Synergism Between Lignin And Polycarboxylate And Synthesis Of Lignin Grafting Polycarboxylate Water Reducer

Polycarboxylate(PCE)has the advantages of low dosage and high water-reducing rate,which can significantly improve the working performance,mechanical properties and durability in architectural engineering.However,due to compatibility problems with other admixtures,problems such as bleeding and segregation often arised in applications.Besides,with the emergence of high-performance concrete,PCE is also in urgent need of further improvement.As the first generation of water reducing agent,lignin has good biocompatibility and is often used as a compound product in the field of admixtures.In order to solve the problem of water segregation of polycarboxylate,and to improve the dispersion of lignin superplasticizer,the synergistic effect and molecular structure design of polycarboxylate and lignin were studied respectively,to seek the optimization of the two superplasticizers.The main research methods and conclusions are as follows:(1)To solve the compatibility problems between polycarboxylate and kraft lignin,lignosulfonate,compound water reducer KPC and LPC series were prepared by different proportion of lignin and lignosulfonate respectively.The dispersion performance of KPC and LPC was evaluated by slump test,setting time,rheological test and microstructure analysis testing.The results showed that in KPC series,with the increase of KL mass fraction,the intial slurry fluidity and concrete fluidity decrease.For LPC series,LPC10 showed synergistic effect of the two types of superplasticizers,which not only had good initial fluidity,but also had small slurry-loss,and could improve the phenomenon of bleeding segregation,with the best comprehensive effect.XPS showed that the addition of KL would reduce the thickness of the adsorption layer,while the addition of LS would increase the thickness of the adsorption layer.LPC10 had the largest thickness of the adsorption layer,which was 4.59 nm.The results of cement setting time,XRD showed that the addition of KL and LS could affect the hydration effect of cement.(2)Lignin unsaturated ester(ACL)was prepared by reacting KL with acryloyl chloride(AC).Then lignin grafting polycarboxylate superplasticizer(PCE-ACLs)were synthesized by using ACL as part of the large monomer.The dispersion performance of PCE-ACLs was evaluated by slump test and rheological test et al.PCE-ACL1 had a good dispersion effect,its fluidity could be 283 mm when the dosage was 0.2%,and the net slurry outflow time of PCE-ACL1 was 13.9s,which had a good viscosity reduction effect.The concrete has an initial slump of 225 mm,an initial extension of 490 mm and a 28-day compressive strength of 43.8MPa,with the best comprehensive effect.The results showed that PCE-ACLs had better surface activity.The adsorption of PCE-ACLs on cement particles could be described as Langmuir model and pseudo-second-order model.The adsorption layer thickness of PCE-ACL1 on cement particles was 3.75 nm,slightly higher than that of PCE,indicating that PCE-ACL1 had good steric hindrance.