on the $L/D=4$ sample set. Care must be taken to ensure methodologies adopted for UCS testing of jointed rock do not influence the mechanisms by which failure can occur. In some cases, strict adherence to methods set out in popular testing standards may need to be reconsidered.

Effects of two of the most important factors influencing permanent deformation of styrene–butadiene–styrene (SBS)-modified and unmodified asphalt—frequency and temperature as well as their interactive effects—are studied using dynamic creep test. The authors used a sophisticated experimental design method known as central composite design (CCD) that provides a continuous mathematical equation for the response (permanent deformation, in this study) based on the independent factors as well as their interactions. Using this design method enhances the statistical validation of laboratory results based on the least-required test. Dynamic creep tests were conducted at three levels of temperature ($-5$, 17.5, and 40°C) and three levels of loading frequency (0.5, 5.25, and 10 Hz). According to the obtained results, first-order terms of frequency and temperature as well as their interactive term were statistically significant in permanent strain of hot mix asphalt (HMA). Further, it was realized that temperature susceptibility of polymer modified mixture is considerably lower than unmodified mixture at intermediate to high temperatures.

Precast concrete sandwich panels have been used in building construction since the 1960s. These sandwich wall panels are constructed with two wythes of concrete separated by a layer of thermal foam plastic insulation and a shear connector mechanism between concrete wythes. Recently, more research is focused on fiber-reinforced composite grids as shear connectors due to their superior thermal performance compared to other connectors such as steel or solid concrete. However, while there are guidelines for design of concrete sandwich panels, there is no standardized guidance that provides testing and capacity determination for composite shear connectors. Therefore, testing and acceptance criteria were developed to evaluate the shear transfer capacities of fiber-reinforced composite grid connectors used in combination with rigid insulation in concrete sandwich panel construction. The criteria are intended to standardize testing and evaluation of the interaction between concrete and composite shear connectors so manufacturers can provide consistent results, and the data pool generated by standardized testing can support the formulation of design assumptions.

This study presents the characteristics of municipal solid waste (MSW) incineration ash obtained from an electric energy generation plant and evaluates the MSW ash applicability in base road pavement layers through the mixture of ash with a nonlateritic regional clay soil. Chemical, physical, and mechanical tests and the mechanistic-empirical design for a typical pavement structure were carried out on the pure soil and also in the soil mixture with the addition of different ash content (20 and 40%). Fly ash reduced the expansion of the material, showing an increase in the California bearing ratio (CBR) and resilient modulus value. The results are satisfactory, depending on the content and type of ash used, highlighting the positive work of MSW fly ash for its use in base road pavement layers.

Pervious concrete pavements (PCP) are increasingly recognized and used as a best management practice to control stormwater runoff and for low-volume traffic. However, there are limited studies on the structural integrity of the PCP section on performance under vehicular loads. This study investigated the mechanical properties of field samples and the structural integrity of PCP when subjected to traffic loads using the falling weight deflectometer (FWD). The compressive strength for cored samples from the field installation was about 11.5 MPa with an average unit weight of $\mathrm{1,792}\mathrm{kg}/{\mathrm{m}}^3$. The deflection of the PCP sections at the load application point was about 1.7 to 4 times of the impervious concrete section, dependent on the subbase characterization. The composition of the PCP subbase materials and the compaction effort of the layers significantly affected the deflection. Back-calculation analysis showed that the loosely compacted subbase layers had lower elastic moduli and exhibited higher deflection responses, which compromised the structural integrity of the PCP systems to traffic loadings.

Regular use of artificial neural networks (ANN) analysis for predicting the vertical swelling percentage of expansive clays may lead to inappropriate results in terms of their geophysical behavior. This paper presents two new ANN Models derived from a two-stage procedure. The models were estimated using the same data set from the previous paper, and their statistical fit was clearly found to be superior in comparison to the previous models. Furthermore, one of these two models exhibited the expected geophysical behavior. As this new ANN Model yields higher predicted swelling-percentage values, it can definitely be regarded as a preferable one in the sense of enlarging the safety margin in heave calculations.