Design And Application Of High And Ultra-high Strength Engineered Cementitious Composites

Engineered cementitious composites(ECC)were developed to overcome the brittleness and improve crack resistance ability of concrete.However,application of traditional ECC was limited due to its low strength and high shrinkage performance.Present research focuses on the design and application of ECC with characteristics of high strength,low shrinkage and moderate ductility under normal curing conditions.Hence,experiments on strength,shrinkage and ductility were carried out,research and analysis of ECC-Steel composite bridge deck were launched as well.Based on low water to binder ratio cementitious system,strength of different cements,quartz sand and supplementary cementing materials were tested to form high and ultra-high strength cement matrix.Through the addition of 2% PVA fiber and different volume fraction of steel fiber from 0 to 2%,influence of steel fiber volume on mechanical properties of cementitious composites were studied.Cracking strength were enhanced by additional steel fiber,similar results were found in tensile strength and strain of high and ultra-high strength PVA-ECC,meanwhile,crack width was reduced due to proper steel fiber volume in cementitious system to 25-45?m.High strength ECC with 80-120 MPa cubic compressive strength was obtained.When 1.0% steel fiber was applied,tensile strength was 7-9MPa while tensile strain was 8000-10000 ?m/m.Zeolite was introduced as internal curing agent to reduce shrinkage of ECC,methods of high temperature calcinations and pre water absorption were utilized to regulate the deformation of high strength ECC.Through integrated experiments of internal temperature,relative humidity and shrinkage,effect of shrinkage reduction were analyzed.In addition,anti crack effects of high strength ECC were evaluated by ring tests.Results indicate that when quartz sand in the mix was 15-20% substituted by calcinated zeolite with pre absorbed water,shrinkage of high strength ECC decreased notably and internal relative humidity increased apparently,shrinkage performance of high strength ECC were well controlled.Regarding the applications of high strength ECC in structures,separate high and ultra high strength ECC with different shrinkage performance were adopted in the bending research of ECC-Steel composite bridge deck.Based on shrinkage,elastic modulus and ring tests tensile creep results,finite element analysis model was built to calculate shrinkage stress in ECC layer.According to cracking strength of respective ECC,cracking load of ECC-Steel composite bridge deck under flexural conditions was obtained.Results manifest that anti crack ability of composite bridge deck was greatly influence by shrinkage of ECC,materials with higher strength and larger shrinkage exhibited lower cracking load,of all the test mixes,high stregnth ECC series with sulfoaluminate cement under internal curing condition possesses the best anti cracking performance.Calculation results of cracking loads were in good agreement with experimental results,methods of shrinkage stress computing based on early-age shrinkage and creep from ring tests outcomes was reliable.