Study On Strengthening And Toughening Properties Of Alkali-resistance Bundling Glass Fiber Reinforced Concrete

With the rapid development of major civil engineering projects such as high-speed railways,heavy-duty pavements,large-span bridge floor,heavy-duty airport runways,industrial floors,underground pipe galleries,energy storage hydropower stations,subway shield segments and fabricated components,the crack resistance,long-term durability,crack control ability,impact resistance and fatigue resistance of concrete have all made higher requirements.At present,synthetic fibers with low elastic modulus and low strength or rust-prone steel fiber and steel mesh are generally used as reinforcing materials for concrete.These reinforcing materials still do not solve the technical problems of cracking and deformation capacity of concrete.Alkali-resistant glass fiber reinforced concrete is highly valued by scholars both at home and abroad for its excellent mechanical properties such as tensile strength,bending strength,and crack resistance.However,researches on alkali-resistant glass fiber reinforced concrete at home and abroad are mainly focused on the alkali-resistant glass fiber cloth reinforced ribs and shotcrete,and there are few studies on the basic mechanical properties and the mechanisms of strengthening and toughening.The study on the strengthening and toughening properties of alkali-resistant glass fiber reinforced concrete is of great significance for its engineering application.In this paper,the alkali-resistant glass fiber reinforced concrete with the volume fraction of 0.25%,0.45% and 0.75% and the steel fiber concrete with the volume fraction of 0.45% and the crude polyolefin fiber concrete with the volume fraction of 0.75% were subjected to cube compression test,cube splitting tensile test,axial tensile test,four-point bending toughness test and three-point notched beam fracture test.The influence of fiber fraction on the mechanical properties of alkali-resistant bundling glass fiber reinforced concrete was analyzed and compared with the steel fiber concrete and crude polypropylene fiber concrete with the same volume fraction.At the same time,The interfacial bonding strength between alkali-resistant glass fiber and mortar matrix was studied by using pull-out test.The effects of the embedding length of bundling glass fiber monofilament,the water-cement-ratio and the age of the matrix were analyzed and the critical embedding length of the fiber was determined.In the end,the strengthening and toughening mechanism of glass fiber reinforced concrete is analyzed.The main research results obtained in this paper are as follows:(1)The cube compressive strength of glass fiber reinforced concrete increased with the increase of fiber volume fraction.With the incorporation of glass fiber,the brittleness of the specimen was significantly reduced and the integrity of the specimen is better.The cube compressive strength increased by 1.74%,3.65%,and 6.82% respectively compared to the plain concrete when the the ratio of glass fiber was 0.25%,0.45%,and 0.75%.The effect of low glass fiber content on the splitting tensile strength of concrete cube was not obvious.The cube splitting tensile strength increased by 19.10% when the glass fiber addition rate was 0.75%,and increased by 4.2% when compared with the same volume fraction polypropylene fiber reinforced concrete.(2)The axial tensile properties of glass fiber reinforced concrete was better than that of crude polypropylene fiber concrete with the same volume fraction,and the tensile strength and ultimate tensile strain are slightly higher than that of steel fiber reinforced concrete with the same volume.When the glass fiber volume fraction is 0.75%,the flexural toughness value and peak intensity are increased by 191.73% and 11.47% higher than that of plain concrete,and the fracture toughness and fracture energy are increased by 28.16% and 268.69% higher than that of plain concrete,the flexural toughness and fracture mechanics index of alkali-resistant bundling glass fiber reinforced concrete increase greatly with this volume fraction.(3)With the increase of the embedding length of glass fiber monofilament,the interfacial bonding strength decreased at first and then gradually increased.Meanwhile,the interfacial bonding strength gradually increased when the water-cement-ratio increased from 0.30 to 0.40.In addition,the interfacial bonding strength increased with the curing age.The critical embedding length of glass fiber monofilament was determined to be between 27.5mm and 30 mm when the water-cement-ratio was 0.35.(4)Glass fiber can improve the performance of concrete and reduce the generation of original micro-cracks in the concrete.Glass fiber can transmit stress across the cracks through interface bonding,so that glass fiber concrete can withstand greater loads and exhibit better toughness.