Study On The Preparation Technology Of Self-compacting Fair-faced Concrete For Precast Members In Complex Environment

The self-compacting fair-faced concrete studied in this paper was a new type of green concrete that combined the two technologies of self-compacting concrete and fair-faced concrete,which was convenient for construction and had decorative effect,high research and application value.However,the large fluidity of self-compacting concrete was required sufficient cementations materials and large sand rate to support,and most self-compacting concrete had a high viscosity,leading to the difficulty in eliminating bubble enrichment,which was inconsistent with the requirement of no holes on the surface of fair-faced concrete.And when the sand rate was low,it was more conducive to the control of apparent quality.Concrete vibration process was more conducive to the elimination of bubbles in the slurry,but self-compacting concrete vibration would increase the possibility of bleeding concrete.Therefore,it was particularly important to study the preparation and application technology of self-compacting fair-faced concrete.In this paper,it was based on engineering of self-compacting concrete precast water bridge in Hohhot,according to local climate conditions and engineering needs to design the C50 and C60 two self-compacting concrete strength grade,and the designed working performance and durability of the concrete study,the study found that,for C50self-compacting concrete with P·O 42.5 cement,and cement materials should be controlled in 560~580 kg/m~3,gelling material ratio of two coal fly ash and mineral powder,fine aggregate fineness modulus was in control of 2.7~3.0,sand ratio between 44%~48%,concrete was showed better liquidity and adhesiveness;For C60 self-compacting concrete with P·O 52.5 cement,the total amount of cementing material should be controlled within540~560 kg/m~3,gelling material ratio of two coal fly ash and mineral powder,fine aggregate fineness modulus was in control of 2.7~3.0,the sand ratio should be controlled within 44%~48%.Concrete showed good working performance,the designed C50 and C60 concrete anti-freeze grade could reach above F200;The cracking area per unit area would be controlled within the range of 0.30mm~2/m~2;28d electric flux could be controlled within 800C;The 56d electric flux could be controlled within 500C Then the apparent quality defects of self-compacting fair-faced concrete precast members were studied,mainly studied the air content,vibration time,release agent,the influence of forming die apparent performance of concrete,test results showed that appropriate extension of the vibrating time(around 10 seconds),chose special water-based release agent,and the combination of the steel mold forming mode,could effectively reduce the concrete surface pores,the surface was more dense.Finally,the research results were applied to practical engineering,and the control points of concrete production and pouring process and the control points of precast members production process were put forward.As far as the engineering application effect was concerned,the high-strength self-compacting fair-faced concrete designed in this paper could meet the construction requirements in terms of concrete material quality and appearance quality,which had been unanimously praised by the construction unit and provided certain reference value for the construction and application of similar projects in the future.