Flexure and shear strength of Fiber modified lightweight aggregates concrete and its application in water retaining structures Adnan Qadir 1 , Uneb Gazder 2 Department of Civil Engineering, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia. Email: aagader@kau.edu.sa(corresponding author) Department of Urban and Infrastructure Engineering, NED University of Engineering and Technology, Karachi, Pakistan. Email: unebgazdar@gmail.com Abstract Lightweight aggregate concrete is being successfully used as structural concrete in developed countries of the world, however third world countries like Pakistan is still struggling to come up with the practical applications of lightweight concrete in building construction. One reason is due to the lack of reliable data about its performance as structural member in building construction. The presented study inspected the flexural and shear tolerance of fiber reinforced lightweight aggregate concrete (LFC) through testing of six (06) beam specimens cast, cured and tested after 28 days for the purpose. An overhead tank of 1000 gallon capacity, was also constructed in the study to verify the application of LFC by observing its water retention behavior. The experimental design included a mix design of concrete at a target strength of 21 MPa for control sample natural aggregate as well as for synthetic aggregate modified with polypropylene fibers. Compressive strengths of both categories of concrete were also determined by crushing the cylindrical samples at the age of 7, 14, 21 and 28 days. The cast beams were later subjected to the application of two point loading test till failure. It was found that the beams fabricated with LFC was better resistant to cracks as compared to normal weight concrete (NWC) beams both in terms of number and crack width. It can be concluded on the basis of the results that the experimented LFC has revolutionized the concept of using lightweight aggregates in regular structures that consequently would help in a sustainable environment. The study also concluded that the constructed water tank with LFC was thermally efficient and structurally sound since it showed no sign of seepage for the observed period, thus proved to be good water retention structure. Keywords: Lightweight Aggregate Concrete, Normal weight concrete, Polypropylene Fibers, Flexure Strength, Overhead Tank