Browsing by Author "Subramaniam, DN"

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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.
item: Conference-Full-text
Seasonal changes and coastal erosion in the South Western part of Sri Lanka
(2008-05) Subramaniam, DN; Amarakoon, GGNN; Gunathunga, SGAS; Pathinayaka, RC; Indeewara, VGD; Vijitha, AVP; Rathnayake, NP; Karunaratne, S
Sri Lanka is an Island, the economy of which relies very much on the developments of the coastal region, which supports tourism and fisheries. In addition, especially in the South-Western part of the country, the infrastructure lays in the proximity to the coast and the land is more precious and valuable. Further, the constructions around the coastal expanse, alter the sand dynamics of the coastal belt, increasing erosion and deposition at specific points. The erosion cannot be identified at a glance in one day, but when considering long-term sustainable developments, the loss of expanse due to erosion becomes vital. Hence, in this study we analysed the erosion pattern and gross land loss along South-Western part of Sri Lanka, considering duration of 6 months (Jun/07 till Jan/08). The variations of beach profile were determined from leveling perpendicular to the beach at 10 predetermined locations at one month interval. Grain size variations were also analysed from the samples collected from the mean sea level from each sampling locations. A strong correlation was observed at this location between the monsoon and erosion, while at Egodauyana, Panadura Moya, kani Lanka hotel and Payagala revealed rapid changes in erosion/deposition. Although the rainfall influences the beach variation, longshore currents, tides and coastal features (natural and artificial) are found to be dominating at these locations.