Study On Properties And Technology Of High-toughness Synthetic Fiber Cement Based Thin Layer Overlay Material

High-toughness fiber reinforced cement-based material?ECC?is a kind of chaotic distribution short fiber reinforced cement-based composite material with ultra-high toughness based on meso-mechanical design.Its ultimate tensile strain can reach 2%under tensile load.Above,it shows excellent bending deformation ability and micro-crack control ability,but the current ECC design idea is basically to improve the uniformity by removing the coarse aggregate in the matrix,and to ensure the full utilization of the fiber bridging effect.This led to the early shrinkage of fiber-reinforced cement-based materials,which greatly limited its application in road engineering.In addition,the types of fibers used in the ECC materials currently studied are mostly polyvinyl alcohol?PVA?fibers imported from Japan,and the price is much higher than that of domestic fibers,which greatly increases the production cost of ECC,and the quality of domestic PVA fibers.Less than Japan imported fiber,so in recent years,ECC has not been widely promoted in the construction of transportation infrastructure.This paper focuses on the high-toughness synthetic fiber cement-based materials as a new thin layer of overcoat material.By referring to the traditional ECC idea,the test mix ratio is re-adjusted,and a high-toughness,low-shrinkage,early-strength synthetic fiber cement-based cover that meets the engineering requirements is developed.The surface material is proposed to replace the PVA fiber with low modulus and high elongation polypropylene?PP?fiber.The improvement effect and difference of PVA fiber on various aspects of cement-based materials are investigated.Based on this,two kinds of properties are explored.The possibility of synthetic fiber mixing,using the"fiber hybrid effect function"to optimize the optimal blending ratio under different fiber content for practical engineering applications.In addition,this paper also deeply discusses some problems in the construction technology of high-toughness synthetic fiber cement-based thin layer overlay,and numerically simulates the cracking behavior of synthetic fiber cement-based thin layer overlay in actual engineering based on ABAQUS software.The main research results show that:?1?In the traditional ECC ratio,the appropriate amount of pebbles and expansion agent and the replacement of part of the cement with fly ash can effectively improve the early shrinkage of ECC materials.After the combination ratio,the dry shrinkage is only 0.4-0.5of the traditional ECC.Times or so,equivalent to ordinary concrete;?2?The synthetic fiber with the content of 1%to 2%has a significant increase in the early flexural strength of the cement-based material,but the effect of the increase in age is weakened,and the PVA fiber with the same amount is more advantageous.The high-toughness synthetic fiber cement-based thin-layer overcoat material studied in this paper can reach 6.03⁷.14MPa in 1d age,and has already been opened to traffic.The flexural strength of 28d age is 8.67¹0.13MPa,which can meet the extremely heavy weight.And special traffic level requirements;?3?The effect of synthetic fiber on the compressive strength of cement-based materials is very small and the compressive strength tends to decrease to some extent with the increase of fiber content.The compressive strength of the synthetic fiber cement-based materials studied in this paper is between 43.9 and 48.4 MPa,and the compressive strength at 28d age is between 53.1 and 55.3 MPa,which far exceeds the general Portland cement.Requirements for compressive strength;?4?The addition of synthetic fiber with 1%²%can greatly improve the bending toughness,fracture toughness and impact toughness of cement-based specimens.The improvement of bending toughness of cement-based specimens by PVA fiber is mainly reflected in the initial stage of deformation and bending toughness.The index₅ is about4.36⁴.71 times of the cement-based test piece,while the PP fiber is mainly reflected in the later stage of deformation,and the bending toughness index₁₀ is about 5.47⁷.93times of the prime cement-based test piece.The improvement of fracture toughness of PP-based specimens is mainly reflected in the energy absorption capacity of the post-crack load.The fracture energy gain ratio is 1188.6%²645.4%,which is about 3.8-5.5 times of PVA fiber cement-based specimens.The crack instability instability is not as good as that of PVA fiber,and the fracture toughness gain ratio is 17.05%-32.53%,which is only 0.5-0.7 times of the PVA fiber cement-based test piece.Both PP fiber and PVA fiber can effectively improve the impact toughness of cement-based specimens.Compared with plain cement-based specimens,the number of cracks in synthetic fiber-based specimens increased by 1.5 to 9 times under the repeated action of impact load.The number of cracks and impact energy is increased by 3 to 14 times;?5?The blending capacity of 1%²%synthetic fiber has significant improvement on the wear resistance and dry shrinkage performance of the cement-based material.Compared with the plain cement-based test piece,the wear amount is reduced by12.5%⁴0.8%,and the shrinkage is reduced.The strain is reduced by 10.6%to 33.0%;?6?The interface agent with polymer emulsion and cement mixing ratio of 1:1.5¹:2can significantly increase the bond strength between new and old materials.The flexural strength of bonded specimens at 28d age reaches 7.61MPa⁷.92MPa.?about 85%⁸8%of the flexural strength of the complete fiber cement-based test piece?,the interfacial shear strength reaches 3.7MPa⁴.11MPa?corresponding to the shear strength of the integrally cast cement-based test piece?;?7?Under the action of the axle load of the vehicle,the shear stress?_xy and the tensile stress?₁ in the overlay surface layer show a high degree of stress concentration near the initial crack.Compared with the ordinary concrete cover,the stress concentration phenomenon in the synthetic fiber cement-based thin layer cover is improved,and the stress intensity factor at the reflective crack tip is significantly reduced.Both the polypropylene fiber and the polyvinyl alcohol fiber cement-based thin layer cover can effectively suppress the generation and expansion of the super-heavy-axis reflection crack,and the suppression effect of the two on the reflection crack is equivalent.