Micromechanics of an Ultra Lightweight Engineered Cementitious Composite Containing Polymeric Latex Admixture

An ultra-lightweight engineered cementitious composite (ECC) mixture has been recently developed as a durable alternative to the conventional cement-based fireproofing material for steel structures. The newly developed mixture has a dry density of 550 kg/m³, yet as a fireproofing material, it shows considerable tensile strength above 1 MPa and tensile strain capacity greater than 2%. This newly developed mixture is much more lightweight than any previously developed ECC material. It uses high tenacity polypropylene (HTPP) fibers as fiber reinforcement; and an acrylic latex based admixture is incorporated into the mix composition. All these leads to significantly different micromechanical properties from all previously developed normal-weight and lightweight ECC mixtures. In this paper, investigations have been conducted to fully understand the unique micromechanics of the newly developed material. Specifically, single fiber pull-out tests were conducted. The test result showed that a cement-polymer co-matrix was formed in presence of the latex admixture. As a result, the interfacial bond between the lightweight matrix and HTPP fibers was significantly enhanced. A scale-linking model was also used to show that such enhanced interfacial bond contributed to an increase of tensile strength and strain-hardening potential. The current research provides useful data for understanding the behavior of lightweight ECC and polymer modified ECC materials and can also serve as a guideline for future development of similar materials.