Search

Highlights • Cement paste is recommended as a good alternative surface coating material of LWA-PCM for a better compatibility. • Exothermic/endothermic events validate that PCM can delay or prevent ice formation. • When the replacement of LWA is up to 50% vol., the heat released by PCM is sufficiently high to inhibit ice formation. • Time offset between solidification of PCM and pore solution is relevant to effective utilization of PCM in improving freeze-thaw resistance of concrete. Abstract This paper investigates the preparation and assessment of mortar-phase change materials (PCM) systems to gain a full understanding of using the heat stored in PCMs to delay or prevent ice formation in concrete. Desirable PCMs and light weight aggregates (LWA), which act as carriers of the PCMs, were first selected based on their thermal and physical properties. LWAs containing PCMs were prepared and assessed for different combinations of materials. Cyclic freeze-thaw mass loss, latent heat attenuation, and FTIR tests were conducted to characterize the stabilities of the LWA-PCMs. The thermal performances of the mortars containing LWA-PCMs were investigated using a longitudinal guarded comparative calorimeter (LGCC) that was operated under quasi-steady state conditions during the cooling/heating process. The results confirmed that PCMs can be steadily absorbed in LWAs without chemical reactions or great losses in latent heat when the LWA-PCMs were coated in a certain way. Cement paste was recommended to coat the surface of the LWA-PCMs for better compatibility with the system than that of traditional coating materials. The ability of the PCM to delay or prevent ice formation in mortar was verified from the exothermic/endothermic events associated with the phase transformations of the pore solution and PCM. In the present study, when up to 50% vol. of the LWA was replaced as carriers of PCM, the heat released by the PCM was sufficiently high to inhibit ice formation. [ABSTRACT FROM AUTHOR]

Concrete highway and airport pavements are designed to be long lasting; however, some concrete pavements have shown premature deterioration at the cracks and joints. It has been hypothesized that one cause of this deterioration is associated with fluid ingress, especially in cases where those fluids contain deicing salts. This paper examines fluid ingress in mortar using a cross-sectional geometry that is similar to a typical concrete pavement joint. Time-dependent and spatial aspects of fluid ingress are examined using neutron radiography (NR), which was performed using the thermal neutron radiography station at the neutron spallation source at the Paul Scherrer Institut (PSI). Specifically, this paper examines the role of the initial relative humidity (or degree of saturation) and air content on the fluid ingress. The work indicates that the initial fluid ingress reaches a specific degree of saturation relatively rapidly, where the large capillary and gel pores appear to be filled in (commonly referred to as the nick point in sorption tests) and the entrapped and entrained air pores fill in more slowly over time. [ABSTRACT FROM AUTHOR]

Abstract: The damage evolution of concrete subjected to 4-point flexural fatigue load and closed freeze/thaw cycles simultaneously was experimentally studied. The responses on a separate fatigue load at 20°C and −25°C were tested to simulate the specimens with “thawed” or “frozen” pore water respectively. This damage, characterized by the residual strain, is 15.7% lower of the “frozen” state and 30.8% higher caused by the two loads than that of the “thawed” state. More interfacial cracking related signals were observed in the frequency domain using acoustic emission. The micrographys illustrate the cracks originate from the two damage sources, referring to the pores and the interfacial zones. [Copyright &y& Elsevier]

• AE temporal parameters demonstrate an effect of multiple healing of cracks. • AE energy vs. FMA spectrum provides insights on the cracking mechanisms of matrix and interface. • The value of AF/RA confirms the contribution of the cracking modes to the characteristic spectrum. • The higher addition of microcapsules results in a higher ratio of shear to tensile cracks. The multiple damaging and healing of cracks in cement paste by microcapsules was experimentally investigated under various flexural loading scenarios. The crack formation in the loading process was detected in situ using the acoustic emission (AE) technique, in which passive and active sensing modes were combined to provide complementary information on the overall damage and local cracking. The AE analysis was conducted based on the differentiated features of the signals in terms of the temporal and spectral descriptors to distinguish the cracking mechanisms. The results indicate the alleviated damage of the specimens due to healing of cracks based on the active sensing mode. The time-dependent hits and cumulative energy demonstrate new cracking sources in the healing specimens. The changes in the variation of hits (versus amplitude) and the AE energy (versus duration time) reveal that the new cracking sources were the failure of the pre-attached crack space by the adhesive according to the calibration. The distinguished characteristics of the maximum frequency of the waveforms provide further insights into the cracking mechanisms of matrix and interface. The plot of the average frequency (AF) versus the RA index illustrates that the cracking modes contribute to the characteristic spectrum. [ABSTRACT FROM AUTHOR]

Highlights • The self-healing capability of steam-cured mortar was investigated for the first time. • AE signals can distinguish damage stage between healing products and host matrix. • The amount and energy of healing products can be qualitatively assessed by AE signals. Abstract The objective of this work is to investigate the self-healing performances of steam-cured mortars with mineral additives (e.g., calcium-based materials, chemical expansive agents and crystalline components). The self-healing capabilities of crack was evaluated by transport tests and acoustic emission (AE) analysis for cracked mortars. The two representative AE parameters, i.e., amplitude and energy, were used to reveal the characteristics of healing products. The results showed that the improvement of transport properties of cracked steam-cured mortars were more effective compared to standard-cured mortars. The healing efficiency can be further improved by utilizing mineral additives. The differences of damage stage between healing products and host matrix can be distinguished by AE signals. Upon reloading of steam-cured mortar with mineral materials, the number of amplitude were much larger and the cumulative energy was much higher compared to other mortar. It indicated that the steam-cured mortar with mineral materials possessed larger amount and much higher energy healing products in the crack to some extent, which were well consistent with that of transport properties and microscopic observation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The properties of PMCM and PA under temperature cycle curing regimes were investigated. • Degree of cement hydration contributes to the strength of mortar under 5/20 °C. • 20/80 °C increases the mechanical properties of PA causing an increase in strength of mortar. Polyacrylate dispersion-modified cement mortar (PMCM) has been widely studied as a good repair material, but the majority of studies have focused on the curing conditions with constant temperature, while the temperature of its application environment usually varies with time. Therefore, for the variable temperature environment that PMCM may suffer in winter and summer, the mechanical and deformation properties of PMCM and the mechanical properties of polyacrylate dispersion (PA) were investigated by simulating the winter and summer curing regimes through low-temperature cycles of 5 and 20 °C (5/20 °C) and high-temperature cycles of 20 and 80 °C (20/80 °C). XRD, TG-DSC and MIP were used to characterize the microscopic properties and explain the mechanism. In addition, 5, 20 and 80 °C were set as control curing temperatures. The results show that PMCM under 5/20 °C has a higher porosity and greater drying shrinkage compared to 5 and 20 °C, but strength and hydration degree are between the two curing regimes. Compared with 20 °C, the high-temperature stages of 20/80 and 80 °C promote the hydration of the mortar but increase drying shrinkage and porosity, reducing its strength. However, both regimes, especially 20/80 °C, allow the mechanical properties of PA to be enhanced, causing an increase in the cohesion of the modified mortar, which not only compensates for the disadvantages of large porosity but also further increases the strength, indicating that PMCM not only resists the effects of high-temperature cycling or high-temperature environments on strength but even performs better. [ABSTRACT FROM AUTHOR]

• A non-destructive assessment method based on EIS is proposed to evaluate the effect of electrodeposition. • Proposing the equivalent circuit model to describe and analyze the cracking and electrodeposition repair process. • The influence of concrete's w/c ratio, crack width, and crack tortuosity on EIS have been calculated and discussed through equivalent circuit model. In this study, the electrochemical impedance spectrum (EIS) is proposed to evaluate the effectiveness of concrete cracks repaired through electrodeposition. The EIS responses of the concrete cracking and electrodeposition repairing processes are investigated. The obtained results show that the impedance of concrete decreases with increasing crack width. The impedance of concrete increases gradually during the electrodeposition process. In order to characterize and forecast the EIS responses during the concrete cracking and electrodeposition repairing processes, a new equivalent circuit model is proposed. The crack repairing rates are defined in terms of the crack resistance and total impedance of concrete. After 14 days of electrodeposition repairing, the crack repairing rates can eventually reach 79.35% and 77.81% in terms of crack resistance and total impedance, respectively. In addition, the influences of the w/c ratio, crack width, and crack tortuosity of concrete on the EIS responses of concrete repaired by the electrodeposition process are calculated and discussed. [ABSTRACT FROM AUTHOR]

• A novel rapid crack-healing approach is proposed by electric-induced in-situ synthesis of ettringite. • Electric-induced in-situ synthesis of ettringite to heal concrete cracks is feasible under the asymmetric healing condition. • Electric field-induced ettringite can significantly shorten the healing time. • The rapid healing mechanism was disclosed through both the macroscopic and microscopic tests. Cracking is inevitable in concrete and can seriously threaten the durability of the structures. This paper proposed electric-induced in-situ synthesis of ettringite as a crack healing strategy for concrete structure. Composite solutions of aluminum sulfate and calcium acetate with four different molar ratios of Ca to Al (1, 3, 5, 7) were used as electrolyte solutions. The effectiveness of healing was evaluated by crack closure ratio, permeability, and coverage ratio of the crack section, while the composition and microstructure of products were also investigated. From the results, when the Ca-Al ratio is 3 or 5, the crack closure time shortened to 1 day, and the permeability coefficient reduced by nearly 4 orders of magnitude compared to the unrepaired specimen after healing for 7 days. Of all the groups, the products penetrated the entire crack, and the coverage ratio of crack section can reach more than 60 % when the Ca-Al ratio is 5. Additionally, ettringite was detected as the main phase of products by X-ray diffraction and thermogravimetric analysis (TGA). Needle-shaped ettringite can be observed during the whole healing period through scanning electron microscopy (SEM). In-situ synthesized ettringite crystals evolved from small and short prismatic shapes to long and acicular shapes. These crystals overlapped with each other and formed a dense network structure. [ABSTRACT FROM AUTHOR]