Study On Basic Mechanical Properties Of The Activated Recycled Brick ECC

Engineered Cementitious Composites(ECC)is the fiber-reinforced composite material proposed by V C Li of Michigan State University based on the principles of micromechanics and fracture mechanics.It has good strain hardening characteristics and crack control ability under tensile load,and its ultimate tensile strain can be stabilized above 3%.Because of the good durability and long-term performance of ECC,it has great application potential in improving the seismic performance of structures.However,the amount of cementitious materials in ECC is huge,and the consumption of cement will cause many resource and environmental problems.On the other hand,a large number of abandoned buildings are demolished because of the development of urbanization,and the amount of clay brick waste is increasing.The treatment of these construction wastes has social,economic and environmental effect.A large number of studies have shown that the recycled brick powder(which is generally defined as less than 0.16 mm in particle size)produced by crushing and grinding waste clay bricks has potential activity and could replace the cement to a certain extent after being activited.This article attempted to use three activation methods such as physical activation,chemical activation and high temperature activation to treat recycled brick powder.After evaluation and analysis,the most suitable activation method was used to process the recycled brick powder.Then the activited recycled brick powder was used to replace a part of the cement to prepare RBP-ECC(Recycled Brick Powder-Engineered Cementitious Composites,referred to as RBP-ECC),and the best replacement rates of recycled brick powder was obtained by testing the flexural strength,compressive strength,uniaxial tensile performance and four-point bending performance.Then the influence of different water-cementitious ratio,sand-cementitious ratio,fiber content and age on the basic mechanical properties of RBP-ECC was studied and analyzed.The main conclusions are as follows:(1)Compared with the chemical excitation method and high temperature excitation method,the activity index of the recycled brick powder treated by the physical excitation method was higher.As the ball milling time increases,the activity of the recycled brick powder first increased and then decreased,and the activity was highest at 45 minutes.After comprehensively considering material sustainability indicators,ball milling for 30 minutes was selected as the activity excitation method for recycled brick powder.(2)The recycled brick powder after ball milling for 30 minutes was substituted for cement with different substitution rates to prepare RBP-ECC.The test results showed that the maximum of ultimate tensile strain could reach 5.222%,and the maximum of ultimate deflection could reach 55.527 mm,the energy intensity,carbon dioxide emissions and costs can be reduced by up to 40% or more.After considering of the mechanical properties of RBP-ECC under different replacement rates and calculating its sustainability indicators quantitatively,20 percents was selected as the optimal replacement rateby guided by the theories of “low carbon and energy saving”,“cost reduction” and “strength and toughness”.(3)The flexural strength of RBP-ECC was in the range of 11.4 MPa to 20.9 MPa,and the compressive strength was in the range of 16.1 MPa to 36.8 MPa.Both of them decreased with the increase of water-cementitious ratio,increased with the increase of sand-to-cementitious ratio,and increased with the increase of fiber content.The flexural strength and compressive strength of RBP-ECC both increased as the curing age became longer.(4)Under uniaxial tensile load,except for a few mix ratios,the ultimate tensile strain of RBP-ECC can reach more than 2%,showing obvious strain hardening characteristics,and multi-slit cracking can be observed during the loading process.The initial cracking strength of RBP-ECC was in the range of 1.028MPa～3.069 MPa,and the ultimate tensile strength was in the range of 1.944MPa～4.135 MPa.Various performance indicators varied with water-to-binder ratio,sand-to-cementitious ratio,fiber content and age.Fluctuating,the RBP-ECC ultimate tensile strain was the largest when the water-to-cementitious ratio was 0.4,the sand-to-cementitious ratio was 0.3,the fiber content was 2%,and the age was 3d.(5)Under the action of four-point bending load,except for the fiber content of1.25%,the ultimate deflection of RBP-ECC could reach more than 30 mm,and both could show better deformation and hardening ability.The cracking strength of RBPECC was in the range of 2.346MPa～5.229 MPa,and the ultimate tensile strength was in the range of 5.7MPa～10.341 MPa.Each performance index fluctuated with the changes of water-cementitious ratio,sand-cementitious ratio,fiber content and age.RBP-ECC had the best flexural toughness when the water-to-cementitious ratio was0.375,the sand-to-cementitious ratio was 0.35,the fiber content was 2%,and the age was 14 d.(6)After comprehensive analysis of the tensile and compression indicators and bending and tensile properties of RBP-ECC,the optimal mix ratio parameters after optimization were 0.325 water-to-cementitious ratio,0.35 sand-to-cementitious ratio,and 2% fiber content.