Current practice reveals that no adaptation of self-healing concrete mix designs are made for the introduction of healing agents. However, the inclusion of healing agent may downgrade the concrete ...properties to some extent. Therefore, an optimization of mix design is necessary in order to eliminate the possible negative effects induced by the healing agents and also to potentially improve the self-healing and self-sealing abilities. In this paper, seven concrete mix designs were studied with crystalline admixture (CA) as a prospective healing agent to stimulate the autogenous healing mechanism. Several design parameters were opted namely (1) dosage of CA from 0 to 2% by cement mass, (2) water-cement (w/c) ratio between 0.46 and 0.52, and (3) cement content in the range of 320 to 360 kg/m3. The self-healing and self-sealing performances were investigated by the indicators of crack closure and the permeability rate, respectively. Results showed that the addition of CA demonstrated an advanced progress on the crack closure with increasing the healing time. The size of the crack considerably influenced healing performance. All in all, the effects of mix design parameters in terms of improvements of healing and sealing efficiencies are discussed and a recommendation for optimizing the mix design is proposed.
Self-healing concrete has emerged as one of the prospective materials to be used in future constructions, substituting conventional concrete with the view of extending the service life of the ...structures. As a proof of concept, over the last several years, many studies have been executed on the effectiveness of the addition of self-healing agents on crack sealing and healing in mortar, while studies on the concrete level are still rather limited. In most cases, mix designs were not optimized regarding the properties of the fresh concrete mixture, properties of the hardened concrete and self-healing efficiency, meaning that the healing agent was just added on top of the normal mix (no adaptations of the concrete mix design for the introduction of healing agents). A comprehensive review has been conducted on the concrete mix design and the impact of healing agents (e.g., crystalline admixtures, bacteria, polymers and minerals, of which some are encapsulated in microcapsules or macrocapsules) on the properties of fresh and hardened concrete. Eventually, the remaining research gaps in knowledge are identified.
This paper brings a new insight into understanding the influence of macrocapsules in packing systems, which can be useful in designing the inert structure of self-healing concrete. A variety of ...tubular macrocapsules, in terms of types and sizes, was used to assess the capsules' effect in the packing, together with various aggregate types and fractions. The voids ratios (
) of aggregate mixtures were evaluated experimentally and compared with the prediction via the particle packing model of Dewar. The packing of coarse particles was found to be considerably affected by the presence of macrocapsules, while no capsules' effect on the packing of fine particles was attained. A higher capsule dosage and capsule aspect ratio led to a higher voids ratio. In the formulation of the inert structure, the packing disturbance due to capsules can be minimised by increasing the content of fine aggregates over coarse aggregates. Dewar's model showed a good compatibility with experimental results in the absence of capsules. However, the model needed to be upgraded for the introduction of tubular macrocapsules. Accordingly, the effect of macrocapsules was extensively analysed and a '
model' for capsules (with some limitations) was finally proposed, offering a high predicting accuracy.
Although steel reinforcements are used to withstand tensile forces in concrete, cracks are an unavoidable phenomenon. The presence of cracks, in fact, increases the risk for lowering the service life ...and durability of concrete structures. A critical issue occurs when due to splitting forces, cracks appear in concrete along the tensioned rebars which damage the bonding between the steel and concrete matrix. As a mitigation plan, the cracks should be healed at short notice and the bonding has to be recovered by the potential use of healing agents. This paper aims to investigate the bond behaviour of steel reinforcement in self-healing concrete. Two biomasses were employed as healing agents namely HTN (bacteria-based) and YEAST (fungi-based). The fresh and hardened properties of the normal and self-healing concretes were initially evaluated. The bond properties were investigated by performing pull-out tests on three different states of concrete: uncracked, cracked, and healed. Results revealed that the additions of biomasses did not induce negative effects on the compressive strength of hardened concrete. Moreover, the average bond strength of uncracked concretes containing HTN and YEAST improved by 20% and 8%, respectively, as compared with normal concrete. The introduction of a crack caused a significant reduction in bond strength regardless of the addition of healing agents. Nevertheless, it was found that the bond strength was slightly recovered after healing under water immersion.
Despite the robust ability of microcapsules (MIC) to break and release agent for healing/sealing efficacy, the reduction of concrete strength has been a major issue when using MIC. In this study, the ...optimisation of concrete mix design was initiated with employing three main parameters: MIC size (56, 93 μm), MIC dosage (0, 3, 6% by weight of cement) and water-cement (w/c) ratio (0.40, 0.50, 0.60). The used microcapsules consisted of water repellent agent core acting as a sealing agent and polyurethane as the shell material. Results confirmed the MIC dosage as the most significant factor affecting the mechanical properties, while no significant effect on the MIC size. Further, the MIC effect can be reduced by changing the concrete mix design from low to high w/c. The sealing efficiency of concrete was remarkably improved with the inclusion of MIC and a good bond between the capsules and concrete matrix was attained.
•The mix design optimisation allows to minimize the drawback of using microcapsules.•The sealing efficiency is significantly enhanced by the addition of microcapsules.•A good bonding of microcapsules with concrete matrix is showcased.
Self-healing concrete is considered as a new generation of concrete with the ability to heal cracks without human intervention. The healing agents are incorporated into the concrete to activate the ...healing mechanism and to improve the healing efficiency. While both lab- and large-scale projects have shown that the addition of healing agents can have a possible positive effect on the hardened concrete properties (e.g. compressive strength), unfortunately, the evaluation of fresh properties of self-healing concrete mixes is often neglected. In the current study, the effect of healing agents is clearly identified starting from the paste level. Different techniques were used to study the effect of healing agents on the consistency, viscosity and adsorption behaviour of PCE-based superplasticizer in cement paste. A crystalline admixture and bacteria were used as healing agents, and CEM III/A was used as the binder component of the paste. The results showed that the inclusion of bacteria did not influence the rheological properties of the cement paste and no incompatibility issues were found with the superplasticizer. On the other hand, the presence of the crystalline admixture in the paste interfered with the rheological properties of the cement paste as a reduction of workability, an increase of paste viscosity, and an increased adsorption of superplasticizer.
The use of macrocapsules in self-healing applications offers a potential benefit by carrying a larger amount of healing agent in comparison with microcapsules. However, the application of ...macrocapsules is still limited to paste and mortar levels on lab-scale. This is due to a concern that most capsules might be broken when mixed with concrete components. In this study, cementitious tubular capsules were used and they were considered as a partial replacement of coarse aggregates (2 vol% gravel). The capsules have a dimension of 54 mm and 9 mm in length and outer diameter, respectively. A water-repellent agent (WRA) was entrapped in the capsules as a proposed agent to seal the crack. Initial results revealed high survivability of capsules during concrete mixing: 100% survival ratio when tested in a drum mixer and 70–95% when tested in a planetary mixer. The mechanical and self-sealing properties of concrete containing embedded capsules were evaluated. With the addition of capsules, around 8% reduction of compressive strength was noticed, but no further effect on splitting tensile strength was detected as compared with concrete without capsules. Ultrasonic pulse velocity (UPV) tests confirmed that the presence of capsules also did not significantly affect the compactness of the hardened concrete. Furthermore, the embedded capsules were able to break when a crack was introduced and it was found that 90% sealing efficiency was achieved by capsule-based concrete as a result of the successful release of sealing agent into the crack.
•The addition of healing agents to the concrete improves the bond strength of rebar.•Longitudinal cracking decreases the bond strength between steel rebar and concrete.•The autonomous self-healing ...effect promotes a slight bond strength recovery.•Crack closure is evident by the inclusion of healing agents.
The appearance of cracks in structural reinforced concrete is inevitable and when out of control, it can be the cause of concrete failure. The ingress of water and harmful substances via the cracks is critical as the embedded steel reinforcements in the concrete can be corroded. Crack formation will directly weaken the bond between the reinforcing bar and concrete. To mitigate this issue, cracks should be repaired and closed relatively fast and this can potentially be obtained by incorporating self-healing technologies. Self-healing concrete demonstrates a good healing efficiency by the use of smart materials which allow for autonomous healing or enhance the autogenous healing mechanism of concrete. However, it is questioned whether the precipitates only artificially close the crack or also contribute to improve the bond with the reinforcement. In this study, an experimental investigation was conducted to evaluate the bond properties of self-healing concrete by means of pull-out tests. Four types of healing agents were used including two non-axenic biomass agents (HTN and YEAST) and two commercial agents (crystalline admixture and bacteria (CA and BAC)). The fresh properties and mechanical properties of the concrete including the healing agents were initially investigated. Pull-out tests were executed on uncracked, cracked and healed specimens. Two healing periods (28 and 112 days water immersion) were considered to evaluate the effect of healing time on bond recovery. Test results confirm that the addition of healing agents induced a better improvement of bond properties of steel reinforcement in uncracked concretes with respect to the reference concrete (no healing agent added). The highest bond strength enhancement by 57% on uncracked concrete was obtained with the addition of CA, while the inclusion of other agents such BAC, HTN and YEAST also possessed the bond strength improvement by 47, 21 and 7%, respectively. The presence of a longitudinal crack in concrete significantly reduced the bond strength up to 80% and this effect was not significantly affected by the crack size, when considering cracks in the range of 200─500 µm, and the introduction of healing agents. Nevertheless, the bond properties were slightly recovered after healing due to self-healing effects and formation of healing products in the crack was clearly visible.
This paper aims to examine the engineering properties of ternary blended no-cement mortar which subjected to the various elevated temperatures exposure. The mortars were produced by mixing ground ...granulated blast furnace slag (S), Type-F fly ash (F) and circulating fluidized bed combustion (CFBC) fly ash (C). The water-to-binder ratio was fixed at 0.40 and the CFBC fly ash content was fixed at 15 wt.% of the mixture that acts as the main activator. The specimens were exposed to the elevated temperatures ranging from 200°C to 800°C. The mass loss, compressive strength, and ultrasonic pulse velocity were determined before and after exposure to the elevated temperatures. The obtained results showed after exposed to high temperature, the mortar weight reduction was discovered in the range of 6.0–8.7% when temperature rose from 200°C to 600°C, and decreased significantly up to 12.4% as temperature reached 800°C. The major strength loss occurred after 600°C with the residual compressive strength approximately at 44.2%. At 200°C, increased strength was found on SFC mixture and when temperature rose to 400°C, the specimens still can resist the load reliably with the strength loss less than 8.0%. Consequently, SFC mortar generates good durability and heat resistance below 400°C.
Tujuan dari penelitian ini adalah untuk meneliti dampak digital marketing terhadap keputusan pemilihan perguruan tinggi oleh mahasiswa, dengan mediator kesadaran merek. Penelitian ini difokuskan pada ...mahasiswa aktif di Universitas Logistik dan Bisnis Internasional, menggunakan metode penelitian kuantitatif dengan pengembangan dan pengujian empat hipotesis. Analisis dilakukan melalui pemodelan persamaan struktural dengan bantuan aplikasi SEM-AMOS. Populasi penelitian melibatkan mahasiswa aktif pada tahun ajaran 2022/2023 dan 2023/2024, dengan sampel sebanyak 400 dan yang berhasil terkumpul dan diolah sebanyak 110 siswa.
Temuan empiris menunjukkan bahwa aspek-aspek digital marketing, terutama media sosial dan website, memiliki pengaruh positif yang signifikan terhadap keputusan pemilihan mahasiswa di Universitas Logistik dan Bisnis Internasional. Hasil uji variabel kesadaran merek juga menunjukkan dampak positif yang signifikan dalam memediasi pengaruh pemasaran digital, terutama melalui media sosial, pada keputusan pemilihan mahasiswa. Namun, pada dimensi website, kesadaran merek tidak signifikan memediasi keputusan pemilihan.
Implikasi dari hasil ini menyarankan bahwa Universitas Logistik dan Bisnis Internasional perlu meningkatkan strategi pemasaran digital, khususnya dalam pengelolaan website, guna lebih efektif mempengaruhi mahasiswa dalam menentukan pilihan mereka. Diharapkan bahwa perbaikan ini akan lebih membentuk kesadaran merek di kalangan mahasiswa dan calon mahasiswa di Universitas Logistik dan Bisnis Internasional.
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