Research On Structural Improvement Of Polycarboxylate Superplasticizers And Their Effects On Concrete

The high performance and long life of concrete structures are closely related to the national economy,environmental protection,and sustainable development.It is an important research topic in concrete science and a research hotspot in countries all over the world.Rheological properties can reflect the workability of concrete,and the pore structure and distribution can reflect the mechanical properties of concrete.Rheological properties,pore structure and distribution affect the durability of concrete and are important factors influencing the service of high performance concrete.Polycarboxylate superplasticizers can improve the mechanical properties of concrete and improve the durability of concrete,and gradually become the preferred admixture for the preparation of high performance concrete.Synthesis of polycarboxylate superplasticizers and the use of polycarboxylate superplasticizers to control the rheological properties,pore structure and distribution of concrete are problems that need to be solved in engineering practice in the field of high performance concrete.In this paper,the structural improvement of polycarboxylate superplasticizers and their effects on concrete are studied,and the relationship between the molecular structure of improved polycarboxylate superplasticizers and various properties of concrete is investigated.Firstly,the synthesis of the improved polycarboxylate superplasticizers were carried out,and the effects of different side chain densities,different main chain polymerization degrees,different side chain polymerization degrees,different ester functional groups,functional monomers,etc.on the performance of polycarboxylate superplasticizers are discussed.Successfully synthesized polycarboxylate superplasticizers with different molecular structures and properties;secondly,the resistance of polycarboxylate superplasticizers to montmorillonite in the aggregate and the influence on the rheological properties of cement mortar were studied.The law,the influence law on the hydration process and pore structure and distribution of cement-based materials,as well as the compatibility relationship with concrete materials,and the effect of polycarboxylate superplasticizers on the working performance,mechanical properties and durability of High Performance Concrete.The specific content is as follows:(1)A series of improved polycarboxylate superplasticizers were synthesized by the water-phase free radical polymerization method and ascorbic acid-hydrogen peroxide reduction initiation system,under the action of the chain transfer agent mercaptopropionic acid(MPA),and the structure and performance were studied.In the copolymer of isobutenyl polyglycol ether and acrylic acid,the molecular weight of polycarboxylate superplasticizers tend to gradually increase as the density of the side link branches gradually decreases.For isobutenyl polyglycol ether HPEG2400 and acrylic acid AA synthetic polycarboxylic acid water reducer,when the side link density is 25%,the main chain polymerization degree is11.56,16.88,24.74,and the weight average molecular weight is 30600-65500,the dispersion performance of polycarboxylate superplasticizers are better.Polycarboxylate superplasticizer PC-J with good dispersibility was synthesized by HPEG2400 and AA.The synthesis process parameters are the density of side link branches is 25%,n(MPA): n(HPEG2400)=0.1,HP accounts for 1.0% of the mass of percentage of HPEG2400,and ascorbic acid(VC)accounts for 25% of the mass percentage of HP;Polycarboxylate superplasticizer PC-H with good dispersion retention is synthesized by introducing the ester-containing functional group monomer HEA.The synthesis process parameters are n(AA): n(HEA): n(MPA):n(HPEG2400)=1.6:2.4:0.1:1,HP accounts for 1.0% of the mass of percentage of HPEG2400,and VC accounts for 25% of hydrogen peroxide(HP)mass percentage;The polycarboxylate water-reducing agent PC-Z with good early-strength performance was synthesized by introducing the ultra-long side chain monomer isobutenyl polyglycol ether(HPEG4000).The synthesis process parameters are the density of side chain branches is 25%,n(MPA): n(HPEG4000)=0.1,HP accounts for 1.0% of the mass of percentage of HPEG4000,and VC accounts for 25% of the mass percentage of HP.When the cationic monomer acryloyloxyethyl trimethyl ammonium chloride(DAC)is introduced,the synthesized polycarboxylate superplasticizers have excellent montmorillonite resistance and dispersion retention.The analysis results of infrared spectroscopy,proton nuclear magnetic resonance spectroscopy,DSC,GPC,etc.indicate the functional group structure and polymer structure characteristics of the polycarboxylate superplasticizers.(2)Using the rheological research method,the influence law on the structure of the improved polycarboxylate superplasticizers and the rheological properties of cement mortar,including the fluidity of cement mortar and the rheological parameters of cement mortar,were analyzed,and Bingham model was fitted with relevant regularity.Under the same conditions of water consumption and rotation speed,the initial state of the shear stress of each group of water reducing agents corresponding to cement mortar is NF>PC-J>PC-H>PC-Z;the order of the shear stress of the corresponding cement mortar with each group of water reducing agents at 100 min is NF>PC-Z>PC-J>PC-H.The introduction of ester functional group polycarboxylate superplasticizer improves the rheological properties of cement mortar after time and reduces the shear stress of cement mortar;the introduction of ultra-long side chain polycarboxylate superplasticizer makes the rheological properties of the cement mortar after time become worse,and the shear stress of the cement mortar is increased;the order of the effect of each group of water reducing agents on the delay of the cement hydration process is PC-H>PC-J>PC-Z>NF>blank.The shorter side chain and ester functional groups of PC-H can slow down the hydration rate of cement,but have little effect on the later hydration of cement;the ultra-long side chain of PC-Z can be beneficial to the formation of dense cement stone structure,PC-Z makes the pore structure and pore size distribution of hardened concrete smaller,and can significantly improve the mechanical properties of cement-based materials.(3)The structure and application performance of the improved polycarboxylate superplasticizers have been adjusted and studied,including the compatibility of polycarboxylate superplasticizers and concrete materials,and the performance and mechanical properties of polycarboxylate superplasticizers for high performance concrete.The influence of polycarboxylate superplasticizers on the micro-pore structure of machine-made sand concrete and river sand concrete,and the effect of polycarboxylate superplasticizers on the impact of durability and durability.The results show that the selected PC-J has the characteristics of good compatibility,low content,high water reduction rate,and low slump loss of the formulated concrete.The formulated C80 self-compacting high-performance pumping concrete has low viscosity,high strength,self-compacting,high durability and other characteristics;the optimized PC-Z prepared Dalian Metro C50 segment concrete has a 1d compressive strength of 30.2 MPa;and the combination of polycarboxylate superplasticizers PC-J and PC-H can significantly improve the external compatibility of the agent with river sand and machine-made sand,and the porosity of machine-made sand concrete decreases with the increase of sand ratio,and the harmless pore size is much better than that of river sand concrete.Through the synthesis and performance research of the improved polycarboxylate superplasticizers,as well as the subsequent industrialized scale-up production and mixing ratio adjustment test,it is shown that the structure of the improved polycarboxylate superplasticizers are closely related to the various properties of concrete.The structural parameters of polycarboxylate superplasticizers can well control the various properties of high performance concrete.It also shows that the research system is effective and provides new ideas and methods for the basic research on the application of high performance concrete additives.