Study On Preparation And Performance Of High Density Cement Board With Low Water-cement Ratio

After being printed on the surface,the cement board is used as a building decoration material,which can be used not only for the decoration of indoor walls,but also for indoor ceilings.Compared with calcium silicate board,the cement board has a simple preparation process,does not require high temperature steaming and consumes a lot of energy,and has good mechanical properties.Compared with gypsum board,it does not absorb moisture and deformation,has good durability,low cost,and more widely used.However,the preparation of cement board is still wet forming,the process is complex,and the mechanical properties of the board are poor,resulting in its use field is severely limited.In order to develop a widely used cement board with simple preparation process and excellent performance,based on the low water-cement ratio low-pressure molding process,the method of uniform mixing and microstructure control of only material composition under the condition of low water-cement ratio was proposed in this paper.The method is not only cheap and easy to get,but also simple in forming process and excellent in performance.Besides,organic polymer powder and recycled rubber particles are added to improve its toughness;slag and fly ash are added to reduce raw material costs;ultrafine quartz sand is added to prevent board cracking caused by dry shrinkage;finally,fiber is added to further improve its bending and bending properties.With the SEM,DSC,XRD,heat of hydration and other test methods,its composition,structure and performance were analyzed in depth.The main research conclusions are as follows:(1)The addition of organic polymer powder improved the flexural strength of cement board.Through the study of five different types of organic polymer powder,it is found that the addition of A2 powder could effectively improve the flexural strength.When the amount of powder was 2%,the flexural strength of cement board on 28 d reached 18.9MPa,which is 9.5% higher than that of the reference.In terms of board deflection performance,B3 powder has the greatest improvement on the deflection of cement board.When the content of B3 powder was 2%,the deflection of cement board curing 28 d was 30% higher than that of the reference.In addition,the incorporation of organic polymer powder also reduced the water absorption,porosity and dry density of cement board.When the content of A2 powder is 2%,the water absorption rate of the board decreases by 13%,the porosity decreases by 0.6% and the apparent density decreases by 1.8% when the cement board is curing for 28d(2)The XRD analysis of cement hydration products shows that the addition of organic polymer increase the production of Ca(OH)2.Through the test of hydration heat of cement mixed with organic polymer powder with low water-cement ratio,it is found that organic powder can reduce the hydration heat release rate of cement.(3)Although the incorporation of slag and fly ash reduces the flexural strength of cement board,but the flexural strength can reach 15.5MPa and 15.3MPa respectively when the content of slag and fly ash reaches 40%,which still has good mechanical properties.In addition,the incorporation of slag and fly ash reduces the apparent density of cement board and the weight of the board.The addition of ultrafine quartz sand reduce the cracking problem of cement board due to cement shrinkage in the late maintenance period,and the ultrafine quartz sand formed a certain particle size matching with cement particles,which increased the density of cement board.(4)Through the test of hydration heat,it is found that fly ash can reduce the hydration heat release rate of cement,and the hydration rate will decrease with the increase of the content.It can be seen from SEM diagram that fly ash does not participate in hydration reaction in the early stage of cement hydration,but in the late stage of hydration,it has a secondary hydration reaction with cement to produce hydration products.Mixed with slag in the process of hydration will appear obvious hydration exothermic peak in the second,and more obvious with the increase of dosage,When the content of slag is 40%,the exothermic rate of the second peak of hydration is almost the same as that of the first peak.In addition,compared with the cement hydration rate of W/C=0.3,the rate of the second peak of hydration with slag appears in advance.(5)The addition of recycled waste rubber particles is mainly to improve the flexibility of the cement board.By blending two different fineness rubber powders and testing their performance,it is found that when the 120 mesh rubber powder content is 2%,the cement board is cured until 28 d The flexural strength can reach 15.1MPa,the deflection is improved by 6.3% compared with the reference,and the flexibility of the cement board is significantly improved.In addition,the addition of rubber powder also reduces the apparent density of the cement board,reduces the weight of the board,and is more conducive to use as an indoor ceiling board.(6)The addition of polypropylene fiber greatly improved the flexural strength of cement board,but the flexural strength decreased after the high content,one of the main reasons is that the increase of fiber content leads to the difficulty of dispersion and agglomeration.When the polypropylene fiber content is 0.5%,the flexural strength reaches 20.5MPa,which is an increase of 16.6% compared with the blank group.When the copper plating steel fiber content reached 0.7% and the curing age is 3d,the deflection of the cement board increased by 49.2% compared with the reference,and when the curing age reaches 28 d,the deflection of the cement board increase by 51.9% compared with the reference.