Preparation And Properties Of Hydrophobic Autoclaved Microporous Silicate Materials

Autoclaved aerated concrete（AAC）is a kind of microporous silicate material,which has the characteristics of light weight,heat insulation,sound-absorbing/sound-insulating,fireproof and non-combustible,etc.,and is widely used in the energy conservation and heat preservation of modern buildings.However,due to the high porosity of autoclaved aerated concrete,it is easy to absorb water,which will lead to the decrease of strength and thermal insulation performance,thus seriously affecting its service performance.Therefore,the problem of water absorption of autoclaved aerated concrete urgently needs to be solved.In this paper,the ceramic waste residue powder is used as the main raw material to prepare the B03 grade(dry bulk density less than 325 kg·m^-3)hydrophobic type autoclaved aerated concrete microporous silicate material.examines the AAC influence factors of water imbibition,studied by matrix structure optimization and chemical modification method and the process parameters to reduce water imbibition,hate agent on the influence law of the preparation and properties of AAC,received the sample of the waterproof effect is good and performance characterization and evaluation was carried out.The porosity of grade B03 AAC is as high as 86%,and the mass water absorption rate is usually more than 180%(according to the dry density of 325 kg·m^-3,the theoretical water absorption rate is 268%).Good porosity structure can reduce the through-hole ratio,reduce the water absorption of AAC,and improve the mechanical strength and thermal insulation performance.By optimizing the basic formula of AAC,the effects of water-to-material ratio and the amount of air-entraining agent（aluminum powder）on water absorption were discussed.The results show that reducing the water-to-feed ratio is beneficial to the decrease of water absorption,but it will increase the dry density;increase the amount of air-entraining agent,the dry density of AAC sample will be reduced from 324.3 kg·m^-3 to 292.1 kg·m^-3,but the resistance The compressive strength decreases accordingly,the lowest is 0.89 MPa,which is lower than the national standard qualified product strength,and the water absorption rate also increases,from 117.32%to 148.56%.The B03 grade AAC sample prepared by using water ratio of 0.81 and air-entraining agent 0.18%has a water absorption rate of about120%,which is more than 60%lower than the usual water absorption rate.It can be seen that the water absorption rate can be reduced to some extent by structural optimization.Chemical modification is to change the water absorption of AAC by a water repellent,from hydrophilic to hydrophobic,to achieve waterproofing.On the basis of the optimization of the matrix structure,two modification methods of water-repellent and surface coating waterproofing were discussed.By investigating the effect of water-repellent agent on the aluminum powder paste,the thickening of the slurry and the pre-evaporation,the saturated water absorption of the sample and the surface water-repellent sample were tested.It was found that the silane is suitable for internal mixing and waterproofing;the infiltrated crystalline waterproof emulsion for surface waterproofing;the aqueous zinc stearate emulsion can reduce the pore size of AAC and is advantageous for compressive strength.When the amount of silane added was 0.25%,the water absorption of the sample is 93.44%,which is nearly 90%lower than that of the unmodified sample.The compressive strength of the sample is 1.24 MPa,and the thermal conductivity is only 0.062 W·（m·K）^-1.The comprehensive performance is better than that of the B03 national standard.Aiming at the surface waterproofing,the waterproofing effects of silane powder,zinc stearate powder and osmotic crystallization emulsion were studied by immersion method,and the osmotic crystallization emulsion was selected as the research object.Then,the effects of impregnation and spraying on surface waterproofing were studied.The results show that the waterproofing effect of dip treatment is better than spray treatment.The spray method requires a higher concentration of permeable crystallization emulsion.When the concentration of emulsion is 30%,the water absorption rate of the sample is 18.02%.The water absorption rate of the impregnation sample was 16.14%when the concentration of emulsion was 15%.With the crystallization of the emulsion infiltrated into the body,the water resistance was further improved,and the water absorption rate of the sample after 12months was only 4.64%.In conclusion,although the structural optimization can reduce the water absorption to a certain extent,the effect is not obvious,and the chemical modification method is preferable.Water-repellent agent is waterproof and surface-coated with water,which can reduce its water absorption,and each has certain advantages.In comparison,the surface waterproofing process is relatively simple,and has little effect on the mechanical and physical properties of AAC,but the surface waterproof layer loses its waterproof effect once it is destroyed,so it is suitable for conditions that are not easily caused by physical damage;Although the internal blending method is less durable,the durability and overall performance of the waterproofing are more advantageous,and the conditions of use thereof are broader.The internal mixing and waterproofing can make the water repellent evenly distributed in the material body,which is beneficial to lasting waterproofing,and will be the main development trend in the future.