Chloride Ingress Research Articles

Durability of Nano-Reinforced Recycled Aggregate Concrete under Load and Chloride Ingress.

The improved performance of recycled aggregate has an important impact on its use in engineering. In this study, to improve the weak surface properties, recycled aggregates were treated by nano-silica slurry and applied to concrete beam specimens. Under the action of cracks caused by continuous load and drying-wetting cycles with chloride ingress, the effects of different recycled aggregate additions, nano-silica contents and crack widths on the self-healing performance of cracks and the resistance to chloride ingress of the recycled concrete beams were investigated. It was found that the self-healing rate of cracks increased first and then decreased with increased nano-silica content, reaching a maximum when the content reached 0.4%. Greater amounts of additive in the recycled aggregate increased the concentration of free chloride ions in cracks. However, this concentration was found to be weakened in nano-reinforced aggregate. From a comprehensive perspective, the relative chloride ion concentration can be effectively reduced by controlling the crack width to be smaller than 0.12 mm and using improved recycled aggregates treated with 0.2% nano-silica material. This study provides a reference for the application of recycled aggregate concrete under severe environmental and load conditions.

Durability characteristics and quantification of ultra-high strength alkali-activated concrete

Clinkerless ultra-high strength concrete formulated using alkali-activated binders (AAB-UHSC) emerges as a green high-performance construction material, but its durability characteristics have not been systematically investigated yet. In this work, the resistances of AAB-UHSC against water absorption, carbonation, chloride diffusion, and chloride-induced electrochemical corrosion of steel, are quantitatively evaluated and compared with those of ordinary Portland cement (OPC)-based UHSC and normal-strength AAB (AAB-NSC) counterparts. The results show that in comparison with OPC-UHSC of similar strength of ∼150 MPa, AAB-UHSC has lower water-permeable porosity and demonstrates superior performance against water absorption and chloride ingress, but a weaker carbonation resistance. However, despite lower CO2 uptake capacity, the carbonation resistance of AAB-UHSC is about six times stronger than that of AAB-NSC, owing to its highly densified microstructure. Under the same chloride level and relative humidity conditions, the corrosion rate of steel embedded in AAB-UHSC is higher than that in OPC-UHSC, likely due to its higher moisture content and [Cl−]/[OH−] ratio that expedite steel dissolution. Moreover, the incorporation of steel fibers has limited influence on the transport-related durability performance of AAB-UHSC, implying a densified interfacial zone between steel fibers and AAB-UHSC matrices.

Laser-induced breakdown spectroscopy - a tool for the chemical investigation of concrete infrastructure

LIBS is a complementary method to XRF and can detect all elements without the need for vacuum conditions. Automated systems are already commercially available capable of scanning surfaces with a resolution of up to 0.1 mm within a few minutes. In addition to possible applications in R&D, LIBS is also used for practical applications in building materials laboratories and even on-site. In view of ageing infrastructure facilities, a reliable assessment of the condition of concrete structures is of increasing interest. For concrete structures, the ingress of potential harmful ions is affecting the serviceability and eventually structural performance. Pitting corrosion induced by penetrating chlorides is the dominant deterioration mechanism. Condition assessment based on frequently performed chloride profiling can be useful to identify the extent and evolution of chloride ingress. This could prove to be more economical than extensive repairs, especially for important infrastructure facilities. Currently the most common procedure for determining the chloride content is wet chemical analysis with standard resolution of 10 mm. The heterogeneity is not considered. LIBS is an economical alternative for determining the chloride content at depth intervals of 1 mm or less. It provides 2D distributions of multiple elements and can locate spots with higher concentrations. The results are directly correlated to the mass of binder and can also be performed on-site with a mobile LIBS-System. The application of a LIBS-system is presented. Calibration is required for quantitative analysis. Concrete cores were drilled, sliced and analyzed to determine the 2D-distribution of harmful elements. By comparing the chloride ingress and the carbonation, the interaction of both processes can be visualized in a measurement that takes less than 10 minutes for a 50 mm x 100 mm drill core. A leaflet on the use of LIBS for the chloride ingress assessment has been completed.

Monitoring chloride diffusion in BFS concrete using an Electrical Resistivity Tomography device

Corrosion of steel bars in Reinforced Concrete (RC) due to the penetration of chlorides coming from seawater is one of the main pathologies leading to degradation of marine structures. Destructive Evaluation (DE) methods like coring from concrete in such marine environment are difficult and expensive for the survey of marine RC structures. Whereas, Non-Destructive Evaluation (NDE) methods based on the wave propagation (electric and electromagnetic) can reduce the number of cores necessary to evaluate the health of the studied structures. The aim of this work is to study the chloride ingress into saturated concrete by using the NDE methods and especially the Electrical Resistivity Tomography device. Accordingly, chlorides diffusion campaign with two different chloride concentration ([NaCl] = 35 and 90 g/L) was carried out on two slab of concrete contains slag addition. Apparent resistivities are then inverted in order to obtain a resistivity profile versus depth with two different software: Res1D and Ceris. Moreover, resistivity measurements were performed regularly on the slabs to obtain the resistivity profiles. On the other hand, a calibration method was realized to relate the resistivity to the chloride content for each type of concrete. The chloride profiles evaluated by NDT are then compared to those obtained by a destructive method (potentiometric titration) at three different exposure periods. The long-term goal is to use directly the NDE results in the model of chloride ingress into saturated concrete

Residual mechanical properties of steel fiber reinforced concrete damaged by alkali silica reaction and subsequent sodium chloride exposure

Infrastructures treated with de-icing salts and those which are in direct contact with sea water are subjected to degradation by chloride ingress. Concrete composed of reactive sources of silica and used near such regions can suffer from both, alkali silica reaction (ASR) and chloride ingress subsequently. This research aims at empirically investigating the residual mechanical properties of plain and steel fiber reinforced concrete damaged by alkali silica reaction (ASR) and subsequent chloride ion ingress. Accelerated degradation tests on three concrete mixes such as plain concrete (PC,control), steel fiber reinforced concrete (SFRC) and high strength fiber reinforced concrete (HSFRC) were done. Specimens were initially damaged by ASR, and then submerged in chloride solution at temperature ranges of 5 o C, 25 o C and 40 o C. 1 mol/L NaOH solution and 3% NaCl solution were used for a period of 20 and 40 weeks. Steel fibers were found to be effective in reducing surface crack widths at 5 o C and 25 o C. Accelerated mortar bar test showed that steel fibers were able to reduce expansion by 31.5% and 65.3% using single and double hooked fibers. By examining the residual compressive and flexure strengths, it was found that exposure to chloride environment aided in hydration reaction which counter-balanced the damage due to ASR. Fiber-matrix bonding developed over time inducing friction which led to higher ductility and less damage in flexure strength in steel fiber reinforced concrete prisms.

Application of machine learning technique for predicting and evaluating chloride ingress in concrete

Application of machine learning technique for predicting and evaluating chloride ingress in concrete

Microstructure and macro properties of sustainable alkali-activated fly ash mortar with various construction waste fines as binder replacement up to 100%

Utilizing construction waste fines as eco-friendly binder for sustainable alkali-activated materials provides new approach to recycling construction waste. This work investigated the characterization of alkali-activated fly ash mortar (AAM) incorporating construction waste fines at varied types and replacement levels. The results showed that incorporating waste paste powder containing abundant hydrated products refined the pore size of AAM, but mixing waste mortar powder and waste concrete powder that contained massive inert quartz and calcite adversely affected the alkali-activated reaction and pore structure of AAM. The incorporation of construction waste fines was found to reduce the fluidity but increased the drying shrinkage of AAM. At identical replacement level of construction waste fines, the waste paste powder incorporated AMM has lower fluidity and greater drying shrinkage than the waste mortar powder or waste concrete powder incorporated AAM. Substituting waste paste powder for fly ash improved the mechanical strength of AAM, but the strength decreased as waste mortar powder or waste concrete powder was incorporated. Particularly, the AAM blended with 100% construction waste fines still owned good strength. Mixing construction waste powder reduced the chloride diffusion coefficient and chloride ingress depth of AAM, and the waste paste powder mixed AAM had better chloride resistance than the waste mortar powder or waste concrete powder mixed AAM. Therefore, the hydrated products in construction waste fines was revealed to benefit the micro-characteristics of alkali-activated materials, and optimizing the type and replacement level of construction waste fines can achieve sustainable AAM with good mechanical strength and chloride ingress resistance.

Chloride Ingress Resistance, Microstructure and Mechanical Properties of Lightweight Mortars with Natural Cork and Expanded Clay Prepared Using Sustainable Blended Cements

The use of lightweight aggregates in construction materials is a good solution for increasing the contribution to sustainability of civil engineering works, such as maritime ones. In this regard, the possibility of using cork granulates and expanded clay is a current research topic. The combination of eco-friendly cements with lightweight aggregates could provide solutions for developing new building materials. In this work, it has been studied mortars prepared with sustainable cements and the lightweight aggregates of natural cork and expanded clay. These cements incorporated slag, limestone and fly ash. Reference mortars with only sand as aggregate were also made. The total porosity and pore size distributions were obtained. The non-steady-state chloride migration coefficient and compressive and flexural strengths were also determined. The tests were performed at 28 days and 1 year. The differences in the total porosity between the natural cork and expanded clay series were not high, depending on the binder. Natural cork mortars showed similar or slightly higher migration coefficients than the reference and expanded clay mortars at 1 year. This adequate chloride resistance and the low mechanical strengths observed for the natural cork mortars recommend the possible use of this new aggregate in non-structural cement-based materials for civil engineering works exposed to maritime environments.

Combined Effects of Sulfate and Chloride Attack on Steel Reinforced Mortar under Drying–Immersion Cycles

In this study, X-ray microcomputed tomography (XCT) and nanoindentation techniques were used to evaluate the synergistic action between sulfate and chloride ingress under cyclic drying–immersion conditions on steel-reinforced mortars. Three salt solutions, namely 3% NaCl (Sc), 5% Na2SO4 (Ss), and 5% Na2SO4 + 3% NaCl (Scs), were used and 24 drying–immersion cycles were applied. The results showed that the chloride caused more severe corrosion on steel reinforcement than the sulfate while under the influence of Scs, and the presence of sulfate suppressed the steel corrosion caused by chloride. In terms the damage to the mortar cover, after 24 drying–immersion cycles, the sulfate caused the most severe damage (volume loss of approximately 7.1%) while the chloride resulted in the least damage (volume loss of approximately 2.6%). By comparing Ss and Scs, it was also found that chloride suppressed the sulfate attack by reducing the damage to the mortar cover (volume loss of approximately 6.3% for Scs). Moreover, the degradation of mortar specimens was found to be layer-dependent, as was the distribution of micro-mechanics. Regarding the micro-mechanics, the specimens of the three solutions performed differently in terms of the aforementioned properties, depending on which underlying mechanism was analyzed. This research could allow for a more accurate assessment of the factors influencing building structures in a typical aggressive marine environment.

Fatigue life prediction for prestressed concrete beams under corrosion deterioration process

The coupled effect of corrosion and fatigue on performance degradation of prestressed concrete (PC) bridges is a dynamic process. This paper proposed a novel framework for the fatigue life prediction of corroded PC beams, where the chloride ingress process, pitting corrosion, cross-sectional area reduction of steel, pretension force loss, and fatigue damage accumulation of materials were considered. A dynamic residual cross-sectional area-based method was developed to estimate fatigue damage accumulation of materials, and competition between concrete failure criterion and Miner’s rule of cumulative damage theory of strand was included. Following this, the fatigue damage of naturally corroded PC beams was discussed, and an experimental study on the fatigue behavior of pre-corroded PC beams was conducted to validate the proposed model. The prediction results agreed well with the experimental observations. The results showed that the effects of load amplitude and vehicle load frequency on the prediction results were clarified. The deterioration of corroded PC beams is more sensitive to load amplitude than load frequency. With the corrosion rate of strand increasing to 3%, the failure mode of pre-corroded PC beams changes from the brittle fracture of steel bars to the brittle fracture of strands. Fatigue failure is caused by the sudden brittle fracture of longitudinal steel bar for naturally corroded beam. The proposed method provides a satisfactory result for evaluating the damage accumulation of PC beams with corroded strands or steel bar.

On the correlations between different chloride transport parameters and their role in service life estimation

ABSTRACT In this article, the role of chloride transport parameters in the service life estimation of a reinforced concrete structure is discussed. This article also lists several qualitative and quantitative test methods used to measure resistance to ingress of chloride in concrete systems with their advantageous and critique properties. The relationship between the rapid assessment methods such as resistivity and the diffusion coefficient is put forward. A review of the ageing coefficient for different binder types is presented. The importance to characterise and account for the environmental factors such as exposure condition and ambient temperature variation is emphasised based on its impact on the chloride build-up rate. A parametric study is carried out to identify the role of different factors associated with chloride transport property in service life estimation. The prediction of chloride build-up rates for various binder composites based on analytical and numerical approaches is summarised along with relevant input parameters.

Prevention of Corrosion in Post-Tensioned Structures: Electrically Isolated Tendons

Post-tensioning structures with metallic ducts risk corrosion, rupture or collapses due to chloride ingress. The use of tight corrugated polymer ducts combined with electrically isolated anchorages (EIT) changed the situation. Laboratory and many field applications proved the tightness of the duct, showing resistance values higher or much higher than 50 kΩm, the acceptance criteria for a tight duct. The most important fact is that EIT tendons allow quality control and long-term monitoring of the duct tightness. EIT ducts (also with resistance values below the threshold criteria) can be monitored over the whole service life: only a progressive decrease of the measured resistance indicates a corrosion risk for this specific tendon. The most important structural elements can be easily monitored for the first time and damage initiation can be detected early. After a successful use in Europe EIT technology is now expanding progressively in the US.

Time-Dependent Reliability Assessment Method for RC Simply Supported T-Beam Bridges Based on Lateral Load Distribution Influenced by Reinforcement Corrosion

The safety and reliability of bridges gradually decrease over time under the influence of disadvantageous environmental factors, primarily due to reinforcement corrosion caused by chloride ingress. The traditional lateral load distribution (LLD) theory does not consider the influence of corrosion, which degrades the accuracy of bridge performance and reliability calculation. A time-dependent reliability assessment method for simply supported T-beam bridges is proposed in this paper, which considers the influence of reinforcement corrosion on LLD. Firstly, the steel corrosion process and degree are predicted based on the chloride ingress model, into which the water/cement ratio and concrete strength are innovatively introduced in order to improve the prediction accuracy. Secondly, the effective stiffness calculation method for corroded reinforcement bridges is established with the moment of inertia and section crack condition employed. Thirdly, the modified eccentric compression method is improved by the effective stiffness and iterative algorithm, which is suitable for the LLD calculation of corroded reinforcement bridges. The time-dependent vehicle load effect can be computed combined with the probability distribution of live load. Finally, the time-dependent reliability of the flexural bearing capacity is obtained by the Monte Carlo method and Bayesian theory without prior information. A simply supported bridge with five T-beams is taken as an example for analysis. It is indicated that the results calculated by the traditional reliability method are conservative, which cannot make a true and accurate evaluation. The method proposed in this paper can effectively reduce the assessment error caused by model uncertainty while considering the interaction between reinforcement corrosion and vehicle live load effect.

Study on Bond-Slip Behavior between Seawater Sea-Sand Concrete and Carbon Fiber-Reinforced Polymer (CFRP) Bars with Different Surface Shapes.

The application of CFRP bar and seawater sea-sand concrete (SSSC) in construction can overcome the shortcomings in conventional reinforced concrete, such as corrosion induced by carbonation and chloride ingress. In this study, the bond-slip behavior between an SSSC cube and CFRP bar has been investigated, and different CFRP bar surface shapes have been considered. A total of 27 specimens (9 groups) were fabricated for a pull-out test, where three types of CFRP bar with different surface shapes were used: smooth regular bars, double-wrapped bars and ribbed bars. Bond strength, bond-slip curve, and failure mode have been presented and discussed. FE models have been constructed and validated by experimental results. The effect of concrete compressive strength and relative area of ribs on bond strength has been studied through numerical simulations. It is found that the bond strength increased with concrete compressive strength, and the ribbed bar had significantly higher bond strength than the smooth regular bar. Pull-out failure was observed when the cover-depth-to-bar-diameter ratio was no less than 4 and, otherwise, splitting failure occurred. In addition, a simple formula has been proposed to approximately evaluate the bond strength between an SSSC cube and CFRP bar and validated by experimental results, and analytical expressions for different bond-slip curves have also been developed.

Application of magnesium alloy sacrificial anode for restraining chloride ingress into mortar

This study aims to restrain the chloride ingress into mortar by magnesium alloy sacrificial anode system. Cube reinforced mortar specimens with embedded magnesium alloy anode meshes were prepared. The output electrochemical parameters of magnesium alloy mesh, the chloride profiles and corrosion electrochemical performance of steel in mortars immersed in chloride-contaminated solutions were detected. Besides, the visual inspection of steel surface after immersion was performed. The results indicate that the magnesium alloy mesh can restrain effectively chloride ingress into mortar. With increasing water-cement ratio and chloride content, the galvanic potential and current density between the steel and magnesium alloy mesh increase. The chloride diffusion coefficient of mortar decreases after the application of magnesium alloy sacrificial anode and the decreased magnitude rises with increasing water-cement ratio, chloride concentration and decreasing steel cover thickness. The mitigation of steel corrosion and morphology of the steel surface after immersion further demonstrate the good effect of magnesium alloy sacrificial anode on reducing chloride ingress into mortar.

High and normal strength concrete using grounded vitrified clay pipe (GVCP)

Several challenges faced the carbon footprint reduction of concrete production. Recycling waste materials from different industries to produce green concrete would be a proper solution due to their low cost and space-saving for landfill purposes. One of these industries is manufacturing vitrified clay pipes used for sewage, which show high resistance to the aggressive environment. However, vastly deteriorated pipes are disposed of as waste in landfills while processing. Additionally, the vitrified clay pipes are sourced from the kaolin burnt at a temperature above 800 °C while processing; no literature introduces the disposal wastes as supplementary cementitious material (SCMs). Nevertheless, other wastes such as ceramic sourced by metakaolin were introduced. This paper studies the grounded vitrified clay pipe (GVCP) as SCMs for producing green concrete. The methodology encountered examining the durability and mechanical properties of concrete using GVCP. Two group sets suggested; normal and high concrete strength with 0, 5, 10, 15, 20, and 25% cement replacement by GVCP. Slump, compressive and flexural strengths, and abrasion were assessed while microstructure analysis handled. The results showed that the optimized values would be 10% and 20% for normal and high concrete strength in which mechanical properties are provided. The study also suggested a coefficient of 1.52 and 0.7 for ACI 318 and EN 1992-1 flexural provision. The GVCP showed higher resistance to chloride ingress of fewer than 1000 coulombs even at a high water-to-cement ratio of 0.64. The X-ray diffraction (XRD) revealed that GVCP provided more CSH gels, increasing compressive strength at later ages.

Characterization of sustainable mortar containing high-quality recycled manufactured sand crushed from recycled coarse aggregate

The current utilization of low-quality recycled fine aggregate sourced from concrete waste acting as river sand replacement cannot achieve the preparation required for high-quality recycled mortar, due to abundant existence of hardened old mortar in recycled fine aggregate. In this work, an innovative and viable approach is proposed to crush recycled coarse aggregate into recycled manufactured sand, which has high-quality properties similar to the manufactured sand crushed from natural stone, for preparing high-quality recycled mortar with high strength and good durability. The results showed that recycled manufactured sand constituted by large proportion of natural stone particles and small proportion of old mortar, owned higher apparent density and lower water absorption than recycled fine aggregate. Incorporating recycled fine aggregate increased the drying shrinkage and decreased the mechanical strength; however, the substitution of natural river sand by recycled manufactured sand in mortar decreased the drying shrinkage as a result of its irregular shape and coarse surface, meanwhile, first increased and then declined the mechanical strength following the increase of the replacing percentage, amongst which the mortar containing 50% recycled manufactured sand showed the best mechanical strength. The tested mortars with recycled manufactured sand showed a general increment in the water and chloride ingress yet exhibited the water absorption and chloride ingress much lower than the mortar with recycled fine aggregate. Particularly, decreasing the content of hardened old mortar in recycled manufactured sand further improved the properties of recycled mortar.

The effect of pore microstructure on strength and chloride ingress in blended cement based on low kaolin clay

The objective of this study is to analyse the mechanical and durability properties of a high-performance mortars based on low grade kaolin clay and the effect of electrical conductivity and pore microstructure on the chloride penetration resistance. A total of six mixes were prepared with binary and ternary binders in which a high volume of cement was replaced by low-grade calcined kaolin clay, fly ash and limestone powder. The percentage of kaolinite in the clay used from the Southeast European region was less than 20%. The variations in compressive strength and chloride transport coefficient were analysed experimentally and related to the pore structure and electrical conductivity. Compressive strength, chloride migration and diffusion coefficients, and bulk conductivity were determined using mortar samples, while the pore size distribution was determined by mercury intrusion porosimetry (MIP) on hardened cement paste after 7,28, and 90 days of curing. To understand the capillary absorption of these mixtures, sorptivity indices were measured after 28 and 90 days. The experimental characteristics of the pore size distribution, such as mean pore entry radius (r0.5), permeable porosity (P), capillary porosity (ɸ), and critical pore diameter (rc), were calculated using the cumulative data of the intruded volume as a function of pressure obtained by MIP. In addition, the extrusion-intrusion curve was used to calculate the pore entrapment fraction (α) and the degree of inter-connectivity of the pore structure. The evolution of pore structure parameters was monitored for up to 90 days and their effects on strength and chloride penetration were studied in detail. The results showed that all mixes (even those with low kaolinite content) can be used in high performance cement systems and the pore structure has a limited effect on chloride penetration.

Modelling chloride ingress into in‐service cracked reinforced concrete structures exposed to de‐icing salt environment and climate change: Part 1

Modelling chloride ingress into in‐service cracked reinforced concrete structures exposed to de‐icing salt environment and climate change: Part 1

Impact of fly ash production and sourcing changes on chemical and physical aspects of concrete durability

Changes in coal-fired power technology have recently been introduced, influencing emissions and efficiency, which may affect fly ash. Similarly, shortages of low lime fly ash, with power stations being taken out of service, mean recovery/processing of material from wet holding areas (e.g. stockpiles) is receiving attention. Previous research has considered the effect of these fly ashes on chloride ingress and carbonation of concrete. In the current study, chemical (sulfate attack and alkali-aggregate reaction (AAR)) and physical (freeze–thaw (salt) scaling and abrasion) processes causing concrete deterioration are investigated. These used laboratory tests and practical concrete mixes, with comparisons made against three reference fly ashes of different fineness, and data from earlier studies (late 1990 s/early 2000 s). The results indicate minor differences between fly ash concretes for sulfate attack and AAR, where small expansions were obtained. Although specific fly ash influences were not identifiable, air-entrained concretes gave acceptable freeze–thaw scaling performance (0.45 water/cement ratio), while abrasion generally followed concrete strength. Similar effects were found to the earlier studies. The changing technologies and wet storage may influence fly ash characteristics, however, they generally follow typical behaviour for the concrete properties examined and suggest continued suitability for use.