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Two metallo-triangles SA and SB with cis-TPE motifs were constructed and their fluorescence properties were explored. Compared with dilute solution, both triangles SA and SB exhibited significant AIE behavior in the aggregated states.

Dye aggregates have attracted a great deal of attention due to their widespread applications in organic light-emitting devices, light-harvesting systems, etc. However, the strategies to precisely control chromophores with specific spatial arrangements still remain a great challenge. In this work, a series of double- and triple-decker supramolecular complexes are successfully constructed by coordination-driven self-assembly of carefully designed shape-complementary ligands, one claw-like tetraphenylethylene (TPE)-based host ligand and three tetratopic or ditopic guest ligands. The spatial configurations of these assemblies (one double-decker and three "S-shaped" or "X-shaped" triple-decker structures) depend on the angles of these TPE-derived ligands. Notably, the three triple-decker structures are geometric isomers. Furthermore, photophysical studies show that these complexes exhibit different ratios of radiative (k

Establishing an effective method to enhance the adhesion of mortar on recycled concrete aggregate (RCA) is key to the utilization of RCA. In this paper, a novel and simple approach for strengthening the mortar layer of RCA by treatment with a crystallizing agent (CA) was proposed, and the effects of different treatment regime on the density, water absorption, mineral composition, and microstructure of RCA were determined. Moreover, the performance of CA-treated RCA in recycled aggregate concrete (RAC) was investigated, and its mechanism of the treatment was explored at both the microscopic and macroscopic levels. The results showed that CA treatment significantly improved the overall performance of RCA by increasing the density and calcium silicate hydrate (C–S–H) content, which enhanced the properties of the new and old interfacial transition zones and enhanced the mechanical properties of the RAC. The improvements were attributed to the reaction of CA with calcium-rich hydration products in the mortar layer of RCA, which formed C–S–H precipitates. The newly-formed C–S–H filled the pores of RCA and blocked cracks, which improved the compactness of the RCA.

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.

The nanoscratch test has been identified as one of the important tools for evaluating the mechanical and tribological properties of materials. This paper reviews the current researches on the nanoscratch test using to characterise the mechanical properties of three typical materials, including thin film, polymer composite and concrete, from the perspectives of the Berkovich indenter, parameter selection, mode selection, and analysis of resulting data. In addition, to provide a deep understanding on the test from different magnitude, a comparison between the microscratch test and nanoscratch test on the evaluation of tribological performance is also provided in this paper. The characterisation by nanoscratch test of two structural samples, in terms of layered film structures (thin film and coating sample) and single layer block structure (polymer composite sample and concrete samples) are also described in this paper, which aims to provides a deep understand on the evaluation the adhesion, tribological and interfacial properties of the typical materials samples by nanoscratch test. Finally, the coefficient of friction and critical load are discussed, which are two important parameters in tribological properties and adhesion properties.

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.

In this study, self-healing cementitious materials based on urea-formaldehyde microcapsules were investigated. Electrochemical impedance spectroscopy tests were conducted on specimens with a single crack and a model describing the relationship between the impedance parameters and the degree of damage was established by equivalent circuit fitting. The model was applied to multi-crack specimens that were representative of actual engineering conditions and the coefficients of the model of the multi-crack specimens were determined. Based on this model, the trends of the repair rate for different self-healing times were obtained. The dynamic elastic modulus of all the specimens was tested for verifying the reliability of this model, and the repair rate of the dynamic elastic modulus was calculated according to a similar method. It is found that the repair rate of the dynamic elastic modulus and the damage repair rate were not uniform in value, but with a similar variation trend. The results demonstrated the reliability of the proposed non-destructive method.

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.

The production of alkali activated slag composites (AASCs) generally requires a large amount of slag, and waste expanded perlite (WEP) is a type of industrial waste that can be used as green supplementary cementitious material (SCM) in the building industry. In this study, the feasibility of using ground WEP as a sustainable replacement for slag in AASCs was evaluated. The process of hydration, mechanical properties, and ecological and economic performance of the AASCs with ground WEP (WEP-AASCs) were investigated in this study. The results showed that the 28–day compressive strength of WEP-AASCs at 10, 30, and 50 vol% WEP decreased by 2.4 MPa (4%), 7.3 MPa (12%), and 9.4 MPa (16%), respectively, compared to AASCs without WEP. In addition, both the heat of reaction and reaction peak of WEP–AASCs by thermogravimetric analysis decreased with the increasing additions of ground WEP. Combined with the X-ray diffraction (XRD) and scanning electron microscope (SEM) of WEP–AASCs, it was found that the addition of ground WEP did not change the reaction products in the AASCs. Based on the economic and ecological analyses, reductions in cost (6–19%), embodied energy (5–24%), and embodied CO2 emissions (3.2–16%) can be achieved, compared to AASCs without ground WEP. Therefore, WEP is suitable for use as SCM in AASCs, and presents promising applications based on the identified performance and sustainability.

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.

To obtain the mechanical parameters for a microcapsule, such as the Young's modulus, yield stress, and hardening coefficients using different mechanical constitutive models, parameter identification must be implemented using inverse analysis. In the present study, a new approach combining the finite-element method and an optimisation procedure is proposed for determining the constitutive parameters of urea-formaldehyde microcapsules, in which three types of elastic-plastic constitutive models are considered: the power-law hardening model, the elastic-perfectly plastic model, and the elastic-perfectly plastic model with linear hardening. A nonlinear optimisation procedure is applied to determine the minimum of the multivariable objective function, which is defined as the norm of the difference between the numerical and experimental results. The efficiency and robustness of the proposed method are verified with different initial values and numbers of elements. The force-displacement curves from a numerical simulation show good agreement with the experimental data, indicating that the proposed approach and the mechanical parameters determined are reliable.

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.

Characterization of the mechanical properties of urea-formaldehyde microcapsules filled with epoxy resin is of importance for achieving self-healing of cementitious composites. In this study, the morphology of microcapsules, including diameter and thickness, was characterized using scanning electron microscopy. The mechanical properties of single microcapsules, including Young's modulus and hardness, were determined through a nanoindentation technology based on the elastic contact theory using a Berkovich indenter. Moreover, to investigate the structural effects of microcapsules, a diamond plate indenter was used, and the Young's modulus of the microcapsule wall was calculated through the ordinary least square optimization method according to three analytical solutions on the basis of thin shell theory, namely Reissner, Pogorelov, and Lukasiewicz methods. It is shown that the results of the contact and thin shell theory were similar, in which the similarity occurs only in the case of a small deformation. When the deformation was large (indentation depth >900 nm), the structural effect became significant. In addition, the finite element method was applied to simulate the mechanical response of the microcapsules using the results obtained. The validity of the approach was approved.

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.

In this computational study, the nanoscale mechanical properties of C-S-H composite materials under different temperatures are evaluated with molecular dynamics (MD). The effects of different proportions of crystals, levels of porosity, and degrees of temperature on the nanoscale mechanical properties of the C-S-H composites are investigated. The initial computational models are built up based on tobermorite and jennite crystals, and the geometries of the models are then optimized before performing MD simulations at 25 °C, 80 °C, and 200–1500 °C with the interval of 100 °C, respectively. The resulting mechanical properties of the composites are evaluated under different conditions. The self-consistent (SC), Mori-Tanaka (MT), and Voigt methods are used to understand the effects of crystal proportions and porosities on the mechanical properties of the C-S-H composites at three representative temperatures. It is found that both the bulk and shear moduli of the C-S-H composites are decreased with the increasing temperature. Regarding the influence of porosity, a specific proportional relationship is obtained based on the results with the SC, MT, and Voigt methods. The reported findings provide a better insight into the thermomechanical response of the C-S-H composites.

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.

The brittleness of microcapsule shell greatly restricts its self-healing performance since it is easily ruptured during the mixing process. Based on the heat releasing nature during cement hydration, a novel concept of temperature-adaptive microcapsule (TAM) was proposed, which can exhibit a switchable mechanical property with temperature. In this paper, a series of TAM with polymethylmethacrylate-methacrylate shell and magnesium oxide core was prepared with four designed transition temperature, and were characterised by Fourier transform infrared spectroscopy, nano-indentation tests, scanning electron microscopy, thermalgravity analysis and particle size analysis, which confirmed the success in preparing the TAM. Moreover, the performance of proposed microcapsules in cement was investigated by determining the breakage rate of microcapsule and recovery rate of cement paste under different mixing temperature. The results illustrated that compared to lower mixing temperature, a 75% reduction in breakage rate and a 5% increment in recovery rate was observed in TAM embedded cementitious paste at an elevated mixing temperature. This work should provide a promising approach to improve the performance of microcapsules for self-healing cementitious materials.