Mortar Matrix Research Articles

Experimental study on recycling rubber to increase the impact resistance of cement mortar

The COVID-19 pandemic has led to a surge in medical waste generation, posing hazards to both the environment and global health. The impacts of the COVID-19 pandemic’s medical waste hazard may persist long after the pandemic itself subsides. Improper disposal of medical waste can contaminate environment, posing risks to ecosystems and public health. Discarded medical rubber gloves, for example, can become a source of infection, improper disposal of these gloves can escalate the spread of infectious diseases and increase the risk of transmission of the virus to the general public. This study proposes an innovative and sustainable method to reinforce cement mortar by adding recycled glove rubber as an additive to cement mortar to increase its resistance to impact loads. This study conducted uniaxial compression tests, separating hopkinson pressure bar (SHPB) experiments and SEM observations to evaluate the quasi-static compressive strength and dynamic stress of recycled rubber fiber mortar (RRFM) with varying recycled rubber fiber (RRF) contents (0, 1%, 2%, 3%). Strain curves, dynamic increase factor (DIF), energy absorption rules, failure modes, and microstructure of RRFM mixtures. The experimental results demonstrate that with the addition of RRF, the dynamic stress-strain curve flattens and the peak strain gradually increases. The RRFM sample shows stronger toughness. In comparison to regular cement mortar (NM), RRFM has a higher DIF and specific absorbed energy, a faster increase in dynamic compressive strength, and the ability to absorb more energy per unit volume. Under the same impact load, RRFM has fewer and smaller cracks than NM. Scanning electron microscopy (SEM) testing also observed that RRF formed a strong connection pattern with the cement mortar matrix.

Ginger powder as sustainable and eco-friendly corrosion inhibitor for the protection of steel reinforcement bars

In the present studies, ginger powder has been used as an eco-friendly admixture for the cement mortar. Different amounts i.e. 0 wt% (M1), 0.10 wt% (M2), 0.25 wt% (M3) and 0.50 wt% (M4) ginger powder was mixed in the cement mortar (M1) and assessed the durability. The ginger powder with 0.50 wt% (M4) improves the compressive strength by 17 % owing to the water reducing capability, which enhance the hydration reaction and fill the pore matrix of the cement mortar. The active ingredient of ginger powder i.e. shogaol adsorbs on the steel rebar surface through leaching mechanism by interaction of oxygen (O) and п-electrons with iron (Fe) and provide corrosion protection at longer duration of continuous immersion in 3.5 wt% NaCl solution. Following 173 d in a 3.5 wt% NaCl solution, the M4 sample exhibits 82.10 % corrosion inhibition efficiency. Therefore, it is suggested that ginger powder could be a potential eco-friendly admixture to be used in construction industries to get high durability performance in the coastal areas.

Mesoscale Modeling of Microcapsule-Based Self-Healing Cementitious Composites under Dynamic Splitting Tension

Microcapsule-based self-healing cementitious composite (MSCC) offers autonomous damage repair, extending the service life of structures. However, most of the existing studies focus on static behavior and healing effectiveness but rarely explore dynamic responses. This study developed the mesoscale modeling approach to investigate MSCC behavior under dynamic split tensile loading. At the mesoscale, MSCC can be treated as a four-phase composite consisting of coarse aggregates, interfacial transition zones, cement mortar, and microcapsules. Alternatively, it can be simplified as a two-phase composite comprising a homogeneous mortar matrix and microcapsules. Four-phase and two-phase mesoscale MSCC models were developed for 2D simulations, while a two-phase 3D model was also developed for comparison. Mesoscale numerical simulations were conducted based on Split-Hopkinson Pressure Bar Brazilian disk-splitting tests, considering various strain rates. Simulation results of different mesoscale models were compared with experimental results. All of the models accurately predicted the tensile strength of MSCC, with the 2D four-phase model providing the best representation of failure modes and crack propagation. Both experimental and numerical data exhibited obvious strain rate effects, indicating that MSCC’s mechanical properties were sensitive to the loading rate. Dynamic increase factors were obtained, quantifying rate sensitivity. The obtained dynamic mechanical properties of MSCC provide insights for designing MSCC components and structures that can better withstand collisions or explosions.

Confinement Mechanism of Basalt TRM-Confined Concrete: The Role of the Mortar Matrix

Confinement Mechanism of Basalt TRM-Confined Concrete: The Role of the Mortar Matrix

A multi-scale modeling method for tensile properties of strain-hardening cementitious composites

The synergistic design of components of Strain-Hardening Cementitious Composites (SHCC) based on micromechanics is the critical to realize its high strength and ductility. We have developed a mesoscale model for revealing effects of mesoscopic parameter of SHCC on its multiple cracking behavior. However, the heterogeneity of mortar in SHCC, which may influence the saturated multiple cracking, was usually absent in the existing mesoscale model. In this paper, a sub-mesoscale model of mortar considering the fine aggregates, hydrated cement paste, and interfacial transition zones (ITZ) are introduced into the previous SHCC mesoscale model. A parameter transfer method linking these two scales is proposed. By linking them, the parameter design of SHCC of different scales can be considered comprehensively. The proposed model is validated by the three-point bending test and uniaxial tensile test of SHCC. The effects of fine aggregate volume, tensile strength of hydrated cement paste and tensile strength of interfacial transition zone on the mechanical behavior are parametrically analyzed via the validated model. The results show that the increase of the volume content of fine aggregate will reduce the tensile strength and elastic modulus of SHCC mortar matrix, while the strength of hydrated cement paste has a significant increase in the first crack stress of SHCC, and the ITZ strength mainly affects the elastic modulus of SHCC mortar. The developed model provides a reference for the material optimization design of SHCC.

Evaluation of carbon nanotube (CNT) cement-based traffic sensor incorporating steel slag based on Accelerated Pavement Test (APT)

ABSTRACT In this study, a carbon nanotube (CNT) cement composite containing CNT and steel slag was developed and its application in traffic information sensing was studied. The mix ratio of steel slag cement mortar matrix and CNT cement composite was determined by mechanical properties and electrical conductivity tests. Then the CNT cement composite intelligent sensing device was prepared and an Accelerated Pavement Test equipment was used to test its piezoresistive response curve. The test results show that steel slag and CNT enhance mechanical properties and electrical conductivity. The vehicle speed and wheelbase were calculated based on the piezoresistive response results, and the calculation errors of the wheel speed (0.375 and 0.844 km/h) were less than 10% and 20%, respectively. The wheelbase estimate has a maximum error of approximately 12% and 15% for wheel speeds of 0.375 and 0.844 km/h, respectively. Therefore, the CNT cement composite containing steel slag developed in this study has the potential to serve as a traffic sensor.

Enhancing toughness in cement-based composites: Unraveling the composite effect mechanisms of polymers and fibers through physic testing and molecular dynamics simulations

To reveal the toughening mechanism of polymers and fibers in composite applications, a combination of physical tests (uniaxial compression, flexural fracture, single fiber pull-out, scanning electron microscopy, and X-ray diffraction (XRD)) and molecular dynamics simulations have been carried out. Three polymers, i.e. ethylene-vinyl acetate copolymer (EVA), styrene-acrylate copolymer (SAE), and styrene-butadiene copolymer (SB), and two fibers, i.e. polypropylene fiber (PP) and polyvinyl alcohol fiber (PVA) are considered. Their composite effect mechanisms are explained in the viewpoint of three scales. At the macro-scale, the pull-out tests of single fiber show that the polymer increased the equivalent bond strength between the fiber and the mortar matrix. At micro-scale, it was observed from the SEM experiments that the fiber and polymer film inhibited the crack extension at different scales, besides the polymer could absorb on the fiber surface to improve the interfacial transition zone (ITZ) density around the fiber and increase the roughness of the fiber surface. At nano-scale, MD simulations demonstrate that three polymers facilitated the bond strength between PP fiber and C–S–H at the nano-scale, mainly because of the formation of Ca–O coordination bond and H-bonds between the polymers and C–S–H, and the presence of van der Waals forces between the polymers and PP fiber. However, SAE facilitated the bonding between the PVA fibers and the C–S–H, which originated from the coordination bonds formed between Ca ions on the surface of SAE and O atoms in PVA. In addition, the large number of H-bonds formed between SAE and PVA.

Unveiling the self-healing behavior of marine exposed concrete: Nondestructive ultrasonic detection and Vickers hardness characterization

Cracking is a widespread phenomenon throughout the service of concrete structures for marine and offshore engineering. In this paper, the effect of sulfate ions and related cations on the crack closure behavior of cracked mortar in chloride-containing environments was studied. To this end, the mortars are cracked before transferring to the pure chloride solution as well as composite chloride and sulfate solutions (CNS and CMS series). The self-healing behavior is assessed by the evolution of crack width, water absorption, and nondestructive ultrasonic detection. The Vickers hardness test is applied to evaluate the micro-hardness of self-healing products generated in the crack gaps. Thermodynamic modeling of the phase volume expansion from the mortar matrix to the crack surface is conducted using Gibb’s free energy theory to explore the self-healing mechanisms. Experiment results suggest that the existence of sulfate ions in chloride-containing solutions is beneficial for crack closure, and self-healing could be more obvious if the cations that bind to sulfate are magnesium ions. The distributions of Vickers hardness on the mortar surface across the crack reveal that the brucite layer diminishes the overall Vickers hardness of the mortar matrix, whereas it is favorable for the micro-hardness enhancement of self-healing products in the CMS series. Thermodynamic modeling interprets the expansion rates relative to the original unhydrated cement under the action of different soaking solutions.

Effect of recycled fiber modified by CNTs-epoxy resin composite coating on mechanical properties of mortar

In this study, the wastes GFRP was mechanically crushed and recycled GFRP fibers with a uniform aspect ratio were obtained through vibration screening and water separation treatment. In light of the surface-based interfacial defects present in recycled GFRP fibers, an epoxy resin-based nanocomposite coating reinforced with carbon nanotubes (CNTs) was employed for interfacial modification. The chemical properties of the recycled GFRP fibers before and after modification were characterised by XRD, FTIR and DTA. The changes in alkali resistance, mechanical properties and microstructure of the recycled fibers before and after modification were investigated by Alkali resistance test, mechanical testing and Scanning Electron Microscopy (SEM). Results indicated that the improvement of the coating on the fibers mainly included, blocking the erosion of alkali ions on the surface of the fibers and improving the mechanical properties of the fibers, reduced the shrinkage, and water absorption, with the highest compressive and flexural strength of 59.60 MPa and 7.13 MPa, respectively. The surface roughness due to the presence of resin and CNTs prevents easy debonding of fibers from the mortar. This property promotes strong bonding of fibers with the mortar matrix resulting in more effective fiber performance and improved mortar strength while enabling fiber recycling.

Modeling the effect of material heterogeneity on the thermo-mechanical behavior of concrete using mesoscale and stochastic field approaches

The adverse impact of high temperatures on concrete is a well-recognized issue that can lead to significant mechanical deterioration and structural integrity loss. Factors such as aggregate type, cement composition, temperature, duration of exposure, and moisture content can substantially influence the fire resistance of concrete. To simulate and better understand the effects arising from the heterogeneity of concrete in a fire situation, a mesoscale approach is proposed, using the Mesh Fragmentation Technique (MFT) to assess the complex thermo-mechanical behavior of concrete. The MFT introduces high aspect ratio interface elements to model crack propagation and interfacial transition zones by means of an appropriated tensile damage constitutive law. In this extended framework, a fully-coupled thermo-mechanical model is proposed. The modeling approach includes considerations of both macroscopic and mesoscopic scales, in which the coarse aggregate, mortar matrix and interfacial transition zones are represented. Besides, a stochastic distribution is assumed for the material properties to account for the lower scale heterogeneity. The main novelty proposed in this study consists in the synergy of mesoscale and stochastic approaches that are herein combined to model the effect of heterogeneity on the concurrent macro-mesoscale thermo-mechanical behavior of concrete. To validate the numerical model’s capabilities in capturing thermally induced cracks, benchmark cases and a simulation of a bending beam exposed to elevated temperatures are presented. The results demonstrate the potential of the proposed approach in predicting the behavior of concrete subjected to thermal loading and the role played by heterogeneity in the thermally induced cracking.

Mesoscale modelling and simulation of irradiation-induced expansion in concrete

The effects of irradiation on concrete is a topic of concern in nuclear applications, where for some specific members the material may be exposed at long-term to significant levels of neutron radiation. In this study, the effects of radiation-induced volumetric expansion (RIVE) of aggregates on concrete behaviour are investigated numerically at the mesoscale. Cylindrical concrete specimens constituted of 3 phases, namely mortar matrix, polyhedral aggregates and interfaces between both of these phases, are generated in 3D. Besides RIVE of aggregates, temperature increase due to the energy deposited during the irradiation, drying and damage development are considered in the finite element simulations. A phase-field approach and a cohesive-zone model are applied to describe damage in the matrix and interfaces, respectively. The simulation results are compared to experimental data of concrete specimens exposed to significant neutron fluences exceeding 6 × 10–19 n/cm2, in terms of residual Young modulus, compressive strength, temperatures evolution and overall expansion of the specimens. Globally, with an adequate calibration of parameters and in particular those related to the damage evolution laws, the simulation results of residual mechanical properties are in relatively good agreement with the experimental data. In addition, specimen expansions are well reproduced, providing that RIVE effects are also considered for the mortar phase, which is justified by the significant volume fraction of embedded sand grains. Mortar RIVE is modelled with the same approach as aggregate RIVE by applying a proportionality parameter, whose effect is discussed. Finally, simulations predict an intense drying of the specimens due to temperature increase.

A Study on the Mechanical and Wear-Resistance Properties of Hybrid Fiber Mortar Composites with Low Water-Cement Ratios.

Based on mortar composites with a low water-cement ratio, the effects of hybrid aramid fiber (AF), calcium sulfate whisker (CSW), and basalt fiber (BF) on their mechanical properties and wear resistance were studied, and the correlation between wear resistance and compressive strength are discussed. A microstructure analysis was conducted through scanning electron microscopy (SEM) and the nitrogen-adsorption method (BET). The research results show that compared with the control group, the compressive strength, flexural strength, and wear resistance of the hybrid AF, CSW, and BF mortar composites with a low water-cement ratio increased by up to 33.6%, 32%, and 40.8%, respectively; there is a certain linear trend between wear resistance and compressive strength, but the discreteness is large. The microstructure analysis shows that CSW, AF, and BF mainly dissipate energy through bonding, friction, mechanical interlocking with the mortar matrix, and their own pull out and fracture, thereby enhancing and toughening the mortar. A single doping of CSW and co-doping of CSW and AF can refine the pore structure of the mortar, making the mortar structure more compact.

Properties of Cementitious Composite Reinforced with Recycled Pulp from Beverage Cartons

This study presents a comprehensive evaluation of the effects of the refining level of recycled pulp from beverage cartons (RPBC) on the properties of its cementitious composite. The RPBC with various freeness levels, ranging from 400 to 650 mL of the Canadian Standard Freeness test method (CSF), was prepared using a high-speed fruit blender. The specimens were formed by the slurry de-watering method with 8wt% fiber content and mortar matrix with a sand-to-cement ratio of 1:1. The key findings reveal that the cementitious composites reinforced with the RPBC exhibited a maximum value of flexural strength of 11.17 MPa and the freeness of 550 mL CSF. The fracture toughness values of the RPBC composites were significantly improved compared to that of the control specimen. However, the values decreased by about 14% to 20 % as the freeness reduced from 650 to 400 mL CSF. The bulk density and porosity of the RPBCC were not significantly affected by the freeness of RPBC.

Predicting peak tensile stress in mesoscale concrete considering size effects: A data-physical hybrid-driven approach

The size effect and strength discreteness observed in concrete stem primarily from its mesoscopic heterogeneity. Despite this understanding, establishing a clear relationship between the macroscopic and mesoscopic mechanical behaviors remains a considerable challenge. While some advancements have been made in studying the size effect of concrete, particularly regarding the rate effect, there has been relatively less emphasis on addressing the influence of random meso-component distribution. To investigate the tensile behaviors of concrete across varying low strain rates (10−5 s−1∼10−1 s−1) and model sizes, a meso-model dataset was established comprising double edge notched concrete with mortar matrix, coarse aggregate, and interface transition zone. A convolutional neural network introducing physical parameters was implemented to capture the potential non-linear relationship of concrete from meso-structure, strain rate and model size to tensile peak stress. Subsequently, the data-driven solution for the “Static and Dynamic unified” Size Effect Law (SD-SEL) in concrete tensile strength was developed by deconstructing the back propagation (BP) neural network to enhance its rationality, followed by the verification of the proposed formula. The findings indicate that the Data-Physical Hybrid-Driven approach effectively analyzes the mechanical response of concrete without the need for complex mechanical derivations, offering a promising tool for studying the size effect of composite materials.

Invariant-based interpretation of anisotropic damage induced by cyclic loading

Damage of quasi-brittle materials appears as micro-cracks and is represented by a tensorial internal variable. Established anisotropic damage models are dedicated to monotonic –possibly multiaxial– loading. Additionally, the effective visualization and the interpretation of anisotropic damage are challenging. In materials with heterogeneous meso-structure, e.g., concrete, the damage field, and the corresponding induced anisotropy are heterogeneous as the orientation depends on the local mechanical state. The post-processing can be performed in the principal damage basis, but this basis can be a field that varies spatially and temporally. The present work addresses both problems: (i) the enhancement of an anisotropic damage model to tackle cyclic and alternate loading on quasi-brittle materials and (ii) the interpretation of the damage-induced anisotropy due to complex loading, such as alternate and non proportional ones. In the proposed model, the strain-based damage criterion function, more precisely the consolidation function, is constructed to be dependent on the so-called active damage. We define different invariant-based indicators of the anisotropy of both the damage and the effective elasticity tensors. These indicators are assessed for homogeneous and heterogeneous fields representing an aggregate embedded in a mortar matrix.

Properties of Fiber-Reinforced Geopolymer Mortar Using Coal Gangue and Aeolian Sand.

Geopolymers, as a novel cementitious material, exhibit typical brittle failure characteristics under stress. To mitigate this brittleness, fibers can be incorporated to enhance toughness. This study investigates the effects of varying polypropylene fiber (PPF) content and fiber length on the flowability, mechanical properties, and flexural toughness of coal gangue-based geopolymers. Microstructural changes and porosity variations within the Fiber-Reinforced Geopolymer Mortar(GMPF) matrix were observed using scanning electron microscope (SEM) and Low field NMR(LF-NMR) to elucidate the toughening mechanism of PPF-reinforced geopolymers. The introduction of fibers into the geopolymer matrix demonstrated an initial bridging effect in the viscous geopolymer slurry, with a 3.0 vol% fiber content reducing fluidity by 5.6%. Early mechanical properties of GMPF were enhanced with fiber addition; at 1.5 vol% fiber content and 15 mm length, the 3-day flexural and compressive strengths increased by 30.81% and 17.4%, respectively. Furthermore, polypropylene fibers significantly improved the matrix's flexural toughness, which showed an increasing trend with higher fiber content. At a 3.0 vol% fiber content, the flexural toughness index increased by 198.35%. The data indicated that a fiber length of 12 mm yielded the best toughening effect, with an 84.03% increase in the flexural toughness index. SEM observations revealed a strong interfacial bond between fibers and the matrix, with noticeable damage on the fiber surface due to frictional forces, and fiber pull-out being the predominant failure mode. Porosity testing results indicated that fiber incorporation substantially improved the internal pore structure of the matrix, reducing the median pore diameter of mesopores and converting mesopores to micropores. Additionally, the number of harmless and less harmful pores increased by 23.01%, while the number of more harmful pores decreased by 30.43%.

Uncertainties quantification for damage localization in concrete based on Bayesian method

The presence of defects in concrete can diminish load-bearing capacity of structures, giving rise to potential concerns regarding safety and durability. Thus, a method that enhances the sensitivity, resolution and robustness of damage localization is critically necessary to assess the condition of concrete structures. This research presents a damage localization method based on Bayesian probabilistic fusion, and uncertainties from measurement and identification process are considered and quantified. The likelihood function is constructed based on the hyperbola-based damage localization method, and the posterior distributions of unknown parameters are calculated via Bayesian theorem combined with measurement data. Furthermore, a meso-level finite element model is established, wherein the concrete medium is considered as a three-phase composite material consisting of polygonal aggregates, mortar matrix and interface transition zones. Owing to the meso-level modeling, the propagation behavior of stress waves within concrete and complicated interactions between stress waves and concrete internal structures can be better characterized. Finally, the damage information, time-difference-of arrival, is extracted from the response signals and the efficiency of the proposed method is verified numerically. The numerical results demonstrate that the proposed probabilistic fusion method outperforms the conventional hyperbola-based method in terms of achieving high spatial resolution and resilience in damage localization.

Influence of Nanoparticles and PVA Fibers on Concrete and Mortar on Microstructural and Durability Properties

Nanoparticles are one of the effective methodologies implemented in concrete technology. The main objective of this research is to study the influence of nano alumina with different percentage variations ranging from 1% to 3% along with the incorporation of PVA fibers. From the mechanical properties test, the optimum dosage was determined to further study the durability behavior. This research work also investigates the hybridization of two nanoparticles such as nano silica (NS) and nano alumina (NA). The results show that the increasing quantity of NA reduces the compressive strength of the mortar due to agglomeration (cluster of particles), which results in a greater molecular attraction force. From the test results, it is concluded that the optimum dosage has been attained with an addition of 2% NA with 0.3% PVA. The compression strength test results at 14 days and 28 days reveal that the addition of NA tends the mineral admixture to react at early ages in the hydration process, which produces a new chemical compound to fill the pores. The rapid chloride penetration (RCPT) test results at 28 days significantly improved with the incorporation of nanoparticles due to their effective size and chemical reaction towards the other compounds. The test results from the hybridization of nanoparticles showed that the compressive strength was significantly enhanced compared to that of the control mortar and mortar with NA. They are effective up to certain limits beyond that addition, and the workability was reduced. Amongst all mixtures, the maximum compression strength has been attained for the mix with the addition of NA 0.5% and NS 2.5% comparatively. The microstructural properties of mortar were also studied through scanning electron microscope (SEM) analysis. The results showed that the incorporation of nanoparticles in the mortar matrix turns homogeneous with fewer pores and greater amount of hydration compounds; thereby, pore refinement has improved the hydration compounds remarkably.

Numerical study on dynamic shear properties of concrete under high loading rates

Under high dynamic loads, the destruction of concrete structures is significantly influenced by the dynamic shear properties of concrete, especially when local failure occurs. Previous experimental studies have demonstrated that the shear behaviors of concrete exhibit a considerable strain rate effect. This study aims to numerically investigate the influence of the material parameters and the stress states on the shear properties and to further explore the mechanism of the shear strain rate effect. A mesoscale concrete model with the consideration of randomly distributed coarse aggregates, mortar matrix, and interfacial transition zone (ITZ) is developed to simulate the responses of concrete specimens subjected to shear loads at various loading rates. The model was validated by comparing numerical results with experimental data. Parametric studies were conducted to examine the influence of concrete parameters and confining pressures on its dynamic direct shear strength. The results indicate that the rate effect on the direct shear strength of concrete is substantial. The main reason is that more aggregates are damaged under high loading rates. Larger coarse aggregate size, smaller shear section size and high strength of ITZ could increase the rate sensitivity of the concrete in varying degrees. Additionally, confining pressure significantly enhances the direct shear strength of concrete but mitigates the influence of loading rates.

Application of supervised learning for classification of cracking and non-cracking major damage in TRMs based on AE features

Textile reinforced mortar composites (TRMs) experience various types of damage. In this study, these damage mechanisms (such as cracking and non-cracking) were understood or distinguished with the help of acoustic emissions (AE). Four types of TRMs made of a single mortar matrix and two types of carbon textiles (coated and noncoated) were evaluated under uniaxial tension. Meanwhile, the acoustic emissions were monitored during the tensile test.The study showed that AE features are sensitive to damage evolution but more importantly that TRMs are complex and various modes can coexist. Similarly, the evolution of improved b-value (Ib) also demonstrated sensitivity to the existence of damage. Finally, the supervised learning models (trained on AE data) demonstrated that information on the instant of cracking obtained through digital image correlation (DIC) can be successfully coupled with AE features to separate the cracking and non-cracking damage types with accuracy of above 80 %.