| In recent years,the construction of basic engineering in northwest China has been developing rapidly and the dosage of concrete surged.With the increase of service time,a large number of existing reinforced concrete structures appeared different degrees of diseases,such as cracks,denudation,core concrete collapse and structural deviation.Using appropriate repairing materials and bonding methods to repair shallow damaged areas of concrete in time not only can improve the safety and durability of reinforced concrete structures,but also can reduce the risk of secondary reinforcement on components.Lots of reinforced concrete structures in northwest China were in a complex service environment with multi-factor coupling effects such as wet and dry cycles,freezethaw cycles and salt erosion for a long time.The existing repair materials and bonding methods were difficult to meet the needs of the repair engineering in northwest China.Therefore,it is urgent to develop repair materials and bonding technologies suitable for typical shallow concrete diseases in northwest China.Based on the causes and characteristics of the shallow layer diseases of concrete under typical northwest environment,52.5R ordinary Portland cement was taken as the base material.Two common types of cement-based materials,i.e.,mortar and fine stone concrete,were prepared as the repair materials,and four materials,i.e.,silica,sodium silicate,basalt fiber and UEA expansion agent were selected to modify and strengthen its properties.Through experiments,the workability,volume stability,the mechanical properties of repaired mortar and fine stone concrete were studied and corresponding the resistance to the combined erosion ability of sodium sulfate dry-wet cycle and freeze-thaw cycle was also be investigated.The bonding technology between old concrete substrate with different strength grades and repaired materials,and corresponding the resistance to same erosion above were also studied.The prediction models of the mechanical indexes of repaired materials and the bond strength between repaired materials and old concrete substrate under sulfate multi-factors were also established,which laid a theoretical foundation for the studies of the repair materials of superficial damages and the bond technologies of new/old interface of concrete in complex in northwest China environment.The main research contents of this paper are as follows:(1)With the orthogonal test method and the deviation maximization and gray correlation comprehensive evaluation system,the mortar consistency,concrete collapse and the cube compressive strength at 3,7 and 28 days,and the change rates of length at 1,3,7,14,28,45,60 and 90 days were taken as evaluation indexes.The configuration parameters of three groups of repaired mortar and repaired fine stone concrete with moderate workability,good volume stability,high early strength and good late strength development were preliminarily selected.(2)Based on the preliminary optimization results of repairing materials,the sulphate-wet and dry cycle tests and rapid freeze-thaw tests were carried out to study the changes of macroscopic properties and microscopic phases of the optimized repaired mortar and repaired fine stone concrete.Through regression analysis,the relationships between the compressive strength and flexurepressure ratio of repaired mortar and the number of dry-wet cycles and freeze-thaw cycles were established.The relationships between the peak stress and corresponding strain of repaired fine stone concrete and above numbers were also established.(3)Bond strength between old concrete substrate of different strength levels and repairing materials involving repair material mix ratio,interface agent types and bonding interface treatment methods were investigated.The changing rules of the bonding strength of the interface between new/old materials of concrete under different influencing factors were analyzed,and corresponding bonding technology was optimized.(4)Based on the optimization results of the bonding technology,the durability of the bonding sample with new/old materials and interfaces under the two factors of sulfate and dry-wet cycles and the three factors of sulfate,dry-wet cycles and freeze-thaw cycles were investigated.The changes in morphology,quality and bond strength between old concrete substrate with different strength levels and repaired materials were analyzed.The relationship between bond strength and the number of wet and dry cycles and freeze-thaw cycles was established by regression analysis. |
