Study On Preparation And Application Of Retarded Cement Additive

Retarder plays an important role in the field of cement concrete.In this paper,the effects of two kinds of silane coupling agents modified micron-sized silica industrial products（mSiO₂）,2-hydroxyethyl methacrylate（EGMP）and phosphate modified polycarboxylate retarder（PPCE）on the properties of the cement paste such as fluidity and fluidity retention were investigated.Combined with the characterization results of hydration heat and XRD,ATR-FTIR,and SEM of hydration products at various stages,the retardation and mechanism of silanization-modified mSiO₂,EGMP and PPCE in cement slurry were studied.The main contents are as follows:（1）Modification of micron-sized silica（mSiO₂）with aminopropyltriethoxysilane（APTES）andγ-methacryloxypropyltrimethoxysilane（MOPTMS）to prepare APTES@mSiO₂（AS）and MOPTMS@mSiO₂（MS）,respectively.The dispersibility and stability of AS and MS in saturated Ca（OH）₂ were investigated.The effect of modified silica on the performance and hydration process of cement paste was investigated.The effect of silanized SiO₂ on the mechanical properties of cement mortar was evaluated.The results show that AS and MS exhibit excellent dispersion and stability in alkaline environments and aqueous solutions.Compared with mSiO₂,the decreasing trend of calcium ion concentration in CH solution with AS and MS added.The fluidity of AS and MS cement pastes increased by 41.67%and 33.33%,respectively,and the Standard consistency of water consumption of the cement paste decreased,the retardation effect was significant,and the initial settling time was extended by 80 and146 min,the final setting time was extended by 101 and 279 min,respectively.Analysis of hydration heat and hydration products of cement paste show that AS and MS can delay the hydration process of cement slurry,which is mainly reflected in the delay of the hydration process of cement paste during the induction period.Sca@mSiO₂ is beneficial to the development of the strength hardened mortar 28d.（2）The effect of EGMP on the dispersibility of cement paste and the concentration of cations in the paste solution was investigated.The effect of EGMP on the hydration process of the cement paste was examined.The results showed that with the increase of EGMP content,the cement paste initial fluidity decreased.When the EGMP content increased to 0.35%,the initial fluidity was already lower than 175 mm,but the fluidity of the cement paste maintained excellents performance.After 3h fluidity increased slightly compared with the initial.After the addition of EGMP,the decrease of cation concentration in the cement pastes was more rapid than that of PCE.The hydration results of show that the cement slurry with EGMP has obvious retardation effect,which is mainly reflected in the hydration induction period of cement paste.When W/C is 0.29,the optimal addition amount of EGMP is0.15%⁰.35%at 0.2%PCE dosage.（3）Using EGMP,AA and TPEG as monomers,thioglycolic acid as chain transfer agent,a phosphate ester-copolymerized phosphate polycarboxylate retarder（PPCE）was synthesized under H₂O₂-Vc redox initiation system.Optimized synthesis reaction conditions.The influence of PPCE on the performance of cement paste and hydration process was investigated.It has been confirmed that PPCE has the effect of low dosage,high dispersion and excellent slump loss resistant in cement paste.PPCE has higher cation coordinative capacity in cement paste than PCE,and therefore has a significantly retarder performance compared with PCE.Among them,PPCE-1（1:3.5:0.5）has higher dispersion performance than PCE.The analysis results of cement products show that the retardation of PPCE on the cement paste still shows in the hydration induction period.