MECHANICAL AND THERMAL CHARACTERIZATION OF HTP FIBER REINFORCED LIGHTWEIGHT ENGINEERED CEMENTITIOUS COMPOSITES (HTP-LECC)

Abstract

In this study, the matrix rheology, mechanical performances and thermal insulation properties of high tenacity polypropylene fiber (HTP) incorporated lightweight engineered cementitious composites were investigated. Matrices were prepared by using air entraining admixture 2, 4 and 8% of cement weight and HTP fibers added to matrices by 2% of total matrix volume. Before fiber addition, rheological properties of matrices were investigated by using a ball type rheometer. After fiber addition, the air entrainment percentages of composites were determined through theoretical calculations, aerometer test, and image processing methodology for comparison purpose. Specimens were cast into: 25x60x300 mm prismatic molds for flexural strength and thermal tests; dog-bone molds for tension tests; 50x50x50 mm cubes for compression tests. Crack numbers and crack widths of specimens were measured additionally to the mechanical test by using a portable hand microscope at unloaded state in order to investigate crack properties after flexural and tensile test. Thermal properties of composites were also investigated by thermal conductivity and thermal permeability measurements. The thermal conductivity values of composites were achieved by using prismatic specimens before flexural tests. Correlations between air-dry densities and thermal conductivities were calculated. Additionally, thermal permeability of composites were obtained by using a novel thermal camera integrated test setup, which simulates actual site conditions, and related with the thermal conductivity test results. In conclusion, composites were lightweightened by 19-35%. The accuracy of the aerometer test was confirmed by image processing technique. Yield stress and viscosity of matrices were decreased by increasing air entraining admixture dosage and 8% of air entraining admixture dosage was found much preferable in terms of consistency preservation. First crack (in both flexural and tensile tests) flexural, tensile and compressive strengths of composites were decreased by increasing air entrainment percentage. By taking air entrained composites into account, deflection and strain capacity of HTP-LECCs were increased by increased admixture dosage. Also, crack numbers were increased and crack widths were decreased by increasing admixture dosage within air entrained composites. Thermal permeability of composites were investigated by novel thermal camera test setup. Strong correlation (R=0.96) was found between thermal conductivity and thermal permeability tests.