Browsing by Author "Hettiarachchi, HACK"

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item: Thesis-Full-text
Development of a theoretical packing model incorporating the effect of vibration, shape and surface texture
Hettiarachchi, HACK; Mampearachchi, WK
Determination of packing density of a particulate mixture is still an open problem for researchers and scientists. The complex and random nature of particle behavior in a mixture and effect of various external factors have made it more and more complicated to develop theoretical and analytical models to predict the packing density. This study focused on the effect of vibration frequency, particle shape and surface texture on packing density. Initially, laboratory experiments were carried out to determine the use of packing concepts in concrete mixture design for interlocking concrete block pavers (ICBP). The approach found to be successful. However, determination of packing density of aggregate mixtures in laboratory was time consuming and difficult. Hence, the use of packing models to determine the packing density was studied. Validity of existing packing models for the aggregate mixtures was studied and as a result the 3-parameter model was found to be the only model that incorporates loosening effect, wall effect and wedging effect and the percentage error of 3-parameter model found to be lesser than that of Toufar model and compressible packing model. Hence, the 3-parameter model was selected for the modification. The results obtained from experiments were then analyzed and relationships were developed isolating the effect of vibration, surface texture and particle shape. Three effects were combined, and the packing density variations were obtained to incorporate the effects and modify the 3-parameter model. The packing density and vibration shows a 3rd order polynomial behavior while shape and surface texture shows a linear relationship with packing density. The developed model was validated for more than 300 independent data. The behavior of loosening effect, wall effect and wedging effect with vibration, surface texture and shape were also analyzed. The wall effect is affected by both surface texture and vibration frequency. The loosening effect is affected only by particle shape and the wedging effect does not affect by any of these factors.
item: Conference-Abstract
Development of thermally comfortable paving block arrangement for pedestrian walkways
(Department of Civil Engineering, University of Moratuwa., 2014-08) Hettiarachchi, HACK; Mampearachchi, WK; Pasindu, HR
Interlocking concrete block pavements are used to pave walkways, parking lots, roadside pavements, open spaces, religious places etc. where people used to walk. The pavements are subjected to heavy thermal loads during day time in tropical countries like Sri Lanka. Surface temperature of these pavements rise up to more than 50 degrees of Celsius during daytime. Maintaining surface temperature at a comfortable level is one of the key challenges that modern block pavers are facing. To reduce the effect of temperature rise and maintain the thermal comfort, the behavior of the ICBP under different conditions need to be analyzed. Thermal behavior of interlocking concrete block pavement is mainly governed by the solar radiation. When the pavement is exposed to solar radiation the block gets heated. Several factors such as heat capacity, convection film coefficient, heat conductivity directly affect the temperature of the ICBP. A finite element model was developed to predict the thermal behavior of the ICBP and the model was validated using obtained experimental data. The verified model was used to predict the thermal behavior of different arrangements. Simulation was done changing the physic of the block and also changing the laying arrangement of the block. When the simulation was done for different conditions it is observed that,  Increasing the gap does not affect significantly in reducing temperature  Leaving the gap with air can reduce the temperature  Block with vertical holes can be effectively used to reduce the temperature of top surface on pedestrian pavements.  Change in the block size can be used effectively to reduce the surface temperature Combination of above mentioned parameters were also simulated and the temperature reduction of selected combination was observed.
item: Article-Full-text
Effect of surface texture, size ratio and large particle volume fraction on packing density of binary spherical mixtures
(Elsevier, 2020) Hettiarachchi, HACK; Mampearachchi, WK
The packing density of a particulate mixture is an important aspect of materials sciences and engineering. The packing density of a mixture depends on several parameters. This study considers the combined effect of vibration frequency, size ratio and large particle volume proportion on packing density of binary spherical mixtures.When all other parameters are constant, the increase of vibration frequency increases the packing density to a maximum and further increase of vibration frequency decreases the packing density of a mixture. The relationship found to be following a 3rd order polynomial curve. The increase of size ratio decreases the packing density linearly. The increase of large particle volume proportion also increases the packing density to a maximum and further increase of large particle proportion reduces the packing density rapidly. This variation also follows a polynomial pattern. These relationships were analyzed to develop a model incorporating combined effect and design graphs were developed from the derived model. The design graphs can be easily used to determine the packing density for a given vibration frequency and given size ratio.
item: Conference-Abstract
Modified 3 parameter model incorporating particle shape, texture and vibration to predict packing density of binary particulate mixtures
(Department of Civil Engineering, University of Moratuwa, 2018-09) Hettiarachchi, HACK; Mampearachchi, WK; Pasindu, HR
Particle packing density is one of the most important parameters in materials engineering. Ultra-high-performance concrete (UHPC), lightweight concrete, porous concrete, advanced ceramic materials, porous asphalt, filter materials are some of the major applications based on the packing density. Determination of packing density of a particulate mixture is a complicated and a laborious process. Hence, many researchers investigated the behaviour of particulate systems in a confined space in order to develop mathematical relationships to predict particle packing density. Several particle packing models have been developed so far such as Toufar model (Toufar, Born, & Klose, 1976), Compressible packing model (CPM) (Sedran & De Larrard, 1999) , 3-Parameter model (Kwan, Chan, & Wong, 2013), Linear packing density model (Stovall, De Larrard, & Buil, 1986) etc. However, due to the complexity of the particulate systems, many of these models are based on several basic assumptions; spherical shape, random loose packing method, smooth particles etc. A study carried out by Hettiarachchi and Mampearachchi (2017) revealed that the packing models can be effectively utilized to improve concrete mixtures for Interlocking concrete block pavers (ICBP). Nevertheless, the study also revealed that the packing models do not accurately predict the packing densities and 3-parameter model predictions are showing a close relationship with the actual packing densities. Hence, the objective of this study was to modify the 3-parameter model incorporating particle shape, surface texture and vibration frequency. A vibration table and a vibration hammer were used to apply vibration to the particles. Spherical glass beads were quoted with sand dust of various sizes to achieve different surface textures. Aggregates of various shape factors were taken to investigate the effect of shape. Each effect was isolated, and the packing density of the mixtures were measured varying the large particle volumetric fraction. Effect of the size ratio was also investigated by varying the size of the two particle classes of the mixture. The variation of packing density with vibration, shape and texture were analysed and the combined effect was modeled using regression analysis. The 3-parameter model was then modified using back calculation techniques to develop relationships with each effect. The modified 3-parameter model was validated using over 300 experimental data. The modified 3-parameter model found to be in correlation with the experimental data with a correlation coefficient of 0.95. In conclusion, the developed model will be able to predict the packing density of complex mixtures with high accuracy to provide more realistic outcomes which will benefit the materials engineering greatly.
item: Conference-Abstract
Sustainable concrete mix design for interlocking concrete block pavers (ICBP)
(Department of Civil Engineering, University of Moratuwa., 2016-08) Hettiarachchi, HACK; Mampearachchi, WK; Pasindu, HR
Heavy usage of cement in modern construction industry has led to numerous environmental problems. The cement industry is one of the main industries which release carbon dioxide, a major greenhouse gas. Raw material extraction to manufacture cement is another major environmental impact. Heavy damage to the limestone deposits on earth when mining is causing major environmental pollution. (Mishra & Siddiqui, 2014) Reduction of cement usage in concrete industry is critical for a sustainable future. Particle packing optimization method can be successfully used to reduce the cement content while maintaining the quality of the concrete. Selecting aggregate proportions to achieve required qualities of concrete is a challenging task. When a unit volume of concrete is considered, this volume consists of aggregates and cement paste. Aggregate form the skeleton of concrete and cement paste will be used fill the voids in between aggregates and coat the aggregate to ensure proper bonding. Packing of aggregate is a main factor for a high quality concrete. Optimization of aggregate is the process of determining the most suitable aggregate particle sizes and distribution to minimize the voids content of an aggregate mix. An optimized aggregate mix will have lesser amount of voids which needs to be filled with cement paste resulting low cement, high quality concrete. Particle packing optimization is the process of selecting optimum aggregate proportions that result in minimum voids and maximum density thus requirement of cement and water can be minimized. Optimization of aggregates to achieve higher strengths with lower cement content has been studied for various applications over the past decade. Theoretical packing models such as Toufar, De Larrad, CPM, LPDM, power curve, Shilstone chart etc. were analyzed to determine the most suitable packing model. Though those studies were successful for more generalized applications there were limitations when applying the results for specialized applications such as zero slump concrete, pre cast concrete products, roller compacted concrete self-compacting concrete, high performance concrete etc. The main reason for such limitations in generalized approach is the variation of the required properties of concrete in each application such as low water content requirement in zero slump concrete, roller compacted concrete and pre cast concrete, high water requirements in self-compacting concrete etc. The concept of particle packing is adopted to determine sustainable concrete mix for interlocking concrete block pavers (ICBP). Typically the aggregates used for the concrete are 12mm coarse aggregates with manufactured sand and natural sand as fine aggregates. Fresh concrete is poured into the mold and both vibration and compaction is applied to cast the block. The mold is removed soon after the block is cast. Hence a low water cement ratio and high green strength needs to prevent edge falling and cracking of freshly cast ICBP. Present industrial practice seems to be far less economical due to the use of high amount of cement, wastage of aggregates, and high energy consumption of machines due to improper mix proportions. The manufacturers use high amount of cement to achieve higher strengths. There are high variations in strength within the same batch of blocks. The main reasons for such variations is the lack of consistency in mixing, segregation of aggregates when pouring concrete mixture to the molds, lack of proper curing practices, not following a proper water/cement ratio as intuition is used to measure the adequate water content etc. Hence high strength variations within the same batch is visible. This study proposes improved sustainable mix design using packing density method by optimization of parameters such as water cement ratio, coarse to fine aggregate ratio, quarry dust to natural sand ratio, cement content and compaction effort. The results of the study shows that the cement content can be reduced by 37% by optimizing the aggregate content used in the concrete mix.
item: Article-Full-text
Validity of aggregate packing models in mixture design of interlocking concrete block pavers (ICBP)
(Taylor & Francis, 2019) Hettiarachchi, HACK; Mampearachchi, WK
Interlocking concrete block pavers (ICBP) are manufactured using a semi dry concrete mix and vibration and compression are applied by electrical or hydraulic machines to cast the blocks. Hence the concrete mixture characteristics differ from concrete mixtures that we use for general purposes. When determining the mix proportions for the mix design, several properties of the block need to be considered. Maintaining required strength and surface texture, producing mixes with optimum water content to maintain the green strength while avoiding slumping are some of the challenges faced by the industry. To overcome such challenges a mix design using aggregate packing optimisation can be used effectively. There are number of theoretical packing models available for concrete mix optimisations and each model has its own pros and cons. Most of the models are successfully used for more generalised concrete applications and these models have not been used for more specialised applications such as ICBP. This study considers Modified Toufar model, three parameter model and compressible packing model to determine the validity of applying for ICBP. The theoretical models are compared with laboratory and field packing density experiments and the results indicate that the models are not accurately predicting the packing density for mix design of ICBP. Hence the study suggests developing a new theoretical packing model that accommodates production procedures together with mixture performances to enhance the mix design procedure as well as the performance of ICBP.