Coral Aggregate Research Articles

Analysis of microstructure and compressive properties of full coral concrete under fiber reinforcement

Based on the compressive tests of 120 cubes in 10 groups, the effects of different chopped fibers (polypropylene fiber PPF, glass fiber GF, basalt fiber BF) and their content on the compressive properties of coral aggregate seawater concrete (CASC) were studied. The microstructure of CASC was analyzed by scanning electron microscopy (SEM), and the relationship between microstructure and macroscopic properties was established. The results show that the growth rate of compressive strength of fiber CASC is fast in the early stage and slow in the late stage. When 1 kg/m3, 2 kg/m3 and 3 kg/m3 of PPF were added to the CASC, the compressive strength increased by 6.2 %, 17.4 % and 9.9 %, respectively. SEM images show that PPF forms a dense, chaotic three-dimensional mesh structure in the matrix, which can effectively inhibit crack extension within a certain doping range. Compared with BF and GF, PPF has a more significant effect on improving the mechanical properties of CASC, and the optimal PPF content is 2 kg/m3. Adding PPF could improve the brittleness of concrete and make it show good ductility when it is destroyed.

Impact Toughness Analysis and Numerical Simulation of Coral Aggregate Concrete at Various Strength Grades: Experimental and Data Investigations

This paper comprehensively investigates the dynamic mechanical properties of concrete by employing a 75 mm diameter Split Hopkinson Pressure Bar (SHPB). To be detailed further, dynamic compression experiments are conducted on coral aggregate seawater concrete (CASC) to unveil the relationship between the toughness ratio, strain rate, and different strength grades. A three-dimensional random convex polyhedral aggregate mesoscopic model is also utilized to simulate the damage modes of concrete and its components under varying strain rates. Additionally, the impact of different aggregate volume rates on the damage modes of CASC is also studied. The results show that strain rate has a significant effect on CASC, and the strength grade influences both the damage mode and toughness index of the concrete. The growth rate of the toughness index exhibits a distinct change when the 28-day compressive strength of CASC ranges between 60 and 80 MPa, with three times an increment in the toughness index of high-strength CASC comparing to low-strength CASC undergoing high strain. The introduction of pre-peak and post-peak toughness highlights the lowest pre-to-post-peak toughness ratio at a strain rate of approximately 80 s−1, which indicates a shift in the concrete’s damage mode. Various damage modes of CASC are under dynamic impact and are consequently defined based on these findings. The LS-DYNA finite element software is employed to analyze the damage morphology of CASC at different strain rates, and the numerical simulation results align with the experimental observations. By comparing the numerical simulation results of different models with varying aggregate volume rates, it is reported that CASC’s failure mode is minimized at an aggregate volume rate of 20%.

Study on Static Mechanical Properties and Numerical Simulation of Coral Aggregate Seawater Shotcrete with Reasonable Mix Proportion

This study aims to explore the static mechanical characteristics of coral aggregate seawater shotcrete (CASS) using an appropriate mix proportion. The orthogonal experiments consisting of four-factor and three-level were conducted to explore an optimal mix proportion of CASS. On a macro-scale, quasi-static compression and splitting tests of CASS with optimal mix proportion at various curing ages employed a combination of acoustic emission (AE) and digital image correlation (DIC) techniques were carried out using an electro-hydraulic servo-controlled test machine. A comparative analysis of static mechanical properties at different curing ages was conducted between the CASS and ordinary aggregate seawater shotcrete (OASS). On a micro-scale, the numerical specimens based on particle flow code (PFC) were subjected to multi-level microcracks division for quantitive analysis of the failure mechanism of specimens. The results show that the optimal mix proportion of CASS consists of 700 kg/m3 of cementitious materials content, a water–binder ratio of 0.45, a sand ratio of 60%, and a dosage of 8% for the accelerator amount. The tensile failure is the primary failure mechanism under uniaxial compression and Brazilian splitting, and the specimens will be closer to the brittle material with increased curing age. The Brazilian splitting failure caused by the arc-shaped main crack initiates from the loading points and propagates along the loading line to the center. Compared with OASS, the CASS has an approximately equal early and low later strength mainly because of the minerals’ filling or unfilling effect on coral pores. The rate of increase in CASS is swifter during the initial strength phase and decelerates during the subsequent stages of strength development. The failure in CASS is experienced primarily within the cement mortar and bonding surface between the cement mortar and aggregate.

Impact characterization of coral aggregate reinforced concrete beam: A 3D numerical study

Coral aggregate concrete (CAC), an innovative construction material, utilizes abundant marine resources, including coral aggregates and seawater. In the realm of reef engineering, CAC is widely used in structural elements such as reinforced beams and columns. This paper presents a three-dimensional (3D) mesoscale model to assess the impact behavior of coral aggregate reinforced concrete beams (CARCB), incorporating the heterogeneity characteristics of CAC and the explicit simulation of reinforcement components. The 3D mesoscale modelling approach developed in this paper was validated by previous experimental data of CARCB, and used for extensive parametric studies evaluating effects such as concrete strength grade, reinforcement ratio, and impact velocity on the static and dynamic bending behaviors of CARCB. Finally, based on the mesoscopic cracking process and damage patterns of CARCB under static and dynamic loads, this study illustrates the corresponding macroscopic mechanical behaviors and failure mechanisms. Results indicate that the predominant forms of flexural failure in CARCBs are tensile cracking in the mid-span region and diagonal shear cracking. Results demonstrate that the predominant forms of flexural failure in CARCBs are tensile cracking in the mid-span region and diagonal shear cracking. Specifically, local bending failures and symmetrical diagonal shear cracks were evident in the CARCBs subjected to dynamic loads, closely resembling those in ordinary concrete beams. With increasing concrete strength grades (C30 to C60) and reinforcement ratios (0.9 %–1.7 %), a significant reduction in the mid-span ultimate deflection of CARCB is observed, indicating enhanced impact resistance. Additionally, as the impact velocity increases from 1 m/s to 50 m/s, the mid-span ultimate deflection of CARCB is magnified by a factor of approximately 200, indicating intensified dynamic damage to CARCB with increasing impact velocities.

Predicting compressive strength of fiber-reinforced coral aggregate concrete: Interpretable optimized XGBoost model and experimental validation

The addition of macro and micro fibers can enhance the compressive strength of fiber-reinforced coral aggregate concrete (FRCAC-CS). Traditional explicit models for FRCAC-CS suffer from shortcomings related to accuracy and generalization capabilities. To address this issue, a comprehensive database for FRCAC-CS was established by collecting 834 sets of experimental data from 15 literature sources. The hunger games search algorithm (HGS), sooty tern optimization algorithm, and whales optimization algorithm were used to optimize the hyperparameters of the XGBoost algorithm, resulting in optimized XGBoost models for FRCAC-CS. The performance of the prediction models was assessed through comparisons between predicted and actual values, model residual distribution, and performance evaluation metrics. Sensitivity analysis was conducted using the Shapley additive explanations method. Subsequently, 9 different mix proportions were formulated to validate the performance of the optimal model. The results suggest that the HGS–XGBoost model yields predictions that are closer to the actual values, exhibiting smaller mean and standard deviation in model residuals. The five major performance evaluation metrics, including RMSE, MSE, MAPE, MAE, and R2, for the HGS–XGBoost model are 0.91, 0.83, 2.35, 0.77, and 0.99, respectively, surpassing those of other models. Sensitivity analysis highlights the water–to–binder ratio and total aggregate content as the two most crucial factors among the mix components. Decreasing the water–to–binder ratio and the total aggregate content improves the FRCAC-CS. The experimental results from the 9 mix proportions demonstrate that the error between predicted and experimental values is below 7%, affirming the HGS–XGBoost model’s adequate accuracy and generalization capabilities for new datasets. This study introduces a novel AI-based prediction method for FRCAC-CS, establishing the groundwork for its potential application in reef construction.

Internal curing of fine coral aggregate in cement mortars with low water-to-cement ratio: Difference in freshwater and seawater

Fine coral aggregate has a porous structure and high water absorption, which can be used as an internal curing medium. In this study, the pore characteristics and water absorption-desorption of fine coral aggregate were investigated, as well as the difference in internal curing of fine coral aggregate between freshwater and seawater mixed cement mortars with a low water-to-cement ratio. The results showed that the pore size of fine coral aggregates is mostly larger than 1 μm. In addition, the seawater can promote the hydration of cement, improve the early strength, and increase autogenous shrinkage and later-age drying shrinkage of cement mortars. On the other hand, it can accelerate the release of internal curing water from fine coral aggregates into the matrix. Based on experiments, three stages of early autogenous shrinkage development were discussed and an autogenous shrinkage calculation model for cement mortars mixed with seawater and fine coral aggregates was proposed. Moreover, the optimal volume replacement content of fine coral aggregate in cement mortars mixed with freshwater or seawater was calculated, which indicates that it is necessary to modify the pore structure of fine coral aggregates.

Predicting corrosion behaviour of steel reinforcement in eco-friendly coral aggregate concrete based on hybrid machine learning methods

ABSTRACT This study proposes a machine learning-assisted method for assessing steel reinforcement corrosion, utilising data on chloride ion concentration (CIC) and chloride ion concentration threshold (CCT) from eco-friendly coral aggregate concrete (EFCAC). A total of 2185 data points were collected to establish the EFCAC-CIC database. A multi-objective slime mould optimised support vector regression (MOSMA-SVR) model for EFCAC-CIC was developed. The significance of each feature to EFCAC-CIC was analysed. Subsequently, a graphical user interface (GUI) was developed based on the MOSMA-SVR model. Finally, the GUI and EFCAC-CCT were used to assess the corrosion behaviour of reinforcement. Results indicate that the MOSMA-SVR model provides predictions that are closer to the actual values, with smaller mean errors and standard deviations. The performance indicators, including coefficient of determination, mean absolute error, mean absolute percentage error, mean square error, root mean square error, and a20-index, of the MOSMA-SVR model are 0.987, 0.0124, 0.0332, 2.91e − 4, 0.0171 and 0.9991, respectively, and they are superior to those of the other tested models. The water type and the water–binder ratio are identified as the two most critical factors. Furthermore, by integrating the GUI and feature importance analysis results, chloride salt-resistant EFCAC can be designed. When this is combined with the GUI and EFCAC-CCT, the corrosion of rebar in EFCAC can be assessed in real time.

Seismic performance and skeleton curve model of prefabricated coral aggregate concrete-filled aluminum tube joint

Corrosion-resistant and high load-carrying capacity coral aggregate concrete-filled aluminum tube (CCFAT) structures show promising applications in island construction. However, research on CCFAT joints related to structural safety remains scarce. To advance the engineering application of this structure, a novel prefabricated CCFAT beam-column semi-rigid joint with bolt connections is designed in this study. The seismic performance of the joint is investigated through a pseudo-static method, analyzing the effects of each parameter on failure mode, hysteresis curve, deformation characteristics, and energy dissipation performance, considering the earthquake-prone nature of islands. The primary objective of this study is to explore the influence of different parameters on the seismic performance of the CCFAT joint and establish the moment-rotation relationship of this joint. It is observed that the ultimate moment relationship between the beam and connector significantly impacts the failure mode of the joint, thus affecting its seismic performance. Hence, prioritizing the ultimate moment relationship between the beam and connector in the design phase is crucial to avoid undesirable joint failures. The skeleton curve of CCFAT joints differs significantly from that of steel and reinforced concrete structures, rendering existing joint theories inapplicable to CCFAT joints. Considering joint material, structure, and failure mode, this paper proposes a theoretical calculation method for the initial stiffness and ultimate moment of the CCFAT joints. This method is based on the component method and mechanical model, establishing an exponential three-parameter skeleton curve model for the joint. This model enables an accurate prediction of the moment-rotation relationship of the CCFAT joint, aiding in its seismic performance evaluation.

Mesoscopic investigation of the matrix pores and ITZ effects on the mechanical properties of seawater sea-sand coral aggregate concrete

In this study, the matrix pores and ITZ effects on the mechanical properties of seawater sea-sand coral aggregate concrete (SSCAC) were investigated via the meso-element equivalent method. The effective modulus and strength of aggregate and matrix in SSCAC at different scale level were derived via the Voigt model and Mori-Tanaka method. A three-step equivalence process was established to consider the influence of the matrix pores. The surface permeability zone for coral aggregate was proposed to explain the strength enhanced effect of the interface transition zone (ITZ) in SSCAC. A comparisons study was carried out to analyze the difference between SSCAC and ordinary Portland concrete about the stress-strain relationships, failure patterns, and failure mechanisms. Finally, the impact of porosity variations on the mechanical properties development of SSCAC have been investigated, which indicate that the compressive and splitting tensile strengths of SSCAC present distinct three-stage variations with respect to porosity. A sensitive range of ITZ effect was proposed to reveal that as porosity within 7%–18%, the variation of porosity can influence the ratio of splitting tensile strength to compressive strength of SSCAC remarkably. To ensure optimal performance in both splitting tensile strength and compressive strength, it is recommended to maintain the porosity of SSCAC within the range of 5%–10%.

Investigation on chloride releasing from coral aggregates to cement paste in coral aggregate concrete

Coral aggregate concrete (CAC) is one of the most commonly used building materials in construction on marine islands, but the chlorides contained in the coral aggregates (CA) could affect the durability of CAC with steel bars embedded. In this paper, an analytical solution for the diffusion of chlorides from CA into the cement paste in CAC was derivated and the model was established. Studies on chloride releasing behaviours in CAC through an experimental setup of CAC interface specimens with five mixes were conducted. From the analytical model, the chloride diffusion coefficient DCl can be obtained and, different from other reported chloride diffusion coefficient from harden specimen, this coefficient could be the only factor that describes the chloride transport in CAC from the mixing stage. The chloride releasing rate αCl from CA was also calculated and quantified. The results show that the chloride release rate from CA decayed with time and significant chloride release occurred in the first 30 days from the mixture of raw materials, the released amount of chlorides from CA was positively correlated to the average pore size of cement pastes, and the chloride diffusion coefficient of CA in this study was 2–3 magnitudes higher than that of hardened cement paste.

Mesoscopic mechanical study on quasi-static compression of coral aggregate seawater concrete after high temperature exposure

Coral aggregate seawater concrete (CASC) is a pioneering concrete made by blending and curing coral reefs, coral sands, cement, mineral admixtures, chemical additives, and seawater. The investigation of its mechanical properties is important for both theoretical and engineering purposes. This paper aims to investigate the quasi-static mechanical properties of CASC after exposure to high temperatures using a combined approach of experiments and numerical simulations. The simulation uses LS-DYNA software and a three-dimensional random aggregate mesoscopic model to analyze the process of concrete damage and crack propagation. Various mechanical parameters such as peak stress, peak strain, and compressive strength after exposure to different temperatures are calculated. The simulation results show that under quasi-static uniaxial compressive loading, microcracks initiate within the mortar and interfacial transition zone (ITZ) of CASC. These cracks then propagate through the coarse aggregates, leading to aggregate failure and the disintegration of the concrete structure. The macroscopic damage traits of CASC specimens reveal concentrated damage in the central region. As the temperature increases during heat treatment, the severity of damage to CASC specimens also increases. However, as the strength grade increases, the damage condition of CASC tends to improve.

Experimental study on the mechanical properties and uniaxial compressive constitutive relationship of sea sand coral concrete

The use of seawater, sea sand and coral to formulate concrete for marine engineering construction is an effective measure for rationally allocating resources and alleviating resource shortages. To promote the engineering application of marine concrete, it is necessary to study the mechanical properties and microstructure of marine concrete. In this study, sea sand coral concrete (SSCC) with strength grades of C20–C40 was prepared, and the compressive and flexural tests were conducted to observe the stress process and damage morphology of the specimens and to establish a constitutive model for SSCC under uniaxial compression. In addition, the microstructures of the SSCC hydration products and interfacial transition zone (ITZ) were observed via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the damage surface of the SSCC occurred directly through the coral aggregate, and the damage process was sudden and brief. Under uniaxial compression, the trend of the rising section of the stress-strain curve of SSCC with different strength grades are basically the same, but the shape of the descending section vary greatly, and the higher the strength grade is, the steeper the slope of the descending section. Quantitative relationships between compressive strength, elastic modulus, peak strain and peak stress and cube compressive strength were established. Based on the experimental results, a two-stage uniaxial compression constitutive model for SSCC was proposed, and the established constitutive model can effectively predict the stress-strain behavior of SSCC. In addition, the XRD patterns show that the early hydration rate of SSCC is faster than that of ordinary concrete (OC), which leads to a faster early strength development of SSCC. The SEM images show that the coral aggregate binds better to the cement matrix than the crushed gravel aggregate does and that the microstructure of the SSCC is denser than that of OC.

Flexural behavior of FRP bars reinforced seawater coral aggregate concrete beams incorporating alkali-activated materials

Flexural behavior of FRP bars reinforced seawater coral aggregate concrete beams incorporating alkali-activated materials

Investigation of electrical resistivity for fiber-reinforced coral aggregate concrete

The application of fiber-reinforced coral aggregate concrete (FRCAC) holds importance in alleviating material scarcity for island and reef construction and in enhancing structural performance. Electrical resistivity, a nondestructive metric, can be employed to assess the comprehensive performance of FRCAC. Therefore, FRCAC was prepared by incorporating basalt fibers (BF), basalt fibers (MBF), and steel fibers (SF) into coral aggregate concrete in this study. The influence of fiber content, fiber addition form, curing time, and erosion time on the electrical resistivity of FRCAC (FRCAC-ER) was analyzed. Mechanistic analysis of the differences in FRCAC-ER was conducted by mercury intrusion porosimetry and scanning electron microscopy. A predictive model for FRCAC-ER was established using the multi-objective slime mold optimization support vector regression (MOSMA-SVR) algorithm. Results indicate that the optimal fiber content for single fiber incorporation is 0.05% for BF, 1.5% for MBF, and 1.5% for SF. The optimal content decreases to 1% when hybrid fibers (MBF+BF or SF+BF) are used. The microscopic analysis reveals that excessive fiber content increases porosity, reduces the proportion of harmless and less-harmful pores, and increases the proportion of more-harmful pores. Extending the curing time improves FRCAC-ER. At curing times of 3 and 7 days, FRCAC-ER reaches 70–75% and 80–85% of the 28-day resistivity, respectively. Seawater erosion reduces the erosion coefficient of FRCAC-ER, with a more pronounced decrease as the exposure time lengthens. The MOSMA-SVR predictive model for FRCAC-ER demonstrates superior predictive accuracy, model error distribution, and performance evaluation indicators compared with other models. The SF proportion and the water-binder ratio emerge as the most crucial ingredient parameters, exhibiting a negative correlation. A graphical user interface for FRCAC-ER has been developed to assist researchers in predicting and quantifying FRCAC-ER effectively. This research employs resistivity as a metric to gauge FRCAC performance and enhance its overall capabilities, thereby establishing a foundational framework for reef construction.

Revealing the failure mechanism of high strength seawater coral aggregate reinforced concrete slabs based on acoustic emission technology: Parameter analysis and DBN-BPNN classification

In this study, high strength seawater coral aggregate concrete (SCAC) with a compressive strength of 80 MPa was prepared, and seawater coral aggregate reinforced concrete slab (SCARCS) was designed with epoxy-coated steel bars. Combining with the AE technology, monotonic flexural static tests were conducted on SCARCS specimens with three varying reinforcement ratios (i.e., 0.85%, 1.13%, and 1.41%). Results showed that the increasing the reinforcement ratio led to an increase in peak bearing capacity and a decrease in center deflections at the peak. The loading process can be divided into four stages based on the varying magnitudes of the b-value and Ib-value. The primary mode of failure was tensile microcracks at various stages, and the ratio of shear microcracks reached its maximum value in the final stage of loading. Besides, based on the signal intensity analysis, it can be observed that the scale and complexity of cracks propagation inside the SCARCS specimen increased as the reinforcement ratio rose. In addition, back propagation neural network (BPNN) classification model optimized by deep belief network (DBN) algorithm was proposed to predict the damage degree of SCARCS during loading, and the average prediction accuracy of the proposed model was shown to be over 89%. The classification outcomes demonstrated that with an increase in the reinforcement ratio of SCARCS, the proportion of AE signals in Cluster 3 increased, while the proportion of AE signals in Cluster 2 dropped. Notably, both the average frequency and energy presented an ascending trend. The findings of this study provided valuable insights for designing and assessing the safety of SCAC structures for essential island and reef engineering infrastructure.

Vertical distribution of epibenthic megafauna of a large seamount west of Cape Verde islands (tropical North Atlantic)

Seamounts are thought to function as hotspots of megafauna diversity due to their topology and environmental characteristics. However, assessments of megafauna communities inhabiting seamounts, including diversity and density, are scarce. In this study, we provide megafauna diversity and density estimates for a recently discovered, not yet characterized seamount region (Boetius seamounts) west of Cape Verde (N17° 16′, W29° 26′). We investigated the distribution of epibenthic megafauna over a large depth gradient from the seamount’s summit at 1400 m down to 3200 m water depth and provided qualitative and quantitative analyses based on quantified video data. In utilizing an ocean floor observation system (OFOS), calibrated videos were taken as a horizontal transect from the north-eastern flank of the seamount, differentiating between an upper, coral-rich region (−1354/−2358 m) and a deeper, sponge-rich region (−2358/−3218 m). Taxa were morphologically distinguished, and their diversity and densities were estimated and related to substrate types. Both the upper and deeper seamount region hosted unique communities with significantly higher megafauna richness at the seamount’s summit. Megafauna densities differed significantly between the upper (0.297 ± 0.167 Ind./m2) and deeper community (0.112 ± 0.114 Ind./m). The seamount showed a vertical zonation with dense aggregations of deep-sea corals dominating the seamount’s upper region and colonies of the glass sponges Poliopogon amadou dominating the deeper region. The results are discussed in light of detected substrate preferences and co-occurrence of species and are compared with findings from other Atlantic seamounts.

Deterioration of bond performance between BFRP bars and coral aggregate concrete incorporating slag-based geopolymers under seawater corrosion environments

The utilization of durable geopolymers instead of ordinary Portland cement (OPC) for developing geopolymer-based seawater coral aggregated concrete (GPCAC) in coastal constructions contributed to the improved marine resource utilization and the reduced CO2 emissions and construction costs. Thus, this study investigated the durability of GPCAC and its bond performance with basalt fiber-reinforced polymer (BFRP) bars under seawater drying-wetting cycles, and cement-based CAC was also selected as a comparison. The bond characteristics and degradation mechanisms of slag-based GPCAC and cement-based CAC specimens were compared and analyzed under different seawater exposure condition. Experimental results revealed that both GPCAC and CAC specimens demonstrated various degrees of degradation in bond strength, whereas their initial bond stiffness exhibited a slight increase owing to the hygroscopic expansion of the superficial epoxy resin of BFRP bars, after being exposed to seawater environmental attacks. This degraded bond strength was primarily attributed to the existence of corrosive ions (i.e., SO42-, Mg2+, and Cl-) in seawater and free OH- in concrete capillary pores. These compounds chemically reacted with the slurry hydration products and the resin matrix, which resulted in the decreasing of concrete strength, the hydrolysis of the resin matrix, the deterioration of fibers, and fiber-resin interface debonding. Compared with CAC specimens, GPCAC specimens achieved better resistance to seawater attacks owing to the more dense and stable reaction products formed by geopolymers compared to OPC. After being subjected to 60 °C seawater attacks for 12 months, approximately 4.9% and 12.0% reductions in the bond strength were reported for GPCAC and CAC specimens, respectively. Finally, the residual bond strength of both GPCAC and CAC specimens was predicted after being served in seawater erosion conditions for 50 years.

Investigation on compressive strength of coral aggregate concrete: Hybrid machine learning models and experimental validation

The compressive strength of coral aggregate concrete (CAC-CS) holds importance in structural engineering and architectural design. Thus, this study establishes machine learning models for the prediction of CAC-CS and assesses their accuracy and generalization capability. The importance of input variables is analyzed by using Shapley additive explanations (SHAP) and single-variable fluctuations. A user-friendly graphical user interface (GUI) for CAC-CS prediction is developed to facilitate practical use. The accuracy of the GUI is subsequently validated through experiments. Results demonstrate that the genetic algorithm-optimized backpropagation neural network (GA-BP) model provides predictions that are closely aligned with experimental values. The GA-BP model minimizes the mean and standard deviation of its residual distribution. The performance indicators, including correlation coefficient, mean absolute error, mean absolute percentage error, mean square error, and root mean square error, of the GA-BP model are 0.98, 3.78, 10.95, 11.08, and 3.33, respectively, and are superior to those of the other tested models. The analysis of SHAP values and single-variable fluctuations reveals that among the factors influencing CAC-CS, water-binder ratio and curing age are the most sensitive. Reducing the water-binder ratio and increasing the curing age enhances CAC-CS. Additionally, the sensitivity analysis of mineral admixtures and the water-binder ratio in experiments aligns with the analysis of SHAP values and single-variable fluctuations. The error between the experimental values and GUI predictions for 14 mixture designs is less than 5 %, thus validating the accuracy and generalization capability of the GUI proposed in this study. In conclusion, this research provides practical guidelines for preparing CAC and contributes to the conservation and development of island resources.

Microstructural Analysis of Corrosion Products of Steel Rebar in Coral Aggregate Seawater Concrete

Microstructural Analysis of Corrosion Products of Steel Rebar in Coral Aggregate Seawater Concrete

Acoustic emission characteristics of stainless steel reinforced geopolymer coral concrete beams under four-point bending

The fabrication of geopolymer coral aggregate concrete beams (GCACB) can effectively address the challenges associated with constrained concrete raw materials and structural erosion in island construction. Acoustic emission technology (AE) presents an appealing solution for non-destructive evaluation and structural health monitoring. In this study, 6 specimens were conducted to examine the flexural behavior of GCACB accounting for variation in the reinforcement ratios under the four-point bending test, simultaneously recording the corresponding AE data. Then, the effect of the AE parameters on crack development was analyzed. By utilizing the GMM algorithm, the crack pattern classification was investigated. Finally, the GCACB damage was evaluated based on two different AE b-value analysis methods. The findings indicate that the cracks within GCACB predominantly occur along the coral coarse aggregate with low strength and high brittleness. The presence of reinforcement ratio has an enhancement on both the flexural capacity and deformation capacity of GCACB while impeding the crack width. It seems that a positive correlation between increasing crack damage and cumulative hits and AE energy occurs. Based on the enhanced GMM model, the cracks are categorized into tensile crack, shear crack, and mixed crack, with tensile crack predominating. A probabilistic division line is established for the RA-AF relationship that progressively leans towards the AF axis as the reinforcement ratio increases. In contrast to the b-value obtained from the GBR method, the Aki method demonstrates enhanced predictive capability for GCACB damage.