The effect of chemical composition on portland cement clinker grindability

The relationship between specific power consumption (kWh/t) and Blaine fineness attained during grinding of the Portland clinker is represented by an exponential function. This function varies by stages. For each stage the following equation may be written: In kWh/t = a + bS, where S is the Blaine fineness and a and b are constants assuming different values at each stage. The values of these constants for the first stage, up to about 250 m²/kg Blaine, are not significantly affected by the chemical composition of the clinker, while at the second stage, about 250 – 500 m²/kg Blaine, the values of the constants are affected by C₃A, C₄AF, K₂O and MgO contents.     

Reliable specific surface area measurements on anhydrous cements

The specific surface area (SSA) of anhydrous cement has a direct impact on its reactivity and on the properties of fresh and hardened concrete. However, measuring this physical parameter is non-trivial.The choice of the degassing conditions (temperature, pressure and time) is essential for reliable SSA measurements by nitrogen adsorption because of the dehydration of the gypsum it contains. Such dehydration involves a significant increase of the SSA_BET, whereas Blaine test is poorly sensitive to the hydration state and structural modification of the calcium sulfate carrier. Because of this, SSA_BET values may be more variable than Blaine fineness. More consistent SSA_BET results could be obtained by degassing anhydrous cement samples at 40 °C under N₂ flow for 16 h, as at these conditions the cement composition is preserved.     

Differential comminution of gypsum in cements ground in different mills

Identical mixes containing fixed amounts of ordinary Portland cement clinker and gypsum were ground in two types of industrial cement mills—viz. ball mill (BM) and vertical roller mill (VRM)—to identical Blaine fineness to examine the effect of any possible differential comminution of gypsum on cement setting times. The present investigation demonstrates that during comminution of cements, the degree of crystallinity of gypsum, as determined by X-ray diffraction (XRD), changes with used grinding mills and this causes changes in setting times of similar cements even when ground to identical Blaine fineness.     

助磨介质作用下旋窑熟料微细化过程及其效果评价

通过对助磨介质作用下不同粉磨细度的旋窑熟料所配制的硅酸盐水泥的物理性能检测,对助磨介质作用下旋窑熟料的微细化效果进行了评价。结果表明,对水泥熟料来说,早期的快速水化不一定能得到高强度的水泥,因此熟料微细化的评价要从水化性能和粉磨能耗上综合考虑,在实验中,旋窑熟料的最佳粉磨细度为5 000m2/g,而加入助磨剂可显著降低粉磨能耗,在达到同样效果时缩短25％的粉磨时间。     

Modeling the coupled effects of temperature and fineness of Portland cement on the hydration kinetics in cement paste

This paper revisits the coupled impacts of fineness and temperature on the kinetics of Portland cement hydration. The approach consists in i) modeling the impact of fineness on cement dissolution through the hypothesis that the surface dissolution rate of cement particles is independent of their size, in order to, in a second step, ii) model the impact of temperature on the kinetics of cement dissolution. The analysis of the experimental results shows that the effect of cement fineness on the hydration kinetics can be captured by a simple hypothesis: for any age, the reacted thickness of cement grains can be considered independent of the initial cement particle size. In addition, the analysis of the results at different temperatures shows that a constant activation energy can account for the effect of temperature on the hydration kinetics, with an Arrhenius equation applied to the kinetics of surface dissolution. The results from the model give a good agreement with the experimental results in a significant number of combinations (different Portland cements, water/cement ratio from 0.5 to 0.6, cement Blaine fineness from 3500 to 6600 cm²/g, temperature histories between 20 and 60 °C).     

Effects of slag content,fineness and additive to cement pastes on the corrosion behaviour of embedded reinforcing steel

Previous studies proved that the slag content of the blast furnace slag-Portland cement mix could be increased, while retaining the engineering properties of the produced slag cement pastes within the normal range and increasing the fineness of the mix. The corrosion behaviour of reinforcing steel embedded in the cement pastes giving the optimum mechanical properties was studied using the galvanostatic polarisation technique. The most corrosion-resistant mix has been determined. The effect of adding CaCl₂ to a paste of this mix on the corrosion behaviour of embedded reinforcing steel has been investigated. For the purpose of comparison, anodic polarisation tests were carried out using pastes having the composition of the most corrosion-resistant mix but at the Blaine area of the ordinary slag cement. Portland and normal slag cements were also tested. The threshold concentration of CaCl₂, below which breakdown of steel passivity did not occur, has been determined. The results of this study might have practical implications in the field.     

Influence of the fineness of sewage sludge ash on the mortar properties

Sewage sludge ash (SSA) is a recycled material and can be used in cement mortar as pozzolan. To improve the mortar properties, this research utilized mechanical grinding to adjust the fineness of SSA. Finely ground SSA with Blaine fineness of 500-1000 m²/kg was added to mortar to replace 20% of portland cement. The initial and final setting times of SSA-cement paste simultaneously prolonged when SSA fineness increased. Because of the lubricant effect and morphology improvement, the workability of SSA mortar increased when fineness increased. In addition, the pozzolanic activity of SSA and the compressive strength of mortar increased when SSA fineness did. The strength activity index (SAI) value approximately increased 5% when SSA fineness increased per 100 m²/kg. According to the results, the application of mechanical grinding to adjust SSA fineness was an effective modification to improve SSA mortar properties including workability and compressive strength.     

The effect of grinding process on mechanical properties and alkali–silica reaction resistance of fly ash incorporated cement mortars

The effect of fineness of fly ash on mechanical properties and alkali–silica reaction resistance of cement mortar mixtures incorporating fly ash has been investigated within the scope of this study. Blaine fineness of fly ash has been increased to 907 m²/kg from its original 290 m²/kg value by a ball mill. Test samples were prepared by replacing cement 20, 40 and 60%, with finer and coarser fly ashes and kept under standard and steam curing conditions until testing. Test results showed that grinding process improved the mechanical properties of all samples significantly. The beneficial effect of grinding fly ash, may increase utilization of this by-product in precast and ready-mix concrete industries. Incorporation of fly ash with different fineness values and ratios also decreased the expansions to harmless levels of cement mortars due to alkali–silica reaction.     

Superplasticized portland cement: production and compressive strength of mortars and concrete

This paper deals with the effect of intergrinding different percentages of a naphthalene-based superplasticizer with Portland cement clinker and gypsum on the fineness of the product, and on the water requirement and the compressive strength of the mortars made with the superplasticized cement. The properties of the fresh and hardened concrete made with the superplasticized cements were also investigated. The results showed that the intergrinding of a given amount of a naphthalene-based superplasticizer with Portland clinker and gypsum reduced the grinding time required for obtaining the same Blaine fineness as that of the control Portland cement without the superplasticizer. The water requirement of the mortars made with the superplasticized cements was similar to that of the mortars made with the control Portland cements when the same amount of the superplasticizer was added at the mortar mixer; for a given grinding time and a Blaine fineness of 4500 cm²/g, the mortars made with the superplasticized cement had higher compressive strength than those made with the control Portland cement. For a given grinding time or Blaine fineness of cement ≥5000 cm²/g, the slump loss, air content stability, bleeding, autogenous temperature rise, setting times, and compressive strength of the concrete made with the superplasticized cements were generally comparable to those of the concrete made with the control Portland cements when the superplasticizer was added at the concrete mixer.     

Electrochemical nucleation from molten salts—II: Time dependent phenomena in electrochemical nucleation

The double pulse potential step method has been used to investigate the kinetics of nucleation of metal deposition from molten salts and from aqueous solution. The time lag or induction period, τ₀, required for the growth of stable nuclei was determined as a function of overpotential. η. The relationship between log τ₀ and η was found to be markedly non-linear and the existing theory is re-examined and modified to allow for the effect of nucleus size and interfacial tension on the charge-transfer kinetics themselves.     

Effect of Blaine fineness of recycling brick powder replacing cementitious materials in self compacting mortar

The present study aims to investigate the use of recycling brick powder (RBP) as a fractional replacement of cement in self compacting mortar. Cement was replaced by recycling brick powder in different proportions (0, 5, 10, 15 and 20%) by weight of cement. Three Blaine fineness (SSB) were used in this study (3900, 4300, and 5200 cm²/g). The experimental results showed that the substitution of cement by recycling brick powder with higher content (20%) decreases the workability of self compacting mortar (about 3%) and reduces its passing ability (about 30%). On the other hand, the increase of Blaine fineness of (RBP) led to improve the Fresh behaviour of mortars when the content of recycling brick powder kept constant. Mechanical performances of mortars in terms of compressive and tensile strength were improved by 13 and 105% respectively. Economically, the substitution of cement with 10% of brick powder gives a win of 10% of cement with an increase of 13% in compressive strength and 107% in tensile strength.     

固硫灰做水泥混合材及缓凝剂的研究

研究固硫灰做水泥混合材及缓凝剂,其细度和掺量对水泥性能的影响.试验结果表明,10％～30％不同细度的固硫灰掺入硅酸盐水泥熟料中后,所制备的水泥安定性合格、凝结时间正常;强度随着细度的增加而增加,随着掺量的增加先增加后降低;磨细处理有利于降低水泥的总膨胀能.同时通过研究发现,固硫灰的掺量和细度对水泥早期水化产物的形成有较大的影响,掺磨细固硫灰水泥所形成的AFt是粗大的针棒状结构,而掺未磨细固硫灰水泥形成细小的AFt和大量的AFm.     

Effect of large amounts of natural pozzolan addition on properties of blended cements

In this study, the effects of 35, 45, and 55 wt.% natural pozzolan addition on the properties of blended cement pastes and mortars were investigated. Blended cements with 450 m²/kg Blaine fineness were produced from a Turkish volcanic tuff in a laboratory mill by intergrinding portland cement clinker, natural pozzolan, and gypsum. The cements were tested for particle size distribution, setting time, heat of hydration, compressive strength, alkali-silica activity, and sulfate resistance. Cement pastes were tested by TGA for Ca(OH)₂ content and by XRD for the crystalline hydration products. The compressive strength of the mortars made with blended cements containing large amounts of natural pozzolan was lower than that of the portland cement at all tested ages up to 91 days. Blended cements containing large amounts of pozzolan exhibited much less expansion with respect to portland cement in accelerated alkali-silica test and in a 36-week sulfate immersion test.     

Influence of the fineness of pozzolan on the strength of lime natural-pozzolan cement pastes

The fineness of a cement is an important factor affecting the rate of strength development. This paper examines the importance of the fineness of natural pozzolans to the strength development of lime-pozzolan cements (LPCs). A natural pozzolan from Bolivia, which is typical of natural pozzolans found in South and Central America, was ground to various finenesses, blended with lime with a mass ratio of 80:20, and the resulting LPC was used to make hardened cement paste cylinders. In some pastes 4% sodium sulphate or 4% sodium chloride activator was used to enhance strength development. Strength of the cylinders were measured at ages from 3 to 90 days during continuous moist curing at 50°C. The experimental results show that there is a good linear correlation between the Blaine fineness of the natural pozzolan and compressive strength at all ages and for all pastes. The fineness of the natural pozzolan has its most significant effect on early strength gain. The addition of chemical activator increases both the rate of strength gain and the sensitivity of strength gain to fineness.     

Correlating cement characteristics with rheology of paste

The influence of cement characteristics such as cement fineness and clinker composition on the “flow resistance” measured as the area under the shear stress-shear rate flow curve has been investigated. Three different types of plasticizers namely naphthalene sulphonate-formaldehyde condensate, polyether grafted polyacrylate, and lignosulphonate have been tested in this context on 6 different cements. The flow resistance correlated well with the cement characteristic (Blaine·{d·cC₃A + [1 − d]·C₃S}) where the factor d represents relative reactivity of cubic C₃A and C₃S while cC₃A and C₃S represent the content of these minerals. It was found to be either a linear or exponential function of the combined cement characteristic depending on plasticizer type and dosage. The correlation was valid for a mix of pure cement and cement with fly ash, limestone filler (4%), as well as pastes with constant silica fume dosage, when the mineral contents were determined by Rietveld analysis of X-ray diffractograms.     

Microwave dielectric relaxation in binary mixtures of poly(ethylene glycols) in solution

The average relaxation time τ₀, relaxation times corresponding to segmental motion τ₁ and group rotations τ₂, of a series of binary mixtures of poly(ethylene glycols) (PEG 200+PEG 300, PEG 400+PEG 600, PEG 1500+PEG 4000, PEG 6000+PEG 9000, PEG 200+PEG 1500, PEG 300+PEG 4000, PEG 400+PEG 6000 and PEG 600+PEG 9000) have been carried out in dilute solutions of benzene and carbon tetrachloride at 9·83GHz. The effect on chain flexibility due to inter- and intra-molecular association in these binary mixtures is discussed by comparing relaxation times of these mixtures with their individual relaxation times in solution. It is inferred that the extent of hydrogen bonding in different binary mixtures is not similar and is influenced by solvent environment, but there is correlation between τ₀ and τ₁ values in all these binary mixtures, which may be because of hydrogen bonding. The observed τ₂ values in all these mixtures suggests that the chain-ends remain excluded from the intermolecular association and τ₂ is independent of the polymer constituents of the mixture and solvent. It is also equal to the τ₂ values of the individual polymers. © 1998 SCI.     

Long-range hydrodynamic response of particulate liquids and liquid-laden solids

In viscous particulate liquids, such as suspensions and polymer solutions, the large-distance steady-state flow due to a local disturbance is commonly described in terms of hydrodynamic screening—beyond a correlation length ξ the response drops from that of the pure solvent, characterized by its viscosity η₀, to that of the macroscopic liquid with viscosity η > η₀ For cases where η >> η₀ we show, based on general conservation arguments, that this screening picture, while being asymptotically correct, should be refined in an essential way. The crossover between the microscopic and macroscopic behaviors occurs gradually over a wide range of distances, ξ < r < (η / η₀)^1/2 ξ In liquid-laden solids, such as colloidal glasses, gels, and liquid-filled porous media, where η → ∞, this intermediate behavior takes over the entire large-distance response. The intermediate flow field, arising from the effect of mass displacement rather than momentum diffusion, has several unique characteristics: (i) It has a dipolar shape with l/r ³ spatial decay, negative transverse components, and vanishing angular average. (ii) Its amplitude depends on the liquid properties through η₀ and ξ alone; thus, in cases where ξ is fixed by geometry (e.g., for particulate liquids tightly confined in solid matrices), the large-distance response is independent of particle concentration. (iii) The intermediate field builds up non-diffusively, with a distance-independent relaxation rate, making it dominant at large distances before steady state has been reached. We demonstrate these general properties in three model systems.     

Open and closed circuit dry grinding of cement mill rejects in a pilot scale vertical stirred mill

In this study, separator rejects of a closed circuit cement tube milling were dry ground in a 10-l pilot scale vertical stirred mill. Tests were done as open and closed circuit. The results were evaluated by size distributions, Blaine surface area of the products and the specific energy consumed during the tests. Mill capacity and the stirring speeds were the investigated parameters for the open circuit tests, whereas closed circuit tests were carried out at a constant stirring speed but variable discharge rate. Five speed levels used in the open circuit grinding tests are 200, 400, 600, 800 and 1000 rpm. The capacities were determined to obtain product Blaine surface areas in the limits between 2000 and 5000 cm²/g. Closed circuit tests have resulted in 87%, 182% and 452% circulating loads.     

Hardened Portland blast-furnace slag cement pastes II. The corrosion behavior of steel reinforcement

The corrosion behavior of reinforcing steel embedded in various slag cement pastes was studied using the galvanostatic polarization technique. The corrosion resistance is appreciably affected by the degree of fineness of the dry slag cement. In pastes produced from high Blaine area cement, the behavior of embedded steel was very close to that in normal or type I portland cement paste, and is much better than a low Blaine area cement. W/C ratios of 0.25 and 0.40 provided a better passivating medium as compared with W/C ratios of 0.18 and 0.70. Effects of lime or gypsum addition were also investigated and comparatively studied for their action on the corrosion of embedded steel. The results obtained were supported by corrosion rates obtained using the linear polarization technique.     

The effect of particle size distribution on the properties of blended cements incorporating GGBFS and natural pozzolan (NP)

This paper investigates the effect of particle size distribution on the properties of blended cements incorporating ground granulated blast-furnace slag (GGBFS) and natural pozzolan (NP). Pure Portland cement (PPC), NP and GGBFS were used to obtain blended cements that contain 10, 20, 30% additives. The cements were produced by intergrinding and separate grinding and then blending. Each group had two different Blaine fineness of 280 m²/g and 480 m²/g. According to the particle size distribution (PSD) curves, 46% of the coarser specimens and 69% of the finer specimens passed through the 20 μm sieve. It was observed that the separately ground specimens were relatively finer than the interground ones and had higher compressive strength and sulfate resistance. The separately ground coarser specimens had the lowest heat of hydration. The separately ground finer specimens, which had the highest compressive strength and sulfate resistance, had the highest percent passing for each sieve size. For these specimens 34, 69, 81 and 99% passed through 5, 20, 30 and 55 μm sieves, respectively. For the interground specimens, which had the same fineness, the respective values for the same sieves were 32, 68, 75 and 94%.