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Transport properties of pseudo ductile cementitious composites

Authors Zhao, Zhiyuan
Issue Date 2012
Summary The transport properties of concrete are important parameters governing the durability of reinforced concrete structures. As the opening of cracks can significantly degrade the transport properties, the crack control ability of materials is also important for maintaining high durability under practical situations. This study focuses on the water permeability and chloride diffusivity of pseudo-ductile cementitious composites (PDCC), which exhibits strain-hardening behavior in tension accompanied by the formation of closely spaced cracks with very small opening. , Concrete structures with a surface layer of PDCC can potentially exhibit excellent durability. However, former work related to the design of PDCC has focused on the achievement of pseudo-ductility, so good transport properties at the un-cracked state are not guaranteed. In this investigation, water permeability and chloride diffusivity tests are carried out together with direct tensile test on a number of PDCC compositions. The effect of various mix design parameters (including pozzolan/cement ratio, pozzolan type, sand/binder ratio, percentage of rubber particles and dosage of pore blocking admixture) on both the pseudo-ductility and the transport properties can hence be studied. From the results, we have identified PDCC compositions with (i) tensile ductility over 0.9% and excellent control of crack opening, and (ii) transport properties similar to high performance concrete. The findings pave the way for optimizing PDCC mix design for both mechanical performance and long-term durability. As part of our study, the transport properties of cracked PDCC specimens are also measured. The PDCC has good crack width control capability and a large number of fine cracks instead of a single main crack are formed under tensile loading. With transport properties measured from both cracked and un-cracked specimens, the effect of cracking can be quantified. The results show that the crack width is the key factor that affects the transport properties, as a tiny increase of the crack width can lead to a large increase of transport through the crack. For the same deformation, the crack opening in PDCC is much less than that in normal concrete, so the change in transport properties is also much smaller. According to the results of the present investigation, PDCC has a high potential for practical application as a surface layer or permanent formwork for the construction of durable concrete structures.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2012
Language English
Format Thesis
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