Development and microstructural characterization of ultra-lightweight aggregate concrete incorporating different sizes of polypropylene fibers

In this study, ultra-lightweight concrete with an oven-dry density of 800 kg/m³ was produced using expanded glass as the lightweight aggregate. Polypropylene fibers of different sizes were incorporated into the specimens to examine their effects on the material properties, such as drying shrinkage and flexural strength. The target dry density was achieved by applying the packing density concept to optimize the mix grading and calculate the content of each concrete component. Specimens with different ratios of short and long fibers were produced. Their fresh state, mechanical performance, and physical properties were extensively analyzed using various methods, including X-ray micro-computed tomography to examine the microstructure. The experimental results indicated a significant reduction in drying shrinkage for the fiber incorporated specimens, dependent on the fiber length and content. The compressive strength of the specimens exceeded 12 MPa. Moreover, the inclusion of polypropylene fibers notably enhanced the flexural strength by approximately 60%, while the lower density contributed to substantially reduced thermal conductivity by up to 26%, which is beneficial for thermal insulation. These results confirm that polypropylene fibers can be used to produce ultra-lightweight concrete with self-leveling properties, without compromising mechanical and physical performance.