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.     

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.     

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.     

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。     

Interactions of polymers and organic admixtures on portland cement hydration

Interaction of polymers and other organic admixtures on Portland cement hydration is reviewed. This has been compiled in a systematic way. First hydration of Portland cement is described in short. Later, interaction with 4 important components of Portland cement is discussed. Finally interphase effects in polymer modified hydraulic cement are discussed. It is concluded that polymers and organic admixtures interact with the components of Portland cement when they come in contact with water. This interaction is due to ionic binding, causing cross-links which inhibit the film formation property of polymers and influence considerably the crystallisation process during the hardening of concrete. Some low molecular weight organic substances also have a considerable influence on Portland cement during its reaction with water.     

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.     

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。     

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.     

添加EVA对水泥砂浆水化过程的影响

本文采用偏光显微镜、X射线衍射、综合热分析、红外光谱、扫描电镜等手段研究了添加EVA对水泥砂浆水化过程的影响。实验结果表明,聚合物的加入对各龄期水泥水化进程会有一定的抑制作用。     

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.     

含硫铝酸钙硅酸盐水泥中粉煤灰活化机理

用差示扫描-热重分析扫描电镜和化学分析法研究了含硫铝酸钙粉煤灰硅酸盐水泥和含硫铝酸钙矿渣硅酸盐水泥水化过程中水化产物的种类、形状、数量和孔溶液离子浓度等方面的变化规律.借助固体高分辨核磁共振波谱技术对水泥中硅氧四面体不同聚合状态的分布,Al的不同配位状态进行分析.结果表明:含硫铝酸钙硅酸盐水泥对粉煤灰激发作用大于对矿渣的激发作用,含硫铝酸钙粉煤灰水泥水化放热量多,促进粉煤灰玻璃体中AlO2-的溶出,在较高温度粉煤灰玻璃体网络结构激活,解聚速率加快.     

Effect of polysaccharides on the hydration of cement paste at early ages

This work deals with the relative efficiency of polysaccharides and their influence on cement hydration. Several parameters such as the structure, concentration, average molecular weight, and soluble fraction value of polysaccharides were examined. Cement hydration was monitored by isothermal calorimetry, thermogravimetry (TGA), and Fourier transform infrared (FTIR) spectroscopy. Results clearly show that retardation increases with higher polysaccharide-to-cement weight ratio (P/C). Low-molecular-weight starch showed enhanced retarding effect on the hydration of cement. The retardation effect of polysaccharides is also dependent on the composition of cement.     

The interface between polymer-modified cement paste and aggregates

The effects of polymer dispersions on the structure of the interfacial zone between portland cement paste and aggregates (limestone and granite) have been investigated. EDAX analyses of the polymer modified composites showed that a relatively high polymer content is present at the paste-aggregate interface. Scanning electron microscope (SEM) observations of fractured surfaces of the plain cement paste-aggregate interface revealed large calcium hydroxide crystals which are orientated with their c-axes perpendicular to the interface. With increasing polymer content cement hydration products become indistinct, and microcracks appeared to be bridged-up by the polymer film.     

Gas-phase and liquid-phase hydration of C3A

In cement manufacturing an important problems is the tendency of cement to combine with water vapour during the grinding, transport and storage. Prehydrated cement may result in retardation of the strength development of the concrete.As it is mainly the clinker mineral C₃A which reacts with acqueous vapour, some experiments concerning hydration of C₃A in the gas phase and liquid phase have been carried out. Variable parameters were temperature, relative humidity and hydration time. The morphology and composition of the hydration products were characterized by using scanning electron microscopy, XRD and thermal analysis.During gas-phase hydration gel, hexagonal and cubic phases were formed. The liquid hydration products were shown to be identical whether the C₃A was almost pure or contaminated with minor components such as C₁₂A₇, free lime or chemically bound water formed during water-vapour hydration. However, if the amount of chemically bound water exceeds 3% the hydration products were anomalous showing rounded, irregular C₃AH₆ aggregates regardless of hydration conditions.The properties of the water-vapour hydrated C₃A might be connected with the retardation of strength when using prehydrated cement, but no possible mechanism has been found.     

Studies on premix water-soluble polymer cement pastes - I

Studies were carried out on the effect of adding some water-soluble polymers to the cement mix on some important physico-chemical and mechanical properties of the hardened pastes. The polymer was found to act as a retarder for hydration at early ages, then it acts as an accelerator. The compressive strength results were found to be affected by the nature of the hydration products, their degree of compaction, their average grain size, and by induced orientation of the crystallites. All these factors are affected by the presence of the polymer.     

Characterization and Utilization of Polystyrene and Polyacrylamide-Graft-Methoxypolyethylene as Cement Admixtures

A series of polystyrene-g-methoxypolyoxyethylene (PS-g-MPOE) was prepared by solution polymerization technique using benzoyl peroxide as an initiator and another series of polyacrylamide-g-methoxypolyoxyethylene (PAM-g-MPOE) was prepared by using potassium persulfate initiator. The prepared grafted copolymers were characterized by infrared (IR), thermogravimetric analysis (TGA) and rheological properties. The results illustrated that the solution of PS-g-MPOE in water behaved as a Newtonian fluid, but the solution of PAM-g-MPOE as pseudoplastic at higher acrylamide ratios. The TGA analysis showed that the thermal stability of PAM-g-MPOE was highest. Some of these polymers were evaluated as cement admixtures. The water of consistency and setting time of the cement pastes premixed with the polymers decreased sharply than those of the blank, i.e., these polymer admixtures can act as superplastisizers and at the same time as accelerators. The combined water and free lime contents as well as compressive strength of the cement pastes premixed with PS-g-MPOE or PAM-g-MPOE were slightly lower than the blank at the early ages up to 7 d, and then became higher during the later hydration ages. Their total porosities are higher during the early ages and lower during the later ages of hydration. The SEM images confirmed that the addition of the organic polymer solutions to the cement powder does not affect the chemical composition of the normal hydration products, but only affects the physical state, shape or morphology and size of crystals of the formed hydrates.     

The effects of nano-C-S-H with different polymer stabilizers on early cement hydration

A promising approach to accelerate cement hydration known as “seeding technology” has been discovered using nano-particles to provide additional nucleation sites for growing of C-S-H. Two different types of polymer, polycarboxylate (PCE) and polysulfonate (PSE) were used as stabilizer to synthesize nano-C-S-H via co-precipitation process. The obtained C-S-H-polymer composites were characterized by means of XRD, FTIR, thermogravimetric analysis (TGA), TEM, dynamic laser scattering (DLS), and BET. DLS measurement shows that the particle size of the obtained C-S-H-polymer suspension ranges from 82.6 to 589.9 nm. The results of DLS and BET show that the particle size of the C-S-H particles synthesized using PCE polymer as stabilizer is smaller than those synthesized with PSE polymer, and hence the specific surface area is much higher. FTIR and TGA results confirm the presence of the polymers in the obtained C-S-H composites particles. XRD results indicate that the presence of the polymers reduces the crystallinity of C-S-H due to the absence of the d002 peak at 2θ of 7°. The calorimetry results show that the main hydration peak of cement is dramatically increased by the addition of the C-S-H-polymer composites. It is interestingly found that the acceleration effect of the C-S-H-polymer composites is linearly proportional to the total surface area of the nanoparticles introduced into the cement pastes. At the same time, it is found that the secondary hydration peak, usually known as the sulfate-depletion peak, is greatly advanced by addition of the C-S-H nano-particles in comparison with the blank cement paste. The acceleration effect of the nano-C-S-H is further verified in a pure C₃S system.     

Retardation effect of styrene-acrylate copolymer latexes on cement hydration

Interactions between styrene-acrylate latexes and cement are investigated with emphasis of the charge properties of the polymer particles by means of calorimetry, adsorption measurement, and confocal laser scanning microscope. Three latexes with varied surface charges of polymer particles were prepared by respectively using methacrylic acid (MAA), sodium styrene sulfonate (SSS) and methyl poly(ethylene glycol) methacrylate (MPEGMA) as water soluble monomers during synthesis. It is found that the polymer latexes retard cement hydration in two manners, namely the delaying effect represented by a delayed hydration peak and the slowing down effect characterized by a reduced main hydration peak during the acceleration period. The delaying effect is closely related to the concentration of carboxylic groups existing in the latex, while the depression effect of hydration rate is majorly caused by the adsorption of polymer particles on surface of cement grains and proportional to the total charge density of polymer particles.     

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.     

环氧水泥砂浆的改性机理

通过对环氧改性水泥净浆的水化程度和砂浆的孔结构研究，借助于扫描电镜分析，探讨了聚合物对水泥砂浆的改性机理。聚合物的存在一方面延缓了水泥的水化速度，另一方面改善了硬化浆体的毛细孔结构，一部分聚合物在硬化浆体中形成不连续的薄膜。所以聚合物的改性作用是上述两方面的综合作用。