Study On Performance Optimization Of Polycarboxylate Superplasticizer And Compatibility Between Polycarboxylate Superplasticizer And Cementitious Materials System

Compatibility of water reducing agent with cement or composite cementitious material in the field of cement and concrete has gained widely attention.Compatibility has important effects on working performance of fresh concrete and the mechanical properties of concrete in the later stage.In order to improve the compatibility of polycarboxylic water reducing agent with cement-based cementitious materials,the preparation of polycarboxylic water reducing agent was optimized and the compatibility the polycarboxylic and its separate liquid(obtained by membrane separation)with different cement-based cementitious materials was systematically studied.On the basis of this,the total organic carbon absorption(TOC),X-ray photoelectron spectroscopy(XPS),environmental scanning electron microscope(ESEM),thermal analysis(DSC/TG)and resistivity etc.were employed to study the adsorption morphology,adsorption fractionation behavior of the self-made polycarboxylic water reducing agent(PC0)and its separated components on the surface of the cement particles and its influence on the initial hydration process of cement paste have been studied.Moreover,the effect of molecular weight on the compatibility of polycarboxylic water reducing agent with cement has been studied theoretically.Polycarboxylic water reducing agent is a polymer copolymer with comb structure.Previous research was characterized by the average molecular weight,ignoring the influence of the distribution characteristics of the molecular weight.In this paper,the polycarboxylic water reducing agent is accurately separated by ultrafiltration membrane separation method with different molecular weight intervals,and the adsorption and dispersion properties of the separated components is studied in the range of different molecular weight,and the hierarchical adsorption behavior of polycarboxylic water reducing agent by molecular weight and molecular structure has been revealed.It points out the clear direction for development of polycarboxylic water reducing agent with the better performance and compatibility and lays the foundation for the fine research of this kind of water reducing agent.The results show that:(1)By the orthogonal test,the introduction of a variety of adsorption functional groups and optimization of synthesis process can optimize the molecular weight distribution index of the synthesized polymer and improve the performance of the polycarboxylic water reducing agent.Compared with the existing products in the market,the water reducing rate is enhanced and the compatibility with cement is better.The specific synthesis process is as follows:polyoxypropylene ether(XPEG)is added first,acrylic acid(AA)is added at one time,methacrylic acid(MAA),initiator ammonium persulfate(APS),chain transfer agent sodium methane sulfonate(SMAS)are added dropwise.The best dropping time of MAA is 180 min.The reaction temperature should be 55~65?C.The experimental ratio of the synthetic is macromonomer selects 2400 molecular weight,200g,m(MAA)=10g,m(AA)=9g,m(APS)=0.8g,m(SMAS)=1g.The molecular weight of polycarboxylic water reducing agent sample was measured by the multi angle laser scattering instrument.The weight-average molar mass is 107900 Da,and the molecular weight distribution index(M_w/M_n)was 2.085.Through the infrared spectrum test,it is indicated that the monomers are effectively polymerized,in which the polymerization between XPEG,MAA and AA is an irregular copolymerization.(2)Polycarboxylic water reducing agent(PC0)was prepared by the optimized process,after ultrafiltration cup membrane separation according to the molecular weight range for more than 100 k(F1),50 k to 100 k(F2),10 k~50 k(F3),under 10 k(F4),the weight-average molar mass of the F1,F2,F3 and F4 are 215700Da?79160 Da?28570 Da?3751 Da.By analyzing the initial fluidity of the three cement pastes,the compatibility of polycarboxylic water reducing agent and its separation components with the same kind of cement is:F2>F1>PC0>F3>F4.When the molecular weight of the polycarboxylic water reducing agent ranges from 79160 to 215700 Da,the compatibility with different cements is better.When the molecular weight is below79160 Da,the compatibility becomes worse.The small molecular weight component of polycarboxylic water reducing agent is the main cause of its poor compatibility.(3)By comparing the compatibility of the polycarboxylic water reducing agent/its separate components with different composite cementitious material paste,the following results have been obtained.In composite system of fly ash or mineral powder or silica fume with cement,F2 with moderate molecular weight has good compatibility with cementitious material.The components with larger molecular weight or smaller molecular weight can deteriorate the compatibility of water reducing agent and cementitious material system to some extent.(4)The self-made polycarboxylic water reducing agent PC0 molecule is curled up on the surface of the particles rather than linear.Moreover,the degree of curl gradually increases with the increase of dosage.The adsorption of PC0 on the surface of cement particles is gradually graded adsorption and the component with smaller molecular weight is more easily adsorbed on the surface of the cement particles,then the molecules with larger molecular weight is adsorbed.The introduction of PC0 delays the dissolution of cement minerals,and the trend of the delay is more obvious with the increase of the content of PC0.According to DCS/TG analysis,it is shown that the addition of PC0 has no effect on the type of cement hydration products,but reduces the amount of the hydration products.By the XRD analysis of cement samples,it is concluded that the addition of PC0 to cement paste does not produce new phases but delays the formation of ettringite(AFt)in early hydrating age.From the XPS analysis of cement samples,it is found that the relatively high carbon content on the surface of cement particles results from the adsorption of PC0.With the development of hydration process,the PC0 molecules on the surface of particles are consumed and are same as the blank samples until 28d.The ESEM analysis of cement samples shows that PC0 has a good dispersing effect on the flocculation structure in cement paste and can open the flocculation structure with larger volume and release the flocculation water to increase the fluidity of the slurry.In this paper,the compatibility and its mechanism of the polycarboxylic water reducing agent and its separate component with the cement-based cementitious material has been studied.The macroscopic properties and microstructure are combined to provides a theoretical basis for the development and application of the polycarboxylic water reducing agent with high compatibility.It is helpful to guide the synthesis of novel polycarboxylic water reducing agent and the choice of cementitious material,and promote the development of high performance concrete and other special concrete technologies.