Experimental Study On Durability And Improvement Techniques For The Lightweight Concrete

Durability is an important factor affecting the service life of engineering structures.As a new type of building materials,lightweight concrete has been widely used in geotechnical engineering with excellent characteristics.However,in the practical engineering,lightweight concrete is affected not only by various loads,but also a variety of natural factors of the environment,which may cause damage or even destruction in harsh environmental conditions as a result of poor durability.The lack of understanding to the durability of lightweight concrete may bring some hidden troubles to the engineering quality during construction,which may cause unnecessary economic loss in the later use process.However,there is still little research on the durability of lightweight concrete.Therefore,it is necessary to study the durability of lightweight concrete systematically.According to the durability problems that may occur in the course of using lightweight concrete,lightweight concrete was prepared by introducing preformed foam into ordinary Portland cement slurry.And a series of durability tests were carried out to investigate the durability of light-weight concrete with different density in this paper,such as modified permeability test,drying shrinkage test and freeze-thaw test,etc.In addition,glass fiber,fly ash and silica fume were used to replace part of the cement to produce lightweight concrete,and the effects of glass fiber,fly ash and silica fume on the durability were discussed.The main conclusions are as follows:The permeability test results illustrated that penetration time of lightweight concrete increased with the increase of density,but increased at first and then decreased with the increase of water cement ratio.Glass fiber had little influence on the improvement of impermeability for the samples with low density,while for the samples with high density,adding glass fiber could significantly improve the impermeability.Fly ash had a good of morphological effect,microaggregate filling effect and pozzolanic activity,which could improve the internal structure of lightweight concrete and significantly improved the impermeability of lightweight concrete with density of 700 kg/m3 and 1000 kg/m3 in a certain amount,but not conducive to the improvement of impermeability for the lightweight concrete with density of 400 kg/m3 as a result of strong retarding effect caused by fly ash.Silica fume could significantly improve the impermeability of lightweight concrete in a smaller dosage range,but mixed with excessive would reduce the impermeability.The drying shrinkage test illustrated that drying shrinkage of lightweight concrete increased with curing time,and it grew very fast in early period,but tended to be stable in late period.The drying shrinkage decreased with the increase of density.Adding glass fiber could effectively inhibit the drying shrinkage.With the increase of the content of glass fiber,the dry shrinkage of lightweight concrete gradually decreased,and there was an optimal content.A certain amount of fly ash could decrease the drying shrinkage,but mixed with excessive would delay the setting time,and the stability of the slurry became poor,resulting in a larger shrinkage deformation.Silicon fume could reduce the shrinkage of the lightweight concrete with low density in some degree.While for high density lightweight concrete,adding silicon fume would increase the drying shrinkage,especially the early shrinkage.The freeze-thaw test showed that frost resistance of lightweight concrete increased with the increase of density.The compressive strength decreased with the increase of freeze-thaw cycles,and it decreased slowly in early period,but faster in late period.The mass first increased and then decreased with freeze-thaw cycles,and the lower the density,the more the mass loss in the early time and faster the mass increased in the late time.Adding glass fiber or fly ash could significantly improve the frost resistance of foamed lightweight concrete.And the rate of compressive strength loss and mass loss were significantly smaller than the ordinary lightweight concrete,also the glass fiber samples had better flaking resistance.For the samples with low density,silicon fume was beneficial to improve the frost resistance,while for the samples with density of 700kg/m3 and 1000 kg/m3,adding silicon fume had negative effect on the frost resistance.