Chloride Penetration Resistance Of Concrete Research Articles

Mechanical Properties and Chloride Penetration Resistance of Concrete Combined with Ground Granulate Blast Furnace Slag and Macro Synthetic Fiber

Concrete with good mechanical properties and durability has always been a necessity in engineering. The addition of fibers and supplementary cementitious materials to concrete can enhance its mechanical and durability performance through a series of chemical and physical interactions. This study aims to investigate the effects of key parameters on the compressive strength, splitting tensile strength, and chloride penetration resistance of concrete combined with ground granulate blast furnace slag (GGBS) and macro polypropylene synthetic fiber (MSF). Based on the Taguchi method, a total of eighteen mixtures were evaluated, considering the effects of GGBS content, MSF content, water-to-binder (w/b) ratio, and chloride solution concentration on concrete properties. The results showed that the w/b ratio has a significant impact on the properties of concrete, which are enhanced by a decrease in w/b ratio. The GGBS content had little effect on the 28-day strength of concrete, which even decreased with a large GGBS content, but GGBS had a positive effect on the long-term strength of concrete. Moreover, the chloride penetration resistance of concrete was enhanced by an increase in the GGBS content. The MSF content had no obvious effects on the compressive strength and chloride penetration resistance of concrete, but it could enhance the splitting tensile strength to some extent, and this enhancement was more obvious over time. The chloride diffusion coefficient of concrete changed with the concentration of chloride solution, and the two increased simultaneously.

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.

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.

Experimental study on durability of basalt fiber concrete after elevated temperature

AbstractThe durability of concrete material after exposure to elevated temperatures is important for the serviceability prediction of concrete structures in a fire disaster scenario. Existing researches show that an appropriate amount of basalt fiber can significantly improve the splitting tensile strength and chloride penetration resistance of concrete. However, the mechanical properties of basalt fiber concrete after elevated temperatures and its durability properties are still not clear. In this paper, the mechanical properties, carbonization law, and chloride ion penetration law of ordinary concrete and basalt fiber concrete under high temperatures are studied. The concept of a burnt layer for concrete exposed to elevated temperatures is proposed, and the thickness of this burnt layer for concrete under different temperatures was measured. The results show that the addition of basalt fiber can inhibit the carbonization of concrete at elevated temperatures, diminish the thickness of the burnt layer, and significantly improve the chloride penetration resistance of concrete.

Study on the Durability of Concrete under an Underwater Coupling Environment

The durability of the concrete structure under the coupling effect of underwater corrosion particles has always been one of the hot issues at home and abroad. Aiming at the damage problem of the underground concrete structure in a marine and offshore chloride corrosion environment, based on the pile foundation engineering of the Coastal Industrial Park, the corrosion resistance test of pile foundation concrete is carried out. By preparing 7 kinds of pile foundation concrete samples with different mix proportions, the mechanical properties of concrete with different ages were analyzed under the coupling environment of groundwater. The chloride penetration resistance of concrete was analyzed by the RCM method, and the sulfate corrosion resistance was analyzed by the 17D accelerated simulation test. The test results show that with the decrease of the water-cement ratio and the increase of the cementitious material, the concrete damage is less and the durability is improved. It is suggested that the water-cement ratio of 0.34 and the cementitious material of 480 kg/m3 be selected for the preparation of the pile foundation concrete; when the content of fly ash is 15%, the antisulfuric acid corrosion ability of the concrete cementitious system can be enhanced and the concrete with 40% mineral powder has strong antichloride ion corrosion ability; the results show that the chloride diffusion coefficient of concrete samples with seven mix proportions is less than 6 ∗ 10–12 m2/s, which can meet the durability design requirements and reduce the damage of concrete. The sulfate corrosion resistance of concrete samples with high-efficiency additives is the best.

The Rapid Chloride Migration Test in Assessing the Chloride Penetration Resistance of Normal and Lightweight Concrete

Chloride-induced corrosion has been one of the main causes of reinforced concrete deterioration. One of the most used methods in assessing the chloride penetration resistance of concrete is the rapid chloride migration test (RCMT). This is an expeditious and simple method but may not be representative of the chloride transport behaviour of concrete in real environment. Other methods, like immersion (IT) and wetting–drying tests (WDT), allow for a more accurate approach to reality, but are laborious and very time-consuming. This paper aims to analyse the capacity of RCMT in assessing the chloride penetration resistance of common concrete produced with different types of aggregate (normal and lightweight) and paste composition (variable type of binder and water/binder ratio). To this end, the RCMT results were compared with those obtained from the same concretes under long-term IT and WDT. A reasonable correlation between the RCMT and diffusion tests was found, when slow-reactive supplementary materials or porous lightweight aggregates surrounded by weak pastes were not considered. A poorer correlation was found when concrete was exposed under wetting–drying conditions. Nevertheless, the RCMT was able to sort concretes in different classes of chloride penetration resistance under distinct exposure conditions, regardless of the type of aggregate and water/binder ratio.

Compressive Strength, Splitting Tensile Strength, and Chloride Penetration Resistance of Concrete with Supplementary Cementitious Materials

This article presents the outcomes of a study that examined the durability and mechanical characteristics of self-consolidating concrete (SCC) mix in which a percentage of the required ordinary Portland cement (OPC) was substituted with either fly ash or ground granulated blast furnace slag (GGBS). The first part of the study evaluates the chloride penetration resistance and compressive strength of SCC mixes in which OPC in a designed control mix was partially replaced in a series of mixes by fly ash in percentages ranging from 10% to 40%. It noted that replacing OPC with fly ash at each of the four percentages studies improved chloride resistance of concrete compared to the control mix made of 100% OPC as binder. The 40% fly ash mix was the best performer in terms of resistance to chloride migration in contrast with the 100% OPC mix. Samples prepared using the 40% fly ash mix SCC mixes had the lowest compressive strength after 7 days of moist curing. However, the 28-day compressive strength of 40% fly ash mix was a healthy 55.75 MPa, only slightly lower than the 100% OPC mix. Tests also showed that adding 2% or fewer basalt fibres to the SCC mix in which 40% of OPC improves concrete resistance to chloride migration in contrast with the 40% fly ash mix that didn’t contain basalt fibres. This paper also reports the relationship between splitting tensile strength and compressive strength of SCC mixes in which up to 80% of OPC was substituted with GGBS. A total of eight mixes were produced by varying the amounts of GGBS used to replace the OPC content of the control mix. The fresh properties were assessed through the flow test, visual stability index (VSI), and the T50. An empirical relationship was developed to predict the splitting tensile strength based on 28-day compressive strength, and its accuracy was evaluated in comparison to formulas in various design codes.

Effects of load-induced micro-cracks on chloride penetration resistance in different types of concrete

Chloride penetration resistance of concrete is one of the key parameters for the durability design of reinforced concrete structures located in chloride-bearing environments. In all the current available durability models, service life is evaluated considering concrete in uncracked conditions, which is rarely found in practice. This work investigates chloride penetration resistance of concrete in uncracked and micro-cracked configurations, evaluated in terms of chloride migration coefficient through non-steady state migration test (Rapid Chloride Migration test). Prismatic specimens were manufactured considering six different concrete types and two different times of curing. In micro-cracked configuration, cracks were obtained with a specifically developed loading procedure. Micro-cracks were characterized at the end of the exposure test, in terms of crack width at the exposed surface and crack depth. Results showed that cracks were 5–70 μm wide and up to 40 mm deep, always causing an increase in chloride penetration, that should be evaluated considering both crack width and crack depth, with respect to sound conditions. The effects on the chloride penetration seemed to be more pronounced on the more impervious concretes.

Durability of Sustainable Self-Consolidating Concrete

Supplementary cementitious materials such as fly ash, silica fume and ground granulated blast furnace slag (GGBS) have been used widely to partially replace cement in producing self-consolidating concrete (SCC). The production of cement is associated with emission of significant amounts of CO2 and increases the human footprint on the environment. Fly ash, silica fume, and GGBS are recycled industrial by-products that also impart favorable fresh and hardened properties on concrete. This study aims to assess the effect of the amounts of fly ash and silica fume on strength and chloride penetration resistance of concrete. Rapid Chloride Penetration Test (RCPT) was used to assess the ability of SCC to resist ingress of chlorides into concrete. SCC mixes with different dosages of fly ash and silica fume were developed and tested at different curing ages. Test results showed that replacing 20% of cement with fly ash produced the highest compressive strength of 67.96 MPa among all fly ash-cement binary mixes. Results also showed that replacing15% of cement with silica fume produced the highest compressive strength of 95.3 MPa among fly ash-cement binary mixes. Using fly ash and silica fume consistently increased the concrete resistance to chloride penetration at the early ages. Silica fume at all dosages results in low or very low levels of chloride penetration at all curing ages of concrete.

Effect of Superabsorbent Polymer on the Properties of Concrete.

Incorporating superabsorbent polymer (SAP), which has the abilities of absorption and desorption in concrete can achieve the effect of internal curing. The influences of the volume, particle size and ways of entrained water of SAP on the workability, compressive strength, shrinkage, carbonation resistance and chloride penetration resistance of concrete were analyzed through the macroscopic and microscopic test. The results show that pre-absorbed SAP can increase the slump of the mixture, but SAP without water absorption and pre-absorbed SAP with the deduction of internal curing water from mixing water can reduce the slump. The improvement effects of SAP on compressive strength of concrete increase gradually with the increase of age. Especially from 28 days, the compressive strength of concrete increases obviously. At later age, the compressive strengths of SAP concrete under natural curing environment exceed the strength of reference concrete under natural curing environment and nearly reach the strengths of reference concrete under standard curing environment. SAP effectively reduces the shrinkage of concrete, improves the concrete’s abilities of carbonation resistance and chloride penetration resistance. The microscopic test results show that SAP can effectively improve the micro structure and make the pore structure refined. When SAP is added into concrete, the gel pores and small capillary pores are increased, the size of big capillary pores and air pores are reduced.

Influence of iron mill scale additive on the physico-mechanical properties and chloride penetration resistance of concrete

Reinforced concrete structures are normally exposed to various aggressive environmental conditions; thus it is essential to protect the steel reinforcement from corrosion and the concrete from degradation. This experimental study is aimed at optimising the physico-mechanical properties of reinforced concrete by using iron mill scale as a replacement for cement. Reinforced cement mortars and concrete specimens with and without the addition of iron mill scale were partially immersed in 3·5% w/w sodium chloride solution for 17 months and 130 d, respectively. The mill scale was added to the aforementioned cementitious composites in proportions of 5% and 10% by weight of cement. Its effect on chloride penetration resistance was evaluated using various standardised and non-standardised experimental techniques. The results showed that the additive increased the resistance of reinforced cementitious composites to chloride penetration, reduced the corrosion of steel reinforcement and improved the compressive strength of concrete. Furthermore, iron mill scale decreased the concentration of chloride ions in cement mortars which were partially immersed in sodium chloride solution.

Effect of metakaolin on the chloride ingress properties of concrete

Research and practical experience have shown that partial replacement of cement by metakaolin improves concrete durability as a result of the refinement of the pore structure. While much research has been presented on concrete performance with metakaolin, it is scarce concerning the transport properties of chlorides in concrete with metakaolin, in natural conditions (i.e., un-accelerated). This study determines the chloride diffusion coefficients for several concretes with vary levels of cement replacement with metakaolin, and compares these results with chloride migration coefficients obtained from accelerated laboratory testing. In this study, two cement types (CEM I 42,5R and CEM IV/A 42,5) and two cement contents levels where used with metakaolin replacement levels varying from 10-20%. Concretes where tested for fresh properties, compressive strength, electrical resistivity, chloride ingress characteristics (natural diffusion and migration), and mercury intrusion porosimetry. The results show improved strength, durability properties and chloride penetration resistance of concretes with metakaolin. Furthermore, the use of metakaolin in fly ash concrete improves the early age performance of the concrete (<90 days), counteracting the delay in strength and durability gain typically associated with fly ash concrete. The results obtained from this study fulfil the lack of critical input for service life design models of reinforced concrete structures in chloride environments, with emphasis on concretes with metakaolin replacement.

Evaluation of chloride-penetration resistance of metakaolin concrete by means of a diffusion – Binding model and of the k-value concept

In this paper, the effect of the addition of metakaolin on chloride-penetration resistance of concrete is investigated. Greek kaolin thermally treated at defined conditions and a commercial metakaolin were used. Eight mixture proportions were used to produce high performance concrete, where metakaolin replaced either cement or sand in percentages 10% or 20% by weight of the control cement content. The specimens were placed in a NaCl solution for 90 days and the concentration of total and free (unbound) chloride was determined. The chloride penetration was studied by means of a fundamental model taking into account diffusion and binding (adsorption & desorption) processes. The efficiency factors (k-values) for the studied metakaolins were determined. Both metakaolins present a considerable chloride-penetration resistance, depending on active silica and alumina contents, and their addition significantly decreases chloride penetration leading to improved concrete durability.

The performance of concrete exposed to marine environments: Predictive modelling and use of laboratory/on site test methods

This paper reports an approach by which laboratory based testing and numerical modelling can be combined to predict the long term performance of a range of concretes exposed to marine environments. Firstly, a critical review of the test methods for assessing the chloride penetration resistance of concrete is given. The repeatability of the different test results is also included. In addition to the test methods, a numerical simulation model is used to explore the test data further to obtain long-term chloride ingress trends. The combined use of testing and modelling is validated with the help of long-term chloride ingress data from a North Sea exposure site. In summary, the paper outlines a methodology for determining the long term performance of concrete in marine environments.

Study on Chloride Penetration Resistance of High Volume Slag Powder Concrete

The influences of Portland cement substituted by slag powder in a high proportion (50% and 70%) on the chloride penetration resistance of concrete were studied. The results show that: the penetrability of Portland cement concrete reduced by one grade if 0.5% water reducer is added, but the water binder ratio is not the decisive factor for the permeability. There is a negative correlation between 6h electric flux and compressive strength only when concrete with same cementing materials. High volume slag powder concrete has excellent resistance to chloride ion permeability, which declines further with the increment of slag powder quantity added, the permeability coefficient of the concrete with 50% and 70% content of slag powder is as low as 27.8%~32.3% that of Portland cement concrete.

Durability of Sugar Cane Bagasse Ash (SCBA) Concrete towards Chloride Ion Penetration

In this study, the effect of sugar cane bagasse ash (SCBA) on chloride penetration resistance of concrete was investigated. 100-mm side cubes were cast and cured in water for 28 days followed by six months curing in 4% NaCl solution. The resistance to chloride penetration was assessed by measuring the chloride penetration depth, weight loss, compressive strength loss and bond strength loss. Chloride penetration depth was measured using AgNO3–based method. It was obtained that inclusion of SCBA in concrete significantly reduced the chloride penetration depth, weight loss, compressive strength loss and bond loss that was attributed to the fine particles of SCBA that filled up the pores and prevented the chloride ingress in the concrete.

Influence of sodium aluminate on cement hydration and concrete properties

The influences of sodium aluminate (SA) on cement hydration were studied. Heat evolution of cement pastes with and without SA was monitored by a differential scanning calorimeter (DSC). Hydration products were identified using scanning electron microscope (SEM), X-ray diffraction (XRD), thermal analysis (TG–DSC), and mass spectrum (MS). Pore structures of cement pastes were analyzed using nitrogen absorption method. Concrete strength and chloride penetration resistance were also evaluated. The mechanisms by which SA contributes to cement hydration and microstructure development were explored. The results indicate that addition of SA resulted in changed calcium sulfoaluminate morphology, form acicular AFt to tabular AFm. Adding of SA increased the volume of small capillary pores (5–30nm) and reduced the volume of larger pores (>30nm). Cement setting time reduced significantly as SA addition reached up to 4%. 1.5% SA addition can enhance concrete strength at early age but reduce it at later age. Addition of SA also improved chloride penetration resistance of concrete.

Developing Structural Lightweight Concrete Using Volcanic Scoria Available in Saudi Arabia

This experimental investigation explored the feasibility of using volcanic scoria rocks located in the north-western region of Saudi Arabia for producing structural lightweight concretes (SLWCs). Several concrete mixes were designed, produced, and tested, to study the effects of various material and composition parameters on workability, unit weight, strength properties, and chloride penetration resistance of concrete. Test results indicated that the volcanic scoria could be used as coarse and fine aggregates for producing a series of lightweight concretes exhibiting strengths in the structural range. The SLWCs developed had a 7-day compressive strength of about 53–76 % of the 28-day compressive strength, a 28-day splitting tensile strength of about 9–11 % of the compressive strength, a 28-day flexural strength of about 10–15 % of compressive strength, and Poisson’s ratio of about 0.19–0.21. The modulus of elasticity could be expressed with a formula similar to the one proposed by ACI 318-08. The stress–strain diagrams of the SLWCs produced were comparable to those for normal-weight concrete (NWC) with larger strain capacity at peak stress ranging from 2,600 to 3,300 μ compared to 2,000 μ for NWC. The 28-day chloride penetration resistance of the SLWCs developed falls within low to moderate range according to the criteria of ASTM C 1202.

Chloride penetration resistance of concrete containing ground fly ash, bottom ash and rice husk ash

This research presents the effect of various ground pozzolanic materials in blended cement concrete on the strength and chloride penetration resistance. An experimental investigation dealing with concrete incorporating ground fly ash (GFA), ground bottom ash (GBA) and ground rice husk ash (GRHA). The concretes were mixed by replacing each pozzolan to Ordinary Portland cement at levels of 0%, 10%, 20% and 40% by weight of binder. Three different water to cement ratios (0.35, 0.48 and 0.62) were used and type F superplasticizer was added to keep the required slump. Compressive strength and chloride permeability were determined at the ages of 28, 60, and 90 days. Furthermore, using this experimental database, linear and nonlinear multiple regression techniques were developed to construct a mathematical model of chloride permeability in concretes. Experimental results indicated that the incorporation of GFA, GBA and GRHA as a partial cement replacement significantly improved compressive strength and chloride penetration resistance. The chloride penetration of blended concrete continuously decreases with an increase in pozzolan content up to 40% of cement replacement and yields the highest reduction in the chloride permeability. Compressive strength of concretes incorporating with these pozzolans was obviously higher than those of the control concretes at all ages. In addition, the nonlinear technique gives a higher degree of accuracy than the linear regression based on statistical parameters and provides fairly reasonable absolute fraction of variance (<TEX>$R^2$</TEX>) of 0.974 and 0.960 for the charge passed and chloride penetration depth, respectively.

Effect of chemical composition of slag on chloride penetration resistance of concrete

Three ground granulated slags (FeMn arc-furnace (GGAS), Corex (GGCS) and blastfurnace (GGBS) slags) of varying chemical composition, and from different sources were used to make concretes using two w/b ratios (0.40 and 0.60) and three slag replacement levels (20%, 35% and 50%). The effect of chemical composition and replacement level of slags on the chloride penetration resistance of the concretes was assessed using the chloride conductivity test. The results showed that the chloride penetration resistance of concrete increases with decreasing w/b ratio and increasing slag replacement level. In the GGAS concretes, despite having relatively low SiO2 and high MgO content, its significantly high Mn2O3 and low Al2O3 content was found to have a negative effect on the chloride penetration resistance of the concrete. The significantly high chloride penetration resistance of GGCS concretes was partly attributed to both its high CaO content and particle fineness. Only GGCS concretes showed a trend of increasing chloride penetration resistance with increased particle fineness; GGBS and GGAS concretes did not show any trend between particle fineness and chloride penetration resistance. The slag activity index was found to be a better indicator of chloride penetration resistance in concrete than the slag hydraulic index.