Interfacial Transition Zone Research Articles

Reuse of waste rockwool for improving the performance of LC3-based mortars made with natural and recycled aggregates for sustainable building solutions

The objective of this study is to investigate the effect of waste rockwool (RW) addition on the thermo-physical, mechanical, and fire resistance properties of limestone calcined clay cement (LC3)-based mortars. LC3 binder has been produced by replacing 60 wt% of OPC with limestone (LS) powder and metakaolin (MK) at a percentage of LS to MK of 1:2 (wt%). Waste RW was added at various ratios of 1, 3 and 5 % (by weight of binder) into two types of LC3-based mortars made with natural sand (NS) and ferrochrome waste slag (FCS) aggregates with a binder-to-aggregate vol% of 1:3. Upon the addition of 5 wt% of waste RW, significant enhancements of about 19 % and 21 % were obtained for the compressive strength of NS and FCS mortars, respectively, and attributed to the improved physical packing. After exposure to standard fire for 1 h with a maximum applied temperature of 945 °C, residual strengths of about 57.5 % and 63.8 % have been maintained by the sand and FCS-blended LC3 mortars, respectively. Generally, the incorporation of RW led to a slight increase in the thermal conductivity of both types of mortars; however, the FCS-blended LC3 mortar possessed relatively higher increment rates as compared with the sand mortar, which is helpful in improving the thermal performance in hot climate regions. Remarkable improvements in the microstructure characteristics in terms of compactness, uniformity, and interfacial transition zone (ITZ) tightness were attained by RW addition. Lifecycle assessment (LCA) results demonstrated that about 38–45 % lower carbon emission is associated with the designed LC3-based mortars than the conventional OPC mortar.

Synergetic optimizing particle size distributions of aggregate and cementitious materials: Toward lower chloride diffusivity of concrete

Particle size distributions (PSDs) of aggregate and cementitious material dominate the microstructure and properties developments of concrete. Optimizing the proportion of aggregate can mitigate chloride ingress pathways, leading to a significant increase in surface area and augmented generation of the interfacial transition zone (ITZ). Overemphasis on aggregate proportion can compromise workability of fresh concrete due to limited cement paste lubrication. Although gap-graded distribution benefits cementitious material hydration, accurately classifying cementitious components for broad implementation is challenging. This study designed the aggregate proportion and PSD based on a proposed diluted packing region with low estimated chloride diffusivity. The gap-graded distribution at the cementitious material scale was conveniently achieved by incorporating fine ground blast furnace slag and coarse fly ash into commercial Portland cement. Consequently, dual-scale designed concretes, taking into account PSDs at both aggregate and cementitious material scales, were proposed. These concretes exhibited chloride diffusion coefficients ranging in (1.26–1.46)×10−12 m2/s, with aggregate proportions spanning 52 % to 74 %. Their compressive strength was comparable with Portland cement concrete, even with 60 % supplementary cementitious materials (SCMs). The improved properties of the dual-scale designed concrete can be attributed to the high aggregate proportion with rational PSD, which does not result in a significant rise in the ITZ proportion. Efficient hydration of the cementitious material is beneficial to microstructure densification and chloride binding capacity improvement, helps to increase the chloride diffusion distance and hinder the penetration of chloride. This study provides insights into designing chloride-resistant concrete with less Portland cement reliance.

Effect of microwave curing on the properties of aggregate-mastic interfacial transition zones in cement emulsified bitumen mixture containing steel slag

The poor properties of the aggregate-mastic interfacial transition zones (ITZ) are the core factor for the low structural strength of cement emulsified bitumen mixture (CEBM), while incorporating steel slag with high microwave responsiveness into CEBM and followed by microwave curing may be an effective method to enhance ITZ properties. To verify this hypothesis, the ITZ properties of CEBM containing steel slag were characterised and analysed by a series of techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and nanoindentation. The results showed that the ITZ properties increased continuously with microwave curing time. Specifically, the thickness of ITZ continuously decreased, while the elastic modulus and hardness continuously increased. When the microwave curing time was less than 7 min, the growth in cement hydrates and temperature simultaneously enhanced the ITZ properties. When the microwave curing time exceeded 7 min, the cement hydrates gradually decreased due to the water content falling below the minimum required for cement hydration, and the improvement of ITZ properties mainly depended on the temperature rise. Remarkably, the microwave heating characteristics of steel slag resulted in a tighter bond with bitumen, which led to consistently better surface ITZ properties than limestone. However, it should be avoided that the microwave curing time is too long, as this would result in the steel slag temperature being too high and aging its surface bitumen. Additionally, the indirect tensile strength of CEBM affected by the ITZ properties was still increased even after the decrease in cement hydrates.

Low-carbon UHPC with glass powder and shell powder: Deformation, compressive strength, microstructure and ecological evaluation

Waste glass and shells are by-products generated in the production process of the construction industry and aquaculture respectively. The high-value treatment of these materials presents a global challenge. Converting waste glass and shells into solid waste-based ultra-high performance concrete (UHPC) mixtures is an eco-friendly strategy. In this study, glass powder (GP) and oyster shell powder (OSP) were mixed to prepare composite supplementary cementitious materials (GOS) and partially replace cement. The compressive strength, drying shrinkage, microstructure, and environmental impact of GOS-containing UHPC were investigated. Results indicate that adding GOS reduces the fluidity of UHPC mixtures, with further decreases as GOS content increases. Replacing cement with an appropriate amount of GOS (10 wt%-20 wt%) enhances the compressive strength of UHPC, though higher GOS levels reduce its strength. Meanwhile, the drying shrinkage deformation of UHPC decreases significantly as the GOS substitution level increases. The 28-d drying shrinkage deformation of the specimen added with 20 wt% GOS is 574 μm/m, which is 61.96 % lower than the control group. Additionally, the specimen added with 20 wt% GOS shows significantly improved compactness and enhanced bonding at the interfacial transition zone. Compared with traditional UHPC, GOS-containing UHPC has lower carbon emissions and costs, effectively utilizes waste, and promotes sustainable development.

Optimization of Cohesive Parameters in the Interfacial Transition Zone of Rubberized Concrete Based on the Response Surface Method.

Rubber concrete has been applied to a certain extent in fatigue-resistant structures due to its good durability. Based on a cohesive model of rubber composed of a five-phase material containing mortar, aggregate, rubber, aggregate-mortar interfacial transition zone (ITZ), and rubber-mortar ITZ, this paper studies the influence of the cohesive parameters in the rubber-mortar ITZ on the fatigue problem of rubber concrete on the mesoscopic scale. As the weak part of cement-based composite materials, the ITZ has a great influence on the mechanical properties and durability of concrete, but the performance of the ITZ is difficult to test in macro experiments, resulting in difficulties in determining its simulation parameters. Based on the cohesive model with a rubber content of 5%, this study uses Monofactor analysis and the Plackett-Burman test to quickly and effectively determine the primary and secondary influences of the cohesive model parameters in the rubber-mortar ITZ; further, the response surface method is used to optimize the cohesive parameters in the rubber-mortar ITZ, and the numerical simulation results after optimizing the cohesive parameters are compared and analyzed with the simulation results before optimization. The results show that, under the setting of the optimized parameters, the simulation results of each item of the optimal cohesive model parameters in the rubber-mortar ITZ are in line with the reality and closer to the experimental data, and they are also applicable to rubber concrete models with different rubber dosing.

Influence of molybdenum tailings replacing river sand on mechanical properties and concrete microstructure

Many tailings are piled up, occupying land and polluting the environment. Tailings replace river sand to prepare concrete. It can reduce the tailings stockpile and slow the consumption of non-renewable resources. This study discussed the feasibility of molybdenum tailings (MTs) replacing river sand in preparing concrete. Firstly, the influence of the MTs addition amount on concrete strength was analyzed. Secondly, nuclear magnetic resonance (NMR), x-ray diffraction (XRD), thermogravimetric (TG-DTG), and scanning electron microscope (SEM) were used to characterize the microscopic characteristics of concrete with different MTs contents. The results showed that good gradation of fine aggregate could improve the strength of concrete. The optimum replacement rate of MTs was 20 %, and the 28-day compressive strength and tensile strength of concrete increased by 10.9 % and 14.9 %, respectively, compared with the control group. It cannot be considered that the greater the total porosity, the greater the strength of concrete, which was mainly determined by the proportion of pores with different pore sizes in the total pores. When the amount of MTs added was 20 %, the MTs played a role in dilution, promoting cement hydration. The hydration products can not only effectively fill the internal pores of the concrete but also improve the bond strength between the tailings and the hardened slurry, thus improving the strength of the concrete. When the content of tailings added was 50 % and 100 %, cement hydration was blocked, increasing concrete porosity, and the interfacial transition zone (ITZ) became looser, thus weakening the strength of concrete.

Impact of Interfacial Transition Zone on Concrete Mechanical Properties: A Comparative Analysis of Multiphase Inclusion Theory and Numerical Simulations

With the increasing implementation of sustainable development strategies, recycled concrete (RC) has garnered attention in research circles due to its substantial environmental and economic advantages. The presence and properties of various interface transition zones (ITZs) in RC play a vital role in its mechanical properties. This research uses a combination of multiphase inclusion theory and finite element numerical simulation to investigate and compare the impact of ITZs on concrete’s mechanical properties. The multiphase inclusion theory offers a theoretical framework for understanding ITZ behavior in concrete, categorizing it into new mortar, old mortar, new ITZ, old ITZ, and natural aggregate based on meso-structure. With simplified RC at the mesoscale, the study accurately predicts the mechanical properties of RC by adjusting the elastic modulus, Poisson’s ratio, and thickness of new and old ITZ models. Through finite element simulation and theoretical validation, the study achieves a minimal error of 6.24% in predicting the elastic modulus and 1.75% in predicting Poisson’s ratio. These results highlight the effectiveness of multiphase inclusion theory in capturing the meso-structure characteristics of RC and forecasting its macroscopic mechanical behavior while comprehensively considering the complexity of ITZs.

Comparative study on calculation methods for compressive strength of low strength aggregate concrete

The compressive strength of concrete with low strength aggregate volume fractions of 10%, 20%, and 30% was calculated using both the graphical analysis method and mesomechanics method. In the calculation method based on graphical analysis, three-dimensional random spherical aggregate models of concrete with different volume contents of low strength aggregate were established and sliced. The results show that the graphical analysis method can effectively calculate the compressive strength of concrete with different volume contents of low strength aggregate. In the graphical analysis method, the relative errors of the calculated compressive strength of concrete with low strength aggregate volume fractions of 10%, 20%, and 30% were 4.84%, 4.84%, and 6.43%, respectively. Three-phase concrete models composed of mortar, aggregate, and interfacial transition zone were analyzed through the method of mesomechanics. The calculation results of the mesomechanics method show that the compressive strength of concrete was controlled by low strength aggregate, and the calculated compressive strength of concrete decreased with the increase in low strength aggregate volume content. In the mesomechanics method, the relative errors of the calculated compressive strength of concrete with low strength aggregate volume fractions of 10%, 20%, and 30% were 1.36%, 1.74%, and 3.7%, respectively. It can be found that the calculation results of the mesomechanics method are closer to the test values and have smaller relative errors, which indicate that the calculation method of mesomechanics theory is superior to the method of graphical analysis.

Stripping of aggregate from mortar in waste concrete heated by microwave: Mechanisms of differential-temperature stress and vapor expansion pressure

Microwave heating, which is used for pre-treatment of concrete before it is comminuted, stands as a strong candidate for selective liberation of multiphase materials like concrete. This paper is concerned with the selective liberation of concrete's raw constituents (particularly aggregate) for recycling by considering the water content of concrete as a parameter of microwave heating for the first time. The deterioration law of the concrete's performance was characterized by the variation in the splitting tensile strength and relative dynamic modulus after heating by microwave at different water contents. Besides, tests were conducted to evaluate the performance of the interface transition zone (ITZ) between aggregate and mortar as well as to investigate the reasons for the stripping behavior of aggregate-mortar, which included the interface tensile strength test, temperature measurement, and porosity test. The deterioration law of splitting tensile strength and relative dynamic modulus revealed that the performance of concrete was subject to different degrees of damage depending on the water content. Furthermore, experimental results showed that interface bonding strength between aggregate and mortar was dramatically impaired, and a large temperature difference was generated between the aggregate and mortar during microwave heating. Meanwhile, the permeable pores increased considerably even when the specimens were dried. In the presence of water, the intactness of ITZ between aggregate and mortar was destroyed by microwave heating, and its performance was significantly lowered, which led to the occurrence of stripping behavior between aggregate and mortar. This was reaffirmed by the microstructure presented by scanning electron microscopy. Thus, the newly developed microwave pre-treatment improved by providing appropriate water contents for concrete corresponding to different strength grades is a promising method for recycling aggregate from waste concrete.

Evolution of LWAC–OC interfacial properties during sulfate dry–wet cycles: Bonding strength and micro–properties

The interface properties between lightweight aggregate concrete (LWAC) and ordinary concrete (OC) have drawn significant research interest. However, its evolution during sulfate dry–wet cycles has yet to be elucidated. Therefore, the LWAC–OC composite specimens were subjected to 15 cycles of dry and wet cycles test, using 5 wt% sodium sulfate solution. The dry–wet cycling method consisted of complete immersion for 7 days, followed by natural drying for 8 days. Moreover, tests for splitting tensile, direct shear, scanning electron microscopy and microhardness were conducted on the LWAC–OC interfaces at varying numbers of dry and wet cycles. The results showed that the failure mode of specimens changed from mixed cohesive failure to interfacial bonding failure during sulfate dry–wet cycles. Direct shear and splitting tensile strength slightly increased and then markedly decreased as the number of dry–wet cycles increased. The ratio of direct shear strength to splitting tensile strength showed a distinct negative linear relationship with the number of sulfate dry–wet cycles. Moreover, when the number of dry–wet cycles increased, the porosity of interfacial transition zone first decreased and then increased. The mean value of the interfacial micro–hardness first increased and then decreased. Interfacial micro–properties correlated well with bonding strength throughout the process.

Optimization of steam curing process for Chinese Western and Northeast regions' high‐speed railway concrete prefabricated components

AbstractThis article aims to address the issues of high curing temperatures and thermal damage in the production of prefabricated concrete components for high‐speed railways in high‐altitude and high‐latitude cold regions of China. Various steam‐curing processes for concrete are designed to optimize the high‐quality preparation process of steam‐cured concrete prefabricated components in cold environments. With the goal of controlling the residual expansion deformation and considering the overall impact of curing process on the mechanics, durability, and interface transition zone of steam‐cured concrete, the main conclusions obtained in this study are as follows. Within a pre‐curing time of 3–6 h, when the curing temperature is maintained at 45–60°C, the final residual expansion deformation can be controlled below 300 με. The compressive strength, dynamic elastic modulus, peak stress, water absorption and Chloride ion resistance of steam‐cured concrete show the great improvement under above curing processes. Curing at 80°C should be actively avoided, and it is recommended to adopt a 6 h pre‐curing time with a maximum curing temperature of 45°C, especially for cold regions in China. This study can serve as a valuable reference and provide support for the preparation of prefabricated concrete components in Chinese high‐altitude and high‐latitude areas.

Influence of acidity and alkalinity of water environment on water stability of asphalt mixture: Phase II-microscopic erosion mechanism

Acidity and alkalinity of water environments have been proven to influence the water stability of asphalt mixture. However, the relevant influencing mechanism still remains unclear. To fulfill this research gap, this study conducted a series of microscopic tests, aiming at unveiling the microscopic erosion mechanism of the water environment on the water stability of asphalt mixture for better moisture stability achieved. Specifically, the asphalt-aggregate interfacial transition zone (ITZ) samples were prepared by combining #70 asphalt with limestone and granite, respectively, which were then immersed in water solutions at 3 different pH levels (pH = 3.0, 7.0, and 11.0) for 7 days. The chemical composition and microstructure of the asphalt film on the surface of the ITZ samples pre and post-treatment were scrutinized using the Fourier Transform Infrared Spectroscopy (FTIR) and the Atomic Force Microscope (AFM), while the development of microcracks at the asphalt-aggregate interface were identified and traced utilizing the Scanning Electron Microscope (SEM). The test results indicate that after treatment with acidic and alkaline aqueous solutions, the asphalt film's surface is enriched with polar components such as asphaltenes, resins, and aromatic fractions. The migration of these polar components to the surface of the asphalt film reduces the adhesion between asphalt-aggregate, leading to the formation of microcracks at the asphalt-aggregate interface. The most severe crack development occurs in alkaline water environment, followed by acidic water environment. It is interestingly noted that the adhesion at the asphalt-granite interface is improved under the acidic environment. This improvement may be attributed to the covalent nature of silica, which hinders the adsorption of ions from acidic solution into the asphalt film. This hindrance effectively prevents water intrusion at the asphalt-aggregate interface, thereby reducing the adhesion loss. These findings can help elucidate the mechanism of water damage in asphalt pavement exposed to real-world conditions and enhance its water stability with effective countermeasures proposed.

Leaching-induced deterioration of shear bonding strength and micro-Vickers hardness of the ITZ modified by micro-SiO2 and nano-SiO2

The interfacial transition zone (ITZ) serves as a critical juncture between aggregate and cement paste in concrete, particularly vulnerable to calcium leaching. This study investigates the impact of water-cement (w/c) ratio and micro-SiO2 and nano-SiO2 content on the deterioration of shear bonding strength and micro-Vickers hardness of the ITZ during leaching. Analysis of ITZ micro-structure and elemental composition is conducted using backscattering electron microscope and energy dispersive spectroscopy (BSEM/EDS), and a deterioration model for the shear bonding strength of the leached ITZ is established. Results indicate that during leaching, shear bonding strength and micro-Vickers hardness of the ITZ are approximately 28 % and 67 % of those of the cement paste, respectively. A linear relationship between the shear bonding strength of the ITZ and its micro-Vickers hardness is observed when employing the same type of admixture. Mechanical properties and leaching resistance of the ITZ diminish progressively with increasing w/c ratio. Conversely, they exhibit an initial enhancement followed by decline with increasing micro-SiO2 and nano-SiO2 contents, with optimal contents of 8 % and 2 %, respectively. Micro-SiO2 and nano-SiO2 are found to enhance long- and short-term leaching resistance of cement-based materials, respectively. Additionally, the shear bonding strength of the ITZ decreases linearly with increased degree of area leaching. These findings enhance our understanding of the deterioration behavior of the ITZ and provide an important foundation for studying the durability changes of concrete subjected to calcium leaching.

Effect of grain size on ductility and failure mechanism of fiber-reinforced coral sand cement-based composites

Fiber offers the potential for enhancing the resistance to deformation in engineering cement-based composites (ECC). However, replacing quartz sand in ECC with coral sand containing a large number of internal pores will make the interaction between aggregate, interface transition zone, and cementitious materials more complex. To investigate the influence of coral sand particle size and Polyvinyl alcohol (PVA) fiber content on the compression behaviour and internal microstructure of fiber-reinforced coral sand cement-based composites (FRCSCC), we conducted uniaxial compressive strength tests and real-time measurements of P-wave and S-wave velocities. We tested various mechanical parameters, such as density, elastic modulus, compressive strength, wave velocities, and toughness index. The findings revealed a notable trend in relation to the coral sand particle size. Specifically, as the particle size increased, the compressive strength of FRCSCC decreased by 26 % and the elastic modulus reduced by 11 %. During uniaxial compression, the calculated cumulative voltage energy (CVE) from P-wave and S-wave can be divided into three stages: elastic deformation, microcrack and macrocrack propagation, and main crack formation. Moreover, the increase of coral sand particle size from 0.075 mm to 1.00 mm resulted in the rise of residual stress from 8.7 % to 18.2 %, followed by the increase of toughness index from 2.5 to 3.2. Scanning electron microscope (SEM) images reveal that the main failure modes of PVA fiber in FRCSCC specimens during uniaxial compression are debonding pull-out and tearing. Larger particle sizes of coral sand are associated with uneven fiber dispersion, increased fiber fractures, and diminished ductility of the specimens. The results establish a theoretical foundation for offshore engineering construction.

Nano-computed tomography analysis of downscaled cement sheath samples: Insights into porosity distribution

Mitigating greenhouse gas emissions from hydrocarbon wells is an industrywide challenge, with microstructural variations in the cement sheaths lining the wells recognized as key factors in forming leakage pathways. To better understand the microstructural variations in cement sheaths and the corresponding mechanisms, downscaled samples simulating rock–cement–casing and casing–cement–casing cement sheaths were prepared and then scanned using nano-computed tomography at resolutions of 11.93 μm and 6.80 μm, respectively. Both the radial and axial porosity of regions of interest were quantified and analyzed. The results showed that radial porosity distributions were quite different between the rock–cement–casing and casing–cement–casing samples. In the rock–cement–casing samples, the radial porosity decreased from the cement–rock to the cement–casing interface due to cement migration, while in the casing–cement–casing samples, the highest radial porosities occurred in both the cement–casing interfaces due to the influence of an interfacial transition zone. The axial porosity distribution was similar in all the rock–cement–casing and casing–cement–casing samples because the porosity decreased from the top to the bottom due to the particle settling phenomenon. These findings enhance our understanding of the factors affecting gas leakage pathways from wells, and the proposed methodology can be used to optimize cement blends to produce effective wellbore barriers.

Optimization mechanism of metakaolin on micro-mechanical properties and pore characteristics of steel fiber-cement matrix interface

The study investigated the influence of aeolian sand and metakaolin (MK) on the micro-mechanical properties and pore structure characteristics of the interfacial transition zone (ITZ) between steel fibers and matrix in steel fiber-reinforced cement-based materials by nanoindentation, scanning electron microscopy (SEM) imaging, and energy-dispersive spectroscopy (EDS) analysis. The results demonstrated that including MK and aeolian sand led to a denser and uniform micro-structure in the ITZ, along with reducing the porosity and refining the pore size within there. Furthermore, MK could enhance the micromechanical properties of the C-(A)-S-H) gel by increasing the Al/Si ratio. Finally, the Copula function further confirmed the correlation between porosity (pore size >0.2 μm) and micro-mechanical properties in the ITZ. This study provides a theoretical basis for the engineering application of aeolian sand and metakaolin, and proves the feasibility of porosity to characterize the microscopic mechanical properties of the interfacial transition zone of cement-based materials. Thus, it has specific engineering value and academic significance.

Reinforcement effects on the tensile properties of seawater sea-sand engineered cementitious composites reinforced with multi-scale hybrid fibers

The preparation of seawater sea-sand engineered cementitious composites (SS-ECC) holds great potential for development in coastal and marine infrastructure. To improve its compressive strength and tensile properties, this study investigated the crack characteristics, micro-mechanics, fibers reinforcement index, and micro-structure of SS-ECC using a multi-scale hybrid fibers system consisting of CaCO3 whiskers, PE fibers, and stainless steel fibers (SSF). The aim was to gain an in-depth understanding of the reinforcement effects of multi-scale hybrid fibers. The results showed that CaCO3 whiskers increased the number of cracks and the stability of crack evolution in SS-ECC during the ultimate tensile state by bridging the matrix micro-cracks, improving the matrix micro-structure, and filling the interfacial transition zones between the macroscopic fibers (PE fibers and SSF) and the matrix. Additionally, it reduced the crack width and spacing. These combined effects increased the compressive strength, tensile strength, and tensile strain capacity of SS-ECC by 12.8%, 15.7%, and 11.9%, respectively. Finally, the reinforcement effects of multi-scale hybrid fibers were analyzed based on the pseudo-strain hardening performance indices, fibers reinforcement index, and hybrid coefficient. This analysis provides reference and insight for the design of multi-scale hybrid fibers SS-ECC with a high comprehensive performance (σcσtε/w) index.

Mesoscopic simulations of a fracture process in reinforced concrete beam in bending using a 2D coupled DEM/micro-CT approach

In this study, a complex fracture process in a short rectangular concrete (RC) beam reinforced by one longitudinal bar (without vertical reinforcement) and subjected to quasi-static three-point bending was numerically explored in 2D conditions. A critical diagonal shear crack in the beam caused it to fail during the experiment. The numerical simulations were conducted with a classical particle discrete element method (DEM). A three-phase concrete description (aggregate, mortar, and interfacial transitional zones (ITZs) around aggregates) accounted for the concrete heterogeneity. In mesoscopic DEM calculations based on a 2D X-ray CT scan, the actual shape and placement of aggregate particles in concrete were taken for granted. In the study, the steel bar with ribs was replicated. ITZ was also assumed between the bar and mortar. Without imposing any bond-slip law, a geometrical bar/concrete interface condition was explicitly considered. The focus was on the force–deflection diagram, fracture process, contact forces, and stresses along the bar. A good level of agreement about the evolution of the vertical force versus the deflection and failure mechanism was attained between DEM analyses and in-house laboratory tests despite simplified 2D conditions. A strong effect of concrete mesostructure on the crack pattern was found.

Effect of metakaolin content and shape design on strength performance of lightweight rubberized geopolymer mortars incorporated slag-waste glass powders

Lightweight rubberized geopolymer (LRGP) has gained attention due to its economic, engineering, and environmental benefits. With the rising human demands, the need for alternative materials to meet the requirements of infrastructural expansion, and global industrialization required. Based on those facts, this study aimed to develop of lightweight geopolymer mortars using wastes rubber as fine aggregate (WRA) to replace the natural aggregates, which metakaolin (MK), wastes bottle glass (WBG) and granulated blast furnace slag (GBFS) used as precursor materials with alkaline activator contained low molarity of sodium hydroxide solution and sodium silicate and cured at ambient temperatures. The effect of WRA on physical, mechanical, and microstructural properties of metakaolin-based rubberized geopolymer has been evaluated by using several tests such as compressive, flexural and tensile strength. As well as morphology and chemical reaction on LRGP by using AFM, FESEM, EDX, FTIR and XRD tests. In addition, a sustainable shape design has been cast and subjected to compressive strength to obtain the strength performance of the proposed LRGP mortar. At optimal mixture, the SEM images exhibited improvement in the interfacial transition zone (ITZ) among WRA and binder, leading rubberized geopolymer with 15% WRA to achieve a strength of 27.47 MPa after 28 days and with a reduction in density by 7.2%. The findings of this study can provide valuable insights on utilizing WRA in the shape design and formulation of geopolymer mortar, a key ingredient in the development of functional environmentally friendly building materials.

Valorization of steel slag into sustainable high-performance radiation shielding concrete

The disposal of steel slag (SS) has become a serious ecological problem due to the waste of massive land resources. This study reveals the huge potential of recycling SS as heavy aggregates to develop radiation shielding concrete (RSC). The physical characteristics, radiation attenuation capabilities, microstructure, and environmental and ecological impacts of SS-based RSC are comprehensively evaluated and compared with those of normal concrete and the commonly used heavy concrete. The test results indicate that SS-based RSC is prospective to substitute the commonly used heavy concrete, emerging as a sustainable and efficient material for radiation shielding in nuclear energy engineering. Specifically, due to the reaction of cementitious active substances in the surface of SS, the developed SS-based RSC exhibits a fantastic interfacial transition zone (ITZ), and a compact pore structure, thereby showing excellent mechanical properties. The maximum compressive strength of developed SS-based RSC reaches 47.4 MPa. In terms of gamma ray attenuation property, due to the introduction of heavy nuclei and the increase in density, the gamma ray attenuation capacity of developed SS-based RSC is 17.2 % higher than that of normal concrete. The neutron attenuation property is also slightly enhanced due to the refinement effect of SS on pore structure of RSC. Life cycle assessment and unit cost evaluation results demonstrate that compared with barite based-RSC, SS-based RSC can save 97.6 % in cost, 52.0 % in energy consumption, and 70.4 % in carbon emission. The developed SS-based RSC exhibits excellent mechanical properties and radiation attenuation capacities, contributing to the further application of radiation shielding materials. Besides, this approach achieves the high-value recycling of SS, providing new insights for the utilization of high-density solid wastes.