Sustainable construction is the future trend. Look around you and find a waste material. try to add it to a concrete mix with different ratios and study the new material properties and the behavior. Also, you can focus on the costs or the uses of such material.
You need to research for development of alternate building material which is eco friendly and having less embodied energy from the locally available waste material.
You may also try development of smart material which can keep building warm in winter and cool in summer to save energy.