Study On The Effect Of Nanosilica On The Properties Of Cementious Grouts For Sleeve Of Rebar Splicing

The prefabricated building trend has been one of China’s construction industry’s growth avenues and will continue to be a significant trend in the coming years.A growing number of issues,including the node problem,have emerged with the growth of prefabricated buildings,nevertheless.A typical node connecting technique was sleeve grouting connection.The integrity and stability of prefabricated building structures are directly impacted by cementious grouts used for sleeve of rebar splicing（referred to as grouts）.However,there were numerous downsides,including poor durability in the uneven grouts,low early strength,and slow grouth of long-term strength.A portion of the cement was replaced with fly ash（FA）and ground granulated blast-furnace slag（GGBS）,and nanosilica（NS）was used to enhance the properties of grouts.This dissertation used the experimental method of control variables to investigate the effects of water-binder ratio,binder-sand ratio,mineral admixture con ent,and admixture content on the properties of grouts starting from various compositions of grouts.Silane coupling agent and polycarboxylate superplasticizer（PCE）were used to modify the surface of NS.On the fuidity,compressive strength,salt erosion and freeze-thaw resistance of grouts,the effects of modified NS（NS-KH-PCE）were investigated.The hydration products and microstructure of grouts were examined by using XRD,SEM,and TG.The following are the dissertation’s conclusions:（1）The basic mix ratio of the grouts was produced after determining the quantity of each grout component using the control variable method:The optimum water-binder ratio and binder-sand ratio were both set at 1.0.FA and GGBS were given a content of 10%,whereas PCE,defoamer,and plastic expansion agent had optimal contents of 0.5%,0.1%,and 0.05%,respectively.（2）The fluidity of grouts could be slightly improved by adding a little content of NS（0.2%）,but the impact on the growth of compressive strength was little by mixing less NS.The fluidity and compressive strength of grouts were reduced,though,if too much NS was added.Compressive strength was improved by mixed NS for 1d but reduced for 3d.The effect of NS on compressive strength was negligible after 28d.By working together,NS and PCE were able to increase the compressive strength for 3d while attenuating the detrimental effects of NS on grout fluidity to some extent.However,there was little of an impact on the compressive strength for 28d.（3）The hydrophilic group of NS was changed by chemical modification and the PCE with Steric effects was grafted onto the surface of NS Chemical modification could greatly reduce the agglomeration and water consumption of NS,while simultaneously enhancing the fluidity and compressive strength of grouts.The NS-KH-PCE content that worked best was 0.8%.The grout’s initial fluidity and fluidity after 30 minutes were,respectively,335mm and 320mm under this content.Compressive strengths for 1d,3d,and 28d were 43.3 MPa,78.3 MPa,and 115.8 MPa,respectively.These values were greater than those of the reference group by 12.8%,14.3%,and 10.1%.The effects of NS-KH-PCE were more pronounced,and the integration of NS improved the salt erosion and freeze-thaw resistance of grouts.（4）According to XRD examination,the main components of the hydration product of grouts were Ca（OH）₂,ettringite,and unhydrated C₂S and C₃S.Additional C-S-H gel was produced,as shown by TG,as a result of NS-KH-PCE reaction with the Ca（OH）₂ in Portland cement’s hydration product.When compared to the reference group,the sample for 1d revealed a 7.5%increase in Ca（OH）₂ consumption,while the sample for 28d showed a 25%increase.By using SEM for observation,the addition of NS-KH-PCE increased the densification of the grouts’ microstructure.Because of the chemical modification of NS,the grouts exhibited better microstructure,greater fluidity,and better compressive strength.