Study On Plant Fiber Reinforced Cement-based Composites

The rapid development of the construction industry has also brought a series of influences on resources and environment.It is necessary for the construction industry to develop and use the green building materials with a sustainable development.The plant fiber has some characteristics,such as rich resources,reproduction,recycle,low price and so on,so it has a huge potential to replace the synthetic fiber reinforced cement-based composites.Therefore,the use of plant fiber reinforced cement-based composites has attracted more attention for research.However,there are still many problems for the plant fiber reinforced cement-based composites to be solved,such as poor adhesion between plant fiber and cement matrix,poor mechanical properties of composites,etc.At present,the researchers produce the plant nanocellulose to replace the plant fiber so as to improve the properties of cement-based composites.This paper takes plant nanocellulose and plant fiber cement-based composites as the research object,studies the influence of plant fiber and plant nanocellulose on the properties of cement-based composites,and analyzes their mechanisms by fiber pretreatment,composites preparation,composites strength test,accelerated aging damage test of composites.(1)Wheat straw fiber cement-based composite is taken as the research object.Two different pretreatments are conducted on wheat straw,and the straw fiber is added into the cement-based composite with the content of 5-20% before and after pretreatment.The mass loss rate and water absorption rate of straw fibers before and after pretreatment as well as the mechanical properties and water absorption rate of composites are studied.The results show that the pretreatment could remove some substance in the straw fibers,and the straw fiber treated by 4% sodium hydroxide solution has the maximum straw loss rate of 36.15% and water absorption rate of 1.67%.In addition,the mechanical properties of the straw fiber composites pretreated by this method are higher than those of the untreated straw fiber composites and the straw fiber composites treated by cold water with the same addition.The straw fiber composites treated by 5% sodium hydroxide solution has the best compressive strength of 9.77 MPa,flexural strength of 2.62 MPa,and the lowest water absorption rate of 9.32%.The results show that the pretreatment could effectively remove the waxy layer on the surface of the straw fiber,and the precipitation can affect the hydration of cement,which benefits the the bonding between the fiber and the cement matrix.At the same time,it is found that the toughness of the composites increases after adding straw fiber,but the mechanical properties decrease to a certain extent,which can be improved by this pretreatment.(2)Nanocellulose cement-based composites are taken as the research object.By dispersing the nanocellulose with different ways,nanocellulose with a content of 0.025-0.3% is added into the cement-based composites to study the mechanical properties and durability of the composites.The results show that the high-speed homogenizer can effectively disperse the nanocellulose.Nanocellulose obviously reduces the fluidity of cement mortar.Moreover,a small amount of nanocellulose can enhance the mechanical properties of composites,but excessive nanocellulose would result in the agglomeration,which would adversely affect the mechanical properties of composites.The compressive strength enhancement of nanocellulose composites with a content of 0.075% is the best,and the compressive strength is 38.86 MPa,increasing by 28.17%.Nanocellulose shows the most obvious increase in the flexural strength of the composites,and the best effect is achieved by adding 0.1 % of nanocellulose.The flexural strength is 9.17 MPa,increasing by 55.69%.However,nanocellulose does not improve the durability of the composites.(3)The mechanism of nanocellulose in cement-based composites is studied.Most of the nanocellulose in cement mortar is adsorbed on the surface of cement particles and a few of them is in free state.Nanocellulose has a high specific surface area,and the surface is rich in carboxyl groups,so it can easily adsorb the cement particles and water molecules,reduce the fluidity of cement mortar and delay the early hydration of cement.Simultaneously,it can also strengthen the adsorption and bonding effect of cement hydration products and enhance the mechanical strength of the materials on the macro level.To sum up,straw fiber can improve the toughness and reduce the quality of the composite,but it can not enhance the mechanical properties of the composite.However,the nanocellulose nanomaterials can significantly improve the compressive strength,flexural strength and water absorption of cement-based composites as well as can reduce the fluidity of cement mortar and delay the early hydration of cement.In the future,both forms of plant fiber materials have great potential in the field of building materials,and they can play an important role in practical engineering by rational utilization.