Macro Performance Research Articles

Study on Microstructure of Recycled Aggregate Concrete by Scanning Electron Microscopy: A Review

Recycled Aggregate Concrete (RAC) is a new type of concrete made by utilizing waste concrete as aggregate after treatment. With the enhancement of environmental awareness and resource conservation, but the microstructural part of recycled aggregate concrete is not as important as the macro performance enhancement aspect by scholars. And Scanning Electron Microscope (SEM) is a powerful tool for microanalysis, which can provide high-resolution images of samples as well as information on surface morphology and microstructure. In this paper, the micro-structure of RAC will be comprehensively analyzed according to the performance characteristics of RAC materials and the relevant analysis technology of SEM. Based on the microscopic technology of SEM, the research progress of the micro-structure of RAC was carried out, and the morphology and distribution characteristics of recycled aggregate particles, pore structure and porosity, the interface combination between recycled aggregate and cement matrix, and the relationship between micro-structure and RAC properties were summarized, which provided theoretical support for the future understanding of the micro-structure of RAC, increased the understanding of the micro-structure of RAC materials, and more systematically understood the application of microscopic analysis methods in RAC.

Macro Performances and Microstructures of Graphene Oxide-Modified Cement Mortar Under Steam Curing Conditions

Macro Performances and Microstructures of Graphene Oxide-Modified Cement Mortar Under Steam Curing Conditions

Limestone calcined clay-based engineered cementitious composites (LC3-ECC) with recycled sand: Macro performance and micro mechanism

Limestone calcined clay cement (LC3) contributes to the development of sustainable cement-based materials. In this study, LC3 was combined with fly ash (FA) and recycled sands (RS) to develop engineered cementitious composites (ECC). Three FA/LC3 ratios (1, 1.5, and 2) and three RS particle sizes (0.15–1.18 mm, 0.15–2.36 mm, and 0.15–4.75 mm) were studied. Compared to ordinary Portland cement (OPC)-based paste, the LC3 substitution resulted in higher hydration heat and hydration degree, forming more hydration products. Although LC3 substitution produced a slightly lower compressive strength, a more robust tensile strain-hardening behavior than OPC-based ECC was achieved. The increasing FA/LC3 ratios gradually reduced compressive strength, tensile strength, and crack width. The multiple cracking behavior with controlled widths of LC3-based ECC was found to be more stable, which could be traced to the superior properties of fiber/matrix interfacial transition zone. In addition, utilizing RS as fine aggregates with various particle sizes could achieve an ultra-high tensile strain capacity exceeding 8 % for LC3-based ECC, thereby enhancing its utilization efficiency. Furthermore, the utilization of LC3 resulted in 28.6–47.1 % and 6.6–22.0 % reductions in carbon emission and embodied energy, respectively. The combination of LC3 and RS holds a promising approach to developing sustainable ECC with desirable mechanical performance.

Characterization of microstructure and moisture distribution evolution of concrete using AC impedance spectroscopy

In this study, the AC impedance responses of concrete with different microstructures and water contents at elevated temperatures are examined. First, an equivalent circuit model of concrete is proposed. The simulation results of the equivalent circuit are in good agreement with the AC impedance spectrum. Then, semi-infinite, infinite, and barrier diffusion modes of water diffusion within concrete are proposed. The quantitative relationships between AC impedance parameters and moisture content of concrete are established. Finally, the equivalent porosity and thermal damage are characterized using AC impedance parameters. Both show linear relation with the total porosity obtained experimentally by porosity tests. Therefore, AC impedance spectroscopy can quantitatively characterize the internal microstructure and moisture content evolution, and further reveal the mechanism of the macro performance of concrete.

Characterization of Interface Transition Zone in Asphalt Mixture Using Mechanical and Microscopic Methods.

An enormous surge in the pavement sector requires the evaluation of interface bonding in asphalt composite, since the assessment of bonding brings considerable cost savings. Microscopic and mechanical analyses were performed to study the status of the interface transition zone of four groups of asphalt mixtures, using thin-slice preparation to obtain asphalt mixture slices with a flat surface for microscopic analysis. The interface transition zones were characterized using good knowledge of blending or diffusion phenomena by conducting tests both at the micro and macro levels to determine mixture quality. Asphalt mixture components were observed using fluorescence microscopy imaging and evaluated by the gray value change law. Asphalt mixture groups, (virgin, recycled of 30% aged and 70% unaged, 6%, and 4% rejuvenator dosage mixtures) under the same process parameters, which are a mixing time of 270 s and a mixing temperature of 150 °C, been considered optimum for component fusion in a hot asphalt mixture were used. This study relied on the influence of morphology law, assessed through rutting tests for high temperature performance, semi-circular bending tests for low temperature performance, and pull-off tests for interface bonding strength. The relationship between interface transition zones and macro performance was studied. The self-developed pull-off method was a research innovation which can be used as an alternative to study interface transition zones in asphalt mixtures, and provides the necessary data needed with 3D surface failure mode calculations. The device measured the bonding strength of a single aggregate in distinct positions using the bitumen penetration test method. The main goals were to determine a correction factor, identify the appropriate alteration, and compute the actual fracture surface area. Using scanning electron microscopy for interface characterization and micro-morphologies of mortar transition zone, our analysis provides adequate knowledge about interface position and the components present. The applied approaches to characterize asphalt mixture interfaces proved workable and reliable, as all methods have similar trends with useful information to determine asphalt pavement quality.

Insights on the mechanical properties and failure mechanisms of calcium silicate hydrates based on deep-learning potential molecular dynamics

The molecular-scale mechanical properties of calcium silicate hydrates are crucial to the macro performance of cementitious materials, while achieving coincidence between accuracy and efficiency in computational simulations still remains a challenge. This study utilizes a deep-learning potential, specifically developed for calcium silicate hydrates based on artificial neural network, to achieve molecular dynamics simulations with accuracy comparable to first-principle methods. With this potential, the elastic properties and uniaxial mechanical behaviors are explored, wherein the anisotropy and impact mechanism of calcium ratios are analyzed. The results add to evidence that the deep-learning potential possess a higher accuracy than common force fields. The anisotropy of elastic modulus is mainly attributed to different atomic interactions in various directions, while the anisotropy of strength is additionally affected by the form of failure. This study may advance the accurate molecular-scale simulation and deepen the understanding of the strength source and cohesion mechanism of cement-based materials.

Study on the influence of early frost attack on the performance of cement mortar

The loss of strength and durability caused by early frost attack is the macro performance of internal microstructure deterioration. Understanding the influence mechanism of early frost attack at the micro level is necessary to avoid or minimize the early frost attack to macro performance. In this study, the influence of early frost attack on the strength, water sorptivity, chloride permeability, and microstructure of cement mortar was investigated. The fresh mortars were pre-cured for 10, 12, 14, and 16 h and then frozen at −10 °C for 7 days to simulate an early frost attack. After freezing, the standard curing (20 °C) was carried out until the testing. It is found that after standard curing of 28 days, the strength of early-frozen mortar can reach more than 95 % of the 28-day strength of unfrozen mortar. Interestingly, the sorptivity coefficient and total charge passed of early-frozen mortar are much higher than the level of unfrozen mortar, and the loss of resistance to water penetration and chloride ion penetration exceeds 20 %, indicating that early frost attack causes more severe damage to the durability than to the strength of mortar. Mercury intrusion porosimetry (MIP) results show that early frost attack can increase the pore volume of >50 nm and coarsen the pores within 10–50 nm. Correspondingly, key pore parameters (critical pore diameter, threshold pore diameter, and tortuosity) that affect the durability of mortar are also negatively affected. Energy dispersive spectroscopy (EDS) analysis also shows that after suffering early frost attack, the interfacial transition zone (ITZ) thickness of mortar is increased from 4 to 10 μm to 8–13 μm, and the probability of high Ca/Si ratios (4–10) in the ITZ is also increased. Finally, it is concluded that the coupling effect of pore structure coarsening and ITZ degradation leads to more severe durability loss.

Role of graphene oxide as a powerful nano-catalyst in sodium hydroxide-activated slag and its impact on interfacial transition zone

The use of nanocarbon materials to enhance the toughness of fragile cementitious materials has attracted increasing attention for investigation. This study examines the effects of incorporating graphene oxide (GO) into NaOH-activated slag (AAS) pastes and mortars, focusing on workability, phase composition, mechanical properties, and the local mechanical properties of the interfacial transition zone (ITZ) between sand and paste. The experimental results indicate that the addition of GO decreases the flowability of NaOH-AAS pastes, with noticeable aggregation at concentrations above 0.03 wt%. Furthermore, GO enhances the hydration degree of ground granulated blast furnace slag (GGBS), leading to an increased amount of C-A-S-H gel without introducing new phases. In terms of macro performance, incorporating 0.03 wt% GO significantly improves the compressive and flexural strengths of NaOH-AAS mortars by 10.6 % and 17.9 %, respectively. Additionally, the presence of GO reduces the ITZ thickness from 30 to 15 micrometres in NaOH-AAS mortars, which likely contributes to the enhanced mechanical performance.

New magnesium cement optimized in MgO-K2HPO4-SiO2 system and its hardening performance

Silica fume (SF) is commonly used in producing magnesium potassium phosphate cement (MPC) and magnesium silicate hydrate cement (MSHC). However, its roles in magnesium cement would differ from each other when mono hydrogen phosphate was involved. This paper aims to find optimized compositions in MgO-K2HPO4 DKP- SF system with comprehensive considerations of the micro and macro performances. Ternary contour maps were designed to determine the optimized proportions of MgO, DKP and SF. The hydration reaction mechanism was analyzed with a variety of techniques including XRD, SEM, TG-DTG and NMR. Magnesium cement containing 60–75 % dead-burnt MgO, 10–25 % DKP and 12.5–25 % SF exhibited excellent compressive strength and volume stability. K-struvite and M-S-H were confirmed to promote the hydration and hardening performance of the blended MgO-DKP-SF system with optimized proportions. An excess of soluble K+ from DKP may precipitate as KOH and then dissolute in solution, increasing pH and release of Si from SF.

High performance CaCO3-based composites using sodium tripolyphosphate as phase controlling additive: Bamboo fiber driven high strength development

Due to the limited carbonation degree caused by the surface densification of carbonated products, the development of high-strength carbonated composites remains challenging. In this work, bamboo fiber (BFs) is utilized as a reaction reinforcing agent along with sodium tripolyphosphate (STPP) as a CaCO3 phase controlling additive to prepare high-strength bamboo fiber reinforced carbonated wollastonite composites (BFRCWs). The phase composition and microstructure are systematically investigated by multiscale physicochemical analysis, followed by the determination of macro properties and volume deformation. Results indicate that BF and STPP have a synergistic effect on the microstructural formation and macro performance of BFRCWs. STPP-treated BF (ST-BF) can serve as an internal curing agent and the porous structure of BF provides more channels for ion and CO2 transport, whereas CaCO3 phase composition and cementitious behavior is modified by STPP. The addition of ST-BF, particularly for long fibers, accelerates the carbonation reaction, resulting in an increased ratio of poorly crystalline CaCO3 and a refined pore structure. With increasing ST-BF dosage (0–3 vol%), the cementitious reaction is enhanced, but excessive fibers (3 vol%) incorporation introduces additional porosity, consequently reducing compressive strength. The desired pore structure with the optimal 2 vol% ST-BF (3–6 mm) shows the highest strength of 103.5 MPa at 28 days.

Investigation of the macro performance and mechanism of biochar modified ultra-high performance concrete

Ultra-high performance concrete (UHPC), an extraordinary category of cementitious composites, showcases unparalleled mechanical and durability properties. Given the current disparity in carbon levels and the environmental hazards associated with cement production, various types of biochar materials have been incorporated into cement composites. This approach offers a mutually advantageous solution, effectively reducing CO2 emissions while simultaneously preserving natural resources. This study aims to evaluate the use of palm shells, a waste biomass, as a substitute for aggregate in the UHPC matrix. The investigation focused on replacing 1–40 % of sand, specifically considering apricot, date, and peach shells biochar at an 8 % replacement. A comprehensive analysis was carried out on a total of 12 combinations, encompassing a control group. For biochar-mortar admixtures, a decrease in workability and density were observed. Replacing 1 % of sand with biochar in UHPC mortar improved compressive strength, but increasing biochar dosage weakened it. Biochar-mortar was demonstrated a dual impact on drying shrinkage. Mixtures with higher biochar dosages showed a slight increase in permeability. Incorporating 1 % biochar into UHPC led to a slightly lower electrical flux value. SEM images were obtained, highlighting the compact morphological structure seen in both the control and the 1 % biochar mortar. MIP test showed nearly 1.6 times increase in the 2-dimensional porosity, from 10.49 % (control) to 16.83 % for sample which had 30 % biochar. Based on the results obtained, it could be concluded that biochar possesses the capability, which enhances the properties of UHPC mortar when used as a partial replacement for conventional fine aggregate in minor fractions.

Study on the Effect of XYPEX Admixture on the Performance of Panel Concrete and Microscopic Mechanism

The influence of different XYPEX content on the performance of dam panel concrete was studied through laboratory tests. The test results show that a certain amount of XYPEX can improve the compressive strength and impermeability of panel concrete. According to the scanning electron microscope photos, XYPEX admixture has a good filling effect on the internal pores of concrete in the microstructure, and the macro performance is improved for impermeability, but the effect on the visible cracks on the surface of concrete is small. The research results fill the gap in the research field of XYPEX admixture in dam panel concrete, provide a new idea for improving the durability of panel concrete, and provide technical support and data support for the future application of XYPEX admixture in water conservancy and hydropower projects.

Utilization of recycled coral sand and aluminum scraps in foam concrete: Preparation, insulation of environmental noise and heat, and pore structure

The utilization of industrial and marine wastes in building materials can significantly mitigate resource consumption and environmental hazards. In this study, the waste aluminum scraps and coral sand were utilized as foaming agent and fillers for foam concrete (FC) to address application challenges associated with industrial and marine wastes. Simultaneously, their impact on the mechanical property, heat and noise insulation properties, as well as pore structure of FC were investigated. The response surface methodology was used to optimize the mix design of FC. Heat and noise insulation characteristics of FC were tested by a visible infrared thermometer and a self-manufactured soundproof device, while the pore characteristic was analyzed by digital image processing technique. Additionally, the effect of foaming agents and coral sand on the internal pore structure of FC was studied by means of microscopic analysis(FTIR, XRD, SEM). The results show that foam content significantly influenced the performance of FC. As the foam content reached 15%, the compressive strength was the worst (ranging from 1.26 to 1.59MPa). Additionally, foam and coral sand inhibited the expansion of sulfoaluminate cement. At 15% foam content and 30% coral sand content, the thermal conductivity decreased to 0.082 W/(m·℃), representing a reduction of 52.5% compared to the control group. Regarding noise reduction performance, a foam content of 10% yields optimal results. The heat and noise insulation properties were both improved due to the enhanced porous structure of coral sand. However, excessive admixtures, such as 50 % content of coral sand, could weaken the strength by destroying the fine pore structure. Microscopic analysis further revealed that foaming agents could affect the hydration of cement with little impact on macro performance. Moreover, they also enhanced the toughness of bubbles and changed the surface structure of pore walls to ensure the integrity of the pore structure of FC.

Optimizing the infoproduct launch process: integrating the communication macrostrategy and paid traffic key performance indicators through the VERSALTO method

The global market, especially in the Digital Marketing area, has experienced enormous growth and a high degree of impact due to advances in technology, the growing number of smartphone users and the daily time spent using smartphones by these users. Within this market, the infoproducts sector has emerged as a specific and high-potential segment, directly connecting end consumers with information products, such as courses, mentoring, training, e-books and much more. The unique potential of this sector lies in its ability to overcome barriers that exist in other markets, making it possible to reach niche audiences and audiences on a global scale, often with low-cost operations and high return on investment (ROI). Despite the enormous potential of this emerging market, it lacks consolidated research on macro performance indicators in infoproduct operations, particularly the interaction between indicators of paid traffic operations and communication strategies, which directly affect the financial results of digital launches. In this context, this study aims to present the VERSALTO method, a framework designed to plan and analyze communication macro strategies and paid traffic indicators for infoproduct launches, demonstrating the interrelationship between these KPIs and the communication macro strategy, in addition to developing knowledge academic on the topic. To develop the method and demonstrate its practical application, this research analyzes two case studies with revenues exceeding 100 thousand Brazilian reais (20 thousand American dollars). Through this analysis, the interrelationship between paid traffic indicators and the communication macro strategy used in infoproduct launches was visualized. In this way, this study provides crucial insights for optimizing strategies and generating more profitable results in the dynamic digital marketing landscape.

Mechanism of concrete damage under the coupled action of freeze-thaw cycle and low-stress impact fatigue load：From pore structure to energy dissipation

The interaction mechanism behind concrete damage induced by the combined effects of freeze-thaw cycles and fatigue load (FTF) remains insufficiently understood. This study aims to shed light on this mechanism by employing three sets of specimens, each subjected to different conditions: freeze-thaw cycles alone, low-stress impact fatigue (LIF) load alone, and FTF coupled action. Macro performance and microstructural changes of these specimens were measured after each testing round to analyze the evolution of concrete damage. Additionally, the influence of load duration on the damage under the coupled action was also explored. Results indicated that under FTF action, when LIF loading is applied for a short duration, freeze-thaw cycles play a dominant role in concrete damage, while the influence of LIF loading is minimal. However, when LIF loading is sustained for an extended period coupled with freeze-thaw cycles, it can accelerate concrete degradation. This can be attributed to the accumulation of micro-cracks during longer loading duration, eventually manifesting as visible cracks. These cracks link adjacent pores and increase the number of interconnected pores. This, coupled with freeze-thaw damage increasing the probability of crack forming, results in accelerated deterioration of concrete. The mechanism underlying this concrete deterioration was also analyzed from an energy dissipation prospect.

Study on the attributes of transverse surface waves in a layered piezoelectric semi-space with surface elasticity theory and extended stroh formalism

Previous works on surface acoustic wave sensors have shown great limitations in selecting piezoelectric materials and the wave propagation direction. To eliminate such limitations in the technological revolution of SAW sensors, the current paper's main purpose is to explore how wave propagation orientation affects the performance of SAW macro- and nano-sensors. Based on Extended Stroh formalism, the theoretical forms are derived and exploited to present the wavenumber of transverse waves in an arbitrary direction of the piezoelectric medium. Furthermore, we consider surface elasticity theory to acquire the phase velocity equation on the basis of the expression of the wavenumber. More intuitively, a physical model is set up to obtain the horizontal shear stiffness of the surface and bulk layers. Then, the numerical case is carried out to determine the relationship between phase velocity and wave propagation orientation. By comparing the numerical study and the physical model, it can be found that the empirical formula of shear stiffness for bulk and surface layers offers a helpful route to precisely predict the mechanical attributes of SAW macro- and nano-sensors, respectively. The summaries of the current theoretical work benefit the manufacturing of surface acoustic wave sensors with improved performance.

Characterization of rutting damage based on two-dimensional image analysis of changes in mesoscopic aggregate properties of asphalt mixtures

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

Study on the Inhibition Characteristics of Coal Spontaneous Combustion by Silica Gel Foam.

The spontaneous combustion of residual coal in abandoned mining areas severely affects the safe and efficient extraction of coal, employee occupational health, and regional environmental ecology. A technical measure for preventing and controlling the spontaneous combustion of residual coal involves injecting antispontaneous combustion materials into abandoned areas. In this study, the composition, preparation, and mechanism of action of silica gel foam, a material used to suppress spontaneous combustion during coal mining, were investigated to improve the performance of materials designed to prevent spontaneous combustion in abandoned areas. The inhibitory efficiency improved, and the mechanical strength and stability of the foam liquid film increased upon adding modified antioxidants and nanosilica particles to the gel foam. Macro performance tests, microstructural characterization, and chemical inhibition mechanism analyses verified the efficacy of silica gel foam for suppressing spontaneous combustion. The air leakage resistance of the silica gel foam effectively increased the air leakage resistance of the coal samples at different pressures. New radicals formed during the spontaneous combustion of coal comprising different inhibitors, as indicated by the g-factor results of electron paramagnetic resonance (EPR) spectroscopy analysis; the formation of radicals initially decreased and then increased when the inhibitor material changed. The concentration of free radicals decreased markedly during the spontaneous combustion process of both raw and inhibited coal samples at low oxidation temperatures (∼60-100 °C), indicating a marked inhibitory effect.

Application of SCMs and seawater to cement-bonded calcareous sand: Macro performance, micro mechanism, and strength prediction

Cement-bonded calcareous sand (C-BCS) demonstrates promising potential for marine island construction due to its exceptional mechanical properties. However, challenges such as freshwater scarcity and the erosive effects of seawater hinder the extensive utilization of C-BCS. To address this, this study comprehensively examines the feasibility of incorporating supplementary cementitious materials (SCMs) and seawater in C-BCS, focusing on macroscopic properties, microscopic mechanisms, and strength prediction. Macroscopic tests reveal that blast furnace slag and silica fume effectively enhance the hydration process and mechanical properties of C-BCS. Moreover, the cemented specimens developed in this study partially meet the strength standards for road pavement sub-base and airport runway upper-base applications. Microscopic analyses indicate that calcareous sand serves as a plentiful source of calcium, facilitating the formation of calcium aluminate silicate hydrate (C-A-S-H) and tobermorite when combined with Al2O3 and reactive SiO2 from slag and silica fume. This enhances the mechanical properties of the samples and their resistance against seawater erosion. Additionally, a back propagation (BP) neural network model accurately predicts the unconfined compressive strength of the cemented specimens. The findings of this study support the broader implementation of SCMs and seawater in practical island engineering projects involving C-BCS.

Evaluation of urea hydrolysis for MICP technique applied in recycled aggregate: Concentration of urea and bacterial spores

Aggregate is an indispensable raw material for concrete. Microbial induced carbonate precipitation (MICP) is an environmentally friendly aggregate modification method, which could modify recycled aggregate (RA) to replace natural aggregate for the preparation of concrete in the future. The urea hydrolysis is the key to modified RA by MICP. Biological calcium carbonate is generated during mineralization reaction in modification solution to fill the weak part of aggregate, which will enhance the performance of RA. The bacterial solution and urea solution, as the sources of CO32- in biological CaCO3, jointly affect the modification effect of RA. In this paper, the different ratios of bacterial solution concentration (×108 cells/mL) to urea concentration (mg urea/mL) are used for exploring the improvement effect and the cooperative enhancement mechanism of recycled coarse aggregate (4.75 mm-9.5 mm). The results show that the bacterial mineralization efficiency is most improved when bacterial solution concentration/urea concentration (B/U) is in the optimal interval of 5–6 because 1 mg urea provides a moderate number of bacteria during the modification period. In the interval, the precipitation amount of biological CaCO3 and effective CaCO3 that could modify RA is larger, and the pores of the attached mortar of RA are better filled and blocked. Therefore, the macro performance of RA is greatly improved in the internal. When the B/U is outside the optimal interval, the modification effect is poor because the amount of biological CaCO3 and effective CaCO3 is too less to fill pores or too more to enter pores.