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Magnesium oxychloride cement (MOC) as a green cement has superior mechanical properties such as high strength and quick gain of early strength, however the inherent brittleness has limited its applications where ductility is crucial. To enhance the strength and ductility, a novel hybrid fibre-reinforced MOC-based composite (FRMOC) is developed for the first time using polyethylene (PE) fibres and basalt fibres (BF) to reinforce the MOC. A systematic investigation of the effect of fibre dosage on the flowability, rheological properties, compressive strength, and tensile properties of the developed FRMOC is conducted in this study. The results revealed that the addition of fibre reduces flowability while increasing the yield stress and plastic viscosity. The 1-day compressive strength of the FRMOC reached 68.2–85.4% of the corresponding value at 28 days, demonstrating its high early strength characteristic. The mix with 1.25% PE and 0.75% BF exhibited the maximum compressive strength at all curing ages. All the mixes consistently demonstrated excellent tensile strength and tensile strain capability (ductility), with the tensile strength and tensile strain capacity of 10.95 MPa and 4.41% achieved for the mix of 2% PE fibre, and 8.49 MPa and 2.43% for the mix of 1.25% PE and 0.75% BF respectively. Moreover, a decline in strength characteristics and strain capacity was observed as BF percentages increased. Scanning electron microscope (SEM) analysis was further employed to investigate the morphological changes in the FRMOC matrix at the microscale to discover the fibre reinforcing mechanism. • Hybrid fibre reinforced MOC (FRMOC) with enhanced strength and ductility is developed. • FRMOC demonstrates high-early-strength characteristic. • Rheological, physical, and mechanical properties were evaluated. • 1.25% PE and 0.75% BF-reinforced FRMOC exhibited maximum tensile strength and strain capacity. • Microstructural analysis is performed to analyse the morphological alterations. [ABSTRACT FROM AUTHOR]

Melia dubia is a rapidly expanding tree species in southern India, but its main drawback has been limited use in wood-based panel products until recently. To address this research gap, this study aimed to develop three reinforcement materials for producing Reinforced Laminated Veneer Lumber (RLVL) using Melia dubia. Three types of reinforcement materials, chopped glass fiber mat (CGM), glass fiber mesh (GM), and bamboo mat (BM) were employed in two layers to manufacture RLVL. The investigated parameters included physical, mechanical, and bonding performance. Furthermore, morphological images were analyzed using optical and scanning electron microscopes. The research findings revealed that the highest performance was demonstrated by BM, followed by GM and CGM. These results suggest that all three reinforcements enhanced the mechanical properties and overall performance of RLVL. Arranging the reinforcement layers closer to the surface veneer layer in the assembly resulted in outstanding mechanical properties for RLVL. The performance is superior to solid wood made from the same wood species. The findings indicate that RLVL demonstrated superior mechanical properties to laminated veneer lumber (LVL) and solid wood. The modulus of rupture for LVL reinforced with CGM, GM and BM was 7.27%, 30.91%, and 32.73% greater respectively, than that of unreinforced LVL. The composite LVL reinforced with bamboo and glass matting exhibits potential for successful utilization in outdoor structural applications, including beams, rafters, and purlins. • LVL reinforced with CGM, GM, and BM exhibited excellent modulus of rupture. • RLVL demonstrated superior mechanical properties to LVL and solid wood. • LVL reinforced with GM and BM can successfully utilized in outdoor structural applications. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effect of using single and combined marble dust (MD), granite dust (GD) and nano alumina (NA) on the performance of Portland cement concrete. MD and GD were separately replaced by different percentages of cement (2, 4, 6, 8 and 10 wt%). Furthermore, NA was used as addition by different percentages (0.25, 0.5, 0.75, 1.0 and 1.25 wt%) in the individual mixtures. The optimal ratios for MD, GD and NA were used to design two concrete mixtures with combined 6%MD+ 1%NA and 6%GD+ 1%NA. The physical properties (consistency, initial and final setting times), the workability (slump cone test), the mechanical properties (compressive, splitting tensile and flexural strengths) and microstructure analysis (X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray (EDX)) were carried on the single and combined mixtures in addition to control mix. Results revealed a rise in the water quantity needed to achieve standard consistency, along with a reduction in both initial and final setting times, as the content of GD and NA increased. However, in comparison to the control mix, minor effects in the consistency or the setting times was observed when various MD contents were used. Regarding workability, its consistently decreased in all cases in correlation with the surface area of the materials utilized. The highest reduction was observed when employing NA, characterized by the largest surface area, followed by GD, and then MD, which had a marginal effect on workability. For hardened concrete, there was an improvement in strengths of samples with replacing individually MD and GD content up to 6% at all curing ages, followed by a decrease in strengths when the content reached 10% of cement replacement compared to control sample. Concrete mixtures with addition of NA showed significant improvement in strengths at all percentages of addition until reached the maximum increase in strength at 1% then slightly decreased. Concrete with combined (6%MD+1%NA) and (6%GD+1%NA) show significantly improved mechanical properties and compact microstructure enriched with C-S-H in comparison to concrete samples using 6%MD, 6%GD and 1%NA separately. • The water of consistency increased while the initial and final setting times were shortened. • The workability of concrete was significantly diminished by NA particles. • An improvement in strength was recorded for the combined use of 6% MD and 1% NA. • An enhancement of flexural and tensile strength was attributed to the individual use of MD, GD, and NA additives. • The results of EDX analysis confirmed that lower Ca/Si ratio led to higher mechanical properties. [ABSTRACT FROM AUTHOR]

• A simplified approach for optimized acid-mechanical treatment of RCA is developed. • The highest quality RCA is obtained through acid-mechanical treatment. • The compressive strength of RAC is obtained around 16.06% higher than NAC. • Other physical, mechanical, or durability properties of RAC are closer to NAC. • Sorptivity of RAC is obtained almost equal to that of NAC. Present research develops an optimized acid-mechanical treatment for recycled concrete aggregate (RCA). RCA prepared in the laboratory jaw crusher is further soaked for 24 h in a mild acetic acid solution. Acid-soaked recycled aggregates (SR) are mechanically treated at a series of charges and drum revolutions using Los Angeles machines. A performance-based quality identification approach is used to compare acid-mechanically treated recycled concrete aggregates (SRij). The VIKOR indices (QI) for each SRij is calculated by applying a multi-criteria decision-making approach. Based on performance, three SRij with the lowest QI are selected for an experimental study. The present research achieves 71.27 MPa compressive strength for concrete composed of a SRij with the lowest QI. This strength is around 16.06% higher than concrete composed of parent aggregate. Flexural strength, split tensile strength, fracture energy, ultrasonic pulse velocity (UPV) values, rapid-chloride penetration test (RCPT) values, water absorption, and abrasion resistance are in the range of what is expected for parent aggregate concrete. The scanning electron microscope (SEM) image analysis shows that the well compacted and uniform surface morphology of aggregate strengthens the newly developed interfacial transition zone (NITZ) and old interfacial transition zone (OITZ). Acid treatment reduces microcrack lengths and widths and mechanical treatment reduces microcracks and pores by reducing adherent mortar optimally. X-ray diffraction (XRD) analysis shows the lower calcium hydroxide (CH) content in the mortar attached to the SR. A reduced CH content lowers the porosity in the adhered mortar. Thus, improved quality of attached mortar and its reduced porosity strengthen the old interfacial transition zone (OITZ) and lowers the sorptivity of the concrete than reported and almost equal to that of parent aggregate concrete. [ABSTRACT FROM AUTHOR]

• The feasibility of CSNGS for road base material was investigated. • The optimum ratio of CSG for road base was calculated and analyzed. • The application potential of CSG in road base materials was evaluated. • The strength mechanism of CSG mixture was revealed. The development of the Coal-based synthetic natural gas industry inevitably produced lots of slags. The application of coal-based synthetic natural gas slag (CSNGS) to road base not only effectively alleviated the accumulation and pollution of CSNGS, but also reduced the consumption of resources, which had significant economic and social benefits. However, CSNGS has a higher crushing value and water absorption, thus its mix design, mechanical properties and pavement performance must be further investigated when applied as the raw material of novel cementing material and aggregate. The purpose of this study is to investigate and comparatively analyze the optimal mixing ratio and mechanism of the strength of CSNGS applied in road base. For this, this study prepared the precursor of geopolymer by milling CSNGS into powder and mixing it with 20% cement. Then sodium hydroxide and sodium silicate were used as alkali activators to activate CSNGS, and the 7d unconfined compressive strength was used as the evaluation index to develop the optimal mix ratio of coal-based synthetic natural gas slag geopolymer (CSG). CSNGS with particle sizes ranging from 0 to 4.75 mm and 0 to 9.5 mm were used as aggregates to replace natural stones, then the cement and CSG were selected respectively to stabilize the slags-aggregates, and the relevant tests were carried out to investigate the mechanical and road properties. The results showed that the performance of CSG stabilized aggregates was lower than cement stabilized aggregates in the tests of unconfined compressive strength, splitting strength, unconfined compressive modulus of resilience, dry-wet cycles, and freeze–thaw cycles. The performance of the mixture deteriorated with the incorporation of CSNGS when the cementitious material was cement. The temperature shrinkage test found that the shrinkage of CSG stabilized specimens was less than cement stabilized specimens, which indicated that CSG had excellent anti-cracking potential. In addition, the temperature shrinkage coefficients of mixtures with different CSNGS dosages varied with temperature when the cementitious material was cement. Finally, to further verify the macroscopic test results, this study combined with scanning electron microscope (SEM) test to deeply analyze the strength formation mechanism of several mixtures. [ABSTRACT FROM AUTHOR]

[Display omitted] • PHA, a novel agricultural waste ash, was used as a replacement for OPC in UHSC. • The ideal replacement ratio of PHA was 5%, and the optimal treatment temp was 600 °C. • PHA lowered the water permeability of UHSC at all substitution rates applied. • The measured mechanical properties are compatible with the microstructural analysis. Cement production is classified as a highly contaminating process in recent decades, and numerous efforts have been accomplished to reduce cement used in construction for more sustainability. Cement complementary materials make an ecological impact on its manufacturing, in which the cement production cost can be reduced. In this investigation, peanut husk ash (PHA), as a newly abundant agro-industrial waste ash, was used as a substitution for ordinary Portland cement (OPC) in ultra-high-strength concrete (UHSC). PHA was heat-treated at various temperatures of 400, 500, 600, and 700 °C and utilized with substitution rates of 2.5%, 5.0%, and 7.5%. In addition, recycled granite was utilized as a coarse aggregate in UHSC. Thirteen mixes were prepared and tested to examine the fresh, mechanical, physical, and microstructure characteristics of the proposed UHSC. Concrete slump, compressive strength, indirect tensile strength, flexural strength, bond strength, modulus of elasticity, and water permeability were the measurements in this study. In addition, microstructure characteristics were obtained through X-ray diffraction analysis (XRD), thermo gravimetric analysis (TGA), and scanning electron microscope (SEM). The acquired outcomes revealed that utilizing 5% PHA as a partial substitution of OPC achieved high mechanical characteristics, and the optimal temperature for treating the peanut husk ash was 600 °C. The results of this experimental investigation can contribute well to illustrating the effect of utilizing PHA as a novel agricultural waste ash in UHSC to achieve significant financial benefits and a favorable ecological impact. [ABSTRACT FROM AUTHOR]

• The post-fire mechanical properties of Grade 12.9 bolts were investigated. • The modulus of elasticity did not significantly change after a heating-cooling cycle. • The strength decreased after a heating-cooling cycle with temperatures above 400 °C. • The effect of diameter on the post-fire yield and tensile strengths was negligible. • SEM images showed remarkable changes in microstructure for elevated temperatures. This paper aims to experimentally investigate the post-fire mechanical properties of Grade 12.9 high-strength bolts. To evaluate the effects of elevated temperatures and the bolt diameter on the post-fire mechanical properties, seven different diameters of the Grade 12.9 bolts were heated based on a standard temperature–time diagram with the ranges of 20 to 900 °C. Upon air-cooling and reaching room temperature (a heating and cooling cycle), 105 bolt specimens were subjected to the standard tensile test. The experimental results, including the post-fire stress–strain curve, yield strength, tensile strength, modulus of elasticity, and ductility, were presented. The results indicated that changes in mechanical properties were noticeable for temperatures higher than 400 °C. Although the post-fire modulus of elasticity did not significantly change, the post-fire yield and tensile strengths decreased substantially if the maximum temperature exceeded 400 °C. After heating up to 900 °C and then cooling down and reaching ambient temperature, Grade 12.9 steel bolts showed a 60% reduction in strength. The comparison of the results showed that the effect of diameter on the post-fire yield and tensile strengths of Grade 12.9 bolts was insignificant and could be neglected, but on elastic modulus and ductility, the diameter effect needs to be considered. In addition, the scanning electron microscope (SEM) images indicated that the elevated temperatures remarkably changed the microstructural characteristics of the Grade 12.9 bolts. Finally, based on the test results, the prediction equations of the post-fire mechanical properties of the Grade 12.9 high-strength bolts were proposed. [ABSTRACT FROM AUTHOR]

• Stress–strain curve characteristics of RAC under different freeze–thaw cycles. • Two damage modes of mesoscopic fracture and yield were considered. • The peak nominal stress state and the critical state were distinguished. • The mesoscopic damage evolution mechanism of RAC under loading was analyzed. • The critical state was recommended as the limit state of the constitutive model. In order to study the uniaxial compressive mechanical properties and damage evolution of recycled aggregate concrete (RAC) containing silica fume (SF) under freeze–thaw cycles, the RAC with SF replaced partial cement was prepared. The replacement rates were 0% and 9%. The RAC were subjected to 0, 50, 75, 100, 125 freeze–thaw cycles and uniaxial compression tests. The microstructure, micro-crack propagation process and reaction products were observed by acoustic emission (AE) and scanning electron microscope (SEM). The statistical damage theory was used to explore the mesoscopic damage evolution mechanism of RAC. The results showed that the peak stress and modulus of elasticity of the specimen tended to decrease, the peak strain and mass loss rate gradually increased with the increase of the number of freeze–thaw cycles(N). The compressive strength of RAC with S = 0% decreases from −41.52MPa to −11.23MPa when N increases from 0 to 125. The addition of SF produced additional volcanic ash reactions, resulting in an increase in ettringite (AFt), which reduces the porosity of RAC and is able to increase the compressive strength at different N significantly. Compressive strength increases by 21.84% and 12.06% at N = 0 and 125, respectively. Considering the existence of two mesoscopic damage modes of fracture and yield, the deformation failure mechanism of RAC was analyzed from the perspective of effective stress. The all five characteristic parameters characterizing the mesoscopic damage show significant regular change with increase of the number of cycles. The relationship between the macroscopic mechanical properties of RAC and the mesoscopic damage mechanism was established by analyzing the evolution law for the characteristic parameters. [ABSTRACT FROM AUTHOR]

In this work, recently developed Zrn1 glass fibres belonging to the SrO–Mn 2 O 3 –Fe 2 O 3 –MgO–ZrO 2 –SiO 2 (SMFMZS) system have been used as reinforcing materials in cement. The highest (2.610 N/mm 2 ) compressive strength value was obtained with the addition of 3 wt% of Zrn1 fibres into Portland cement. The microstructural behaviour of these fibres along with commercially available ones in the cement structure were investigated using a scanning electron microscope (SEM). Microstructures were fully compatible with mechanical results obtained. Eventually, it was determined that Zrn1 fibre can be a good candidate for cement reinforcement leading to high strength values. [ABSTRACT FROM AUTHOR]

In this paper, a new type of grout material composed of gypsum, quicklime, soil and admixtures was investigated on its suitability for cracks reparation in earthen sites. A series of experimental investigations such as fluidity, setting time, compressive strength, flexural strength, shrinkage, freeze-thaw stability, XRD, SEM and DSC-TG analysis were conducted. The results indicate that increasing percentage of soil led to increment of fluidity, setting time and shrinkage ratios, instead, notable decrease of compressive strength, flexural strength and weight loss after freeze-thaw cycles were obtained. Amount of 60% soil, 32% gypsum and 8% quicklime might be the optimum mix. [ABSTRACT FROM AUTHOR]

A new magnesium oxysulfate (MOS) cement was prepared with the modification of sodium malate. The microscopic morphology of MOS cement was examined by scanning electron microscope (SEM). X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) was used to characterize the crystalline degree and molecular structure of MOS cement. The characterization results indicated that quantities of 517 phase magnesium oxysulfate whiskers were detected in the modified MOS cement. The flexural strength and water resistance of MOS cement were increased by the addition of sodium malate and the mechanism was also discussed according to the characterization results mentioned above. [ABSTRACT FROM AUTHOR]

[Display omitted] • The contribution of WGP in strength enhancement of concrete is strongly affected by the fineness of its particles. • WGP could lead to the generation of more CSH by helping cement grains disperse more uniformly in the concrete matrix. • 0.5 % PP fibers acts synergically in the presence of UFG as 10 % cement substitution, resulting in the superior mechanical performance of concrete. • Less ecological impacts are reported by using UFG as cement replacement in concrete mix, without impacting its hardened properties. • PP fiber inclusion increases one of the ecological impacts related to energy consumption. Using waste glass powder (WGP) as a source of silica in the production of cement-based materials could form denser matrix and address the ecological challenge of its deposition. This study introduces two grades of fineness of WGP: fine glass powder (FGP) and ultrafine glass powder (UFG) as 5 % and 10 % substitution for cement in the production of concrete reinforced by polypropylene (PP) fiber. Nine concrete mixes are investigated for their mechanical and ecological performances. Additionally, the study of mixes' microstructure is reported to observe the influence of WGP and PP fibers contributions on the hardened matrix. ‌Based upon the results, FGP incorporation significantly enhances the FRC compressive strength from 7 to 90 days (between 40 % and 60 %). However, the highest mechanical performance is achieved by 10 % UFG as cement replacement and 0.5 % PP fiber inclusion. Moreover, scanning electron microscope (SEM) results show more chemical activity of UFG, and less calcium hydroxide presented in the hardened matrix. In terms of ecological concerns, between 5 % and 10 % lower CO 2 and SO 2 emissions and water usage indices for proposed concrete mixes containing WGP, and PP fiber are obtained, while the required energy consumption for preparing these mixes significantly increases (around 15–45 %) due to UFG and PP fiber incorporation in FRC. [ABSTRACT FROM AUTHOR]

• Replacement within 5% is proposed for municipal solid waste biochar to cement. • Biochar replacement enhances the flexural and splitting tensile strength. • Freeze-thaw resistance are not impacted by biochar. • Biochar promoted the carbonation in cement matrix. Global municipal solid waste (MSW) generation and cement manufacture pose catastrophic threats to the environment. Although positive impacts have been demonstrated for biochar originating from single biomass in concrete, limited studies focused on the biochar from the pyrolysis of municipal solid waste, and the freeze–thaw resistance of biochar concrete still remains unknown. This paper explored the feasibility of biochar derived from MSW at 600℃ to replace 1%-30% cement by weight in concrete. Properties of water absorption, setting time, mechanical properties and freeze–thaw resistance for the mixture systems were studied with the inspections of Scanning electron microscope (SEM), Fourier transforms infrared spectrometer (FT-IR) and X-ray diffraction (XRD). The results suggested that biochar replacement reduced the setting time of the binder system with an increase in water requirement of normal consistency. The compressive strength of concrete was increased by 9.2% with less than 5% of cement replaced. Biochar markedly improved the flexural and splitting tensile strength of concrete and thus played a beneficial role in toughness by 20% at 10% cement replaced. Concrete with a tiny proportion of biochar exhibited the weakest freeze–thaw resistance than control and 10% replacement. Biochar replacement promoted the formation of calcium carbonate. Biochar replacement for partial cement in concrete provides a sustainable option for municipal solid waste management and building energy consumption reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Producibility of green, SFRSCC containing CS has been investigated. • CS can improve the fresh concrete characteristics and strengthen its microstructure. • Increasing the SF volume affects the concrete performance negatively and improves the strength parameters. • Sensitivity analyses have shown steel fibers are more effective on strength parameters. • ANN models perform better than MRA models in predicting the strength parameters. The copper slag waste (CSW) is an industrial by-product, the annual production of which is huge and its disposal and management are a big challenge for environmentalists. This research has comprehensively studied, experimentally and numerically, the possibility of substituting 20–60% copper slag (CS) for natural coarse aggregates in self-compacting concretes (SCCs) reinforced with 0.1, 0.3 and 0.5% hooked-end steel fibers. According to the results, increasing the CS volume improves the characteristics of the fresh concrete, but there is an obvious drop in its flowability, fillability and passability at the highest steel fiber (SF) volume. Although increasing CS reduces the compressive strength of concretes containing low SF volumes, positive CS effects on the concrete strength are evident at the highest SF volume. Based on the scanning electron microscope (SEM) images, in concretes containing 0.1% SF, an increase in CS increases the tensile strength, and increasing this volume up to 30% makes the concrete microstructure homogeneous and integrated. To check the statistical importance of the results of the tensile and compressive strengths, use was made of the analysis of variance (ANOVA) method. To reduce costs (and human errors) and avoid time wastage, artificial neural network (ANN) prediction models and robust multiple regression analyses (MRA) methods were used to predict the compressive and tensile strengths. Results of this research confirm that using CS in producing steel fiber reinforced self-compacting concrete (SFRSCC) has technical, environmental and economic advantages. [ABSTRACT FROM AUTHOR]

• MGO applied as the early strength agents in the low temperature. • MGO effectively compensate the early mechanical strength. • Nucleation effect of MGO accelerated the hydration reaction. The mechanical strength of cement mortar is normally decreased in a low-temperature environment, which is mainly due to the slow cement hydration reaction rate and an increase in the total pore volume, especially the harmful pore volume. With the modification of nano-materials, the early mechanical strength of cement-based materials can be effectively compensated. In this study, the effect of multilayer graphene oxide (MGO) on the early mechanical properties and microstructure of cement mortar at low temperatures of 0 °C, 5 °C, and 10 °C is studied by measuring the fluidity, setting time, mechanical property, scanning electron microscope (SEM), thermogravimetric (TG), and nitrogen adsorption/desorption test. Compared with the mechanical strength of control mortar with curing temperature of 20 °C, the mortars with the addition of MGO curing at low temperature present higher mechanical strength and denser microstructure. And the mechanism of the interaction between cement particles and MGO nano particles at low temperatures (0 °C, 5 °C, and 10 °C) is further discussed. The initial hydration reaction of MGO mortar is accelerated, which is mainly due to the nucleation effect of MGO and chemical reactions between –COOH on the edge of MGO nanosheets and the Ca2+ of Ca(OH) 2. The promotion of the initial hydration refined the pore diameter of samples by reducing the pore size and total porosity, thus making the microstructure of samples denser and enhancing the strength of specimens. [ABSTRACT FROM AUTHOR]

With the flourish development of energy-saving solutions for building, the demands of phase change material (PCM) modified building materials are urgently increasing. Herein, we report a novel route to prepare clay geopolymer mortar incorporated PCM by vacuum absorption method, where PCM is produced with paraffin as heat-absorbing material and expanded perlite as p supportive material by vacuum adsorption method. The paraffin immobilized in three-dimensional network structure during the process of phase change is evidenced by scanning electron microscope (SEM), different scanning calorimetry (DSC), compressive strength, dry density and thermal conductivity. The proportion of paraffin in the composite is 55.47% by mass, and the phase change temperature and latent heat were 35.59 °C and 96.77 J/g, respectively. The compressive strength, dry apparent density, and thermal conductivity coefficient were 8.0 MPa, 1678 kg/m 3 , and 0.46 W m −1 K −1 , respectively. [ABSTRACT FROM AUTHOR]

• The green and sustainable cement-based material—UHPC was used as the repairing material to strengthen the existing cementitious substrate. • Mechanical, electrochemical and microstructural characteristics of the bonded composite systems were investigated. • The performance developments of the composite systems in a chloride-rich environment were presented. • Styrene-butadiene rubber (SBR) latex were considered to enhance the bonding properties and the electrochemical performances of the composite systems. This study investigates the mechanical, electrochemical and microstructural characteristics of UHPC bonded cementitious composite systems concerning the influences of chloride attack. The bonded composite systems with styrene-butadiene rubber (SBR) latex content of 0, 2 %, 4 %, 6 %, 8 % in UHPC layers were prepared. The experimental groups were immersed in saturated sodium chloride solution whereas the reference groups were cured in clean water. The compressive, bonding and flexural strength of the bonded systems were tested at different curing ages. The free corrosion potential, AC impedance spectroscopy and polarization resistance were considered to figure out their electrochemical behaviors. Furthermore, X-ray diffraction (XRD), pore structure characteristics as well as scanning electron microscope (SEM) observations were employed to show some light on the internal mechanism at a microscale level. Results indicate that the chloride-rich environment demonstrated certain adverse effects on the system's mechanical properties, especially the bonding strength, which could be reduced by 20 % on average at 56d. Proper content of SBR latex was conducive to the system's bonding strength. However, when the dosage was too large, a remarkable adverse effect on compressive strength was seen. The addition of SBR latex could further delay the corrosion of the reinforcement inside the system, from 28d of the systems without latex to 42d with 4 % SBR latex. The microstructural investigations confirmed that in a chloride-rich environment, the total pore volume was reduced by 29.4 % at 28d. A dense transition zone was observed between the substrate and the UHPC layer with a width of about 0.1 μm in clean water curing, whereas it became relatively loose and obvious bonding holes appeared in this area under severe chloride attack. [ABSTRACT FROM AUTHOR]

• The mechanical properties and pore structure deterioration of FRCs in five freeze-thaw media (i.e. WF, NF, SSF, SCF, HSF) were studied. • The influence of the SCF on the mechanical properties of FRCs is the greatest, followed by the HSF, SSF, WF and NF. • There is an optimal fiber dosage for the FRCs to resist freeze-thaw cycle and salt erosion. • The porosities and salt corrosion degree of the FRCs exposed on the freeze-thaw cycles significantly increased. More engineering infrastructures have been built in cold regions and even permafrost area with salt-rich media, such as seawater, saline soil or groundwater. In such environment, the concrete is not only destroyed by freeze-thaw processes, but also damaged by corrosion. Therefore, this study investigated the mechanical properties and pore structure deterioration of fiber-reinforced concrete (FRC) in five types freeze-thaw media, i.e., water (WF), natural air (NF), 5 % sodium sulfate solution (SSF), 5 % sodium chloride solution (SCF), a mixture of the 5 % sodium sulfate and 5 % sodium chloride solution (HSF). A total of 180 freeze-thaw cycles were carried out on steel fiber-reinforced concrete (SFRC), polypropylene fiber-reinforced concrete (PPFRC), and basalt fiber-reinforced concrete (BFRC). The compressive strength and elastic modulus of FRCs after freeze-thaw cycles were measured to observe the influence of different media and fibers on the mechanical properties. The deterioration of the pore structure of the FRCs was observed by SEM (scanning electron microscope), XRD (X-ray diffraction), and MIP (mercury intrusion porosimetry) tests. The results show that the influence of the SCF on the mechanical properties of concrete is the greatest, followed by HSF, SSF, WF and NF. Moreover, there is an optimal fiber dosage for the FRCs to resist freeze-thaw cycles and salt erosion, the optimal fiber dosages for the SFRC, PPFRC and BFRC were 2 %, 2 ‰ and 0.5 ‰, respectively. Additionally, compared to the concrete not exposed to freeze-thaw cycles in the NF, the porosities of the FRCs exposed to the freeze-thaw cycles significantly increased. Under the same freeze-thaw media, the porosity of the BFRC is larger than that of the PPFRC. Furthermore, for the FRCs in the SSF, the proportions of gel micro-pores (<10 nm) decreased with the number of freeze-thaw cycles, whereas the proportions of capillary pores (10–5000 nm) and macro-pores (>5000 nm) increased. [ABSTRACT FROM AUTHOR]

A new artificial reef concrete (NARC) with sulphoaluminate cement, marine sand and sea water et al. was proposed. The effect of cement type, sand type and water type on the workability (namely slump, slump loss cohesiveness, water retention), mechanical properties namely compressive strength, splitting tensile strength and dynamic elastic modulus) and affinity (namely surface initial pH value and the leaching rate of alkaline material in concrete) of concrete was studied. The microstructure of concrete was detected by X-ray diffraction, scanning electron microscope and pore structure analyzer, respectively. The studies show that NARC has superior workability, mechanical properties and affinity compared to ordinary Portland cement concrete with river sand and fresh water. Therefore, the feasibility of NARC in artificial reef is verified. [ABSTRACT FROM AUTHOR]

• Geopolymer can be synthesis using lunar in-situ high temperature. • Time-varying curing temperature influences the strength development. • Lunar extreme temperature causes deterioration in the mechanical properties. • Zeolitic phase materials are products of geopolymerization reaction. Lunar base construction is of great importance for deep space exploration, and the establishment of lunar pavements for the movement of machinery and transportation of materials is essential to improve construction efficiency. Lunar regolith as an in-situ resource has been demonstrated to be used as raw materials to prepare geopolymers for lunar pavements. In this paper, geopolymers based on lunar regolith simulant with different concentrations of alkali activator were synthesized using the natural high-temperature of the lunar surface. Then, the durability of the resulting geopolymer under lunar high and cryogenic temperature was investigated. The flexural and compressive strength was tested, and the microstructure was characterized using Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS), 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (29Si MAS-NMR), and Mercury Intrusion Porosimetry (MIP). The results of the curing section showed that the geopolymer with 8 mol/L sodium hydroxide (NaOH) generated high strength and dense structure, and the period of 420 h–492 h of a lunar day corresponding to a temperature variation from 84.5 °C to 33.5 °C in 72 h was suitable for preparation, with 5.7 MPa and 31.2 MPa 72-h flexural and compressive strength. Three test points were selected on the lunar 30° latitude temperature curve, corresponding to before and after the cryogenic attack, and after high temperature again to investigate the durability of the geopolymer, and the degradation was found noticeable. The flexural strength decreased about 49% and 70%, and the compressive strength decreased about 15% and 18% after the cryogenic temperature and high temperature again, respectively. Microscopic observations revealed that the geopolymer structure was significantly granulated with obvious cracks and increased porosity. In addition, the formation of the zeolitic phase was unexpectedly found, leading to interfacial cracks and mechanical strength reduction of the geopolymer. This paper will be beneficial to explore the evolution of properties of lunar pavement construction materials in the lunar environment. [ABSTRACT FROM AUTHOR]

• A new type of polyurethane-urea binder used for grooving grouting surface pavement was proposed. • The mechanical properties of polyurethane-urea binder were verified. • The interfacial bonding properties of polyurethane-urea binder were verified. • The UV aging mechanism of polyurethane-urea binder was revealed. Grooved grouting surface pavement has certain advantages in ice-suppression and ice-breaking, and would not cause damage to the surrounding environment. However, when ordinary polyurethane (PU) is used as the binder of grouting material, the interfacial adhesion and durability between grouting material and asphalt mixture are insufficient. Therefore, a new polyurethane-urea (PUU) binder was prepared for the surface pavement of groove grouting in this study. Firstly, the gelation time of PUU binder with different polyuria (PUa) content was tested. Then, the mechanical properties of PUU binder were verified through the shore A hardness test, tensile strength and dynamic thermal mechanical analysis (DMA). The interfacial bonding properties of PUU binder were tested by shear and pull-out tests The UV aging mechanism of PUU binder was revealed by means of Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscope (SEM) and Tensile strength test. Finally, the wear resistance of PUU binder was verified by Akron wear test. The test results show that the allowable content of ethyl acetate should be controlled within 5–10%. The mechanical properties of PUU were significantly improved by adding a certain proportion of PUa. When the content of PUa is 30% and 40%, the interfacial bonding strength of PUU binder increases significantly, in which the Shear strength increases by 17.1% and 18.1%, and the Pull-out strength increases by 31.7% and 34.9%, respectively. In conclusion, the recommended dosage range of PUa is 30–40%. [ABSTRACT FROM AUTHOR]

• The ITZ characteristics are examined by SEM-EDS and microscopic nanoindentation. • The mechanical properties and durability of full-grade concrete specimens are investigated. • The utilization of ASRS has significant economic and environmental benefits. • The ASRS can be utilized as aggregates in lower tensile strength requirements dam concrete. Aggregates with surface rust stains (ASRS) is very common in the construction of water conservancy and hydropower projects. The purpose of this paper is to provide the possibility to utilize rusted raw rocks as aggregate in dam concrete. The physical and chemical properties of rusted raw rocks are measured. In addition, comparisons of their mechanics and the durability of dam concrete prepared by ASRS and rust-free limestone aggregates (RFLA) are investigated. The characteristics of interfacial transition zone (ITZ) between aggregate and paste are investigated by the means of scanning electron microscope with energy dispersive spectrum (SEM-EDS) and nano-indentation technology. The results show the apparent density and uniaxial compressive strength of ASRS are lower than the RFLA by 10 kg/m3 and 5.3 MPa, respectively. The compressive strengths of ASRS concrete are approximate those of RFLA concrete. The tensile strength of ASRS concrete is lower than that of RFLA concrete by 13 %. The ASRS slightly reduces the dam concrete frost resistance and impermeability. The ITZ average thickness of the ASRS sample is thicker than that of the RFLA sample by 15.0–20.0 μm. The values of indentation modulus and hardness observed across the ITZ in the ASRS sample are lower than those of the RFLA sample by 6.31 GPa and 0.11 GPa, respectively. The ASRS can be utilized as aggregates in dam concrete, such as in the structure with lower tensile strength requirements. [ABSTRACT FROM AUTHOR]

• Two new double-component early strength agents were developed by combined calcium formate and methacrylic acid with cement paste powder respectively. • The mechanical strength of cement mortar was significantly improved by adding double-component early strength agents. • The hydration products increase and porosity decreases of mortar with the addition of double-component early strength agents. • The influences of curing temperature and water-cement ratio on strength development were studied. This paper investigated the effects of calcium formate and methacrylic acid combined with cement paste powder on flowability, setting time, and mechanical strength of cement mortar. The effects of curing temperature and water-cement ratio on the hydration of cement mortar incorporating these two double-component early strength agents were also studied. Experimental results show that the 0.5, 1, 3 and 28-day compressive strength increased by 96.7% (89.3%), 81.7% (75.6%), 74.7% (67.4%) and 50.1% (49.9%) when 1.0% calcium formate (or 0.5% methacrylic acid) combined with 1.0% cement paste powder. These two types of double-component early strength agents presented an excellent synergistic effect. Higher curing temperature can accelerate the early hydration of cement but has a negative impact on the later strength. X-ray diffraction (XRD), Fourier transformation infrared spectroscope (FTIR), mercury intrusion porosimeter (MIP), and scanning electron microscope (SEM) results show that combined accelerating admixtures can accelerate the hydration of cement and decrease the porosity of cement mortar. Finally, the cost evaluation indicates that double-component early strength agents are applicable to manufacture high early-age strength cement-based materials. [ABSTRACT FROM AUTHOR]

• Nodes effect on the mechanical properties of LBL units was studied by experiments. • Failure modes of LBL units under compression, tension and shear were analyzed. • The stress–strain relationship models of LBL units were studied. • Bamboo nodes showed considerable adverse effect on tensile properties of LBL units. Mechanical properties of laminated bamboo lumber (LBL) units with and without nodes were experimentally studied under various loading conditions such as compression along parallel and perpendicular to the grain as well as tension and shear along parallel to the grain direction. Small specimens were carefully manufactured from Moso bamboo investigate to the effect of nodes on key mechanical properties including strength, ductility, elastic modulus and failure modes under considered loading cases. Results showed that nodes clearly have some beneficial effect on compression resistance of LBL units, albeit the effect is dependent on grain direction. On the other hand, the presence of nodes showed an adverse effect on the tensile resistance but did not have any meaningful effect on shear resistance. Elastic modulus under different loading conditions was also affected due to the presence of nodes. The behavior of LBL units under compression and shear were nonlinear and showed good agreement with Ramberg-Osgood type analytical models when calibrated using obtained results. In addition, the microstructure of LBL units was scanned using an electron microscope and it was obvious that those units are a two-phase composite material like natural bamboo. [ABSTRACT FROM AUTHOR]

• Powder almond shell was produced and then Christal dye was absorbed as a textile waste. • Effect of christal violet dyed almond shell (VDSA) was investigated by substitution with cement. • Fresh, hardened and durability properties of self-compacting mortar incorporation with VDSA are considered. • Optimum VDSA content is determined between the 5.0% and 12.5% in terms of fresh and hardened state properties. • VDSA, as a textile industry waste, can be used in SCMs to prevent disposal accumulation. The aim of the current experimental study is to investigate the effect of waste textile dye absorbed almond shell on fresh and mechanical characteristics of self-compacting mortar (SCMs). In this context, eight SCMs were designed by substituting Violet Dye Solution adsorbed Almond shell (VDSA) at the rate of 0%, 2.5%, 5.0%, 7.5%, 10.0%, 12.5%, 15.0% and 17.5% as a cement on weight basis including the control mix. To measure the rheological properties of SCMs, mini slump and V-Funnel tests were conducted. A total of 72 beams of 40x40x160 mm3 dimension specimens were casted and immersed in water curing at the end of the 7, 28 and 56 days to determine the mechanical parameters. 48 cubes of 50x50x50 mm3 dimensions were casted and kept in the curing tank to determine durability characteristics such as porosity, sorptivity and specific gravity. Quantitative analyses are also performed by using Scanning Electron Microscopes (SEM), X-ray Diffraction Analysis (XRD), Energy-Dispersive X-ray Spectroscopy (EDS) and Fourier Transform Infrared (FTIR). The experimental results indicated that as the content of VDSA enchases, a remarkable enhancement in flexural strength at early days age and 28 days age strength. Whereas, increasing the content of VDSA resulted in a considerable decrease in compressive strength higher than 5%. [ABSTRACT FROM AUTHOR]

• The mechanical properties of RAC with MK and fiber including PF and BF were studied. • The pore structure of RAC was analyzed by NMR. • The RAC with MK and fiber are studied from macro and micro perspectives. • The results that 15% MK and PF cloud enhance the performance of RAC most obviously were showed. The paper aimed to study the compound effect of metakaolin (MK) and fiber, including polyvinyl alcohol (PVA) fiber (PF)and basalt fiber (BF) on the recycled aggregate concrete (RAC). Eighteen kinds of RAC were prepared and divided into three groups, namely the RAC mixed with MK (RM) group replacing cement rate of 0%, 5%, 10%, 15%, 20% and 25%, the RM-BF group mixed with 1.3% BF (percentage of cementitious material) based on the RM group, and the RM-PF group mixed with 1.3% PF based on the RM group. The mechanical properties such as compressive strength, splitting tensile strength, flexural strength, and bending toughness were studied, and the pore structure was analyzed by nuclear magnetic resonance (NMR). In addition, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the crystal composition and micro morphology. The results showed that MK had a positive effect on the improvement of the mechanical properties and the improvement of microstructure of RAC, and this positive effect first increased and then decreased with the increase of MK substitution rate. For the RM-PF group and RM-BF group, the study indicated that the mechanical properties and microstructure of RAC under the combined effect of fiber and MK were further improved. Especially in terms of mechanical properties, the splitting tensile strength and flexural strength enhancement was more significant. The internal pores of RAC with MK substitution rate of 15% and fibers were significantly reduced, and a large amount of calcium silicate hydrate (C-S-H) gel was generated inside RAC, which had the best adhesion to the fiber. It was believed that RAC with PF and 15% MK had the most significantly enhanced performance. [ABSTRACT FROM AUTHOR]

• Coarse aggregate to make concrete kerbs was partially replaced by recycled plastics. • The performance of three types of plastics was compared. • The abrasion resistance could be improved for PET and PP RPC up to 20%. • The mixtures meet the strength requirement of kerb design. This paper investigates the feasibility of using three types of recycled plastic waste to partially replace the coarse aggregate for kerbing application. The recycled plastic wastes adopted in the research include Polyethylene Terephthalate (PET), High Density Polyethylene (HDPE) and Polypropylene (PP). Various properties of the mixes were assessed including fresh concrete properties (workability, fresh density, and air content), mechanical properties (compressive strength, indirect tensile strength, flexural strength and static chord modulus of elasticity) and durability properties (water absorption, water sorptivity, abrasion resistance and drying shrinkage). Scanning electron microscope (SEM) analysis was used to investigate the microstructures of the specimens. Results showed that utilization of plastic aggregate in concrete reduced overall workability and fresh density of concrete; using plastic waste as partial replacement for natural coarse aggregate up to 20% satisfies the kerb design requirement and the strength loss is not detrimental. Up to 20% replacement of PET and PP showed an improved abrasion resistance compared to the control mix. PET exhibited an acceptable drying shrinkage compared to the control mix. The analysis of microstructural observations showed that mixes containing PET exhibited better bond strength compared to HDPE and PP. [ABSTRACT FROM AUTHOR]

• Basalt and carbon fiber in oil well cement were considered. • Mechanical properties of cement was evaluated by compressive and splitting tensile testing. • SEM analysis shows that the basalt and carbon fiber arrest cracking at different levels. In order to study the hybrid effect of basalt fiber and carbon fiber on the mechanical properties of oil well cement, the response surface design method was adopted to optimize the mixed content of basalt fiber and carbon fiber in oil well cement. With the help of X-ray diffraction (XRD) and scanning electron microscope (SEM) characterization, the crushed samples of oil well cement mixed basalt fiber and carbon fiber was micro-analyzed, and the enhancement mechanism of basalt fiber and carbon fiber on the compressive strength and splitting tensile strength of oil well cement was explored. The research results showed that basalt fiber and carbon fiber mixed can significantly increase the compressive strength and splitting tensile strength of oil well cement. Compared with oil well cement without fiber, the maximum compressive strength of oil well cement with mixed fiber for the curing time of 3 days, 7 days and 28 days was increased by 48.94%, 24.05% and 25.68%, respectively. The maximum splitting tensile strength of oil well cement with mixed fiber for curing time of 3 days, 7 days and 28 days was increased by 151.14%, 68.01% and 46.28%, respectively. Moreover, addition of 0.55 wt% basalt fibers and 0.09 wt% carbon fibers in oil well cement leads to more ductile behavior with higher peak compressive strength after 3 days curing time. Addition of 0.29 wt% basalt fibers and 0.32 wt% carbon fibers in oil well cement leads to more ductile behavior with higher peak splitting tensile strength after 3 days curing time. The addition of carbon fiber and basalt fiber does not change the hydrates of oil well cement after oil well cement hydration. The improvement of the mechanical properties of fiber-reinforced oil well cement mainly depends on the fiber bridging, crack deflection and fiber pulling out or breaking. Based on the theory of linear elastic fracture mechanics, a fiber oil well cement crack resistance model was constructed. The results of this study provide a certain reference for the application of fiber-reinforced oil well cement with requirements for tensile and crack resistance in oil and gas well cementing projects. [ABSTRACT FROM AUTHOR]

• UHPC incorporated with MPCM was developed as structural–functional integrated construction material. • MPCM-UHPC possesses high mechanical properties and favorable heat storage efficiency. • Good chemical compatibility between UHPC and MPCM was experimentally verified. • The addition of MPCM strengthened the interface between steel fiber and matrix. A novel structural–functional integrated concrete (MPCM-UHPC) with excellent mechanical properties and thermal storage capacity was developed by incorporating microencapsulated phase change material (MPCM) into ultra-high performance concrete (UHPC). The indoor tests were performed to determine the thermal performance of MPCM-UHPC. Mechanical properties and autogenous shrinkage strain of MPCM-UHPC were evaluated. The microstructure, thermal stability, chemical structure and crystal structure of the composite material were investigated by mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), thermal gravimetric analyzer (TGA), Fourier transformation infrared spectroscope (FTIR) and X-ray diffraction (XRD). The results show that no chemically phenomenological interaction between MPCM and cementitious components occurs in the hydration process. However, the incorporation of MPCM increased air voids content in cementitious matrix, thus inducing harmful effect on the mechanical properties and autogenous shrinkage of MPCM-UHPC. From indoor performance test, the surface temperature of UHPC with 10 wt% MPCM was 3.9 °C lower than that of control group. Compressive tests results show that it possesses a considerable compressive strength of 78 MPa. Therefore, the MPCM-UHPC composite is a promising structural–functional integrated building material. [ABSTRACT FROM AUTHOR]

• Epoxy resins were affected mechanically and chemically from corrosive environment significantly. • While the acidic environment aging adversely effects the properties of epoxy resin, it is determined that salty water environment aging increase the strength of epoxy resin. • The MWCNT nano particles reinforcement diminish the endurance of epoxy resin against the aging environment. In this study, the effects of different harsh aging environments on the chemical and mechanical properties of neat and multiwall carbon nanotubes (MWCNT) reinforced epoxy resins were investigated. The neat and 1 wt% MWCNT reinforced epoxy resins were exposed to four different corrosive environments, namely deionized water, NaCl solution (10 wt% NaCl), H 2 SO 4 solution (10 wt% H 2 SO 4), and HCl solution (10 wt% HCl. The mass variation results revealed that the highest absorption rates were found in specimens aged in both acidic environments. The highest amount of absorption was observed in the H 2 SO 4 environment, measured approximately 3% for neat epoxy , and 6.5% for MWCNT reinforced epoxy resin. FT-IR spectrums showed that the most affected peaks belong to specimens aged in both acidic environments. Tensile test results revealed that the aging process in H 2 SO 4 solution and deionized water deteriorated the strength of specimens. According to the literature, it was reported that the strength of specimens aged in NaCl solution environment is decreased. However, the same trend has not been in this study. In our study, the strength of specimens aged in NaCl solution environment increased impressively by 29%, which makes this study more striking. Another important point analyzed from the tensile test results was that the MWCNT nanoparticle reinforcement adversely affects the strength of the epoxy resin. So, it can be clearly stated that the use of expensive MWCNTs as filler of epoxy resin is not useful to improve its aging resistance. The scanning electron microscope (SEM) and optical microscope images showed that acidic environments result in different fracture mechanisms from typical polymer damaged surfaces reported in available researches. [ABSTRACT FROM AUTHOR]

• Water/binder ratio can affect the optimal fiber content. • Full curves of water absorption were obtained. • Pore size or porosity characteristics of hardened concrete were analyzed. This paper presents the results of a comprehensive experimental work investigating the effect of glass fiber (GF) and polypropylene fiber (PPF) on the mechanical and microstructural properties of concrete as a function of the water/binder ratio and fiber content. Different water/binder ratios (0.30 and 0.35), GF and PPF contents (0.45, 0.90, and 1.35% by volume fractions), and curing times (7 and 28 d) were used during the experiment to prepare the concrete specimens. The compressive, four-point flexural, and splitting tensile strengths and the full curves of water absorption of the glass-fiber-reinforced concrete (GFRC) and polypropylene-fiber-reinforced concrete (PPFRC) were obtained. The strength differences and water absorption properties of GFRC/PPFRC were analyzed in depth. Scanning electron microscope observation was undertaken to analyze the mechanism of the water/binder ratio and fiber effects. The results showed that the water/binder ratio can affect the optimal fiber content. When discussing the effect of fibers on the improvement of concrete mechanical or microstructural properties, the influence of the water/binder ratio should be considered. The improvement effect of GF on water absorption was significantly superior to that of PPF. When the water/binder ratio was 0.30, the water absorption of GFRC and PPFRC tended to be stable as the test proceeded, while when the water/binder ratio increased to 0.35, the water absorption of the GFRC and PPFRC with the highest fiber dosage still increased with the prolongation of testing time. [ABSTRACT FROM AUTHOR]

• The post-fire mechanical properties of corroded grade D36 marine steel are presented. • The distributions of corrosion products affect the post-fire properties of the steel. • 900 °C treatment significantly enhances the mechanical properties of the material. • The high temperature influences the microstructures and fracture morphologies. Corrosion and high temperature are two main detrimental factors that degenerate the mechanical properties and lead to decrease both in strength and durability of steel. The combined influence of corrosion and high temperature on the mechanical properties of grade D36 marine steel is proposed in this study. A series of tests were conducted to determine the post-fire mechanical properties of corroded marine steel. Specimens were corroded by a saltspray test, and then heated to 500 °C or 900 °C. Afterward, stress–strain curves, elastic modulus, yield stress and ultimate strength of the specimens were obtained from tensile coupon tests. Three-dimensional laser scanning was used to evaluate the impact of corrosion. The microstructure and fracture morphology analyses were carried out by metallographic microscope and scanning electron microscope (SEM), respectively. It was found that corrosion and high temperature have significant influence not only on the mechanical properties, but also on the microstructures and corresponding fracture morphology of grade D36 marine steel. [ABSTRACT FROM AUTHOR]

• Micromorphology of the PU grout materials of different densities were analyzed. • Uniaxial compression test was conducted on the PU grout materials. • Effects of density, size of PU samples on the compressive strength were studied. • The preferred geometric size of PU samples for the uniaxial compression test is suggested. Polyurethane (PU) is increasingly adopted as grouting materials in the non-excavation rehabilitation of infrastructures. The compressive strength of PU materials is the key to achieving a desirable grouting effect. However, the geometric sizes of PU samples in the uniaxial compression test are not specified yet, which makes the test results less universal. Here, PU samples with a square cross-section were prepared with different densities and geometric sizes. The micromorphology of the PU matrices was investigated via a scanning electron microscope (SEM). Uniaxial compression tests were conducted, and the effects of density, side length ( l ), and height to side length ratio ( H / l ) of the samples on the mechanical properties were analyzed. The results show that micro foams in PU matrices have average equivalent diameters and average eccentricities of 50–116 μm and 0.55–0.78, respectively. When the density increases, the foams become smaller and more sphere-like. Under the uniaxial load, until strain hardening occurs, both the varied density, l and H / l bring little influence on the variation laws of stress with the strain. The mechanical properties of PU grouting materials increase with the increased density following a power function. When l or H / l changes, the mechanical properties of low-density PU (≤0.30 g/cm3) are little affected while those of high-density PU vary significantly but irregularly. The larger PU samples may be weaker than the smaller ones but may also be stronger. Cubic PU samples with a side length of 40 or 50 mm are preferred for the uniaxial compression test. [ABSTRACT FROM AUTHOR]

• Using Response Surface Methodology to understand properties of polyvinyl alcohol/acrylonitrile on bamboo nanocomposite. • Characterization and optimisation mechanical properties of polyvinyl alcohol/acrylonitrile on bamboo nanocomposite. • Modification using chemical improved the properties of polyvinyl alcohol/acrylonitrile on bamboo nanocomposite. Bamboo is a natural resource that has prospect to substitute wood in many engineering applications. In this work, mechanical properties of bamboo nanocomposite based on polyvinyl alcohol (PVA)/acrylonitrile/nanoclay was evaluated using response surface methodology (RSM). The developed nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infra-red (FTIR), Scanning electron microscope (SEM), Differential scanning colometry (DSC), and Thermo gravimetry analysis (TGA) to study their compositional, morphological and thermal properties. Models were developed to predict modulus of elasticity and modulus of rupture of the nanocomposites. The developed models fitted the experimental values with R2 close to 1 and residuals normal probability plot fitted to straight line. Optimized values of MOE and MOR were 12.82 GPa and 105.52 MPa respectively at 10 wt% clay loading, 15 wt% PVA/acrylonitrile loading and modification time of 5 min. The melting and decomposition temperature of the nanocomposites have shown significant improvement compared to the raw bamboo. [ABSTRACT FROM AUTHOR]

• Multi-layer graphene (MLG) were used to reinforce reactive powder concrete (RPC). • Reinforcing mechanism of MLG to RPC was investigated through electrical properties. • Compressive strength and pore solution resistance were negatively correlated. • Adding MLG can fill pores, reduce pore size and reduce weakened area in RPC. • Incorporating MLG can reduce CaO/SiO 2 ratio of C-S-H gel and size of CH crystal. The utilization of multi-layer graphenes (MLGs) as reinforcement for reactive powder concrete (RPC) is motivated by their flat morphology, unique stacking structure, high stiffness/strength, and high electron mobility. This paper studied compressive strength, flexural strength and flexural stress-strain relationship of MLGs reinforced RPC (MRRPC). Electrical properties including electrical resistivity and electrochemical impedance spectroscopy were tested to characterize RPC's pore structure firstly. Besides, the microstructure of MRRPC was observed using scanning electron microscope, and CaO/SiO 2 ratio of C-S-H gel was obtained by energy dispersive spectrometer. The results show that the MRRPC filled with 0.5 wt% MLGs exhibits maximum compressive strength of 123.2 MPa. MRRPC filled with 0.75 wt% MLGs presents maximum flexural strength of 11.08 MPa, along with 18.7% enhancement to ultimate flexural strain. Electrical properties' results suggest pore structure of RPC can be modified by MLGs. Negative correlation between compressive strength and two electrical parameters including electrical resistivity increase and pore solution resistance is observed. Moreover, CaO/SiO 2 ratio of C-S-H gel is decreased and size of calcium hydroxide crystal is reduced along with the addition of MLGs, implying MLGs can fill pores and reduce weakened areas in RPC matrix effectively. [ABSTRACT FROM AUTHOR]

• Combined use of nanoparticles can be more effective in enhancing mechanical properties of concrete at ambient and elevated temperatures that single form. • The most optimum mix to enhance mechanical properties was (NS + NA) with 1.5% hybrid combination. • The microstructure of concrete can be significantly improved by increasing the percentage of nanomaterials from 0.5 to 1.5%. • the decrease in residual compressive strength of control and nano-added concrete was highly significant, especially for 500 and 800 °C. The main aim of this study is to investigate the effects of nano-SiO 2 (NS), nano-Al 2 O 3 (NA), nano-TiO 2 (NT) and nano-Fe 2 O 3 (NF) particles in single, binary, ternary, and quaternary combinations on compressive, splitting tensile, and flexural strengths of concrete. The residual compressive strength of control and nano-added concretes are also determined at 300, 500, and 800 °C elevated temperatures. Furthermore, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses have been conducted to examine the chemical composition and microstructure of concrete samples. The main parameters investigated were the amount and various combinations of NS, NA, NT and NF, producing thirty-one concrete batches, one control and thirty NS, NA, NT and NF added concrete mixes. The total nanoparticle amounts in the concrete mixes of 0.5%, 1%, and 1.5% by weight of cement were studied. A total of 558 concrete specimens with nanoparticles were tested at 28 days to determine compressive, splitting tensile, flexural, and residual compressive strength of concretes at ambient and elevated temperatures. It can be clearly concluded that NS and NA particles are more effective than NT and NF particles in improving the mechanical properties of concrete. The largest increase in compressive, splitting tensile, and flexural strength was obtained for 1.5% of NS and NA hybrid combination as 13.95%, 18.55%, and 21.88%, respectively. Furthermore, the residual compressive strength of single and hybrid nano-added concrete specimens significantly reduced, especially at 800 °C. Although the largest decrease in residual compressive strength of 57.65% was recorded for control concrete, the lowest reduction of 41.59% was observed for concrete with 1.5% of NS and NA hybrid combination at 800 °C. [ABSTRACT FROM AUTHOR]

• The effects of GNP on concrete materials prepared with alkali activated cement were investigated. • Minor compressive strength gain was obtained at 0.2 vol% of GNP. • The addition of GNP at 0.2 vol% reduced the sorptivity of alkali activated cement concrete by about 35% • The addition of GNP was observed to significantly improve the abrasion resistance of concrete. The effects of the addition of graphene nanoplatelets (GNPs) on the microstructure, heat of hydration, mechanical properties and durability characteristics of alkali activated binders were investigated. A simple mixing process led to reasonably uniform dispersion of GNPs in the matrix, with minor agglomeration of GNPs detected via scanning electron microscopy. Tests on engineering properties indicated that the compressive strength of the alkali activated binder increased with the addition of GNPs at relatively low concentrations. Gains were also realized in the abrasion resistance and moisture sorptivity of the binder with GNPs addition. The heat of hydration investigations indicated that the addition of GNPs accelerates the hydration process and increases the amount of hydration products, especially at early ages. Scanning electron microscope investigations further indicated that GNPs could impede the development of microcracks and mitigate their propagation within matrix; indications of good bonding between the GNPs and the alkali activated matrix were also noted. [ABSTRACT FROM AUTHOR]

• It is the best for strength and workability with 20% replacement of aeolian sand. • Influence mechanism of aeolian sand on strength of concrete is revealed. • Effect of aeolian sand on strength is due to its chemical and physical properties. • Strength prediction model for ASC agrees well with the test results. The aim of this work is to promote the utilization of aeolian sand for concrete production. The workability and mechanical property of aeolian sand concrete (ASC) is studied. The effect mechanisms of aeolian sand on the mechanical property of concrete are revealed from multiple scales. For the macro scale, use the pressure tester to test the compressive strength. For the mesoscopic, use the scanning electron microscope (SEM) to observe the structure of the interface transition zone (ITZ) and the nuclear magnetic resonance (NMR) to test the pore structure. Meanwhile, the distribution of chemical bonds is analyzed by the Fourier transform infrared (FT-IR) spectrometer and the microstructure of hydration products are characterized by the SEM for the microscopic. The results show that using parts of aeolian sand can improve the working and mechanical property of concrete. The physical influence mechanism is that it perfects the gradation of the aggregate and increases the density of concrete, reduces the effect of aggregate size and micro-region bleeding, improves the structure of ITZ and pores. For the chemical, it may accelerate the hydration reaction speed of cement and change the microstructure of hydration products. Finally, a strength prediction model of ASC is established based on the published and tested data, which agrees well with the tested result. [ABSTRACT FROM AUTHOR]

• Mechanical properties of G20Mn5QT cast steel at low temperatures were determined. • Parameters in VGM/SMCS were calibrated for G20Mn5QT cast steel at low temperatures. • VGM/SMCS are applicable for G20Mn5QT cast steel at low temperatures. • Characteristic length of G20Mn5QT cast steel decreases with the drop of the temperature. With superior structural performances, G20Mn5QT cast steel has been extensively used in fabricating complex joints in steel constructions. Fracture failure of G20Mn5QT cast steel is then an important issue, especially for low-temperature situations. In this paper, mechanical properties of G20Mn5QT cast steel at low temperatures were studied by tensile coupon tests and Charpy impact tests. The effects of the low temperature on mechanical properties and the ductile-brittle transition temperature of G20Mn5QT cast steel were obtained based on the test results. The void growth model (VGM) and the stress modified critical strain (SMCS) model, which are two typical micromechanical fracture models, were calibrated for G20Mn5QT cast steel by experiments and complementary FEA on smooth notched tensile (SNT) specimens at four temperature levels, 20°C, −20°C, −40°C and −60°C. For each temperature level, the material parameters in VGM and SMCS calculated based on test results of all six different specimens are in very good consistence. This consistency indicates the applicability of VGM and SMCS for predicting the ductile fracture of G20Mn5QT cast steel, even at the temperature of −60°C, which is much lower than the transition temperature of the material. The calibrated material parameters representing the resistance to ductile fracture of the material decrease linearly with the drop of the temperature. The characteristic length of G20Mn5QT cast steel was also determined by observation of fractured surfaces of test specimens with the scanning electron microscope, which has the tendency to decrease with the drop of the temperature. [ABSTRACT FROM AUTHOR]

• Improved fresh properties were found by introducing MCSW and FA in HSSCC. • FA used up to 25% in ternary mixes resulted in comparable compressive strength with the 5SF mix. • Combined use of MCSW up to 10% and FA up to 15% along with 5% SF resulted in better resistance to water absorption. • SEM analysis indicated improved microstructure by combined use of MCSW up to 10% and FA up to 15% along with 5% SF. Disposal of marble cutting slurry waste (MCSW) has acquired a disastrous proportion and is a leading cause of environmental and health-related issues. On the other hand, high strength self-compacting concrete (HSSCC) is being widely used which requires a higher quantity of cement and ultimately resulting in the substantial CO 2 emission to the environment. The aim of this study is to produce economical and eco-efficient HSSCC using MCSW, fly ash (FA), and silica fume (SF). This would help to beneficially use MCSW and minimize the need to use large quantities of cement in HSSCC production, thus significantly reducing CO 2 emissions. Total sixteen number of HSSCC mixes in binary, ternary and quaternary form were prepared by incorporating MCSW, FA, and SF as a replacement of cement. Among all HSSCC mixes, one mix was prepared with a 100% cement binder which was named as control mix. The impact on fresh properties was assessed by slump flow, T 500 time, V-funnel time, fresh density, L-box height ratio, J-ring flow, and J-ring step height. Mechanical performance in terms of compressive strength, and other properties like percentage of water absorption, percentage of voids, and dry bulk density were also examined. The microstructural investigation was carried out using the Scanning electron microscope (SEM) and Fourier transform infrared radiation (FTIR) techniques. It was observed that the incorporation of MCSW and FA improved the fresh properties of HSSCC. A combined use of 10% MCSW and 15% FA with 5% SF as cement replacement resulted in enhanced mechanical performance and amended microstructure. [ABSTRACT FROM AUTHOR]

• A comprehensive microstructure analysis and mechanical tests on UHPC is performed. • Effect of different parameters on UHPC is investigated in detail. • Strengthening mechanism on microstructure and mechanical properties of UHPC concrete is studied. • A new optimal mix ratio of UHPC is proposed. In this paper, the strengthening mechanism of curing temperature, fine aggregate gradation, reactive materials, water reducer type, dosage and types of fibers on the microstructures and mechanical properties of Ultra-high-Performance Concrete (UHPC) was analyzed in detail by means of microstructure analysis using Scanning Electron Microscope (SEM) and mechanical tests. Based on the mechanical tests and analysis of the microstructure, a new optimal mix proportion of UHPC was also developed by considering the economic benefits. It is found that the gradation of UHPC fine aggregate can achieve the densest stacking state gradation after the optimization of mix proportion. Gradation Optimization promotes UHPC to be hydrated step by step. A large amount of hydrated calcium silicate (C-S-H) gel and a small amount of crystal produced in the early hydration phase together form the original structure of the concrete. The initial hydration products consume a large amount of Ca (OH) 2 to produce C-S-H and other cementitious substances by so called Secondary Hydration Reaction, the C-S-H can further catalyst hydration. It is also found that the low water-cement ratio can reduce porosity and improve the compactness and compressive strength of UHPC microstructure. The fibers can effectively delay the appearance and development of micro-cracks in the concrete matrix, help to improve the toughness, ductility and flexural properties of UHPC, and avoid brittle failure. High temperature curing is beneficial to the formation of cementitious substances with lower calcium-silicate ratio (C/S) and catalyst the occurrence of secondary hydration reaction. [ABSTRACT FROM AUTHOR]

• The marble dust particles will be re-used and blended with PP to produce a novel composite materia. • The addition of marble dust into the PP matrix improved the mechanical properties. • The mechanical properties increased with decreasing particle size. • SEM images show the dust particles dispersion, agglomeration and the pullout of this particles. The main objective of this study is to review the capability of using marble dust particles as reinforcing materials in polymeric composites. In this study, it is intended to obtain a novel composite material by using these particles as reinforcement in polypropylene (PP) matrix. The effect of different particle sizes (35–1350 μm) and the weight percentage of marble dust particles (10–70 wt%) on the thermal and mechanical properties were investigated. In addition, thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and Energy-dispersive X-ray spectroscopy (EDX) of the dust particles were studied. It was found that the thermal and the mechanical properties (such as flexural strength, compressive strength, elastic modulus and hardness) of the composites were improved by adding the dust particles into the PP matrix. The experimental results were observed and the optimum conditions were determined. The fracture surface of the tested samples under bending was studied using scanning electron microscope (SEM). SEM images show the dust particles agglomeration and the pullout of this particles which are responsible for the strength reduction in the composites. [ABSTRACT FROM AUTHOR]

• Evenly dispersed graphene nanoplates (GNPs) achieved in aqueous solution. • Several methods were employed for GNPs characterizations. • The effect of GNPs on hydration product of cement was fully discussed. • The mechanism of GNPs on hydration reaction had been summarized. Graphene nanoplatelets (GNPs) with extraordinary mechanical properties have been widely cooperated in special and high-performance composites. However, the impact of GNPs on hydration process in cement composites is still ambiguous and controversial. In this research, the GNPs was dispersed by dispersants with ultrasonication. The GNPs/cement composites were prepared and their hydration process were monitored by isothermal calorimetry (TAM Air) and 29Si NMR analysis. In addition, the pore structure and microstructure of GNPs/cement composites were tested with Mercury intrusion porosimeter (MIP) and Scanning electron microscope (SEM). And phase analysis was discussed by analysis of XRD and TG/DTG spectrums. The experimental results suggest that GNPs may contribute to accelerate the hydration reaction and more hydration products generated because of sufficient ion exchange in earlier ages and in this basis, a more compact microstructure and better mechanical properties of GNPs cement composites achieved. [ABSTRACT FROM AUTHOR]