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The development in field of hybrid vehicles, telecommunication and energy sectors require dielectric materials having high-energy storage density with optimum thermal stability to operate in certain environment. To fulfil such requirement a new set of materials along the ternary solid solutions of 0.92Bi0.5(1-x)-La(x)Na0.5TiO3 -0.06Ba(Zr0.2Ti0.8)O3-0.02NaNbO3 (NB1-xLxT-BZT-NN) (x = 0, 0.03, 0.05, 0.07) were fabricated through solid-state mix oxide route. The XRD patterns analysis confirmed a structural phase transformation from rhombohedral to the tetragonal-P4bm phase when x content increased from 0 to 0.07. The SEM study revealed, dense microstructure for all ceramics accompanied by a decrease in the average grain from 1.66 μm to 1.05 μm leading to high densities for these materials with an increase in the x content. The dielectric breakdown field increased from ∼115 to 137 kV cm−1 resulting in an increase in recoverable energy density from ∼0.68 to 1.14 J cm−3 with the increase in x content. Furthermore, excellent temperature stability (±15%) in dielectric permittivity was observed in a wide temperature range for each ceramic. In the present study, a recoverable energy density of 1.14 J cm−3 along with an efficiency of 70.6% was obtained for the composition of x = 0.07.

This research study is conducted to investigate the flexural behaviour of steel fiber reinforced concrete (SFRC) prisms incorporating different types and volume fractions of steel fibers, various grades of concrete, and different specimen depths, all tested under displacement control mode using four-point loading configuration. Two types of steel fibers (hooked end and straight) were incorporated into the concrete mixes at two different dosages (1% and 2%). Concrete mixes with compressive strengths of 40, 50, and 70 MPa were used to cast the samples. Specimen depth was also among the test variables, where prisms of depth 100, 150 and 200 mm were tested to study the size effect on the flexural behaviour of SFRC. Test results indicated that for the straight-end steel fibers, the increase in the fiber volume fraction from 1 to 2% had a noticeable effect on both flexural strength (or Modulus of Rupture, MOR) and associated prism mid-span deflection. However, for the hooked end steel fibers, there was only a limited increase in the same measured values due to reduced workability of the SFRC fresh mix. The test results also have shown that the increase in the concrete compressive strength had only a modest effect on the average MOR value, but a noticeable effect on average mid-span deflection at peak load. The latter was attributed to the relatively long length and the hooked end geometry of the steel fibers. Finally, test results revealed that specimen depth had an impact on the measured flexural strength, where increase in specimen depth was associated with reduced MOR values, a phenomenon that is commonly referred to in the literature as size effect.

This paper presents the results of an experimental investigation on the shear capacity of reinforced concrete beams. The beams under consideration are reinforced with glass fiber-reinforced polymer (GFRP) bars. Also, the effect of shear strengthening on such beams is studied. For this purpose a total of four beams were tested where two served as control beams, while the other two were strengthened using U shape carbon fiber-reinforced polymer (CFRP) sheets, bonded externally. Each beam is 2.4 m long, simply supported and subjected to a four-point load under displacement control mode. The strengthened beams showed a noticeable increase in the load-bearing capacity of the specimen. The failure load recorded of these specimens was 208 kN, an increase of 25%. Moreover, the mode of failure changed from pure shear to concrete crushing in the compression zone. The results indicate that using CFRP sheets to strengthen GFRP reinforced beams in shear is a viable option. However, the results also suggest that the known adverse interaction between EB-CFRP and conventional steel stirrups could be applicable between EB-CFRP and GFRP shear reinforcement in strengthened beams. Therefore the predicted EB-CFRP shear capacity by ACI 440.2R turned to be unconservative when compared to the experimental results.

Given the high environmental impact of OPC concrete on CO2 emissions, the construction industry is moving towards low carbon alternate binders. In recent years geo-polymer concrete (GPC) has come to the forefront of such efforts. However, challenges remain for GPC to be considered as a main-stream construction material. Since GPC is relatively new material in construction industry, many of its mechanical properties are still not fully understood. The current work looks at the strength properties of ambient cured GPC. This research paper is part of an ongoing investigation on GPC and reports some results of the mechanical properties of ambient-cured GPC. In this study, the stress-strain behavior and compressive strength of such GPC and its dependency on various parameters (ratio and type of activator and proportions & type of pre-cursor materials) is investigated. The results indicate that the compressive strength of GPC is greatly dependent on the proportion of Ground Granulated Blast Furnace Slag (GGBFS) and ratio of activators. It was found that increasing the percentage of GGBFS increased the compressive strength but at the expense of setting time of the mix. The mixes that had GGBFS around 20% of the binder material returned a compressive strength of less than 25 MPa which may not be suitable for structural applications. Whereas, the increase in percentage of GGBFS from 20 to 80% resulted in compressive strength of 40 MPa and higher. The stress-strain relationship of the mixes was compared to two analytical models existed in the literature.

This paper presents results from an ongoing research that is intended to study the behavior of URM walls for out-of-plane action. The effect of fiber reinforced shotcrete (FRS) as a strengthening method for the URM walls is examined. Eight URM walls were built inside a precast reinforced concrete boundary frame and strengthened with cement-based shotcrete mixes reinforced with different types of fibers. The masonry wall is 1.2x 1.2 m, and the masonry units were hollow concrete blocks (10 x 20 x 40 cm). Conventional fiber reinforced concrete (FRC) and engineered cementitious composite (ECC) were used as the strengthening layers sprayed on the surface of masonry walls. Control walls with plain shotcrete and conventional plastering mortar were also examined. Synthetic macro-fibers at dosage rate of 6 kg/m3 in FRC mix and Polyethylene micro-fibers at a dosage rate of 16 kg/m3 in ECC mix were considered in this study. The walls were placed in a carefully designed set up and tested under static central load using a hydraulic actuator with a capacity of 500 kN. The parameters recorded during testing were the applied load and out-of-plane displacement of the walls. Cracking pattern and failure modes were also monitored. The reported test results demonstrate that FRC and ECC mixes can significantly increase the out of plane strength and ductility of the URM walls.

Theoretical EMI shielding performance of few layered graphene-thermoplastic polyurethane composite is predicted based on experimental dielectric characteristics. Initially, the EMI shielding effectiveness is estimated for a range of composites based on graphene nanosheets (GNS) volume fraction (V f) at room temperature. An overall attenuation of ~2 dB is predicted at the maximum GNS concentration (0.0055 V f) mainly due to reflection phenomena as a function of frequency (25 kHz–5 MHz). The electrical network formation at 0.0055 V f GNS is evident from the predicted EMI shielding results. The 0.0055 V f GNS-TPU composite is then evaluated for an estimation of EMI shielding effectiveness at elevated temperatures. An increasing trend in EMI shielding effectiveness is predicted as a function of temperature which reaches ~80 dB (25 kHz) at 453 K. Further increase in temperature (463–473 K) takes attenuation to well above 100 dB. The GNS–GNS interaction at elevated temperatures is responsible for the huge attenuation clearly depicted by the reflection phenomena. The attenuation due to absorption phenomena is quite suppressed in the lower frequency with an increasing trend being observed around 5 MHz.