Browsing by Author "Sajeevan, M"

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item: Conference-Full-text
investigating impact of boundary layer in pervious concrete
(Springer, 2021) Sajeevan, M; Ahilash, N; Subramaniam, DN; Pasindu, HR; Bandara, S; Mampearachchi, WK; Fwa, TF
Pervious concrete is a green concrete because of its environmental benefits including reduced carbon footprint. However, industrial application of pervious concrete is limited by uncertainty of its mechanical properties. While porosity plays an important role in mechanical properties and understanding on porosity distribution and characteristics is essential in optimising design of pervious concrete. Image analysis is a modern tool which could employ different analyses techniques and significantly reduce error than in conventional methods of analysing porosity. This study aims to analyse distribution of porosity in pervious concrete, using image analyses tools. Cubes were cast, cores were obtained, and images of the surfaces were painted and photographed. Image was converted to binary and analysed and total porosity of cubes were obtained. A small layer in the top and bottom have high porosity than total porosity and between those layers the porosity,which is lower than total porosity, is called effective porosity. Therefore, the top and bottom boundary layers were analysed with design parameters. Top boundary layer of a concrete cube is 4.7 mm and it does not depend on design parameters. The bottom boundary layer of the concrete cube increases with the aggregate to cement ratio and decreases with applied compaction energy. For blows more than 45, the bottom boundary layer does not significantly change. Minimum required number of blows for the 1st layer of the cube to get optimum bottom boundary layer is 10 for all Aggregate to cement ratio (A/C) except for design with A/C of 2.5.
item: Conference-Full-text
Optimising pervious concrete design with partial replacement of cement with fly ash
(Springer, 2021) Ahilash, N; Sajeevan, M; Subramaniam, DN; Rajakulendran, M; Pasindu, HR; Bandara, S; Mampearachchi, WK; Fwa, TF
Pervious concrete is a light-weight concrete that does not contain fine aggregates (sand) and of enhanced porosity compared to conventional concrete. Partial replacement of cement paste bywastematerial, reduces environmental impact both by reducing carbon footprint of cement usage and usage of waste material. Partial replacement of cement by fly ash in conventional concrete is an accepted substitution that also significantly enhance mechanical properties. However, porous concrete being different from conventional concrete, studies are scarce in applicability of such replacements in porous concrete. This study aims to optimise partial replacement of cement by fly ash in porous concrete. By changing the aggregate to cement ratio (A/C) and water cement ratio (W/C) mix designs were formulated, cubes were cast and slump and compressive strength of fresh concrete were monitored. Having obtained highest strength of A/C of 2.5 cubes were cast with varying W/C ratio (0.3, 0.35, 0.4 and 0.45) and the percentage of replacement of cement by fly ash (5, 10, 15 and 20%). Replacement of 10% was observed to be optimum replacement while higher theW/Cwas advantageous for compressive strength. However, for porous concrete the slump of the fresh concrete should be below 15 mm. Therefore, the optimum W/C was 0.3. Finally, the mix design with 2.5 Aggregate to cement ratio, 0.3 water to cement ratio and 10% replacement of cement by fly ash gives 15.22 MPa (95% CI 14.8–15.6 MPa) strength. It is 13% extra strength than using 100% cement for binder.