Multi-scale Constitutive Relation And Design Theory Of Ecological High Ductility Cementitious Composites Under Variable Temperature Conditions

Ecological High Ductility Cementitious Composites(ECO-HDCC)have high ductility and high energy absorption capacity,which can prevent the normal cement-based materials from brittle failure.Because of these excellent performance,ECO-HDCC material has become a very good choice for energy disspation elements in building structures.For the promotion of ECO-HDCC localization,we also need to take into account the impact of temperature factors.However,the high ductility criterion and design theory of ECO-HDCC under different temperature conditions and the influence of temperature change on the multi-scale constitutive relation of PVA fiber,fiber-matrix interface,matrix and ECO-HDCC are lack of relevant research.In this paper,the design model of ECO-HDCC is modified by introducing temperature parameters.The effects of different temperatures on the properties of fiber,fiber-matrix interface,matrix and ECO-HDCC tensile properties were investigated.And high ductility criterion of high volume of fly ash ECO-HDCC with strength of C25?C55 can be proposed with two new paramaters the ratio of various temperature complementary energy J'?AT and the ratio of various temperature crack tip toughness J?T.Furthermore,the tensile stress-strain constitutive relationship of ECO-HDCC under variable temperature was established.The design theory of high volume of fly ash ECO-HDCC with strength of C25?C55 under the condition of variable temperature was presented.Firstly,the influence of temperature on the tensile strength of PVA fiber was studied.It was found that the tensile strength of the domestic short-cut special PVA fiber was reduced through high temperature and low temperature treatment.The tensile strength of the fiber treated at 180 ? was 29%lower than that at 20 ?.In addition,the influence of different temperature and the change of fly ash content and water-binder ratio on the constitutive relation and key parameters of micromechanical properties of fiber-matrix interface were studied.It was concluded that the increase of fly ash content and the increase of water-binder ratio resulted in the decrease of chemical bond and friction stress between the fiber and the matrix,and the chemical bonding force was more sensitive to the change of fly ash content while the friction bond stress was more affected by water-cement ratio.The chemical bond between the surrounding matrix and the fiber is reduced after the temperature treatment.The chemical bond force after the treatment at 0 ? is the smallest,3.053 J/m2,which is approximately half of that at room temperature.In the same water-binder ratio,the order of chemical bond is:0 ?<60 ?<30 ?<20 ?;friction bond stress after temperature treatment is increased.The friction bond stress under-30? is 1.6?2 times than under 20?.Secondly,the influence of temperature on the fracture toughness and elastic modulus of ECO-HDCC matrix was investigated.It is found that the fracture toughness of the matrix increases with the increase of temperature at-30 ??180 ?,and the fracture toughness at 180 ? is about twice that of-30 ?.The temperature treatment reduces the elastic modulus of the matrix.The reduction of elastic modulus under low temperature is more obvious.Moreover,the addition of fly ash reduces the fracture toughness and elastic modulus of the matrix,and the increase of the water-binder ratio also reduces the fracture toughness and elastic modulus of the matrix.What's more,the effects of different temperature,fly ash content and water-binder ratio on the macroscopic tensile properties of ECO-HDCC were conducted.It was deduced that the addition of fly ash and the change of ECO-HDCC matrix strength reduced the initial tensile strength and ultimate tensile strength,but increased the tensile strain of ECO-HDCC.Moreover,the effect of the change of water-binder ratio on the tensile properties is more outstanding.The tensile strength and the ultimate tensile strength decreased by 22%?26%and 14%?21%,the ultimate tensile strain increased by 18%?54%after fly ash content increased 20%.The water-binder ratio increased by 0.05,the tensile strength is reduced by 15%?18%and 12%?19%,respectively and the increase of ultimate tensile strain is 120%?188%.The effect of temperature on the uniaxial tensile properties of ECO-HDCC is more complicated.The increase of temperature can improve the tensile properties of ECO-HDCC.However,the excessive temperature will cause the tensile properties of ECO-HDCC to be lost while the low temperature increase tensile performance both in strength and elongation.The best properties is achieved at 0?.Finally,the ECO-HDCC tensile constitutive relation and design theory under variable temperature conditions are proposed.Two new parameters the ratio of various temperature complementary energy J'?T and the ratio of various temperature crack tip toughness J?T are defined.When J'?T>0.04 and 0.7<J?T<2,the ductility of high fly ash content ECO-HDCC of strength grade C25?C55 can steadily more than 0.5%.In addition,the bilinear model was used to modify the classical design theory of high ductility cementitious composites.The uniaxial tensile stress-strain constitutive relation of ECO-HDCC under variable temperature was established.And the design theory under variable temperature was raised which is appropriate for strength grade C25?C55 high fly ash content ECO-HDCC.The results of this study can provide with theoretical guidance of ECO-HDCC to material design and engineering application.Theoretical significance and engineering application value is pointed out.