ABSTRACT Fly ash is used partially as a replacement to cement to make the concrete. Fly ash contains SiO2 and Al2O3, which contribute to increase the strength of concrete. In the current investigation, fly ash has been replaced with varying percentages of nanosize in concrete, and the strength of the resulting hardened concrete has been evaluated. The production of nanosized fly ash has been made by the ball milling process and the analyses has been completed using scanning electron microscope (SEM) and X-ray diffraction (XRD), in order to determine the chemical and physical composition of the nanoparticles of fly ash. The nano fly ash concrete (NFAC) have been undergone for the durability tests of acid, sulphate and chloride attack. The concrete with 23% of nano fly ash replaced with cement performs well against these adverse conditions. The comparison has been made between the conventional (CC), raw fly ash (RFAC) and NFAC. Nano fly ash makes concrete much denser and more resistant to cracking. So the durability behaviour of NFAC is much better than CC and RFAC. The percentage of reduction in strength after durability aspects is varies from 0.03% to 10.75% for the NFAC.

ABSTRACT River sand is becoming increasingly scarce. As a result, an alternative material is required to replace river sand in order to save river sand. In the construction of quality concrete, artificial aggregate is now frequently employed as a substitute for river sand. Coconut fibre ash (CFA) aggregate obtained from Coconut fibre is prevalent in India. Partially replacing river sand (fine aggregate) with presaturated CFA aggregate for self curing purpose is presented in the paper. Fine aggregates were replaced by CFA aggregate by 5%, 10%, 15%, 20% and 25% by volume. The workability and strength characteristics of the concrete are studied. Internal curing is the solution to today's water scarcity's insufficient curing. During compared to other mixtures, test results show that the concrete mix with 20% CFA aggregate produced better results when self curing.

RESUMO Este artigo apresenta o desempenho de flexão de seções tubulares de aço recobertas com concreto reforçado com fibras híbridas recentemente desenvolvidas. Os parâmetros de teste são fração de volume de fibra e taxa de hibridação de fibra. Inicialmente foram estudadas as propriedades mecânicas para 10 misturas de concreto mono-fibras reforçadas utilizando fibras de aço e polipropileno com frações volumétricas de 0,5%, 1,0%, 1,5%, 2,0% e 2,5%. Com base no desempenho, determinou-se a dosagem ideal de fibras em cada fibra, com a mesma fração volumétrica foram desenvolvidas três diferentes híbridas de fibra. Desenvolveu-se concreto reforçado de fibra híbrida, concreto convencional e concreto reforçado com fibra monofásica ideal nas vigas tubulares de aço preenchidas com concreto para determinar o desempenho de flexão. Os resultados do teste mostram que, os feixes tubulares de aço reforçados com concreto reforçado com fibra exibem uma melhora significativa no desempenho de flexão.

ABSTRACT This paper presents the flexural performance of newly developed hybrid fiber reinforced concrete-filled steel tubular sections. The test parametres are fiber volume fraction and fiber hybridation ratio. Initially mechanical properties studied for 10 mono fiber reinforced concrete mixes using steel and Polypropylene fibres with 0.5%, 1.0%, 1.5%, 2.0% and 2.5% volume fraction. Based on the performance optimum fiber dosage was determined in each fiber, with the same volume fraction three different fiber hybridation was developed. Developed hybrid fiber reinforcement concrete, conventional concrete and optimum mono fiber reinforced concrete was used in the concrete-filled steel tubular beams and columns to determine the structural performance. The test results shows that, fiber reinforced concrete-filled steel tubular beams display significant improvement in the flexural performance.