Research On Precast Fair-faced Concrete Wall Panels And Precast Decorative Concrete Sandwich Wall Panels

With the development of prefabricated buildings in full swing in China,a large number of wall panels,stairs and other parts and components are transferred to the factory workshop of prefabricated components.The application of fair-faced concrete technology to the production of precast concrete components can improve the appearance quality and market competitiveness of precast concrete products.When producing precast concrete elements in indoor workshops,it can effectively control and improve the concrete construction level to provide effective protection for fair-faced concrete technology.The prefabricated wall panels of fair-faced concrete reduce the decorative works of the external walls of the building and conform to the development trend of energy conservation and environmental protection.However,the finished product rate of precast concrete wall panels is still low,so it is extremely necessary to study the technology of fair-faced concrete.In this paper,experimental research on the prefabricated wall panel of fair-faced concrete and its related materials is carried out.Firstly,experimental research of ordinary fair-faced concrete wall panels is carried out.The mix ratio test of C40 fair-faced concrete for non-winter conditions(15-35℃)is carried out.Through controlling variables,the effects of water-binder ratio,amount of cementing material,sand rate and mineral admixture on the appearance quality of fair-faced water concrete are studied.The suitable mix ratio of fair-faced concrete whose appearance quality is better than the current standard is:water:cement:slag:sand:gravel:polycarboxylic water reducer=174.8 kg:305.9 kg:131.1 kg:700.0 kg:1050.0 kg:3.5 kg.The compressive strength at the third day is 23.3 MPa,and the compressive strength at the twenty-eighth day is45.9 MPa.The total area of the pores on the surface of the wall panels is only 6.1 cm~2/m~2.The maximum pore diameter is 2.9 mm.The mix ratio of C40 fresh water concrete for winter conditions(5-15℃)is adjusted on the basis of non-winter mix ratio.The mix ratio of fair-faced concrete is:water:cement:slag:sand:gravel:polycarboxylic water reducer=174.8kg:368.0 kg:92.0 kg:647.5 kg:1102.5 kg:3.9 kg.The compressive strength at the third day is 22.1 MPa,and the compressive strength at the twenty-eighth day is 46.3 MPa.The total area of pores on the surface of the fair-faced concrete wall panels is 8.2 cm~2/m~2.The maximum pore diameter is 3.7 mm.In terms of the construction technology of ordinary fair-faced concrete,it is concluded that the steel formwork should be selected as the formwork for the production of ordinary fair-faced concrete prefabricated components in the precast concrete elements workshop,and that the mold should be designed as a smooth chamfered structure at the edge of the concrete edge.Among the five release agents,ASL release agent has the best effect.Integral vibrating is the best vibrating method for the production of fair-faced concrete wall panels.Secondly,the experimental research on the tile pattern decorative concrete and its sandwich wall panel is carried out.The results of the ceramic tile decorative concrete molding and its appearance quality analysis test show that the silicone mold is suitable for molding surface-textured decorative concrete.Before using,the silicone mold should be immersed in water,and a machine oil with high viscosity should be used as the mold release agent.After thermal calculation of sandwich wall panels,when the thickness of the outer leaf wallboard is60 mm and the thickness of the inner leaf wallboard is 200 mm,the thickness of 30 mm extruded polystyrene board or the thickness of 40 mm foamed concrete board is used as the middle insulation layer.Its thermal performance meets the local standards of Jiangsu Province.The tile decorative sandwich wall panel can realize the self-insulation and the integrated effect of decoration and insulation.According to the preparation test of the precast decorative sandwich wall panels,the production process route is summarized,and the construction technical points are analyzed.Thirdly,the experimental study of mold release agent for fair-faced concrete is conducted.The emulsification of palm oil is carried out by reverse emulsification technology.The best emulsifier HLB value of 40 wt.%palm oil emulsion is about 9.In order to improve the stability of the emulsion,select the commonly used emulsifier Span 40(SP40),Span 80(SP80),Tween 40(TU40),Tween 80(TU80),alkylphenol polyoxyethylene Ether(OP-10)and sodium dodecylbenzene sulfonate(SDBS)for mixed emulsifier study.The optimal mixing emulsifier ratio is SP80:OP10:SDBS=0.38:0.20:0.42.The formula of self-made palm oil-based release agent is:m(palm oil):m(SP80):m(OP10):m(SDBS):m(xanthan gum):m(triethanolamine):m(water)=1:0.0475:0.025:0.0525:0.005:0.005:1.375.The raw material cost of the release agent is 3.824 yuan/kg.According to the mold release performance test,when the dilution ratio of the mold release agent with water is 1:3,the adhesion of concrete on the steel mold is only 1.0 g/m~2,which meets the requirement of fair-faced concrete.When the dilution ratio is 1:5,the adhesion of concrete is 4.9 g/m~2,which meets the requirements of the ordinary concrete.Finally,in order to meet the demand for repairing precast concrete components,an experimental study on repairing mortar of fair-faced concrete is carried out.Through orthogonal test,the optimal repair mortar formulation is:m(cement):m(sand):m(water):m(rubber powder):m(cellulose ether):m(starch ether):m(water reducing agent)=1:1.4:0.35:0.02:0.001:0.0003:0.0025.The bond tensile strength at the fourteenth day is 2.48MPa.The interface bending strength at the 28th day is 2.98MPa.The compressive strength at the 28th day is 43.4MPa.The flexural strength at the 28th day is 11.2MPa.The ratio of the compressive strength and the flexural strength is 3.9.The fluidity is 142 mm.The shrinkage rate is 0.041%.Adjust the color of the repair mortar by mixing with titanium dioxide to be consistent with the color of the surface of the clean concrete to be repaired.The repair mortar can be mixed with titanium dioxide in the range of 0-4 wt.%,all performance of which meet the requirements of industry standards.