Effects Of Different Scales Cellulose Fibers On The Microstructure And Hydration Characteristics Of Cement Paste

In the process of micro structure formation,the cement paste causes uneven internal force due to the differences in the performance of the various groups of water and the resulting primary defects is the root cause of the deterioration and durability.The use of fiber to modify cement-based composite materials is an effective means to improve its comprehensive performance.The cellulose fiber has the advantages of high aspect ratio,high specific strength,high specific surface area,high tensile strength,strong adhesion and low cost,so that it has prominent advantages in the micro structure induction and toughening modification.In this paper,cellulose fibers were treated with H₂SO₄ acid solution to prepare cellulose fibers with sub-micro and nanometer scale and the samples were characterized by IR,SEM and particle size analysis.The results show that the characteristic functional groups and molecular structure of the cellulose fibers does not change and the scale decreases gradually after acid hydrolysis.That is,the natural cellulose fiber is gradually stripped under the effect of acid solution to become a fiber with diameters ranging from tens of microns to hundreds of nanometers.Its diameter decreases with the increase of the concentration of H₂SO₄ solution and the extension of reaction time.Cellulose fibers with different sizes were introduced into the cement paste and the influence of cellulose fiber size on the microstructure of the paste was studied by SEM.The results show that cellulose fiber make the cement hydration product C-S-H gel and adhere to its surface by the hydrophilicity and super absorbency of cellulose fibers.At the early stage of hydration,the macro scale cellulose fibers swell due to water absorption and dry shrinkage,the void phenomenon occurred later after the release of water,reducing the density of muddy mud,thus affecting the volume stability of cement-based composite materials.The micro-nano cellulose fibers were matched with the cement hydration products C-S-H gel scale,the nucleation of the crystal induced hydration products along the fiber direction of the growth in the early stage and promote the hydration of cement in a certain extent.With the continuousgrowth of hydration products on the surface of the fiber,the fibers are gradually embedded.IR,TG-DSC,hydration heat,NMR,XRD and other testing techniques were used to study the effects of cellulose fibers on the hydration characteristics of cement.The results show that the initial cellulose fiber will absorb moisture and reduce the actual water cement slurry ratio.its hydration exothermic rate is low and its early heat release is low.In the later stage,the water consumption of cement paste is gradually consumed,the moisture absorbed by cellulose fibers is released under the action of humidity gradient and capillary pressure and ensure the continuous hydration of the cement particles.Therefore,the total heat release rate is similar to that of pure cement and the cellulose fiber is not involved in the hydration reaction of cement,but the regulation of micro scale fiber is helpful to improve the C-S-H gel polymerization degree.In this paper,the macro mechanical properties of cellulose fiber cement matrix composites were studied.The results show that cellulose fiber of small size can obviously improve the flexural strength of cement matrix composites and inhibit the shrinkage of cement paste.