Chloride Migration Coefficient Research Articles

Effects of mix composition on the mechanical, physical and durability properties of alkali-activated calcined clay/slag concrete cured under ambient condition

Alkali-activated concrete (AAC), a possible alternative to ordinary Portland cement (OPC), provides increased environmental advantages, notably lower carbon emissions. Likewise, similar to OPC, it faces durability problems under severe environments. This study evaluated the effectiveness and durability of alkali-activated concretes containing low-grade calcined clay and granulated blast furnace slag (GGBFS), using NaOH/KOH as activators and MgO and superabsorbent polymer (SAP) as additives. The study's focus was on their physical-mechanical characteristics and performance under accelerated carbonation and chloride diffusion. Findings showed that calcined clay-GGBFS alkali-activated concretes exhibited a compressive strength range of 41.2–53.3 MPa, positioning them as a viable concrete for many structural usages. Nevertheless, the modified-RCPT (10 V) and NT Build 492 tests showed all concretes falling into the "high chloride penetrability" category, with values exceeding 350 coulombs and 13.5 (×10−12 m2/s) for the non-steady-state migration coefficient (Dnssm). NaOH and sodium silicate led to higher compressive strengths compared to KOH. Furthermore, the chloride migration coefficient of alkali-activated concrete blends ranged from 55.68 to 121.14 (× 10−12 m2/s). The incorporation of 0.6 % SAP decreased compressive strength but improved the non-steady-state migration coefficient (Dnssm). Lastly, MgO-enriched samples showed the lowest water absorption and carbonation depth, attributed to the buffering action of magnesium phases, reducing carbonate formations, as revealed by XRD analysis.

Research on quantitative design methods for the durability of reinforced concrete structures in a hot ocean environment

This paper establishes a quantitative design method for the durability of concrete structures in cross-sea bridges through investigation, rapid chloride migration coefficient method (RCM) and theoretical calculation, considering the impact of temperature on chloride ion diffusion rates in a hot marine salt erosion environment. Combined with the RCM test and bridge service data, a quantitative design method for bridge concrete durability is proposed. Test results show that the growth rate of the chloride ion diffusion coefficient of concrete is approximately 1.028 for every 1 °C increase. For every 5 °C increase, the growth rate of the chloride diffusion coefficient of concrete is about 1.15, and the cover depth of the concrete structure should be multiplied by a coefficient of 1.07. Therefore, the concrete cover depth should be appropriately increased, considering the influence of ambient temperature. Furthermore, fly ash, slag, and stone powder can increase the concrete’s resistance to chloride corrosion. When the influence of temperature on the chloride ion diffusion coefficient is considered, the durability design of the concrete structure of the sea-crossing bridge is conducted, which is beneficial for ensuring their service life.

Prediction and prevention of concrete chloride penetration: machine learning and MICP techniques

The chloride migration coefficient (CMC) of concrete is crucial for evaluating its durability. This study develops ensemble models to predict the CMC of concrete, addressing the limitations of traditional, labor-intensive laboratory tests. We developed three ensemble models: an inverse variance-based model, an Artificial Neural Network (ANN)-based model, and a tree-based model using the random forest regression algorithm. These models were trained on a dataset comprising 843 concrete mix proportions from existing literature. Results indicate that ensemble models outperform single models such as ANN and Support Vector Regression (SVR) in predicting CMC, with the combined random forest and ANN model showing the highest accuracy. Sensitivity analysis using Shapley Additive Explanations (SHAP) reveals that the CMC is most influenced by the water-to-cement ratio and curing age. Additionally, we designed a graphical user interface (GUI) to facilitate the practical application of our models. This research offers a robust methodology for evaluating concrete durability and potential for extending the prediction to other concrete properties.

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.

Enhancing mechanical performance and durability of high strength mortar with incineration bottom ash via Al2O3 micro-powder: An experimental study

The untreated application of municipal solid waste incineration bottom ash (IBA) in cementitious materials can lead to compromised workability, deterioration of mechanical properties, and compromise durability. This paper examines the potential of utilizing Al2O3 micro-powder (ALMP) to enhance the mechanical performance and durability of cementitious materials fabricated with IBA. This paper focuses on the effect of different dosages of ALMP on the workability, mechanical performance and durability of high strength mortar (HSM) prepared by IBA. In addition, effect of ALMP on the ultrasonic pulse velocity (UPV), dynamic modulus of elasticity (DME) and microstructure of HSM was also investigated. Finally, the micro-mechanical performance of HSM paste was determined via nanoindentation experiment. Our study discovered that the integration of ALMP in HSM contrived with IBA notably amplified the flexural and compressive strengths by ranges of 1.12 %∼9.84 % and 3.78 %∼21.26 %, respectively. Simultaneously, the ALMP improved the UPV by an interval of 3.16 %∼9.49 %, and the DME by a parameter of 9.64 %∼18.69 %. Additionally, we observed considerable lowering of drying shrinkage in HSM by 4.96 %∼28.36 % and decline in the chloride migration coefficient by 7.45 %∼38.75 % due to ALMP's presence. Overall, based on the observed impact of ALMP on HSM's workability, mechanical properties, and microstructure, we suggest 10 wt% as the optimal doping amount for ALMP in HSM. Our investigation puts forward that implementing IBA in place of traditional quartz sand in the preparation of HSM could potentially attenuate energy consumption, carbon emissions, and production overheads. The findings of this study may offer instructive significance for improving the resource utilization of IBA in cement-based materials.

Investigation on chloride migration behavior of metakaolin-quartz-limestone blended cementitious materials with electrochemical impedance spectroscopy method

Calcined clay and limestone powder composites offer a viable solution for reducing carbon emissions in building materials by allowing significant cement replacement. However, there is a need for further investigation into their impact on durability, especially for low-grade clays. In this study, different ratios of metakaolin and quartz powder are utilized to simulate various grades of calcined clay, while limestone powder is incorporated as a partial cement substitute. Initially, the influence of metakaolin content on rapid chloride migration was analyzed. Subsequently, various analytical techniques such as free water content, Mercury Intrusion Porosimetry (MIP), X-ray diffraction (XRD)/Rietveld method, and electrochemical impedance spectroscopy (EIS) test were employed to investigate the effects of metakaolin contents on the pore structure, phase assemblage, and electrochemical parameters of the blended cementitious system. The relationship between chloride migration coefficient and free water content, critical pore size, and impedance parameters was established to determine the key indicators for chloride migration. The study revealed that systems with partial metakaolin content demonstrate improved chloride resistance in the blended system, which could be predicted using Rct1 from the EIS test. Furthermore, the inclusion of metakaolin and limestone powder facilitated the formation of Monocarboaluminate (Mc) and Hemicarboaluminate (Hc), leading to the refinement of the pore structure and inhibition of chloride transport within the blended material. This study indicates the potential of low-grade calcined clay to enhance the overall durability of the blended cementitious system while contributing to carbon emissions reduction.

Analyzing chloride diffusion for durability predictions of concrete using contemporary machine learning strategies

Analyzing the migration of chloride ions in concrete can enhance its durability and decrease the probability of corrosion. Furthermore, machine learning (ML) offers a promising, cost-effective, and less intricate alternative to traditional experimental methods for accurately forecasting cementitious composites' chloride migration coefficient (Dnssm). This study utilized advanced ML methods like support vector machine (SVM), artificial neural network (ANN), and k-nearest neighbor (KNN) to forecast the Dnssm of concrete accurately. A comprehensive database was established considering significant input features that can impact Dnssm. The models undergo verification with unseen data, utilizing various statistical performance measures. The verification findings validate that all three models (SVM, KNN, ANN) accurately predicted the Dnssm with high precision. However, the SVM model outperformed with a higher coefficient of determination (R2) score of 0.90, whereas ANN and KNN yielded R2 scores of 0.88 and 0.83, respectively. The model has the capacity to substitute laborious, resource-intensive and time-consuming lab testing. Moreover, the RReliefF analysis indicated that water/binder and cement type are the prominent input factors affecting the target variable Dnssm.

Effect of surface activity of recycled fine aggregates from clay bricks on the hydration, microstructure and chloride transport of concrete

Use of recycled fine aggregates from clay bricks (RFCB) in the preparation of eco-friendly concrete was proposed to tackle the river sand (RS) shortage and satisfy the construction demand. This study explored the surface activity of RFCB influenced by additional water and particle size distribution (PSD) on the hydration, microstructure and chloride transport of concrete. Compared to the RS, more silica and alumina released from RFCB depending on its PSD under alkaline environment was noted, which verified its appreciable surface activity. Overall, the presence of RFCB could hinder early hydration process because of the higher additional water, while the surface activity and nucleation effect supplied from finer RFCB were beneficial for the improvement of the hydration kinetics. Furthermore, inclusion of RFCB increased the total pore volume and porosity but performed better in refining the pore size distribution, thus decreased the average pore diameter. The surface activity of RFCB decreased CH content while increased chemical bond water and additional hydrates, thereby leading to enhancement of the compactness of interface, cement matrix and surface rim. More importantly, RFCB helped to decrease the chloride migration coefficient and electric flux. Though the surface activity of RFCB was beneficial in the strength development, it could not offset a deteriorated influence of porous RFCB with a higher replacement.

The adsorption and diffusion behavior of chloride in recycled aggregate concrete incorporated with calcined LDHs

Recycled concrete aggregate (RCA) is an important form for reusing of waste concrete. However, the presence of corrosive ions, specifically chloride ions, which are absorbed on the surface of RCA or infiltrated from the external environment, significantly affects the mechanical performance and durability of recycled aggregate concrete (RAC). This paper aims to suppress the erosion and diffusion of chloride ions in RAC by adding calcined layered double hydroxides (LDOs), utilizing the restructuring and anions exchange properties of LDOs. The dissolution ratio of chloride ions carried by RCA and the adsorption efficiency of LDOs on the leaching ions were analyzed using the silver nitrate titration method. The maximum chloride adsorption capacity of the LDOs is 31.052 mg/g. Additionally, the inhibitory effect and mechanism of LDOs on chloride ion attack were detailed evaluated by the techniques combining mercury intrusion porosimetry (MIP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM and EDS), rapid chloride migration coefficient method (RCM), and electrochemical impedance spectrum. The results indicate that LDOs exhibit a good adsorption effect on chloride ions leaching from RCA, and the adsorption efficiency is negative correlation with the pH value. Furthermore, the small size effect of LDOs plays a filling role in the pores of concrete, increasing the compactness and penetration resistance of chloride ions of RAC. This work provides a promising approach to enhance the mechanical and durability properties of RAC by incorporating with LDOs utilizing its chloride ion capture feature and nano-filling effect. And the findings of this research can also be extended to the use of LDOs for treatment of other corrosive anions, such as SO42− and CO32− in RAC, demonstrating its applicability in a broader context.

Characteristics of non-steady-state chloride migration of self-compacting concrete containing recycled concrete aggregate made of fly ash and silica fume

Chloride migration poses a significant challenge to the long-term durability of concrete structures due to its potential to corrode reinforcement and deteriorate the structure. This study focuses on chloride migration in self-compacting concrete (SCC) made with pozzolans, namely silica fume (SF) and fly ash (FA), along with recycled concrete aggregate (RCA). Particularly, the effects of external electrical potential (power-on) duration and RCA content on the features of SCC were examined, alongside the influence of pozzolanic materials, focusing on the chloride migration coefficient and mechanical properties. Six groups of SCC mixtures were created with varying proportions of SF and FA, and different levels of RCA replaced the natural coarse aggregate. The findings reveal a multifaceted impact on SCC behaviour. The chloride migration coefficient exhibits a distinct pattern as the power-on duration increases from 12 to 36 h. Initially, the coefficient increases and then decreases, demonstrating a healing and sealing mechanism within the concrete matrix, which enhances resistance to chloride penetration. The chloride migration coefficient significantly decreased with adding SF and FA. With 15% SF and 30% FA, the coefficient decreased to 59.9% and 49.5%, respectively. Moreover, incorporating RCA in SCC mixtures significantly influences coefficient levels. RCA inclusion at 20% remarkably decreased the coefficient after 12 h by 16.17%. Subsequently, the levels decreased by 39.49% and 46.87% after 24 and 36 h, respectively, compared to the control mixture. This behaviour highlights the importance of RCA in enhancing the resistance of SCC to chloride ingress, a crucial factor for long-term durability. Additionally, mechanical properties such as splitting tensile strength, ultrasonic pulse velocity and surface hardness consistently improved with longer power-on durations and higher RCA and SF content. SCC with RCA and pozzolanic materials exhibits enhanced chloride resistance and superior mechanical performance, making it ideal for sustainable concrete production.

Utilization of Waste Brick Powder as a Partial Replacement of Portland Cement in Mortars

Partially substituting Portland cement (PC) with waste brick powder (WBP) is an effective method to reduce environmental pollution. In this paper, the effects of a WBP with low pozzolanic activity on the fresh and hardened properties of blended cement with 0–40% WBP or 50% of WBP+GGBFS (by mass) were studied. Sodium sulphate (SS) (1.5 and 2.5%, related to powder mass) was used to activate the blended cement with 40% WBP or 50% WBP+GGBFS at 20 °C. Results show that the performance of blended cement is decreased with the increase in WBP content since the WBP with low pozzolanic activity mainly contributes to the dilution effect. Binary cement with 10% WBP shows a similar carbonation depth and chloride migration coefficient to PC. Ternary cement with 10% WBP and 40% GGBFS exhibits a slightly lower strength at 90 days and a lower chloride migration coefficient than PC. The SS solution increases the compressive strength at 2 days and decreases the compressive strength at 28 and 90 days. Moreover, the SS solution results in a lower carbonation depth and chloride migration coefficient, except for ternary cement with 10% WBP and 40% GGBFS, which shows a higher carbonation depth at 42 and 68 days. This paper provides a reference for the application of WBP to produce green mortars.

Unveiling non-steady chloride migration insights through explainable machine learning

This study explores the influence of concrete mix ingredients on the non-steady chloride migration coefficient (Dnssm) using an explainable machine learning (XML) approach that integrates Extreme Gradient Boosting (XGBoost) and Shapley Additive Explanations (SHAP). The dataset, comprising 204 observations from literature, is utilized to train the XGBoost algorithm for predicting Dnssm. The model demonstrates notable performance metrics with (MAE = 1.61 × 10−12 m2/s, RMSE = 2.38 × 10−12 m2/s, and R2 = 0.95) in the training set and (MAE = 2.22 × 10−12 m2/s, RMSE = 3.18 × 10−12 m2/s, and R2 = 0.87) and the test set. The SHAP method provides comprehensive insights into feature importance, offering valuable information about the relationships and dependencies among various features. The top five features identified as significant contributors include coarse aggregate, superplasticizer, concrete age, cement, and water. Visualization of SHAP values through diverse plots proves essential for obtaining a thorough understanding of feature influence. The explainability of the model's results contributes new insights, aiding in the development of optimal and sustainable concrete with enhanced resistance to chloride penetration. Furthermore, the model's explainability fosters trust in its predictions, facilitating seamless integration into real-world applications.

Relationship between Chloride Migration, Bulk Electrical Conductivity and Formation Factor of Blended Cement Pastes

Abstract This study investigates the links between the non-steady-state chloride migration coefficient, the bulk electrical conductivity and the formation factor of blended cement paste specimens. 18 different binders were tested: two Portland cements (low- and high-alkali) in combination with limestone filler, fly ash, calcined clay, two biomass ashes, sewage sludge ash and crushed brick, as well as two Portland composite cements. In addition, the latter and the low-alkali Portland cement were tested in concrete as well for comparison. Mixes with high-alkali cement showed better resistance to chloride transport, and the effect of supplementary cementitious materials was found to be strongly linked with their reactivity. Moreover, the results showed a clear correlation of the migration coefficient with the bulk electrical conductivity and, to a lesser extent, with the formation factor. However, these relationships are strongly influenced by the methods used to determine conductivities and they need to be validated for higher maturities. Finally, the results suggested a fairly good correspondence between the results obtained on paste and concrete.

Recycling of landfill waste tyre in construction materials: Durability of concrete made with chipped rubber

The goal of current research is to study the effect of waste tyre as a replacement for coarse aggregate at high levels in concrete for non-structural applications to address one of the serious environmental concerns. To reach this aim, waste rubber in a size range of 10–15 mm which needs less energy and cost for grinding compared to fine rubber was used. The total volume of coarse aggregate was substituted by rubber at the rates of 25%, 50%, 60%, 70% and 80%. Mechanical properties were studied through compressive and flexural strength and hardened density tests. Moreover, durability was comprehensively investigated via water absorption, drying shrinkage, electrical resistivity, chloride migration, carbonation resistance and resistance against acid attack tests. Sound absorption performance of different mixes at low and high frequencies were also compared to monitor the impact of rubber content. The results indicated that by the addition of rubber mechanical properties reduced, nevertheless, durability improved. Using rubber enhances the concrete ductility and reduces the density making it appropriate for lightweight concrete. The chloride migration coefficient was reduced up to 80% and electrical resistivity increased up to 87%, by using 80% rubber. Besides, rubberised concrete developed in this research demonstrated superior functional advantages over plain concrete in terms of acoustic performance and sustainability. Despite having lower strength by using rubber in concrete, rubberised concrete made with high content of cost-effective coarse rubber particle is appropriate for non-structural usages particularly in regions where either possibility of aggressive environment is a concern or noise attenuation is critical.

Characterization of permeability of seawater iron tailings mortar based on inter-pore connection

Permeability is an important factor affecting the durability as the connection between pores provides a channel for water and ion permeation. However, the mechanism governing the influence of inter-pore connection is still unclear. This paper quantitatively calculates the connectivity and complexity of inter-pore connections based on pore structure scan images, and investigates the effect of different aggregates on the resistance of mortar to chloride-ion migration. Seawater ordinary mortar (SOM) and seawater iron tailings mortar (STM) were prepared. Pore scans and tests for chloride migration coefficient and chloride-ion content were conducted. Based on the maximum Feret diameter of the pores, the complexity index, Kci, was defined to characterize the complexity of inter-pore connections, and this extends existing calculation methods from one-dimensional to two-dimensional in nature. However,the complexity index correlates with the chloride migration coefficient and chloride-ion content well for seawater ordinary mortar only but not for seawater iron tailings mortar. Therefore, the critical image diameter, dic, was defined to characterize the connectivity of pores. This also overcomes the shortcomings of the MIP method, which does not give the spatial pore distribution. Last, the modified complexity index, Kmci, which modifies the complexity index using the critical image diameter, was presented. It is shown to correlate with test results well for both seawater ordinary and iron tailings mortars. Replacing Kci with Kmci greatly improves the linear correlation of complexity of inter-pore connection with chloride penetration resistance for seawater iron tailings mortar, with the correlation coefficient R increasing from 0.45 to 0.88.

Assessing durability properties of ultra-high performance concrete-class materials

Ultra-high performance concrete (UHPC) is a class of concrete materials that has received significant attention from the infrastructure community due to its favorable mechanical and durability performance. As the use of UHPC in infrastructure projects is becoming more common, there is an increasing interest in identifying appropriate testing techniques to assess the durability properties of UHPC-class materials. The dense microstructure of UHPC-class materials and the presence of a high concentration of fiber reinforcement have made it difficult to rely on existing standard testing approaches for concrete durability assessment. This study explores the application of various conventional-concrete durability test methods to UHPC, including electrical resistivity (American Association of State Highway and Transportation Officials (AASHTO) TP 119-22), freeze–thaw (ASTM C666), water absorption (ASTM C1585), and rapid chloride migration test (NT BUILD 492). The selected tests are meant to qualify and quantify the microstructural penetrability of UHPC to ions and fluids, a surrogate property commonly used as an indicator of durability. The findings from this study indicate that electrical resistivity can be used as a durability indicator for UHPC-class materials. Moreover, strong correlation between electrical resistivity and the chloride migration coefficient is identified, a potential benefit given that chloride migration can be used to estimate service lives of UHPC-class materials. Other tests, including freeze–thaw and water absorption, although identifying the favorable performance of UHPC relative to conventional concrete, were unable to provide insightful information through which the performance of individual UHPCs could be differentiated.

An efficient machine learning approach for predicting concrete chloride resistance using a comprehensive dataset

By conducting an analysis of chloride migration in concrete, it is possible to enhance the durability of concrete structures and mitigate the risk of corrosion. In addition, the utilization of machine learning techniques that can effectively forecast the chloride migration coefficient of concrete shows potential as a financially viable and less complex substitute for labour-intensive experimental evaluations. The existing models for predicting chloride resistance encounter two primary challenges: the constraints imposed by a limited dataset and the absence of certain input variables. These factors collectively contribute to a decrease in the overall effectiveness of these models. Therefore, this study aims to propose an advanced approach for dataset cleaning, utilizing a comprehensive experimental dataset comprising 1073 pre-existing experimental outcomes. The proposed model for predicting the chloride diffusion coefficient incorporates various input variables, such as water content, cement content, slag content, fly ash content, silica fume content, fine aggregate content, coarse aggregate content, superplasticizer content, fresh density, compressive strength, age of compressive strength test, and age of migration test. The utilization of the artificial neural network (ANN) technique is also employed for the processing of missing data. The current supervised learning incorporates both regression and classification tasks. The efficacy of the proposed models for accurately predicting the chloride diffusion coefficient has been effectively validated. The findings indicate that the XGBoost and SVM algorithms exhibit superior performance compared to other regression prediction algorithms, as evidenced by their high R2 scores of 0.94 and 0.91, respectively. In relation to classification algorithms, the findings demonstrate that the Random Forest, LightGBM, and XGBoost models exhibit the highest levels of accuracy, specifically 0.93, 0.96, and 0.97, respectively. Furthermore, a website has been developed that is capable of predicting the chloride migration coefficient and chloride penetration resistance of concrete.

Study on the durability of 3D printed calcium sulphoaluminate cement-based materials related to rheology control

Since 3D printed structure is conducted by the style of dimension reduction, the defects typically occur between the printing layers due to the poor rheological properties, which affects the durability most. This study focuses on exploring the durability of 3D printed calcium sulphoaluminate cement-based materials (CSACMs) with slag powder based on the correlation between printed structures and rheological parameters. Experimental results show that both the static and dynamic yield stress of 3D printed CSACMs exhibits a gradual increase with the slag powder content increases, while the thixotropy improves continually until reaching a maximum content at 15%. In this case, an increase in slag powder content leads to a significant reduction for structure deformation. However, poor printability occurs when the content of slag powder exceeds 15%. Besides, the chloride migration coefficient and maximum electric flux decreases from 7.28 × 10−12 to 3.27 × 10−12 m2/s and 1347 to 711 K, respectively, when the content of slag powder increases from 0 to 10%. Meanwhile, the freezing resistance and linear shrinkage are improved. Based on the radar map correlation, structure deformation is significantly influenced by thixotropy, which is a crucial factor that can impact the durability of 3D printed CSACMs. In conclusion, the controllable rheology of 3D printed CSACMs are advantageous for improving the printed structures and durability.

Durability assessment of industrial by-product and marine resource-based ultra-high-performance concrete

The increasing demand for concrete and the associated environmental impacts such as depletion of natural resources (e.g., fresh water, river sand, and coarse aggregates) have prompted the development of seawater and sea-sand concrete (SWSSC). On the other hand, incorporating industrial by-products in concrete as supplementary cementitious materials (SCMs) can offset the cement carbon footprint. Utilizing seawater, sea sand, and industrial wastes in ultra-high-performance concrete (UHPC) fabrication can lead to a sustainable as well as durable construction material, especially suited for marine infrastructure development. This experimental work investigates the durability properties of ultra-high-performance seawater and sea-sand concrete (UHP-SWSSC) with partial substitution of cement by ground granulated blast furnace slag and silica fume as SCMs. Five mixes were developed with varying proportions of SCMs as cement replacement (0% as control mix, 25% and 50% by mass) and water-to-binder ratio (0.15, 0.2 and 0.25). In addition to mechanical behaviour through standard axial compression tests on cube specimens, several durability indicators such as water absorption, sorptivity, the permeability of chloride ions, and volume of permeable voids were measured over time. Results reveal that the incorporation of SCMs in UHP-SWSSC although improves the mechanical properties marginally, significantly enhances the durability performance. In comparison to the control mix, 53%, 75%, and 95% reductions in the volume of permeable voids, rate of water absorption and non-steady state chloride migration coefficient were observed in a 50% SCM replaced mix, respectively. Addition of ground slag and silica fume induced a relatively compact matrix through refinement of the microstructure, which made the resulting concrete nearly impermeable to ion movements. An optimum water-to-binder ratio of 0.2 was established, below which neither the strength nor the durability characteristics improved further.

Effect of pore structure on durability and mechanical performance of 3D printed concrete

The application of 3D printed concrete (3DPC) technology in the construction industry has become widespread in recent years. This paper provided a method for the 3DPC mix design and investigated the mechanical performance and durability of 3DPC. In this study, two optimized mixes were obtained based on the particle dense packing theory and the least squares method for calculating the proportions of binder for 3DPC. The microstructure of 3DPC was investigated by X-CT scanning to characterize its porosity for discussion of the anisotropic mechanical performance in the 3DPC. In addition, the frost resistance and chloride ion penetration resistance of 3DPC had been investigated. The results showed that the pore connectivity of 3DPC was better than that of casting concrete and the pores accumulated near the interface. In addition, the porosity calculation results showed that the porosity of the interface between layers was lower than that of the interface between filaments in 3DPC. All specimens of 3DPC showed excellent frost resistance with a maximum mass loss of only 0.18% and the average flexural strength and compressive strength of 3DPC were only reduced by 31.2% and 21.0% respectively after 300 freeze–thaw cycles. The maximum chloride migration coefficients for the 3D printed concrete specimen was 79 × 10-14 m2/s and the glass fiber enhanced the chloride ion penetration resistance of the specimens.