Experimental Study On Erosive Wear For Concrete And Protective Materials Under Strong Wind-sand Environment In Northwest

The opened Lanzhou-xinjiang high speed railway passes through the five strong wind area. In the strong wind area, the concrete bridge beam body, bridge pier and railway roadbed are suffered seriously from erosion wear by grains of sand carried by strong winds, which causes such as the surface of a bridge pier concrete spalling and micro cracks between cement and aggregate, and these injuries may worsen the other disease and damage of concrete structure, and reduce the durability of the concrete structure. The reduction of durability for concrete structure not only influences its design life, at the same time, causes huge maintenance costs, but also causes a great hidden trouble to the safety of the train operation.In regard to erosion wear of concrete structure material, the erosion wear by water-dragged rubble for hydraulic concrete structure material was researched, including experimental method, erosion wear mechanism, evaluation index and anti-wear measures, and making some progresses. However, in wind sand environment(gas-solid two phase flow), the researches for concrete structure material erosion wear, including experiment method, erosion wear mechanism and protection, repairing materials, were also rare. Therefor, in the thesis, based on the characteristics of gobi wind-sand flow environment, the erosion wear tests of concrete, modified epoxy resin, epoxy resin matrix composites and cement matrix protection and repair mortar were carried out by sediment-air injection method to study the behavious of erosion wear and the mechanisms of erosion wear. Furthermore, based on the field tests and laboratory experiments of modified epoxy resin matrix composites, the feasibility of the modified epoxy resin matrix composites used as protective material for concrete structure in wind-blown sand flow environment was discussed. The main research contents and conclusions are as follows:(1)The erosion wear testing machine was builded, referencing ASTMC418-2005 “concrete erosion wear standard test method”, which are made up of four parts, such as the air supply system, the sand supply system, the spray gun and nozzle system and the sample room. The size distribution of collected sand particle was analyzed, and the sand particle size range for indoor experiment was determined. The relationship between air velocity and air pressure was tested, in order to determine the test speed.(2) The effects of wind-sand flow velocity, impact angle, impact time and erosive particle mass flow rate on erosive wear rates of concretes have been investigated. Experimental results show that the relationship between erosion rates of concretes and wind-sand flow velocity meets the power exponent relationship, and the fitting speed index is 2.0-3.2, which is consistent with the erosion rule of the brittle material. For all concrete samples, erosion rates are highest at 90° impingement angle, and lowest at 45° impingement angle, in accordance with erosion rule of brittle materials. The erosion rates for concrete reduce firstly and then increase with the increase of erosive particle mass flow rate. The erosion wear mechanisms of concrete are cracking and spalling of set cement on the surface of concrete and selective erosion wear of mortar in sub-surface of concrete.(3)The bisphenol A type epoxy resin has been modified through asphalt, nano-silica and modified alicyclic amine curing agent and the durability and erosion wear resistance have been studied. The results show that these modifier agents can enhance mechanical properties, durability and erosion wear resistance of epoxy. The modified epoxy indicates semi-ductile erosion behaviour, and the peak erosion rate is at 45° impingement angle, and the erosion resistance has been improved tremendously compared to concrete. The normal and the tangential component of erosion particle energy cause erosion of the modified epoxy resin, in which the normal component of energy causes crack and breakage of material surface, and the tangential component causes cutting of material surface.(4) The glass(carbon) fiber reinforced epoxy resin composites were prepared, and the effects of resin content, fiber orientation, fiber cloth type and erosion parameters on erosion wear were studied. Results show that epoxy matrix composites indicate semi-ductile erosion behaviour, with peak erosion rate at 45°-60° impingement angle. For unidirectional fiber reinforced epoxy matrix composites, their erosion rate presents exponential relationship with wind-sand flow velocity, and the velocity index is 2.1-2.8, at the same condition, the erosion rate of perpendicular impacting is higher than that of parallel erosion, furthermore, the higher the resin content, the higher the erosion resistance of the composites. Main erosion wear mechanisms of the composites are the generation of micro cracks, fiber bending fracture, stripping between fiber and matrix, and microscopic cutting of matrix.(5) The different cement-based protection and repair mortars were prepared, and the effects of strength grade, sand gradation, acrylic-emulsion content, fiber type and content on erosive wear rates were studied. For all samples, the erosive wear rates increase with increasing impingement velocity. The erosive wear rates of PP and PVA fiber reinforced mortars present zigzag change with the increase of erosion angle, and the rest present the same erosion rule of brittle material. The greater strength grade and sand gradation are, the lower erosive wear rates are. A certain dosage of acrylic-emulsion can form a special polymer membrane structure in the mortar and improve the toughness and abrasion resistance of mortar. Appropriate amount of PP and PVA fiber can enhance the tougheness and strength of mortar, which can improve the erosion resistance of mortar, especially at high impingement angle.