Journal of Materials in Civil Engineering

Paving geotextiles are becoming increasingly used in highway construction overlays in order to recover cracked asphalt pavements. In antireflective cracking systems, the geosynthetic should have the ability to absorb and retain the asphalt tack coat to effectively bond the system to the existing pavement and overlay. However, the type and rate of tack coat impregnation can significantly influence the reinforcement mechanism, potentially leading to early overlay failure. Stiffness has been identified as the governing property to quantify the potential contribution of the interlayer to the asphalt overlay strength. In addition, the overall behavior of reinforced asphalt pavements may also be incorporated with an increased tensile strength of the geosynthetic. With the purpose of quantifying the often significant changes in the mechanical behavior of paving geosynthetics that occur after bitumen impregnation, a series of tensile strength tests were conducted in this study using nonwoven geotextiles with different rates of asphalt emulsion. Evaluation of the geosynthetics changes in tensile strength and tensile stiffness with increasing tack coat rates provides insight on the identification of an optimum bitumen dosage for these materials. A tack coat rate equal to the asphalt retention capacity was specifically evaluated in this study and was generally found to be the optimum rate that leads to the highest tensile strength and stiffness of impregnated of geotextiles.

Foamed asphalt binders are increasingly being used to produce warm mix asphalt. This paper presents the findings from a study conducted to (1) identify a repeatable and accurate method to characterize the quality of asphalt binder foams, and (2) use this method to evaluate the influence of water content, binder type, and foaming device on the quality of foamed binders. Laser and ultrasonic distance-measuring tools were used in combination with digital imaging of the foamed surface to quantify and better understand the expansion and decay of foamed asphalt binders over time. Measurements obtained from these methods were used to evaluate the extent and stability of foams produced using three different asphalt binders at three water contents and two laboratory foaming devices. Rheological properties and moisture content of selected binder residues were also measured. Results indicate that both the laser- and ultrasonic-based methods were promising in terms of their ability to provide a repeatable and detailed history of the change in volume of the foamed asphalt binder as the foam collapses. It was also shown that water content and binder type have a significant influence on the maximum expansion ratio and rate of collapse of foams. Higher water contents were associated with higher expansion ratios but also faster rates of collapse. The two foaming devices used in this study produced foams with similar properties. Rheological tests conducted on foamed binder residues revealed that the foaming process slightly increased the high temperature continuous performance grade (PG) of the binder.

High-strength concretes (HSC) were prepared with five different binder contents, each of which had several silica fume (SF) ratios (0–15%). The compressive strength was determined at 3, 7, and 28 days, resulting in a total of 60 sets of data. In a fuzzy logic (FL) algorithm, three input variables (SF content, binder content, and age) and the output variable (compressive strength) were fuzzified using triangular membership functions. A total of 24 fuzzy rules were inferred from 60% of the data. Moreover, the FL model was tested against an artificial neural networks (ANNs) model. The results show that FL can successfully be applied to predict the compressive strength of HSC. Three input variables were sufficient to obtain accurate results. The operators used in constructing the FL model were found to be appropriate for compressive strength prediction. The performance of FL was comparable to that of ANN. The extrapolation capability of FL and ANNs were found to be satisfactory.

The aim of this study is to investigate the performance of geopolymer concrete prepared using blended ash of pulverized fuel ash and palm oil fuel ash from agroindustrial waste along with alkaline activators when exposed to a 5% sodium sulphate solution for up to 18 months. Ordinary portland cement (OPC) concrete was also prepared as the control concrete. The main parameters studied were the evaluation of mass change, compressive strength, products of degradation, and microstructural changes. The deterioration was examined using X-ray diffraction (XRD), a Fourier transform infrared spectroscopy (FTIR), a thermogravimetry analyzer (TGA), and a field emission scanning electron microscope (FESEM). The results of geopolymer and OPC concretes were compared and discussed. The compressive strength of geopolymer concrete, when exposed to a 5% sodium sulphate solution for more than 1 year, was superior to that of OPC concrete. These materials could be used for making sulphate-resistant concretes, attributable to a more stable cross-linked aluminosilicate polymer structure formed in the geopolymer concrete.

Cold in-place recycling (CIR) has been increasingly applied in many areas of China, but there is no widely accepted method for the mix design of CIR. The compaction of cold recycled mixtures in the field varies significantly in different working conditions. It is therefore necessary to study the compaction characteristics of cold recycled mixtures. In this study, the primary compactibility energy index (PCEI) and secondary compactibility energy index (SCEI) of CIR were defined from the gyration compaction curve to evaluate the effect of compaction temperature, asphalt emulsion content, moisture content, aggregate gradation, and initial cure time. The control variable method was adopted to conduct the CIR compaction tests. The compaction parameters of CIR were obtained and analyzed statistically. The results from this study indicate that the SCEI of cold recycled mixtures is significantly affected by all variables and the regression of $N_{\text{des}}$ is linear relative to the compaction temperature and asphalt emulsion content. The effect of compaction temperature is much more significant than the other factors. Based on the effect of moisture content on PCEI and SCEI, a new method to determine the optimum moisture content of CIR is provided. The effect of initial cure time actually represents the effect of moisture content to some extent.

Self-compacting concrete (SCC) has become increasingly popular in recent years, particularly in constructing heavily reinforced concrete structures cast with a stay-in-place form (e.g., concrete-filled tubular columns) where the quality of concrete is difficult to control and/or examine. When used in fiber-reinforced polymer (FRP) tubes, the SCC is subjected to confinement from the FRP tube. While many studies have been conducted on confined normal concrete (NC), research on confined SCC has been very limited. The few existing studies on confined SCC (e.g., steel-confined SCC and FRP-confined SCC) have shown that the behavior of confined SCC may be different from that of confined NC of the same unconfined strength. Against this background, this paper presents the results of a series of axial compression tests conducted to gain a better understanding of the behavior of FRP-confined SCC. The test variables included the concrete strength as well as the type and thickness of the FRP jacket. Similar to FRP-confined NC, the present tests showed that the strength and ductility of SCC can also be significantly enhanced by FRP confinement, and its stress-strain curve also has a bilinear shape. A comparison between the test results and an accurate stress-strain model developed for FRP-confined NC is also presented. The comparison shows that the behavior of FRP-confined SCC is generally similar to that of FRP-confined NC, although the lateral expansion of the former appears to be a little larger.

Although uncertainties in material properties have been addressed in the design of flexible pavements, most current modeling techniques assume that pavement layers are homogeneous. The paper addresses the influence of the spatial variability of the resilient moduli of pavement layers by evaluating the effect of the variance and correlation length on the pavement responses to loading. The integration of the spatially varying log-normal random field with the finite-difference method has been achieved through an exponential autocorrelation function. The variation in the correlation length was found to have a marginal effect on the mean values of the critical strains and a noticeable effect on the standard deviation which decreases with decreases in correlation length. This reduction in the variance arises because of the spatial averaging phenomenon over the softer and stiffer zones generated because of spatial variability. The increase in the mean value of critical strains with decreasing correlation length, although minor, illustrates that pavement performance is adversely affected by the presence of spatially varying layers. The study also confirmed that the higher the variability in the pavement layer moduli, introduced through a higher value of coefficient of variation (COV), the higher the variability in the pavement response. The study concludes that ignoring spatial variability by modeling the pavement layers as homogeneous that have very short correlation lengths can result in the underestimation of the critical strains and thus an inaccurate assessment of the pavement performance.

The interesting properties of shape memory alloys (SMA) have increased the investigation, study, and development of possible applications of these alloys in the field of civil engineering. This paper presents a state of the knowledge of existing studies and applications of SMAs in distinguishing their properties: superelasticity, shape memory, and damping. The main objective of this paper is to discuss the advantages of concrete structures and improvements in their behavior when using SMAs and to collect critical unsolved aspects of SMAs that could be a starting point for the development of future research in this field.

Techniques for making epoxy-coated reinforcement more corrosion resistant, including epoxies with increased adhesion to the steel; concrete with a decreased water cement ratio; concrete containing calcium nitrite or one of two organic corrosion inhibitors; bars with a primer coating containing microencapsulated calcium nitrite applied prior to epoxy application; and bars coated with zinc prior to epoxy application are compared based on the chloride content required to initiate corrosion and corrosion losses using the southern exposure and cracked beam tests. The coatings on all bars are penetrated prior to testing to simulate damage in the field. The results indicate that, even when damaged, conventional epoxy coatings result in much higher concrete chloride contents at corrosion initiation and much lower corrosion losses than exhibited by conventional reinforcement. A reduced water-cement ratio, corrosion inhibitors, and the primer coating containing microencapsulated calcium nitrite provide protection in uncracked but less or no protection in cracked concrete. The bars coated with zinc prior to epoxy application exhibit relatively high corrosion rates because of preferential losses to the zinc, and no improvement in corrosion performance is observed for epoxies with increased adhesion.

Lightweight coarse aggregate from five sources found in the United Arab Emirates (UAE) were previously evaluated. The evaluation focused on influence of the physical properties of the aggregates on strength development. Target unit weight less than $\mathrm{2,000}\mathrm{kg}/{\mathrm{m}}^3$, compressive strength of 40 MPa or higher, and achieving the flowability requirements for self-consolidating concrete (SCC) were the evaluation criteria considered during the development. Aggregate from three sources met the evaluation criteria; however, one of the sources was no longer available in UAE. Therefore, an extensive investigation was conducted to evaluate properties of the other two sources, especially durability related properties. In this paper, results of the compressive, flexure, splitting tensile strength, and modulus of elasticity are presented and discussed. In addition, scanning electron microscope (SEM) scans and rapid chloride permeability tests (RCPT) were conducted. Results showed that both sources met the requirements for structural applications. However, one source showed better performance in all tests, which was supported by the examination of the microstructure of the hardened concrete.

A new experimental method is proposed for assessing the cracking tendency of concrete using elliptical ring specimens subject to restrained shrinkage. To explore the mechanism of this method, a numerical model is developed to analyze stress development and crack initiation in concrete rings in which the effect of concrete shrinkage is simulated by a fictitious temperature drop applied on concrete causing the same strain as that induced by shrinkage. Stress developed in a concrete ring is then obtained through a combined thermal and structural analysis. Based on the maximum tensile stress cracking criterion, numerical results are in accordance with experimental results on cracking age for a range of circular and elliptical concrete rings with different geometries. Geometrical factor, i.e., the ratio between the major and minor semiaxes of an elliptical ring, is the main factor that affects tensile stress developed and consequently concrete cracking age in restrained ring specimens. Elliptical rings with appropriate geometry can enable crack initiation much earlier than circular rings, which consequently are able to accelerate the ring test for assessing the cracking potential of concrete. Discussions are made on effects of ring geometry on features of cracking, crack position, and stress development in concrete rings subject to restrained shrinkage to further explore the mechanism of the elliptical ring test for assessing the cracking potential of concrete.

The thermal stress and tensile creep of early-age concrete that occur during the exothermic chemical reactions between water and cement may result in harmful cracks. Heat of hydration and creep of early-age concrete are described in this paper. An equation for evaluating hydration degree is presented, and a finite-element program for a thermal analysis of hydration heat is developed. Based on the theory of creep and heat of hydration of early-age concrete, the temperature and strains in a subway station structure were simulated using the finite element method. The predicted results are in good agreement with the site-measured data. A parametric analysis of ambient temperature and concrete slab thickness was also conducted. The analysis results indicate that it is not advantageous to reduce the temperature difference, whether the ambient temperature is too high or too low. Creep does not always reduce the undesirable tensile stresses; it may increase structural tensile stresses during the early-age stage of concrete.

Crushed waste glass bottles accumulating in stockpiles around New Zealand are an environmental concern, but also provide an available resource for potential use in concrete by partially replacing coarse and fine natural aggregates. The objective of this study was to test the fundamental properties of concrete that utilized 20% waste glass as a partial replacement for coarse and fine natural aggregates. It is demonstrated that the waste glass has a negative effect on concrete properties, including air content, compressive strength, and flexural strength, while also contributing to the problematic alkali-silica reaction. The use of supplementary cementitious materials such as fly ash or microsilica was found to improve the properties of concrete that utilized waste glass, especially with regards to inhibiting the alkali-silica reaction, and hence it was established that waste glass should be used with either fly ash or microsilica mainly due to concerns regarding the development of the alkali-silica reaction caused by the waste glass trialed in this study.

The intent of this paper is to identify the basic physical laws governing particle kinematics in a shotcrete spray. This paper presents a governing equation based on Newton’s second law where nozzle and airflow characteristics, and particle features are used to predict impact velocity of the material exiting the nozzle. Experimental values obtained using high-speed imaging measurements on marbles and aggregate particles correlate well with the results of numerical simulations on a simplified spraying system. With the controlling parameters of particle kinematics fully understood, the analysis of the governing equations offers essential elements for nozzle optimization and new mix design investigations. This paper also addresses the necessity of broadening the investigation to the entire spray of particles exiting the nozzle for a complete understanding of the spraying process on placement mechanisms at a process scale.