Study On Synthesis And Performance Of Low Surface Tension Polycarboxylate Superplasticizer

In modern concrete,chemical admixtures are an important component.In particular,the application of polycarboxylate superplasticizer has made a qualitative leap in the quality of concrete,which has greatly promoted the development of modern architecture.However,the low water-binder ratio is commonly used in modern concrete,which makes the problem of concrete drying shrinkage and auto-shrinkage increasingly serious.At present,various measures are used to improve and solve the problem of early shrinkage and cracking of concrete,but the effect is still not satisfactory.Since the advent of polycarboxylate superplasticizer,it has become a new generation of high-efficiency water-reducing agent that has attracted much attention.It has the advantages of high water-reducing rate,environmental protection,and functional designability.It has been widely used in various projects.At present,many scholars use the designability of the molecular structure of polycarboxylate superplasticizer to synthesize various functional polycarboxylate superplasticizers,which can achieve high water-reduction rates while improving other properties of concrete.In this paper,based on the molecular design of polycarboxylate superplasticizer and the concrete drying shrinkage mechanism,a low surface tension polycarboxylate superplasticizer SRPCE was synthesized.Firstly,a low surface tension monomer MD with polymerization activity is synthesized through esterification reaction.The best esterification conditions are determined by measuring the esterification rate: the acid-to-alcohol ratio is3:1,the reaction temperature is 130℃,and the reaction The time is 4.5h and the amount of catalyst is 4%.Then MD,methallyl polyoxyethylene ether,acrylic acid and other monomers are polymerized to synthesize a low surface tension type polycarboxylate superplasticizer.In the polymerization reaction,through controlled variables and single factor analysis,the optimal polymerization conditions were determined as follows: the reaction temperature is40℃,the dropping time is 3h,the holding time is 2h,the reactant concentration is 40%,and the amount of APS is 3% of the monomer mass,n(AA): n(TPEG): n(MD)= 20:5:4.Infrared spectrometer(IR)and gel chromatography(GPC)were used to characterize the molecular structure and molecular weight of the low surface tension polycarboxylate superplasticizer.The results showed that there were expected functional groups in the product,indicating that the low surface tension monomer was successfully grafted onto the polycarboxylate superplasticizer.GPC showed that the molecular weight was about 20,000.The application performance of self-made low surface tension polycarboxylate superplasticizer(SRPCE),shrinkage reducer(SRA)and ordinary polycarboxylate superplasticizer(PCE)were compared.The fluidity of the pure slurry of SRPCE and PCE is almost the same,and the fluidity loss of SRPCE is smaller,and it has good fluidity retention.The 28 d shrinkage rate of the mortar mixed with SRPCE is 28.6%,which has a good shrinkage reduction effect.SRPCE has good adaptability to concrete,has good working performance,and has no adverse effect on the strength of mortar and concrete.Adding SRPCE can reduce the pore volume with a pore diameter of 2.5-50 nm,reduce the number of less harmful pores and harmful pores,optimize the pore structure of cement,and play a significant role in reducing dry shrinkage.The mechanism of the low surface tension type polycarboxylate superplasticizer was analyzed from the surface tension of the solution,the Zeta potential,the adsorption capacity,the evaporation rate and the hydration of the cement.The results show that the polycarboxylate superplasticizer grafted with MD monomer can significantly reduce the surface tension of the solution.When the concentration is 2.0%,the surface tension of water can be reduced from 72.1 m N/m to 35.6 m N/m,and the surface Tension stability is maintained well;PCE and SRPCE both reduce the Zeta potential,and the change trend is consistent with the change trend of fluidity and adsorption capacity;the addition of PCE and SRPCE reduces the evaporation rate of the solution and slows down the evaporation of water,to a certain extent It has the effect of shrinking;it has no special influence on the hydration products and morphology of cement.