Chamod Finds a New and Improved Recipe for Concrete Mixture

Dr. Chamod Hettiarachchi

What if you knew the formula for a magic potion that gives you remarkable strength, but is yet cheap? Chamod Hettiarachchi looks at  how he could mix two materials to get the best combined effect  to  improve the properties of the mixture. Mixtures are used regularly in manufacturing, production and construction industries. 

Prof:W.K. Mampearachchi

The ability to control the packing density of particles insuch mixtures will open up a myriad of possibilities for these industries. One could "play" with the combination of ingredients to set the packing density of a particular mixture so as to obtain the required properties such as strength, permeability and weight, with a cost-effective blend of ingredients. 

Chamod Hettiarachchi began his education at Urapola primary college, and completed his secondary education from Royal College, Colombo. He entered the Faculty of Engineering at the University of Moratuwa and completed his Bachelors in Civil Engineering with an upper 2nd class in the year 2014. He then joined the Department of Civil Engineering  as a Research Assistant. During this time, Chamod found interest in the packing density of binary mixtures, that is, mixtures of two aggregate sizes. Aggregates are broad category of particulate material of different sizes used in construction. Examples include sand, gravel, crushed stone, slag etc. This interest led him to discover that the available packing models did not allow one to find the optimal packing density. He also found that the local construction industry uses trial and error methods for aggregate mixtures, which do not give good results in terms of cost and construction quality. He therefore saw an opportunity for further research. He specifically focused on developing an analytical model to find the packing density of concrete mixtures used in interlocking paving blocks in his PhD research.

Prof. Wasantha Mampearachchi from the Department of Civil Engineering served as Chamod's supervisor for this research. He was able to win a grant to support Chamod and his research from the Senate Research Committee of the University of Moratuwa. With his Civil Engineering knowledge, Chamod argued that vibration, particulate shape, size, and surface texture would be of most importance for packing density of an aggregate mixture. To test and confirm his view, large and small particles as well as fine and coarse aggregates of different quantities were investigated with different degrees of vibration.Interlocking blocks were made and tested in the laboratory. Further, SMS Holdings, which is currently the largest block manufacturer in Sri Lanka assisted Chamod to manufacture them in their factory. Using the test results, relationships between the packing density and vibration, surface texture and particle shape were developed and tested.

Chamod was able to show how the strength of an interlocking block was related to the voids content. A high packing density with closely fitted voids will result in high strength of the interlocking block. Extending this result, Chamod also found a formula for how the strength of an interlocking block can be controlled by fitting the voids density as closely or as loosely as needed.

Chamod's new model surpasses those currently available. The benefits of this model go beyond just knowing the optimal packing density of two materials. It helps to manufacture high quality, durable material for less cost, making them more affordable for construction projects. In the long term, this approach would improve the quality and cost saving in production of concrete mixtures for various applications in construction industry. In taking this research forward, Chamod feels that it is possible to look into how multiple aggregates behave in this model. Also, the model can be tested in different industries.

Chamod's research has been accepted for publication in renowned international journals such as Powder Technology and Road Material and Pavement Design, showing its relevance to the worldwide construction industry.

Chamod was nominated by the National Academy of Sciences of Sri Lanka to attend the Royal Society Commonwealth Science Conference 2017 in Singapore as an outstanding PhD student. Speaking of his experiences as a PhD candidate, Dr. Chamod Hettiarachchi said, "As a postgraduate student, I gained the ability to solve problems, successfully meet deadlines, and learned to better communicate and network". He also said that his international exposure helped him improve his presentation and communication skills.

Dr. Hettiarachchi is now an entrepreneur and the proud founder of UNICON, a manufacturing company for paving and masonry blocks. He intends to patent his findings in the near future. He will be continuing with his academic career and is due to take up a postdoctoral position shortly with the Tongji University in China.

Prof. Mampearachchi has earned multiple degrees in Civil Engineering, a Bachelors from the University of Moratuwa, a Masters from the University of South Florida and a PhD from the University of Florida. He is a seasoned researcher, leading research on road construction materials in the Transportation Engineering group of the Department of Civil Engineering.


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