Service Life Of Concrete Structures Research Articles

Effect of Amount of Fibre and Damage Level on Service Life of SFR Recycled Concrete in Aggressive Environment

The paper presents a numerical calculation of the service life of concrete structures considering the effect of chlorides in the case of the material properties of structural lightweight waste aggregate concrete. Different amounts of fibres (0.0%, 1.0%, and 1.5%) and different values of compressive preloading (0%, 50%, and 100% of the ultimate strength capacity-USC) were considered. The subject of the research was the comparison of the influence of the constant diffusion coefficient and the time-dependent diffusion coefficient regarding the service life of the selected structure. Nine groups of material characteristics in combination with two numerical models are compared. A time-dependent diffusion coefficient and maturation coefficient, which were determined based on long-term monitoring (up to 461 days), were accepted for the numerical modelling. Thanks to time-dependent parameters, it is possible to observe the results of the theoretical service life of the structure and the influence of the mentioned factors. The analysed structure can be considered as the upper layer of an industrial floor in a chemical plant. It is important to determine the theoretical service life at which the structure shall be inspected or replaced. The results, in general, show that a higher amount of fibres reduces the service life as well as the preloading of the structure. An exception was a mixture with 1% of fibre loaded to 50% USC, which shows a lower diffusion coefficient than the specimens without preloading.

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.

Removal of 80-Year-Old Gravity Dam and Mechanical Properties of Aging Dam Concrete

Service life of concrete structures depends on the structure design, construction management, and the durability of concrete in aggressive exposure conditions. The old Fengman Dam is an 80-year-old gravity dam, and due to design and construction defects, it has worked with leakage and freeze-thawing problems for more than 70 years. In this study, the durability of the dam concrete is investigated, and a coring program is conducted. The static and dynamic mechanical properties of aging dam concrete (ADC) are tested and the micropores are also observed by scanning electron microscope. Young laboratory concrete (LC) with similar compression strength of the ADC is prepared for comparison. The experimental results show that despite the harsh working conditions, the ADC exhibits good mechanical characteristics in terms of static and dynamic strength and microporosity of interfacial transition zones. The dam concrete is proved to exhibit good durability, and the service life of old Fengman Dam was limited by the poor construction management.

Study on the Influence of Three Factors on Mass Loss and Surface Fractal Dimension of Concrete in Sulfuric Acid Environments

When exposed to sulfuric acid environments, the service life of concrete structures would be reduced due to the high alkalinity of concrete. The influence of three factors including water/cement ratio, the pH value of the solution, and the chemical composition of the aggregate on the resistance of concrete subjected to sulfuric acid has been widely investigated by previous researchers. This paper aims to investigate the influence of these three factors on the durability evaluation indicators including mass loss and surface fractal dimension through orthogonal experiments, which has been reported rarely in previous research. Four combinations of coarse and fine aggregate including gravel and river sand, gravel and crushed marble sand, crushed marble stone and river sand, and crushed marble stone and marble sand were adopted, and three water/cement ratios including 0.35, 0.45, and 0.55 were selected, and the sulfuric acid solution pH values 0.95, 2, and 4 were chosen in this paper. The results showed that the larger the water/cement ratio, the smaller the mass loss and the surface fractal dimension of the specimens, and with the decrease of the pH value of the sulfuric acid solution, the mass loss and the surface fractal dimension of the specimens would be increased. The concrete specimen containing gravel and river sand had the greatest surface fractal dimension and greatest mass loss, while the concrete specimen containing crushed marble sand had a smaller surface fractal dimension and a smaller mass loss. The dominant and secondary order of three factors on mass loss and surface fractal dimension of concrete subjected to sulfuric acid was the pH value of the solution > the chemical composition of the aggregate > the water/cement ratio.

Experimental study on durability of fiber reinforced concrete: Effect of cellulose fiber, polyvinyl alcohol fiber and polyolefin fiber

The durability of concrete reinforced by cellulose fiber (CTF), polyvinyl alcohol fiber (PF) and polyolefin fiber (VS) is comprehensively studied in this paper. Relevant durability tests are conducted to explore the effect of different fiber types and dosages on durability performance demonstrated in the resistance to drying shrinkage, water permeability, crack, carbonization and chloride ion penetration. Besides single fiber reinforced concrete, synergistic effect of hybrid fibers on durability is also studied, and the service life of fiber reinforced concrete in carbonization environment and chloride ion corrosive environment is further predicted. In addition, the structure of fiber reinforced concrete is analyzed from the micro perspective by using the optical and electron microscope. The results showed that: (1) The addition of CTF can effectively enhance the all five aspects of durability performance, including the resistance to drying shrinkage, water permeability, crack, carbonization and chloride ion penetration. The addition of PF can enhance the durability properties except for chloride ion penetration resistance. Generally, though with few exceptions, the increased dosage of CTF or PF would improve the strengthening effect on the durability of single fiber reinforced concrete. The addition of VS can either enhance or weaken the above five aspects of durability properties, and its effect varies much with the fiber dosage. (2) Hybrid fiber is found to have a positive synergistic effect and enhance the above five aspects of durability properties of concrete. The concrete reinforced with the hybrid fiber combination of 1.2 kg/m3 CTF, 2.0 kg/m3 PF and 2.0 kg/m3 VS may achieve the optimal durability properties. (3) CTF, PF and VS, especially their hybrid combinations, are found to effectively prolong the service life of concrete structure in the carbonization and chloride ion corrosive environment. The research findings obtained in this paper can supplement the study on the durability of fiber reinforced concrete, and provide suggestions for suitable fiber type and dosage selection in actual engineering designs of fiber reinforced concrete.

Residual strength of concrete subjected to fatigue based on machine learning technique

AbstractThis study utilizes the machine learning technique to solve the complex fatigue problem of concrete materials. To this end, several learning algorithms were addressed including the random forest (RF), support vector machine (SVM), and artificial neural networks (ANNs) models. Extensive experimental data were collected from literature to train the machine learning models for estimating the maximum number of cycles at failure (i.e., the so‐called fatigue life). A machine learning model providing the best correlation was chosen through verifications. On this basis, a strength degradation model of concrete under fatigue loading was finally proposed to evaluate the residual strength of concrete after fatigue damage, which is a key factor in determining the remaining service life of concrete structures.

Study on damage rules on concrete under corrosion of freeze-thaw and saline solution

Coastal concrete in cold area is subjected to chemical attacks and freeze-thaw cycles, which both considerably decrease the service life of concrete structures. In this research, we mainly analyzed and assessed the durability of concrete under the coupling action of chlorine ion, sulfate ion and freeze-thaw cycles by designing the orthogonal experiment. In the process of conducting the experiment, the relative dynamic elastic modulus, the mass loss rate, the thickness of damage layer, the velocity of ultrasonic wave and other damage indexes which reflect the damage law of concrete under the coupling action were measured or calculated and the range analysis and variance analysis were used to study the influence degree of different factors. Then the damage evolution equation and the damage constitutive model of concrete were established on the basis of the analysis for damage indexes and the results of mechanical tests. The comparison results showed that the theoretical values well agreed with the experimental ones and the damage model acquired can potentially be used to predict the damage degree of concrete under the coupling effect of chlorine ion, sulfate ion and freeze-thaw cycles.

Exogenous healing in concrete with pH-sustained internal carbonation

In this study, experimental investigations were conducted on enhancing the crack-healing potential of concrete using the internal carbonation process. The objective is to overcome one major limitation of autogenous healing (limited carbonation) by using Sodium Carbonate (Na2CO3) solution as a healing agent. To replicate the different types of damages and internal cracking that could arise during the service life of concrete structures, the effects of drying shrinkage and mechanical stresses on the crack-healing proclivity of cement-based materials were explored. A novel technique to measure crack-healing under constantly applied stress is also introduced for better assessment of healing in real-world situations. Results show a significant improvement in healing by using 0.95 M Na2CO3 solution over plain water. Moreover, permeability observations under stress revealed that the potential for healing by the proposed mechanism is strongly dependant on the stress level in samples. In the later part of the paper, Service Life Predictions were also undertaken by utilizing chloride ion diffusion coefficients extracted from the measured permeability coefficients and service life models available in the literature. Results from comparison of predicted service life indicate that at least in qualitative terms, healing with internal carbonation using the Na2CO3 solution led to an increase in the service life of concrete composites.

Comparative analysis of concrete behaviour under compressive creep and cyclic loading

The expected deformations during service life of concrete structures are described using creep models, developed for constant loading. Thereby, the effect of cyclic loading superimposed to constant loading, ubiquitously observed in practice, is excluded. Thus, the strain development due to static creep and cyclic loading of a normal strength concrete are comparatively investigated considering the influence of the minimum stress level and the load frequency. The results show that cyclic deformations are significantly higher than creep strains despite similar mean stress levels and are considerably affected by the influences. Therefore, for modelling cyclic deformation developments these influences must be considered.

Investigation of the effects of corrosion on bond strength of steel in concrete using neural network

Corrosion of steel reinforcement due to hostile environments is regarded as one vital structural health concerns in concrete structures. Specifically, the development of corrosion affects the necessary bond strength of rebar in concrete contributing to the loss of resilience and possible structural failures. It is thus essential to understand the effects of corrosion on bond strength so that remedial measures can be done on existing and deteriorating RC structures. Hence, this study investigated through laboratory experiments and Artificial Neural Network (ANN) modeling the effects of corrosion on bond strength. Experimental results showed that at small amounts of corrosion less than 0.27%, the bond strength was observed to increase. At these levels, the amounts of corrosion products were sufficient enough to expand freely through the permeable structure of concrete and occupy the pore spaces. Beyond this level, however, the bond strength of concrete deteriorated significantly. There was an observed average decrease of 1.391 MPa in the bond strength values for every percent increase in the amount of corrosion. The expansive and progressive internal radial stress due to corrosion resulted to the development of internal and surface cracks in concrete. In the parametric investigation of the derived ANN model, the bond strength was also observed to decline continuously with the growth of corrosion derivatives as represented by the relative magnitudes of the ultrasonic pulse velocity (UPV). The prediction results of the model can be utilized as basis for design and select appropriate mitigating measures to prolong the service life of concrete structures.

A Numerical Study on Chloride Diffusion in Cracked Concrete

The cracks in concrete are a fast transport path for chlorides and influence the service life of concrete structures in chloride environments. This study aimed to reveal the effect of crack geometry on chloride diffusion in cracked concrete. The chloride diffusion process in cracked concrete was simulated with the finite difference method by solving Fick’s law. The results showed that the apparent chloride diffusivity was lower in more tortuous cracks, and the cracks with more narrow points also showed lower apparent chloride diffusivity. For tortuous cracks, a higher crack width meant relatively more straight cracks, and consequently, higher apparent chloride diffusivity, while a lower crack width resulted in more tortuous cracks and lower apparent chloride diffusivity. The crack depth showed a more significant influence on the chloride penetration depth in cracked concrete than crack geometry did. Compared with rectangular and V-shaped cracks, the chloride diffusion process in cracked concrete with a tortuous crack was slower at the early immersion age. At the same crack depth, the crack geometry showed a marginal influence on the chloride penetration depth in cracked concrete during long-term immersion.

Experimental study on sulfate erosion resistance of nano-CaCO3 modified concrete

In the saline soil environment of western China, salts can corrode ordinary cement concrete seriously, and the durability of concrete structure deteriorates gradually until it fails. This impedes the application of ordinary Portland cement concrete in this area. Aiming at the problem of the short service life of concrete in the harsh environment of western China, this study examines the performance of nano-CaCO3 modified concrete in a sulfate environment. The durability of the concrete was evaluated by the apparent phenomena on the relative quality evaluation parameter, the relative dynamic elastic modulus evaluation parameter, and the comprehensive damage evaluation parameter. The microstructure of corroded products was investigated using scanning electron microscopy to reveal the deterioration mechanism. The results show that the addition of 1% nano-CaCO3 can enhance the resistance of concrete to sulfate corrosion, and the service life of concrete structures will increase significantly.

A simple method to create hydrophobic mortar using bacteria grown in liquid cultures

The ingress of water-soluble aggressive species is a major cause to the reduced service life of concrete structures. Bulk modification by adding hydrophobic agents in the cementitious materials is commonly applied to reduce water penetration into the concrete matrix. However, conventional hydrophobic modifications of concrete are associated with several unresolved major drawbacks such as high cost and toxicity. Here, we investigate the impact of safe and easy-to-culture bacteria on the hydrophobic properties of concrete. We demonstrate that hydrophobic concrete can be conveniently created by using the liquid culture of bacteria without the need of growing biofilms as suggested by previous research, even with a strain that does not present innate hydrophobicity. These key findings greatly improve the feasibility for the large-scale application of water resistance cementitious materials. Scanning electron microscopy and X-ray diffraction analyses indicated higher levels of micro-calcite formations with the increased addition of bacteria. These micro-calcite structures account for the dramatic increase in surface roughness which leads to elevated hydrophobic properties of the hybrid concrete. This phenomenon is reminiscent of the “lotus-leaf effect”, with ultrahydrophobicity arising from the nano- and microscopic topologies of surfaces. Bacteria-modified cement presents distinct heat-flow profiles during hydration consistent with the increased calcite formation. Taken together, this research gives unprecedented mechanistic insight into the design of microbial-modified concrete with hydrophobic properties particularly useful in floating and offshore structures. Given the large repertoire of bacteria still to be used, our work sets the stage for the future design of microbial-based hydrophobic concrete that can be tailored with additional functions such as self-healing and odor removal.

Thermodynamic Study of Cement Paste under Sulfate Attack: A Review

Sulfate attack reduces the service life of concrete structures, which isn't possible to repair simply. Implementation of many factors influencing the sulfate resistance, sample scaling, and results in the least possible time is some problems of experimental studies. Therefore, numerical simulations, as well as the new methods along with experimental studies, have been led to better evaluation of sulfate attack within a shorter time and at a lower cost. In the present study, the effective factors, causes, and mechanisms of sulfate attack, examples of this phenomenon in real projects, and the previous studies in this regard, in particular, the development of the thermodynamic study of cement under sulfate attack as a fast and inexpensive solution have been reviewed. The present investigation is divided into three parts, first the sulfate attack mechanism, second the factors influencing phases containing sulfate formation, and third a review of the methods and results of the studies, focusing on the development of thermodynamic models in cement sulfate attack especially. Finally, the results of the studies show that common experimental methods related to concrete sulfate resistance evaluation can't always simulate what is actually happening; subsequently, the results of experimental studies and real cases are sometimes different. So, numerical models, in particular, thermodynamic simulation, either alone or in combination with experimental studies, can be a desirable solution for enhancing the ability to predict engineering behavior of concrete structures in the sulfate environment. Subsequently, it results in making better decisions to tackle and prevent deterioration caused by sulfate attack.

Effect of water‐to‐cement ratio on service life of reinforced concrete structures in chloride environment

AbstractCracking of concrete induced by rebar corrosion is a main cause for deterioration of reinforced concrete structures especially for those exposed to chloride environment. In all of the parameters influencing the service life of concrete structures, water‐to‐cement ratio is a very important one for it determines the resistance of concrete against chloride aggression and corrosion‐induced damage. In this paper, the parameters in corrosion process influenced by water‐to‐cement ratio of concrete (w/c) are screened all‐round which include concrete tensile strength ft, elastic modulus Ec, porous zone thickness δ0, corrosion current density icorr, critical chloride content Ccr, and chloride diffusion coefficient Dcl. The influences of w/c on the chloride penetration stage and the corrosion damage stage are studied. The first stage is expressed by Fick's second law, and the second stage is calculated using a commonly used analytical model, i.e. the thick‐walled cylinder model. It is found that with the increase of w/c, the change of some parameters (ft↑, Ccr↑, Dcl↓, icorr↓) will induce increase of the service life, while the change of the others (Ec↑, δ0↓) will induce decrease of the service life. The diffusion stage and damage stage both shorten with the increase of w/c, and thus the total service life decreases with the increase of w/c. These results show that the increase of w/c presents a negative effect on the service life of concrete structures in total. In addition, with the increase of w/c, the service life for various concrete cover thicknesses and rebar diameters decrease in a similar tendency. For probability analyses, it is found that the probability density curves under different w/c are almost symmetric but show a little left‐skewed, and the total service life for various w/c fluctuates about 0.6 to 1.0 year.

Comparison of Microbially Induced Healing Solutions for Crack Repairs of Cement-Based Infrastructure

Reinforced concrete crack repair and maintenance costs are around 84% to 125% higher than construction costs, which emphasises the need to increase the infrastructure service life. Prolongation of the designed service life of concrete structures can have significant economic and ecological benefits by minimising the maintenance actions and related increase of carbon and energy expenditure, making it more sustainable. Different mechanisms such as diffusion, permeation and capillary action are responsible for the transport of fluids inside the concrete, which can impact on the structure service life. This paper presents data on microbially induced repair and self-healing solutions for cementitious materials available in the contemporary literature and compares results of compressive strength test and capillary water absorption test, which are relevant to their sealing and mechanical characteristics. The results of the repair and self-healing solutions (relative to unassisted recovery processes) were “normalized.” Externally applied bacteria-based solutions can improve the compressive strength of cementitious materials from 13% to 27%. The internal solution based solely on bacterial suspension had 19% improvement efficacy. Results also show that “hybrid” solutions, based on both bio-based and non-bio-based components, whether externally or internally applied, have the potential for best repair results, synergistically combining their benefits.

Mechanical Performance of Recycled Aggregate Concrete Containing Lathe Waste Steel Fibre

The increasing demand, diminishing supplies, and growing pressure on natural resources have necessitated recycling and reusing waste. Several kinds of research have been done on the reuse and recycling of debris from building projects. Thus, with a view to the reuse of waste materials, the elimination of environmental contamination, the reduction of overhead costs of concrete, and the extension of the service life of concrete structures, this research aimed to study the feasibility of utilizing recycled concrete aggregate (RCA) with constant inclusion of waste steel fibre (LWSF) in concrete by evaluating its workability, compressive and splitting tensile strengths. A concrete mix ratio of 1:2:4 by weight of cement, sand, and granite was adopted with a water-cement ratio of 0.45. Five different concrete mixes were prepared in this study; one normal aggregate concrete (NAC) and four (4) other mixes with 25%, 50%, 75%, and 100% recycled aggregate content with a constant 1.5% addition of LWSF. The result of workability shows a reduction with an increase in the percentage replacement level. The recycled aggregate concrete (RAC) was characterized by lower compressive strength as compared with the NAC. When the replacement ratio increased from 25% to 50%, a significant reduction of about 14% and 30% were observed in the compressive strength at 7-days, but at 28-days slight increase in the compressive strength was observed. Also, a decrease in splitting tensile strength as the percentage replacement of crushed granite (CG) with RCA is increased was observed. Overall, the findings showed that the RAC-containing LWSF is environmentally sustainable and would significantly reduce the global greenhouse impact and building materials' overall quality.
 Keywords: Recycled concrete, lathe waste, steel fibre, compressive strength, tensile strength

The role of bacterially induced calcite precipitation in self-healing of cement paste

Self-healing processes in cementitious materials have been intensively studied in recent years. They present a promising way to increase the durability of concrete and extend the service life of concrete structures, thus mitigating the impacts of the construction industry on public budgets and the environment. The role of bacterially induced calcite precipitation (BICP), the basis of one of the processes, is not fully understood yet, even though many researchers have reported improved mechanical properties or water tightness of cracked cementitious composites self-healed in the presence of bacteria. Therefore, the authors of this paper are focused on detailed characterization of BICP with the purpose of determining the direct impact of bacteria on the self-healing in cement composites. Three different bacterial strains, namely Sporosarcina pasteurii (SP), Bacillus cohnii (BC) and Bacillus pseudofirmus (BP) were studied. Their viability and metabolic activity in optimal and sub-optimal conditions were compared. Several analytical methods (XRF, TGA, TCD, FTIR) were used to characterize the attainable BICP depending on the particular strains. BP proved to be the most suitable bacterium, showing excellent viability and sufficient calcite production, even in sub-optimal conditions (10 °C temperature). Microscopic analysis of the self-healing products in artificially cracked cement paste showed that the application of BP with precipitation media lead to complete sealing of the crack by very dense calcite crystals (less than 1 μm), while porous structure of larger crystals (up to 30 μm) was formed in reference samples not treated with the bacteria, where only spontaneously induced calcite precipitation (SICP) occurred. As a result, it was proved that the bacteria directly contribute to the self-healing of cementitious materials and that BICP leads to the formation of a superior crack-sealing material.

High-Durability Concrete with Supplementary Cementitious Admixtures Used in Corrosive Environments

Durability of concrete is of great significance to prolong the service life of concrete structures in corrosive environments. Aiming at the economical and environment-friendly production of concrete by comprehensive utilization of the supplementary cementitious materials made of industrial byproducts, the resistances to chloride penetration, sulfate attack, and frost of high-performance concrete were studied in this paper. Fifteen concretes were designed at different water–binder ratio with the changes of contents of fly ash (FA), silica fume (SF), ground granulated blast-furnace slag (GGBS), and admixture of sulfate corrosion-resistance (AS). The compressive strength, the total electric flux of chloride penetrability, the sulfate resistance coefficient, and the indices of freezing and thawing were measured. Results indicate that, depending on the chemical composition, fineness, and pozzolanic activity, the supplementary cementitious admixtures had different effects on the compressive strength and the durability of concrete; despite having a higher fineness and pozzolanic activity, the GGBS gave out a negative effect on concrete due to a similar chemical composition with cement; the SF and FA presented beneficial effects on concrete whether they were used singly with GGBS or jointly with GGBS; the AS improved the compressive strength and the sulfate corrosion resistance of concrete. In general, the grade of durability was positively related to the compressive strength of concrete. Except for the concretes admixed only with GGBS or with GGBS and FA, others had super durability with the compressive strength varying from 70 MPa to 113 MPa. The concretes with water to binder ratio of 0.29 and total binders of 500 kg/m3 admixed with 7% FA + 8% SF + 8% GGBS or 7% FA + 8% SF + 8% GGBS + (10~12)% AS presented the highest grades of resistances specified in China codes to chloride penetration, sulfate corrosion, and frost, while the compressive strength was about 100 MPa.

Performance test on resistance to chloride ion corrosion in concrete structure added with special protection in road and bridge engineering

In view of the intrusion of seawater into concrete structures, a large number of harmful substances, especially chloride ions, can be brought in, which can significantly shorten the actual service life of concrete structures, resulting in serious waste of resources. In this paper, the chloride ion accelerated corrosion test on the concrete structure of road and bridge engineering is carried out to test the chloride ion concentration in different depths of concrete with special protection and without special protection at different corrosion times, and the effect of special protection is studied to study the diffusion coefficient and chloride ion concentration on the concrete surface of road and bridge engineering. The test results show that the diffusion coefficient of chloride ion in concrete can be reduced by 31.3% and the concentration of chloride ion on concrete surface can be reduced by 22.67% by special protective measures.