The building structure faces the dual challenge of CO₂ emission reduction and performance/sustainability improvement of construction materials. In this respect, in recent times, interest in the incorporation of natural fibers into cementitious systems has been rising as a promising route for attaining these objectives. This paper investigates the effects of adding Phragmites-Australis (Ph-A) fibers on the properties of flexural and compressive strength and length change, including chemical shrinkage, drying shrinkage, and expansion, of cement mortar when exposed to elevated temperature (45°C). Ph-A fibers were added by volume of mix with different percentages of 0, 0.5, 1 and 2%. Furthermore, a maturity equation was used for the prediction of shrinkage behavior including ultimate shrinkage, time scale factors, and hydration rates. Experimental results revealed that the addition of 1% Ph-A fibers significantly improved flexural and compressive strength while density decreased with increasing fiber content. Besides, the addition of 2% Ph-A fibers reduced chemical shrinkage by 25%, autogenous shrinkage by 12.4%, drying shrinkage by 17.8%, and expansion by 14.9% compared to the control mix. The maturity equation presented very good agreement with the experimental data, confirming its reliability in shrinkage predictions. These results put into evidence the potential of Ph-A fibers to enhance the mechanical and dimensional performance of cement mortar, offering a sustainable solution for reducing environmental impact and advancing durable construction materials.

mortar, Ph-A fiber, length stability, mechanical properties, elevated temperature, sustainability