Chloride Diffusion Resistance Research Articles

Design of a hydrophobic nano-SiO2-modified ER@EC microcapsule: Improving rheology, regulating hydration while preserving self-healing in cementitious materials

Microcapsule-based self-healing concrete chronically suffers from rheology deterioration and hydration stagnation due to the hydrophilic and hygroscopic nature of microcapsules, limiting its efficacy and broader application. To address these issues, a novel hydrophobic nano-SiO2-modified epoxy resin (ER)@ethyl cellulose (EC) microcapsule was developed and characterized. Examinations revealed that both 5 % and 7 % SiO2-modified ER@EC microcapsules displayed favorable fundamental properties for cement-based materials, featuring high core contents (53.08 % and 48.04 %) and water contact angles over 90°. Compared to the unmodified capsules, the incorporation of 7 % SiO2-modified capsules prominently enhanced the rheology and hydration exotherm of fresh cement pastes, attributed to floc disassembly caused by electrostatic repulsion and increased water volume induced by replacement and ball-bearing effects. Moreover, incorporating a 4 % dosage of 5 % SiO2-modified capsules exhibited prominent healing efficiencies of 6.14 % for compressive strength and 35.11 % for chloride diffusion resistance. The hydrophobic nano-SiO2-modified ER@EC microcapsules actively improved rheology and hydration exotherm while preserving the ability to self-heal cracks in cement-based materials.

Effect of nano-metakaolin on the chloride diffusion resistance of cement mortar with addition of fly ash

This study examines the improvement of nano-metakaolin (NMK) on the chloride ion diffusion resistance (CDR) of fly ash (FA) cement-based materials. The rapid chloride diffusion (RCM) method was employed to compare the effects of nano Al2O3, nano CaCO3, nano SiO2, nano attapulgite clay, and NMK on the CDR of cement mortar, and a suitable nanomaterial was identified. Subsequently, the influence of NMK on the CDR, flexural and compressive strengths of FA cement mortar was examined. The chloride ion concentration of NMK/FA cement paste under simulated salt environment were measured. The action mechanism of NMK on the CDR of FA cement mortar was explored through mercury intrusion porosimetry and scanning electron microscopy tests. The results reveal that among these nanomaterials, NMK exhibited the highest cost-effectiveness in enhancing CDR of cement mortar, with a suitable content of 5 wt%. NMK demonstrated a significant improvement in the CDR of FA cement mortar, particularly at a hydration age of 7d. Incorporating 5 wt% NMK into the cement mortar with addition of 30 wt% FA resulted in a 73% reduction in chloride ion diffusion coefficient (Dcl) compared to the cement mortar with the addition of 30 wt% FA at 7d. NMK enhances both flexural and compressive strengths of FA cement mortar at various hydration ages (3, 7, 14, 28 d). The addition of 5 wt% NMK makes a increment of about 10% for the flexural strength of cement mortar with 30 wt% FA at 7d. Moreover, NMK results in a denser internal structure of FA cement mortar, facilitates the generation of C–S–H gel, and reduces the more-harmful pores and harmful pores while increasing harmless and of less-harmful pores cement paste. Additionally, NMK exhibited the most substantial reduction in chloride ion concentration within FA cement paste at 7d. In general, NMK significantly enhances CDR, flexural and compressive strengths of FA cement mortar, especially at a hydration age of 7d.

Effect of a Crystalline Admixture on the Permeability Properties of Concrete and the Resistance to Corrosion of Embedded Steel

Reinforced concrete structure durability hinges on concrete permeability, which relies on the characteristics of the inner porous network. Harmful ions and gases can accelerate steel corrosion. Permeability-reducing admixtures (PRA), including crystalline admixtures (CA), are commonly used to mitigate this. This study examines a commercial CA’s impact on durability-related aspects in concrete specimens. Two concrete mixtures with matching proportions were prepared: a reference mix and another mix with a commercial crystalline admixture. Several properties were studied, such as compressive strength, density, porosity, electrical resistivity, water absorption capacity, chloride diffusion, air permeability, and corrosion resistance. The studied admixture in concrete yields several positive outcomes such as a slight reduction in mixing water, a potential 6% increase in concrete’s compressive strength and the development of a denser and less permeable structure with 3% lower porosity and water absorption than the reference mix. Electrical resistivity improves by 10%. Unidirectional chloride diffusion tests show no differences. Air permeability decreases by from 36% to 55%, and the water absorption rate diminishes by 23%. The admixture potentially reduces the scatter in corrosion initiation periods for steel reinforcements, delaying corrosion onset by around 60 days, although more extensive experiments are needed for definitive conclusions.

Developing Geopolymer Concrete by Using Ferronickel Slag and Ground-Granulated Blast-Furnace Slag

Geopolymer concrete is gaining recognition as an environmentally friendly alternative to traditional cement-based materials, offering potential solutions for reducing the carbon emissions of the construction industry. This study aims to develop GGBFS–FNS geopolymers utilising ferronickel slag (FNS) and ground-granulated blast-furnace slag (GGBFS). Ground FNS (GFNS) is a potential candidate for replacing fly ash in geopolymers. This research aims to develop for the first time a GGBFS–FNS alkali-activated concrete. Numerous trials were conducted including different GGBFS–FNS blend percentages, several chemical admixtures and varying activator concentrations to develop the optimal binder mix composition. The effects of different chemical admixtures on the properties of geopolymer pastes, mortars, and concretes were investigated. The study evaluated setting time, compressive strength, shrinkage, and physical and durability properties. The results indicate that conventional admixtures have limited impact on the setting time, while increasing the water/solid ratio and decreasing the GGBFS content could extend the initial and final setting times. The presence of FNS aggregate could improve the compressive strength of geopolymer mortars. The water absorber admixture was highly effective in reducing shrinkage and increasing chloride diffusion resistance. The geopolymer mix containing 50 wt.% GFNS and 50 wt.% GGBFS with the presence of the water absorber admixture presented high chloride diffusion resistance, non-reactivity to the alkali–silica reaction and high sulphate resistance. Overall, the GGBFS–FNS geopolymers exhibited promising potential for engineering applications as an environmentally friendly material, particularly in aggressive environments.

Influence of Silica Nanoparticles on the Properties of Nanocomposite Based on Epoxy as Concrete Protective Coating

Concrete structure especially that exposed to aggressive environment is deteriorated leading to damage of concrete buildings. Concrete coating is one of the most effective methods used for concrete protection. In this work epoxy was modified with nanosilica (NS) with different loadings. Epoxy nanosilica (EP-NS) composite was formulated and used as concrete protective coating after evaluate its properties regarding drying time, dry film thickness (DFT), adhesion strength. The coated concretes ware tested as; water absorption, contact angle (hydrophobicity) and chloride diffusion resistance by ion exchange method. Although, durability of coated concretes were examined by determining change in weight and change in compressive strength after immersion in both sulfuric acid and sodium chloride solution separately. The study revealed that, the optimum NS content is 3 % by total weight of coating. The prepared EP-NS coatings have significant protection mechanism for enhancing concrete performance against the postulated aggressive attack. Keywords: protective coating, polymer nanocomposite coating

Chloride Diffusion in Concrete Made with Coal Fly Ash Ternary and Ground Granulated Blast-Furnace Slag Portland Cements.

Ternary Portland cement usage with a high amount of cement constituents different from clinker can afford great climate change advantages by lowering the Portland cement clinker content in the final product. This will contribute to cutting greenhouse gas emissions to close to zero by 2050. Such ternary Portland cements can be composed of different amounts of ground granulated blast-furnace slag (GBFS), coal fly ash (CFA), and clinker (K). Cements made with GGBFS, or CFA boast pozzolanic characteristics. Therefore, they would improve both the concrete compressive strength at later ages and durability. The 28- and 90-days mechanical strength test, non-steady state chloride migration test, described in NT BUILD 492, and natural chloride diffusion test (NT BUILD 443) were performed in concrete. Ternary cements made with GBFS and/or CFA presented better chloride diffusion resistance than concrete made with plain Portland cements. Furthermore, the development of compressive strength was delayed. The service life study was developed for concretes made with ternary cements with regard to the chloride penetration case.

Microstructure as a key parameter for understanding chloride ingress in alkali-activated mortars

This study aims to evaluate the influence of microstructural properties on the chloride diffusion resistance of alkali-activated materials (AAMs) based on blast furnace slag and/or fly ash, with variable activator doses (represented as Na2O%). Resistance to chloride penetration was tested using accelerated chloride penetration (NT BUILD 443) and chloride migration (NT BUILD 492) tests. Addition of slag to alkali-activated mortars mainly based on fly ash reduced porosity and chloride permeability. Chloride penetration decreased with increasing Na2O%, but porosity and pore structure did not follow the same trend. The pore threshold (dth) and critical pore radius (rcrit) determined by mercury intrusion porosimetry had a good correlation with the chloride diffusion coefficient. Both the quantification of reaction products and the correlation between chloride penetration and pore surface area indicated that physical chloride adsorption on the C-A-S-H/N-A-S-H gel surfaces predominated over chemical chloride binding.

Effect of exposure temperatures on chloride penetration resistance of concrete incorporating polypropylene Fibers, silica fume and metakaolin

• The diffusion resistance of silica fume (SF) concrete was 1.4–7.3 less than OPC concrete. • The diffusion resistance of metakaolin (MK) concrete was 1.2–3.9 less than OPC concrete. • The effect of 10% SF on migration resistance was almost similar to that of 15% MK. • Models to predict the service life of RC structures in hot environments were developed. Rapid degradation of reinforced concrete (RC) has become a serious concern due to its reduction of life span and high unexpected maintenance cost. Chloride penetration and subsequent corrosion are the primary causes of such concrete deterioration. This study investigated the effects of polypropylene fibers, metakaolin and silica fume on chloride diffusion and migration resistance of concrete at different exposure temperatures. Eight concrete mixes were prepared using a water/binder ratio of 0.38, cement replacement of 0, 5, 10, and 15 % by either silica fume (SF) or metakaolin (MK) with zero or 0.6 kg/m 3 polypropylene fibers (PPFs). Furthermore, concrete resistance to chloride diffusion at four different exposure temperatures (23, 38, 53 and 68 °C) and chloride migration at 23 °C was evaluated. The results showed that both pozzolanic admixtures, SF and MK, significantly reduced apparent chloride diffusion coefficient (D a ) and chloride migration coefficient (D nssm ). However, PPFs concretes incorporating MK showed inferior chloride diffusion than those containing SF. D a for PPFs concretes incorporating SF and MK were 1.4–7.3 and 1.2–3.9 times less than Type I cement concrete, respectively. While D nssm for PPFs concretes incorporating SF and MK were 1.7–6.3 and 1.5–3.2 times less than Type I cement concrete, respectively. The results also showed that the effect of 15 % MK on D nssm and D a was almost similar to that of 10 % SF. The D a increased slightly at exposure temperatures of 23 and 38 °C. However, at higher exposure temperatures of 53 and 68 °C, a significant increase in D a was noted. Eight models were developed using regression analysis and were validated by comparing the predicted apparent chloride diffusion coefficient values with the measured ones. The validation of the developed models showed that the predicted D a values were within ± 7 % error margin. The developed chloride diffusion models in the current study allow us to predict and quantify the long life of future realizations of RC structures in marine hot environments.

The role of CaO and MgO incorporation in chloride resistance of sodium carbonate-activated slag

Partial substitution of CaO or MgO for slag accelerates the reaction kinetics and strength gains of sodium carbonate (Na2CO3)-activated slags, yet their impact on the durability performance remains unknown. This study compares the effects of CaO and MgO substitution at various contents (2.5% and 5%) on the fresh properties, reaction kinetics, phase assemblage, pore structure, chloride binding capacity and chloride diffusion resistance of Na2CO3-activated slags. The results show that in addition to its higher effectiveness in boosting strength development, the substitution of CaO for slag results in superior enhancement in chloride binding and resistance of Na2CO3-activated slag compared to the system modified by MgO. Hydrotalcite is identified to have a comparable contribution to the chloride binding of CaO- and MgO-modified AAS, but the greater Friedel's salt formation is the main reason for the higher chloride immobilisation capacity of the CaO-modified AAS. The results demonstrate the technical promises of CaO and MgO as substitutes to control reaction kinetics of Na2CO3-activated slag while improving its chloride durability.

Durability of polypropylene fiber reinforced concrete: Literatures review


 
 
 
 
 
 
 
 Use of polypropylene fibers to reinforce concrete has attracted widespread attention from both researchers and construction industry because of the numerous characteristics they have, compared to other types of fibers. This paper critically reviews the current state of knowledge of impacting the inclusion of polypropylene fibers on concrete durability. Detailed review on the different durability properties including: Water and gas permeability, sorptivity, water absorption, chloride diffusion, carbonation, and frost resistance. The influence of polypropylene fibers on these properties is discussed in this paper.
 
 
 
 
 
 
 
 
 

Hydration behavior and chloride ingress in cement mortar incorporating a novel core@shell admixture

A coupled addition of layered double hydroxides (LDHs) (with a high chloride binding capacity) and zeolite (as a pozzolanic material) in concrete is conducive to reducing external chloride ingress. This study aims to evaluate the chloride transport resistance of concrete using a novel Linde type A zeolite (zeolite-LTA)@Mg–Al LDHs (zeolite@LDHs) core@shell material. The effect of the core@shell admixture on cement hydration and chloride penetration into cement mortar were investigated by a comparative experiment. The results showed that the addition of zeolite@LDHs material in cement mortar shortened the setting time, slightly reduced the hytration heat, and exerted a marginal effect on the compressive strength and flexural strength. More importantly, a synergistic effect of LDHs' excellent chloride binding ability and zeolite induced pore refinement remarkably augments the chloride diffusion resistance of the zeolite-LTA@LDHs incorporated cement mortars.

Effect of curing time on the chloride diffusion of alkali-activated slag

Resistance to chloride penetration plays a crucial role in preventing premature corrosion of reinforced concrete in marine environments or when using de-icing salts. For reinforced concrete with ordinary Portland cement (OPC), the curing of concrete is vital in ensuring that the designed chloride penetration resistance of concrete is achieved. The method and duration of curing are especially important with alkali-activated slag (AAS) to allow proper reaction and development of the pore structure. AAS generally needs to be cured under closed conditions for at least 28 d to achieve the desired quality. The objective of this study was to analyse the effect of curing time on the development of chloride diffusion resistance and pore structure of alkali-activated slag mortar. Chloride diffusion resistance was analysed at 7, 28, and 90 d using non-steady-state chloride migration according to NT BUILD 492 and accelerated chloride testing according to NT BUILD 443, both of which were originally developed for OPC. Mercury intrusion porosimetry (MIP) was used to evaluate the effect of pore structure on chloride penetration. The diffusion results of alkali-activated mortar showed that high resistance to chlorides can be achieved after only 7 d of curing, which is attributed to the development of fine porosity of alkali-activated slag at an early age.

Microstructure and Chloride Diffusion Properties of Hardened Fly Ash Cement Paste with Three-dimensional Graphene

In this paper, the influence of three-dimensional graphene (3DG) on the microstructure and chloride diffusion properties of fly ash cement paste was investigated. 3DG accounting for 0.0–0.2% of cement mass was evenly dispersed in hardened cement paste containing fly ash by using ultrasonic and polycarboxylate superplasticizer. The microstructure of the cement paste was characterized by mercury intrusion test (MIP), X-ray diffraction (XRD), and scanning electron microscope (SEM). The results indicate that an appropriate amount of 3DG accelerates the secondary hydration of fly ash and provides a platform for the growth of cement hydration crystals. Moreover, the hydrated crystal fills the pores, reduces the harmful porosity, and refines the pore structure. The enhanced microstructure significantly improved mechanical properties and chloride diffusion resistance of hardened fly ash cement. With the addition of 0.1% 3DG, the compressive strength increased by 31.33%, and the chloride diffusion coefficient was reduced by 49.44%. The findings are beneficial to promote the generalized application of 3DG in cement in the marine environment.

Effect of crystallizer treatment on chloride diffusion and microstructure of recycled aggregate concrete

The crystallizer (CA) treatment on recycled concrete aggregate (RCA) can improve its quality and further benefit the utilisation of RCA in manufacturing recycled aggregate concrete (RAC). Unfortunately, the long-term properties of RAC with CA treated RCA have not been fully explored yet. Therefore, this paper is aim to evaluate the performance of CA treatment on RCA and the durability and permeability of corresponding RAC. To achieve the goal, the permeability of RAC with different RCA replacement ratios was investigated by capillary water absorption test and rapid chloride migration test, and the effects of CA on the interfacial transition zone (ITZ) and pore structure were determined through mercury intrusion porosimetry and scanning electron microscope. The results showed that CA treatment significantly improved the chloride diffusion resistance of RAC due to the calcium silicate hydrate (C-S-H) formed by the reaction between CA treatment and calcium-rich hydrates. The formed C-S-H can partially fill the pores and micro-cracks in adhesive mortar and ITZ, compact the microstructure and reduce the pore size, thus improving the permeability of RAC.

Effects of aggregate and interface characteristics on chloride diffusion in concrete based on 3D random aggregate model

The chloride diffusion in concrete with different aggregate volume ratios (AVR) and interfacial transition zone (ITZ) were studied in this paper. According to the finite element method, the 3D concrete model with aggregates and ITZ is modeled, and the chloride diffusion characteristics were numerically simulated and compared with the experimental results. Furthermore, the reasons for the better chloride resistance of nanocomposite concrete are studied. The results show that the established model can well reflect the material properties of concrete and has a good application effect on chloride diffusion. The increase of AVR inhibited the chloride diffusion and there is significant influence on the simulation results when use different AVR to back calculation. However, it is little influence on the simulation results when change the ITZ condition of back calculation. The better chloride diffusion resistance of nanocomposite concrete is mainly due to the improved anti-diffusion properties of the ITZ.

Effects of Autogenous and Stimulated Self-Healing on Durability and Mechanical Performance of UHPFRC: Validation of Tailored Test Method through Multi-Performance Healing-Induced Recovery Indices

Chloride diffusion and penetration, and consequently chloride-induced corrosion of reinforcement, are among the most common mechanisms of deterioration of concrete structures, and, as such, the most widely and deeply investigated as well. The benefits of using Ultra-High Performance (Fiber-Reinforced) Concrete—UHP(FR)C to extend the service life of concrete structures in “chloride attack” scenarios have been addressed, mainly focusing on higher “intrinsic” durability of the aforementioned category of materials due to their compact microstructure. Scant, if nil, information exists on the chloride diffusion and penetration resistance of UHPC in the cracked state, which would be of the utmost importance, also considering the peculiar (tensile) behavior of the material and its high inborn autogenous healing capacity. On the other hand, studies aimed at quantifying the delay in chloride penetration promoted by self-healing, both autogenous and autonomous, of cracked (ordinary) concrete have started being promoted, further highlighting the need to investigate the multidirectional features of the phenomenon, in the direction both parallel and orthogonal to cracks. In this paper, a tailored experimental methodology is presented and validated to measure, with reference to its multidirectional features, the chloride penetration in cracked UHPC and the effects on it of self-healing, both autogenous and stimulated via crystalline admixtures. The methodology is based on micro-core drilling in different positions and at different depths of UHPC disks cracked in splitting and submitted to different exposure/healing times in a 33 g/L NaCl aqueous solution. Its validation is completed through comparison with visual image analysis of crack sealing on the same specimens as well as with the assessment of crack sealing and of mechanical and permeability healing-induced recovery performed, as previously validated by the authors, on companion specimens.

Chloride ion binding effect and corrosion resistance of geopolymer materials prepared with seawater and coral sand

In this work, the chloride binding capacities and chloride diffusion resistance of alkali-activated fly ash and slag powder geopolymer systems prepared with seawater and coral sand are investigated. Through the macro tests (e.g., chloride ion binding ratio, electric flux, etc.), stripping C-S-H, C/N-A-S-H from anhydrous particles and a variety of microscopic tests (e.g., MIP, XRD, SEM-EDS), the chloride binding mechanism of ordinary Portland cement (OPC) and geopolymer are analyzed and compared. The result shows that the chloride binding capacity of geopolymer samples under standard curing is better than that of OPC samples under the same condition (for instance, the 28-day chloride binding coefficient of geopolymer (FS1): 83.372%, OPC (R1): 73.223%). And the binding of chloride ion can be improved to a certain extent by increasing the initial chloride concentration. Geopolymer bounds the chloride ions through physical absorption or chemical reaction with cement compositions. The porous structure of C/N-(A)-S-H gel and high content of Al element promote the chloride binding capacity. The additional porous coral sand can reduce the chloride resistance capacity of specimens. But with slag proportion increasing, the geopolymer shows better chloride resistance capacity (for example the chloride diffusion coefficient decreases by 98% from 152.61 m2/s to 2.86 m2/s when slag proportion increased from 10% to 90%). The chloride diffusivity of geopolymers measured by the electric flux method has a large deviation, which is not suitable for direct evaluating of resistance to chloride penetration of geopolymer system.

Mechanical Properties and Durability of Sustainable Concrete Containing Various Industrial Solid Wastes

Benefits of replacing ordinary Portland cement with industrial solid wastes are promising for reducing cement production and solving environmental problems associated with industrial solid wastes. In this study, an experimental investigation was conducted to evaluate the performance of sustainable concrete containing different industrial solid wastes (e.g., waste glass, coal gangue, fly ash, and slag), with the attention on the mechanical strength, chloride transport property, and pore structure characteristics. Three water to binder ratios (i.e., 0.38, 0.48, and 0.65) and three replacement levels (i.e., 10%, 20%, and 30%) were considered in this work. The test results show that regardless of the content and type of industrial solid wastes, the inclusion of industrial solid wastes generally exerts a negative influence on the mechanical properties, especially under high water to binder ratios. However, acceptable mechanical strength can still be achieved in these sustainable concretes. In addition, the inclusion of industrial solid wastes could enhance the chloride diffusion resistance of concrete, and also the concrete with waste glass powder showed the best performance. Furthermore, the incorporation of industrial solid wastes has a refinement effect on the microstructure of the matrix, manifesting as decreased cumulative pore volume and compacted microstructural morphology.

Mechanical and durability assessment of cement-based and\xa0alkali-activated coating mortars in an aggressive marine environment

Coatings are used as practical solutions against the intrusion of corrosive ions into concrete structures, particularly, in the harsh marine environment. In the present study, the effectiveness of using cement-based and geopolymer-based coatings produced using by-product materials has been evaluated. Silica fume and GGBFS at their optimum dosages were incorporated into mortar mixtures as a cement replacement, and mixtures of NaOH or KOH and sodium silicate solutions were used in the alkali-activated mortars. Shrinkage test, RCMT, and capillary absorption test as common experiments for durability analysis, as well as tests related to the mechanical and bonding properties including compressive strength test, pull-off test, and shear bonding strength test were carried out on the specimens. According to the results, both geopolymer and cement-based mortars improved the compressive and bonding strengths, and chloride diffusion resistance of coatings compared to the OPC mortar. Silica fume was found to be more effective in the strength development of mortars at young ages, while GGBFS was more responsible for acting as a filler and producing further gel in the older ages. The major drawback with geopolymer mortars is the high rate of water absorption and shrinkage coefficient in the early hours, which shows the importance of curing of these mortars at young ages. Overall, the mix design produced with 30% GGBFS and 7.5% silica fume showed the highest durability and mechanical properties and proved to be more compatible with the harsh environment of the Persian Gulf.

Assessing alkali-activated concrete performance in chloride environments using NT Build 492

The production of Portland cement is responsible for approximately 5–7% of the worldwide CO2 emission. Geopolymer concrete (GPC) presents potential to become a more sustainable alternative to Portland cement and reduce the environment impact of the concrete industry. Marine environment is one of the most corrosion issues for reinforced concrete structures. Chloride migration test (Nordtest NT Build 492) and bulk diffusion chloride test (ASTM C1556) has been widely used to assess chloride diffusion resistance of Portland cement concrete. NT Build 492, involving externally applied electrical voltage, provides fast and adequate assessment of chloride penetration resistance of Portland cement concrete. However, the utilization of NT Build 492 for GPCs requires recalibration due to their different microstructure and pore solution composition compared to Portland cement concrete. This study aims to establish performance-based criteria for GPCs in marine environments using NT Build 492 and ASTM C1556 test protocols. Experimental results revealed a good correlation between chloride migration coefficients (NT Build 492) and chloride diffusion coefficients (ASTM C1556). In addition, chloride concentration at the colour change boundary used to calculate the chloride migration coefficients in NT Build 492 has been recalibrated for the chemistry of GPCs pore solution.