Service Life Of Concrete Research Articles

Assessment of Strength and Deformation Characteristics of High-Strength Concrete in Structures and the Dynamics of Their Changes over Time

Based on the data from numerous production and laboratory tests, an analysis of the actual values of the main standardized strength and deformation characteristics of high-strength concrete of classes B60-B100 was carried out: ultimate resistance to axial compression, initial modulus of elasticity and Poisson’s ratio. It has been established that the values of prismatic strength (Rb) are close to cubic (R), and the ratio between them (prismatic strength coefficient) is not lower than 0.85. A comparison of Rb values with those calculated for limit states of the 1st group according to SP 63.13330.2018 shows that for concrete classes above B70 in the regulatory document they are unreasonably underestimated. The value of the coefficient of variation of high-strength concretes does not exceed 6.5%, which is predetermined by the features of their compositions, which ensure stability of consistency, segregation stability and technological reliability of concrete mixtures. The values of the initial elastic modulus (Eb) exceed the normative ones provided for by SP 63.13330.2018.The dependence of the values of the initial modulus of elasticity of concrete of the same class on the nature of the coarse aggregate has been established. According to experimental data, the elastic modulus can vary in the range of up to 19% depending on the characteristics of the coarse aggregate used. This variability of Eb is consistent with the recommendations of EN 1992-1-1:2004 Eurocode 2, but is not taken into account in SP 63.13330.2018. The time factor affects the change in the values of strength (R and Rb) and elastic modulus (Eb). According to the data obtained, in the period from 28 days to 1.5 years the increase in strength was 15–17%, elastic modulus – 8.8–9.8%. It has been established that changes in these characteristics over time are described by mathematical models and, accordingly, can be predicted depending on the age of concrete. The results obtained indicate that the standardized parameters of SP 63.13330.2018 do not fully take into account the service life of modern high-strength concrete, which makes it necessary to make changes to the specified document.

Unleashing the potential of bio-based concrete: Investigating its long-term mechanical strength and drying shrinkage in real climatic environments

Natural climatic conditions have significant negative impacts on the long-term mechanical properties and dimensional stability of bio-based concrete considering the high water absorption of bio-aggregates and corresponding biodegradations. In this study, the effects of three hydrophobic treatments (integral mixing, aggregate coating, concrete coating) on the physical properties, mechanical strengths, and drying shrinkage characteristics of bio-based peach kernel shell concrete in real climatic natural environments are investigated. Results show that bio-based peach kernel shell concrete has lower mechanical strength in outdoor climatic conditions than in indoor standard curing conditions. The swelling and shrinkage process causes the visible microcrack and debonding between bio-based materials and mortar interface. The drying shrinkage of bio-based peach kernel shell concrete in outdoor conditions is highly dependent on real climatic environments, including temperature, humidity and rainfall. The hydrophobic surface-coated concrete exhibits excellent resistance to real climatic environments, as well as good mechanical strength and dimensional stability, with 15.7% less drying shrinkage in 18 months, compared to reference concrete. Moreover, cellulose and hemicellulose of heat-treated bio-aggregates do not degrade over time in outdoor conditions due to the enhanced biodegradation resistance. The hydrophobic surface coating treatment is recommended for enhancing the service life of bio-based peach kernel shell concrete in real climatic environments.

Early hydration studies of cementitious materials incorporating nanoalumina

Concrete technologists use different types of additives such as fly ash, slag, natural pozzolans and nanomaterials toenhance concrete performance and durability. However, a detailed explanation of the early-age hydration process and microstructural modification of concrete in the presence of nanomaterials remains to be presented and extensive research is required for strategic modification of cementitious systems. This study focused on the precise monitoring of early-age hydration with the incorporation of nanoalumina (nAl) in tricalcium silicate (C3S) and Portland cement paste and mortar. The dosage of nAl was varied from 1 to 5% (by weight) in C3S and from 0.1 to 1.0% in Portland cement, with a water/cement ratio of 0.4. The hydration studies showed that the nAl increased the cross-linkage in calcium silicate hydrate gel through substitution of aluminium by silicon, which was responsible for the enhancement of the modulus of elasticity (by 40%) with 1.0% nAl) after 7 days of hydration. In summary, the incorporation of nAl modified the concrete microstructure in the initial days of hydration, leading to higher concrete performance and longer service lives of concrete structures.

Frost resistance and life prediction of equal strength concrete under negative temperature curing

The compressive strength of concrete cured at −3 °C increases with age and can reach an equal strength to that of concrete cured at 28d of standard curing. However, the frost resistance of concrete with equal strength remains unclear. The mass loss, relative dynamic elastic modulus, peak stress, and peak strain of concrete are selected for evaluating the frost resistance of equal strength concrete. The results show that the negative temperature curing reduces the frost resistance of equal strength concrete, and the frost resistance of concrete decreases with the water-binder ratio. The optimal initial air content of equal strength concrete for frost resistance is between 4% and 5%. The calculation models of the relative peak stress and relative peak strain of equal strength concrete are established considering the initial air content and freeze–thaw cycle times. Based on the rapid coefficient method, the relationship between laboratory accelerated testing and the on-site service life of concrete is established, taking the relative dynamic elastic modulus reduced to 60% as the criterion of freeze–thaw failure, the life prediction of equal strength concrete is carried out. The equal strength concrete cured at −3 °C cannot achieve equal frost resistance and service life.

Mechanism of inhibitors in control of corrosion of steel in concrete

Reinforced concrete is the most abundantly used material in the infrastructure industry. Corrosion of reinforcing steel is the most critical and significant problem that the building industry faces. This durability issue is primarily caused due to chloride attack or carbonation of concrete. Among other techniques used in producing high-performance concrete, the use of corrosion inhibitors is the most attractive from the view of cost and ease of application. There is a diverse range of available corrosion inhibitors that are classified based on their origin, mechanism of protection, and composition. This paper covers a critical overview of the different mechanisms of corrosion protection offered by corrosion inhibitors. Furthermore, the stricter enforcement of environmental rules has prompted and inspired researchers to focus on developing non-toxic and ecologically acceptable corrosion inhibitors. This paper also gives a brief account of the ecological sustainability and toxicity issues concerning the commercially available inhibitors and the versatility and effectiveness of green corrosion inhibitors compared to synthetic corrosion inhibitors. This account of corrosion inhibitors attempts to contribute towards developing awareness and understanding of the primary mechanism of protection and the use of innovative and green materials to increase the service life of steel-reinforced concrete.

Service Life Prediction of Concrete Coated with Surface Protection Materials by Ultrasonic Velocity in Cold Region

Lithium silicate (LS) crack repairing material, working as a crystal waterproof material, could be used to strengthen concrete made from solid waste materials. This paper presents the results of water absorption and rapid freeze–thaw tests with concrete specimens coated with LS. Concrete specimens with different water–binder ratios and air content (0.35–1 and 0.55–4.5) were tested. The moisture uptake and water absorption coefficient were analyzed in the water absorption test. The water absorption coefficient of LS-coated specimens was lower than that of uncoated specimens, resulting in a lower total moisture content. The relative dynamic modulus of elasticity was calculated by the fundamental transverse frequency (Er) and ultrasonic velocity (Ev), respectively. Er and Ev exhibited similar attenuation characteristics, and the attenuation of LS-coated specimens was lower than that of uncoated specimens. A two-segment freeze–thaw damage model based on Er and Ev was employed to predict the service life of concrete. The relative errors of the service life results calculated by Er and Ev were within 10%. The two-segment freeze–thaw model could be used for the service life prediction of concrete structures. The present work provides new insight into using LS to improve the service life of concrete.

Potential of Pyrogenic Nanosilica to Enhance the Service Life of Concrete

Potential of Pyrogenic Nanosilica to Enhance the Service Life of Concrete

Optimising internal curing parameters for autonomous curing of normal-strength concrete

Autogenous curing, also known as internal curing (IC), has revolutionised the way high-performance concrete (HPC) and high-strength concrete (HSC) are cured. IC improves the service life of concrete by lowering early-age cracking and enhancing durability. However, normal-strength concrete (NSC), the most commonly used type in the industry, is typically cured using conventional methods. Researchers are thus looking at ways to reproduce the positive results found in internally cured HSC/HPC in NSC. Studies have shown that IC is feasible in NSC despite its higher permeability, which results in loss of internal curing water (ICW). However, no comprehensive study has attempted to assess how the type, size and amount of IC agents affect the properties of NSC. The aim of this work was thus to optimise IC parameters for autonomous curing of NSC. The findings of this study support the notion that IC is possible in concrete with a high water/cement ratio and that, compared with lightweight aggregates (LWAs), superabsorbent polymers significantly impacted the durability properties of the NSC. Moreover, varying the size of the IC agent (LWA) had little effect on NSC properties, while increasing the amount of ICW considerably improved the durability properties.

Mechanical performance of steel-polypropylene hybrid fiber reinforced concrete subject to uniaxial constant-amplitude cyclic compression: Fatigue behavior and unified fatigue equation

In the natural environment, concrete-built structures are frequently undergoing repetitive loadings, e.g., earthquake, automobile traffic, or wind during their entire service life. Those repetitive cyclic loadings trigger gradual initiation, expansion and coalesce of inner cracks, resulting in progressive deterioration of mechanical performance until eventual fatigue failure. This paper presents a hybrid fiber reinforcing strategy that could significantly increase the service life of concrete. In this work, the compressive fatigue performance of steel-polypropylene hybrid fiber reinforced concrete (HFRC) under fatigue compression was investigated. A total of 36 groups of prismatic specimens were tested for various stress levels (0.7, 0.8, and 0.9). With respect to the fatigue deformation, fatigue life, and fatigue strength, the effects of fiber parameters were analyzed, including steel fiber volume fractions (1%, 1.5%, and 2%) and aspect ratios (30, 60, and 80), as well as polypropylene fiber volume fractions (0.1%, 0.15%, and 0.2%) and aspect ratios (167, 280, and 396). The results showed that the incorporation of hybrid fiber exerts a pronounced impact on the fatigue performance of concrete. Specifically, in contrast to plain concrete, the ultimate fatigue deformation and fatigue strength of HFRC could be increased by up to 63.29% and 37.18%, respectively. In addition, owing to a positive synergetic effect generated in the hybrid system, HFRC is more superior to polypropylene fiber reinforced concrete (PFRC) or steel fiber reinforced concrete (SFRC) in fatigue performance. Furthermore, a unified fatigue model was proposed to estimate the fatigue strength of HFRC with consideration of fiber parameters. The predictions were found to correlate well with available experimental results, demonstrating a wide applicability of the model in prediction of fatigue life of concrete with reasonable accuracy.

Application of the novel-structured multivariable grey model with various orders to forecast the bending strength of concrete

Bending strength of concrete is one of the significant indexes to measure the mechanical properties of concrete. A reliable prediction about the bending strength of concrete is of great importance to maintain the health state and service life of concrete. However, it is difficult to obtain reliable data of large samples due to the high cost, serious destructiveness and complex influencing factors of concrete bending strength test data collection. In view of this, based on the multivariable grey prediction model whose modeling object is small data, we construct a new novel-structured multivariable grey prediction model with various orders for predicting the bending strength of concrete. It defines and optimizes the accumulative orders differentially and introduces a nonlinear correction term to expand the model structure. Then, the bending strength of concrete is modeled using the new model, and its comprehensive error is only 0.035 %, which is much smaller than the conventional NSGM(1,N) and FMGM(1,N) models (5.232 % and 2.624 %, respectively). The findings provide a new modeling method for the prediction of concrete bending strength in areas with large temperature difference, and have significance for enriching and improving the methodologies of grey prediction models.

Effects of Ambient Humidity on Water Migration and Hydrate Change in Early-Age Hardened Cement Paste.

Ultra-low humidity environments will lead to changes in the microstructure of C-S-H, which will reduce the mechanical properties and service life of cement-based concrete. Thus, to further explore the mechanism on the microscale, this paper studied the water migration and the changes in the hydration products in white cement that was cured for 7 days at 20 °C and at different ambient relative humidities (RHs). The migration and transformation of different types of water in cement paste were studied by low-field nuclear magnetic resonance (NMR). At the same time, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to analyze semi-quantitatively the crystal phase in the hydration products. The results showed that in the first 7 days of the curing process, the content of the different types of water and the hydration products in the cement samples were influenced by the ambient RH. The total water content of the samples will decrease with the decrease in the RH; when the RH decreases to 54% or below, the chemically bound water in the samples will increase with the decline in the RH. Additionally, when the ambient RH is lower than 54%, the grossular will gradually transform into hydrogrossular crystals with the decrease in the RH, and the hibschite with less chemically bound water will transform into katoite with more chemically bound water. In future research, the water migration and hydrate changes under different curing ages, drying processes, and coupling effects should be explored.

A functional and robust super‐hydrophobic PCC coating based on the induced assembly of modified zirconium phosphate

AbstractImproving the permeability of concrete is one of the important measures to extend the service life of concrete. In addition, for marine engineering, sewerage projects, and so on, mechanical stability and microbial induced corrosion of concrete structures cannot be ignored. We demonstrated a method to prepare high‐performance super‐hydrophobic (SHP) coating using functional zirconium phosphate (ZrP) and polydopamine (PDA) as the primary materials. The micro‐nano rough structures were constructed on the concrete surface by alternating organic–inorganic assembly guided by each other. The coatings' apparent morphology, composition, and structure were analyzed using various surface analysis techniques. Based on the construction of micro‐nano rough structures by the induced assembly of functional ZrP, the silane treatment significantly improved the water contact angle of the coating (WCA = 154° ± 3°), and the coating exhibited relatively high wear resistance, reaching 135° WCA even after 30 friction cycles. The water absorption of the specimens treated with the SHP composite coating was reduced by 79% to treated with silane. Meanwhile, the SHP composite coating showed excellent antimicrobial and anti‐ice properties, due to the role of the functional ZrP and alternating organic–inorganic assembly. It was expected that the composite coating might potentially promote and accelerate applied superhydrophobic anticorrosive coating development for marine concrete durability.

Molecular insights into the adsorption of chloride ions in calcium silicate hydrate gels: The synergistic effect of calcium to silicon ratio and sulfate ion

Corrosion of steel bars by chloride ions is one of the main reasons for determining the service life of marine concrete. In this work, the effects of calcium to silicon (C/S) ratio and SO42− concentration on Cl− adsorption in calcium silicate hydrate (C–S–H) gels were systematically studied by molecular dynamics simulations. Atomic-scale results show that higher C/S ratio induces more Cl− adsorption. The presence of SO42− not only reduces the Cl− adsorption but also buffers the adsorption caused by increasing C/S ratio. The Cl− adsorption is caused by the attraction of interlayer Ca (Cah) and hydroxyl groups in low C/S gel, while in high C/S ratio C–S–H gel is mainly contributed by Cah. More Cl− adsorption at the C–S–H interface ensures less Cl− accumulation in zones surrounding the reinforcement. The insights into ion adsorption behaviour should provide useful information for prolonging the durability of marine concrete by designing appropriate compositions.

The verification of the possibility of alkalis penetration from the surrounding environment into the concrete pavement slabs

The short material service life of concrete is currently a frequently discussed topic, especially for newly constructed roadways with cement concrete pavement. This early degradation of cement concrete pavement slabs is a major problem that threatens the service life of sub-sections or the entire road. As some partial results demonstrate, a possible cause of this degradation can be seen in the surrounding road environment, namely the possibility of transferring aggressive substances to the concrete pavement slab. This paper is concerned with the verification of the possibility of the penetration of alkalis penetration from the surrounding environment into the concrete pavement slab by simulating the effect of different external conditions and environments.

Damage Mechanism and Modeling of Concrete in Freeze–Thaw Cycles: A Review

The deterioration of concrete microstructures in freeze–thaw (F–T) cycles is the primary reason for the reduction in the service life of concrete. This paper reviews recent progress in the theory of damage mechanisms and damage models of concrete in F–T cycles. It is a detailed review of the salt-freeze coupling condition, microstructure testing, and models for the evolution of concrete properties that are subjected to F–T damage. Summarized in this paper are the deterioration theory of water phase transition; the mechanism of chloride-F–T and sulfate-F–T damage; the microstructure testing of hydration products, pore structure, microcracks, and interfacial transition zones (ITZ). Furthermore, F–T damage models for the macrostructure are presented. Finally, the issues that are existing in the research and outlook of concrete F–T damage are highlighted and discussed. This paper is helpful in understanding the evolution of F–T damage, and also provides a comprehensive insight into possible future challenges for the sustainable design and specifications of concrete in cold environments.

Cleaner construction of durable green rooftop in residential buildings with municipal water supply

Rooftop vegetation is a popular choice among architects and builders at present because of its aesthetical appeal and environmental benefits. It has consistently been regarded as a sustainable and eco-friendly approach to the construction of buildings. Recently, people have adopted rooftop vegetation in their homes, and it has become popular. Large scale roof gardens in commercial buildings are safe due to proper design and protection techniques by experts. Due to economic constraints, rooftop vegetation in normal residential buildings cannot follow stringent regulations and expensive protection techniques. However, it is to be kept in mind that any rooftop vegetation endeavour, if not properly designed and maintained, might result in severe durability problems in roof concrete. There are unseen drawbacks to simple practices of concrete rooftop vegetation in common residential buildings, specifically the presence of aggressive agents in treated water from the public water supply, which is commonly used to irrigate the vegetation in such buildings. The effect of vegetation on the concrete roof and its influence on various salient aspects, specifically the durability of concrete, is discussed in this paper. The influence of chlorides and sulphates present in the municipal treated water used for watering plants and shrubs on the durability of concrete is also presented. Moreover, the chloride threshold value of the reinforcement is between 0.1% and 1.5%. The total charges passed through concrete are also reduced to less than 1000 Columbus with the addition of agricultural by-products. In addition, root intrusion tendency of commonly grown plants on rooftop and corrosion due to agricultural chemicals are also mentioned. In the latter sections, remedial measures are highlighted to minimize the negative impacts of rooftop vegetation on the durability of concrete. In addition, to highlight the impact of chlorides on the roof concrete, the study also presented the chloride permeability and service life of blended concrete.

Application of Polyacrylic Hydrogel in Durability and Reduction of Environmental Impacts of Concrete through ANN.

While adding superabsorbent polymer hydrogel particles to fresh concrete admixtures, they act as internal curing agents that absorb and then release large amounts of water and reduce self-desiccation and volumetric shrinkage of cement that finally result in hardened concrete with increased durability and strength. The entrainment of microscopic air bubbles in the concrete paste can substantially improve the resistance of concrete. When the volume and distribution of entrained air are adequately managed, the microstructure is protected from the pressure produced by freezing water. This study addresses the design and application of hydrogel nanoparticles as internal curing agents in concrete, as well as new findings on crucial hydrogel–ion interactions. When mixed into concrete, hydrogel particles produce their stored water to power the curing reaction, resulting in less volumetric shrinkage and cracking and thereby prolonging the service life of concrete. The mechanical and swelling performance qualities of the hydrogel are very sensitive to multivalent cations found naturally in concrete mixes, such as aluminum and calcium. The interactions between hydrogel nanoparticles and alkaline cementitious mixes are described in this study, while emphasizing how the chemical structure and shape of the hydrogel particles regulate swelling behavior and internal curing efficiency to eliminate voids in the admixture. Moreover, in this study, an artificial neural network (ANN) was utilized to precisely and quickly analyze the test results of the compressive strength and durability of concrete. The addition of multivalent cations reduced swelling capacity and changed swelling kinetics, resulting in fast deswelling behavior and the creation of a mechanically stiff shell in certain hydrogel compositions. Notably, when hydrogel particles were added to a mixture, they reduced shrinkage while encouraged the creation of particular inorganic phases within the void area formerly held by the swelled particle.

Monitoring of Ion Mobility in the Cement Matrix to Establish Sensitivity to the ASR Caused by External Sources

The possibility of the formation of an alkali–silicate reaction (ASR) is a crucial issue for the service life of concrete. The coexistence of key parameters such as the presence of alkalis, reactive SiO2, humidity, and temperature predetermine the possibility of its formation and application. When an ASR gel forms, it results in the concreting cracking and spalling as well as in the deterioration of its overall properties. The risk of ASR depends on the concentration of alkalis and their mobility, which influence their ability to penetrate the concrete. The objective of this study was to determine the ionic mobility of not only Na+ and K+, but Ca2+ as well, from external sources (0.5 and 1.0 mol/L solutions of Na/K carbonate, nitrate, and hydroxide) to a cementitious matrix as the precursor for ASR. The concentrations of ions in both the immersion solutions (ICP) and the cementitious matrix itself (SEM-EDX) were studied as a function of time, from 0 to 120 days, for leaching, and according to temperature (25 and 40 °C). The reaction products were characterized using SEM-EDX. Different diffusion rates and behavior were observed depending on the anion type of the external alkali source. Both sodium and potassium ions in all the three environments studied, namely carbonate, hydroxide, and nitrate, penetrated into the composite and further into its structure by different mechanisms. The action of hydroxides, in particular, transformed the original hydration products into calcium-silicate-hydrate (CASH) or ASR gel, while nitrates crystallized in pores and did not cause any changes in the hydration product. The driving force was the increased temperature of the experiment as well as the increased concentration of the solution to which the test specimen was exposed.

Prediction of Concrete Compressive Strength in Saline Soil Environments.

Saline soil in Western China contains high concentrations of chloride ions, sulfate ions, and other corrosive ions, and the performance of concrete will substantially deteriorate from exposure to this environment. Therefore, it is of great significance to study and predict the concrete compressive strength in saline soil environments. In this paper, the effects of corrosion on concrete were analyzed from the aspects of surface damage, damage depth, and X-ray diffraction (XRD) of the corrosion products. The effects of corrosion were quantified by damage depth and corrosion depth. Then, considering the corrosion effects combined with Fick’s diffusion law, a time-dependent model of concrete compressive strength and a time-dependent model of damage depth were established. The results show that the deterioration of concrete gradually developed from the surface to the interior, and that the interface of the concrete specimen was equivalent to three parts: a failure zone, a filling zone, and an undisturbed zone. The results also showed that the time-varying model of concrete compressive strength proposed by the author was fully applicable, with an error of less than five percent. The service life of concrete predicted by the damage depth was found to be about 253 months (21.1 years), and the service life predicted by the time-varying compressive strength model was about 187 months (15.6 years). Both prediction results were far less than the normal concrete service life of 50 years. In addition, the long-term compressive strength of the corroded concrete was about 90% of that of the noncorroded concrete, which did not deteriorate with the corrosion time.

Concrete Curing Performance Assessment Based on Gas Permeability Testing in the Lab and on Site.

Durability is an essential aspect of the lifetime performance of concrete components. The adequate surface quality and thus the service life of concrete can be achieved, among other things, by appropriate curing during hydration. To measure and control the curing quality, appropriate procedures are required. Gas permeability allows conclusions to be drawn about the porosity of concrete, which has a significant impact on durability. In this contribution, the effect of different curing methods on gas permeability is presented with the help of laboratory and on-site tests, showing that inadequate curing leads to increased permeability in the near-surface area of concrete. The measurement results of concrete samples and components with the same composition but varying curing treatment are compared and evaluated. Influences such as concrete composition and environmental factors on the quality of concrete are observed, and recommendations are made for a reliable assessment of the surface quality as a result of the investigated curing measures.