Synthesis And Application Of Concrete Water Reducers Based On Natural Polymers

Within the framework of the theory of Materials Process Engineering, kinds of novel concrete water reducers based on natural polymers were synthesized in present paper from the view of renewable materials and environmental protection. The optium conditions of these products and their properties were investigated systemically.According molecular design theory, cotton cellulose was hydrolysis to get Leveling-Off Degree of Polymerization (LODP) cellulose. After basification with 30% Sodium Hydroxide (NaOH), the LODP cellulose was suspended in Isopropanol aqueous solvent and reacted with 1,4-butanesultone(BS) under certain temperature. Finally, water soluble Sulfobutylated Cellulose ether (SBC) was synthesized. The factors which affected the properties of SBC, such as reactant ratio, reaction temperature, and reaction time, were discussed. Hydroxylethylcellulose sulfate was synthesized via Hydroxylethylcellulose (HEC) and-Chlorosulfonic Acid (CSA).In order to investigate the properties of starch derivatives, starch maleate half ester (SMHE) was obtained by microwave radiation. The molecular structure of these products were characterized with modern analysis methods, such as FT-IR, Nuclear Magnetic Resonance (NMR), Scanning Electronic Microscopy (SEM), Inductively-Coupled Plasma Spectrometer (ICP), and Gel Permeation Chromatography (GPC). The performances of SBC, SMHE and SHEC in cement suspension were investigated. The zeta—potential of cement particles adsorbed water reducers, the adsorbed amount of water reducers and the thickness adsorbed layer of water reducers on cement particles were determined. The hydration properties and the apparent pattern of hydrate were analyzed, also.The optimum conditions for SBC were obtained as followed: n(NaOH):n(AGU):n(BS) is 2.5:1:1.7, reaction temperature is 75℃, and reaction time is 4.5hr. The product had intrinsic viscosity of 35.3ml/g (Viscosity Average Molecular Weight, M_ηwas about 29,000g/mol), the Degree of Substitution (DS) of sulfobutyl group was 0.38, the fluidity of cement paste with 1% of the product reached 182mm. The DS was improved from 0.38 to 0.67 by the method of fractional basification; the number average molecular weight was 6177g/mol. And the fluidity with 1% SBC also improved, reached to 270mm. The DS of SMHE was 0.49, and M_ηwas 7286g/mol; the DS of SHEC was 0.49, and Mn was 1978g/mol. SMHE and SHE also could improve fluidity of cement paste in appropriate dosage with set retarding. In the present experiment, the higher the DS was, and the lower the M_ηwas, the better the fluidity of cement paste with SBC was. The zeta-potential of cement particles with SBC could be improved from +8.9mV to -31mV, and the value changed little in 120min. SBC also could improve the retainable fluidity of cement paste. Langmiur-type adsorption occurred during the process of adsorption of SBC, SMHE and SNF on cement particles. The maximum adsorption capacities of SBCs were from 4.66mg/g to 5.49mg/g, and that of SNF and SMHE was 11.23mg/g and 9.73mg/g, respectively. The adsorbed layer of SNF on cement particles was 0.82nm, that of SBC and SMHE was 3.72nm and 6.82nm, respectively, the former was about 4.5 times of that of SNF, and the latter was about 8.3 times of that of SNF. The results of XPS spectrum of Ca2p indicated that chemical adsorption occurred when SNF, SBC and SMHE was adsorbed on cement particles.In order to discuss the mechanism of SBC, the empirical formulas were applied to calculate the forces between cement particles in cement suspension system. The results indicated that the Van der Waals force was weaken for the formation of 3.72nm SBC layer on cement particles, thus when the adsorbed layers compressed each other, the steric force became stronger than electronic repulsive force and Van der Waals attractive force, and steric force was dominant force under this situation. While the adsorbed layer didn't contact each other, the electronic static repulsive force could make cement particles dispersed. So we got the mechanism of SBC was synergism of steric force and electronic repulsive force.The saturated point of water reducers in concrete was an important parameter for the application of water reducers, and novel method to determine the parameter was developed in the paper. Firstly, the cement flocculation particle distribution after SPs added was tested; and then, fractal dimensions (Df) were counted; finally, the relationship between Df and dosage of SPs was discussed. The results indicated that the Df was affected greatly by the dosage of SP. When the dosage reaches certain range, a saltation of Df will occur. The dosage range corresponding to the saltation of SPs fitted well with the saturation point measured by cement paste fluidity. Thus the saturation point of SPs can be ascertained via Df. The method has some advantages, such as simple, convenient, and cement and water reducers saving.Based on flocculation theory of cement, the flocculated volumes of cement pastes with or without SPs were investigated, and the water-reducing factor (L) was educed. Ls trended to different constants in range from 0 to 1 for different SPs. The Ls had effect on the hydration of cements and the compatibility between SPs and cements. Water content of concrete decreased accompanying the L increasing, and approximately was equal to real water content in the same workability. The results indicated that L could guide concrete mix design.The water reducing ratio of SBC was affected by the structure of SBC. The ratio of mortar with 1% SBC ranged form 11.2% to 16.5%, and that of concrete ranged from 9% to 19.5%. The bending strength and compressive strength of mortar with SBC8 were improved obviously. The concrete with SBC8 could have good workability, lower bleeding ratio, lower slump loss and good water retention. The applications of SBC8 in C40 concrete indicated that SBCs have potential to be developed as high range water reducer.