Service Life Of Concrete Research Articles

Research on the carbonation resistance of concretes containing dolomite powder

This study focused on the carbonation resistance of concretes incorporating dolomite powder with water–binder ratio (w/b) of 0.55 and 0.36. The micro-morphology, micro-pore structure and carbonation depth of cement-based materials incorporating dolomite powder were investigated by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and carbonization test box. The 28-day carbonation depth of concretes with a w/b of 0.55 in the case of dolomite powder at 50 wt% replacement level decreased by 39.62% compared with that of pure concretes. The carbonation resistance of concretes was improved with increasing dolomite powder dosage due to the fact that dolomite powder had the pore refinement efficiency on the carbonated cement pastes. The service life of concretes with a w/b of 0.55 incorporating dolomite powder under natural carbonation condition was obtained based on Alekseyev’s carbonation correction model. The durability life of concrete structure with a w/b of 0.55 was prolonged with the addition of dolomite powder. After carbonation for 28 days, concretes with a w/b of 0.36 were hardly affected by carbonation corrosion. The pore structure of concretes with a w/b of 0.36 became dense, inhibiting the penetration of CO2 into the concretes due to a lower water–binder ratio.

On the implementation of the interpretable data-intelligence model for designing service life of structural concrete in a marine environment

Modeling the durability design of reinforced concrete structures is a particularly crucial challenge for identifying the behavior of marine concrete. In this research, novel interpretable equation-based models based on Fick's second law of diffusion for designing the service life of structural concrete were presented. To do so, a Machine Learning (ML) approach based on linear and non-linear methods including Multivariate Adaptive Regression Splines (MARS), Gene Expression Programming (GEP), and M5p Model Tree (MT) was performed to predict the apparent surface chloride concentration (Cs) in the zones of the marine environment. A comprehensive database is comprising of 642 field exposure experimental and environmental records was utilized to develop ML methods. The proposed ML models were investigated in terms of performance evaluation, error measurements, and visual consideration, MARS model (r=0.890,WI=93.9%andRMSE=0.804%bindercontent, (tidal zone) and r=0.901,WI=93.5%andRMSE=0.818%bindercontent (splash zone) and r=0.875,WI=86.8%andRMSE=0.883%bindercontent (submerged zone)) outperformed the proposed GEP, MT and empirical equations. Furthermore, simulation of Monte-Carlo analysis was extended to verify the proposed ML predictive models. Evaluation of the sensitivity analysis presented that the water to binder ratio, annual mean temperature, and exposure time were the most influential factors in predicting the Cs of reinforced concrete structures. Also, a parametric assessment has been performed for the presentation of the robustness of the proposed ML model. The modeling results presented new insight into the designing of the service life of reinforced concrete with superiority promotion of ML methods.

Microscopic modelling of gas diffusivity in unsaturated cementitious materials considering multiple diffusion regimes

Common degradations of concrete including reinforcement corrosion and carbonation are highly associated with the transport of aggressive gases. However, it is still challenging to accurately understand the gas diffusion behaviour and determine the gas diffusivity in unsaturated cementitious materials. This study proposes a pore-scale model for simulating gas diffusivity in unsaturated cement paste covering multiple gas diffusion mechanisms. The representative volume elements of colloidal calcium silicate hydrate and heterogeneous cement paste with various water saturation degrees are established, capturing the structural attributes of hierarchical cement paste and water-gas distribution with minimum surface energy. A finite difference model for diffusion considering Knudsen effect and molecular diffusion is developed to simulate the diffusion process of various gases through partially saturated cement pastes with different pore structures. Results indicate that gas diffusivity decreases with the increasing water saturation level, the evolution of which can be divided into stable, decreasing and non-diffusive stages. The gas diffusion in partially saturated cement paste is highly dependent on the pore structure and diffusive gas type. The results obtained from this study are expected to provide a deeper insight into the solution of diffusion-related durability problems and the prediction of service life of concrete.

Utilisation of sea sand as partial replacement of fines in resin bonded cement concrete

The usage of aggregates has caused serious ecological problems leading to the requirement of an alternative material to meet the demand. The alternative construction material for the upcoming graduates thus chosen for replacing cement and aggregates should not only meet the design and strength requirements but also the ecological criteria. The present research work tries to improve the service life of sea sand concrete by using them in combination with epoxy resin. The scope of the work revolves around the extended to earlier assessment of the properties of concrete manufactured using sea sand as replacement for natural river sand upto 50% and 12% epoxy resin as partial substitute for cement.

Mechanical Properties and Micromorphology of Calcium Oxide Expansion Agent on River Sand/Machine‐Made Sand Concrete

Freeze‐thaw damage is one of the main factors affecting the service life and durability of concrete. Optimizing the microscopic pore distribution of concrete is an effective measure to improve its frost resistance. This paper takes mixed sand (machine‐made sand + river sand) concrete as the research object and analyzes the influence mechanism of different content of CaO expansion agent on the physical and mechanical properties and frost resistance of mixed sand concrete. Concrete samples with different calcium oxide contents (0%, 6%, 8%, and 10%) were prepared by mass substitution with fly ash. Early air content, slump, compressive strength testing, and other analysis methods are used to determine the physical and mechanical properties of river sand‐manufactured sand concrete with different calcium oxide expansion agent blending ratios. Freeze‐thaw cycles were observed under X‐ray computed tomography, SEM, and EDS to explore the mechanical properties, porosity, and microstructures of the samples. The concrete air content increases, the porosity first decreases and then increases, and its compressive strength decreases as the mixing ratio of calcium oxide expansion agent increases, but the mixing ratio has little effect on the slump. When the content of calcium oxide in concrete is higher than 8%, the mass compressive strength and relative dynamic elastic modulus of concrete increase with the increase of substituting calcium oxide expansion agent. The cross section of the concrete sample is a two‐dimensional plane before freezing‐thawing, and the pore structure densified as CaO content increases. However, new cracks are generated in the sample with 10% expansion agent content. After 400 freezing‐thawing cycles, 0% and 6% calcium oxide expansive samples have irregular three‐dimensional structures with concave and convex, and many connected holes and penetrating cracks appear. There are a small number of disconnected void clusters in the section of the sample with 8% and 10% content. A large number of calcium hydroxide ((Ca(OH)2) crystals fill the pores and cracks and improve the frost resistance of concrete.

Reinforced Concrete Structure Performance in Marine Structures: Analyzing Durability Indexes to Obtain More Accurate Corrosion Initiation Time Predictions.

This paper presents a comparison of six index properties collected during durability inspections of five Mexican seaports. Typical durability indicators such as compressive strength, saturated electrical resistivity, ultrasonic pulse velocity, percent total void content, capillary porosity, and chloride concentration profiles were analyzed to obtain empirical correlations with the non-steady-state chloride diffusion coefficient. These indices were compared to determine correlation coefficients that are the most important for obtaining better corrosion initiation forecasting. Two models of corrosion initiation time (ti) were used: Fick’s second law of diffusion and the reported UNE-83994-2 (Spanish Association for Standardization, UNE) in which electrical resistivity was used to calculate concrete service life. The data from both models were cleaned using correlated variables, and the initial variables were compared with ti. The main result achieved was the verification of the feasibility of using correlations of variables to clean unnecessary data in order to calculate ti. Additionally, electrical resistivity was identified as one of the main durability indexes for in-service concrete structures exposed to marine environments. This is important because electrical resistivity is a non-destructive and reliable test that can be measured both in the laboratory and in the field very easily.

Use of Mixed Microbial Cultures to Protect Recycled Concrete Surfaces: A Preliminary Study.

One approach to tackle the problems created by the vast amounts of construction and demolition waste (CDW) generated worldwide while at the same time lengthening concrete durability and service life is to foster the use of recycled aggregate (RA) rather than natural aggregate (NA). This article discusses the use of polyhydroxyalkanoates (PHAs)-producing mixed microbial cultures (MMCs) to treat the surface of recycled concrete with a view to increase its resistance to water-mediated deterioration. The microorganisms were cultured in a minimal medium using waste pinewood bio-oil as a carbon source. Post-application variations in substrate permeability were determined with the water drop absorption and penetration by water under pressure tests. The significant reduction in water absorption recorded reveals that this bioproduct is a promising surface treatment for recycled concrete.

BACTERIA BASED SELF-HEALING CONCRETE :A REVIEW

Concrete is one of the most commonly used building materials, and which is prone to cracking. The service life of concrete is significantly reduced due to these cracks. Replacement are High costs and difficulties in avoiding the cracks, various methods are in place to prevent crack formation such as filling in the gaps. It has been demonstrated current treatment methods of concrete are Chemical and polymer applications which they are a source of health and environmental issues, and they are only getting worse successful under some situations. As a result, environmentally sustainable treatment methods will be required in the near future. The potential for long-term, rapid, and active crack repair distinguishes the microbial self-healing method, which is also environmentally friendly. in addition, microbial self-healing Thanks to the effectiveness of this procedure, which out performs most treatment methods. Concrete compatibility and effective bonding capability assemblages. This paper gives an overview of the various microbial methods for producing calcium carbonate (CaCO3). Future challenges in microbial crack treatment are discussed, as well as recommendations for future research areas.

Use of scratch tracking method to study the dissolution of alpine aggregates subject to alkali silica reaction

Alkali silica reaction (ASR) can significantly affect the service life of concrete. The dissolution of aggregates has a direct impact on gel formation and thus on the macroscopic expansion. The conventional expansion tests and other investigations confirmed ASR reactivity of three aggregates from different locations in Switzerland. The reactive minerals within alpine and composite aggregates were identified using an innovative scratch-tracking method. This method helps to study aggregate dissolution if measuring the amount of released Si is not enough, because: several minerals release Si or Al and/or new phases are probable to form during dissolution experiment. The scratch-tracking method on theses alpine aggregates showed faster dissolution of feldspars and quartz while muscovite was hardly affected. The dissolution of the aggregates in solution confirmed these differences between minerals.

Evaluation Carbonation Service Life of Mortar-Coated Concrete Considering Global Warming

Mortar finishing is frequently used to improve the carbonation service life of structural concrete. Moreover, carbonation is aggravated due to global warmings, such as the increase of CO2 concentration and temperature. This study shows a probability-based approach for evaluating the carbonation service life of coated concrete considering global warming. First, a carbonation model is proposed for assessing the carbonation depth of concrete with mortar finishing. The effect of global warming on carbonation is considered in the carbonation model. Second, a probability-based method is employed to determine the carbonation service life considering the thickness and mixtures of mortar finishing and substrate concrete. Based on the statistical analysis of calculation results, we find that for a concrete structural with 50 years’ service life, 15% service life will be reduced due to global warming.

Evaluation of self-healing performance of concrete containing fly ash and fibres

ABSTRACT Since the existence of cracks reduces the concrete service life, the self-healing ability of concrete has attracted the attention of researchers. In this article, effects of fly ash and steel/polypropylene fibres on the self-healing ability of concrete were investigated separately and together. The cylindrical specimens were pre-cracked by means of a tensile strength test at 28 days. Secondary tensile test was performed immediately after pre-cracking and 28 and 56 days after re-curing in water. Also, to monitor microcracks in concrete after pre-cracking and during the self-healing period, the ultrasonic pulse velocity and permeability tests were conducted. The results showed that 15% fly ash replacement led to 94% reduction in permeability and almost complete recovery in secondary tensile strength after 8 weeks of re-curing. Although the specimen with polypropylene lost lower tensile strength among specimens with fibre immediately after pre-loading (22%), the improvement rate of those during the self-healing period was only 27%.

Performance of GGBS Cement Concrete under Natural Carbonation and Accelerated Carbonation Exposure

One of the primary problems related to reinforced concrete structures is carbonation of concrete. In many cases, depth of carbonation on reinforced concrete structures is used to evaluate concrete service life. Factors that can substantially affect carbonation resistance of concrete are temperature, relative humidity, cement composition, concentration of external aggressive agents, quality of concrete, and depth of concrete cover. This paper investigates the effect of varying the proportions of blended Portland cement (ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBS)) on mechanical and microstructural properties of concrete exposed to two different CO2 exposure conditions. Concrete cubes cast with OPC, and various percentages of GGBS (0%, 30%, 50%, and 70%) were subjected to natural (indoor) and accelerated carbonation exposure. The aim of this paper is to present the research findings and authenticate the literature results of carbonation by using GGBS cement in partial replacement of OPC. The concretes with OPC are compared to concretes with various percentages of GGBS, to assess the carbonation depth as well as rate of carbonation of GGBS-based concretes, under both accelerated carbonation and natural carbonation exposure conditions. Even though GGBS cement increases the carbonation depth, the results are not the same with different GGBS replacement percentages. A correlation is made between concrete samples exposed to 15 ± 2% carbon dioxide (CO2) concentration and those exposed to natural CO2 concentration. The results reveal that the products formed by carbonation are similar under both exposure conditions. The experimental tests also revealed that GGBS cement concrete has a lower carbonation resistance than OPC concrete, due to the consumption of portlandite by the pozzolanic reaction. The combination of 70% OPC and 30% GGBS behaved well enough with respect to accelerated carbonation exposure, the depth of carbonation being roughly equivalent to that of control group (100% OPC). The results also show that rate of carbonation becomes more sensitive as the percentage of GGBS replacement increases (binder ratio), rather than duration of curing. Concretes exposed to natural carbonation (indoor) achieved lower carbonation rates than those exposed to accelerated carbonation.

Investigation on Numerical Simulation of Chloride Transport in Unsaturated Concrete

Marine atmosphere environment accelerates the process of chloride penetration into concrete under the coupling effect of ambient temperature and relative humidity, thereby reducing the durability and service life of concrete. This paper aims to investigate the change of water equilibrium saturation and the chloride transport properties of concrete materials in different environments. The water equilibrium saturation tests at three temperatures and five relative humidity (RH) and salt spray erosion tests at three temperatures were performed. The influence of RH and temperature on the equilibrium saturation of concrete and the influence of temperature and time on the chloride diffusion coefficient are investigated. The results show that, in the process of moisture absorption and desorption, the equilibrium saturation of concrete gradually decreases as temperature rises. At the same depth of concrete, the chloride content gradually increases with temperature increasing, as well as the chloride diffusion coefficient. However, as the corrosion time of salt spray increases, the altering of chloride diffusion coefficient becomes less. Based on the Kelvin equation, a relationship between capillary pressure and water saturation in concrete was established, and a moisture transfer model for concrete in the process of moisture absorption and desorption was derived. Further, based on the established chloride diffusion equation and heat balance equation, a model of temperature‐wet‐chloride coupling chloride transfer was derived. Theory model simulation results show the transfer speed of chloride under the coupling of diffusion and capillary is higher than pure diffusion in moisture in the absorption process. However, the opposite is true in the desorption process. Moreover, with the increment of saturation rate, the capillary effect on chloride transport is enhanced.

ПРОГНОЗ СРОКОВ БЕЗОПАСНОЙ СЛУЖБЫ ГОРНОКАПИТАЛЬНЫХ ВЫРАБОТОК

The paper presents the results of the study of the actual condition and service life of capital mine workings of the mine "Mnogovershinnoye". Typical forms of assessment of geo-logical conditions with subsequent estimation of the time of standing of the mine workings without support were established. The main types of supports and the character of their dis-turbance during the operation of workings have been determined with the subsequent sub-stantiation of the service life of mud-base concrete, metal arch and anchor supports under different conditions. On the basis of the commissioning date of capital mine workings at the mine "Mnogovershinnoe" a list of workings with the expired service life was made; there was stated the necessity of visual and instrumental examination of supports to assess their wear degree with the following repair-restoration works to maintain mine workings in the operable state.

Research on prediction of concrete frost resistance based on random forest

Poor frost resistance of concrete will accelerate the deterioration of concrete structure and shorten the service life of concrete. This paper predicts the frost resistance of concrete and selects the initial index of factors that affect the frost resistance of concrete. The random forest algorithm is introduced to remove the unimportant indicators in the initial indicator system of the concrete mix ratio and determine the optimal indicator combination. The relative dynamic elastic modulus is used as the output index of random forest to predict the frost resistance of concrete. The proposed random forest model provides a reasonable and effective method for concrete frost resistance prediction.

Scenarios for Life Cycle Studies of Bridge Concrete Structure Maintenance

The sustainability of structures during their construction and service life has become a widespread topic of interest. To ensure the sustainability of bridges, maintenance databases can be analyzed to determine the status changes and required maintenance of existing bridges. The results of this analysis can then be used to predict the environmental impacts and costs incurred during ongoing maintenance of new bridges to prepare accordingly for the future. To prepare for future events, this study utilizes the US National Bridge Inventory to analyze changes in the condition rating of bridge decks and substructures according to their service years, and suggests maintenance scenarios for the service life of bridge deck and substructure concrete by investigating the maintenance activities according to service years. The factors for applying the scenarios in Korea and conceptual equations for life cycle studies which apply the scenarios are discussed for further study in the life cycle assessment field of bridges.

Service Life Modeling of Concrete with SCMs Using Effective Diffusion Coefficient and a New Binding Model

This paper presents a new algorithm that predicts the service life of concrete contains supplementary cementitious materials, SCMs, and determines time of corrosion initiation. The algorithm drives effective diffusivity from an apparent diffusion model, using experimental binding data performed in the lab, temperature, free ion concentration, and carbonation, and generates free chloride profiles for concrete with and without SCMs by using Fick’s law in a finite element model. Adjusting diffusion coefficient at each step of the solution, by addressing the impact of different parameters, simplifies the algorithm and reduces calculation time without jeopardizing the results’ quality. Results generated by the model compare well to the performance of concrete blocks constructed in an exposure site on the east coast of Saudi Arabia. The exposure site hosted five different mixes of Portland cement and SCMs, and the concrete blocks were exposed to harsh weather over the period of two years. Linear polarization and chloride profiling assessed the performance of the mixes against corrosion activities. Lab work identified the performance of the mixes through binding capacity and chloride profiling. Statistical analysis evidenced the accuracy of the model through correlation and regression analysis. Furthermore, a new proposed binding model, produced from binding data in different studies, alters the experimental binding data in the algorithm to decouple the solution from experimental values. The algorithm proves its accuracy when compared to the experimental free chloride profile. The proposed transport model proves that using effective diffusion and binding capacity are enough to generate reliable results, and the effective diffusion can be calibrated with environmental conditions such as temperature, age, and carbonation. Finally, the algorithm presents its features in an object-oriented programming using C# and user friendly web interface.

Synthesis of CaFeAl layered double hydroxides 2D nanosheets and the adsorption behaviour of chloride in simulated marine concrete

Chloride-induced reinforcement corrosion in marine concrete structures adversely impacts its durability, which leads to the decrease of the actual service life of concrete. Three kinds of layered double hydroxides (LDHs), CaFe–NO3 LDHs (LDHs-CF), CaAl–NO3 LDHs (LDHs-CA) and CaFeAl–NO3 LDHs (LDHs-CFA), were synthesized to bind chloride. The results showed that all of the synthetized LDHs could effectively adsorb chloride from simulated concrete pore solutions (SCPSs) and artificial seawater (ASW) through the surface adsorption and ion exchange. The maximum chloride adsorption capacity of the LDHs-CFA was 3.18 mmol g−1. The adsorption process could be described by the Langmuir isotherm and pseudo-second-order kinetic models. For the chloride desorption experiments, the chloride desorption rate of the LDHs-CF (29.20%) and LDHs-CFA (39.31%) were lower than that of the LDHs-CA (47.45%), because the presence of Fe3+ in LDHs suppressed the concentration of dissolved metals, and a crystal transformation occurred to form 3CaO·Fe2O3·0.5CaSO4·0.5CaCl2·10H2O, exhibiting excellent stability for LDHs-CF and LDHs-CFA. In conclusion, LDHs show excellent chloride binding behaviour, which makes it promising to achieve the goal of high efficiency and stability of chloride binding for marine concrete by LDHs.

Service life of GGBFS concrete under carbonation through probabilistic method considering cold joint and tensile stress

Carbonation is a typical deterioration phenomenon which accelerates steel corrosion through pH drop in pore water by intrusion of external carbon dioxide (CO2). Many researches have been performed on carbonation process considering carbonic reaction, mixture conditions, and exterior conditions. Recently probabilistic approaches have been adopted for considering engineering uncertainties such as complicated material behavior, simple evaluation system, and limited sample numbers. In the study, the service life variation was evaluated considering several effects of induced tensile stress level, cold joint, and GGBFS (Ground Granulated Blast Furnace Slag) through probabilistic approach. Utilizing the previous test results, the effect of loading conditions on carbonation depth was investigated. Four design parameters like cover depth, exterior CO2 concentration, carbonatable material, and CO2 diffusion coefficient were assumed as random variables for probability analysis. Through MCS (Monte Carlo Simulation) with normal distributions and intended PDF (Probability of Durability Failure) of 10%, variations of service life were simulated for the RC structure under loading conditions. The effects of COVs (Coefficient of Variation) for design parameters were also simulated. The comparisons of the predicted service life from the probabilistic and deterministic methods were quantitatively discussed, and the safety index with service life was also investigated. The results of this study can provide useful information on maintenance priority and service life evaluation for RC structures containing cold joint subjected to tensile stress.

Study on the service life prediction of freeze–thaw damaged concrete with high permeability and inorganic crystal waterproof agent additions based on ultrasonic velocity

Based on a rapid freeze–thaw test of inner-doped silicon-ash concrete specimens that were coated using three different externally coated inorganic coating methods, ultrasonic wave velocity and dynamic elastic modulus measurements were employed. The characteristics of the ultrasonic wave velocity attenuation and dynamic elastic modulus of the concrete utilizing three types of inorganic coating methods under the effect of freeze–thaw cycles were analysed. Based on the theory of damage mechanics and the evolution equation for freeze–thaw or corrosion damaged concrete, the damage evolution equations of the relative dynamic elastic modulus for three types of inorganic coated concrete were verified by a large amount of experimental data under the action of a single freeze–thaw factor. According to the relative dynamic elastic modulus formula, based on the ultrasonic wave velocity of Ababneh, the relative ultrasonic velocity was determined to be 0.7746 when the relative dynamic elastic modulus was 0.60. The equivalent freeze–thaw damage model of the ultrasonic wave velocity of the concrete was established, the concept of relative ultrasonic wave velocity was proposed, the relative dynamic elastic modulus method was verified, and the relative P-wave velocity and relative shear wave velocity of Ababneh for the three types of concrete under the effect of freeze–thaw cycles was determined for service life prediction. The above three methods can accurately predict the service life of concrete. Ultimately, the service life of concrete materials in different mix proportions and use areas will be able to be predicted using ultrasonic non-destructive testing in the future.