Experimental Studay On Drying Shrinkage And Crack Resistance Of Aligned Steel Fiber Reinforced Cementitious Composites

Cracking caused by shrinkage deformation of cement-based composites has been one of the problems puzzling concrete engineering.Cracking of concrete seriously affects the life of concrete structures.Therefore,controlling the occurrence and development of cracks in cement-based materials and improving their durability are the key to improve the quality and service life of concrete projects.Adding steel fibers can effectively improve the crack resistance of cement-based composites and reduce the width and number of cracks.As a new type of composite material,aligned steel fiber reinforced cement-based composites have excellent tensile and flexural properties.The shrinkage deformation and crack resistance of aligned steel fiber reinforced cement-based composites are different from those of traditional steel fiber reinforced cementbased composites due to the particularity of directional distribution of steel fiber.At the same time,in practical engineering,There are many cracks in cement-based composites due to shrinkage.such as 45 degree cracks in the corner of the floor due to restraint of contraction deformation in two directions,and transverse cracks perpendicular to the long side of the strip structure such as pavement due to restraint at the bottom.These cracks have the same result that they are along a specific direction.The steel fiber orientation method is adopted to make the steel fiber axial direction perpendicular to the crack direction which may occur.The crack suppression effect of steel fiber in the drying shrinkage process of concrete is utilized to the maximum extent,so as to reduce the possibility of concrete cracking and increase the service life of components.Therefore,it is of great practical significance to study the effect of steel fiber orientation on the shrinkage properties of cement matrix composites.To this end,the specific research work and results of this paper are as follows:(1)The free drying shrinkage of aligned steel fiber reinforced cement-based composites and steel fiber reinforced cement-based composites under different matrix materials,steel fiber content and water cement ratio of matrix materials were studied through experiments.The results show that the drying shrinkage strain of aligned steel fiber reinforced cementbased composites is less than that of steel fiber reinforced cement-based composites;with the increase of curing age and steel fiber content,the shrinkage strain of aligned steel fiber reinforced cement-based composites is smaller than that of steel fiber reinforced cementbased composites(2)Stress transfer between steel fiber and cement-based materials is analyzed,and the effect of steel fiber orientation on shrinkage strain is studied.The regularity of the effect of steel fiber orientation on shrinkage of cement-based materials is mastered.That is to say,compared with steel fiber reinforced cement matrix composites,the direction of steel fiber in aligned steel fiber reinforced cement matrix composites is parallel to the measurement direction,and the shrinkage in this direction is effectively restrained by the bonding between steel fiber and matrix.A free drying shrinkage model of aligned steel fiber reinforced cement matrix composites was established.Compared with the test results,the model predictions were basically in agreement with the test results,which showed that the model was reasonable.(3)Through The plate test,the shrinkage cracks of aligned steel fiber reinforced cementbased composites and steel fiber reinforced cement-based composites in different directions can be contrasted and observed,and we do some evaluation of the crack resistance of aligned steel fiber reinforced cement-based composites,and analyze the shrinkage performance of aligned steel fiber reinforced cement-based composites from the crack resistance angle.The results show that the crack resistance of aligned steel fiber reinforced cement-based composites perpendicular to steel fiber direction is better than that of steel fiber reinforced cement matrix composites,while the crack resistance parallel to steel fiber direction is worse than that of steel fiber reinforced cement composites.