Journal of Materials in Civil Engineering

The experimental results of five concrete mixes subjected to high temperatures are presented in this paper with the aim of highlighting explosive spalling. The specimens were subjected to heating-cooling cycles from room temperature to 150, 300, 450, or 600°C. Two levels of heating rates (i.e., 0.1 and $1°\mathrm{C}/\min$) with a fixed time of one hour at the maximum temperature and a free cooling were imposed. The experimental results showed a link between the evolution of the thermal gradient in the specimens and the specimens’ weight losses. The results also showed that the thermal stability of the concrete mixes was a function of the water to cement ratio, heating rate, and specimen dimensions. The scale effect on the spalling phenomenon was demonstrated, and a critical temperature was determined. The factors leading to the explosive spalling of the concrete were studied and identified as (1) low permeability, (2) weak water departure from the concrete, and (3) an increase of the thermal gradient. It appeared that the thermal gradient (i.e., thermal stress) alone could not explain the explosive spalling of concrete.

An extensive field investigation was carried out to determine the properties of subgrade soils treated with lime in pavements that had been in service for at least five years. Six sites were selected for the field tests. At each site, standard penetration test (SPT), dynamic cone penetration test (DCPT), and falling weight deflectometer (FWD) tests were performed to evaluate the in situ stiffness and/or strength properties of the lime-treated subgrade. In addition, laboratory tests on soil samples taken from the SPT spoon were done to obtain index properties. The long-term performance of the subgrade was evaluated by comparing the soil indexes and stiffness and/or strength properties of the lime-treated subgrade soil with those of the natural soil. In addition, pH, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) tests were conducted for both lime-treated and natural soils. The field and laboratory investigation showed that (1) the lime remains in the soil even after 11 years of service of the road; (2) the addition of lime decreases the plasticity of the soil and increases its California bearing ration (CBR); and (3) the construction quality determined from the field tests was highly variable.

In this paper, the results of laboratory investigations into the time development of the shrinkage of polypropylene fiber-reinforced high-performance concrete have been analyzed. The volumetric content of polypropylene fibers contained in the investigated concretes varied from 0 to 0.75%. Within this context, the influence of both dry and previously moistened polypropylene fibers added to the concrete on the shrinkage of the composites was examined. Electronic measurements conducted from the beginning of the hardening of the concrete also covered the early stage of autogenous shrinkage that, in high-performance composites, accounts for a significant part of total shrinkage. To compare the shrinkage of fiber-reinforced concrete with that of a comparable concrete without polypropylene fibers, the shrinkage of such a comparable concrete without fibers was also included in the measurements. The measurement results of the shrinkage of polypropylene fiber-reinforced concrete and of a comparable concrete without polypropylene fibers, as presented graphically in this paper, clearly show that the autogenous as well as the total shrinkage of fiber-reinforced concrete is less than the shrinkage of a comparable concrete without fibers. By increasing the content of the fibers up to 0.5% of the volume of the composite, the shrinkage of the fiber-reinforced concrete was considerably reduced, whereas with further increasing of the fiber content, the shrinkage reduction rate became relatively insignificant. The concrete that had been reinforced by previously moistened polypropylene fibers, which served as an internal water reserve, exhibited a lesser degree of early autogenous shrinkage than the concrete that had been reinforced by dry polypropylene fibers. The drying shrinkage of high-performance concrete, reinforced by previously moistened polypropylene fibers, was, however, approximately twice as large as that of dry polypropylene fiber-reinforced high-performance concrete. Whereas the workability of the composite deteriorated considerably already in the case of a volumetric content of moistened polypropylene fibers greater than 0.25%, in the case of the use of dry polypropylene fibers, this deterioration was even more conspicuous.

Incorporation of rubber particles in portland cement concrete is an effective way of consuming waste rubber. This paper presents results of a study on the fatigue properties of plain concrete, rubberized concrete, and polypropylene fiber (PPF) reinforced rubberized concrete. Fatigue tests demonstrate that the inclusion of 60-kg rubber particles in $1{\mathrm{m}}^3$ concrete can greatly increase the fatigue life of concrete and that the addition of PPF to rubberized concrete can further enhance the fatigue life. The S-N equations for the three types of concrete are obtained by linear regression. Analyzing the acoustic emission (AE) signals recorded during the fatigue test reveals that both the activity and intensity of AE signals detected in rubberized concrete are much lower than in plain concrete. Good linear correlation between the hit and the minimum strain is observed for both concretes. Analyzing the distribution of energy during the cyclic loading shows that the fatigue process of concretes can be separated into three stages, which correspond to the initiation, the steady propagation, and the coalescence of microcracks to macrocracks, respectively. By analyzing the Fecility effect, the difference in the damage process between rubberized concrete and plain concrete is further examined. This investigation demonstrates that the health condition of a concrete under repeated loading can be assessed by real-time monitoring of AE activity and energy with the help of the AE technique.

The temperature of the existing asphalt pavement, which is to be recycled, would change from a low morning temperature of the spring/fall season to a high afternoon temperature of summer. However, most agencies do not consider the temperature of the reclaimed asphalt pavement (RAP) materials when they design cold in-place recycling using foamed asphalt (CIR-foam) mixtures. The main objective of this research is to determine whether the temperature of RAP materials would affect the optimum foamed asphalt content (FAC), which would produce the highest wet indirect tensile strength. On the basis of the limited laboratory test results, the temperature of RAP materials would have a significant impact on the wet indirect tensile strength of CIR-foam mixtures. This research supports the field reduction of FAC up to 0.5% when the RAP temperature reaches up to 55°C. The change in the wet indirect tensile strength caused by RAP temperatures was not sufficient to warrant a design method change. Also, improved compaction is expected with RAP materials with higher temperatures. It is recommended that the CIR-foam mix design should be performed using RAP materials heated to an anticipated temperature of the existing asphalt pavement in the field.

A mixture of soil-cement and acrylic resin is used to improve the engineering properties of the soil for construction. This paper presents the results of an investigation into the mechanical behavior of soil-cement mixtures with different percentages of acrylic resin. A series of experiments was conducted on mixtures of soil-cement and soil-cement-resin with different percentages of two different resins. The results show that by increasing the cement content in the soil-cement mixture, the maximum dry density increases, and the optimum water content decreases in compaction tests. Compressive strength tests on soil-cement show that the increase in strength depends on the cement content and the curing time. The results also indicate that the strength of soil-cement is increased considerably by adding acrylic resin as an additive material. For a given cement content, the increase in shear strength is a function of curing time and the percentage of resin.

The use of reclaimed asphalt pavement (RAP) materials in road construction has been proven to reduce both the amount of construction debris disposed of in urban landfills and the rate of depletion of natural resources. However, source-dependent product variability, federal and local environmental regulation, and deficient strength-stiffness characteristics often limit RAP applications in road bases. These limitations have led to new research efforts aimed at exploring novel, cost-effective, chemical and/or mechanical stabilization methods to treat RAP materials before their reuse in pavement construction. In this work, a series of tests were performed on RAP aggregate materials treated with different dosages of portland type I/II cement and with alkali-resistant glass fibers. Tests include permeability, leachate, unconfined compression, and small-strain shear moduli through resonant column testing. Leachate tests include pH, total and volatile dissolved solids, total and volatile suspended solids, and turbidity. Test results confirm the potential of cement-fiber-treated RAP material as an environmentally and structurally sound alternative to nonbonded materials for base and subbase applications in pavement engineering. A companion paper presents the results from a comprehensive repeated-load triaxial test program to investigate the resilient modulus characteristics of cement-treated RAP.

The use of reclaimed asphalt pavement (RAP) aggregate materials in road construction reduces natural resource depletion and promotes the recycling of RAP materials for other applications. However, product variability and low resilient moduli characteristics often limit RAP applications in road bases. Stabilization of RAP materials with cement was hence attempted in a research study to evaluate the effectiveness of cement treatments in enhancing resilient characteristics of RAP aggregates. The present paper describes the results from a series of resilient modulus tests that were conducted in a laboratory environment using a repeated load triaxial test setup. The effects of three different cement dosages and various confining and deviatoric stress levels on the resilient modulus ($M_R$) response of treated RAP materials were studied. $M_R$ values of untreated and cement-treated RAP aggregates ranged from 180 to 340 MPa and 200 to 515 MPa, respectively, which reveal the enhancements with cement treatment. Regression modeling analyses of $M_R$ test results, by using two- and three-parameter models, are also presented. The analyses show that both models are reasonably capable of capturing the effects of stress levels on treated RAP resilient properties. Test results were also analyzed to determine structural coefficients for pavement design purposes, which ranged from 0.16 to 0.22, suggesting a greater structural support of cement-treated RAP layers when compared with untreated aggregates.

Most investigations dealing with research on shear focus on concrete members such as reinforced concrete (RC) and prestressed concrete (PC) beams, columns, and slabs. It is difficult for such investigations, which include effects of reinforcing materials and so on, to evaluate shear cracking load in detail. Cracking caused by shear, however, may be a significant consideration for durability evaluation of concrete structures. Pure shear strength is an important property for estimation of cracking because shear failure is caused by fracture of the element. A simple test setup that employs only a universal testing machine has been found to be suitable for obtaining the pure shear cracking strength of concrete without reinforcement. The purpose of the study is to reevaluate the pure shear cracking strength property of plain concrete elements through testing. Based on laboratory testing, it is reconfirmed that reinforcement has little influence on the pure shear cracking strength. However, the shear cracking strength is strongly related to tensile strength and Poisson’s ratio.

Since the linear elastic layer solution for the layered systems was developed in the 1940s, the linear elastic layer analysis has been systemized and widely used for the designs of roadway pavements as a tool for evaluating the structural soundness of pavements. The primary assumption made in the analysis is that the layered system consisting of materials that are linear elastic; and hence, an application of the elastic layer analysis to asphalt mixtures, which is a well-known viscoelastic material, has been limited. Therefore, the intention of the study was to derive a viscoelastic solution able to take into account the time- and rate-dependent nature of the viscoelastic materials in the multilayered system. In this paper, a linear viscoelastic solution for the multilayered system subjected to a cylindrical unit step (static) load was derived from the elastic solution by using the principle of elastic-viscoelastic correspondence and the numerical inversion of Laplace transforms. The solution was then extended to simulating pavement responses subjected to a moving load by employing the Boltzmann’s superposition principle. The soundness of output from the viscoelastic solution was confirmed by comparing them to those of the finite-element analysis (FEA). Compared to the time and effort required in FEA, the analysis based on the viscoelastic solution was much faster. Therefore, it is expected that the viscoelastic solutions derived in this study will be an effective tool for the design of flexible pavements.

Different countries adopt different values of thermal expansion coefficients for steel cables in their design specifications, which results in the inconsistency for the design of prestressed structures. Therefore, a systematic study was conducted analytically and experimentally on thermal expansion mechanism of steel cables in this paper. First, the thermal expansion mechanism of steel cables was proposed, and the evaluation approach on the linear thermal expansion coefficient of steel cables was developed. The study identified the parameters that significantly affected the thermal expansion coefficient. After that, six types of steel-wire rope cables were tested by a thermal expansion coefficient measuring instrument. The identified parameters of the thermal expansion coefficient for these steel-wire rope cables were examined to show the effectiveness of the proposed approach. The analytical analysis further showed that the linear thermal expansion coefficients of these steel cables decreased with the lay pitch of the steel wires increasing, but the coefficients increased with the diameter of the steel wires increasing. Because the explicit expression of the analytical formula for the thermal expansion coefficients was very complicated, an advanced nonlinear finite-element model (FEM) was established to evaluate the thermal expansion coefficients of steel cables under idealized conditions by using the ANSYS software package. The analysis showed that the test result, the analytical result, and the numerical result were consistent, which exhibited that the FEM was effective to simulate the expansion of steel cables. In addition, 14 types of steel cables were tested. The tested steel cables included steel-wire rope cable, steel strand cable, and steel tendon cable. The thermal expansion coefficients were as follows: the steel-wire rope cable was $1.92\times {10}^{-5}/°\mathrm{C}$; the steel strand cable was $1.38\times {10}^{-5}/°\mathrm{C}$; the steel tendon cable was $1.87\times {10}^{-5}/°\mathrm{C}$; and the steel rod was $1.19\times {10}^{-5}/°\mathrm{C}$. The analytical and experimental results can provide a guideline for the relevant study on prestressed structures.

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are quickly becoming two of the most promising nanomaterials because of their unique mechanical properties. The size and aspect ratio of CNFs and CNTs mean that they can be distributed on a much finer scale than commonly used microreinforcing fibers. As a result, microcracks are interrupted much more quickly during propagation in a nanoreinforced matrix, producing much smaller crack widths at the point of first contact between the moving crack front and the reinforcement. In this study, untreated CNTs and CNFs are added to cement matrix composites in concentrations of 0.1 and 0.2% by weight of cement. The nanofilaments are dispersed by using an ultrasonic mixer and then cast into molds. Each specimen is tested in a custom-made three-point flexural test fixture to record its mechanical properties; namely, the Young’s modulus, flexural strength, ultimate strain capacity, and fracture toughness, at 7, 14, and 28 days. A scanning electron microscope (SEM) is used to discern the difference between crack bridging and fiber pullout. Test results show that the strength, ductility, and fracture toughness can be improved with the addition of low concentrations of either CNTs or CNFs.

As focus is drawn toward more sustainable construction practices, use of bamboo as a structural building material is growing as a topic of interest. It is highly renewable, has low-embodied energy, and has the highest strength-to-weight ratio of steel, concrete, and timber. Composite lumber made from bamboo, termed laminated bamboo lumber (LBL), has gained the particular interest of researchers and practitioners of late, since it has bamboo’s mechanical properties but can be manufactured in well-defined dimensions, similar to commercially available wood products. Its primary drawbacks are that it is difficult to connect and is more costly than competing, locally available materials. This paper presents the advantages and challenges of embracing LBL as an alternative building material. Experimental and analytical data on production, performance, economics, and environmental impact of bamboo and LBL are reviewed, synthesized, and further analyzed to present an overview of the viability of using bamboo as a structural material in North America.

Although the ingress of chloride into concrete is normally controlled by absorption and diffusion mechanisms, external loads can affect this process by modifying the microstructure of concrete. To predict the chloride ingress into real structures under service conditions, the effects of external loads on the chloride transport should be considered. In this paper, the effects of compressive and flexural loads on chloride transport were studied. The experimental results indicated that the chloride concentration and apparent chloride diffusion coefficient $D_{\mathrm{app}}$ decreased with the increase of the compressive stress, up to 55% of the compressive strength, and they increased with the increase of the flexural stress. On the basis of these results, a model for predicting the chloride diffusion process under different loading conditions is established by accounting for various parameters, such as stress level, water-cement ratio, curing time, temperature, concrete age, humidity, and chloride diffusion coefficient. The validation of the proposed model indicated good correlation between the predicted chloride diffusion coefficients and the experimental results.

Corrosive drywall, also known as Chinese drywall, emits gases that cause corrosion of copper components within a building. Corrosive drywall has a strontium content that is often different from tested drywall sourced in North America. The strontium content can be used as a marker for the presence of corrosive drywall, in conjunction with visual evaluation of nearby copper components and confirmatory laboratory tests. This paper presents a methodology for on-site testing of the strontium content of drywall by X-ray fluorescence, along with supplemental laboratory testing of selected samples by exposure-testing of copper coupons. Testing has indicated populations of noncorrosive drywall with strontium contents both lower than and greater than that of the affected drywall.

The corrosion behavior of steel in cracked ordinary portland cement (OPC) and portland pozzolana cement (PPC) concretes when exposed to a chloride-rich environment is presented here. Three water-to-cement ($\mathrm{w}/\mathrm{c}$) ratios, and precrack widths of 0.2 and 0.4 mm were studied. A simple $U$-shaped specimen with precracks under flexural load was used in the study; the specimen has a deformed steel bar of 12 mm diameter placed at the bottom with 20 mm clear cover. Measurements made include chloride ion penetrability, sorptivity, half-cell potential, resistivity, total charge passed and gravimetric weight loss. The chloride ion penetrability of PPC was found to be nearly three times lower than that of OPC. The reduction in the gravimetric weight loss of rebars in PPC with respect to those in OPC is in the range of about 1.5 to 2.0 in the case of precracked concretes. The reduction in diameter (i.e., caused by pitting) is higher for OPCs. Studies showed that PPC is significantly superior to the corresponding uncracked OPCs in terms of corrosion inhibition even under cracked conditions.

In the experiment, a heat-reflective coating (HRC) was applied to the surface of asphalt pavement. The coating temperature reduction principle and the mechanism to mitigate the urban heat island effect (UHI) were explored by analyzing the material characteristics and features of atmospheric absorption spectrum. HRC features a good waterproof ability, strong oil resistance, abrasion resistance, and aging resistance. When it was painted on the surface of the dense-graded asphalt concrete, the pavement temperature could be reduced by approximately 9°C in hot seasons. The comprehensive pavement performance was evaluated through the following tests: antiskid, accelerated abrasion, freeze-thaw cycle, and permeability. The results show the asphalt concrete pavement with adopting HRC has a strong abrasion resistance, a good resistance to temperature fluctuation, and significantly reduces water damage. The skid-resistant ceramic granular should be added in the dense-graded asphalt pavement with HRC, which was shown to greatly improve the antiskid capability.

Early age cracking is usually the result of internal tensile stresses induced by self-desiccation shrinkage (SDS) rather than external loading. Hence, the prediction of early age cracking risk is strongly linked to autogenous shrinkage development. Both the ultimate magnitude of shrinkage and the time zero (TZ), at which shrinkage starts to develop an internal stress, could be decisive for high-performance concrete (HPC) durability. The moment TZ can be considered as the borderline between autoplastic shrinkage and effective shrinkage. Deformation rate curves might be used as a framework to identify the three main phases of hardening that occur in cement paste as hydration progresses, and the development rate of autogenous shrinkage (AS). The present study proposes starting shrinkage measurement (autogenous or total) from the moment when the rate of deformation reaches its maximum value (the first peak in the curve) and the shrinkage strain rate curve pattern changes sharply, or at the end of plastic-shrinkage. To determine the TZ with more accuracy and predict the critical moment when internal stresses may start to develop, continuous shrinkage measurement was carried out on different HPC mixtures designed with three water-to-binder ratios ($w/b$) of 0.26, 0.30, and 0.35, using three binder types. Results have shown that the rate of deformation development at an early age would be a reliable method to distinguish the three main phases of cement hydration reaction: liquid, semiliquid/transition, and hardened. The rate of deformation evolution may also indicate the moment when shrinkage strains evolve quickly and start to build up an internal tensile stress that could lead to cracking. The new method proposed, based on the development of the rate of deformation, has revealed itself to be highly efficient for adequate determination of TZ and could be used for all concrete types independently of specimen size.

Nitrogen oxides (${\mathrm{NO}}_{\mathrm{x}}$) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed by using a photocatalyst such as titanium dioxide (${\mathrm{TiO}}_2$). The main objective of this study was to evaluate the environmental effectiveness of ${\mathrm{TiO}}_2$ coating in photodegrading mixed ${\mathrm{NO}}_2$ and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and ${\mathrm{NO}}_2/{\mathrm{NO}}_{\mathrm{x}}$ ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little effect on ${\mathrm{NO}}_{\mathrm{x}}$ removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with ${\mathrm{NO}}_{\mathrm{x}}$ contact with the photocatalytic surface.

The development and optimization of underwater concrete (UWC) characteristics (i.e., washout loss, threshold water head prior to concrete deterioration, and residual compressive strength) require considerable time, effort, and energy for testing. This paper seeks to propose a new testing method developed on the basis of the concrete-equivalent-mortar (CEM) approach to optimize and simplify evaluating the effect of mixture composition on washout characteristics of UWC cast under different conditions. Washout of CEM was determined using an adapted version of the commonly used CRD C61 test method as well as by simulation using an air-pressurized tube measuring 300 mm in height. Test results showed that CEM mixtures proportioned without coarse aggregates can adequately be used to predict washout characteristics of UWC. Statistical regression models were developed to enable direct estimation of washout loss and threshold water head of CEM and UWC mixtures.

Microstructural damage induced by sulfate attack in concrete is a cause of primary concern in building foundations and other structures. Most research focuses on prevention. In contrast, the concept of damage recovery has not received significant attention. Studies were conducted using alumina-coated-silica nanoparticles to facilitate an electrochemical recovery of strength. Treatments were applied to extract sulfates while the nanoparticles were being injected. Initial sodium sulfate exposure on cylindrical concrete specimens was conducted for a period of 30 days. This exposure induced body cracking and microstructural damage. The specimens were subjected to electrokinetic treatment using a constant current density of $1\mathrm{A}/{\mathrm{m}}^2$ for 7 days. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis revealed significant sulfate content in the sulfate-exposed specimens that was not detected in the treated cases. Raman spectroscopy also indicated a higher C-S-H among the treated specimens, and MIP analysis indicated that the treated specimens exhibited a 40% reduction in threshold pore size. The treated specimens also exhibited a 33% increase in compressive strength while the volume porosity decreased by one-third. These findings indicated that the electrokinetic recovery treatment removed sulfates, reduced the volume porosity, and restored a significant amount of compressive strength.

Granulated slag from metal industries and fly ash from the combustion of coal are industrial by-products that have been used widely as mineral admixtures in normal and high-strength concrete. Because of the reaction between calcium hydroxide and fly ash or slag, the hydration of concrete containing fly ash or slag is much more complex than that of portland cement. In this paper, the production of calcium hydroxide in cement hydration and its consumption in the reaction of mineral admixtures is considered to develop a numerical model that simulates the hydration of concrete containing fly ash or slag. The properties of concrete incorporating fly ash or slag, such as the adiabatic temperature increase, chemically bound water, reaction degree of mineral admixture, and the compressive strength, are determined by the contribution of both cement hydration and the reaction of the mineral admixtures. The proposed model is verified with experimental data from concrete with different water to cement ratios and mineral admixture substitution ratios.

The performance of sucrose in cement hydration, including both the early structure formation and further development of cement paste under different curing temperatures, was studied by measures of setting time, heat evolution, resistivity evolution, compressive strength, and porosity. The results showed that there was a critical dosage ($T_0$) of sucrose. When the dosage was less than $T_0$, the retarding effect was enhanced by increasing the dosage. Greater than $T_0$, sucrose became less retarding and even became accelerating. Increasing the curing temperature decreased the critical dosage ($T_0$). When the dosage was less than 0.08%, sucrose showed less retarding effect at 40°C than at 20°C, but better retarding effect at the dosage of 0.08–0.2%. The strength development of cement paste after the induction period was accelerated at 40°C than at 20°C, although 0.08% sucrose prolonged the induction period.