This paper reports the influence of polymer latex on the fresh and the hardened properties of engineered cementitious composites (ECC), a unique strain-hardening cement-based material featuring extreme tensile strain capacity of 3-5%. Ethylene-vinyl acetate (EVA) dispersible polymer powder was employed in the synthesis of latex-modified ECC (L-ECC). The effects of EVA dosage on viscosity, air content, compressive strength, direct tensile stress-strain relation, four point bending behavior, and microstructure of L-ECC were reported. It was found that the addition of EVA increases the viscosity and the air content of fresh mixture. While the compressive and the tensile strength of L-ECC decrease with increasing EVA dosage, the tensile strain capacity and the toughness of the resulting material show significant enhancement. This is attributed to the change of microstructure as evidenced by the SEM images when EVA is used in the mixture.
The novel technique of using Shape Memory Alloy (SMA) transverse reinforcement to confine concrete has proven its success in increasing the strength and ductility of concrete elements significantly. This new technique exploits the thermally activated shape memory feature of SMAs to apply high and permanent confinement pressure on concrete. Despite the experimental work done in this topic over the last few years, the numerical/analytical efforts are still lacking. This paper utilizes the analytical framework of the damaged plasticity model along with the finite element method (FEM) to predict and study the behavior of SMA confined concrete under uniaxial compression load. The flow rule and hardening/softening function adopted in the models are developed based on previous test results. The results prove that the finite element models can successfully capture the behavior of SMA confined concrete.
A study has been undertaken to investigate the pore structure characteristics, porosity and critical pore diameter of preformed foamed concrete with a density between 1300 and 1900 kg/m3, and its effect on the permeation characteristics, water absorption and permeability. Different measured and calculated methods were adopted to determine the above properties and a comparison between them was done. Porosity was measured by apparent, total vacuum saturation and mercury intrusion porosimetry (MIP) methods, while permeability was measured (by constant and falling head methods) and calculated (by the Katz and Thompson model). Total porosity and dry density are found to be clearly related. The critical pore diameter (from the MIP test) and the pore diameter size (>200nm) are found to be closely related to the permeability of foamed concrete.
Fiber reinforced cementitious mortar (FRCM) systems, innovative strengthening systems, for repairing and strengthening concrete and masonry structures are an alternative option to traditional techniques such as fiber reinforced polymers (FRPs), steel plated bonding, and section enlargement. In this paper, a FRCM strengthening system made of polypara phenylene benzobisoxazole (PBO) fiber mesh embedded in cementitious matrix and bonded to concrete is investigated. There are two main parts in this paper: (i) the effective bond length of PBO mesh in PBO-FRCM system and (ii) the bond stress-slip relationship between PBO mesh and concrete substrate. An experimental program of single pull-out shear tests for the PBO-FRCM system is designed and conducted to verify the above two purposes. The results of this study can be used to estimate the effective bond length of PBO mesh in PBO-FRCM systems and also investigate if the debonding phenomenon occurs in the cementitious matrix or at the fiber and matrix interface. The comparison between the PBO-FRCM system and the ordinary FRP system is also discussed.