Effect of polysaccharides on the hydration of cement suspension

This work compares the effects induced by polysaccharides on the hydration of cement. It also brings new insights into the interaction mechanisms between these two components. Several parameters such as structure, concentration, average molecular weight, and the soluble fraction value of the polysaccharides were examined. The hydration of cement was monitored by conductivity measurement, and ionic chromatography. The influence of polysaccharide structure on the kinetics of cement hydration was revealed. The extent of retardation increases when polysaccharide concentration rises. Dextrins with lower average molecular weights compared with starches favor a higher soluble fraction value and further retard hydration. The growth of hydrates seemed to be more affected by the presence of these admixtures than did the dissolution of anhydrous particles or the nucleation of former hydrates.     

BSE-IA reveals retardation mechanisms of polymer powders on cement hydration

The retardation effects of two polymer powders, styrene butadiene rubber and ethylene-vinyl acetate, on cement hydration and the mechanisms in terms of hydration degree and microstructure characteristics were investigated by the combination of backscattered electron image analysis, scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction. Results show that the cement hydration can be significantly retarded by both polymers with the reductions in cement hydration degrees and hydration products thickness. Polymers retard cement hydration by agglomerating the polymer particles on the surfaces of cement grains, forming films in different thickness and bonding the calcium ions in the pore solutions. Consequentially, the formation of C-S-H and CH is depressed and the Ca/Si ratios in the hydration product layer are raised. The retardation is enhanced with the increase in polymer content. This work helps understand the retardation effect of polymers on cement hydration in depth, which enables rational development of polymer-modified cement-based materials for further applications.     

Alkaline stability of cellulose ethers and impact of their degradation products on cement hydration

Cellulose ethers are polymers frequently introduced into mortar formulations. This study allows to assess the potential role of cellulose ethers degradation on the alteration of the cement hydration kinetics. A retardation mechanism based on the calcium binding capacity of chelates is often proposed to describe the effects of some polysaccharides (e.g. sugars) on cement hydration. The alkaline stability of cellulose ethers has been poorly studied and may represent one way to understand the hydration delay induced by such admixtures. Identification and quantification of the hydroxy carboxylic acids generated during alkaline degradation were performed. The results indicate that cellulose ethers are very stable in alkaline media. We also show that the ability of cellulose ethers to complex calcium ions is negligible. Finally, degradation of cellulose ethers and its impact on the cement hydration kinetics does not seem to be significant.     

缓凝剂对高贝利特硫铝酸盐水泥水化和性能的影响

高贝利特硫铝酸盐(HB-CSA)水泥是一种具有低收缩特性的新型低碳水泥。针对该种水泥凝结硬化不易控制的问题,系统研究了氨基三亚甲基膦酸(ATMP)和葡萄糖酸钠(SG)对HB-CSA水泥水化和凝结硬化的影响。采用等温量热仪、X射线衍射仪和扫描电子显微镜分析了缓凝剂在HB-CSA水泥中的作用机理。结果表明:ATMP可以显著延缓HB-CSA水泥水化进程,延长凝结时间,提高HB-CSA水泥的中后期强度;而SG仅表现出有限的作用。两种缓凝剂与聚羧酸减水剂(PCE)复配可以延迟HB-CSA水泥水化放热速率,抑制钙矾石等早期水化产物的形成,且不同种缓凝剂会使钙矾石呈现出不同的形貌。     

An investigation of the effect of organic solvent on the rheological properties and hydration of cement paste

The influence of ethyl-alcohol and 1–4 dioxane on the rheological properties and hydration of portland cement paste have been studied. The rheological properties are correlated to the cement/liquid interface characteristics. The relationship between viscosity and zeta-potential is discussed. Analyses of the liquid phase composition and conduction calorimetric measurements have been made to quantify the retardation effect of organic solvent on the cement hydration. Ethyl-alcohol has been found to have a greater retardation effect than 1–4 dioxane.     

环氧乳液改性水泥基材水化过程的硬化机理

极端环境和复杂荷载条件对混凝土结构的材料性能提出了更高的要求,聚合物通过改性水泥基材提高混凝土性能的方法已经得到了广泛应用。本研究为揭示环氧乳液改性水泥基材水化过程的硬化机理,通过等温放热试验分析环氧乳液对水泥水化放热过程的影响,结合原位XRD技术跟踪水泥主要矿物熟料和水化产物在水化反应早期的相含量发展。研究结果表明,环氧乳液对水泥水化的阻滞作用与环氧颗粒、水泥矿物熟料和水化产物之间的相互作用有关,并随着水化时间的延长,相互作用效果越明显。在水泥胶凝体系中,环氧乳液会减缓水化放热速率,降低水化放热峰值,减少累积放热量。环氧乳液通过抑制水泥矿物(C₃S、C₃A、石膏)的溶解和水化产物(钙矾石、氢氧化钙)的析出,延缓硅酸盐反应和铝酸盐反应;环氧乳液对水泥水化的影响随着其掺量的增加而增强。     

Preparation of amphoteric polycarboxylate superplasticizers and their performances in cementitious system

A series of amphoteric polycarboxylate (PC) polymers were synthesized by radical copolymerization of acrylic acid (AA), [3‐(methacryloylamino) propyl] trimethylammonium chloride (MAPTAC) and ω‐methoxypolyoxyethylene methacrylate ester (MPEGMA). Cationic groups were introduced in to PC molecules with expectation of less retardation effect on cement hydration compared to the traditional anionic PC superplasticizers. The content of cationic groups in polymer was varied by changing the monomer ratio of MAPTAC to AA in the synthesis recipes. The structure of the synthesized amphoteric PCs was verified by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The performances of the amphoteric PCs were evaluated by measurement of flowability and zeta‐potential of cement pastes and adsorption amount of PC in cement pastes. Impacts of the PCs on cement hydration were studied by isothermal calorimetry. It is concluded that both anionic and cationic PC polymers can be effectively adsorbed onto the surface of cement particles and thus change the zeta potential of cement pastes. The adsorption amounts of the amphoteric PCs decrease with increasing content of cationic units. A proper incorporation of cationic units into PC polymers may lead to a higher fluidizing performance in fresh cement pastes. The amphoteric PC polymers with higher content of cationic units show less retardation effect on cement hydration and hence higher early strength of cementitious materials may be achieved by using amphoteric PCs with appropriated content of cationic units without losing their plasticizing efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41348.     

HPMC and HEMC influence on cement hydration

Cellulose ethers such as hydroxyethylmethyl cellulose (HEMC) and hydroxypropylmethyl cellulose (HPMC) are common admixtures in factory made mortars. Nevertheless, their use principally remains empirical, and no cement-admixture interaction mechanism has ever been rigorously demonstrated. The main issue of this publication deals with the control of secondary effects generated by these admixtures such as the retardation of cement hydration. In this frame, a study of the impact of HEMC and HPMC molecule parameters on the modification of cement hydration was carried out. Minor influence of the molecular weight and of the hydroxypropyl or the hydroxyethyl group content was observed. On the contrary, the results emphasize that the methoxyl group content appears as the key parameter of the hydration delay mechanism.     

Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and interactions with supplementary cementitious materials

Sucrose and zinc oxide (ZnO) are effective cement hydration retarders. The goal of this study was to provide a new look into the ZnO cement hydration mechanism and to investigate impacts of various supplementary cementitious materials (SCMs) on retardation behavior of ZnO and sucrose. Changes in the pore solution composition and reaction kinetics were measured for cementitious systems with ZnO or sucrose that contained rice straw ash (RSA), wheat straw ash, silica fume, metakaolin, and fly ash. Among the SCMs used, RSA dramatically suppressed ZnO and sucrose retardation. Experimental results indicated that the mechanism by which ZnO retards hydration reaction could be nucleation and/or growth poisoning of C-S-H. Reduced retardation of paste samples containing RSA was attributed to the ability of RSA to provide nucleation sites for C-S-H precipitation. This study provides a better understanding of the interaction between SCMs and cement hydration retarders essential in predicting retarder–dose effects.     

Strength, leachability and microstructure characteristics of cement-based solidified plating sludge

The solidification of the stabilized zinc-cyanide plating sludge was carried out using ordinary Portland cement (OPC) and pulverized fuel ash (PFA) as solidification binders. The plating sludge were used at the level of 0%, 10%, 20% and 30% dry weight, and PFA was used to replace OPC at 0%, 10%, 20% and 30% dry weight, respectively. Experimental results showed that a significant reduction in strength was observed when the plating sludge was added to both the OPC and OPC/PFA binders, but the negative effect was minimized when PFA was used as part substitute for OPC. SEM observation reveals that the deposition of the plating sludge on the surface of the clinkers and PFA could be the cause for hydration retardation. In addition, calcium zinc hydroxide hydrate complex and the unreacted di- and tricalcium silicates were the major phases in X-ray diffraction (XRD) patterns of the solidified plating waste hydrated for 28 days, although the retardation effect on hydration reactions but Cr concentration in toxicity characteristic leaching procedure (TCLP) leachates was lower than the U.S. EPA regulatory limit.     

The effect of lead nitrate on the early hydration of portland cement

Solution analysis, calorimetry and electron microscopy have been used to study the retarding effect of Pb(NO₃)₂ admixtures on the early stages of hydration of Portland cement. Analyses of cement filtrates show rapid precipitation of basic lead compounds incorporating nitrate and sulphate. The precipitation is accompanied by an increase in the early heat liberation followed by a longer term retardation. Microscopy shows that the precipitate is largely in colloidal gelatinous form and coats the surfaces of the cement grains. The protective effect of these coatings is clearly responsible for the inhibition of hydration.     

Cement hydration and microstructure formation in the presence of water-soluble polymers

Hardening of cement mortars modified with small amounts of water-soluble polymers implies both cement hydration and polymer film formation. In this paper, the effect of the presence of water-soluble polymers on the cement hydration reactions is investigated by means of isothermal calorimetry, thermal analysis, FT-IR spectroscopy and SEM investigation. In spite of an initial retardation of the hydration reactions, a higher degree of hydration is found after 90 days for 1% PVAA, MC and HEC modified mortars, due to a better dispersion of the cement particles in the mixing water. MC also affects the morphology of the Ca(OH)₂ crystals. Polymer bridges are detected between the layered crystals, gluing the layers together and strengthening the microstructure. Additionally, the internal cohesion of all bulk polymer modified cement pastes is improved. In the presence of the polymers, a more cohesive microstructure with a smaller amount of microcracks is created.     

Hardened portland cement pastes of low porosity VI. Mechanism of the hydration process

The hydration of low-porosity portland cement pastes may be divided into three stages. The first stage starts with a fast hydration until 10 to 15% of the cement is hydrated (pre-dormant period), which is followed by a very slow hydration, caused by the formation of a coating on the cement grains (dormant period). After 15 to 20% of the cement is hydrated, the coating is ruptured, and a fast reaction starts, which lasts until about 30% of the cement is hydrated. This is the second stage of the reaction. In the third stage, the hydration slows down, due to retardation by the accumulating hydration products. The mechanism of the third stage is treated quantitatively. The diffusion through the very narrow pores between the hydration products is activated diffusion, and the apparent energy of activation of the diffusion is calculated.     

Effect of polymer latexes with varied glass transition temperature on cement hydration

Influence of styrene‐acrylate latexes with varied glass transition temperature (T_g) on cement hydration was studied and the mechanism was analyzed. Results show that polymer latexes with varied T_g retard cement hydration to different extents. Specifically, low T_g polymer shows stronger retardation effect than the high T_g polymer. Despite similar surface charges, colloidal particles with lower T_g exhibit higher affinity to surface of cement grains than the high T_g polymer, indicated by the higher adsorption amount and denser covering layer. The low T_g polymer experiences particle packing, deforming, and film forming processes along with the consumption of water during cement hydration, which eventually produces a covering layer of polymer surrounding cement grains. However, for the high T_g polymer, film forming process is absent. Consequently, the higher adsorption amount and the film‐formation process along with cement hydration are the two reasons for the stronger retardation effect of the low T_g polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45264.     

Examination of Portland cement paste hydrated in the presence of malic acid

When malic acid (MA) solutions are added to ordinary Portland cement (OPC), rapid heat evolution takes place, but the hydration is retarded considerably at all the MA concentrations. To understand the mechanism of retardation, UV-visible and IR spectral studies were made and the results have revealed that some interaction occurs between MA and certain constituents of OPC. X-ray diffraction (XRD) and thermogravimetric (TG)/differential thermal analysis (DTA) studies have proved the formation of a new reaction product due to interaction between MA and some of the mineral phases of Portland cement. The retardation of the hydration of Portland cement may be attributed to the formation of this new compound.     

内掺硅烷乳液憎水剂对混凝土性能的影响

通过强度测试、水化热实验、热重分析、毛细吸水实验以及压汞实验研究了内掺硅烷乳液憎水剂对混凝土强度以及毛细吸水性能的影响规律及其机理.结果表明:高掺量硅烷乳液一定程度上抑制水泥水化,从而导致混凝土早龄期抗压强度和劈裂抗拉强度下降以及28 d养护后水泥净浆试块中毛细孔的体积增大.毛细吸水实验表明:28 d龄期混凝土毛细吸水...     

锂盐对硼砂在硫铝酸盐水泥中作用的影响

在硫铝酸盐水泥实际工程应用中,硼砂作为常用的缓凝剂,容易导致硫铝酸盐水泥过度缓凝,为了更好调控水泥的凝结时间,本文研究了锂盐对硼砂在硫铝酸盐水泥中作用的影响,主要从凝结时间、抗压强度、水化产物方面进行了分析.结果表明:当硼砂掺量为0.1％(质量分数,下同)时,氢氧化锂能明显缩短硫铝酸盐水泥的凝结时间,降低水泥的抗压强度...     

Retardation effect of superplasticizer on different cement fractions

Cement hydration is a complex chemical process strongly influenced by the proportions of the various minerals present in the cement, admixtures, and the size of the cement particles. In this note, it is shows that naphthalene based superplasticizer, used at high dosage, does not affect the total heat of hydration but retards the hydration process of portland cement. This retardation, however, is most effective on the medium size fraction of the cement (4 – 30 μm in our case). The superplasticizer does not affect the hydration of the fine fraction (< 4 μm) to that extent due to its richer concentration of SO₃ and alkalies. The coarse fraction of the cement (30 – 72 μm) does not participate (with or without superplasticizer) in the heat evolution process.     

Effects of lithium nitrate admixture on early-age cement hydration

Although the benefits of lithium admixtures for mitigation of alkali-silica reaction (ASR) have been well documented, the potential ancillary effects of lithium compounds on cement and concrete remain largely uncharacterized. To examine the effects of the most common lithium admixture — lithium nitrate — on early-age behavior, the admixture was introduced at dosages of 0% to 400% of the recommended dosage to six cements of varying composition and to a cement-fly ash blend. Behavior was examined by isothermal calorimetry and measurements of chemical shrinkage, autogenous shrinkage, and setting time. Results indicate that lithium nitrate accelerates the early hydration of most cements but may retard hydration after 24 h. In the lowest alkali cement tested, set times were shortened in the presence of lithium nitrate by 15-22%. Higher dosages appeared to increase autogenous shrinkage after 40 days. The replacement of cement by Class F fly ash at 20% by weight appeared to diminish the early acceleration effects, but later hydration retardation and autogenous shrinkage were still observed.     

Effect of polymer latexes with cleaned serum on the phase development of hydrating cement pastes

The effects of polymer latexes on cement hydration were investigated by the combination of isothermal calorimetry, in-situ XRD and Cryo-SEM. Two model latexes with varied amounts of anionic charges were used for measurements after cleaned by dialysis to remove the serum components. This study confirms that in-situ XRD technique can be successfully adapted to hydrating cementitious systems in the presences of polymer latexes to quantitatively follow evolution of mineral phases involved in cement hydration. Results show that both polymers retard aluminate reaction and depress silicate reaction, by delaying the dissolution of C₃A, anhydrite and gypsum and consequently the formation of ettringite, and reducing the dissolution of C₃S and the formation of C-S-H. The anionic colloidal polymers exhibit more pronounced retardation effect on aluminate reaction than on silicate reaction due to stronger electrostatic interaction between the polymer particles and the positively charged aluminate phases. The more charged latex shows stronger retardation.