Journal May 2022

Fly ash concrete-a step forward in sustainable construction of nuclear power plant S. B. Kulkarni, S. N. Bhat, A. Ragupathy, K. Kiran

The recent growth in the construction industry puts India at risk of increasing carbon emission and depletion of natural resources. Additional industrial by-products such as fly ash which is generated in thermal power plants increasing the greenhouse gas (GHG). The utilisation of such industrial byproducts supports the sustainable development of the construction industry and fly ash found to be the best partial replacement for ordinary portland cement (OPC). This paper presents a case study on the development and use of fly ash concrete at Kakrapar Atomic Power Plant-Unit 3 and 4 (KAPP 3 and 4). This manuscript enumerates the various aspects of testing and use of fly ash to produce fly ash concrete, which includes characterisation, source qualification, material testing methods, proportioning of concrete mix, direct blending and determination of hardened concrete properties at 40 and 50 % of cement replacement level. Benefits of fly ash concrete were experienced in both fresh and hardened states of concrete during the construction process, which include reduction in water requirement and fine aggregate content, improved workability, cohesiveness, pumping over long distance/heights, and concrete-ability at congested rebars and embedded parts. Though the rate of strength gain is low at early ages, there is considerable increase in strength at 56 days. The split tensile strength and modulus of elasticity follows the same trend as that of the compressive strength. Also, the rapid chlorideion penetration test (RCPT) values indicate the reduction in permeability of concrete leading to enhanced durability of fly ash concrete.

A study on performance of clay based geopolymers at elevated temperatures Swathy Manohar, K. Mohammed Haneefa, Sundar Rathnarajan, Manu Santhanam

This study investigates performance of clay based geopolymers at elevated temperatures and compares with the conventional geopolymer systems. Class F fly ash, calcined clay, metakaolin, and combination of fly ash-calcined clay are used as binders in various geopolymer mixes. The geopolymer specimens are exposed at 300, 600, and 900°C to evaluate the changes in physical, mechanical and microstructural characteristics which can be corroborated to their performance. Visual observations and mass loss variations showed that metakaolin specimens possessed the most intensive and branched cracking, even at 300°C exposure. Results of compressive strength test and thermogravimetric analysis (TGA) showed that fly ash and fly ash-calcined clay (FACC) mixes perform better than the other two mixes in long temperature range, especially when temperatures cross 120°C. Also, broader humps in the X-ray diffractograms of the FACC samples indicates a high degree of geopolymerisation. Thus, the paper supports the usage of the largely available clays in India after calcination and advocates the suitability of calcined clay for producing geopolymers to be used at elevated temperatures.

Developing axial force-bending moment interaction charts for the Seismic design of RC slender shear walls with boundary elements Shivani Sharma, Narsiram Gurjar, Aiswarya Menon, Ravi Kanth Sriwastav, Dhiman Basu

Explicit formulation for the flexural strength of a shear wall with boundary elements is presented. This development is based on the material properties conforming to the Indian Standard, but the underlying principle applies to other international standards, as well. Integral action of web and boundary elements is retained using the Bernoulli’s assumption of plane section along with the principle of mechanics. Design charts with normalized force and normalized moment as the axes are constructed using this explicit formulation and based on a few normalized geometrical parameters. Various combinations of grade of steel and grade of concrete are used for the construction of design charts to serve dual purposes. Design charts first offer an assessment of the approximate framework generally adopted in seismic design of shear walls with boundary elements involving a force-couple idealization. Interaction charts also offer a handy and offhand tool that best suite to the design office applications. Rectangular shear walls are also considered in the construction of design charts for completeness.

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