Key Engineering Materials Vol. 814

Abstract: The objective of this study was to compare shear bond strength (SBS) and adhesive remnant index (ARI) of domestically made orthodontic adhesives to a commercial orthodontic adhesive, Transbond XT (3M Unitek, USA). Three formulas of an in-house orthodontic adhesive were divided according to monomer ratio (BisGMA:TEGDMA) into group 1 (8:2), 2 (7:3), and 3 (6:4), respectively, with 60-70 weight % of filler amount and 0.5 % of photoinitiator (TPO). Eighty upper human premolars (20 of each group) were bonded with stainless-steel brackets with these experimental and control adhesives. All were cured by LED light-cured unit for 20 seconds. After polymerization for 24 hours, a universal testing machine was used to apply an occlusal shear force to the enamel/bracket interface at a speed of 0.5 mm/min. The ARI scores were evaluated for each debonded tooth. Mean SBS values were analyzed statistically using the One-way ANOVA and the Tukey’s test for multiple comparison. Chi-square test was used to determine significant difference in the ARI scores. The results showed that there was statistical difference in the mean SBS of 4 groups (P<.001). The SBS value of group 1, 2, 3, and control was 18.79 MPa, 18.58 MPa, 23.30 MPa, and 28.02 MPa, respectively. Chi-square comparison for the ARI indicated that there was significant difference (P=.012) between the groups. In conclusion, the experimental adhesive of group 3 yields the higher SBS than in group 1 and group 2. Although these adhesives provide a lower shear bond strength than Transbond XT, they were acceptable for clinical use. Most failures of Transbond XT were found between adhesive-bracket interface, whereas the three in-house experimental adhesives were found mixed failure patterns of ARI.

Abstract: In order to improve the dimensional stability of cement based materials, the effects of shrinkage reducing admixture (SRA) dosage on the shrinkage and crack properties of cement based materials were investigated. The hydration process of the cement pastes was tracked and monitored by hydration calorimeter and adiabatic temperature rise apparatus respectively. The action mechanism of SRA on hydration process of the cement based materials was characterized by differential scanning calorimeter (DSC). The shrinkage and crack results show that the ability of resist cracking of concrete can be effectively improved by SRA. The results of hydration calorimeter and adiabatic temperature rise indicate that the appear time of hydration temperature peak at early age was delayed and the development of hydration heat changed gently at later period by doped SRA. The results of DSC show that the release amount of hydration heat and the production of early calcium hydroxide can be delayed by SRA, however, there has no effects of SRA on the formation of cement hydration products like calcium hydroxide at the later period.

Abstract: Magnesium oxychloride cement (MOC) possesses rapid hardening, high mechanical strength, abrasion resistance, low alkali and low corrosive performances. However, its disadvantages of poor water resistance, easily deformation, moisture absorption and halogenations limit the application. A low cost-effective modifier H₃PO₄/Na₂O·xSiO₂·nH₂O was designed for MOC system. The results showed that the softening coefficient of the modified MOC reaches 0.988 by adding appropriate dosage of the modifier. Gelatinous substances in the modified MOC was produced after soaking in water, which effectively inhibit the hydrolysis of phase 5 (5Mg (OH)₂·MgCl₂·8H₂O) and the formation of Mg (OH)₂, thus improving the water resistance of MOC system. Keywords: Magnesium oxychloride cement; Water resistance; Phosphoric acid

Abstract: This paper presents the relationship between the dynamic cone penetration (DCP) test results and the unconfined compressive strength of lateritic cemented soils. A series of DCP tests and unconfined compressive strength was performed on lateritic cemented soil. The soils sample used in this study was lateritic soil. The test results for the DCP tests are presented in terms of penetration index. It can be observed that the penetration index decreased with increasing curing period and cement content. Moreover, the unconfined compressive strength of cemented soils increased with curing period and cement content. The relationship between unconfined compressive strength and penetration index is presented. A unique relationship for unconfined compressive strength can be obtained.

Abstract: Corrosion of steel in concrete is the most detrimental source for reinforced concrete structures. Among the other effects, corrosion deteriorates the interface between steel and concrete. An axisyimmetric numerical model able to simulate the structural behaviour of bond between steel and concrete is here presented. The model is based on the thick-walled cylinder theory so that bond performance is a direct consequence of radial pressure acting on the rebar and coming from the surrounding elements and corrosion. Both elastic and inelastic contribution of concrete is also taken into account. The model is used to simulate pull-out tests present in literature. The results show the effectiveness of the model and is also compared with an empirical model already proposed in literature.

Abstract: The construction industry continues to develop and the requirements for cement performance are getting higher and higher. At the same time, in the steel industry, the discharge of steel slag is also increasing. The effective reuse of steel slag has become a prominent problem in the steel industry. . Therefore, it is envisaged to use steel slag as a raw material for the cement production process to produce cement and to produce high-performance cement. The main raw materials of this experiment are steel slag, limestone, sandstone and shale. Through the cement preparation process, the cement is made, and then the cement is made into concrete to test its performance. This experiment mainly studies the sintering temperature and holding time variable. In the experimental test, the analysis and comparison were carried out in five aspects of the degree of macroscopic cracking, particle size, density, microstructure and composition. In the comparison experiment of sintering temperature, with the increase of temperature, the flexural and compressive properties of cement gradually increased. In this test, 1200 °C is the most suitable temperature for the performance of the cement. Through the experimental comparison of different holding time, it is known that with the prolonging of the holding time, the microstructure and actual performance of the cement are continuously enhanced. Comprehensive consideration: the ratio of steel slag in cement ratio is 10%, sintering temperature is 1200 °C, and heat preservation is 2h. The steel slag cement prepared under this condition has the strongest performance.

Abstract: By using repeated load triaxial test method, test results of permanent strain of fine sand were obtained. The main factors affecting permanent strain of fine sand samples are water content, degree of compaction and deviator stress. Permanent strain of sand is less sensitive to moisture when compared to clay and silt. Well compacted fine sand subgrade is less affected by the change of water content, which illustrates a more stable long-term performance. Analyze from meso-structure, the ellipsoid shaped particle is less stable than sphere shaped one under the effect to repeated load. Fine sand with smaller amount of ellipsoid shaped particle would have better dynamic behaviors. Predicting models of permanent strain with basic soil physical properties were established using regression analysis.

Abstract: Recently, rebar anchor plate has been widely used in the project, which solve the rebar anchor problem and improve the construction quality. This paper introduced the rebar mechanical anchorage technology background, research content and progress, and rebar anchor plate application, which would offer the guidance and reference for the designers and constructors.

Abstract: The objective of this study is to evaluate the sulfuric acid resistance of the concrete coated with bacterial-glycocalix-based biomimetic coating mortar. The variation of the compressive strength and mass of the coated concrete since the specimen was immersed into an aqueous solution of 5 % sulfuric acid were 0.88 and 12 % at the age of 56 days, respectively, showing a superior deterioration resistance. As a result, it can be concluded that the developed biomimetic coating mortar possesses a great potential for enhancing the deterioration resistance performance of concrete.

Abstract: This study proposes steel bar prefabrication technology including V-type supplementary tie and closed hoops for seismic strengthening of deficient columns. The axial concentric behavior of the columns strengthened with proposed approach in the jacket section was examined using five full-scale specimens. Test results showed that the axial strength of the strengthened columns can be estimated conservatively in accordance with the prediction equations of ACI 318-14 approach. The axial ductility of the strengthened columns was 1.4 times as high as that of the existing column. Overall, the proposed technology is effective in enhancing the axial stiffness, strength, and ductility of the deficient columns.