Search

The mechanical parameters and deterioration mechanisms of sandstone specimens obtained from the hydrofluctuation belt in the Three Gorges Reservoir Region of China were investigated under a combination of freeze-thaw cycles and different chemical solutions. The degradation in several mechanical characteristics was discussed, and the degree of freeze-thaw deterioration of the mechanical behaviors was quantitatively analyzed based on the crack propagation radii and a damage variable that reflects the changes in porosity. The results showed that the mechanical parameters of sandstone had a significant damage deteriorating trend under freeze-thaw cycles and different chemical solutions. And the degree of damage deterioration of fracture toughness KIC was the greatest, followed by that of tensile strength; that of compression strength was the smallest. There was obvious consistency among fracture toughness KIC, tensile strength, and compression strength of sandstone under a combination of freeze-thaw cycles and different chemical solutions; those were obvious linear relationship. The crack propagation radii for the various effects of freeze-thaw cycles and chemical solutions were smaller than those of the natural state and the radii generally decreased with increasing freeze-thaw cycles.

Smart microvascular self-healing bituminous composites are considered a promising approach to prolong pavement service life. The objective of this work was to investigate the microvascular self-healing capability of bituminous material by using hollow fibers with oily rejuvenator through a direct-tension mechanical experiment. The hollow fibers with oily rejuvenator were prepared using a wet-spinning approach by applying polyvinylidene fluoride material. The fixed-length hollow fibers with sealed ends were mixed in bitumen to form composite samples. Through a repetitive tensile method, the tension strength data were used to calculate the self-healing efficiency autonomously by considering crack closure and healing at various healing temperatures and times. The scanning-electron-microscope morphology showed that the polyvinylidene fluoride hollow fibers had a tight interfacial structure with bituminous material without debonding. X-ray computed tomography results indicated that the fibers were distributed homogeneously in bitumen. The fiber content and fiber orientation affected the self-healing capability of bituminous samples at 0 °C. To simplify the influence of the above two factors of the fibers, only one fiber was placed in bitumen samples parallel to the tension direction. With an increase in temperature from 0 to 30 °C, the self-healing capability of the bitumen samples increased dramatically. This phenomenon is attributed to the accelerated penetration speed of rejuvenator in the bitumen. An increase in time increased the self-healing capability of the bitumen samples. The rejuvenator may have sufficient time to leak from the hollow fibers and penetrate the bitumen. The results provide a guide to the microstructural design of the vascular fibers and the application of hollow fibers in self-healing asphalt pavement.

Compatibility, a critical issue between sensing material and host structure, significantly influences the detecting performance (e.g., sensitive, signal-to-noise ratio) of the embedded sensor. To address this issue in concrete-based infrastructural health monitoring, cement-based piezoelectric composites (piezoelectric ceramic particles as a function phase and cementitious materials as a matrix) have attracted continuous attention in the past two decades, dramatically exhibiting superior durability, sensitivity, and compatibility. This review paper performs a synthetical overview of recent advances in theoretical analysis, characterization and simulation, materials selection, the fabrication process, and application of the cement-based piezoelectric composites. The critical issues of each part are also presented. The influencing factors of the materials and fabrication process on the final performance of composites are further discussed. Meanwhile, the application of the composite as a sensing element for various monitoring techniques is summarized. Further study on the experiment and simulation, materials, fabrication technique, and application are also pointed out purposefully.

Microcapsule-based self-healing concrete was used in a tunnel engineering project in the Qianhai area, Shenzhen and the concrete performance was investigated using laboratory and field tests. The physical properties of the microcapsules and the microstructure of the self-healing concrete were experimentally investigated. The effects of the microcapsules on the strength, permeability, and long-term shrinkage of the self-healing concrete were also investigated. The self-healing efficiency was evaluated using a compressive strength test and a rapid chloride migration (RCM) test. The results indicated that the self-healing functionality of the concrete containing 10% microcapsules gradually increased over time. The microcapsules had both positive and negative effects on the microstructure of the self-healing concrete. The use of the microcapsules resulted in a significant increase in the long-term shrinkage but the amount of shrinkage is acceptable for practical applications. No significant difference of the strain evolution was observed between the experimental and control groups in the field test, indicating that the use of microcapsule-based self-healing concrete is feasible and promising to improve the durability of concrete structures, especially in coastal civil engineering.

The healing mechanisms and healing performance of cementitious materials are reviewed, including autogenic self-healing and bacteria-based self-healing, as well as the use of mineral admixtures, polymeric adhesive agents, superabsorbent polymers, and shape memory materials. To determine the robustness of various self-healing methods, several reliable methods for the assessment of the healing efficiency are reviewed in terms of the mechanical properties. In addition, a comprehensive review of the applicable techniques is provided, i.e., microscopy, spectroscopy, thermoanalysis, and imaging for the characterization of the healing products, the microstructure, and the healing process. To demonstrate the applicability of various self-healing methods in engineering practice, the major disadvantages and challenges of the self-healing materials and encapsulation techniques are reviewed and the future development in the field of self-healing cementitious materials is addressed. Finally, an engineering case study on the healing efficiency of cementitious materials for four self-healing systems is discussed.

Hollow fiber containing rejuvenator is a promising smart material for vascular self-healing bituminous materials of pavement. The objective of this work was to experimentally observe the states of self-healing hollow fibers containing rejuvenator in pure bituminous material. Polyvinylidene fluoride (PVDF) hollow fibers containing oily rejuvenator were spun through single-wet-spinning method. The fixed-length hollow fibers with sealed ends were mixed in bitumen forming composite samples. The inter-surface and outer-surface microstructure of hollow fibers were observed by an environmental scan electron microscopy (ESEM). The micropores in fiber-shells were channels for rejuvenator to pass through. X-ray computed tomography (XCT) results indicated that these fibers distributed in bitumen with an integrality state. Three-dimensional reconstruction XCT (3D-XCT) images exhibited the details both of vertical and horizontal distribution of hollow fibers in bitumen. Thermogravimetic analysis (TGA) and a repeated thermal-cycle testament showed that the hollow fibers survived safely in bitumen. No debonding phenomenon was found between the fibers and bitumen. Oily rejuvenator released out of hollow fibers smoothly through the break point of hollow fiber/bitumen composite samples. The break images of hollow fibers in bitumen were also analyzed through 3D-XCT structures. At the same time, the movement tracks of oily rejuvenator out of hollow fibers were observed by a fluorescence microscopy. The rejuvenator permeated through the micropores on a hollow fiber into aged bitumen. These states mean that the self-healing can be triggered through the break points of hollow fibers as well as the self-rejuvenation when bitumen is aging. The above result is evidence that the hollow fibers containing rejuvenator will be a feasible approach to realize the self-healing and self-rejuvenating process of bitumen.

Recycled crumb rubber (RCR) can be sustainable used in alkali activated slag mortar (AASM) to economize nature aggregate consumption and reduce environmental pollution. Meanwhile, external dynamic loads (e.g. wind load and earthquake load) can be effectively counteracted by RCR with superior deformation performance. In this study, the workability, static and dynamic mechanical properties, and environmental impact of AASMs mixed with 0% - 60 vol% of RCR substitution for fine aggregates were investigated. A dynamic mechanical analyzer (DMA) was applied in a frequency range of 0.5–2 Hz at a temperature range of -70–70 °C. The experimental results indicate that the workability and mechanical strengths of AASMs decreased with the increase of RCR replacement rate. The storage modulus of AASM generally decreases with the increase in RCR, however, once the RCR replacement rate reaches 60%, the storage modulus is higher than that of the control mortar, presenting typical behavior of thermoplastic materials. The loss factor significantly increases with the increasing content of RCR, indicating that RCR serves competently as an energy dissipating material. Finally, an economic and ecological evaluation demonstrates that AASM with RCR is beneficial to the environment.

Microcapsule based self-healing concrete can automatically repair damage and improve the durability of concrete structures, the performance of which depends on the binding behavior between the microcapsule wall and cement matrix. However, conventional experimental methods could not provide detailed information on a microscopic level. In this paper, through molecular dynamics simulation, three composite models of Tobermorite (Tobermorite 9 &Aring, Tobermorite 11 &Aring, Tobermorite 14 &Aring, ), a mineral similar to Calcium-Silicate&ndash, Hydrate (C&ndash, S&ndash, H) gel, with the linear urea&ndash, formaldehyde (UF), the shell of the microcapsule, were established to investigate the mechanical properties and interface binding behaviour of the Tobermorite/UF composite. The results showed that the Young&rsquo, s modulus, shear modulus and bulk modulus of Tobermorite/UF were lower than that of &lsquo, pure&rsquo, Tobermorite, whereas the tensile strength and failure strain of Tobermorite/UF were higher than that of &lsquo, Tobermorite. Moreover, through radial distribution function (RDF) analysis, the connection between Tobermorite and UF found a strong interaction between Ca, N, and O, whereas Si from Tobermorite and N from UF did not contribute to the interface binding strength. Finally, high binding energy between the Tobermorite and UF was observed. The research results should provide insights into the interface behavior between the microcapsule wall and the cement matrix.

In this paper a theoretical constitutive model is developed to describe the mechanical properties of corroded steel bars. The model is established based on the assumption that the effect of corrosion on the steel bars only leads to the local reduction of cross-section area of the steel bars. By using a bilinear elastoplastic constitutive equation, a generalized equivalent stress-strain equation is derived for the corroded steel bars, which considers the pitting corrosion nature. The derived stress-strain equation is validated using experimental data. To demonstrate the features of the stress-strain equation, a parametric study is also presented.

The rapidly growing volume of construction and demolition (C&D) waste produced by construction industry has led tremendous pressure on environmental protection. This study focuses on the improvement of the use of C&D waste as recycled fine aggregates (RFA) in cement composites by adding graphene oxide (GO), which is desirable to promote the application of recycled aggregates, decrease the exploitation of natural aggregates (NA) and alleviate environmental burden. In order to investigate the performance enhancement of RFA cement composites, the physico-chemical properties, microstructural performances, and environmental benefits of RFA mortars prepared with different GO contents (0.05 wt%, 0.1 wt%, and 0.2 wt%) have systematically examined. Electrochemical and mercury intrusive analysis revealed that the RFA mortars containing GO exhibited lower porosity and denser pore structure, compared to RFA mortars without any GO. The incorporated GO could further reduce ionic conductivity and thus improve the service life of RFA mortars. In addition, the interfacial transition zone (ITZ) between the RFA and cement paste was filled with hydration products when examined by scanning electron microscopy (SEM). Compared to those of RFA mortars without GO, the 28-day compressive and flexural strengths of RFA mortars with 0.2 wt% GO were increased by 19.2% and 47.5%, respectively. Finally, life cycle assessment (LCA) indicated that, compared to mortars with NA at the equivalent mechanical strengths, RFA mortars (containing 0.2 wt% GO) have better environmental performance (6.7% CO2 emission reduction or 2.2% primary energy demand saving). Overall, the addition of GO could significantly improve the quality of RFA mortars, which could further apparently improve the recycling of C&D waste, and then promote the sustainable development of construction sector.

The aim of this work was to prepare and characterize a novel vascular self-nourishing and self-healing hollow fiber containing oily rejuvenator for aged bitumen. The hollow fibers containing oily rejuvenator were fabricated with micropores by a one-step wet-spinning method using polyvinylidene fluoride (PVDF) resin. Hollow fibers had been successfully prepared based on the test results of morphology, size and chemical structure. The hollow fibers had a good thermal stability with a decomposition temperature of 450 °C. The mechanical properties of fibers satisfied the requirements of use in bituminous materials. Because of the existence of micropores microstructure in fibers, the rejuvenator had the permeability out of fibers. The diffusion behaviors of rejuvenator were also measured by an attenuated total reflection flourier transformed infrared spectroscopy (FTIR-ATR) method. It was found that the diffusion coefficient greatly depended on the pore structure and temperature. A fitting model implied that the diffusion coefficient had a big deviation of Fick’s law and greatly influenced by the pore structure of hollow fibers. It is a guide to design and regulate the microstructure of hollow fibers with appropriate rejuvenator releasing behaviors. All above results implied that the existence of both self-nourishing and self-healing had been successfully proved in aged bitumen using hollow fibers containing oily rejuvenator.

In this study, experimental investigations were conducted on the self-healing potential of concrete. Sulfoaluminate based expansive agents (CSA), crystalline admixture (CA), and calcium hydrogen phosphate were used as part of cementitious materials, and porous ceramsites served as the carrier for sodium carbonate solution. The quantification of the widths/areas of the cracks was performed to examine the feasibility of the approach and optimize mix proportions. A gas permeability test was conducted on two preferred mixes to investigate the change in the gas permeability of pre-cracked samples. After curing in still water for 28 d, the pre-cracked specimens with ceramsites containing sodium carbonate, and appropriate dosages of additives exhibited considerable efficiency in surface crack closure and healing in gas permeability. The SEM results indicated the deeper formation of healing products (CaCO3) in the cracks of the suggested mix when compared to that in the control mix. A healing mechanism was discussed based on the experimental results.

Utilization and processing of waste cathode ray tube (CRT) glass causes serious environmental damage due to its presence of lead and huge growing volume. The use of waste CRT glass in cement-based materials is an effective recycling method, whereas the huge amount of waste CRT glass usually results in severe lead leaching and weakened interfacial bonding. This paper presents an effective method for improving the lead immobilization and microstructure of the interfacial transition zone between cement paste and waste CRT glass (30 and 60 wt% of fine aggregates) using graphene oxide (GO) (up to 0.10 wt%). In order to investigate the environmental compatibility of the GO-waste CRT cement mortars, the standard toxicity characteristic leaching procedure (TCLP) was performed for lead leaching evaluation, and their mechanical properties were examined. Moreover, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) observation with backscattered electron mode were conducted. The results of TCLP indicate that the degrees of lead leaching from the waste CRT cement-based materials with both fine (0.075–0.15 mm) and coarse (8–9.5 mm) size containing 0.1 wt% GO were significantly lower than the regulatory limit specified by the United States Environmental Protection Agency and Chinese standard. The data obtained via mechanical testing revealed that the presence of 60 wt% waste CRT reduced its 28-day compressive and flexural strengths only slightly, whereas 0.1 wt% GO addition significantly increased their values. By analyzing the thermogravimetric and microstructural results, it was found that the increased formation of portlandite (CH) and calcium-silicate-hydrate (C S H) caused by GO addition reduced the number of interconnected cracks and pores and improved the properties of the interface between waste CRT glass and cement paste. This obtained improvement in environmental compatibility of the waste CRT cement mortars not only examines the reduced lead pollution caused by GO addition, but also sustainably promotes the industrial utilization of toxic waste CRT glass.

This paper presents an experimental investigation on the effect of nano-SiO2 on the compressive strength, shrinkage and early cracking sensitivity of lightweight aggregate concrete (LWAC). Two types of ceramsite with different water absorption were used as lightweight aggregate in this study. LWAC with different nano-SiO2 dosage (1%, 2%, 3%) were compared with the reference LWAC to assess the effects of nano-SiO2 on LWAC. Results revealed that the incorporation of 3% nano-SiO2 increased compressive strength of LWAC significantly while the influence of nano-SiO2 on the long-term shrinkage of LWAC was not significant. The total cracking area was decreased with the increase in nano-SiO2 dosages from 1% to 3% by mass of the total binders at early age. The results of scanning electron microscopy (SEM) showed that the interfacial transition zone (ITZ) between lightweight aggregate and paste was enhanced with 3% nano-SiO2 addition. Subsequently, simplified models for compressive strength and shrinkage of LWAC were proposed and a comparison between the experimental data and models was discussed.

The effects of adding organic microcapsules having various particle sizes and composition on the permeability, carbonation resistance, pore structure, and self-healing efficiency of cementitious composite material were studied using rapid chloride migration, water pressure penetration, carbonation, and mercury intrusion porosimetry tests. It was found that increasing microcapsule content to 3% improved pore structure and impermeability. However, with 6% microcapsule content, the material impermeability became even lower than that of a specimen without microcapsules. The variation of particle sizes had a slight negative impact on impermeability although it improved pore structure. Increasing microcapsule content and particle size enhanced impermeability, pore structure, and self-healing efficiency of specimens.

Two kinds of chemically-triggered self-healing systems with novel microcapsules are designed to protect rebar from corrosion in concrete. X-ray micro-computed tomography (XCT) method is employed to non-destructively visualize the protection performance and quantitatively evaluate the efficacy of the self-healing system in a wet-dry cyclic accelerating corrosion test. Environmental scanning electron microscopy (ESEM) system equipped with texture element analysis microscopy (TEAM) is used to verify the results of XCT imaging analysis. The results reveal that the self-healing system-high efficiency is achieved by delaying the depassivation of the rebar and reducing the corrosion rate.

External sulfate attack is a progressive degradation process that may cause expansion, cracking, loss of binder cohesion and increased permeability in cementitious materials. Crystallization pressure theory has often been referred to as the most likely mechanism. However, thus far the stress causing the expansion has not been quantified. In this study, small cement paste pipes with a wall thickness of 2.5 mm were prepared and immersed in sodium sulfate solutions with SO42− ion concentrations of 1.5 g/L and 30 g/L. Three types of longitudinal restraints were applied on the specimens before exposure, which were created by a spring, a thin or a thicker stainless steel bar that was centered in the hollow specimens in order to facilitate the non-, low- or high-restraint condition. The free expansion, restrained expansion and generated stress were quantified. The pore size distribution, sulfur distribution and crack pattern were periodically analyzed during the sulfate immersion tests up to 420 days. The generated stresses were found to be as high as 13.1 MPa in high sulfate solution and 8.3 MPa in low sulfate solution under high-restraint condition after 420-day immersion. For the unrestrained specimens immersed in low sulfate solution, an almost uniform sulfur distribution along the diffusion direction was found at 189-day immersion. However, for the unrestrained specimens immersed in high sulfate solution, a layer or several layers of mainly gypsum were formed subparallel to the exposed surface from 133-day immersion.

Experimental studies are presented on the influence of three types of pre-wetted lightweight aggregates (PLWA), through their volume fractions and moisture content, on the compressive strength and shrinkage of concrete and expansive concrete. Via integrated thermal analysis, the hydration degree during 7 d–28 d was found to be increased by the internal curing. The use of PLWA increased the shrinkage at 240 d due to the significant increase in the shrinkage deformation during the age of 28 d–90 d caused by internal curing. The results also suggest that incorporation of 10-Mas. % expansive agent is useful to diminish the shrinkage, especially by its combined use with PLWA. Predictive models for the compressive strength and shrinkage of concrete containing PLWA were discussed and a unified model predicting the compressive strength and shrinkage of concrete containing PLWA was suggested.

Cement based composite materials (CBCM) with superior mechanical strength and excellent durability are always desirable in practical applications. Although considerable research has been reported in the past decades about the use of Nano materials (NMs) for strength and durability enhancement of cement matrix, there is little information available on the use of graphene nano-sheets and their derivatives (GND) in cement-based materials. Particularly the role of GND in hydration processes and their mechanisms of strengthening in cement matrix are unclear. In this paper, a critical review on recent research findings about GND modified cement-based materials was conducted. The review mainly discussed the influence of GND on properties of cement matrix including microstructure, hydration, mechanical properties, etc. The information revealed in this paper would not only provide a comprehensive understanding of the effect of GND on cement composites, but also provide valuable ideas and guidance for similar studies in the future.

Graphene oxide (GO) has been utilized to strengthen composite materials. In this study, the effects of GO on hydration degrees, macro-mechanical strength and calcium-silicate-hydrate (C-S-H) structure of cement based composites were investigated through comprehensive experimental tests. In addition, the aggregation mechanism of GO was verified by alkaline solution simulations, using Ca(OH)2 and NH3·H2O. Based on the experimental results, it was found that the 3-day and 7-day compressive strengths of cement based composites with 0.2 wt% of GO were increased by 35.7% and 42.3%, respectively as compared to the control. Moreover, the C-S-H structure of cement paste with GO was not observed to have undergone any change via qualitative and quantitative analyses combined with FT-IR, XRD and 29Si-NMR. Besides, the test results of TGA, DTG and 29Si-NMR showed that the hydrated degree of cement paste increased to 10.4% at 28 days when incorporating with 0.1% of GO.

This paper investigated the effect of two types of PCE superplasticisers, including water-reducing and slow-releasing types, on the workability and rheological behaviour of cement mixed with tapwater and seawater. In addition to rheology and minislump tests, the characterisation of PCE on chemical structure and hydrodynamic radius was conducted and the adsorption behaviours were also examined to reveal the underlying mechanisms. The results showed that for the water-reducing type PCE, the seawater led to an obvious decrease in the fluidity of the PCE-superplasticised cement paste whereas it did not significantly change the fluidity of cement with slow-releasing PCE. The addition of both PCEs changed the rheological behaviour of the cementitious materials. Although the mix of seawater decreased the minislump of PCE-superplasticised cement, the adsorption amount of both types of PCE in seawater was increased due to the complexation between the carboxylate group in PCEs and the divalent Mg2+ from the seawater. The reduced dispersion could be attributed to the shrinkage of the PCE backbone and the decreased thickness of the adsorption layer.

The use of CSA cement in practice has been hindered by its unstable performance and short shelf-life caused by the prehydration of CSA clinker. In this study, the effect of ambient humidity on the prehydration rate and process of CSA clinker was investigated. The prehydration degree, ageing progress, and the dynamic change of mineral composition of CSA clinker exposed to five different relative humidities (ranging from 23% to 98%) for up to 180 days were studied. Experiments revealed that the ambient humidity of 60% RH can be considered a threshold value for storage of CSA clinker. Exposure of CSA clinker to RH higher than 60% will not only result in a significant decrease of hydraulic reactivity, but also in agglomeration of the clinker. Although the exposure of CSA clinker to RH lower than 60% has little effect on the hydraulic reactivity, the main hydration peak was found to be slightly delayed with the increase of RH.

Microcapsules containing rejuvenator are particles used to increase the self-healing capability of asphalt. To date, no reports focus on studying their behaviors in asphalt binders between the aggregates. The purpose of this work was to directly observe the states of self-healing microcapsules in asphalt binders. Asphalt samples were prepared by mixing bitumen and various weight contents of microcapsules. Experimental tests were carried out to observe the morphology, integrity, distribution, thermal stability, interface bonding and triggered rupture of microcapsules in asphalt binders. Fluorescence microscope morphologies and X-ray computed tomography images showed that microcapsules survived in asphalt resisting high temperature and strong agitation without premature damage. At the same time, microcapsules were homogenously dispersed in asphalt binders avoiding particles aggregation and adhesion. A circular heating-cooling process was used to simulate temperature changes in the natural environment. It was found that microcapsules still kept a stable state after an extreme temperature change. In addition, interface debonding phenomenon did not appear. Microscopic observation results reflected that microcapsules could be pierced by microcracks in the asphalt binder and the encapsulated rejuvenator flowed out under the force of capillary action. All the above conclusions indicate that microcapsules containing rejuvenator meet the application conditions and play the role of self-healing material in asphalt binders.

An experimental study is carried out with the aim to understand the interacted mechanism between carbonation and chloride aerosol attack in ordinary Portland cement (OPC) concrete. Effects of carbonation on the chloride profile, the chloride binding capacity and the chloride diffusion coefficient are evaluated. Besides, effect of chloride aerosol attack on the carbonation rate is investigated. Concrete specimens with three water-to-cement ratios (0.38, 0.47 and 0.53) are fabricated in this work. Tested results demonstrate that carbonation remarkably affects the chloride profile, reduces the chloride binding capacity, and also accelerates the rate of chloride ion diffusion of concrete. Besides, the presence of chloride aerosol can lead to lower the carbonation depth and increase the pH value of carbonated concrete. Microscopic properties such as morphology, porosity, and pore size distribution for the contaminated concretes are explored by scanning electron microscope and mercury intrusion porosimetry, which provide strong evidence to these research findings.

In this study, experimental investigations are reported on the effects of the moisture content of ceramsite, the replacement rate of aggregates, and the use of expansive agent on the early cracking sensitivity of lightweight aggregate concrete. Three kinds of commercially available lightweight aggregates (clay ceramsite, shale ceramsite, fly ash-clay ceramsite) were used in the experiment. The cracking sensitivity of concrete was investigated via splitting tensile test, plate cracking test and temperature-stress test. The results showed that the cracking sensitivity of concrete decreased with the increases in the moisture content and the replacement rate of aggregates. A model describing the relationship between the moisture content of ceramsite and the restraining stress was presented.

In this study, the construction of a reinforced concrete bridge pier was analyzed from durability point of view. The goal of the study is to analyze the crack iniation condition due to construction and present some recommendations for construction conditions of the reinforced concrete bridge pier. The bridge is located at the western port area of Shenzhen, where the climate is high temperature and humidity. To control the cracking of concrete, a construction simulation was carried out for a heat transfer problem as well as a thermal stress problem. A shrinkage model for heat produced due to cement hydration and a Burger constitutive model to simulate the creep effect are used. The modelling based on Femmasse© is verified by comparing with the testing results of a real underground abutment. For the bridge pier, the temperature and stress distribution, as well as their evolution with time are shown. To simulate the construction condition, four initial concrete temperatures (5

This paper presents an experimental investigation regarding the coupled effect of carbonation and chloride aerosol ingress on the durability performance of fly ash concrete. Test results demonstrate that carbonation significantly affects the chloride ingress profile, reduces the chloride binding capacity, and accelerates the rate of chloride ion diffusion. On the other hand, the carbonation rate of fly ash concrete is reduced by the presence of chlorides aerosol. The interaction nature between concrete carbonation and chloride aerosol ingress is also demonstrated by the microscopic analysis results obtained from scanning electron microscope and mercury intrusion porosimetry.

In order to propose an optimised construction plan and prevent and control the possible occurrence of cracks in concrete structures during construction, a detailed simulation of construction stages is required. The temperature and thermal stresses during the construction of a double-hole, double-deck concrete tunnel structure were analysed in this study, in which the analysis of the early-aged behaviour of a structure was performed considering actual construction conditions, and the cracking conditions were predicted. It was found that the temperature trends obtained from the simulated results were in good agreement with actual data, which indicates the reliability of the simulation results. In addition, the distribution of thermal stresses in the structure indicated that the tunnel structure was at risk of cracking at a number of stress concentration areas under the construction conditions. A parameter analysis of different factors, including the initial concrete temperature (25°C, 30°C, and 35°C), formwork stripping time (48 h, 72 h, and 96 h), and the construction season ambient temperature (summer and winter), was conducted. The formwork stripping time did not have a significant influence. It is recommended that the initial concrete temperature should be controlled to below 30°C during construction.

Self-healing cementitious composites have been developed by using microcapsules. In this study, the effect of the healing agent on the crosslinking and curing reaction kinetics was analyzed. The effect of the diluent n-butyl glycidyl ether (BGE) on the reaction was investigated for five fractions, namely 10.0%, 12.5%, 15.0%, 17.5%, and 20.0% mass fractions to epoxy resin. The Kissinger and Crane equations were used to obtain the activation energy and reaction order with different mass fractions of diluent, as well as the kinetic parameters of the curing reaction. The optimal fraction of BGE was determined as 17.5%. Likewise, the effect of the curing agent MC120D on the reaction kinetics was investigated for 10%, 20%, 30%, 40%, and 50% mass fractions to the diluted epoxy resin. The optimal fraction was determined as 20%. The mechanism of the curing reaction with the healing agent was investigated. The infrared spectra of the cured products of 20% MC120D with BGE/E51 (0.0%, 12.5%, 15.0%, 20.0%, 100%) were analyzed. It is shown that not only the epoxy resin E-51 was cured, but also that the BGE was involved in the cross-linking reaction of the epoxy resin E-51 with MC120D.

A physical triggered self-repairing cementitious composites were built using the microcapsules with the epoxy resin as the core. The influence of the microcapsules dosage, preloading stress and curing days on the uniaxial mechanical properties, pore structure parameters and self-healing efficiency were investigated. The microcapsules had a significant influence on the deformation characteristic to improve the brittleness characteristics and strengthen the ability of plastic characteristics. Microcapsules positively influenced self-healing but negatively affected the pore structure parameters of sound cementitious composites materials. Considering the influence of preloading stress, relationship models to quantitatively predict the influence of the microcapsule dosages on the mechanical properties and pore structure parameters were established, and obtained the statistical relationship between mechanical parameters and pore structure parameters, and so as to indirectly obtain the models among the mechanical parameters, microcapsules dosage, preloading stress and pore structure parameters.

A physical triggered self-healing system was formed by mixing the epoxy/urea-formaldehyde microcapsules into cementitious materials. The effects of the microcapsule contents and strain rate on the mechanical properties, pore structure and self-healing efficiency were investigated in this study. Both the strain rate and microcapsule contents influenced the strength and pore structure. With increasing of the strain rate, the strength of specimens gradually increased. With increasing of microcapsule content, the strength of initial specimens declined to varying degree, the strength of healing specimens gradually increased. Microcapsules had an positively effects on the self-healing but negatively effects on the pore structure parameters of initial specimens. And the microcapsules also had effects of the deformations properties, and improved the brittleness characteristics of the specimens. These findings reflected the self-repairing effects of microcapsule on cementitious materials from a dynamic point of view.

Electrochemical impedance spectroscopy (EIS) provides a potential approach to evaluate the overall breakage situation of self-healing microcapsules in cementitious materials. In this paper, EIS responses of cementitious mortar with insulative epoxy microparticles and conductive graphite microparticles, which was prepared for simulating the breakage situation of the microcapsules, were determined. An equivalent circuit was then proposed and the effect of breakage rate on its parameters was investigated. Moreover, the macroscopic simulation was conducted to explore the mechanism behind and verify the reliability of the model. Based on the results, two factors, in terms of compensation resistance and transfer resistance, were identified as the most significant parameters to detect the breakage rate of microcapsules. The macroscopic simulation revealed that, although the EIS response did not alter with embedding insulative particles, it is greatly affected by the number and the arrangement of the conductive particles, which demonstrated the reliability of the non-destructive approach.

The aging problem of bitumen leads to pavement failure after years of usage. Microcapsules containing rejuvenator is a promising chemical product applied to improve the self-healing ability of bitumen. The aim of this work was to fabricate and characterize the self-healing microcapsules containing bituminous rejuvenator with nano-inorganic/organic hybrid shells. The shell had a two-layer structure: the inside layer material was the cross-linked methanol modified melamine-formaldehyde (MMF) resin and the outside materials was composed of methanol modified MMF resin and nano-particles of calcium carbonate (nano-CaCO3). The forming mechanism of the two-layer structure was described based on a twice-condensation process. Fourier transform infrared spectroscopy (FT-IR) and Energy Dispersive Spectroscopy (EDS) results confirmed the nano-inorganic/organic hybrid structure of shells. The ideal content of nano-CaCO3 particles was optimized through the morphologies observation. The addition of nano-CaCO3 particles did not greatly influence the mean size of microcapsules. On the contrary, the nano-CaCO3 particles increased the shell thickness of microcapsules owing to the loosely composite structure of shells. Thermal stability tests showed that the microcapsules could survive in the bitumen with a temperature of 200 °C. Moreover, the microcapsules could resist a violent temperature change process without destruction attributing to the protection of nano-CaCO3 particles. The nano-particles on microcapsules decreased the deformation possibility of shells tested by nanoindentation.

A strategy to supply molecular oxygen for microbial calcium precipitation was developed for the first time. Firstly, a controlled oxygen-releasing tablet (ORT) containing CaO2 and lactic acid with a suitable ratio of 9:1 was developed. It can provide a stable oxygen supply and maintain pH in the range of 9.5–11.0 for 45 days while contacting with water. In the presence of oxygen, a self-healing bacterium H4 spores germinated more effectively and maintained high metabolic activity. Furthermore, H4 vegetative cells induced 50 % more calcium precipitation than that obtained without oxygen supply. Finally, a binary self-healing system containing bacterial spores and ORT was established. The calcium precipitation experiments showed that H4 in the binary self-healing system precipitated 27.5 mM calcium with oxygen supply after 32 days and dissolved oxygen (DO) concentration of the solution decreased from 15 to 4 mg l−1, while only 6.9 mM calcium precipitation was obtained without oxygen supply. This work can disclose the effect of oxygen on microbial calcium precipitation and further lay a foundation for the establishment of ternary self-healing system containing bacteria, ORT, and nutrients, which will be promising for the self-healing of cracks deep inside the concrete structure.

This study investigated the corrosion behavior and failure mechanism of carbon fiber reinforced polymer (CFRP) employed as an impressed current anode in 3% NaCl solution. The measured feeding voltage and potential indicated that CFRP operated stably at the applied current densities. The experimental results show that the tensile strength of CFRP decreases with increasing charge density. The corrosion rate is approximately 0.02 mm/day for a current density of 6.15 A/m 2 . The failure mechanism is due to corrosion of the epoxy in CFRP, where breakage of C N bonds in the epoxy matrix leads to depolymerization of the epoxy.

The aging problem of bitumen leads to pavement failure after years of usage. To improve its self-healing ability, it has been found that microencapsulated rejuvenator within bitumen may be an alternative approach. The aim of this paper is to investigate a novel multi-self-healing behavior of bitumen using microcapsules containing rejuvenator with different shell thickness and size distribution. The microcapsule sample was composed of three types of microcapsules with different mean size and shell thickness values. A modified beam on elastic foundation (BOEF) method was applied to investigate the mechanical properties of bitumen/microcapsule materials. The results show that these microcapsules were broken by microcracks under different conditions with a good normal distribution. The remaining microcapsules near the microcrack had the ability to leak rejuvenator later when another microcrack generated with even high crack tip strain. After loading–unloading cycles, the multi-self-healing ability of microcapsule/bitumen composite softened through of rejuvenator diffusion into bitumen. Properties of virgin and rejuvenated bitumen also confirmed that the aged bitumen had a multi-recovery ability due to the microcapsules containing rejuvenator. Both models of mechanical healing and physic–chemical healing were applied to analyze the mechanism of the multi-self-healing process. With a constant change and adjustment of microstructure, viscosity and thixotropy of bitumen, it possesses a healing ability numerous times over.

A novel high-throughput strategy was developed to determine the calcium precipitation activity (CPA) of mineralization bacteria used for self-healing of concrete cracks. A bacterial strain designated as H4 with the highest CPA of 94.8 % was screened and identified as a Bacillus species based on 16S rDNA sequence and phylogenetic tree analysis. Furthermore, the effects of certain influential factors on the microbial calcium precipitation process of H4 were evaluated. The results showed that lactate and nitrate are the best carbon and nitrogen sources, with optimal concentrations of approximately 25 and 18 mM, respectively. The H4 strain is able to maintain a high CPA in the pH range of 9.5-11.0, and a suitable initial spore concentration is 4.0 × 10(7) spores/ml. Moreover, an ambient Ca(2+) concentration greater than 60 mM resulted in a serious adverse impact not only on the CPA but also on the growth of H4, suggesting that the maintenance of the Ca(2+) concentration at a low level is necessary for microbial self-healing of concrete cracks.

This paper presents work towards development of a new type of polymeric microcapsule with phenol–formaldehyde (PF) resin as shell and dicyclopentadiene (DCPD) as healing agent for self-healing microcracks in cementitious materials. The PF/DCPD microcapsules were synthesized via in-situ polymerization and characterized by means of optical microscope (OM), scanning electron microscope (SEM) and thermal analysis (TGA). The chemical stability of synthesized microcapsules and the trigger performance were studied respectively in simulated concrete pore solution and hardened cement paste specimens. The results revealed that the synthesized microcapsules possessed excellent stability in both simulated pore solution and real cement environment. X-ray computed tomography (XCT) was applied to observe the status and fracture behavior of microcapsules inside cement paste matrix. Further segmentation and 3D rendering of the reconstructed data obtained from XCT showed that the microcapsules had a good dispersibility with desired trigger sensitivity. The OM investigation of a fractured surface of a cement paste incorporated with microcapsules confirmed that the self-healing function of the microcapsules could be triggered by cracking and the healing agent could be released simultaneously to heal the cracks.

A cementitious self-healing system was built using epoxy/urea-formaldehyde microcapsules. The effects of microcapsule content and soaking in chloride on impermeability, pore structure, and self-healing efficiency were investigated. Both microcapsule content and soaking length influenced impermeability and pore structure. With increasing microcapsule content, the impermeability of sound and damaged cementitious composite material specimens increased and then decreased; the impermeability of healing specimens gradually increased. The healing and recovery rates of impermeability increased up to 90 days soaking and then stabilized. Microcapsules positively influenced self-healing but negatively influenced the microstructure of sound specimens. Models to predict microcapsules’ effect on pore structure and impermeability were established.

In this study, hydrocalumite-like Ca2Al-NO3&minus, layered double hydroxides (Ca-Al LDHs) with different microstructures were synthesized. The crystalline properties, structure composition, morphology and particle size distribution of the Ca-Al LDH (CAL) samples were illustrated. To obtain the chloride uptake performances of CAL, the influences of contact time, initial concentration of Cl&minus, pH of reaction solution and coexistence anions on the chloride uptake were examined systematically. Compared to the CAL samples obtained at a higher aging temperature, CAL synthesized at 60 &deg, C demonstrated the minimum average particle size (6.148 &mu, m) and the best Cl&minus, adsorption capacity (211.324 mg/g). Based on the test results, the main adsorption mechanism of chloride ion on CAL was recognized as an interlayer anion exchanging reaction other than the dissolution-precipitate mode. With the increase in the pH value of reaction solution from 7 to 13, it was found that the amount of chloride ion adsorbed by CAL increased slightly, and the solution could remain at relatively high pH value even after the adsorption. The presence of CO32&minus, and SO42&minus, reduced the adsorption capacity of CAL dramatically as compared with OH&minus, due to the destruction of layered structure and the formation of precipitates (CaCO3 or CaSO4). The interference sequence of the investigated anions on the chloride uptake of CAL was SO42&minus, CO32&minus, and OH&minus, and the order of interlayer anionic affinity was Cl&minus, &gt, OH&minus, NO3&minus, The results illustrated that the synthesized CAL could be used as a promising chloride ion adsorbent for the corrosion inhibition of reinforcement embedded cement-based materials.

In this study, the physical triggered self-healing cementitious composites were prepared by mixing the epoxy resin based microcapsules with the cement, and its mechanical properties and microstructure were investigated as well. The effects of the different content of the microcapsules, proportion of prepressing stress, confining pressure and curing days on the mechanical parameters and microstructure of cementitious composite were carried out by the triaxial compression test and the mercury intrusion porosimetry (MIP) tests. The results indicated that the strength, cohesion, internal friction angle of specimens gradually decreased with an increase in microcapsules content or with an increasing of preloading stress, and the deterioration degree gradually increased with an increase in the microcapsule content or the preloading stress, but peak strain increased to vary degree. The mechanical parameters of the healed samples were repaired to different degrees compared with damaged samples. Microcapsules have significant and positive influences on the healing rates and recovery rates of mechanical properties, pore structure. The healing effect of cementitious materials was improved with increasing microcapsule content. However, the effects of microcapsules on microstructure of sound samples has to be considered.

In this work, silane coupling agent, [3-(2-Aminoethylamino)propyl]trimethoxysilane (KH792), was applied to improve the trigger efficiency of poly(phenol-formaldehyde) (PPF) microcapsules in the cementitious materials. Two schemes of reaction procedure were proposed based on different chemical reaction mechanism. The chemical structure of surface modified microcapsules was investigated by attenuated total reflection-Fourier transformation infrared spectrometry (ATR-FTIR) and then further proofed by X-ray photoelectron spectroscopy (XPS). The thermal properties and the decomposition temperature of the modified microcapsules were characterized by thermal gravimetric analysis (TGA). The morphology of the surface modified microcapsules and the crack surface of microcapsule-embedded cement paste were observed by environmental scanning electron microscope (ESEM). Finally, the influence of microcapsules incorporation and surface modification on the compressive strength of the self-healing cementitious system was evaluated. It was found that the microcapsules modified with reaction scheme 1 possess significantly higher trigger efficiency in cement matrix (41% for S1-10 sample and 63% for S1-30 sample) than the plain microcapsule (22%) and microcapsules modified with reaction scheme 2 (less than 10%). Although the incorporation of PPF microcapsules has an overall negative effect on the mechanical property of cement matrix, longer reaction time of surface modification could slightly mitigate this impact.

Cracking related deterioration is one of the most important sources of risk that seriously influences the integrity and durability of concrete structures. In this study, a novel type of light induced self-healing mechanism was designed and prepared for automatic healing of cracks in concrete. The self-healing mechanism consists of waterproofing cementitious capsules filled with UV adhesive and a UV light radiator. The shell of capsule is made of three separated but organically bonded functional layers. UV adhesive was first time employed as healing agent for concrete self-healing. The survival of the prepared capsules in the cementitious materials and the ability of capsules to break upon crack were testified. The self-healing efficiency in concrete was evaluated in terms of mechanical recovery, water absorption and water permeability. The test results implied that the proposed self-healing mechanism can be used as an ideal option in revitalizing the performance of cracked concrete.

An optimized strategy for the enhancement of microbially induced calcium precipitation including spore viability ensurance, nutrient selection and O2 supply was developed. Firstly, an optimal yeast extract concentration of 5 g/l in sporulation medium was determined based on viable spore yield and spore viability. Furthermore, the effects of certain influential factors on microbial calcium precipitation process of H4 in the presence of oxygen releasing tablet (ORT) were evaluated. The results showed that CaO2 is preferable to other peroxides in improving the calcium precipitation by H4. H4 strain is able to precipitate a highly insoluble calcium at the CaO2 dosage range of 7.5–12.5 g/l, and the most suitable spore concentration is 6 × 108 spores/ml when the spore viability (viable spore ratio) is approximately 50%. Lactate is the best carbon source and nitrate is the best nitrogen source for aerobic incubation. This work has laid a foundation of ternary self-healing system containing bacteria, ORT, and nutrients, which will be promising for the self-healing of cracks deep inside the concrete structure.

Encapsulation of healing agents embedded in a material matrix has become one of the major approaches for achieving self-healing function in cementitious materials in recent years. A novel type of microcapsules based self-healing cementitious composite was developed in Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, Shenzhen University. In this study, both macro performance and the microstructure of the composite are investigated. The macro performance was evaluated by employing the compressive strength and the dynamic modulus, whereas the microstructure was represented by the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter, which are significantly correlated to the pore-size distribution and the compressive strength. The results showed that both the compressive strength and the dynamic modulus, as well as the pore structure parameters such as porosity, cumulative-pore volume, and average-pore diameter of the specimen decrease to some extent with the amount of microcapsules. However, the self-healing rate and the recovery rate of the specimen performance and the pore-structure parameters increase with the amount of microcapsules. The results should confirm the self-healing function of microcapsules in the cementitious composite from macroscopic and microscopic viewpoints.

A review of the research activities and achievements at Shenzhen University is conducted in this paper concerning the creation and further development of novel microcapsule based self-resilience systems for their application in concrete structures. After a brief description of pioneering works in the field starting about 10 years ago, the principles raised in the relevant research are examined, where fundamental terms related to the concept of resilience are discussed. Several breakthrough points are highlighted concerning the three adopted comprehensive self-resilience systems, namely physical, chemical and microbial systems. The major challenges regarding evaluation are emphasized and further development concerning self-resilience in concrete structures will be addressed.

Microencapsulated rejuvenator has been attracted much attention for self-healing bitumen. The diffusion coefficient is one of the key parameters to estimate the feasibility of rejuvenator to age bitumen. The objective of this research was to evaluate diffusion behaviors of microencapsulated rejuvenator in aged bitumen by a FTIR-ATR method. Various microcapsule samples were mixed in bitumen to form thin films. The core material of microcapsules used as rejuvenator was diphenylsilane (DPS), its fairly specific absorption band at 843 cm−1 was selected as a marker band to calculate the diffusion coefficient (D). The microstructure parameters, including contents, mean size and mean shell thickness of microcapsules, were considered to understand the diffusion behaviors under different temperatures (20, 30, 40 and 50 °C) in bitumen. The results showed that a larger mean size of microcapsules did not greatly affect the D values under the same temperature. In contrast, a higher mean shell thickness decreased the D values because of the decrement of damage probability of microcapsules under the same content. With the same microcapsule sample in bitumen, the D values presented a trend of linear increase when the content of microcapsules was increased. All these results indicated that the microstructure affected the diffusion behaviors based on the concentration of released rejuvenator. A preliminary model of diffusion behaviors of microencapsulated rejuvenator in bitumen was given based on the Arrhenius equation considering the microstructure of microcapsules, the amount of released rejuvenator and the age degree of bitumen. This model may be a guide to the construction and application of self-healing bitumen using microcapsules.

The aim of this work was to evaluate the self-healing behaviors of bitumen using microcapsules containing rejuvenator by a modified fracture healing–refracture method through a repetitive tension test. Microcapsules had mean size values of 10, 20 and 30 μm with a same core/shell ratio of 1/1. Various microcapsules/bitumen samples were fabricated with microcapsule contents of 1.0, 3.0 and 5.0 wt. %, respectively. Tension strength values of microcapsules/bitumen samples were measured by a reparative fracture-healing process under different temperatures. It was found that these samples had tensile strength values larger than the data of pure bitumen samples under the same conditions after the four tensile fracture-healing cycles. Fracture morphology investigation and mechanism analysis indicated that the self-healing process was a process consisting of microcapsules being broken, penetrated and diffused. Moreover, the crack healing of bitumen can be considered as a viscosity driven process. The self-healing ability partly repaired the damage of bitumen during service life by comparing the properties of virgin and rejuvenated bitumen.