Effect Of Redispersible Polymer Powders On Properties Of Engineered Cementitious Composite

ECC (Engineered Cementitious Composite) is a kind of fiber reinforcedcement-based composite with high toughness and high energy absorption capacity.Current research in ECC is mainly concentrated on the mechanical properties understatic loads, especially its tensile and flexural properties. However, modificationmethod on ECC is still not widely proposed. In view of this, this paper selected flyash ECC (FA-ECC) and slag ECC (SL-ECC) as the reference group which wasmodified by incorporation of redispersible polymer powders (EVA). Mechanicalproperties of EVA-ECC and normal/reference ECC are studied through directtensile test, four-point bending test, uniaxial compression test, drop hammer impacttest as well as rapid freeze-thaw test. Besides, the effect of freeze-thaw cycles isalso discussed. The main results are as follows.(1) Test of workability shows that the ECC mixture can be mixed more easilyand uniformly after adding EVA, and the amount of superplasticizer needed to reachthe same fluidity is decreased with much higher air content in fresh ECC.(2) To study the influence of EVA on uniaxial tensile and flexural performanceof ECC, direct tensile test and four-point bending test are used. Results show thatEVA can significantly improve the peak tensile strain of fly ash ECC and slag ECC,and the peak deflection and toughness index of fly ash ECC. However, the influenceof EVA on the bend ductility of slag ECC is not obvious.(3) By tests of cubic compression strength, flexural strength, axial compressivestrength and the stress-strain curve under uniaxial compression of EVA-ECC andbased ECC at different ages, following results are gotten: EVA can decrease thecompression strength of FA-ECC and SL-ECC. Cubic compression strength of twodifferent sizes,70.7mm and100mm, are almost the same, which means the sizeeffect of ECC is insignificant. By adding EVA, compression resilience of ECC isimproved, and the descent part of uniaxial compressive stress-strain curve issmoother, but the impact on peak strain is not big. Rational fraction is used to fit thestress-strain curve and to set up suitable constitutive equation which was in goodaccordance with the measured values(4) The drop hammer impact test results indicate that the flexural impactperformance of EVA-ECC is superior to ordinary concrete and steel fiber reinforcedconcrete. Impact energy-consumption is45~248times as much as ordinary concreteand11~62times as steel fiber reinforced concrete, and the highest impact toughnessindex is30times as much as steel fiber reinforced concrete. Adding EVA canimprove the impact-resistance of FA-ECC but weaken that of SL-ECC. (5) After freeze-thaw cycles for the same times, loss of quality, relativelydynamic elastic modulus and compressive strength are all lower than reference ECC,which means EVA-ECC has better frost resistance.