Indian Concrete Journal

Synergism of foam and water dosages in lightweight cellular recycled aggregate concrete Santha Kumar, S. R. Karade, and Aman Kumar Mishra

This present paper reports results of a study conducted to utilize recycled fine aggregates (RFA) obtained from construction and demolition (C&D) waste, as an alternative resource of natural sand for the production of RFA based Lightweight Cellular Concrete (RLWCC). This research particularly focuses to understand the synergetic effect of foam and water dosages on the properties of RLWCC. Three differentfoam-solid ratios, 0.013, 0.026 and 0.053 and three water-solid ratios, 0.228, 0.286 and 0.325 were used in this study. The research outcome inferences that the foam and water contents have a great effect on flowability and its reduction with respect to time, bleeding capacity, microscopic void distribution, densities and strength characteristics of RLWCC. This paper elucidates the behaviour of RLWCC from the material perspective that would enhance the utilization of RLWCC in the construction sector.

Columns should preferably fail in under-reinforced condition – myth or reality Jayanta Nath Chowdhury, and Santanu Bhanja

Ductile failure of reinforced concrete (RC) sections can be ensured only in flexure as all other modes of failure are brittle in nature. Flexure design as per IS: 456 (2000) can be performed within the domain of maximum under-reinforced and balanced conditions as over-reinforced sections are not permitted. Curvature ductility values are maximum for maximum underreinforced sections and minimum for balanced sections. The amount of reinforcements provided in beams define the type of section i.e., under-reinforced, balanced or over-reinforced. As per IS: 456 (2000) all types of sections are permitted in compression. However, for columns with a certain amount of reinforcement, failure can occur in balanced, under-reinforced or over-reinforced conditions depending upon the loading on the section. It is a common notion amongst the designers that similar to beams, columns should also fail in under-reinforced condition to ensure ductile failure. In the present work, using the limit state methodology of IS: 456 (2000), curvature ductility of rectangular RC columns with 0.8 and 4 % reinforcement (distributed on two sides) have been evaluated for three grades of concrete (M20, M40 and M60) with four grades of steel (Fe415, Fe500, Fe550 and Fe600) and different effective covers ( d'/D = 0.05, 0.1, 0.15 and 0.2). Curvature ductility values of sections with identical configurations acting as beams have also been determined. The variation of curvature ductility values of columns failing in highly under-reinforced, balanced and highly over-reinforced conditions are not significant, whereas the corresponding variation is significantly high for beams. Thus, beams can be made considerably more ductile than columns. Hence, the notion amongst the designers that columns should preferably fail in under-reinforced condition does not seem to be justified.

Numerical modelling on strength of concrete under elevated temperatures Swati, and V. K. Verma

Present study deals with the non-linear finite element analysis by the use of ANSYS 2022 software to analyse the compressive strength of different grades of concrete specimens after subjected to the different elevated temperatures and then cooled gradually. The experimental data was taken from research papers of the various researchers. About seventy cubic and cylinder specimens of different sizes were taken for analysis. First, the compressive strength of concrete specimens were calculated at ambient temperature and then these specimens were subjected to different temperatures i.e. (200, 350, 400, 500, 600, etc.) °C and cooled gradually before analysing. After finite element analysis by ANSYS 2022, results were compared with the experimental results of various research papers at ambient and different temperatures. It has been found that finite element analysis is fairly able to predict the compressive strength of concrete subjected to elevated temperatures and different grade of concrete shows different behaviour at different elevated temperatures.

Mechanical, microstructure and durability properties of cement composites using multi-walled carbon nanotubes C. L. Jejurkar, V. Sairam, S. R. Korake, and Ankur Laxman Yadav

In the present work, for uniform and thorough dispersion of carbon nanotubes in concrete a very small amounts of multiwalled carbon nanotubes (MWCNT) have been taken i.e. 0.025, 0.05 and 0.075 % percentage by weight of cement. Proper dispersion of carbon nanotubes was done by the ultrasonication of the MWCNT’s in the presence of high-performance superplasticizer as a surfactant. The degree of dispersion of MWCNT in aqueous solution has been studied by the use of UV-Vis spectra. For testing the strength and durability properties, a w/b ratio of 0.39 is adopted in this study. The various tests conducted in this study are compressive strength, split tensile, flexure test, Ultrasonic pulse velocity (UPV), sorptivity and water absorption. The microstructure study has been done by the use of Scannning Electron Microscope (SEM) imaging and Energy Dispersive X-ray (EDX) analysis. From the strength test results it was observed that with the use of 0.025 % MWCNT there was a significant improvement in compressive, split tensile strength and flexural strength. From the durability tests also, it was observed that the water absorption and sorptivity also decreased with the addition of MWCNT. Evidence of debonding, and also of mesh filling were observed in the microstructure analysis. SEM shows the presence of micro-crack bridging in the composites.

Experimental study between GFRP rebar and steel rebar reinforced concrete beams and its design philosophies Sanket Darji, and D. R. Panchal

Glass fiber reinforced polymer (GFRP) rebar is a rod made of composite material. It has the potential to replace steel rebar as reinforcement in concrete structures. Despite being anti-corrosive, strong, durable and cheaper in longer run, its adaptation in India is being hindered due to lack of Indian design guidelines. In the current research, GFRP rebars reinforced concrete (RC) beams and steel rebars RC beams have been designed as per ACI 440.1R-15 and IS: 456 (2000) respectively. GFRP RC beams were designed as under reinforced, balanced and over reinforced section beams. Total 16 beams have been casted and tested and an experimental and analytical comparative study has been done on its flexural capacity, deflection and design philosophy. The experimental results indicated that over reinforced design shall be preferred as compared to under reinforced and balanced designs for GFRP RC beams. Over reinforced GFRP RC beams successfully achieved strength as well as serviceability criteria.