Study On Preparation And Performance Of Immersed Tunnel Concrete Made From Manufactured Sand

The Dalian Bay Undersea Tunnel is a submarine immersed tunnel under construction.The main length of the project is about 5098m,of which the submarine immersed tunnel is 3080m long and the main structure is designed for 100 years.The Dalian Bay subsea tunnel is in a marine corrosive environment in the cold northern regions,and the service conditions are severe.The penetration of chloride and freeze-thaw damage has a adverse effect on the durability of the concrete structure.In addition,the quality of local river sand in Dalian is generally poor and the resources are scarce.The use of manufactured sand can effectively solve this contradiction.However,the preparation of immersed concrete ultilizing manufactured sand has no experience in engineering applications.This paper mainly takes manufactured sand and manufactured sand concrete as the research object,and is oriented to the production and design requirements of immersed concrete,accomplished the preparation of immersed tunnel concrete.In this paper,the effects of cementitious material content,cementitious material composition,water-to-binder ratio,sand ratio and air content on the performance of manufactured sand concrete were studied.The performance of river sand concrete under the same conditions were compared,and the optimized mixing parameters were determined.The effect of the stone powder content on the hydration heat release of the cementitious material,the mixture performance,strength,early crack resistance and durability of the immersed tube concrete was studied,and the small model block located at the chamfer of the immersed tunnel was placed,the temperature was monitored.The basic laws revealed are as follows:The mix proportion of manufactured sand immersed tunnel concrete was selected as follows:the amount of cementitous material content was 420kg/m~3,and the water-to-binder ratio was 0.33.The cementitious material consists of 55%ordinary Portland cement,15%Grade I fly ash and 30%S95 grade slag powder,with a sand ratio of 41%and a air content of 4 to 6%.The polycarboxylate superplasticizer dosage is1.0%,and the saponin air entraining agent dosage is 0.5%.The workability,strength,hydration heat,early-age cracking and durability of this mixing proportion can meet the performance requirments of the immersed tunnel concrete.When the stone powder content was in the range of 5%~18%,the workability of concrete mixture improved firstly,then gradually deteriorates when the stone powder content exceeds 12%,the air content and frost resistance decreases gradually with the increase of stone powder content.In the range of 7%~13%,the early crack resistance of the immersed tube concrete decreases with the increase of the stone powder content,and the chloride ion permeability decreases with the increase of the stone powder content.The presence of stone powder in the manufactured sand accelerates the hydration of the cementitious material and increases early hydration heat.At a casting temperature of 31.5°C,the maximum internal temperature of the model is 73.6°C,exceeding the specification of 70°C.The temperature difference between the side and the center point is 31.4°C,and the maximum temperature difference is 19.4°C after the upper surface is covered with geotextile.The casting temperature should be lowered and effective heat preservation measures should be taken during construction.