Optimized Design And Key Performance Of Domestic Green High Ductility Cementitious Composites

High Ductility Cementitious Composites (HDCC) has more than 200 times ultimate elongation of ordinary concrete. When it is subjected to bending and tensile loads, HDCC may exhibit a strain-hardening and multiple cracking properties. With high ductility, high toughness and excellent control characteristic crack width, HDCC used as a building material is a good choice for seismic energy dissipation. But at the same time, the higher raw materials and producing costs of traditional HDCC also limits its application in global concrete infrastructures.In this work, we defined a new parameter of effective fiber volume fraction to amend the classic HDCC design model. The plastic viscosity slurry, the fiber dispersion and the micro-mechanical parameters are critical control indexes.Under the guidance of the amended HDCC design model, some low cost and low energy consumption raw materials were alternative to the high-cost and high energy consumption raw materials of traditional HDCC. Except the basic mechanical properties and ultimate elongation of HDCC satisfy the design requirements of most concrete infrastructures, a significant reduction in raw material and production costs are also important for improving the cost-performance ratio of HDCC. The work would theoretically guidant and technically support the practical applications of this domestic green HDCC.Firstly, we studied the microstructure parameters of the PVAF-matrix interfacial zoneand the matrix. Use Single fiber pullout test to obtain the chemical adhesion, friction and slip hardening coefficient between fiber and matrix with different mix design. According to the standard "Norm for fracture test of hydraulic concrete ", we tested the fracture toughness and elastic modulus of different matrixes. By theoretical calculation, the crack tip toughness of matrix, the bridging energy of fiber and the pseudo strain-hardening index of HDCC can be obtained. The study found that when the chemical bonding force between fiber and matrix is (1～3) J/m2, and the friction of fiber-matrix interfacial zone is (2～5) MPa, the ultimate elongation of HDCC could be more than 2% which is satisfied the deformation requirements of almost concrete projects.Secondly, the rheological properties of fresh matrix slurry and PVA fiber dispersion in the matrix have been studied. Use the Rotary viscometer and polarizing microscope, the slurry rheology of matrix and the fiber dispersion degree were detected and analyzed. The results show that the rheological behavior of the slurry could be characterized with Herschel-Bulkley model. If the plastic viscosity of fresh slurry is (1～6) Pa·s,2% volume fraction of domestic PVA fibers could be uniformly dispersed in the matrix and the dispersion coefficient would be more than 0.75.Thirdly, this work investigated the key mechanical properties of HDCC like compressive strength, flexural strength, bending deformation and tensile stress-strain relations of HDCC. The research shows that, the designed green HDCC including domestic PVA fibers and ordinary river sand exhibited strain hardening and multiple cracking properties, as well as its maximum ultimate tensile strain is more than 4%. After analying the tensile stress-strain relations and bending behavior, we proposed a new correction parameter to optimize the classical HDCC design model and reasonablly explaned the test results of S2.Finally, according to above mentioned optimized HDCC design model, two types of domestic green HDCCs were designed and investigated. We used ordinary river sand or red mud as aggregate, fly ash and ground slag as mineral admixtures for these two green HDCC. Micromechanics parameters, fiber dispersion and the mechanical properties of each HDCC have been tested. The ultimate elongation rates of these two types of HDCC could be more than 6%. These results are meaniful for verigy the reasonableness and reliability of the optimized HDCC theoretical design model, furthermore, they could provide a new recycled utilization of red mud in green HDCC.The innovations of this work are:(1) defined a new parameter "effective fiber volume rate" for the first time and controlled the plastic viscosity, the fiber dispersion and the micro-mechanical parameters for important control indexes for revising and optimizing the HDCC design theory and methodology. (2) Using the domestic PVA fiber, ordinary river sand, red mud, slag, fly ash and other inexpensive raw materials, successfully designed and fabricated the highest ultimate elongation of more than 6% of green HDCCs. (3) The red mud has been firstly used as aggregate in HDCC, which supplys a new choice for comprehensive utilization of red mud with a high additional value.