Journal of Materials in Civil Engineering

The maintenance of asphalt pavement has become recognized as a critical issue in China. The objective of this study is to investigate the influence of using rejuvenator sealer materials on aged asphalt by means of laboratory analysis. First, asphalt binder first aged by rolling thin-film oven test and ultraviolet light. This aged asphalt was treated by two kinds of rejuvenator sealer materials. The performances of both aged binder and rejuvenator treated binder were evaluated by means of viscosity, temperature sweep, creep recovery, fatigue, and component analysis tests. The results indicated that both rejuvenator sealer materials can significantly decrease the viscosity and complex modulus of aged asphalt. Moreover, applying rejuvenator sealer materials can balance the asphaltene–maltene ratio of aged asphalt to some degree. Aged asphalt can be efficiently softened with the rejuvenator materials, which proves that rejuvenator sealer materials can be used for maintenance to improve the performance of existing pavements.

To overcome some inferior physical and mechanical properties of recycled aggregate concrete (RAC), an enhancing technique is presented in this paper to improve the performance of RAC by adding a promising chemical admixture, an atomic polymer technology (APT) in the form of a mesoporous inorganic polymer (MIP). The RAC samples with different added amounts of MIP were prepared, and their mechanical and physical properties were measured. Various basic material and durability properties, such as stiffness, strength, and early-age shrinkage, were evaluated. The smart piezoelectric cement modules as either sensors or actuators were fabricated, and they were embedded in concrete beams to monitor the early-age stiffness-gaining process of the RAC samples during its curing stage. The corresponding monitoring techniques based on wave propagation were developed and implemented, through which the gradually improved performance of RAC with increasingly added amounts of MIP was evaluated and the early-age condition of RAC during its curing period were monitored in situ. The findings on the improved mechanical properties of RAC with atomic polymer technology and condition assessment from an early age with smart piezoelectric cement modules will potentially promote widespread application of recycled concrete in engineering, improve the sustainability of RAC structures, and provide viable health-monitoring techniques for RAC structures.

Laboratory tests were conducted to evaluate the feasibility of recycling phosphorus slag into hot-mix asphalt (HMA) as mineral fillers. The elemental composition of phosphorus slag was analyzed by energy dispersive spectroscopy (EDS). The pH value, gradation, hydrophilic index, heat stability, and other properties related to mineral filler in asphalt mixture were also tested. The viscoelastic property of asphalt mastics containing phosphorus slag filler was tested by dynamic shear rheometer (DSR). Ground phosphorus slag was added into two HMAs including traditional dense grade mixture and gap-graded stone mastic asphalt (SMA). Moisture susceptibility and rutting potential tests were conducted to investigate the effects of phosphorus slag filler on the mixtures. Tests showed the pH of the slag was alkaline. It was also hydrophobic and stable at high temperature. Thus, it can be potentially used as an antistripping additive in asphalt mixture. The viscoelasticity test showed that phosphorus slag filler improved the stiffness of asphalt in the similar way as the traditional agriculture (Ag) lime mineral additive. The mixture performance tests indicated that phosphorus slag filler significantly increases the resistance of HMAs to rutting and moisture damage.

Sludge utilization has become the focus of sludge disposal, and this paper presents a study of using sludge, low-quality fly ash, and other raw materials from the Shanghai region to make high-strength ceramsite. The proportions of the mix and the firing conditions suitable to roast the calcined high-strength sludge ceramsite are discussed. The results show that pure sludge materials alone are not suitable for making high-strength ceramsite. High-strength sludge ceramsite was made with a silt–fly ash–waste glass powder of $60:35:5$ under a firing system with a preheating temperature of 600°C, a warm-up time of 20 min, a calcination temperature of 1,150°C, and a roasting time of 15 min. The high-strength sludge ceramsite provided particle strength of 7.1 MPa, apparent density of $\mathrm{1,580}\mathrm{kg}/{\mathrm{m}}^3$, and water absorption of 8.2%. All properties were better than the requirements in the national standards. In addition, the high-strength sludge ceramsite provides important environmental and social benefits due to its consumption of waste and industry by-products such as river sludge and low-quality fly ash.

Industry waste materials are commonly used in road engineering. In this study, crushed ceramic waste aggregates (CWAs) were utilized and added into asphalt mixtures to investigate their potential usage. A finite-element method (FEM) was employed first to examine the effect of material thermal conductivity on the temperature gradient of pavement structure. A significant effect of the surface layer’s conductivity in asphalt pavement on the temperatures (at the top and bottom positions of the middle layer) was found in model simulation. Next, the mix design for asphalt mixtures with different percentages of CWAs was developed, and their thermal properties were tested. It is concluded that asphalt mixtures with a reasonable substitution percentage of CWA can satisfy pavement performance requirements. The addition of CWAs can reduce the thermal conductivity of asphalt mixtures, which is proven helpful in reducing the temperature gradient of pavement. Finally, it is recommended that less than 40% CWA be added into asphalt mixtures to replace natural coarse aggregates considering its effect on the performance of mixtures.

Self-healing is one of the great potential processes for service-life extension of asphalt pavements. However, the underlying mechanism is not explained, and a proper way to measure it is not mentioned. It is necessary to understand the self-healing mechanism and to develop a setup to measure it. In this paper, the self-healing process was hypothesized as the reverse process of cracking. Three new test methods were developed to mimic the self-healing process of cracks in bituminous materials (including bitumen, mastics, and asphalt mixtures) in the laboratory. The results indicate that the proposed crack self-healing assessment methods are capable of ranking the self-healing capability of bituminous materials. The crack self-healing process contains two important phases, namely, crack closure and strength gain. The occurrence of these phases is dependent on healing time and temperature.

The main objective of this paper is to analyze the characteristics of electrically conductive asphalt concrete (ECAC) by adding multiplex electrically conductive materials. First, it is proved that all the mechanical properties of ECAC meet the design requisition in this study. The effects of filler type, filler content, and mixed fillers on the resistivity of asphalt concrete were then systematically investigated. Experimental results showed that the combination function of mixed fillers has appreciable advantages over single powder in electrical conductivity. Both laboratory and field tests were conducted to prove that the ECAC provides an efficient method for snow melting through direct current. In addition, an infrared imaging technology was used to assess the temperature field distribution. Furthermore, the effects of temperature, voltage, and temperature circulation on the resistance of ECAC were explained by the break and rebuild of conductive pathways. Finally, X-ray computed tomography provides insight into the mechanisms of conductivity enhancement for mixed fillers. It is shown that the conductive chain formed in ECAC largely depends on the conductive filler’s distribution in asphalt mortar.

The objective of this paper is to evaluate the healing capacity of steel wool–reinforced porous asphalt concrete. The healing is initiated with induction heating. Bending fracture tests on an elastic foundation are used to prove the healing mechanism. Porous asphalt concrete beams on an elastic foundation were fractured at 5°C; subsequently, they were heated with induction energy, and finally fractured again. The recovered fracture resistance of the beams was used as a healing indicator. Totally fractured porous asphalt beams can regain 78.8% of their bending resistance (strength) when induction heating is applied. It was also found that the optimal heating temperature is 85°C for porous asphalt beams to obtain the highest strength recovery. Reheating of the fractured beams does not decrease the recovery of the flexural resistance, which means that the heating can be repeated when cracks return. On the basis of these findings, it is expected that the healing potential of porous asphalt concrete and the durability of a porous asphalt pavement will be improved by induction heating.

Portland cement pervious concrete (PCPC) has been increasingly used in concrete pavements during recent years. In addition to strength and permeability, abrasion durability is another important property of PCPC. In this study, three laboratory abrasion test methods were investigated for their potential capability of evaluating the abrasion and raveling resistance of PCPC. The three tests are the Cantabro test, the loaded wheel abrasion test, and the surface abrasion test. To evaluate the three test methods, eight PCPC mixtures containing different sizes of coarse aggregates and additives were tested. The comparison of the three abrasion tests indicates that all three tests were fairly effective in differentiating between the PCPC mixtures. However, the results from the Cantabro test may not reflect the abrasion resistance of the mixtures because the failure of the specimens was caused by impact rather than abrasion. With studded wheels and increased wheel load, the loaded wheel abrasion test exhibited best sensitivity and sufficient repeatability. The surface abrasion test successfully differentiated the control mix from other mixtures, but failed to differentiate between the mixtures containing latex and/or fiber, which may be attributed to the unfavorably low weight loss values from this test.

${\mathrm{NO}}_{\mathrm{x}}$ gases affect the diurnal rise and fall of tropospheric ozone. By removing ${\mathrm{NO}}_{\mathrm{x}}$ gases through the use of titanium dioxide (${\mathrm{TiO}}_2$) photocatalytic materials, tropospheric ozone concentrations could be reduced. Recent developments related to the photocatalytic pollution reduction capabilities of ${\mathrm{TiO}}_2$ have led a movement to understand the material properties required to create construction materials which have the potential to reduce ${\mathrm{NO}}_{\mathrm{x}}$ air pollutants. A research program was undertaken to isolate variables that impact the kinetics of ${\mathrm{TiO}}_2$ reaction. Six ${\mathrm{TiO}}_2$ materials were tested for ${\mathrm{NO}}_{\mathrm{x}}$ removal efficiencies. The productive ${\mathrm{TiO}}_2$ materials were then tested at multiple concentrations to determine the effect of ultraviolet (UV) irradiance on their efficiency to reduce ${\mathrm{NO}}_{\mathrm{x}}$ air pollutants. It was found that specific anatase ${\mathrm{TiO}}_2$ phases manufactured and sized to have high levels of photocatalytic activity could reduce ${\mathrm{NO}}_{\mathrm{x}}$ air pollutants at high efficiencies. The ${\mathrm{NO}}_{\mathrm{x}}$ removal efficiency was 2.4 times higher at a UV irradiance of $1,300\mathrm{\mu W}/{\mathrm{cm}}^2$ than at $150\mathrm{\mu W}/{\mathrm{cm}}^2$, equivalent to a sunny or shady surface, respectively.

Semirigid pavement is a type of pavement structure in which a semirigid base layer, usually made up of cement-treated base (CTB) or cement-stabilized base (CSB), is overlaid with a top flexible layer of asphalt mixture. Because a considerable amount of fly ash or other waste materials can be used in CTB or CSB and less petroleum-based virgin asphalt binder is required, semirigid pavements are a type of environmentally friendly and sustainable pavement structure. This paper presents a new approach for semirigid pavement design in China based on the concept of surface deflection at the critical state of the top asphalt mixture layer. On the basis of results from an extensive survey of over 50 highway sections in eight provinces in China, a quantitative relationship was developed between allowable surface deflection at critical state of pavements and accumulative standard axle load, from which an allowable surface deflection at the end of pavement service life was recommended for semirigid asphalt pavements. A method was then proposed to convert the allowable deflection at the end of pavement service life to the design deflection at the initial state of pavements. Finally, a new Chinese design guide for semirigid pavements was developed using the surface deflection at the initial state of pavement as a design criterion. The proposed pavement design guide was validated with two example projects.

It has been observed that permanent deformation (or rut) in the asphalt pavement at an intersection is much more severe than a deformation away from the intersection due to breaking horizontal forces and longer loading time. This paper presents both experimental and numerical investigations of this phenomenon, and the numerical investigations are validated by three-dimensional fiber-reinforced polymer-optical fiber Bragg grating sensors. First, a field investigation of the rutting at four signalized intersections in Nanjing (Jiangsu, China) leads to the conclusion that under braking traffic and static loads, the values of voids in the mineral aggregate (VMA) and air-void content could be less than the minimum desirable values. Second, the permanent deformations associated with tangential and vertical forces and their loading time assessed with the finite-element method are compared with those measured from instrumentations. This analysis demonstrates that hot-mix asphalt pavement at the intersections should maintain adequate VMA to ensure durability, and a minimum desirable percentage of air voids under slow and standing traffic loads during hot summer days. The permanent deformations at the intersections caused by tangential and vertical forces are both serious and need to be restricted. It is also shown that the permanent deformation is sensitive to both the traffic load and its loading time, but the sensitivity of the load is more pronounced.

Due to the use of many warm-mix-asphalt (WMA) additives in the market, the effect of long-term aging on these WMA mixtures is generally unclear; hence, it is necessary to simulate their performance in the laboratory. The objective of this study was to investigate the influence of various WMA additives on the moisture susceptibility of mixtures containing moist aggregates following a long-term aging process. Mass loss (percentage), indirect tensile strength (ITS) of dry and conditioned specimens, deformation (flow), and dissipated energy values were measured. The experimental design included two aggregate moisture contents (0% and approximately 0.5% by weight of the dry mass of the aggregate), two lime contents (1 and 2% lime by weight of dry aggregate), one liquid antistripping agent (ASA), five WMA additives, and two aggregate sources. A common long-term aging procedure was used in this study. The test results indicated that long-term aging improved the moisture resistance of WMA mixtures regardless of WMA additive, ASA, and moisture content. In addition, aggregate source affected the moisture resistance regardless of WMA additive, ASA, and aggregate moisture content. The effects of various WMA additives on the dissipated fracture energy of unaged mixtures are generally similar except that mixtures with Asphamin have relatively lower dry dissipated fracture energy. In addition, the aggregate type affected the dissipated energy value of WMA mixtures regardless of aging states.

This paper reports the results of an initial attempt of using iron ore tailings (IOTs) to develop greener engineered cementitious composites (ECCs). ECC is a unique class of high-performance fiber-reinforced cementitious composites featuring high tensile ductility and durability. However, the high cement usage in ECC limits the material greenness and increases the material cost compared with normal concrete. In this paper, IOTs in powder form are used to partially replace cement to enhance the environmental sustainability of ECC. Mechanical properties and material greenness of ECC containing various proportions of IOTs are investigated. The newly developed versions of ECC in this paper, with a cement content of $117.2–350.2\mathrm{kg}/{\mathrm{m}}^3$, exhibit a tensile ductility of 2.3–3.3%, tensile strength of 5.1–6.0 MPa, and compressive strength of 46–57 MPa at 28 days. The replacement of cement with IOTs results in 10–32% reduction in energy consumption and 29–63% reduction in carbon dioxide emissions in green ECC compared with typical ECC. Thus, the feasibility of producing greener ECC with significantly reduced environmental impact using IOTs, and maintaining the mechanical properties of typical ECC, is experimentally demonstrated in this paper.

Foamed warm-mix asphalt (WMA) has been widely accepted and used in the United States and many other countries around the world. However, several key concerns about WMA technology still need to be answered, including the major issue of moisture-induced damage. Because of the reduced production temperatures and the foaming process with water, moisture may be entrapped in pavements after compaction. The trapped moisture decreases the adhesion between asphalt binder and aggregates and the cohesion among asphalt binder, resulting in stripping and other forms of pavement distress. The neutron scattering technique provides a unique tool for the determination of the microscopic structure of asphalt and for the detection of the presence of moisture and its spatial distributions in asphalt. In particular, small-angle neutron scattering (SANS) in the wave vector transfer range from $0.003-0.5{\AA }^{-1}$ is suitable to probe the spatial density fluctuations in the real space from $200-1\mathrm{nm}$, which has a resolution several orders of magnitude higher than direct imaging techniques. In this study, the SANS technique was utilized to characterize the microstructure of asphalt and to detect the water spatial distributions in foamed asphalt. Two types of asphalt binder and ordinary and heavy water were used to make samples at 150°C using a laboratory foaming device. The samples were then measured using the SANS instrument at the National Institute of Standard and Technology (NIST) Center for Neutron Research (NCNR). The results show that there is no water entity less than 0.1 μm present in the foamed asphalt. Even if moisture does exist in foamed asphalt, it does not cause any structural changes to the asphalt within 0.1 μm.

Studies in recent years have demonstrated that warm-mix asphalt (WMA) additives can effectively reduce the production temperature of crumb-rubber-modified asphalt (CRMA) mixtures without significantly affecting the engineering properties. CRMA pavement mixtures with WMA additives have several environmentally friendly features. However, there is limited research into the influences of different types and content of WMA additives on CRMA properties. In this paper, CRMA was created by mixing an asphalt binder with crumb rubber powder of $-40$ mesh size and 18% by mass of the asphalt. Various application rates of two different WMA additives, Sasobit and Evotherm, were added into the CRMA. CRMA with and without WMA additives were tested for high-temperature behavior, low-temperature behavior, temperature sensitivity, and fatigue resistance properties. Test results indicate that the types and content of WMA additives have a significant impact on various properties of CRMA. Based on the test results, the optimal type and content of WMA additives may be chosen for CRMA pavement mixtures in different environmental conditions.