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Calcium leaching from cement hydrates has been shown to decrease the durability and shorten the service life of the concrete. Earlier studies have focused on investigating the leaching progress in deionized water or ammonium nitrate solutions, neglecting the effects of aggressive ion concentrations, types, and temperatures. In addition, the current equilibrium curve of calcium leaching is based on experimental data in deionized water, and its applicability to calcium leaching in actual marine environments is controversial. In this study, a dissolution experiment was carried out to study the effects of chloride ion concentrations and environmental temperatures. The functional relationship of critical parameters (x1 , x2 , and Csatu) of the equilibrium curves with the chloride ion concentrations and temperatures was established. Furthermore, considering the influence of calcium leaching on porosity and the diffusion coefficient of cementitious materials, the calcium leaching model was established within a time and space framework. The results showed that calcium leaching was accelerated by the increased concentration of chloride ions and the decrease in environmental temperature. In the authors' view, this study lays a theoretical foundation for a transport-reaction-mechanical deterioration model of concrete. [ABSTRACT FROM AUTHOR]

Despite extensive academic research on durability issues caused by sulfate attack, deterioration reasons and expansion mechanisms of concrete remain controversial, with descriptions of expansion development still focusing on phenomenological observations. The present study analyzes the macro-micro property changes of concrete and establishes a time-varying expansion prediction model considering environmental and material parameters. The micropore evolution in different pore categories is investigated, and the primary type and precipitation location of expansive products, as well as the expansion mechanism of concrete, are clarified. The results indicate the possibility of thaumasite sulfate attack (TSA) in concrete at low temperatures. The expansion development of concrete under sulfate attack can be divided into two stages: the expansion latency stage explained by crystallization pressure theory, and the significant expansion stage associated with volume increase theory. The expansion level at the inflection point of the expansion rate was solely related to the intrinsic micropore properties of concrete. • The relationship between macroscopic performance changes and micropore evolution was revealed. • A time-varying prediction model for concrete expansion development under sulfate attack was established. • The precipitation location of products and the expansion mechanism were clarified. [ABSTRACT FROM AUTHOR]

• A experimental study is conducted to investigate the mechanism of calcium leaching of cement hydrates exposed to the sodium sulfate solution. • The influences of sulfate ions concentration and environmental temperature are analyzed on calcium leaching process. • The solid–liquid equilibrium curve describing calcium leaching in deionized water is extended to sodium sulfate solutions. Calcium leaching from cement hydrates to pore solution increases the porosity and reduces the bonding strength of cement hydrates, accelerating the degradation of concrete. Calcium leaching can be quantified by solid–liquid equilibrium curves, which have been studied in deionized water or ammonium nitrate. The research of solid–liquid equilibrium curve of calcium under sulfate attack is limited and its mechanism is poorly understood. Reported here provide insights into the dissolution process of calcium from cement hydrates exposed to the sodium sulfate solution. The experimental programme examines the effects of sulfate ion concentration and temperature. An external sulfate attack (ESA) model considering the influence of calcium leaching is established and validated. The results show that, compared to deionized water, sulfate ions impact strongly the leaching process. Qualitatively, the dissolution of calcium in cement hydrates is accelerated by increasing the concentration of sulfate ions and decreasing the environmental temperature. Quantitatively, the presence of sulfate ions modifies the equilibrium curve describing calcium leaching in deionized water. In addition, the prediction results of the ESA model considering the influence of calcium leaching are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Sulfate-induced deterioration can reduce the service life of a concrete structure. A coupled chemo-transport-damage model for external sulfate attack is developed, which predicts the effects of calcium leaching and temperature on the deterioration processes. Specifically, calcium leaching is described using a solid–liquid equilibrium curve, and temperature effects are included in the creation of a temperature gradient and in the rates of chemical reactions, calcium leaching, and ion transport. The model is validated using published experimental results, and the effects of calcium leaching and temperature on expansion are analyzed. The results show that model predictions agree well with the available experimental data. One conclusion is that calcium leaching has a strong effect on deterioration, and therefore should be included when modeling external sulfate attack. Temperature influences sulfate attack, but a more substantial conclusion about the effect of temperature requires further experimental evidence. [ABSTRACT FROM AUTHOR]

Assessing the long-term durability of concrete structures subjected to external sulfate attack (ESA) poses a significant challenge, primarily due to the lack of a well-defined quantitative metric for durability limit states. Traditional performance indicators such as compressive strength, mass loss, and expansion strain are insufficient for providing a comprehensive understanding of the extent of damage and are often difficult to measure accurately in practice. The primary objective of this study is to introduce a novel durability failure indicator, namely the failure thickness of concrete under ESA exposure, designed to quantitatively assess the ultimate limit state of concrete durability. Experiments were conducted and the results confirmed that the failure thickness can reliably reflect changes in both the elastic modulus and compressive strength of concrete exposed to ESA. A prediction model for estimating the failure thickness was subsequently developed, integrating key influencing factors like sulfate concentration, initial aluminate content, and sulfate ion diffusion coefficient. The established model exhibited a high degree of correlation between the predicted and experimental failure thickness values, with a low margin of error. The findings of this research contribute to serve as a foundation for both lifespan prediction and durability design of concrete structures exposed to sulfate-rich environments. • We propose a durability failure indicator based on critical sulfate concentration. • Concrete performance deterioration can be well characterized by failure thickness. • The validity of the prediction model of failure thickness was confirmed. [ABSTRACT FROM AUTHOR]

Cathode ray tube (CRT) funnel glass has been used to partially or totally replace natural sand as fine aggregate in concrete. It is an effective and environmentally friendly method of recycling the increasing number of discarded CRT in the electronic industry. However, little research has been performed on its durability performance under environmental attacks, in particular in the areas of chloride ion penetration and sulfate attack, the two major environmental attacks on reinforced concrete structures. This study presents an experimental investigation on the durability performances of concrete using CRT funnel glass as fine aggregate in 8% sodium chloride solution, 5% sodium sulfate solution and 10% sodium sulfate solution. Four volume replacement ratios (the ratio of CRT glass to natural sand), i.e. 0%, 30%, 60%, 100%, are considered. The chloride ion content along concrete depth direction, compressive strength and elastic modulus of concrete was measured with attack time. The test results show that although the compressive strength and elastic modulus decrease with increasing content of CRT funnel glass in concrete, the long-term resistance to chloride ion penetration is enhanced by using CRT funnel glass as fine aggregate. Furthermore, the compressive strength, rather than dynamic elastic modulus of concrete containing CRT glass, is more sensitive to sulfate attack. The relative increase in strength of CRT glass concrete is obviously larger than that of control concrete under sulfate attack. This study also provides a reference for the durability design of concrete structures using CRT funnel glass as fine aggregate. [ABSTRACT FROM AUTHOR]

• The performance of concrete under sulfate attack and dry-wet cycles is investigated. • A newly defined index is proposed to describe the progress of sulfate attack. • A novel method is proposed to assess the performance of sulfate-attacked concrete. Sulfate attack is a major cause of concrete durability deteriorations. Mass loss, strength reductions, and expansive strain of concrete specimens are generally used in laboratory testing to identify the resistance of concrete materials to sulfate attack. However, these indicators cannot be directly used to quantitatively predict the bearing capacity of actual concrete structures under sulfate attack. There exists a significant size effect between laboratory and engineering size concrete components. In this study, the durability performance of concrete specimens, exposed to sulfate attack and dry–wet cycles, was investigated. Mass loss, dynamic elastic modulus, compressive strength, and sulfate ions distributions of deteriorated concrete were measured over time. Test results indicate that the newly defined integral area of sulfate ions distributions is a suitable index to describe the non-uniform deteriorations behavior of sulfate–attacked concrete; and a novel method based on the homogenizations theory is proposed to predict the deteriorations level of components of attacked concrete structures, which provides a potential use in assessing the loading capacity of actual concrete structures based on accelerated test results in a laboratory. [ABSTRACT FROM AUTHOR]