Compressive Strength Degradation Research Articles

Mechanical Properties and Fire Resistance of 3D-Printed Cementitious Composites with Plastic Waste

The study focuses on the development of cementitious composites using 3D printing and plastic waste as a sustainable aggregate substitute. This study involves experimenting with various percentages of plastic waste as a partial substitute for ground granulated blast furnace slag (GGBFS) in a control mix. The study examines the anisotropy of the 3D printing process, comparing it with properties of mold-cast samples. In addition, it assesses the fire resistance and mechanical properties of samples at elevated temperatures (100 °C, 300 °C, and 600 °C). Key mechanical properties, including 28-day compressive stress and flexural strength, are determined through experimental testing using a standard compression test and three-point bending test. The study also considers the modulus of elasticity (MOE) in compressive tests to evaluate a sample’s ability to deform elastically and the flexural toughness index to assess energy absorption and crack resistance of flexural samples. Following the experimental testing, the study’s key findings suggest that significant mass loss occurred at 300 °C and above, with plastic samples demonstrating increased mass loss at 600 °C. At 600 °C, plastic degradation led to the formation of voids and cracks within samples due to heightened internal pressure. Anisotropy was evident in 3D-printed samples, with loads parallel to the layer direction resulting in greater compressive strength and MOE. Furthermore, layer direction parallel to the longitudinal axis of flexural samples yielded higher flexural strength and flexural toughness. Mold-cast samples displayed superior compressive strength and stiffer behavior, with higher MOE compared to 3D-printed samples. However, 3D-printed plastic samples exhibited superior flexural strength compared to mold-cast samples, attributed to the alignment of plastic within the samples. The study also observed a reduction in compressive strength with the addition of plastic, explained by the poor bonding of plastic with cement due to its hydrophobic nature. Despite this, flexural strength generally improved with plastic addition, except at 600 °C, where plastic samples showed significant degradation in both compressive and flexural strength due to plastic degradation within the samples.

Experimental assessment of freeze-thaw deterioration in compression-cast fiber-reinforced concrete

An increasing number of critical infrastructures are built in cold and perma-frost regions, resulting in higher susceptibility to damage due to freeze-thaw (F-T) cycles. This paper assesses the mechanical properties and F-T damage evolution of compression-cast fiber-reinforced concrete (CCFRC) through rapid F-T cycling tests. Nine types of fiber-reinforced concrete (FRC) are experimentally investigated through 144 cubic and 39 prismatic specimens. The main parameters considered in the tests include the casting pressure applied during the compression casting procedure (between 0 and 15 MPa), type of the internal added fibers (polypropylene, end-hooked steel, or their combination), fiber content, and number of F-T cycles. The effects of these parameters on the failure modes, strength degradation rates, deterioration evolution, frost resistance durability, microscopic behavior, and F-T resistance of FRC specimens, are examined in detail. The microscopic performance of different specimens is further investigated using the X-ray computed tomography (X-CT), scanning electron microscopy (SEM), and backscattered scanning electron (BSE) tests. Based on the test results, it is shown that: (i) compared with the mass loss rate, the relative dynamic elastic modulus can be a more suitable index to assess the F-T resistance of FRC; (ii) compression casting and addition of fibers can effectively enhance the F-T denudation resistance of CCFRC; (iii) compression casting reduces the compressive and flexural strength degradation rates of CCFRC, but at the expense of more brittle behavior; and (iv) compression casting and use of the mixed polypropylene and end-hooked steel fibers can effectively delay the F-T cycling induced damage, reduce porosity and internal defects, and enhance the micro-structural behavior and F-T resistance of CCFRC. F-T deterioration prediction models are also proposed and shown to provide accurate and effective representation of the behavior of CCFRC materials.

Study on the Microscopic Pore Characteristics and Mechanisms of Disturbance Damage in Zhanjiang Formation Structural Clay

To investigate the microscopic pore evolution characteristics of Zhanjiang Formation structural clay during the disturbance process, unconfined compressive strength tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were conducted on disturbed samples subjected to various disturbance conditions after vibrational disturbance. Based on the evolution characteristics of the microstructure, the microscopic pore characteristics of the disturbance damage of Zhanjiang Formation structural clay were examined. The results indicate the following. (1) The porosity in three-dimensional visualization images of the microstructure reconstructed by ArcGIS 10.1 increases with the disturbance degree, showing a linear growth trend. (2) The correlation analysis between macroscopic mechanics and microscopic pores shows that the unconfined compressive strength of Zhanjiang Formation structural clay is mainly affected by its porosity, with a significant linear negative correlation. Based on this, a reasonable regression model between the microscopic porosity and the unconfined compressive strength has been established. The model can rapidly estimate the unconfined compressive strength from porosity data, facilitating the assessment engineering properties of the soil. (3) The microscopic pore structure of Zhanjiang Formation structural clay exhibits prominent Menger fractal characteristics. The three-dimensional pore fractal dimension has a certain positive correlation with the disturbance degree, and can be utilized to characterize the pore structure and complexity, serving as a significant parameter for the quantitative evaluation of the pore structure characteristics of Zhanjiang Formation structural clay. Consequently, the complexity of the pore structure of the engineering soil can be evaluated by the pore fractal dimension. (4) The impact of disturbance on soil is primarily manifested in the structural changes in secondary clay minerals, transitioning from a relatively intact to a fully adjusted state. During this process, interparticle pores continuously increase, pore structure complexity increases, and interparticle cementation weakens, resulting in the continuous degradation of unconfined compressive strength. This study contributes to a deeper understanding of the disturbance damage characteristics of Zhanjiang Formation structured clays from a microscopic pore perspective, providing a theoretical basis for the engineering construction and operational maintenance in regions with Zhanjiang Formation structural clay.

Enhancing the properties of high-density oil well cement with Qusaiba kaolinite

High-density cement slurries used in oil well cementing often face challenges such as particle settling, poor rheological properties, permeability, and compressive strength degradation, which can compromise zonal isolation and well integrity. This study focuses on using kaolinite, a clay mineral, as an additive due to its potential to improve the performance of high-density cement by modifying key properties. Several concentrations of kaolinite were examined to evaluate their influence on several cement properties such as rheology, thickening time, permeability, porosity, and compressive strength. Additionally, it assesses the impact of kaolinite on cement sheath solids settling using both conventional methods and nuclear magnetic resonance (NMR). The results revealed that an optimal concentration of 1% kaolinite by weight of cement (BWOC) significantly reduced particle settling by 74.4%, enhanced compressive strength by 13%, and lowered permeability and porosity by 74% and 7%, respectively. Additionally, kaolinite improved rheological properties by an 8.4% reduction in plastic viscosity, a 19.4% increase in yield point, and a 30% increase in gel strength. Kaolinite also acted as a retarder, increasing thickening time. These improvements contribute to better cement sheath integrity and wellbore stability, highlighting kaolinite’s potential as an effective additive for high-density cement.

Effect of different calcium sulfate aspect ratios and chitosan addition methods on the interface properties of calcium sulfate/chitosan composite bone cement

AbstractIt is a great challenge to improve the properties of pure calcium sulfate bone cement. Here, two calcium sulfate hemihydrate powders with different aspect ratios were prepared, and three chitosan addition methods were adopted to investigate the effect on the surface and interface properties of calcium sulfate/chitosan composite bone cement. The results showed that it lacked chemical bond between chitosan and calcium sulfate, and the short rod calcium sulfate displayed better interface adhesion with chitosan owing to its smaller size, so it possessed shorter setting time, better compressive strength and slower degradation than the long rod calcium sulfate, while the biocompatibility had no remarkable difference. Moreover, chitosan solution as liquid phase was a better solidification mode than citric acid, and calcium sulfate/chitosan composite as solid phase was the worst mode because of poor interface compatibility. Conclusively, it was a simple, low‐cost, and effective preparation process to choose short rod calcium sulfate powder as solid phase and 1 wt% chitosan solution as liquid phase, which could achieve calcium sulfate/chitosan composite bone cement with the best properties, including setting time, compressive strength, degradation rate, and biocompatibility, displaying a promising application in bone defect repair.

Study on the Influence of Thermoplastic Microcapsules on the Sulfate Resistance and Self-Healing Performance of Limestone Calcined Clay Cement Concrete.

Limestone calcined clay cement (LC3), enhanced through reactions with volcanic ash and the interaction between limestone and clay, significantly improves the performance of cementitious materials. It has the potential to cut CO2 emissions by up to 30% and energy consumption in cement manufacture by 15% to 20%, providing a promising prospect for the large-scale production of low-carbon cement with a lower environmental effect. To effectively manufacture LC3 concrete, this study utilized limestone (15%), calcined clay (30%), and gypsum (5%) as supplementary cementitious materials (SCMs), replacing 50% of ordinary Portland cement (OPC). However, in regions abundant in sulfate, sulfate attack can cause interior cracking of concrete, reducing the longevity of the building. To address this issue, microcapsules containing microcrystalline wax, ceresine wax, and nano-CaCO3 encapsulated in epoxy resin were prepared and successfully incorporated into LC3 concrete. Sulfate resistance tests were conducted through sulfate dry-wet cycles, comparing samples with and without microcapsules. The findings revealed that the initial mechanical and permeability properties of LC3 concrete did not significantly differ from OPC concrete. LC3 concrete with added microcapsules (SP4) exhibited enhanced resistance to sulfate attack, reducing mass loss and compressive strength degradation. SEM images displayed a mesh-like structure of repair products in SP4. After 14 days of self-repair, SP4 exhibited a 44.2% harmful pore ratio, 98.1% compressive strength retention, 88.7% chloride ion diffusion coefficient retention, 91.12 mV maximum amplitude, and 9.14 mV maximum frequency amplitude. The experimental results indicate that the presence of microcapsules enhances the sulfate attack self-healing performance of LC3 concrete.

Quantitative assessment of correlation between compressive strength degradation and microstructural crack information in mortar deteriorated by freeze-thaw cycles

Freeze-thaw cycle (FTC) deterioration poses significant durability challenges to concrete structures. However, the detailed quantitative relationship between FTC-induced internal damage pattern development and mechanical degradation remains underexplored, limiting the accuracy of FTC deterioration assessments. This study aims to provide a comprehensive analysis of microstructural damage progression and its quantitative relationship with mechanical degradation in mortar specimens throughout FTC process. Through establishing an experimental setup applied to specimens at two scales and facilitated by micro-computed tomography (micro-CT), this research concurrently evaluates the microstructural damage progression, mechanical degradation, and expansion of the specimens under various FTC severity levels. The quantification of multiple crack indices reveals a stronger correlation between compressive strength reduction and crack ingression than with increases in crack quantity or width. The findings further highlight the imperative to incorporate both expansion-induced damage and time-dependent fatigue damage in evaluating FTC deterioration, thus laying a foundation for refining FTC prediction models.

An ensemble learning-based prediction model for the compressive strength degradation of concrete containing superabsorbent polymers (SAP)

Super absorbent polymer (SAP) has a capacity to enhance the characteristics of cementitious composites in both their fresh and hardened forms. However, it is essential to recognize that the strength of SAP concrete may decrease. By altering the concrete composition and selecting the appropriate type of SAP, it is possible to reduce this reduction. This work employs machine learning (ML) to tackle the issue of strength degradation. The analysis considers ten distinct variables linked to concrete composition and the type of SAP. The study uses machine learning approaches that involve both regression and classification tasks. The use of ensemble learning greatly improves the quality and accuracy of the results, showing its superiority in combining several models to produce more precise predictions. The findings demonstrate that the Support Vector Machines (SVM) and Extreme Gradient Boosting (XGBoost) regression algorithms accurately forecasted the percentage of reduction in strength in SAP concrete. These predictions were based on the concrete composition and SAP details, resulting in R2 values of 0.90 and 0.88, respectively. Furthermore, XGBoost exhibited the highest accuracy, reaching 0.94, when compared to the various categorization algorithms. According to the results, the mean squared error (MSE) of the ensemble model demonstrated superior outcomes. Furthermore, the SHapley Additive exPlanations (SHAP) reveal that some variables, including SAP%, SAP size, and compressive strength, have a significant influence on the strength reduction model. This study aims to bridge the gap between academic research and practical application by developing a web application that employs ensemble learning to precisely forecast the reduction in compressive strength caused by the usage of SAP.

Research on improving the frost resistance and self-repair performance of limestone calcined clay cement concrete by microcapsules

Limestone calcined clay cement (LC3) concrete has emerged as a pivotal construction material aimed at mitigating carbon emissions and bolstering sustainability. However, LC3 concrete confronts durability challenges in frigid regions attributable to freeze-thaw cycles. Microcapsule self-repair technology, as an innovative paradigm, presents a promising avenue to augment the freeze-thaw resistance and self-repair attributes of LC3 concrete. Within this inquiry, microcapsules containing isophorone diisocyanate (IPDI) and encapsulated with microcrystalline wax, ceresine wax, and CaCO3 were synthesized and effectively integrated into LC3 concrete matrices. Freeze-thaw cycle investigations were conducted to juxtapose LC3 concrete specimens with and without microcapsules. The findings evinced that LC3 concrete augmented with microcapsules demonstrated enhanced resistance to freeze-thaw cycles, thereby mitigating mass loss and compressive strength degradation. Microscopic structural analyses, pore size distribution assessments, mechanical property evaluations, impermeability, and ultrasonic waveform analyses of LC3 concrete samples featuring microcapsules corroborated the heightened freeze-thaw resistance, thus fortifying its applicability in rigorous environments. Moreover, deliberate pre-cracking of the concrete surface unveiled the self-repair efficacy of microcapsules, with empirical observations underscoring the prompt crack remediation capabilities of the implemented technology.

Effects of biogenic sulfuric acid on simulated concrete septic tanks

Concrete is the major construction material for infrastructure development. Concrete sewer septic tanks are Constructed using the conventional ordinary portland cement (OPC) and the Portland pozzolana cement (PPC). However, OPC based concrete sewer systems are susceptible to biological, mechanical, and chemical degradation. Degradation of the concrete septic leads to their failure hence imposing tremendous environmental problems. The aftermath is the emergence of sanitation-related diseases. The wastewater from failing septic systems leads to contamination of the groundwater or the surface water resulting in the pollution of drinking water. Therefore, the need to explore other possibilities and potential construction materials to achieve sustainable sanitation is inevitable. The use of Limestone Calcined Clay Cement (LC3) in the construction of degradation-resistant concrete sewer septic systems has not been well explored in Kenya. LC3 concrete is resistant to the deterioration effects of aggressive media such as acids, chlorides, and sulfates. This paper presents experimental performance and findings of LC3 in aggressive media vis a vis OPC. The LC3 was formulated by mixing clinker, Calcined clay, limestone, and gypsum at percentages of 50 %, 30 %, 15 %, and 5 % respectively. Compressive strength, Sorptivity, and weight loss during the wet and dry cycles for both LC3 and OPC were evaluated. Simulated concrete septic tanks made of LC3 and OPC were made by casting cubes at water cement ratio of 0.5 and cured in fresh water at ambient temperature for 28 days. These cubes were passed through a regime of W-D cycles in the 3% concentration of Biogenic sulfuric acid. It was observed that after 28 days of curing OPC cubes had slightly higher compressive strength than LC3. However LC3 concrete cubes are expected to have higher compressive strength than the OPC. Cubes curing time increases due to increased pozzolanic activity. Biogenic sulphuric acid attacks on hydrated cement products cause a decrease in compressive strength. The water absorption profile of LC3 cubes was lower as compared to OPC cubes. In conclusion, LC3 cubes had a high potential of resisting degradation as compared to OPC cubes. LC3 show more impressive performance, hence LC3 It’s a potential binder for use in the construction of sewer system.
 Keywords: Septic tank, Sorptivity, compressive strength, wet-dry cycles, biological, mechanical, and chemical degradation, sustainable sanitation, LC3.

Thermal stability and strength degradation of lithium slag geopolymer containing fly ash and silica fume

This paper investigates the thermal stability of lithium slag geopolymer (LSG) containing fly ash (FA) and silica fume (SF) exposed up to 900˚C. The effects of elevated temperatures on the microstructural evolution were investigated by thermogravimetric analysis (TGA), X-ray Diffraction (XRD), mineral analysis, surface porosity, and compressive strength of LSG modified by optimum incorporation of fly ash and silica fume. The results indicated that elevated temperature exposure significantly affects compressive strength, surface porosity, void size, weight loss, and phase transformation of fly ash incorporated lithium slag geopolymer (LSGFA) and silica fume incorporated geopolymer (LSGSF). The maximum loss in compressive strength of 44.07% was observed in LSGFA compared to 31.50% loss in LSGSF after exposure at 900˚C. The weight loss of LSGSF was higher than that of LSGFA between 500 and 800˚C and 800–1000˚C indicating a higher degree of dehydroxylation, crystal phase transformation, and viscous sintering observed in the former mix. A larger shrinkage cracking was observed in LSGSF by self-desiccation of the aluminosilicate paste matrix by dehydroxylation of mordenite molecules. Therefore, the degradation of compressive strength is governed by the combination of the crystallization of aluminosilicate gel and the formation of voids.

Sulphate resistance prediction of RAC considering the coupling effect of RCA and water-binder ratio based on experimental analysis and LSSVM

ABSTRACT Waste concrete removed from old pavement can be crushed and sieved as recycled aggregate to prepare concrete, and the application of recycled aggregate concrete (RAC) can reduce the occupation of land resources by the waste concrete and save natural aggregate. In this paper, the influence of proportion of recycled coarse aggregate (RCA) replacing natural coarse aggregate (NCA) and water-binder ratio on the sulphate resistance of RAC was studied, and the compressive strength degradation rate (Df ) was introduced to evaluate the sulphate resistance of RAC. The experimental results showed that the compressive strength of RAC before and after sulphate attacks linearly decreased with the growth of the replacement rate of RCA, water-binder ratio, and the number of sulphate wet-dry cycles, respectively; while Df of RAC increased with the rise of the replacement rate of RCA, water-binder ratio, and sulphate wet-dry cycles, respectively. The results also indicated that Df of all groups of RAC was less than 25%, which can meet the engineering requirements. In addition, the Df model of RAC under a sulphate attack based on experimental data and that based on Least-Squares Support Vector Machine (LSSVM) was built and compared, and both models predict the sulphate resistance of RAC well. The prediction model based on LSSVM has higher prediction accuracy.

Limitations and modifications in the clinical application of calcium sulfate.

Calcium sulfate and calcium sulfate-based biomaterials have been widely used in non-load-bearing bone defects for hundreds of years due to their superior biocompatibility, biodegradability, and non-toxicity. However, lower compressive strength and rapid degradation rate are the main limitations in clinical applications. Excessive absorption causes a sharp increase in sulfate ion and calcium ion concentrations around the bone defect site, resulting in delayed wound healing and hypercalcemia. In addition, the space between calcium sulfate and the host bone, resulting from excessively rapid absorption, has adverse effects on bone healing or fusion techniques. This issue has been recognized and addressed. The lack of sufficient mechanical strength makes it challenging to use calcium sulfate and calcium sulfate-based biomaterials in load-bearing areas. To overcome these defects, the introduction of various inorganic additives, such as calcium carbonate, calcium phosphate, and calcium silicate, into calcium sulfate is an effective measure. Inorganic materials with different physical and chemical properties can greatly improve the properties of calcium sulfate composites. For example, the hydrolysis products of calcium carbonate are alkaline substances that can buffer the acidic environment caused by the degradation of calcium sulfate; calcium phosphate has poor degradation, which can effectively avoid the excessive absorption of calcium sulfate; and calcium silicate can promote the compressive strength and stimulate new bone formation. The purpose of this review is to review the poor properties of calcium sulfate and its complications in clinical application and to explore the effect of various inorganic additives on the physicochemical properties and biological properties of calcium sulfate.

Numerical analysis and design methods of grout-filled GFRP tube repaired corroded CHS T-joints

This study explores the compressive behavior of Grout-Filled GFRP Tube (GFGT) repaired corroded circular hollow section (CHS) T-joints. Finite element models of GFGT repaired corroded joints were developed, validated, and utilized to examine the influence of the joint geometric, material, and chord end stress parameters on the compressive strength and repairing efficiency of the joints. The findings reveal that the ultimate strength of the GFGT repaired joint increases with a thicker GFRP tube, a lower repaired chord section hollow ratio, a higher grout strength, and a longer repaired range. By optimizing the repairing parameters of the grout-filled GFRP tube, the compressive strength of GFGT repaired corroded joints with 16% and 32% corrosion rates can be up to increase to 164% and 147% of the uncorroded counterparts, respectively. The chord end stress exerts a similar but weaker effect on the repaired joints than on the unrepaired joints. A series of suggestions were proposed for repairing joints with different corrosion degrees to achieve a 20% ultimate strength enhancement compared to uncorroded joints. The compressive strength degradation rate of corroded joints was accurately predicted by the design method in the CIDECT and prEN guidelines. The feasibility of the guideline formulae to evaluate the strength reduction rate caused by the chord end preload was verified. A design method to predict the compressive strength of GFGT repaired corroded joints was proposed.

Effect of silica fume on strength of recycled aggregate concrete

The present study deals with investigating the effects of using coarse recycled concrete aggregates (RCA) on compression & split-tensile resilience of M25 grade concrete mixes. Five different mixes of modified recycle aggregate concrete (RAC) were designed and prepared considering replacement proportion of normal coarse aggregates as 0, 25, 50, 75, and 100 % with RCA. The specimens were prepared according to Indian standard codal provisions and experimentally tested for its mechanical characteristics in laboratory conditions. A steep degradation in compressive and tensile strength on increasing RCA proportion was observed, which may result due to improper bonding at interfacial region in RAC mixes. To overcome this strength deterioration, the effect of adding pozzolanic materials like silica fumes is also studied for making strength improvements. The silica fumes as admixture, in percentages of 4%, 8% and 12%, was added in RAC mixes for finding the optimum proportions. Overall, the study provides a sustainable solution for problematic concrete waste dumping while utilizing it in casting new concrete structures of significant strengths.

Durability assessment of fly ash, GGBS, and silica fume based geopolymer concrete with recycled aggregates against acid and sulfate attack

There is a constant drive to develop high-performance concrete with enhanced mechanical and durability characteristics while incorporating environment-friendly materials. The study investigates the synergistic effects of fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF) on the durability characteristics of 100 % recycled aggregate (RA) based geopolymer concrete (GPC) against acid and sulfate attacks. Moreover, its relative performance compared to control samples of ordinary Portland cement (OPC) concrete with natural and recycled aggregates was also assessed. The acid and sulfate resistance were determined by submerging the concrete specimens in the 5 % sulphuric acid (H2SO4), 5 % sodium sulfate (Na2SO4), and 5 % magnesium sulfate (MgSO4) for up to 180 days of exposure duration. The specimens' resistance to chemical attack was assessed by visual observation, changes in weight, and the percentage of compressive strength loss at different time intervals. In addition, the changes in the mineralogical and microstructures of the GPC matrix were also examined using X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) tests. Results indicated that an increased proportion of GGBS and SF positively influenced the durability of GPC, as revealed by reduced mass loss and compressive strength degradation. In addition, the microstructural, mineralogical, and morphological properties depicted enhanced densification and compactness of the GPC matrix due to the formation of CSH, CASH, and NASH gels. GPC-MG15 (FA:GGBS:SF – 35:50:15) yielded the highest strength and durability performance, compensating for the trade-offs of using 100 % RAs in conventional OPC concrete. So, optimized use of these sustainable materials has depicted promising results in aggressive environments while reducing the need for conventional OPC and natural aggregates.

Compressive strength evaluation of cement-based materials in sulphate environment using optimized deep learning technology

Strength serves as a vital performance metric for assessing long-term durability of cement-based materials. Nevertheless, there is a scarcity of models available for predicting residual strength of in-situ structures made of cement-based materials exposed to sulphate conditions. To address this challenge, this study presents a novel approach using deep learning to predict the degradation of compressive strength of cement-based materials under marine environments. Specifically, a deep convolutional neural network (DCNN) is established, consisting of two convolutional layers, one pooling layer, and two fully connected layers. In this innovative model, contents of cement, water-to-cement ratio, sand, sulphate concentration and exposure temperature are selected as inputs, while the output is strength of cement-based materials subjected to sulphate deterioration. To improve the forecast capability, particle swarm optimization is adopted for optimizing hyperparameters of DCNN, which can be implemented by reducing the discrepancy between model prediction and measured strength. Finally, experimental data are used to establish and evaluate proposed method. The results show that the proposed deep learning-based predictive model has the best performance of strength degradation prediction of cement-based materials suffering from sulphate attack via a comparison with other commonly used models. The outcome of this research offers a potential solution for predicting remaining strength of cement-based materials that undergo practical sulphate attack.

Compressive strength degradation of engineered bamboo subjected to fungal attack

Glue laminated bamboo (glubam) is a type of engineered bamboo material developed for applications in building structures and interiors. This paper focuses on the fungal (Aspergillus niger) colonization from 14 to 56 days in thick- and thin-strip glubam board with the investigation of physical, mechanical (compression), and microcosmic properties. Two-degree of carbonization treatment was employed to improve the antifungal property of the thick-strip glubam. After 56 days of infection, the deep-degree carbonized thick-strip glubam presents better anti-mold properties than medium and non-carbonized specimens. For thin-strip glubam, both parallel and perpendicular to the main bamboo fiber direction were considered. The longitudinal thin-strip glubam retains decent compressive properties, while the transverse specimens stay a stable compressive strength along all fungal tests. The paper reports the experimental values of mass loss, color changes, compressive strengths, modulus of elasticity in compression, and microstructure observations from optical and SEM microscopy at different fungal exposure timespans.

Degradation mechanism and evaluation of the carbonation resistance of concrete after high-temperature exposure

High-temperature exposure during fire decreases not only the mechanical properties of concrete structures but also their durability, especially their concrete carbonation resistance. However, the degradation of concrete carbonation resistance after fire exposure remains unclear. Concrete specimens with water/cement (w/c) ratios of 0.4, 0.5, and 0.6 were fabricated to solve such problems, and high-temperature experiments were performed at 400 °C, 500 °C, and 600 °C and sustained for one hour. Then, mechanical and accelerated carbonation experiments were conducted, and the carbonation depths and pH values of concrete were tested. X-ray diffraction, thermogravimetry analysis, and mercury intrusion porosimetry experiments were also performed on concrete with and without high-temperature treatment. Results showed that high-temperature exposure caused severe degradation in concrete compressive strength, relative dynamic modulus of elasticity, and carbonation resistance, and the carbonation resistance loss of concrete was higher than its mechanical property loss. Concrete with lower w/c ratio suffered more losses in mechanical properties, whereas w/c ratio had no obvious effect on the carbonation resistance degradation of fire-damaged concrete. The key mechanism of the decline in the carbonation resistance of concrete after fire was not mainly the alkalinity drop in concrete but the considerable increase in concrete porosity and harmful pores. Instead of the traditional phenolphthalein method, a new method of residual OH- concentration of superficial concrete after accelerated carbonation was proposed to evaluate the carbonation resistance of concrete after fire. The average carbonation resistance of the concrete with the three w/c ratios was reduced by 66.3 %, 84.2 % and 95.1 % after exposure to 400 °C, 500 °C, and 600 °C, respectively.

Optimizing Cement Asphalt Mortar Mixtures for Bridge Expansion Joints in Tropical Climates: Performance and Durability Assessment

In this study, the suitability of various Cement Asphalt Mortar (CAM) mixtures for bridge expansion joint applications in tropical climates was quantitatively assessed. A comprehensive analysis encompassed key properties, including mixing stability, flowability, unconfined compressive strength, expansion characteristics, and resistance to acidic and alkali environments. The influence of high-temperature exposure on unconfined compressive strength and the microstructural features were also examined. The results revealed a discernible trend: lower cement content, in conjunction with anionic Asphalt Emulsion (AE) or epoxy resin, significantly enhanced mixing stability and flowability while contributing to improved unconfined compressive strength and chemical degradation resistance. Notably, epoxy resin emerged as a valuable component in mitigating high-temperature-induced strength reduction, indicating potential promise for CAM mixture design. SEM analysis visually supported these findings by highlighting the microstructural distinctions among CAM mixtures. Quantitatively, the findings indicated that CAM mixtures with a 25% cement content and 75% anionic AE exhibited an 11% improvement in mixing stability, along with a 13% enhancement in flowability, relative to the control mixture with 100% cement. Additionally, CAM mixtures incorporating epoxy resin (at various percentages) with anionic AE exhibited a significant 15% resistance to high-temperature-induced UCS reduction, surpassing other mixtures. The SEM micrographs visually confirmed the superior microstructural connectivity achieved with epoxy resin, further validating the observed enhancements. These quantitative results offer a robust foundation for tailoring CAM mixture compositions to optimize their suitability for rigorous infrastructure projects in tropical climates.