V. Saraswathy

Strength and Durability Performance of Alkali-Activated Rice Husk Ash Geopolymer Mortar

This paper describes the experimental investigation carried out to develop the geopolymer concrete based on alkali-activated rice husk ash (RHA) by sodium hydroxide with sodium silicate. Effect on method of curing and concentration of NaOH on compressive strength as well as the optimum mix proportion of geopolymer mortar was investigated. It is possible to achieve compressive strengths of 31 N/mm2 and 45 N/mm2, respectively for the 10 M alkali-activated geopolymer mortar after 7 and 28 days of casting when cured for 24 hours at 60°C. Results indicated that the increase in curing period and concentration of alkali activator increased the compressive strength. Durability studies were carried out in acid and sulfate media such as H2SO4, HCl, Na2SO4, and MgSO4 environments and found that geopolymer concrete showed very less weight loss when compared to steam-cured mortar specimens. In addition, fluorescent optical microscopy and X-ray diffraction (XRD) studies have shown the formation of new peaks and enhanced the polymerization reaction which is responsible for strength development and hence RHA has great potential as a substitute for ordinary Portland cement concrete.

Oxygen evolution catalytic behaviour of Ni doped Mn3O4 in alkaline medium

Electrocatalytic water splitting/electrolysis are accomplished by employing a precious noble metal and metal oxide catalyst. Due to their limited availability and high cost, recent research has focused on the development of earth abundant, low cost, eco-friendly and non-precious catalysts. Towards this goal, this work aims to the study the effect of Ni doping in Mn3O4 for OER in alkaline medium. Mn3O4 and Ni doped Mn3O4 were synthesized through a simple CTAB assisted co-precipitation reaction followed by calcination. The physical and chemical properties associated with the catalytic activity of the samples were investigated. The results suggest that an optimum of 10 wt% Ni doped Mn3O4 exhibits better catalytic activity compared to pure Mn3O4. It shows a lower overpotential of η = 283 mV vs. RHE at 10 mA cm−2, η = 235 mV vs. RHE at 5 mA cm−2 and Tafel slope of 165 mV dec−1 compared to pure Mn3O4 and 1 and 5 wt% Ni doped Mn3O4. The overpotential obtained in the present study is lower than that of the recent studies on Mn3O4, graphene–Mn3O4, Pt–Mn3O4 and Pd–Mn3O4.

Effect of different alkali salt additions on concrete durability property

Abstract Friedel’s salt (FS) is a versatile material and has several advantages in constructional and metallurgical sectors. In this paper, FS is formed in situ in concrete. The addition of Al2O3 (5% by weight of cement) was maintained constant and the formation of FS was proceed through the various ranges of NaCl, KCl and CaCl2. Among them, CaCl2 addition was found effective in the large formation of FS in concrete. The influence of FS on the mechanical, permeability and corrosion resistance properties of concrete was studied by electrochemical techniques. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron micrographs were used to characterize the formation of FS in concrete.

Supercritical fluid processing for the synthesis of NiS2 nanostructures as efficient electrocatalysts for electrochemical oxygen evolution reactions

In this work, the synthesis of NiS2 nanostructures using a simple and one-step environmentally benign supercritical fluid processing technique within 60 min of reaction time has been demonstrated. Structural and morphological characterization has been performed to confirm that the as-synthesized products are cubic NiS2 nanostructures. Interestingly, the as-prepared NiS2 nanostructures exhibit superior electrocatalytic activity towards the oxygen evolution reaction with a small overpotential of 264 mV vs. RHE at 10 mA cm−2 and a Tafel slope of 105 mV dec−1. Remarkably, the observed catalytic activity of the NiS2 nanostructures bears close resemblance to that of the benchmark IrO2 catalyst, where IrO2 shows an overpotential of 260 mV with a Tafel slope of 95 mV dec−1. Thus, the as-synthesized NiS2 nanostructures can be considered as a promising material for the replacement of noble metal-based IrO2 catalysts.

Corrosion and Leaching Studies in Blended Copper Slag Mortar

The effect of copper slag leaching was evaluated using Atomic Absorption Spectroscopy (AAS) immersed in three aqueous media such as tap water, sea water, and synthetic/artificial rain water. The mechanical and corrosion resistance properties of copper slag admixed concrete was evaluated using compression test and various electrochemical tests, respectively. Sand was totally replaced with copper slag in making the concrete specimens. From the investigations it is observed that the copper slag leaching was found to be very less even after 180 days of exposure in aqueous media. Compressive strength revealed that the addition of copper slag increased the compressive strength of the concrete. Rapid Chloride Penetration Test (RCPT) and other electrochemical tests indicated that copper slag admixed mortar performed equal to the sand mortar in sea water environments.

Stress Corrosion Behavior of Ungrouted Pretensioned Concrete Beams

Prestressed concrete beams of size 150 × 150 × 1000 mm were designed, and two bonded cold-drawn 7 mm steel wires were stressed at 70% UTS under service conditions before concreting. The beams were cast with M40 grade concrete mix with various percentages of chlorides ranging from 0, 1, 2, and 3% by weight of cement and cured for 28 days. After 28 days, the stretching forces were released, the prestressing steel wire was allowed to regain its original length, the tensile stresses were transformed into a compressive stress in the concrete, and the stress corrosion behavior was assessed. Stress corrosion cracking (SCC) is due to the simultaneous action of stress, corrosive media, and material properties. The stress corrosion behavior of ungrouted pretensioned steel was assessed by using various electrochemical techniques such as electrochemical noise, open-circuit potential measurement, AC impedance, and potentiodynamic polarization measurements. The same experiments were conducted for rebars embedded in the concrete beam with various percentages of chlorides ranging from 0, 1, 2, and 3% by weight of chloride. After 30 days of exposure, the beams were tested for their flexural strength measurements to find out the load-bearing capacity.