Influence of High-Robustness Polycarboxylate Superplasticizer on the Performances of Concrete Incorporating Fly Ash and Manufactured Sand

Using ethylene glycol monovinyl polyoxyethylene ether,2-acrylamido-2-methylpropane sulfonic acid(AMPS)and acrylic acid as the main synthetic monomers,a high robustness polycarboxylate superplasticizer was prepared.The effects of initial temperature,ratio of acid to ether,amount of chain transfer agent,and synthesis process on the properties of the superplasticizer were studied.The molecular structure was characterized by GPC(Gel Permeation Chromatography)and IR(Infrared Spectrometer).As shown by the results,when the initial reaction temperature is 15℃,the ratio of acid to ether is 3.4:1 and the acrylic acid pre-neutralization is 15%,The AMPS substitution is 10%,the amount of chain transfer agent is 8%,and the performance of the synthesized superplasticizer is the best.Compared with commercially available ordinary polycarboxylate superplasticizer in C30 concrete prepared with manufactured sand and fly ash,the bleeding rate decreases by 52%,T50 decreases by 1.2 s,and the slump time decreases by 1.1 s.In C60 concrete prepared with fly ash and river sand,the bleeding rate decreases by 46%,T50 decreases by 0.8 s,and the slump time decreases by 3.2 s.

Study on the Hydration and Physical Properties of Cement by M18 Polycarboxylate Superplasticizer Modified Graphene Oxide

Graphene oxide(GO)as a new nano-enhancer in cement-based materials has gained wide attention.However,GO is easy to aggregate in alkaline cement mortar with poor dispersibility.This hinders its application in practical infrastructure construction.In this work,GO-M18 polycarboxylate compound superplasticizer(GM)were obtained by compounding the M18 polycarboxylate superplasticizer with GO solution at different mass ratios.The dispersion of GM in alkaline solution was systematically studied.The phases and functional groups of GM were characterized by XRD and FTIR.The effects of GM on the cement mortar hydration and the formation of microstructure were investigated by measuring the heat of hydration,MIP,TG/DSC,and SEM.The results show that the long-chain structure of the M18 polycarboxylate superplasticizer can increase the interlayer spacing of GO and weaken the force between GO sheets.The modified GO can be uniformly dispersed in the cement slurry.GM can accelerate the early hydration process of cement,which can increase the content of Ca(OH)2 and decrease the grain size.It can optimize the pore size distribution of cement-based materials,increase the density of harmless and less harmful pores,thereby improving mechanical properties.Such methods can transform traditional cement-based materials into stronger,more durable composites,which prolong the life of cement-based materials and reduce the amount of cement used for later maintenance.This provides an idea for achieving sustainability goals in civil engineering.

Effects of Molecular Structure of Polycarboxylate-type Superplasticizer on the Hydration Properties of C_3S

Effects of polycarboxylate-type superplasticizer（PC） molecular structure on the hydration heat of tricalcium silicate（C3S） paste and polymerization degree of hydration products（C-S-H gel） were researched by using TAM AIR isothermal microcalorimetry（TA） and 29Si nuclear magnetic resonance（NMR）.Methoxy polyethylene glycol-methacrylates-based polycarboxylate superplasticizers with different side chain lengths and main chain lengths were employed.PC molecules with shorter main chain or longer side chains caused stronger retardation of C3S early hydration and lesser increase of C3S 3 d hydration degree.NMR measurement indicated that the incorporation of PC increased the hydration degree of C3S paste and the polymerization degree of silicon-oxygen tetrahedron of C-S-H gel.The tendency for C3S 7 d hydration degree to improve was more pronounced while PC molecules with longer main chain or shorter side chain were added.Whereas,PC molecules with longer main chains or longer side chains increased the 7 d polymerization degree of C-S-H gel.

Effect of Crosslink Structure of Bridge Polycarboxylate Superplasticizers on Dispersion Ability

Bridge polycarboxylate superplasticizers（PCs） with crosslink structure were synthesized by using polyethyleneglycol di-acrylate（PEGdA）, replacing partial polyethyleneglycol mono-acrylate （PEGmA） as crosslinking agent. Structures of bridge PCs were analyzed by gel permeation chromatography, and dispersion ability was evaluated by cement paste dispersity variation on time and rheology test. The experimental results showed that, molecular weight（MW） of bridge PCs increased with increase of PEGdA proportion, and MW distribution curve changed from Gaussian to fiat like, which meant notable increase of highly crosslinked copolymer. Bridge PCs led to decreased initial cement paste dispersity and better dispersity retention due to slow releasing. Further research showed that, PEGdA proportion had slight effect on polymerization degree of backbone, MW distribution of backbone deviated from Gaussian distribution and shoulder peaks appeared on distribution curve when PEGdA increased.

Adsorption Mechanism of Polycarboxylate-Based Superplasticizer in CFBC Ash-Portland Cement Paste

Circulating fluidized bed combustion （CFBC） ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby significantly reduce the efficiency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of ＂invalid adsorption site＂ of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion （PCC） fly ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fluidity of CFBC ash-Portland cement paste is lower than that of the PCC fly ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor flowability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration.

Influence of Polycarboxylate Superplasticizer on Rheological Behavior in Cement Paste

Molecular structures of polycarboxylate（PCE） superplasticizer significantly affect the rheological properties of cement paste. Consequently, we employed self-synthesized PCE copolymers with different carboxylic densities to investigate their influence on the rheological behavior of cement paste. Three typical rheological models were applied to analyze the rheological properties, including Power-law model, Bingham model as well as Herschel-Buikley model. In addition, the thixotropical performances of cement paste in the presence of PCE with different carboxylic densities were investigated. The results show that the carboxylic density of PCE greatly influences the dispersing performance of PCE superplasticizers. As carboxylic density increases, the dispersing capability of PCE improves, and P（PEG1-AA6） possesses the strongest dispersing capability, the initial fluidity and 1 h fluidity of cement paste are both the highest, and cement paste has the lowest viscosity and the smallest hysteresis loop.

Synthesis of New Polyether Polycarboxylate Superplasticizer

The effects of various factors on the synthesis process and the performances of product, including batch feeding way and the dosage of the radical initiator, the system concentration, the reaction temperature and the reaction time were discussed. A kind of polycarboxylate superplasticizer with allyl alcohol polyethylene glycol, maleic anhydride and methacrylic acid sulfonic sodium as main raw materials has been synthesized. Their relative effectiveness as dispersants was evaluated in cement paste by measuring paste fluidity. The optimum parameters of technology and the appropriate proportion of raw materials were obtained. As a result,the new high performance superplasticizer suitable for high-performance concrete has been synthesized. The structure of copolymer was characterized and analyzed by FT-IR spectra. Results indicated that product copolymer structure was consistent with the ideal molecular structure designed.

Synthesis and Performance Characterization of a Low Adsorption Clay-resistant Polycarboxylate Superplasticizer

A low adsorption clay-resistant polycarboxylate superplasticizer(KN-PC)was synthesized using acrylic acid and isopentenol polyoxyethylene ether as the main reaction materials.The structural characterization and clay-resistant mechanism of the KN-PC were explored using Fourier transform infrared spectroscopy and X-ray diffraction,and the effect of the KN-PC on the performance of composite paste with various montmorillonite(MMT)contents was analyzed.Compared with ordinary polycarboxylate superplasticizer(PC),the KN-PC has a low sensitivity to the MMT.By the action of the MMT,the adsorption dosage of the KN-PC on the MMT is much smaller than that of the PC.

Effects of Clay on Properties of Polycarboxylate Superplasticizer and Solutions

The infl uence law of clay on mortar fluidity mixed with polycarboxylate superplasticizer was studied. Several methods of inhibiting clay adsorption of polycarboxylate superplasticizer were discussed. The experimental results show that clay has signifi cant effect on the dispersion of polycarboxylate superplasticizer and montmorillonite clay has more signifi cant impact on mortar fluidity than other clays. The pH value and the salts of the solution can affect the adsorption of clay to polycarboxylate superplasticizer. The incorporation of a small amount of sodium hydroxide solution, sodium silicate or cationic surfactants can improve the effect of the clay on the dispersion of polycarboxylate superplasticizer.

Preparation of Polycarboxylate-based Superplasticizer and Its Effects on Zeta Potential and Rheological Property of Cement Paste

A series of polycarboxylate-based superplasticizers(PCs) with different structures were synthesized and the effects of chemical structure on zeta potential and rheological property of cement paste were studied. Residual monomers in each sample of PCs were quantitatively determined. The property of the polymers in cement was tested by micro-electrophoresis apparatus and R/S rheometer. Results showed that the zeta potential and its rheological properties are related with the side-chain length and density of PCs. The PCs having shorter side chain and lower side chain density exhibit higher anionic charge density, thus resulting in higher zeta potential. The effect of side chain density on zeta potential is more notable compared with that of side-chain length, and thus affecting the initial shear yield stress and apparent viscosity of the cement paste. In addition, although increasing the side chain length will result in reduction of the anionic charge density, the steric hindrance effect is obvious, which can effectively improve the dispersion of the cement particles, and reduce the viscosity and shear yield stress of slurry.

Determination of Residual Monomers in Polycarboxylate Superplasticizer Using High Performance Liquid Chromatography

A procedure was developed for the determination of residual monomers in polycarboxylate superplasticizer （PCs） by reversed-phase high performance liquid chromatography （RP-HPLC）.Four kinds of residual monomers were well separated and determined on a SinoChrom ODS-BP （C18） column with mobile phases composed of acetonitrile and phosphate buffer solution.The monomers were detected by UV detector at 205 nm and quantitatively analyzed with an external standard method.For those residual monomers,the linear response ranged from 4.0×10-6 mol·L-1 to 2.0×10-3 mol·L-1.The determination limit of acrylic acid,sodium methylallyl sulfonate and 2-Acrylamido-2-methylpropane sulfonic acid was 0.02×10-5 mol·L-1,while that of methoxy-polyethylene glycol monoacrylate was 0.1×10-5 mol·L-1.The relative standard deviation （RSD） of high concentration samples was less than 1%,while that of the low concentration samples was between 1%-4%.The standard （additional） recovery ratio was 97.4% -104.2%.

Influences of Polycarboxylate Superplasticizers on Rheological Behavior of Low-cement Castables

Influences of different superplasticizers （ STP. KSJSTO and LMS-P） on rheological behavior of low-cement castables and the mechanisms were analyzed. The shear stress and viscosity under different shear rates of matrix slurry were determined using a NXS-I IA rotary viscometer. Effects of different admixtures on the rheological properties of slurry was analyzed theoretically. Sodium tripolyphosphate and poly＇carboxylate superplasticizers KS-JSTO and LMS-P） can improve the fluidity and initial setting time. With STP. the slurry is plastic flow. With KS-JS70 or LMS-P increasing, the slurrv changes from plastic.flow, pseudoplastic flow to dilatant flow successively. Th, e optimum dosages of STP. KS-JSTO and LMS-P are 0. 15%. 0. 25% and 0. 40%, respectively. KS-JS70 and LMS-P can significantly reduce the slurry viscosity and shear stress to improve the workability of construction. Both shear stress and viscosity shall be taken into account for on-site construction.

Effect of molecular structure and slump loss resistance of polycarboxylate superplasticizers on self-compacting concrete

A new kind of polycarboxylate superplasticizer with high slump loss resistance was obtained by designing scheduled molecular structure.The number average molecular mass of the polymer was characterized by the gel permeation chromatography measurements.And chemical structure of the polymer was observed by the Fourier transform infrared spectroscopy(FT-IR).The results show that the good workable maintaining of self-compacting concrete could be achieved through direct adjustment of number average molecular mass and different unsaturated monomer in synthetic process.The FT-IR analysis illustrated that the high slump loss resistance of polycarboxylate superplasticizers with ester and carboxyl group and expectations of molecular structure were designed.

Influences of Soluble Salts on Adsorption Properties of Polycarboxylate Superplasticizers

Polycarboxylate（PC） superplasticizers with different chemical structures were synthesized through free radical co-polymerization reaction.A total organic carbon analyzer was used to investigate adsorption behaviors of PCs,and to evaluate influences of soluble salts on absorption properties of PCs.It is found that adsorption ratios of PCs on cement particles decrease greatly with the addition of Na2SO4;the adsorption ratio of ethers PC with Hydroxyethyl methacrylate（HEMA） group first increases then decreases with the addition of NaCl;the adsorption ratio of esters PC with short side chains first decreases then increases,while the adsorption ratio of ethers PC with HEMA group decreases with the addition of CaCl2;the adsorption ratio of esters PC with short side chains decreases with the addition of Ca（NO3）2;AlCl3 causes the decrease of the adsorption ratio of ethers PC with HEMA group.

反应条件对PCEs分子结构和分散性的影响及机理

采用水溶液自由基共聚法,将乙二醇单乙烯基聚乙二醇醚与丙烯酸共聚合成了聚羧酸系减水剂(PCEs),深入研究了反应温度、滴加时间和链转移剂用量3个主要因素对PCEs分子结构和分散性的影响及机理.结果表明,反应温度和链转移剂用量对乙二醇单乙烯基聚乙二醇醚的转化率、PCEs的相对分子质量及其分布影响较大,导致PCEs在水泥净浆中的分散性和分散保持性有明显的区别,而滴加时间的影响相对较小.

灰钙对掺PCE的磷建筑石膏性能影响研究

为了进一步促进磷建筑石膏的应用,以灰钙为碱性调节剂,对比研究了灰钙掺量对添加或不添加聚羧酸减水剂(PCE)的磷建筑石膏工作性能、力学性能、物相组成及微观形貌的影响。结果表明,在未添加PCE时,随着灰钙掺量的增加,磷建筑石膏p H逐渐增大,水溶性P_(2)O_(5)含量逐渐降低,流动度下降超59.5%,标准稠度用水量升高,强度先降低后升高,但均低于原状磷建筑石膏的强度,抗折、抗压强度最低时较原状磷建筑石膏分别下降63.3%、54.4%。添加PCE后,掺入灰钙可使磷建筑石膏对PCE的吸附量提高10倍以上,从而改善因灰钙掺入对磷建筑石膏流动度、标准稠度用水量、强度造成的不利影响,强度随灰钙掺量的增加先升高后降低再升高,抗折、抗压强度最高时较未掺灰钙时分别提高11.1%、48.9%。XRD及SEM分析结果表明,灰钙主要与磷建筑石膏中H_(3)PO_(4)和H_(2)PO_(4)~-发生反应,生成难溶性无定型小颗粒,降低二水石膏晶体间的相互搭接程度,导致强度下降。在磷建筑石膏生产加工应用中灰钙掺量宜大于1.3%,并搭配PCE使用。

不同侧链密度PCE制备的C-S-H/PCE结构及其对水泥早期水化的影响

装配式建筑的发展使得在预制件生产中使用早强剂的需求越发强烈,人工合成水化硅酸钙(C-S-H)作为一种新型晶种早强剂,能够显著提高水泥基材料的早期强度,但其较差的分散性限制了其应用。文中以不同侧链密度聚羧酸减水剂(PCE)作为分散剂,通过共沉淀法合成了一系列C-S-H/PCE晶种早强剂,利用X射线衍射分析仪(XRD)、傅里叶红外光谱(FT-IR)、纳米粒度仪(DLS)等探究其对C-S-H晶种结构的影响,并深入研究了C-S-H/PCE晶种早强剂对水泥水化行为、硬化体强度和组成结构的影响。结果表明:PCE的侧链密度越小,C-S-H晶种分散得越好,粒径越小,中位粒径可达339.5 nm,晶种颗粒数量增多,可提供更多的成核位点;掺入C-S-H/PCE能显著加速水泥水化,使水化加速期放热峰提前1.3 h,8 h放热量增加10.8%;掺入C-S-H/PCE后,水泥净浆8 h和1 d龄期硬化体的孔隙率降低,抗压强度分别提高13%和15%。

Chemical Structures and Adsorptive Behaviors of Superplasticizers on β-C_2S

The chemical structures of four types of superplasticizers （SPs） and their adsorptive behaviors on β-C2S were investigated. The adsorption properties of SPs on β-C2S were measured and the relationship between the adsorption quantity and the specific surface of β-C2S was analyzed. The experimental results show that the adsorption quantity increases with the surface area increase of β-C2S, but the adsorption quantity per surface area is similar, which means that the main adsorbent is β-C2S itself. Polycarboxylic ester （PCE） showed the highest adsorption amount on β-C2S, followed by β-naphthalene sulfonates （NSF） and formaldehyde-acetone condensates sulfonates （FAS）, amino sulphonate （AS） showed the least adsorption amount on β-C2S. PCE affected the surface potential of β-C2S particles in water differently in comparison with other types of SPs. The adsorption capacity of SPs on β-C2S is determined by factors such as molecular structure, functional groups and molecular weight of SPs.

减水剂改性固废基蒸压加气混凝土的制备与性能研究

以花岗岩石粉、黄河特细砂为硅质材料,以电石渣为钙质材料,以聚羧酸减水剂为改性剂,制备固废基蒸压加气混凝土(AAC)。研究了聚羧酸减水剂掺量对AAC料浆流动性、发气过程、抗压强度、干密度、孔隙率和孔径分布的影响。结果表明,减水剂掺量由0.15%增大到0.30%,料浆初始流动度、发气速率、发气量和孔隙率逐渐增大,制品抗压强度和干密度逐渐降低。减水剂掺量为0.25时,料浆初始流动性270 mm,发气量208 mL,孔隙率82.54%,抗压强度2.9 MPa,干密度509 kg/m^(3),AAC综合性能最优。减水剂掺量大于0.2%时,2 mm以上的大孔基本消失,孔隙率和孔壁无害孔含量对AAC抗压强度影响更明显。

CeO_(2)可见光催化合成APEG保坍抗泥型聚羧酸减水剂

可见光异相催化合成聚羧酸系减水剂是进一步提高单体活性种生成率和减水剂性能的有效手段。本文以CeO_(2)为催化剂,(NH_(4))_(2)S_(2)O_(8)为引发剂,烯丙基聚氧乙烯醚(APGE-1000)、2-丙烯酰胺基-2-甲基丙磺酸和马来酸酐为单体,可见光催化聚合制备出APEG保坍抗泥型聚羧酸减水剂,初始及含泥净浆流动度分别为295 mm和275 mm,30min后经时损失均为零,展现出良好的分散性、保坍性和抗泥性,性能优于相同条件下热聚合制备的同种减水剂。系统表征发现,两者性能存在差距的原因是分子量不同,但两种减水剂具有相同的水化和抗泥机理,均能延缓水泥水化进程并使蒙脱土层出现不完全的剥离或分叉,与聚合方式无关;并且CeO_(2)具有吸收可见光的能力,在可见光照射下可产生的·OH和·O_(2)^(-)参与聚合反应,促进单体活性种的生成,提高了聚羧酸减水剂的分子量和应用性能。