Morphology and microstructure of autoclaved slag-clinker pastes in presence and absence of silica sand

Morphology and microstructure of autoclaved slag-clinker and slag-clinker-sand mixtures were undertaken using scanning electron microscopy. The microstructure of autoclaved slag-clinker hydration products displayed nearly amorphous, fibrous and radial plates of CSH phase, large cubes of hydrogarnet-like hydrates (mainly as C₃ASH₄) as well as hexagonal precipitations of calcium hydroxide. The hydration of slag-clinker-sand mixture (an optimum composition) was associated with the formation of semi-crystalline low-lime tobermorite (mainly as CSH(I)) as well as fibrous and massive plates of crystalline 11Å tobermorite as the main hydration products. The strength development could also be related with the microstructure of the formed hydrates.     

Hydration of low porosity slag-lime pastes

Slag-lime pastes of low porosity (water/solid ratio of 0.20) were hydrated from 6 hours to 180 days at 20°C. The kinetics and mechanisms of the hydration process were studied from the results obtained in this investigation. The depth of the hydrated layer on the slag particles is found to be thin indicating that the hydration reaction is very slow. The molar compositions of the formed hydrates could also be calculated from the free lime, nonevaporable water and uncombined slag contents. A high lime product (molar C/S+A ratio of 2.5–2.6) is formed during the early stage of the hydration process, then the molar C/S+A ratio drops to a value of 1.5 and finally rises to a value of 1.7 at 180 days. The surface areas and pore volumes of hydrates were determined from water and nitrogen adsorption measurements. For water vapor adsorption, the water molecules in the adsorbed phase seem to be highly oriented in an ordered array. This effect might be associated with the polar character of water molecule, when adsorbed on an ionic surface like high lime hydrate. The results of x-ray diffraction and SEM observations indicate only the formation of ill-cyrstallised hydration products.     

Mechanical properties in relation to the microstructure of fibre reinforced portland clinker pastes

Portland clinker was mixed with various water/clinker ratios ranging between 0.7 to 0.2 covering the range for both “normal” and “low” porosity pastes. These pastes were reinforced with five kinds of fibres, all with weight percentages of 0.5 and 3.0. All the samples were tested for compressive and tensile strengths, total porosity, microstructure and degree of hydration. Fibre reinforcement led to an increase in the total porosity and a decrease in the degree of hydration as compared with the neat pastes. Also, compressive strength has to be sacrificed to a certain extent in order to obtain better flexural strength. SEM furnished direct evidence that fibre reinforcement could affect the pore structure, the habit and shape of the hydration products, as well as their spatial distribution. The indication gained is that the mechanical behavior of the mix is due mainly to changes in the physicochemical properties induced by the presence of fibres.     

Hardened alite pastes of various porosities II. Morphology and microstructure

The hardened alite pastes were prepared by using initial water:alite ratios of 0.20, 0.30, 0.45 and 0.60. The microstructures of the low and high porosity pastes were investigated by scanning electron microscopy. The results obtained indicated that the cementing system is really a composite material having a structure controlled by the total pore system of the hardened paste. In low porosity pastes, the hydration products are semi-crystalline; whereas in high porosity pastes, the hydration products possess a massive tabular structure.     

Low-frequency electrical conductivity of cement,clinker and clinker mineral pastes

The electrical conductivity of pastes made of various types of portland cement and clinkers, as well as clinker minerals in the presence and absence of various admixtures was studied. In the investigated range of frequencies (100 Hz − 10 kHz) conductance increases after mixing with water to be followed by a steady decrease. This decrease in some cements is interrupted by a short, transient second increase. The time of this transient maximum (TM) of conductivity can be changed by temperature, grinding fineness, admixtures, carbonation, etc. The intensity of the TM can be reduced or the TM totally eliminated by the addition of gypsum. Clinker + gypsum mixtures show TM in case of a ‘critical’ gypsum content. The effect of accelerators (e.g., calcium chloride, sodium formate) and of retarders (e.g., citric acid) on the conductivity vs. time graphs is shown.     

Effects of densified silica fume on microstructure and compressive strength of blended cement pastes

Some experimental investigations on the microstructure and compressive strength development of silica fume blended cement pastes are presented in this paper. The silica fume replacement varies from 0% to 20% by weight and the water/binder ratio (w/b) is 0.4. The pore structure by mercury intrusion porosimetry (MIP), the micromorphology by scanning electron microscopy (SEM) and the compressive strength at 3, 7, 14, 28, 56 and 90 days have been studied. The test results indicate that the improvements on both microstructure and mechanical properties of hardened cement pastes by silica fume replacement are not effective due to the agglomeration of silica fume particles. The unreacted silica fume remained in cement pastes, the threshold diameter was not reduced and the increase in compressive strength was insignificant up to 28 days. It is suggested that the proper measures should be taken to disperse silica fume agglomeration to make it more effective on improving the properties of materials.     

Morphology and properties of nylon6 and high density polyethylene blends in absence and presence of nanoclay

The morphology and properties of nylon6/HDPE blends without and with nanoclay has been reported. Scanning electron microscopy study of the (70/30 w/w) nylon6/HDPE blends with small amount (0.1 phr) of nanoclay indicated a reduction in the average domain sizes (D) of dispersed HDPE phase and hence better extent of mixing compared to the blend without any nanoclay. X‐ray diffraction study and transmission electron microscopy revealed that nanoclay layers were mostly located in nylon6 matrix of the (70/30 w/w) nylon6/HDPE blend. However, the same effect of nanoclay on the morphology was not observed in (30/70 w/w) nylon6/HDPE blend where HDPE became the matrix. In (30/70 w/w) nylon6/HDPE blend, addition of nanoclay increased the D of dispersed nylon6 domains by preferential location of the clays in side the nylon6 domains. Thus, the clay platelets in the matrix phase acted as barrier that restricted the coalescence of dispersed domains during melt‐mixing. Addition of PE‐g‐MA in both the compositions of nylon6/HDPE blend effectively reduced the D of dispersed phases. Storage modulus and thermal stability of the blend were improved in presence of small amount of clay, whereas addition of PE‐g‐MA lowered the mechanical and thermal properties of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of silica fume on the microstructure of cement pastes: New insights from 1H NMR relaxometry

¹H NMR has been used to characterise white Portland cement paste incorporating 10 wt.% of silica fume. Samples were measured sealed throughout the hydration without sample drying. Paste compositions and C–S–H characteristics are calculated based on ¹H NMR signal intensities and relaxation analysis. The results are compared with a similar study of plain white cement paste. While the presence of silica fume has little influence on C–S–H densities, the chemical composition is impacted. After 28 days of sealed hydration, the Ca/(Si + Al) ratio of the C–S–H is 1.33 and the H₂O/(Si + Al) ratio is 1.10 when 10% of silica fume is added to the white cement. A densification of the C–S–H with time is observed. There are no major changes in capillary, C–S–H gel and interlayer pore sizes for the paste containing silica fume compared to the plain white cement paste. However, the gel/interlayer water ratio increases in the silica fume blend.     

Morphology and mechanical properties of polyamide 12/polypropylene blends in presence and absence of reactive compatibiliser

Blends of polyamide 12 (PA12) and isotactic polypropylene (PP) were prepared by melt mixing in an internal mixer in presence and absence of compatibilisers. The compatibiliser used was maleic anhydride functionalised polypropylene (PP-g-MA). Effect of compatibilisation on the blends has been evaluated from the morphological parameters derived from scanning electron micrographs (SEM) of cryogenically fractured and extracted surfaces of the specimens. The uncompatibilised blends showed two-phase unstable morphology due to high interfacial tension and coalescence effects in the absence of favourable interactions at interface between the individual phases. Incompatibility increased as the concentration of dispersed phase in the blend increased. Compatibilisation stabilised the morphology by reducing the particle size as well as interparticle distance and enhancing the interfacial area and interface adhesion. A critical concentration of compatibiliser required for effective compatibilisation (CMC) was observed beyond which there was no net improvement in interfacial properties and was considered as the point of interfacial saturation. Experimental results were compared with the compatibilisation theories of Noolandi and Hong and Leibler and based on the calculated average interfacial area occupied per compatibiliser molecule it was concluded that the molecular state of compatibiliser at interface changed with concentration. It was supported by the rate constant for change in interfacial tension (K) values which experienced a maximum at CMC followed by drastic reduction. Mechanical properties of the uncompatibilised blends showed inferior properties. It was found that compatibilisation significantly improved the mechanical properties. A good correlation has been observed between the mechanical properties and morphological parameters.     

On the frictional contribution to the viscosity of cement and silica pastes in the presence of adsorbing and non adsorbing polymers

This paper is devoted to the role of hydrodynamic lubrication in the flow of dense suspensions of non-Brownian cement or silica particles. The role of hydrodynamic lubrication is ambiguous since it is primarily a source of viscous dissipation but, by preventing direct contact between particles and friction, it may facilitate flow. We show that in the concentration and shear rate regimes investigated here direct contact friction between cement or silica particles is contributing to the overall energy dissipation. Addition of water-soluble polymers, either adsorbing or not adsorbing, was used as a mean to control friction. We show that, independently of the adsorption capacity of the polymer, it is the non adsorbed polymer which, thanks to hydrodynamic lubrication, prevents direct contacts and reduces the overall energy dissipation. This leads to the counterintuitive situation where by increasing the interstitial fluid viscosity, the suspension viscosity is decreased. When hydrodynamic lubrication is no longer able to avoid direct frictional contact, dilatant and shear-thickening behaviors set in.     

Fracture toughness of autoclaved portland cement/silica mixtures

Fracture toughness measurements made at 11% RH on autoclaved cement/silica mixtures having a wide range of silica contents and porosities yielded a series of curves for K_c versus porosity and K_c versus silica content. Those for preparations having low porosity and silica content were unique. Apparently αC₂S-hydrate, unreacted silica and pores having specific size distribution can act as crack arrestors. K_c versus hardness curves were similar to those for K_c versus porosity. Simple microhardness tests may be useful in predicting fracture toughness of autoclaved cementitious systems.     

率值及氧化镁含量对高镁熟料压蒸膨胀性能的影响研究

本文研究了MgO含量和熟料三率值对高镁熟料压蒸膨胀性的影响。81组高镁熟料结果显示：煅烧条件相同时,影响压蒸膨胀性的顺序为MgO含量﹥IM﹥KH﹥SM,MgO含量和IM是影响压蒸膨胀率的主要因素;采用岩相观测、XRD精修定量、BSE、EDS等微观测试对方镁石在熟料中的晶体生长环境和压蒸膨胀的关系进行了研究,发现方镁石被C₃A与C₄AF掺杂交错的中间相包裹时,压蒸膨胀率较低,当条状、板状C₃A相增加,掺杂交错的中间相减少,方镁石主要被C3A相包裹时,压蒸膨胀率增大。     

硅石在中热硅酸盐水泥熟料生产中的应用

中热硅酸盐水泥熟料生产对原材料要求较严格,但是因周边矿产资源紧缺,导致原有生产用重要硅质材料较难采购,为解决这一问题,采用了硅石进行中热硅酸盐水泥熟料生产.结果表明,利用硅石作为硅质材料生产的中热硅酸盐水泥,碱含量低,水泥后期强度增长好,水化热低.     

河沙在水泥熟料生产中的应用

流经河南焦作的沁河常年要向黄河中带入大量泥沙,为了减少泥沙对沁河、黄河河床的影响,地方政府每年都需投入一定财力治理河道淤积.用河沙作为生产水泥熟料的硅质原料,既可以减少河道淤积,又可变废为宝改善环境.为利用易磨性较差的河沙,我公司5000t/d生产线特意增大了投资,生料磨系统选用ATOX52.5立磨,比其它同规模生产线(ATOX52.0)大了一个型号,主机装机4300kW,比ATOX52.0大200kW左右.     

废渣配料对高镁熟料压蒸膨胀性能的影响研究

使用钢渣、铜渣、矿渣和镁渣进行生料配料,检测了不同废渣对熟料MgO含量为6％的高镁熟料压蒸膨胀性能的影响,结果显示在相同煅烧条件下,四种废渣与对比样相比均降低了高镁熟料的压蒸膨胀率,其中铜渣、矿渣和镁渣对压蒸膨胀率的降低效果优于钢渣;同时通过岩相、XRD定性定量分析、BSE和EDS对熟料中的矿物组成、含量及颗粒尺寸分布...     

高硅沸石在生产优质熟料中的应用

一种高硅沸石与河沙的化学成分十分相近,两次高硅沸石替代河沙配料试磨和窑上试烧的结果表明:高硅沸石配料既利于粉磨又利于煅烧,完全可以替代河沙配料生产优质水泥熟料。高硅沸石质量成分稳定,碱等有害成分较低,储量丰富、价格便宜,增产节能效果十分突出。     

Some comments on the microstructure of hardened cement pastes

The effect of water/cement ratio of hardened cement pastes in the range 0.23 to 0.71 on the micropore structure as revealed by mercury intrusion and nitrogen adsorption porosimetry is discussed. The relationship between these micropores and the solid minerals as revealed by electron microscopy is also discussed.     

还原气氛对水泥熟料矿物组成及显微结构的影响

通过化学全分析、XRD和岩相分析等试验手段，探讨了烧成气氛对水泥熟料的化学成分、矿物组成和显微结构的影响。研究结果表明：在还原气氛下烧成的熟料中，Fe^3＋被还原成Fe^2＋，阿利特发生较严重的分解，形成二次贝利特和fCaO，C3A含量相应增加，同时导致A矿晶体尺寸偏小，晶形发育不良。与氧化气氛烧成熟料相比，还原气氛下烧成的熟料中FeO的含量增加1．60％，fCaO增加了1．71％；Bogue法计算的矿物组成和XRD分析结果显示，C3S、CAF含量降低，C2S、C3A含量明显增加。还原气氛烧成的熟料在水化初期放热迅速，前14h的放热总量明显大于正常煅烧熟料，但14h后水化放热量却明显低于正常烧成的熟料。还原气氛烧成的熟料颜色发黄，强度偏低，易磨性差，凝结时间较短。     

Investigations on the performance of silica fume-incorporated cement pastes and mortars

Studies on the performance of cementitious products with silica fume (SF) are very important, as it is one of the inevitable additives to produce high-performance concrete (HPC). In this study, some experimental investigations on the influence of SF on various preliminary properties of cement pastes and mortars are reported. The properties included specific gravity and normal consistency (NC) of cement and air content and workability of mortar with different SF contents. Pozzolanic and chemical reactions of SF have been studied on setting times, soundness and shrinkage of cement pastes. Further, strength developments in compression and tension in cement mortars have also been studied at various SF contents. SF was varied from 0% to 30% at a constant increment 2.5/5% by weight of cement. Test results show that the SF changes the behavior of cement pastes and mortars significantly. It has been observed that the water-binder (w/b) (cement+SF) ratio seemed to play an important role for the performance of the products with higher SF contents. NC, soundness and drying shrinkage of cement pastes and the strength of mortar increase as the SF content increases, while the initial setting times of cement pastes and the air content and workability of mortar decrease as the SF content increases. However, hardly any influence has been observed on the final setting times of cement pastes. The early age hydration reactions of C₃A and C₃S increase with the addition of SF. The optimum SF content ranges between 15% and 22%.