Alkali-activated materials (AAMs) have been extensively studied due to their high performance and low carbon emissions. However, the long-term durability of AAMs remains a major concern, which is closely related to their microstructures and pore networks. X-ray computed tomography (CT) has emerged as a powerful non-destructive technique for threedimensional microstructural analysis in the field of civil engineering. While CT has been widely used to investigate cement-based materials, its application to AAMs is still limited. In this review, we provide a comprehensive summary of the background information and applications of CT in AAM research, focusing on pore structure analysis, phase identification, degradation analysis, fiber reinforcement, temporal evolution and simulations. Furthermore, the current challenges and future perspectives are also discussed.
This paper reviews numerical studies on the effect of expansion and damage due to alkali-silica reaction (ASR) on the mechanical performance of concrete and reinforced concrete at the structural scale level. Previous research on model development that has focused on the performance of RC members or structures is collected and summarized based on how they operationalize expansion progress. The models can be divided into three categories: models that receive the target expansion amount as an input value, models that use expansion curves, and models that calculate the increase in free expansion by considering the kinetic process of ASR. The aim of the model development can be related to either the deformation of the member or the load capacity for static or dynamic load actions. Expansion transfer under confined conditions is characteristic of the ASR problem, and the methods to model expansion transfer are accordingly summarized. Various considerations concerning the effect of ASR expansion and associated damage on the concrete constitutive laws are also studied. Expansion transfer under multi-axial stress states can be accurately reproduced by the modeling of expansion redistribution and volumetric expansion reduction under stress conditions. There are diverse methods to model the resultant deterioration of mechanical properties, but the primary method is by reducing the strength and elastic modulus according to empirically determined relationships. The ideal modeling approach is still under discussion because the effect of the anisotropic cracking state on the anisotropic mechanical response still requires further study. Finally, current problems of assessment of ASR-damaged concrete structures were discussed, and the significance of the causal correlation between macroscopic expansion behavior and microscale factors was suggested.
Creep strain is a significant factor affecting the dimensional stability and durability of the concrete structure. This paper aims to develop the prediction model B4TW-SCC for the creep of self-compacting concrete (SCC), which still lacks accurate prediction models. Besides, the compressive creep of SCC was experimented with by partially replacing up to 40% of the cement weight with fly ash. The tested results indicated that fly ash is highly effective in decreasing the total and basic creep of SCC, corresponding to an increase in the contents of fly ash. The new prediction model was calibrated based on the B4 model and B4TW-2020 model to fit with the creep database collected from numerous published papers with 212 test curves for total creep and 54 test curves for basic creep. The developed model was capable of the highest accuracy in predicting the creep of SCC compared with the other models, such as the B4, fib and ACI 209R-92 models, and available models of SCC CEB90 (Poppe and De Schutter) model, CEB90 (Kavanaugh) model, and the JSCE (Aslani) model.
This study investigated carbonation-induced corrosion behaviours with different water-to-cement (w/c) ratios and cover thicknesses under different environmental conditions. The relative humidity (RH) and temperature dependence of the corrosion behaviours were determined by considering the water content and electrical resistivity of the mortar and the corrosion rate of the steel reinforcing bar (rebar). Accordingly, corrosion controlling mechanisms were discussed and verified. Prediction methods for the corrosion process under resistive and cathodic control were proposed based on the water content, temperature, and cover thickness. Finally, the proposed corrosion rate prediction method was verified by a field survey on three carbonated reinforced concrete (RC) buildings. The general agreement between the measured and calculated corrosion rates of the steel rebar verified the reliability of the proposed corrosion rate prediction method, contributing to the soundness evaluation of RC members.
Carbonated wollastonite-based clinker is proposed as a potential novel supplementary cementitious material. The clinker can be synthesized from limestone and a silica source, and exhibits a CO2-footprint after carbonation, which is approximately 60-70% less than the one of Portland cement. When carbonated, a silica-rich amorphous phase forms besides various polymorphs of calcium carbonate. When the carbonated clinker is blended with Portland cement, hydration is accelerated, and a significant pozzolanic reaction of the silica-rich amorphous phase takes place. This leads to a positive contribution to compressive strength. In a blend with 30% replacement of Portland cement by the carbonated wollastonite-based clinker almost the same mortar compressive strength is reached after 28 days compared to the plain Portland cement. Further investigations, especially regarding the production of the carbonated clinker, the durability of concrete incorporating this novel material, and life cycle analyses as well as economical assessments are needed.
Concrete structures would commonly suffer from salt frost deterioration in cold climate areas. The governing mechanism of concrete salt frost deterioration was comprehensively influenced by the freezing characteristics of deicing salt solutions. Characteristics of solution density, freezing point, freezing volume variation, and freezing expansion pressure of deicing salt solutions were experimentally investigated. A special device was designed and adopted to determine the freezing expansion pressure of deicing salt solutions. Investigation results indicated that all characteristics of deicing salt solutions were affected by solution concentration. As solution concentration increased, the freezing point and the maximum expansion ratio of solution volume decreased, and the maximum contraction ratio of solution volume increased. Freezing expansion pressure was determined by solution component, solution concentration, and volume saturation degree. As the critical saturation degree of solution volume was reached, freezing expansion pressure increased sharply. The freezing expansion pressure of deicing salt solutions was high enough to cause concrete salt frost deterioration.