Preparation Of Phosphorus-Containing Polycarboxylate Superplasticizer And Its Application In Inorganic Cementitious Materials

Superplasticizer is a polymeric admixture used in cementitious systems,which can enhance the properties of concrete such as workability,mechanical performance and durability significiantly.At present,superplasticizer has become an essential component of concrete.With the rapid development of modern construction industry,natural gravel and river sand have exhausted already and they would be replaced by manufactured gravel and sand containing high amount of clay.Because of the stronger affinity of PCE to clay than to cement,the amount of PCE sorbed on cement particle significantly decreases,leading to the worse cement dispersing efficiency of PCE.Meanwhile,sulfate in cement would affect the compaticity between PCE and cement because of their competitive adsorption.Moreover,as another important cementitious material,calcium sulphate hemihydrate（HH）hardens rapidly when mixing with water,which leads to the workability of gypsum paste difficult to control.In order to get good fluidity of gypsum plaster,more water would be added to HH,resulting in a high porous structure of hardened paste and poor mechanical properties.At present,there is no a PCE with good application effect in gypsum,improving its workability and mechanical strength.Due to its changeability,the molecular structure of PCE can be modified by changing the length of main chain and anion density,adjusting the length and the shape of side chain and introducing functional groups.As a new type of anchoring group,phosphorus-containing group can be introduced into PCE to improve its performance in cement and gypsum,especially enhancing the tolerance of sulfate and clay.In this paper,two type of phosphorus containing PCE（PHS-PCE and P-PCE）were synthesized by using 2-（methacryloyloxy）ethyl phosphate（MOEP）and sodium hypophosphite（SHP）respectively.The performance of phosphorus containing PCE in cement and gypsum were studied systematically and the tolerance of sulfate and clay of phosphorus containing PCE were investigated.Moreover,the effect of phosphorus-containing group in P-PCE on the calcium complexing ability was elaborated by theoretical calculation.Finally,P-PCE was put into use in self-compacting concrete（SCC）.Main research contents and results of this paper as bellow:A 2-（methacryloyloxy）ethyl phosphate（MOEP）modified polycarboxylate superplasticizer（PHS-PCE）was synthesized successfully and the synthesis parameters were optimized through singal-factor experiment.Gel permeation chromatography（GPC）,Fourier transform infrared（FT-IR）,31 P nuclear magnetic resonance（31P NMR）spectroscopy and P elemental analysis measurements were used to characterize the structure of PHS-PCE.The experimental results showed that the phosphonate group was introduced sucessfully.Effect of PHS-PCE on the performance of cement paste was investigated systematically via mini slump and hydration heat test.The results showed that PHS-PCE exhibited superior dispersing performance,more retarding hydration effect and better sulfate and clay tolerance than conventional PCE（C-PCE）.The maximum flow of cement paste containing PHS-PCE could reach up to 295 mm,while that of C-PCE was 285 mm.The setting time of cement paste with C-PCE and P-PCE was 42 min and 72 min longer than that of blank cement paste.The maximum variation of adsorption of PHS-PCE were 12 % and 18 % in the presence of sulfate and clay,whereas that of C-PCE were 15 % and 25 %,leading to better sulfate and clay tolerance.These significant advantages could be ascribed to the high anion density and high calcium complexing capacity induced by the phosphonate group in the molecular structure of PHS-PCE.A sodium hypophosphite（SHP）modified polycarboxylate superplasticizer（P-PCE）was synthesized successfully and the synthesis parameters were optimized through single-factor and orthogonal experiments.It showed that phosphinate group and phosphonate group were introduced by chain transferring and oxidizing.GPC,FT-IR,X-Ray photoelectron spectroscopy（XPS）,31P（MAS）NMR spectroscopy and P elemental analysis measurements were used to characterize the molecular structure of P-PCE.Studies on the P-PCE radical copolymerization kinetics were carried out and the obtained reaction equation was Rp=k [IPEG]-0.9060 [AA] 0.9823 [APS] 0.7472 [VC] 0.6179 [SHP] 0.6635 and the polymerization reaction activation energy Ea calculated under this condition was 24.66 k J/mol.The measurements of C-PCE and P-PCE,including adsorption,hydration heat,zeta potential,surface tension,dispersiblity,mechanical strength and tolerance of sulfate and clay,were also tested.The experimental results showed that the introduction of phosphinate group and phosphonate group into the molecular structure of P-PCE resulted in its anion charge density and calcium complexing capacity increased by 13% and 6.4% respectively,comparing with C-PCE.The maximum flow and initial setting time of cement paste with P-PCE were 20 mm bigger and 50 min longer than that of C-PCE,respectively.Meanwhile,the mechanical strength of cement paste containing P-PCE enhanced more.The adsorption of PCE was affected by sulfate and clay dissimilarly.The maximum variation of adsorption of P-PCE were 9 % and 15 % in the presence of sulfate and clay,whereas that of C-PCE were 15% and 25 %,respectively,leading to the better sulfate and clay resistance of P-PCE.Based on the experimental data,the P-PCE’ mechanisms of sulfate and clay tolerance were assumed.The high anion density of P-PCE reduces the compression of the molecular spatial structure to a certain extent,leading to a smaller decreased value of hydrodynamic radii compared with that of C-PCE.Besides,the P-PCE’s stronger complexing capacity with calcium ion promotes a certain amount of P-PCE to adsorbe on the clay edge,resulting in less consumption.The properties of P-PCE on α-calcium and β-calcium sulfate hemihydrate（α-HH and β-HH）were systematically investigated.The maximum flow of α-HH containing PPCE was 280 mm,while that of C-PCE was 265 mm.Meanwhile,the ratio of water reduction of P-PCE in β-HH was 14.7 % higher than C-PCE.The results also showed that,compared with C-PCE,the adsorption amount,zeta potential and calcium ion complexing abiltiy of PPCE in α-HH increased by 11.2 %,18.2 % and 7.2 %,while that of P-PCE in β-HH increased by 11.8 %,24.5 % and 10%.Besides,the initial setting time of P-PCE in α-HH and β-HH were 6.5 min and 2.2 min longer than C-PCE.The mechanical strength of hardened HH also enhanced more.The reason might be ascribed to the higher adsorption ability of P-PCE because of its stronger complexing capacity with calcium ion,which was induced by phosphoante group and phosphinate group in the P-PCE molecule.Additionally,it also found that PCE played an important function in hindering the calcium sulfate dehydrate（DH）crystallization instead of the dissolution of β-HH,besides restraining the dissolution of α-HH.The introduction of phosphoante group and phosphinate group into the molecule structure on the effect of calcium complexing ability was studied by Hartree-Fock method of ab initio quantum chemistry calculation.The ground-state geometries of acrylic copolymer（PAA）with and without Ca²⁺,PAA containing phosphinate terminal group（PAA-P1）with and without Ca²⁺,PAA containing phosphinate middle group（PAA-P2）with and without Ca²⁺ and PAA containing phosphinate terminal group（PAA-P3）with and without Ca²⁺ were optimized and calculated at 6-31 G level.Based on the the theoretical calculation data,it is conformed that the introduction of phosphoante group and phosphinate group in PCE enhanced the PCE’s complexing capacity with calcium ion.The properties of P-PCE on self-compacting concrete（SCC）was studied.The experimental results showed that the dosage of P-PCE was smaller,the fluidity of SCC and L-box ratio would be higher and the T 500 time,V-funnel time and U-box height difference would be smaller.Besides,the slump-flow diameter,L-box ratio,T 500 time,V-funnel time and U-box height difference were correlated a high level.Compared with C-PCE,the dosage of P-PCE reduced by 5% at the same flow diameter.Meanwlile,the U-box height difference and the larger L-box ratio increased by 12.3 %.Addtionally,the T 500 time,V-funnel time and U-box height difference were 2.2 s,4.7s and 0.4 cm shorter than that of C-PCE.The better J-ring performance of P-PCE was also obtained.The research achievement got a good application in ZQSG-3 project of Weifang-Yantai new high-speed railways construction.