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    PublicationOpen Access
    Correlation of tensile strength of blended cement concrete with specimen dimensions and aggregate size: A practical test review
    (SLIIT, Faculty of Engineering, 2025-02) Amarasinghe, N; Somaratna, N
    Test specimen dimensions affect most strength properties of concrete. The existing empirical relationships in this regard are predominantly based on concrete samples made by using Ordinary Portland cement (OPC). An important recent trend in Sri Lanka has been the increasing use of blended cements. This makes it necessary to examine whether the relationships hold for blended cements as well. In this study, split cylinder tensile strength tests were conducted to determine whether the specimen size and the tensile strength of concrete prepared using a blended cement (Portland Composite Cement (PCC)) display relationships similar to OPC. Tests were conducted on specimens using two cement types – OPC and PCC - and three concrete mix ratios and a range of specimen dimensions to study the effect of the specimen length (L), diameter (D), and aggregate size (a) on the split cylinder tensile strength (T). The data was examined using dimensional analysis based on Buckingham's π theorem. A slight increasing trend was observed in the ratio of split cylinder tensile strength to mean a compressive strength (T/fc,mean) with an increasing L/D ratio. As for the ratio of the aggregate size to the specimen diameter (a/D), the analysis showed an increasing trend in T/fc,mean values with an increasing a/D ratio, indicating a significant correlation between T/fc,mean and a/D. A nonlinear regression analysis was used in an attempt to determine a functional relationship among the non-dimensional parameters T/fc,mean, L/D, and a/D. But the differences in the derived relationships for different concrete mixes were too large for reaching a common relationship. Perhaps this was due to the small number of data points available. It was seen that relationships established for OPC may hold true for PCC too. However, the data used was limited in range and more comprehensive further tests should be conducted to confirm these findings.
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    PublicationEmbargo
    Experimental Investigation of Some Strength Parameter Correlation in Blended Cement Concrete
    (SLIIT, Faculty of Engineering, 2024-10) Chularathna, P. K. G. O. T.; Somaratna, N.
    Sri Lanka has adopted Eurocodes for structural designs. Accordingly, the design of concrete structures should adhere to EN1992 (Eurocode 2). The strength parameters of concrete essential for designs are classified in Eurocode 2 based on the compressive strength of concrete. Most of the other relevant strength parameters are derived using correlations with compressive strength. These correlations based on past empirical test results would typically be valid for concrete made using ordinary Portland cement (OPC). Recently there has been a tendency to use blended cements for concrete. To develop economical and safe designs in such cases the correlations among strength parameters used in EN 1992 should be verified as being applicable to blended cement concrete too. The study presented here was aimed at investigating the applicability of EN 1992 correlation between compressive strength and split cylinder tensile strength to blended cement concretes. Test specimens of concrete made using a blended cement – Portland Composite Cement (PCC) – were cast, cured, and tested under standard conditions for their compressive strength and split cylinder tensile strength. These tests were repeated for greater reliability. For comparison, similar tests were performed on concrete made using OPC also. The measured compressive strengths were used to produce estimated values of corresponding tensile strengths following the EN1992 correlations. Comparisons were made, in graphical form, between the measured tensile strengths and the estimated tensile strengths. Separately for each cement type. They revealed that the test results for OPC concrete, as expected, aligned with EN1992 correlations with a significant margin of safety while those related to blended cement, though complying with EN1992 correlations, provided only a narrow margin of safety. This indicates a need for a higher level of quality assurance for blended cement concrete. As these observations are based on a limited number of tests it is recommended to conduct further comprehensive studies.
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    PublicationEmbargo
    Effect of Surface Modification and Fibre Content on the Mechanical Properties of Coconut Fibre Reinforced Concrete
    (https://www.scientific.net/, 2020-09) Hettiarachchi, C; Tharmarajah, G
    . In the past few decades, concrete has been the most widely used material for structural applications in the world and uses steel reinforcement as aide to meet the flexural, tensile and ductility demands required of concrete structures. Manufacturing of concrete and steel reinforced concrete structures is associated with millions of tons of carbon dioxide emissions and mineral waste. This activity is also responsible for the depletion of a large number of non-renewable resources. Reinforcing steel is also a high cost material, consumes a lot of energy in its production. Consequently, the use of natural fibres as an alternative for steel reinforcement is widely investigated, to promote the use of sustainable concrete structures. This study aims to investigate the effect on durability, flexural, compressive, tensile properties, and workability of concrete by incorporating coir fibre at varying fibre content to find the fibre content which gives optimum results. The fibre contents used were 0%, 0.5%, 1.0%, 1.5% and 2.0% by weight of cement. Furthermore, the effect of modifying the surface of the coir fibres by alkali treatment (i.e. 5 wt.% NaOH solution) and coating the fibres with epoxy paint and polyurethane varnish on coir fibre reinforced concrete (CFRC) were also investigated. Tests conducted on the CFRC specimens included slump test and flexural, compressive and tensile strength tests. Water absorption and sorptivity tests were also conducted to investigate the durability. Slump (workability) and unit weight reduced with an increase in fibre content. The surface modification methods used, had resulted in an increased workability and a reduced unit-weight. A coconut fibre content of 1% produced the best combination of flexural, tensile and compressive properties. Water absorption and sorption rate per unit time, increased with an increase of coir fibre content. It is also found that epoxy paint and alkali treatment of the fibres has a positive effect on the mechanical strength properties and also the durability and workability of the CFRC specimens. However, polyurethane varnish coating had a detrimental effect on the mechanical strength properties of the CFRC specimens.
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    PublicationOpen Access
    EFFECT OF PORCELAIN WASTE AS A FINE AGGREGATE ON THE MECHANICAL PROPERTIES OF CONCRETE
    (University of Peradeniya, 2019-08-13) Kobbekaduwa, K. W. D; Perera, S. V. T
    The demand for concrete keeps significantly increasing worldwide throughout the past few years period. The exponential development rate and construction processes on developing infrastructure facilities all over the globe has resulted this situation. As an outcome of that, the excessive production of concrete has led to several environmental impacts all around the world. This study investigated the suitability of crushed porcelain waste as a replacement for fine aggregates by analysing the strength gains and other mechanical properties depending on the replaced proportions. Porcelain Waste Fine Aggregate (PWFA) which is a low water absorbing material was used in replacing conventional fine aggregates in the proportions of 25%, 50%, 75%, 85% and 100% for the concrete of Grade 30. It was found that the most suitable and economical replacement proportion of PWFA is the 75% mix as it comprised a 28-day compressive strength of 54.31 MPa which is 50% greater than the compressive strength of control mixture. Due to the higher strength, the 75% PWFA Grade 30 mix can be implemented as Grade 45 concrete which can save up to 10% of the cost. The partial replacement of sand using PWFA significantly improved the performance of concrete while addressing several environmental and economic issues related to concrete industry.