Seawater And Sea Sand Concrete Research Articles

Influences of aggregate gradation on alkali-silica reaction of seawater and sea sand concrete

The application of seawater and sea sand concrete (SWSSC) is beneficial for marine engineering, but the impact of aggregate gradation on its alkali-silica reaction (ASR) remains poorly understood. This study aims to bridge this gap by analyzing ASR products, pore characteristics and expansion rate of specimens. The test results reveal that ordinary concrete (OC) exhibits an inhibitory effect on ASR in comparison with to SWSSC. The 14-day expansion of ordinary concrete and SWSSC with the same aggregate gradation are 0.130 % and 0.212 %, showing potential and high risk of ASR, respectively. Moreover, particle size and gradation of aggregate are the key factors influencing the ASR degree of SWSSC. Compared with coarser aggregate, specimens with finer aggregate consume more K+ and Ca2+ ions, generate more ASR-P1, form less porosity, and produce a larger expansion. Additionally, specimens with gap-graded aggregates, as opposed to those with uniform or continuous gradation, show greater consumption of K+ and Ca2+ ions, increased ASR-P1 formation, more harmful pore formation, and a larger expansion. These results offer insights into optimizing aggregate gradation to reduce ASR in SWSSC and improve its durability.

Axial Compression Behavior of Circular Seawater and Sea Sand Concrete Columns Reinforced with Hybrid GFRP-Stainless Steel Bars.

The ductility of FRP-reinforced concrete structures is reduced by the brittleness of FRP bars. To address this issue, this study employs the hybrid reinforcement of stainless steel (SS) and GFRP bars to enhance the ductility of concrete columns. A total of 21 axially compressed seawater and sea sand concrete (SWSSC) circular columns are fabricated, including 15 hybrid GFRP and SS bar-reinforced SWSSC (GFRP-SS-SWSSC) columns, 3 GFRP bar-reinforced SWSSC (GFRP-SWSSC) columns, and 3 SS bar-reinforced SWSSC (SS-SWSSC) columns. The test results are analyzed in terms of failure mode, load-axial displacement curve, bearing capacity, and ductility. Results show that GFRP-SWSSC columns suffer brittle failure, while GFRP-SS-SWSSC columns and SS-SWSSC columns demonstrate ductile failure characteristics. Furthermore, the hybrid reinforcement contributes to an improvement in the bearing capacity of the columns. A calculation equation for the bearing capacity of axially compressed columns was established, providing reasonable predictions of bearing capacities, with a design compressive strain of 2000 με for GFRP bars. It was found that hybrid reinforcement enhanced the ductility of GFRP-SWSSC columns. In addition, when the percentage of the SS reinforcement ratio reaches 50%, the ductility indexes of the GFRP-SS-SWSSC columns closely approach those of the SS-SWSSC columns.

Effects of desalinated sea sand on the alkali–silica reaction of seawater and sea sand concrete

The application of seawater and sea sand concrete (SWSSC) can reduce the construction period and cost of island infrastructure, but it may also bring the risk of alkali–silica reaction (ASR) owing to the presence of alkali ions in seawater and sea sand. To compare the characteristics of ASR between SWSSC and seawater and desalinated sea sand (DSS) concrete, the properties and the ASR products of mortar bars with different DSS content were studied. When the DSS proportion increased from 0% to 100%, the sodium (Na+), potassium (K+) and calcium (Ca2+) ion concentration of the specimens decreased by 22.6, 2.0 and 45.1 mg L−1, respectively, the pH decreased by 0.05 and the expansion of mortar bars was reduced by 0.16%. Desalination of sea sand could not eliminate the risk of ASR of SWSSC completely. The 14 days expansion of mortar bars with 100% DSS was 0.13%, and the precursors of ASR-P1 were observed by SEM. The experimental results of micriscopic tests all showed that with the increase of DSS proportion, the content of Na-shlykovite and ASR-P1 were reduced. A small amount of magnesium (Mg) in ASR products was detected. This study can provide a basis for the application of SWSSC in island infrastructure.

Degradation of mechanical properties and microstructure evolution of basalt-carbon based hybrid FRP bars in real seawater and sea-sand concrete

The degradation of basalt fibre-reinforced polymer (BFRP) bars induced by alkaline environments hinders their application in seawater and sea-sand concrete (SWSC). The use of carbon fibres (CFs) to partially replace basalt fibres in the preparation of hybrid-FRP (HFRP) bars is an effective method for enhancing the durability of BFRP-bar. To evaluate the effectiveness of using CFs to replace part of the basalt fibres in preparing HFRP bars to enhance the durability of BFRP-bar in real SWSC. The tensile and interlayer interface properties of HFRP bars with different CFs hybrid contents (VCF, %) and arrangements in the SWSC were tested after exposure to seawater at different temperatures. Digital microscopy, scanning electron microscopy, X-ray computed tomography and matrix digestion analysis were used to investigate the microstructural evolution of HFRP bars and SWSC after conditioning. The results showed that the VCF increasing to 10% or 25% significantly alleviated the interlaminar shear strength (ILSS) and tensile strength (TS) losses. The maximum enhancements in the ILSS and TS retention for the SWSC-embedded BFRP bar were 19.12% and 17.55%, respectively. The hybrid CFs changed the failure model of the BFRP-bar. Compared with HFRP bars with CFs in the core, HFRP bars are more likely to deteriorate when the CFs are dispersed circumferentially. The hybrid CFs improved the environmental reduction coefficients (ERC) of TS and ILSS of the HFRP bars. Compared with the SWSC, the ERC of the HFRP bars in the normal concrete was significantly improved.

Characteristics of the alkali-silica reaction in seawater and sea sand concrete with different water-cement ratios

Research of seawater and sea sand concrete (SWSSC) is the current hot topic, but effects of water-cement ratios (W/C) on alkali-silica reaction (ASR) of SWSSC haven't been investigated. To solve this issue, the ASR products, pore structure and expansion rate of specimens with different W/C (0.35 ∼ 0.55) were measured. The study shows that pore structure and Na+ consumption are two key factors influencing ASR of SWSSC. When the W/C increases from 0.45 to 0.55, Na+ in specimen replaces K+ in ASR-P1(K0.52Ca1.16Si4O8(OH)2.84·1.5H2O), and ASR-P1 is converted into Na-shlykovite(NaCaSi4O8(OH)3·2.3H2O); the porosity is the dominant factor for the expansion rate of SWSSC. When the W/C increases from 0.35 to 0.45, the Na+ consumption is the dominant factor for the expansion rate of SWSSC. Magnesium element mainly coexists in Na-shlykovite and transition zone in SWSSC with W/C = 0.55. The research results are beneficial to inhibit ASR of SWSSC with different W/C and improve their 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.

Compressive performance of SWSSC-filled CFRP-stainless steel composite tube columns

The structure of concrete confined by carbon fiber-reinforced polymer (CFRP) and stainless steel tubes was investigated. The columns, which take advantage of the ductility and corrosion resistance of stainless steel, are composed of stainless steel tube, core seawater and sea sand concrete (SWSSC) and outer FRP. Forty circular SWSSC-filled FRP-stainless steel composite tube columns (SCFSSCTs) were manufactured and subjected to axial compression tests. After fracturing of the FRP, the failure modes of the specimens mainly showed extrusion expansion, with a small amount of shear failure. The increase in the thickness of the stainless steel and the number of FRP layers resulted in a significant improvement in the load capacity and deformation capacity of the structure, which was more evident in the specimens with higher steel contents. With the increase in the number of FRP layers, the increases in ultimate stress and ultimate strain were 40.4% − 130.0% and 118.6% − 282.4%, respectively, compared with the column with single stainless steel confinement. The stress–strain curves for the SCFSSCTs were similar to those of structures reinforced by FRP and carbon steel and were divided into four stages. Models were proposed to predict the full axial stress–strain curves of SCFSSCTs, including the ultimate point and the peak point.

A comparative study of bare and seawater sea sand concrete wrapped basalt fiber-reinforced polymer bars exposed to laboratory and real marine environments

The high alkalinity of concrete restricts the application of basalt fiber-reinforced polymer (BFRP) bars as reinforcement in seawater and sea sand concrete (SWSSC), but lowering the alkalinity enhances the durability of BFRP bars. This work focuses on the degradation of BFRP bars embedded in SWSSC in the laboratory and real marine environments. The interlaminar shear strength (ILSS) and deterioration mechanisms of BFRP bars wrapped in ordinary and low-alkalinity SWSSCs were investigated using the ILSS test, 1H nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). It was found that the BFRP bars in the natural marine environment suffer from less degradation than those in the accelerated laboratory environment due to the lower temperature. After 180 d of exposure to 55 °C seawater and the field environment, the ILSS retentions of BFRP bars in ordinary SWSSC are 54% and 85%, while those in low-alkalinity SWSSC remain 81% and 97%, respectively. The decreased alkalinity and porosity in low-alkalinity SWSSC also considerably minimize the hydrolysis of epoxy resin in BFRP bars caused by alkaline and moisture erosion. Furthermore, the Arrhenius theory-based model considering temperature and humidity fluctuations, predicts that lowering the alkalinity of SWSSC can greatly enhance the service life of BFRP bars, which can be applied in high-temperature and humidity environments. This study provides insights into using low-alkalinity SWSSC to improve the durability of FRP bars in marine concrete structures.

Combined effects of expansive agents and glass fibres on the fracture performance of seawater and sea-sand concrete

The effects of expansive agents (EAs) and glass fibres (GFs) on the splitting strength and fracture performance of seawater and sea-sand concrete (SSC) were investigated. It was found that adding sole EAs or GFs improved the splitting strength, flexural strength, fracture energy, and initial and unstable fracture toughness of SSC. The combination usage of EAs and GFs maximumly increased the aforementioned indexes by 65%, 75%, 155%, 101%, and 82%, respectively. The optimal EA content was 3%–6% and increased with the increase of GF contents. The constitutive model of SSC reinforced with EAs and GFs under tension proposed in this study agreed well with the experimental results.

Experimental and simulative study of bonding properties on fiber/epoxy interfaces by digital image correlation (DIC) technique and molecular dynamics

Fiber/epoxy interfacial bonding properties play a vital role in the utilization of fiber reinforced polymer (FRP) bars in concrete because almost all durability deficiencies of FRP-reinforced concrete are attributed to the failure of the fiber/epoxy/concrete interface. This study aims to study the evolution of fiber/epoxy debonding under a simulated concrete pore solution environment, combining a self-developed debonding device and the digital image correlation (DIC) technique. The bonding degradation mechanism of the fiber/epoxy interface was revealed by molecular dynamics (MD) simulation. The results show that the interfacial bonding property between glass fiber (GF) and epoxy was superior to that of basalt fiber (BF), and a more significant bonding degradation was observed in BF after the corrosion of water and chloride ions due to the reduction in the number of H-bonds caused by partial replacement of Si by Al, as concluded from MD simulation. Moreover, the bond stresses of GF and BF were reduced to approximately 15% and 12% after 28 days of corrosion in the simulated concrete pore solutions, respectively. Meanwhile, the reduction in bond strength was more significant in the simulated concrete pore solution of seawater and sea sand concrete (SWSSC).

Experimental analysis on water penetration resistance and micro properties of concrete: Effect of supplementary cementitious materials, seawater, sea-sand and water-binder ratio

To evaluate the water penetration resistance of seawater and sea-sand concrete (SSC), this study conducts water penetration test and capillary water absorption test. And scanning electron microscope (SEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), Thermogravimetric analysis and derivative thermogravimetry (TGA-DGA) were used to reveal the micro morphology, pore size distribution, porosity and hydration products of SSC. The effects of water-binder (w/b) ratio, supplementary cementitious materials (SCMs) (fly ash (FA) and limestone and calcined clay (LC2)), and curing age on the resistance to water penetration and micro performance of SSC were studied. The results show that with the smaller the w/b ratio and the increasing of curing age, the more is C–S–H gel and the denser SSC matrix, which is beneficial to resist water diffusion. With the addition of FA, the water penetration resistance of SSC tends to decrease overall. The addition of LC2 can reduce the macro pores obviously and promote cement hydration to generate denser hydration products (C-A-S-H, monosulfate (AFm)) to fill the macropores and free water channels of the matrix and improve the water permeability of SSC. Especially, when the replacement rate of LC2 is 25%, the water penetration depth (WPD) decreases by 55.81%, 51.08%, 48.91% during the curing age of 28 d, 56 d, and 120 d, respectively. With the higher the design compressive strength of SSC, the better is the water penetration resistance. Using the data regression analysis method, the relationship between the compressive strength and the WPD of SSC was established, and the capillary water absorption with time and w/b ratio/FA content has a good non-linear function relationship, and the correlation coefficients are greater than 0.95.

Bond between Fibre-Reinforced Polymer Tubes and Sea Water Sea Sand Concrete: Mechanisms and Effective Parameters: Critical Overview and Discussion

Using fibre-reinforced polymers (FRP) in construction avoids corrosion issues associated with the use of traditional steel reinforcement, while seawater and sea sand concrete (SWSSC) reduces environmental issues and resource shortages caused by the production of traditional concrete. The paper gives an overview of the current research on the bond performance between FRP tube and concrete with particular focus on SWSSC. The review follows a thematic broad-to-narrow approach. It reflects on the current research around the significance and application of FRP and SWSSC and discusses important issues around the bond strength and cyclic behaviour of tubular composites. A review of recent studies of bond strength between FRP and concrete and steel and concrete under static or cyclic loading using pushout tests is presented. In addition, the influence of different parameters on the pushout test results are summarised. Finally, recommendations for future studies are proposed.

Compressive performance of concrete-filled steel tube columns with in-built seawater and sea sand concrete-filled FRP tubes

A structure termed as concrete-filled steel tube (CFST) columns with in-built seawater and sea sand concrete (SWSSC)-filled fiber reinforced polymer (FRP) tubes was investigated. The new composite columns are comprised of outer steel tubes, sandwich ordinary concrete, inner FRP tubes and core SWSSC. Thirty-six CFST columns with in-built SWSSC filled FRP tube and four CFST columns were manufactured, and the influences of the diameter of the FRP tube, FRP layers and the thickness of steel tube on compressive performance of the specimens were studied. The results indicated that the ultimate strength of the specimens was positively related to the FRP layers, diameter of the FRP tube and thickness of the steel tube. The stress–strain curve of new structure consists of four stages, and columns with larger FRP tube diameter and more FRP layers obviously underwent more stress-drop after the ultimate point. The installation of the FRP tube has a more significant strengthening effect on the columns with a thinner steel tube. Models to predict the ultimate stress, ultimate strain, peak stress and peak strain of new structure were proposed. Moreover, a simple model to predict the axial stress–strain response curve of CFST columns with in-built SWSSC-filled FRP tubes was suggested.

Compressive behaviour of FRP-steel wire mesh composite tubes filled with seawater and sea sand concrete

A new structural type of seawater and sea sand concrete (SWSSC)-filled fibre-reinforced polymer (FRP) and steel wire mesh composite tube (SFWCT) was proposed. The steel wire mesh, working as an intermediate layer, was embedded in two layers of FRP. Due to the high corrosion resistance of FRP, the steel wire mesh could maintain a long-term stable working state while the core concrete was effectively confined. Three series of specimens were tested under compressive loading. The test parameters mainly included the number of layers of steel wire mesh, the FRP type and the FRP thickness. The results show that the time to failure was significantly reduced with the new design, as the steel wire mesh could effectively decrease the degree of damage in the specimens and prevent the specimens from immediately losing their bearing capability due to the sudden fracture of the FRP. The accuracies of relevant models were evaluated with the test data, and the model with the best performance was suggested. Moreover, the full stress–strain curves of SFWCTs under compression were simulated, and the calculated results were satisfactory.

Electrochemical Investigations of Steels in Seawater Sea Sand Concrete Environments.

Seawater and sea sand concrete (SWSSC) is an environmentally friendly alternative to ordinary Portland cement concrete for civil construction. However, the detrimental effect of high chloride content of SWSSC on the corrosion resistance of steel reinforcement is a concern. This study undertook the electrochemical corrosion behaviour and surface characterizations of a mild steel and two stainless steels (AISI type 304 and 316) in various simulated concrete environments, including the alkaline + chloride environment (i.e., SWSSC). Open circuit potential (OCP), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were employed. Though chloride is detrimental to the corrosion resistance of mild steels, a simultaneous presence of high alkalinity in SWSSC negate the detrimental effect of chloride. In the case of stainless steels, a high level of alkalinity is found to be detrimental, whereas chloride seems to have less detrimental effect on their corrosion resistance.

Computational AI prediction models for residual tensile strength of GFRP bars aged in the alkaline concrete environment

Based on a comprehensive literature study, the potential variables that can affect the durability of GFRP bars under a harsh alkaline environment especially seawater and sea sand concrete (SWSSC) environment, were investigated and reported in this paper. The study presents a new strategy for finding tensile strength retention (TSR) using empirical models based on the strong non-linear ability of artificial intelligence techniques, i.e., artificial neuro-networking (ANN), gene expression programming (GEP), and adaptive neuro-fuzzy inference system (ANFIS). The diameter of GFRP bars, the volume fraction of glass fibers, the pH value of solutions, the temperature, and the duration of conditioning were considered as input parameters to find TSR of aged GFRP bars. Statistical checks evaluated the trained models, and the results demonstrate that the models provide a reliable estimate of TSR. A simple mathematical prediction formula was developed using the GEP model that can quickly foresee the TSR for aged GFRP bar. In comparison with the GEP model, the ANN model and the ANFIS model provided slightly better results. The parametric study indicates that the large diameter of bars and the high volume fraction of fibers have positive effects on the TSR, while the high temperature and the long duration of conditioning have negative influences.

Austenitic Stainless-Steel Reinforcement for Seawater Sea Sand Concrete: Investigation of Stress Corrosion Cracking

Seawater and sea sand concrete (SWSSC) is a highly attractive alternative to normal concrete (NC) that requires huge amounts of fresh water and river sand. However, reinforcements of stainless steel (instead of mild steel that is used in NC) may be required for SWSSC. This article reports investigation of stress corrosion cracking (SCC) of AISI 316 stainless steel (SS) in simulated SWSSC and NC environments, with and without addition of silica to SWSSC and NC, employing slow strain rate testing (SSRT) at 25 and 60 °C. For the purpose of comparison, SCC of SS was also investigated in simulated seawater (SW) solution. SS showed no SCC at 25 °C in any of the test solutions. Indications of SCC were seen in SW at 60 °C, but no features of SCC in SWSSC and NC at 60 °C, as suggested by scanning electron microscopy (SEM) fractographs. While the absence of SCC in SWSSC and NC is attributed to the highly passivating alkaline condition, its absence in SWSSC also indicates the role of alkalinity to predominate the deleterious role of chloride content of SWSSC. However, the addition of silicate to SWSSC or NC triggers transgranular SCC to SS at 60 °C, as evidenced by the fractography.

Environmental Impacts of Glass- and Carbon-Fiber-Reinforced Polymer Bar-Reinforced Seawater and Sea Sand Concrete Beams Used in Marine Environments: An LCA Case Study.

Application of glass- or carbon-fiber-reinforced polymer (GFRP/CFRP) bars makes the direct use of seawater and sea sand concrete (SWSSC) in construction feasible, which is of high interest in order to conserve the limited resources of fresh water and river sand. The present paper performed the life cycle assessment (LCA) of constructing three kinds of beams (GFRP/CFRP bar-reinforced SWSSC beams, and steel bar-reinforced common concrete (SRC) beam) in marine environments to show the environmental benefits of using FRP bar-reinforced SWSSC beams in marine environments. According to ISO 14040 and ISO 14044, stages including production, transportation, construction, use and end-of-life are within the LCA’s boundary. The ReCiPe method and eight main environmental impact categories were used to characterize the environmental impacts of those beams. LCA results indicate that one cubic meter SWSSC possesses much lower environmental impacts in terms of all eight categories compared with common concrete with the same volume when used in marine environments, with reduction rates from 26.3% to 48.6%. When the two transportation distances were set as 50 and 20 km and without considering the difference in service life, compared to SRC beam, GFRP-SWSSC beam performs better in six categories and CFRP-SWSSC beam performs better in four categories. When considering increased transportation distance and the higher durability performance, the advantageous categories for GFRP-SWSSC and CFRP-SWSSC beams increase to seven and six, respectively. The environmental impacts of all the three beams are mainly affected by the production stages.

Seismic performance of seawater and sea sand concrete-filled ultra-high performance concrete tubes under low-cycle reversed lateral loading

Seawater and sea sand concrete (SWSSC) filled ultra-high performance concrete (UHPC) tube (SFUHPC tube) column is a cement-based tubular composite column, which combines the excellent compressive strength and toughness of UHPC and lateral confining action from fiber reinforced polymer (FRP) hoops. The novel composite system has the potential to be used in marine engineering. The aims of this paper focus on evaluating the seismic performance of SFUHPC tube columns for being designed in costal and marine engineering. A series of low-cycle reversed lateral loading tests were conducted on five relatively large-scale specimens. FRP hoop volumetric ratio, compressive strength of filling SWSSC, and the types of FRP bar were selected as test parameters in this investigation. The failure modes, hysteretic responses and effects of main parameters were studied and discussed. SFUHPC tube columns exhibited flexural failure mode without visible spalling of the UHPC cover. It is noteworthy that the limit plastic drift ratios of all SFUHPC tube columns exceed the specified limits (0.02) in accordance to the rare earthquake requirement in seismic design code. The current study reveals that the proposed composite columns have acceptable ductility and relatively reliable lateral resistant performance for being used in the marine engineering. From the point of view of seismic performance, filling high strength SWSSC in UHPC tube is acceptable for the proposed composite system.

Durability of seawater and sea sand concrete filled filament wound FRP tubes under seawater environments

Using fibre reinforced polymer (FRP) composites together with seawater and sea sand concrete (SWSSC) in coastal areas will overcome the environmental issues of using ordinary concrete and corrosion problems of conventional steel reinforcements. The present research investigates the mechanical properties of different SWSSC filled FRP tubes after exposure to seawater. Glass, carbon, and basalt filament wound FRP tubes were filled with SWSSC and exposed to seawater for different exposure durations at different temperatures. A total number of 567 Hoop tension and compression tests were carried out after conditioning to investigate the mechanical properties degradation of the tubes. In addition, scanning electron microscopy (SEM) and micro computed tomography (micro-CT) analyses were conducted on representative samples to study the degradation mechanisms and damage progression. Finally, the long-term mechanical performance of SWSSC filled tubes under seawater was predicted based on Arrhenius theory and using the experimental data. According to the test data, generally, the samples with multiple fibres direction showed better durability compared to the tubes with fibres oriented in hoop directions. Moreover, carbon tubes experienced the smallest degradation while glass and basalt tubes showed almost the same range of degradation.