Research On Abrasion Resistance Of Ultra-High-Performance Concrete

Cement concrete is the main building material in hydraulic engineering.The spillway,silting pool,bridge pier and dam are subjected to the long-term abrasion erosion of water flow with sand and gravel,so the operation and service life of hydraulic structures are affected seriously.In order to alleviate the engineering problems caused by abrasion failure,it is urgent to develop and apply cement-based materials with high abrasion resistance.Ultra-high-performance concrete（UHPC）has super high compressive strength,bending toughness and excellent durability,which indicates that it has the potential to be used as high abrasion resistance material.However,the abrasion resistance of UHPC has not received adequate attention.Based on this situation,this paper carried out the research on the influencing factors of abrasion resistance of UHPC.Firstly,the hydration and hardening performance of UHPC was studied from four aspects:hydration and heat release characteristics,workability,compressive and volume stability.Then,based on the high-speed underwater method,the influencing rules of water-binder ratio,supplement cementitious materials（SCMs）and steel fiber on abrasion resistance were revealed.Finally,the mechanism of SCMs on abrasion resistance was analyzed by the microstructure,hydration products and pore structure of hardened paste.The main research results are as follows:（1）The abrasion process of UHPC including four stages:partial surface abraded-all surface abraded-quartz sand stripping-abrasion degree intensification.The mass loss rate of UHPC increased with time due to the increasing of surface defects caused by the stripping of quartz sand and the void left by it.（2）The abrasion resistance strength of UHPC decreased gradually with increase of water-binder ratio.When the water-binder ratio increased from 0.16 to 0.18 and 0.2,the abrasion strength decreased by 56.9%and 60.8%.（3）Among supplement cementitious materials,silica fume increased abrasion resistance of UHPC by increasing C-S-H gel,refining pore structure and reducing porosity.10%and 20%silica fume content increased the abrasion strength of UHPC by 52.5%and 60.4%,respectively.Fly ash and slag decreased abrasion strength due to the porosity increased.The decreasing degree of fly ash is more than slag.Nano-Si O₂ caused the problems of particle aggregation and poor molding,which decreased the abrasion resistance.（4）Mass loss is increased due to the loss of steel fibers and the scratches left by them.In the test group with steel fiber,the abrasion strength increased linearly with the steel fiber content.Compared with UHPC without steel fibers,steel fiber can reduce the maximum abrasion depth and surface roughness when the content is more than 1%.（5）The abrasion rate is a more accurate evaluation index than abrasion strength,which can further evaluate the abrasion resistance of the samples with similar abrasion strength.Compared with other indexes,the maximum abrasion depth and surface roughness are more suitable for evaluating abrasion resistance of UHPC with steel fiber.