Search

Highlights • Moisture damage induced by dynamic pore water pressure exhibits a totally different failure mechanism. • Newly proposed dynamic pore water pressure conditioning methods and their applications are reviewed. • Relevant investigations on multiscale numerical simulation and field tests are analyzed. • Challenges on current research and future works are discussed. Abstract Under repeated vehicle loadings, surface runoff and retained water inside asphalt pavement structure will cause dynamic pore water pressure with positive and negative alternations. Such dynamic pore water pressure squeezes and pumps water flow along the inner wall of void channels to strip asphalt film and finally develop into moisture damage. Different from the traditional freeze-thaw and static water immersion mechanisms, dynamic hydraulic scouring induced by vehicle tires demonstrates a more general moisture damage of asphalt pavement in warm seasons or warm regions. This paper reviews extensive research works in the last decade about moisture damage of asphalt pavement induced by dynamic pore water pressure. A field survey of distresses characterization for an asphalt pavement is firstly introduced and analyzed. On the basis of analyzing macro-scale and micro-scale mechanisms of hydraulic scouring, traditional experimental methods for moisture damage evaluation are then discussed. Newly proposed three types of dynamic pore water pressure conditioning systems with their applications, which include pneumatic, piston and other types, are categorized and analyzed. Multiscale experimental investigations considering dynamic pore water pressure are discussed in detail. Numerical simulation on the water-mechanic response, moisture damage characteristics of asphalt pavement and the real-time monitoring of dynamic pore water pressure in field tests are also summarized. Finally, a series of measures to mitigate moisture damage from the perspective of dynamic hydraulic scouring is proposed. [ABSTRACT FROM AUTHOR]

• Presents the typical chemical functionalities and fractions of asphalts. • Reviews microstructural models explaining the chemistry and rheology of asphalts. • Describes the predominant forms of molecular interactions between bitumen molecules based on the chemical functionality of the bitumen. • Explains the behavior of asphalts in terms of molecular interactions. • Collects the laboratory studies which provided some qualitative or quantitative relationships from testing evidence. Asphalt is widely used in pavement constructions where it serves as a binder to bond the aggregates together. The rheology of asphalt, which is an important consideration for selecting the proper asphalt when designing a pavement, is related to its chemical composition and microstructures. Investigating the relationships between rheology and chemistry of asphalts thus has long been a concern of researchers. This paper reviews key works from the beginning of the 20th century to the present, sorts out microstructural models that bridge asphalt chemistry and properties, and collects laboratory studies that investigated the correlation between asphalt chemical parameters and property parameters. Furthermore, the typical molecular species and corresponding molecular interactions in asphalts are also presented, whereby the rheological and phase behavior of asphalt is interpreted from the perspective of molecular interactions. This job could help researchers who are preparing for asphalt genomic studies to have a comprehensive understanding of asphalt behaviors from a chemical point of view. [ABSTRACT FROM AUTHOR]

• Stiffness and relaxation modulus similarly declined with water severities. • Master curves of creep compliance moved up, but inversely did relaxation modulus. • A larger size of coarse aggregate skeleton reduced HMA's moisture sensitivity. • Asphalt showed different reaction mechanisms in different water environments. With the degraded service performance induced by the erosion of dynamic water pressure environment in summer, asphalt pavement has to subsequently overcome the challenge of low-temperature environment in winter. Considering the unique phenomenon of the gradual disintegration of asphalt mixtures' components, it is still a lack of systematic research on moisture damage induced by dynamic water pressure environment from the perspective of viscoelastic properties. This study adopted the bending beam rheometer (BBR) method to evaluate the influence of dynamic water pressure environment on viscoelastic mechanical performance for asphalt mixture. The results indicated that both creep stiffness modulus and relaxation modulus of asphalt mixture showed similar downward trends with the increase in severities of different water environments, while values of relaxation modulus were slightly smaller than that of creep stiffness modulus. Master curves of creep compliance gradually moved upward with the increase in severities of dynamic water pressure environments, while master curves of relaxation modulus inversely moved downward. Specially, master curves of both creep compliance and relaxation modulus exhibited irregular trends for the dynamic water pressure environment of 60 ℃ − 0.414 MPa, which implied that significant erosion had been brought into asphalt mixture. A relative larger size of coarse aggregate skeleton could improve the resistance of asphalt mixture to moisture damage. The positive effect on improving resistance of asphalt mixture to moisture damage induced by SBS modified asphalt binder was stronger than the negative effect induced by the gradation with a relatively small nominal maximum aggregate size (NMAS). Differences existed in the reaction mechanisms of different types of asphalt binder subjected to the erosion of different water environments. [ABSTRACT FROM AUTHOR]

• A lab-scale optical microscopy technique was developed for loaded crack measurement. • Resolution achieved 0.3 µm by optical scan and photogrammetric analyses. • Conventional DIC was found to overestimate crack width for subpixel cracks. • The proposed technique may combine with DIC for accurate and holistic crack measurement. Concrete cracks accelerate the ingress of harmful species and must be gauged accurately for durability evaluation and prediction. As a novel class of ultra-ductile concrete, Engineered Cementitious Composites (ECC) develops multiple sub-hairline cracks that are difficult to visualize using conventional techniques. In this study, a semi in-situ laboratory approach is proposed based on optical microscopy and photogrammetric analysis to enhance the accuracy of crack width measurement in ECC. Microscopic images scanned from the material surface were reconstructed and analyzed to extract the statistics of crack width, location, number, and spacing. Results suggested that general portable microscopes can effectively identify cracks smaller than 2 µm in loaded condition and provide magnified high-resolution crack images that are hardly achieved by regular digital cameras. Crack openings can be isolated via 2D FFT filtering and binarized to attain the datasets of crack spacing and crack width distribution. In contrast to microscopy, conventional digital image correlation (DIC) as an indirect method was found to overestimate sub-pixel crack widths particularly when the crack width and spacing are substantially smaller than the image resolution. In these scenarios, it is recommended to combine optical microscopy with DIC to ensure simultaneously accurate and holistic crack width characterization. The proposed technique can be used for general materials with multiple fine cracks. [ABSTRACT FROM AUTHOR]

• Dynamic response signals showed relatively larger magnitudes in saturated condition than those in dry condition. • Pore water pressure was sensitive to vehicle speed compared with vehicle load. • Vehicle wheels of front and rear axles generated pore water pressure with obvious different magnitudes. • Tread pattern of vehicle wheel would affect the transverse distribution of dynamic pore water pressure. • Prediction model of positive pore water pressure taken both vehicle load and speed into account was proposed. Asphalt pavement exhibits different dynamic responses to vehicle loading in saturated conditions and in dry conditions. It is essential to directly conduct field full-scale tests to systematically investigate comprehensive influence of water on dynamic response of asphalt pavement. However, real vehicles which were often applied in field tests might result in a certain deviation in dynamic responses measured from each field loading test due to the inevitable influence of the driver's subjective operation and the tread pattern on vehicle wheel. This study adopted the full-scale accelerated loading test system to comprehensively characterize dynamic response of asphalt pavement in both dry and saturated conditions based on the strict control of loading vehicle's path. The results indicated that dynamic responses showed relatively larger magnitudes in saturated condition than those in dry condition. Strain and stress respectively showed slowly increasing and decreasing trends with the increase of vehicle load and speed correspondingly. Pore water pressure was apparently sensitive to vehicle speed compared with vehicle load. Pore water pressure generated by the front axle wheels showed obviously larger magnitudes than those produced by the rear axle wheels due to the change in thickness of surface runoff. The transverse distribution of pore water pressure obtained from both field tests and numerical simulation exhibited consistent variation trends. Decline degree of pore water pressure magnitudes was obtained at 86.1% for the two adjacent testing points with a distance of 100 mm under the vehicle wheel, which proved the great influence of the tread pattern of vehicle wheel on the transverse distribution of dynamic pore water pressure. A prediction model of positive pore water pressure that considered vehicle load and speed was proposed. [ABSTRACT FROM AUTHOR]

Accurately predicting the rutting development law of asphalt pavement is of great significance for preventing and controlling pavement diseases. The aggregate skeleton of the asphalt mixture is the main load-bearing part and plays an important role in its anti-rutting performance. However, quantitative and mesoscopic evaluation indicators and standards for aggregate skeletons have not been established. This study aims to reveal the relationship between the mesostructured characteristics of asphalt mixtures and rutting damage. This paper uses two-dimensional image technology to analyze the dynamic change process of internal skeleton information of two graded asphalt mixtures under cyclic wheel load. According to the fractal theory, the fractal dimension and multifractal spectrum of the full-depth aggregate were calculated. The results indicate that the linear regression model between the mesoscopic skeleton information of asphalt mixture and the average rutting depth during the rutting test can be used to quantify the rutting performance. There is an obvious correlation between the fractal dimension of the section aggregate and the loading times, and there is a certain linear relationship between the multifractal spectrum indexes and the loading times. It indicates that the fractal theory index of aggregate can reflect the change of the macro performance of loading times. • The fractal and multifractal analysis of the section aggregate of the rutting test was carried out. • T The relationship between meso skeleton information and rutting depth is established. • The multifractal index of aggregate can reflect the change of macro performance after loading times. [ABSTRACT FROM AUTHOR]

• Three types of ECT array capacitive sensors were developed. • Influence of water content on capacitance signals of sand and mortar was studied. • The capacitance signals simulated by FEM agree with the experimental results. Electrical capacitance tomography (ECT) is a novel non-destructive testing technology that can monitor the moisture content in cement-based materials with the application of a capacitive sensor. In this study, three types of ECT array capacitive sensors were developed, and a series of experiments was implemented using the designed sensors to investigate the influence of the relative humidity of a porous material on the capacitance. The experimental results indicate that the non-homogeneity of the sensitive field is improved within the measurement field by an external electrode sensor. Capacitive sensors with internal electrodes demonstrated more sensitivity to changes in moisture content under the same excitation conditions. In addition, the capacitance signals of sand and cement mortar increased exponentially as the relative humidity increased. Finally, a two-dimensional finite element method (FEM) was used to model the electromagnetic field distribution around capacitive sensors, and the numerical results agreed well with the experimental results, which indicated the feasibility of developing capacitive sensors. These findings may provide theoretical guidance for the engineering applications of capacitive sensors in the non-destructive testing of cement-based materials in the future. [ABSTRACT FROM AUTHOR]

• FAM's performance greatly affected the moisture sensitivity of HMA induced by dynamic water environment. • Short-term conditioning in a harsh dynamic water environment also exhibited a great erosion effect on asphalt materials. • Softening and emulsifying showed more obvious effects on asphalt binder during dynamic water conditioning. • HMA tended to exhibit more elasticity as the increase of environment severity. Moisture damage induced by dynamic pore water pressure commonly occurs in asphalt pavement located in regions with rich rainfall. This kind of moisture damage illustrates a special and quite different mechanism compared with that induced by static water immersion and freeze-thaw. Fine aggregate mixture (FAM) plays a vital role on the entire resistance of hot mix asphalt (HMA) to moisture damage. However, there is still a lack of systematic research on the evaluation of moisture sensitivity for both HMA and its components such as asphalt binder and FAM at the same scale. This study adopted the bending beam rheometer (BBR) method to assess moisture sensitivity for HMA and its components induced by dynamic water environment. The results indicated that the creep stiffness for both HMA and its components declined after being conditioned in dynamic water environment. FAM was quite easily eroded and its maximum decrease extent of creep stiffness could even up to 54.8%. In this case, it was clearly shown that the moisture sensitivity of HMA was greatly affected by its FAM component's performance. The erosion effect of short-term conditioning in a harsh dynamic water environment was comparable to that of long-term conditioning in a mild environment. Softening and emulsifying showed more obvious effects on both asphalt binder and FAM during dynamic water conditioning, which made them exhibit more viscosity. Specially, after the FAM component on the surface of a HMA sample being scoured away, the retained coarse aggregate skeleton made the entire HMA sample still remain a certain mechanical strength and anti-erosion ability. Based on the analysis of the indicator m/S , HMA showed viscous performance in a mild dynamic water environment but tended to exhibit more elasticity with the increase of environment severity. [ABSTRACT FROM AUTHOR]

• Effects of organic corrosion inhibitors on steel corrosion under chloride attack are studied. • Alcoholamines significantly enhance the passive film resistance of steel. • Carboxylic acids can replace the chloride ions attached to the steel surface. Organic corrosion inhibitors (OCIs) are commonly used to enhance reinforced concrete durability in the marine environment. In this contribution, the effects of OCIs on steel corrosion in concrete exposed to coupled deterioration of freeze–thaw cycles and chloride attack have been evaluated. Concrete samples with mild steels were mixed with three commonly used OCIs (alcoholamines-, carboxylic acids-, and esters-based), and exposed to freeze–thaw cyclic test in a 3% NaCl solution. The corrosion-resistance mechanisms of OCIs on steel corrosion were revealed using the open circuit potential test (OPC) and electrochemical impedance spectroscopy measurement (EIS). The steel–concrete interface micromorphology was observed by the optical microscope and the scanning electron microscope (SEM). The results showed that salt-frost resistance of concrete incorporated with alcoholamines-, carboxylic acids-, and esters-based OCIs was improved by about 50%, 350% and 200%, respectively. However, internal damage caused by freeze–thaw cycles was aggravated after adding easter-based OCIs due to the reduction in pore diameter caused by hydrophobic calcium salt lining. Alcoholamines- and carboxylic acids-based OCIs could significantly delay the steel de-passivation. Alcoholamines could increase the passive film resistance and carboxylic acids could replace the chloride attached to the steel surface. [ABSTRACT FROM AUTHOR]

The production of cement mortar has resulted in significant environmental issues. Many scientists have attempted to reduce environmental pollution by using agricultural waste as a substitute for mortar raw materials. This study creatively investigated the physical and mechanical properties of the new green cement mortar made from macadamia nutshell(MN), including compressive strength, flexural strength, and apparent density of 7d, 14d, and 28d. The effects of cement-sand ratio (c/s), nutshell particle size, and MN substitution rate on cement mortar's physical properties were studied using three-factor and three-level orthogonal test design methods. The digital image correlation (DIC) technique was used to analyze the crack development of macadamia nutshell cement mortar (MNM) at different loading stages. The analysis of variance (ANOVA) showed that the cement-sand ratio was the most significant factor affecting the strength of MNM. In addition, adding MN can increase the compressive strength of the mortar compared to the control group. The apparent density of the mortar decreases with the increase of MN addition. • The influence of adding varying particle sizes of the nutshell on the strength of mortar was studied. • The density and flexural strength of mortar decreased with the increase of macadamia nutshell addition. • Macadamia nutshell could be used as an eco-friendly supplementary natural aggregate material. [ABSTRACT FROM AUTHOR]

• The bearing status of the crown of a sewer pipe is mimicked with a fixed pipe segment. • The initiation period of MICC was significantly shortened by pre-adjusting concrete surfaces. • The stress-corrosion effect of concrete in sewers are discussed. Microbiologically induced concrete corrosion (MICC) and stress crack are the most common structural defects in concrete sewer pipes. To investigate the microbial corrosion behavior of cracked concrete pipes under sustained loading, coupons with no load, 100% D-Load, and 120% D-Load were pre-adjusted to a suitable environment for acidophilic sulfur oxidizing bacteria (ASOB) colonization, and then placed together in a microbial chamber for 90-day accelerated corrosion. The corrosion variances of these coupons were compared in terms of surface morphology, crystalline violet staining, pH evolutions, crack width changes, as well as characterization results including Scanning Electron Microscope- Energy Dispersive Spectrometer (SEM-EDS) and X-ray Diffraction (XRD). It was found that the stress level slightly accelerates the pH drop on the coupon surface, positively correlates with the corrosion product content of the semi-corrosive layer, and causes stress-corrosion cracking of the semi-corrosive layer, but has little effect on corrosion loss. Stress-corrosion effects were only found in the semi-deteriorated layer of the stressed coupon, but no significant acceleration effect on corrosion rate was observed. This is explained by the fact that MICC is a non-diffusive corrosion where the semi-deteriorated layer is rather thin. Thus, cracking or not of the semi-deteriorated layer does not affect the corrosion rate. This study improves understanding of the service deterioration of sewage pipes. [ABSTRACT FROM AUTHOR]

The indirect design method for concrete pipes, which estimates the bearing capacity of concrete pipes in a buried environment based on the D-load determined from a three-edge bearing test (TEBT), is a common method for designing concrete pipes. D-load is determined by the load corresponding to the first 3-mm crack, which has been used from the 1930s until today. To explore the potential of modern laboratory techniques as an alternative to the traditional vision method. This study discusses the application and cost-effectiveness of several technologies for detecting D-load, including strain gauges, displacement sensors, acoustic emission, digital image correlation, and infrared thermography, based on TEBT on full-scale double-cage reinforced concrete pipes with internal diameters of 1000, 1500, and 2000 mm. The consistency between D-load values obtained by these approaches along with the predicted value by Heger's model is compared with the D 0.3_visual determined by conventional visual observation in terms of the developed relative reliability. It is found that the method based on acoustic emission techniques is more consistent with the D 0.3_visual than others, but is costly and time-consuming. Also, D e , identified by the load corresponding to the end of the elastic phase of the force–time curve, is a reliable alternative and cost-effective method. This study will provide new insights into the aspect of performance design and evaluation for concrete pipes. • Modern laboratory methods are used to attempt to identify the D-Load of concrete pipes. • The D-load values obtained by the new methods were compared with that from the traditional method. • The cost-effectiveness and reliability of the new methods are discussed. [ABSTRACT FROM AUTHOR]