Water Binder Research Articles

Experimental Study on the Strength and Durability of Manufactured Sand HPC in the Dalian Bay Undersea Immersed Tube Tunnel and Its Engineering Application

The usage of manufactured sand concrete is widespread in modern engineering, and it is important to study its performance to improve the overall engineering quality. This paper presents an experimental study on the working performance and durability of 12 groups of manufactured sand high-performance concrete (MSHPC) with varying mix ratios, in the context of the construction of the Dalian Bay undersea immersed tube tunnel. The study reveals that the stone powder content significantly affects the physical and mechanical properties, as well as the durability, of manufactured sand concrete. At an approximately 9% stone powder content, the concrete achieves the highest slump and best workability. However, excessive stone powder reduces early crack resistance. Furthermore, an optimal stone powder content (ranging from 5% to 13%) enhances the compressive strength, with the 28-day compressive strength reaching 60 MPa at a 13% stone powder content, while the effect on the splitting tensile strength is negligible. The stone powder content does not significantly impact impermeability and frost resistance, but at 7–9%, the RCM method shows the lowest chloride ion diffusion coefficient. Additionally, a lower water–binder ratio enhances resistance to chloride ion diffusion. High-performance RCM concrete with a 9% stone powder content was used in the construction of the Dalian Bay Cross-Harbor Tunnel, achieving 28-day and 56-day compressive strengths of C45 and C50, respectively, an impermeability grade of P14, a chloride ion diffusion coefficient of 1.9 × 10−12 m2/s, and a frost durability index of 92%, meeting the project’s 100-year lifespan design requirements.

Eco-Friendly Shield Muck-Incorporated Grouting Materials: Mix Optimization and Property Evaluation for Silty Clay Tunnel Construction

As shield tunnels increase, managing shield muck strains construction and the environment. To mitigate this problem, shield muck replaced bentonite in silty clay to improve synchronous grouting slurry. Initially, the physical attributes and microstructural composition of shield muck were obtained, alongside an analysis of the effects of the muck content, particle size, and general influencing factors on the slurry properties through standardized tests and regression models. Subsequently, leveraging three-dimensional response surface methodology, admixture interactions and multiple factor impacts on the slurry were explored. Finally, utilizing the SQP optimization technique, an optimal slurry blend ratio tailored for actual project needs was derived for improved muck slurry. The findings reveal with the decreasing bleeding rates as the muck content rises, the particle size diminishes. An inverse relationship exists between the muck content and slurry fluidity. At soil–binder ratios below 0.6, a decrease in the soil–binder ratio intensifies the influence of the water–binder ratio on the slurry density, bleeding rate, and setting time. The fly flash–cement ratio inversely correlates with the slurry bleeding rate, while the ratio greater than 0.6 is positively correlated. For muck particle sizes under 0.2 mm, the fly flash–cement ratio inversely impacts the density, while over 0.2 mm, it correlates positively. The optimal proportion for silty clay stratum synchronous grouting slurry, substituting muck for bentonite, includes a water–binder ratio of 0.559, binder–sand ratio of 0.684, fly flash–cement ratio of 2.080, soil–binder ratio of 0.253, particle size under 0.075 mm, and water-reducing admixture of 0.06.

The Effects of Sodium Silicate and Sodium Citrated on the Properties and Structure of Alkali-Activated Foamed Concrete

Alkali-activated slag cementitious (AASC) foamed concrete (FC) has presented challenges such as rapid setting time and poor working performance. The use of sodium citrate (Na3Cit) as a retarding agent can improve the workability and microstructure of AASC foamed concrete. The effects of the dosage, modulus of water glass (WG, the main component is Na2O·nSiO2), and retarding agent on the properties and structure of FC were studied in this paper. The results indicated that using a water binder ratio of 0.4, WG with a modulus of 1.2, and an additional amount of 15% and 0.5% of Na3Cit, the prepared FC had a flowability of 190 mm. Its initial and final setting times were 3.7 h and 35.3 h. Its 7 d and 28 d compressive strengths reached 1.1 MPa and 1.5 MPa, respectively. After hardening, the pore walls were dense and consistent in size, with few larger pores and nearly spherical shapes. The addition of Na3Cit resulted in the formation of calcium citrate, which adsorbed onto the slag surface. This hindered the initial dissolution of the slag, reduced the number of hydration products produced, and decreased the early strength. With increasing curing time, the slag in the FC mixture dissolved further. This led to the decomposition of a portion of calcium citrate and the release of Ca2+. The Ca2+ reacted with [Si(OH)4]4− and [Al(OH)4]−, creating more C-(A)-S-H gel. This gel filled the voids in the FC and repaired any defects on the pore walls. Ultimately, this process increased the compressive strength of the FC in the later stages.

Study on the preparation and properties of high-performance foamed cement by multi-factor optimization

The promotion of high-performance foamed cement in engineering is consistent with the objectives of energy conservation and sustainable development. In this work, the effects of the water–binder ratio, foam–grout ratio, mineral powder content and magnesium oxide content on the performance of foamed cement were studied. High-performance foamed cement was prepared considering the above four factors. The results indicated that the pore structure of the foamed cement was effectively modified by adjusting the water–binder and foam–grout ratios, while its compressive strength increased and its setting time decreased when mineral powder and magnesium oxide were added. Pore structure and scanning electron microscopy experiments revealed that the surface of the high-performance foamed cement was covered with many hydration products of mineral powder and magnesium oxide, resulting in a more compact and uniform structure. Simultaneously, these hydration products effectively filled pores with diameters ranging from 0 to 0.2 mm in the high-performance foamed cement, refining its pore structure and thereby enhancing its waterproof performance and drywet cycling stability. Compared with those of commercial foamed cement, the setting time of the high-performance foamed cement was 23.48 % shorter, and its compressive strengths at 1 d and 7 d were 245.78 % and 178.62 % greater, respectively. Furthermore, the production cost per cubic meter of the high-performance foamed cement was 107.29 RMB less than that of ordinary cement. In brief, the high-performance foamed cement can be widely used in a variety of engineering applications because of its performance and economic benefits.

Study on the Reuse of Shield Mud from Clay Stratum in Synchronous Grouting Slurry

The purpose of this study is to investigate the feasibility of replacing the fly ash in synchronous grouting material by reusing the shield mud produced in the clay stratum during the shield construction of Wuhan Rail Transit Line 11. The test utilizes the shield mud from the clay stratum to replace the fly ash material in synchronous grouting at percentages of 20%, 40%, 60%, 80%, and 100%, and research and analyses are conducted on the fluidity, stability, strength, and resistance to water dispersion of the slurry after the replacement; at the same time, improvements in the undesirable phenomenon produced by the synchronous grouting slurry are also examined after the replacement. The results show that, when the fly ash is replaced by shield mud at 80%, the mortar still has good stability and strength performance, but, at the same time, the initial value of consistency and the phenomenon of flow time loss is too large. Through the adjustment of the water–binder ratio and the addition of an appropriate amount of a polycarboxylate superplasticizer agent, the adverse phenomenon of the slurry is effectively improved, and the compressive strength and ease of the slurry are also improved. At the same time, when adding an appropriate amount of hydroxyethyl methyl cellulose (HEMC), the slurry has good water dispersion resistance, but, with the gradual increase in HEMC, the fluidity of the slurry deteriorates and the compressive strength decreases. The test proves that the shield mud in the clay stratum can be used to replace most of the fly ash in an appropriate proportion, which not only solves the problem of the shield mud being difficult to work with, but also provides more valuable insights for tunneling projects.

Experimental evaluation of salt corrosion resistance of potassium salt magnesium phosphate cement coating slurry

In this work, a self-compacting potassium salt magnesium phosphate cement (PMPC) coating slurry was prepared by improving the water binder ratio and adding an appropriate amount of water glass (WG) and silica microfume (SMP). By performing long-term solution immersion tests, the following conclusions can be drawn: the remaining flexural and compressive strength values (Δff and Δfc) of the PMPC specimens (M2) containing 2 % WG and 10 % SMP immersed in water, 3.5 % NaCl solution, and 5 % Na2SO4 solution for 540 days were greater than 95 % and 90 %, respectively. In comparison to the reference PMPC specimen without WG and SMP (M0), the Δff and Δfc increased by more than 30 % and 25 %, respectively. After 540 days in 3.5 % NaCl solution and 5 % Na2SO4 solution, the salt corrosion coefficients (Kf and Kc) of the M2 specimen were all greater than 1. After excluding the factor of water corrosion, the salt crystals in the solution had a strengthening effect on the hardened PMPC paste. The M2 specimens experienced volume expansion after being immersed in a solution composed of water, 3.5 % NaCl solution, and 5 % Na2SO4 solution for 540 days (7.21× 10−4, 13.52 × 10−4, and 10.92 × 10−4); this expansion was significantly lower than that of the M0 specimen under the same conditions (13×10−4, 18.5×10−4, and 21.5×10−4) due to the relatively denser initial structure. The initial water absorption rate of M2 (0.64 %–0.66 %) was significantly lower than that of M0 (0.72 %–0.75 %). After soaking in water, 3.5 % NaCl solution, and 5 % Na2SO4 solution for 540 days, the water absorption of the M2 specimens increased by 64.6 %, 7.6 %, and 12.5 %, respectively, which is clearly lower than that of M0 specimens (95.9 %, 22.7 %, and 30.6 %). The increase in the water absorption of the specimen in the salt solution was also obviously smaller than that in the aqueous solution.

The Role of Water Content and Binder to Aggregate Ratio on the Performance of Metakaolin-Based Geopolymer Mortars

Geopolymers are in many applications a perfect alternative to standard cements, especially regarding the sustainable development of green building materials. This experimental study therefore deals with the investigation of different factors, such as the water content and the binder to aggregate ratio, and their influence on the workability of fresh mortar and its mechanical properties and porosity on different size scales. Although increasing the water content improved the workability and flow behaviour of the fresh mortar, at the same time, a reduction in compressive strength in particular and a lesser reduction in flexural strength could be demonstrated. This finding can be attributed to an increase in capillary porosity, as demonstrated by capillary water uptake and mercury intrusion porosimetry measurements. At the same time, the increasing water content led to an improved deaeration effect (low air void content) and to initial segregation (see the µXCT measurements). An alternative approach to enhance the compressive and flexural strengths of the mortar specimens is optimization of the binder to aggregate ratio from 1 to 0.25. This study paves the way for a comprehensive understanding of the underlying chemistry of the geopolymerization reaction and is crucial for the development of sustainable alternatives to cementitious systems.

Gradient erosion mechanism of ultra-low water binder ratio cement-based materials (ULWC) at low temperature: From molecular structure to macroscopic pore structure

The study of damage mechanisms is crucial for enhancing the service performance of low-temperature concrete. This study reveals the gradient erosion mechanism of ULWC behavior under low-temperature. The study employs in-situ detection techniques to analyze the effects of low-temperature on the C-S-H and crystal structures, including internal stress and chemical composition. It also uses 1H NMR and CT to compare the frost heave of gradient pores with the matrix contraction. The results indicate that low-temperatures lead to irreversible degradation of crystal structures and collapse of C-S-H, resulting in spontaneous shrinkage. Furthermore, in the gradient pore structure, the frost heave of gel pores opposes the shrinkage of the matrix, ultimately leading to the reorganization of C-S-H grain stack structure and the refinement of micropores and degradation of macropores. Therefore, the gradient erosion mechanism suggests that although low temperature may disrupt the chemical structure of ULWC, it will refine the pores in the microstructure.

An Integrated Hydration and Property Evaluation Model for Coral Powder–Cement Binary Blends

With the rise in the marine industry and marine tourism, coral powder is increasingly used to make concrete for marine islands. This study proposes a three-parameter hydration model and a hydration kinetic model to predict the performance of coral powder concrete based on previous experimental data. The process of the proposed prediction model is as follows: 1. The input parameters of the three-parameter hydration model are calibrated for the first 7 days using the cumulative hydration heat per gram of cement. The maximum cumulative hydration heat (455.87 J/g cement) and the shape coefficient (−0.87) remain constant. In this study, the hydration rate coefficients for 0%, 10%, and 20% coral powder were 6.91, 6.19, and 5.55, respectively, showing decreases of 10.41% and 19.68% compared with the specimens without coral powder. 2. At 28 days, the cumulative heat release values per gram of cement for 0%, 10%, and 20% coral powder were 389.77, 395.69, and 401.62 J/g, showing increases of 1.52% and 3.04% for the specimens containing 10% and 20% coral powder, respectively. Meanwhile, the hydration degrees for 0%, 10%, and 20% coral powder were 0.855, 0.868, and 0.881, respectively, showing increases of 1.52% and 3.04%. Furthermore, the cumulative heat release values per gram of binder were 389.77, 356.12, and 321.29 J/g, showing decreases of 8.63% and 17.56% for specimens containing 10% and 20% coral powder, respectively. 3. Properties such as compressive strength, ultrasonic pulse velocity (UPV), and surface electrical resistivity were evaluated using the power function and the cumulative hydration heat per gram of binder. 4. At 28 days, the chemically bound water contents for samples with 0%, 10%, and 20% coral powder were 0.2402, 0.2197, and 0.1981 g/g binder, respectively. Moreover, the calcium hydroxide contents were 0.1848, 0.1690, and 0.1524 g/g binder, showing reductions of 8.53% and 17.52% in bound water and 8.54% and 17.53% in calcium hydroxide. 5. A hydration kinetic model is proposed, which can distinguish between the dilution effect and the nucleation effect of coral powder, unlike the three-parameter model, which cannot distinguish between the two effects. Furthermore, the input parameters of the hydration kinetic model remain unchanged for different mixtures, while the input parameters of the three-parameter model must be varied among mixtures. Parameter analysis of the hydration kinetic model indicated that a low water–binder ratio and a high coral powder substitution rate significantly improve the relative reaction level of cement.

Optimization study for cement-based grout mixture ratio of shield tunnel considering spatiotemporal evolution of grout buoyancy

The grout buoyancy for segments during shield tunnel construction can cause significant floating displacement or even cracking of the segments, and the grout buoyancy is directly related to the grout buoyancy volumetric weight (GBVW). This study proposes an optimization process for the mixture ratio of cement-based grout based on the actual engineering environment. Based on a self-designed GBVW test instrument considering the interaction between grout and strata, this study reveals the evolution law of GBVW and the 3D spatial distribution law of grout buoyancy under different mixture ratios in different strata. Then, this study calculates the segment displacement under slurry buoyancy by the multi-factor coupled numerical calculation model. Research shows that the GBVW in different strata exhibits an evolutionary characteristic of sharp fluctuation-rapid decrease-slow decrease-complete disappearance. The upward precipitation of aqueous solutions in grout in different strata occurs during the stage of GBVW sharp fluctuations, and the decrease in GBVW is mainly accompanied by the seepage of aqueous solutions into the lower strata. The average GBVW and the duration of GBVW in muddy soil are larger than those in silty soil and coarse sand, respectively. An increase in the water binder ratio will reduce the GBVW and accelerate the dissipation of GBVW, while an increase in the bentonite water ratio will promote the growth of GBVW. The lower the strata permeability, the more easily the average GBVW is affected by the water cement ratio. The peak GBVW is more easily affected by the water binder ratio, and the duration of GBVW is more easily affected by the water cement ratio.

Bond Behavior of High-Strength Steel Rebar in Ultra-High-Performance Manufactured Sand Concrete: Experiment and Modelling

Manufactured sand (MS), due to its wide availability and cost-effectiveness, is used as an alternative aggregate for quartz sand (QS) in ultra-high-performance concrete (UHPC) to prepare ultra-high-performance manufactured sand concrete (UHPMC). This study aims to assess the bond behavior of 600 MPa-grade, high-strength, hot-rolled ribbed bars (HRB 600) in UHPMC. Thirty specimens were designed for the pull-out tests, taking into account several feature parameters, including MS replacement ratio (0%, 50%, 100%), water–binder ratio (0.17, 0.19, 0.21), steel fiber content (0%, 1%, 2%), and anchorage length (2d, 3d, 4d, 5d). The effects of the feature parameters on the failure mode, bond stress–slip curves, bond strength, bond-slip mechanism, and constitutive model were analyzed and illustrated. The results reveal that the pull-out specimen of UHPMC exhibits three distinct failure modes: rebar pull-out failure, UHPMC splitting failure, and splitting-pull-out failure. The bond strength increases from 46.57 MPa to 56.92 MPa when the steel fiber content increases from 0% to 2%. Additionally, a decrease in anchoring length is beneficial for improving the bond strength; as the anchoring length increases from 2d to 5d, the bonding strength decreases by 35.84%. The bond strength increases with an increase in the MS replacement ratio. As for the water–binder ratio, the bond strength presents the highest value when the water­–binder ratio is 0.17. In addition, a new bond-slip constitutive model applicable to UHPMC and HRB 600 rebar, considering the MS replacement ratio, the water–binder ratio, etc., is proposed, which presents favorable prediction accuracy.

Study on the Effect of Water–Binder Ratio on the Carbonation Resistance of Raw Sea Sand Alkali-Activated Slag Concrete and the Distribution of Chloride Ions after Carbonation

The excessive extraction of river sand has led to significant ecological issues. Moreover, the environmental impact and resource demand of cement production have increasingly turned the spotlight on sea sand as a viable alternative due to its abundance and ease of extraction. Concurrently, alkali-activated binders, a novel type of low-carbon cementitious material, have gained attention for their low energy consumption, high durability, and effective chloride ion fixation capabilities. However, they are susceptible to carbonation. Introducing a controlled sea sand amount can raise the materials’ carbonation resistance, although carbonation may raise the concentration of free Cl− within the structure to levels that could risk the integrity of steel reinforcements by accelerating corrosion. In this context, the current study investigates sea sand alkali-activated slag (SSAS) concrete prepared with varying water–binder (W/B) ratios to evaluate its impact on flowability, mechanical strength, performances, and chloride ion distribution post-carbonation. The results demonstrate that the mechanical property of SSAS concrete diminishes as the water-to-binder ratio increases, with a more pronounced reduction observed. The depth of carbonation in mortar specimens also rises with the W/B ratio, whereas the compressive strength post-carbonation initially decreases before showing an increase as carbonation progresses. Furthermore, carbonation redistributes chloride ions in SSAS, leading to a peak Cl− concentration near the carbonation front. However, this peak amplitude does not show a clear correlation with changes in the W/B ratio. This study provides a theoretical foundation for employing sea sand and alkali-activated concrete.

Analysis of the Influence and Mechanism of Diatomaceous Earth Internal Curing on the Autogenous Shrinkage and Early Crack Resistance of Cement-Based Materials with Low Water–Binder Ratio

Diatomaceous earth (DE), a kind of natural and environmentally friendly concrete admixture with good pozzolanic and water absorption properties, is a potential high-quality internal curing material. DE internal curing agent was prepared by calcining excavated diatomaceous earth and applied in cement-based materials with a low water–binder ratio of 0.35 to study its effects on the autogenous shrinkage and early crack resistance of the materials. The results showed that DE was a kind of microfine powder with a unique and orderly microporous structure, and its main component was SiO2, which had good water-holding and -releasing properties. Pre-absorbed DE could effectively improve the internal relative humidity of cement-based materials with a low water–binder ratio. Under the standard of not reducing the 28 d compressive strength of mortar, compared to the benchmark group without DE, when 1% of cement is replaced by DE of equal mass, DE could effectively reduce the 7 d autogenous shrinkage of mortar by about 36.7% and delay the initial cracking time of mortar under the restraint condition of the ring by 10.7%. Therefore, it is an internal curing material with excellent performance.

Influence of Steam Curing on the Performance of High-strength Concrete Incorporating Metakaolin

This study aims to investigate the influence of steam curing on the performance of high-strength concrete incorporating metakaolin. An experimental study was conducted to investigate the compressive strength, chloride permeability, initial surface absorption, and water absorption, as well as thermal degradation under various steam curing scenarios. Four concrete mixtures were prepared in this study, each with different percentages of metakaolin, as partial substitution of cement weight of 0%, 5%, 10%, and 15%. The water–binder ratio was set to 0.32 in all mixtures. The specimens underwent steam curing for 0, 4, 8, and 16 hours at a temperature of 55 °C. Results indicate that the specimens that have been steam cured and contained metakaolin exhibit improved compressive strength during the initial stages of their strength development. Steam curing has been demonstrated to enhance the concrete’s resistance to chloride penetration and reduce initial surface absorption while increasing water absorption. The optimal replacement of cement with metakaolin to enhance strength and transport properties in high-strength concrete under steam curing regimes is between 10% and 15%. Future research could examine the effects of long-term steam curing on the durability and performance of concrete incorporating an optimal proportion of metakaolin.

Impact of freezing conditions on the characteristics of ultra-low water binder ratio cementitious composites (ULCC): Towards to hydration mechanism and molecular migration model

This study aims to clarify the hydration kinetics and microstructure development of ultra-low water binder ratio cementitious composites (ULCC) at cryogenic temperatures based on experimental and numerical approaches. More exactly, the micro and macro properties of ULCC are firstly investigated by experiments and then the hydration mechanism is analyzed by NMR and molecular dynamics methodology. The results reveal that the hydration of ULCC can still be triggered at −20°C, while the hydration process is significantly delayed and the theoretical maximum hydration degree drops to 59.72 % of room temperature. When the temperature is further reduced to about −80°C, the hydration of ULCC is prevented, while the crystallization of the original product and the C-S-H chain length is decreased. However, in this case, the hydrogen bond stability of water between layers of C-S-H gels is improved, which can be confirmed by molecular simulation. Finally, a hydration kinetic model is constructed to quantitatively predict the development of water migration process and hydration degree in ULCC at freezing temperature.

Predictive Pattern of Undrained Shear Strength in Stabilized Sulfur Rich Silty Soil Based on Binder and Initial Mixing Water Content

A laboratory investigation was conducted to identify principal variables-initial mixing water content, porosity, and binder content- impacting undrained shear strength (qu) of stabilized sulfur-rich silty soil. An equation for predicting qu of stabilized soil was established based on the experimental data. Initially, samples were prepared with soils sample with different initial water and binder contents. Multicem, a binder consisting of a mix of cement and cement kiln dust, was added to the samples. Three different percentages of Multicem were mixed at five different soil water contents to measure qu of stabilized mixtures to understand how water content and porosity levels in the samples affect the performance of the binder and their combined impact on the strength of the samples. The soil-binder mixtures were compacted and subsequently cured in laboratory-controlled environment. The prepared samples were tested in uniaxial compression test apparatus. The results evidenced that binder content and corresponding porosity affect the strength of specimens at an equal water content. The results showed that at equal initial mixing water content, the qu of a sample increased by increasing binder content. Furthermore, it was observed that increase of binder content has a reverse effect on porosity. It was appeared lowering the soil water content, initially increased the strength until an optimum water content. Further lowering water content increased the porosity and consequently decreased qu of samples. Moreover, a ratio of porosity/volumetric binder content was chosen to evaluate the impact of these two variables on strength of samples. This study showed that qu is an exponential function of porosity/binder volumetric content ratio which depends on initial mixing water content of mixtures. It was shown at water content lower than the optimum, results of stabilization are more effective than in soil at higher water contents. Therefore, reducing the water content and thereby porosity has more significant effect on improving qu than increasing the binder content.

Effect of waste oyster shell powder on the micro- and macroproperties and sustainable performance of cement-based materials

A large amount of oyster shell waste is generated globally every year. Proper disposal of discarded oyster shells is crucial for reducing environmental pollution and achieving sustainable development. The aim of this paper was to study the feasibility of using waste oyster shells as a cementitious material to replace cement. The effects of waste oyster shell powder (OSP) with different water–binder ratios (w/b = 0.5, w/b = 0.2) and different substitution rates (10 %, 20 %) on the properties of cement-based materials were studied. The experimental results are as follows: The addition of oyster shell powder reduces the compressive strength, ultrasonic pulse velocity (UPV), surface electrical resistivity and cumulative heat of hydration of the mortar, but the strength loss is smaller for a water-to-binder ratio of 0.2 than for a water-to-binder ratio of 0.5. A good linear relationship between the compressive strength and UPV was also found. A good exponential relationship exists between the surface electrical resistivity and compressive strength. The heat of hydration results show that when the water–binder ratio is 0.5, replacing cement with waste OSP promotes aluminate phase hydration and advances the acceleration period. Finally, the carbon emissions of the mortar were normalized according to the compressive strength, and using OSP instead of cement at a low water–binder ratio was more conducive to reducing CO2 emissions.

Influence of feature-to-feature interactions on chloride migration in type-I cement concrete: A robust modeling approach using extra random forest

Understanding the chloride transport mechanism is crucial for enhancing the durability of structures exposed to chloride-rich environments. This study assessed various machine learning (ML) algorithms for predicting the chloride migration coefficient in type I Portland cement-based concrete. The fine-tuned extra random forest model demonstrated satisfactory predictive capability, with the majority of tested-predicted data points falling within the ±30 % tolerance margin. This calibrated model was employed to explore feature-to-feature interactions affecting concrete resistance to chloride ingress. Examination of partial dependence plots revealed that an increased sensitivity with decreasing water–binder ratio (WB), reaching saturation beyond 0.40 WB, and the increase in curing age substantially reduced chloride diffusion (DN). Further, an augmented dosage of silica fume (SF) decreased DN, with a more pronounced effect of slag (SL) at higher WB, and the impact of superplasticizer (SP) decreased DN at high WB ratios. Concrete incorporating SF showcased optimal resistance to chloride permeability with the highest SF content (20–30 kg/m3). Similarly, high SL content (>150 kg/m3) enhanced resistance. The interactive influence of SF and SP on DN was marginal at low SF dosages (<20 kg/m3) but became complex at higher levels, with potential minimum values observed in the range of 0.5–1.0 kg/m3 SP. For SL-containing concrete, achieving the lowest DN was possible with PC and SL dosages around 200–400 and exceeding 100 kg/m3, respectively. For concrete incorporating Type I PC, an increase in SP content generally had a negligible impact on DN, with a slight tendency to raise values observed at higher cement amounts (exceeding 380 kg/m3). The optimal combination for achieving the minimum DN involved compositions of PC, fine, and coarse aggregate at 200–300, 100–150, and 250–500 kg/m3, respectively.

Study on the Performance Optimization of Plant-Growing Ecological Concrete

The response surface regression model of plant-growing ecological concrete is established based on the factors of the water–binder ratio, fly ash content, and design porosity, with 28-day compressive strength, connectivity porosity, and pH value as response variables. Based on optimizing the mix proportion with the regression model, different dosages of acetic acid are used as excitation agents to increase the compressive strength and reduce the alkalinity of plant-growing ecological concrete to enhance its service life and vegetation performance. The results show that the compressive strength of plant-growing ecological concrete with a water–binder ratio of 0.3, a fly ash content of 26%, and a design porosity of 22% was 10.32 MPa, the connectivity porosity was 20.00%, and the pH value was 11. After the addition of acetic acid at 0.4% of the mass of the cementitious material, the compressive strength increased by 40.29%, and the pH value decreased by 6.33%. This study proposes a cost-effective means and provides data support for the engineering application of plant-growing ecological concrete.

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.