Sulfate resistance of plain and blended cement

This paper presents a laboratory study on the sulfate resistance of blended cement combination of reference Portland cement with high volume ground granulated blast-furnace slag (GGBS) and natural pozzolan (NP). The exposure solutions were tap water containing 5% magnesium sulfate solution and 5% sodium sulfate solution. Two types of grinding method (separately grinding and intergrinding, two finenesses (250 m²/kg and 500 m²/kg) and three different proportions (10%, 20%, and 30% by weight of mixture)) of each of two different additives (GGBS and NP) in equal amounts were employed. In addition to these blends, plain Portland cements without additives were prepared as references specimens. Standard Rilem sample size (40 mm × 40 mm × 160 mm) was used for the experimental study.It was observed that the sulfate resistances of blended cements were significantly higher both against sodium sulfate and magnesium sulfate attacks than references cement. Final strength reductions for finer mixes attacked by magnesium sulfate were marginally lower than those attacked by sodium sulfate. On the other hand, no particular relation was found between the sulfate resistance of the mortars and the grinding methods.     

Influence of dry and wet grinding conditions on fineness and shape of particle size distribution of product in a ball mill

The influence of grinding conditions on the production of fine particles and the width of the particle size distribution produced during ball mill grinding was investigated. The grinding experiments were carried out varying the grinding ball diameter under dry and wet conditions. The relation between the weight passing size observed in an arbitrary cumulative undersize fraction and the grinding time was expressed by modifying Tanaka’s semi-theoretical equation for the grinding limit. The fineness of the product was evaluated by the median particle size in undersize distribution, and the shape of the particle size distributions by three different size ratios calculated using 10%, 20%, 50%, 80% and 90% cumulative weight passing sizes, that showed the width of the particle size distribution. The median particle sizes of product obtained for the grinding limit in wet and dry conditions were around 0.5–0.6 μm and 2 μm, respectively. The width of the particle size distribution in wet grinding decreased with decreasing median particle size of the ground product, and the size distribution in dry grinding became nearly constant. The particle size distribution width was lowered by using smaller grinding balls in wet condition and larger grinding balls in dry condition.     

Grinding effects on the change of particle properties in cupric sulfide,CuS

Cupric sulfide, CuS, was ground by a planetary ball mill under various experimental conditions, including variations in rotation speed and grinding time. The changes in crystal structure, lattice parameter, particle size, pore structure, and specific surface area in the ground powders were determined. With regard to the CuS ground at 700 rpm, the changes of the crystal structure were more remarkable than those of the CuS ground at 300 rpm. The crystallite size decreased (from 18.5 to 8.4 nm) and the lattice strain increased (from 1.60% to 3.09%) in the CuS ground at 700 rpm. Moreover, the lattice parameter a increased, while the lattice parameter c decreased. Grinding at 300 rpm is favorable for inducing changes of the physical properties, such as the growth of pore volume and specific surface area.     

Rheological and hydration characterization of calcium sulfoaluminate cement pastes

Calcium sulfoaluminate (CSA) cements are currently receiving a lot of attention because their manufacture produces less CO₂ than ordinary Portland cement (OPC). However, it is essential to understand all parameters which may affect the hydration processes. This work deals with the study of the effect of several parameters, such as superplasticizer (SP), gypsum contents (10, 20 and 30 wt.%) and w/c ratio (0.4 and 0.5), on the properties of CSA pastes during early hydration. This characterization has been performed through rheological studies, Rietveld quantitative phase analysis of measured X-ray diffraction patterns, thermal analysis and mercury porosimetry for pastes, and by compressive strength measurements for mortars. The effect of the used SP on the rheological properties has been established. Its addition makes little difference to the amount of ettringite formed but strongly decreases the large pore fraction in the pastes. Furthermore, the SP role on compressive strength is variable, as it increases the values for mortars containing 30 wt.% gypsum but decreases the strengths for mortars containing 10 wt.% gypsum.     

Effect of grinding conditions on mechanochemical grafting of poly(1-vinyl-2-pyrrolidone) onto quartz particles

Grinding of quartz in an aqueous solution of 1-vinyl-2-pyrrolidone (VP) in a stirred media mill results in grafting of poly(1-vinyl-2-pyrrolidone) (PVP) onto the quartz particles as proven by FTIR-spectroscopy. The grinding kinetics, the particle size of the final product and the amount of PVP grafted onto the silica particles depend on grinding conditions like VP and quartz concentration, pH and size of grinding media. The grinding kinetics becomes slower in the presence of VP due to the damping effect of the forming PVP chains. The final particle size, however, is almost independent on VP concentration. The amount of PVP grafted onto the silica particles ground for 12 h increases with growing VP concentration because the amount of adsorbed VP and the polymerization rate increase with growing VP concentration.The primary particle size and the kinetics of particle breakage do not depend on the pH-value of the dispersing medium, whereas the degree of agglomeration of the particles decreases with increasing pH-value of the medium. Under alkaline conditions, however, less PVP is grafted onto the quartz particles than under neutral or strong acidic conditions. The reasons for these effects are pH-dependent interactions between the grafted PVP chains and the surface hydroxyl groups on the quartz particles. If the quartz concentration in the suspension decreases the grinding kinetics becomes much faster because the specific energy input increases with decreasing particle concentration if the other process parameters are kept constant. For a very low quartz concentration (1 wt.%), however, after 7 h of grinding the particle size measured by dynamic light scattering starts to increase with grinding time. SEM investigations reveal that grinding of 1 wt.% quartz in aqueous VP solution for longer than 7 h results in the formation of plate-like particles.     

Early carbonation curing of concrete masonry units with Portland limestone cement

The effect of carbonation curing on the mechanical properties and microstructure of concrete masonry units (CMU) with Portland limestone cement (PLC) as binder was examined. Slab samples, representing the web of a CMU, were initially cured at 25 °C and 50% relative humidity for durations up to 18 h. Carbonation was then carried out for 4 h in a chamber at a pressure of 0.1 MPa. Based on Portland limestone cement content, CO₂ uptake of PLC concrete after 18 h of initial curing reached 18%. Carbonated and hydrated concretes showed comparable compressive strength at both early and late ages due to the 18-h initial curing. Carbonation reaction converted early hydration products to a crystalline microstructure and subsequent hydration transformed amorphous carbonates into more crystalline calcite. Portland limestone cement could replace Ordinary Portland Cement (OPC) in making equivalent CMUs which have shown similar carbon sequestration potential.     

Grinding kinetics of red grape seed residue in stirred media mill

The main objective of the present paper was to experimentally investigate the grinding kinetics of red grape seed which is the by-product of winery and juice industry. Stirred media mill was used as a high energy density mill to improve the raw grape seed fineness, i.e. mean particle size approx. 10 µm using various rotor circumferential velocities under dry condition. The effect of stress intensity and stress number on the particle size distribution of ground grape seed was investigated. Optimum conditions (rotor velocity and residence time) were determined, mean particle size close to 10 µm and 5000 cm²/g geometric specific surface area were reached within the studied variables. Additionally, concerning the material structure, FTIR measurements of the ground grape seed samples were carried out which demonstrated that no structural changes were detected. Furthermore, the specific grinding work was measured for each test, in this way energy utilization, efficiency was determined.     

Particle size distribution control and related properties improvements of tungsten powders by fluidized bed jet milling

Fine grinding process of different particle size tungsten powders was carried out by fluidized bed jet milling. The results showed that the jet milling treatment caused deagglomeration of tungsten powders, which led to particles sufficient dispersion and narrow particle size distribution. Grinding gas pressure of 0.70 Mpa made the particles achieve high speed which promoted the particles collision contributing to particle dispersion and shape modification. For tungsten powder with particle size of 3 μm FSSS, a higher packing density with 5.54 g/cm³ was obtained, compared with the 3.71 g/cm³ of the original powder. For tungsten powder with particle size of 1 μm FSSS, the big agglomerates disappeared and the particle size distribution become narrower, while small aggregates about 2–3 μm still exist after the jet milling process. For tungsten powder with particle size of 5 μm and 10 μm FSSS, different medium diameter particle size and narrow particle size distribution of monodisperse tungsten powders can be produced by the optimized jet milling parameters. More important, the effective dispersion, favorable shape modification and precise classification have been achieved in the simple process.     

Thaumasite formation in limestone filler cements exposed to sodium sulphate solution at 20 °C

This paper presents a microstructural analysis of mortars made with OPC (C₃A=6%) and two SRPCs (C₃A < 2% and C₃S=40% and 74%) containing 20% of limestone filler. Specimens analysed were immersed in Na₂SO₄ solution (5% w/w or 0.352 M) with pH control during two years at 20 ± 2 °C. The evolution of attack was determined using XRD semi-quantitative analysis on the material obtained by wearing in layers by millimetre to millimetre of the specimens. Complementary SEM and EDS studies were carried out to confirm the presence of thaumasite. Results show that OPC and high-C₃S SRPC containing 20% limestone filler were found to be more susceptible to sulphate attack than the corresponding plain cement. The attack was characterised by the inward front leading first to the formation of ettringite, later formation of gypsum and finally thaumasite formation, when the decalcification of the mortar lead to the breakdown of C–S–H, providing the required silica. The reaction sequence in Portland limestone cements is essentially the same as in plain Portland cements. The main change is that thaumasite is formed at later stages with decomposition of the ettringite formed during the firsts stage of attack. In SRPC with low C₃S, the attack was limited to the first millimetres and the thaumasite was not detected.     

Microstructure and performance of energetically modified cement (EMC) with high filler content

Energetically modified cement (EMC) has been produced by high intensive grinding/activation of normal portland cement (NPC) together with 20% and 50% quartz sand. EMC concretes were compared to NPC based concrete using the k-factor concept. The k-factor for concrete with w/c = 0.60–0.45 was 0.7–0.9 for 1 d and 1.1–1.3 for 28 d compressive strength. k > 1 for both capillary suction, porosity, vapor diffusion and chloride permeability. For carbonation resistance k was ≈0.55.Microstructure of EMC paste with 50% quartz sand and w/c = 0.40 showed that the quartz was extensively ground and formed agglomerates with cement having a high inner surface. The degree of hydration of the cement in EMC was as high as 71% after 1 d compared to 45% for untreated blend. Refined pore size distribution of EMC versus the blend means that even for equal hydration at higher ages EMC will perform better.     

Use of calcium carbide residue and bagasse ash mixtures as a new cementitious material in concrete

Calcium carbide residue (CCR) is a by-product of the acetylene gas production and bagasse ash (BA) is a by-product obtained from the burning of bagasse for electricity generation in the sugar industry. The mixture between CCR contains a high proportion of calcium hydroxide, while BA is a pozzolanic material, can produce a pozzolanic reaction, resulting in the products similar to those obtained from the cement hydration process. Thus, it is possible to use a mixture of CCR and BA as a cementitious material to substitute for Portland cement in concrete. The results indicated that concrete made with CCR and BA mixtures and containing 90 kg/m³ of Portland cement gave the compressive strength of 32.7 MPa at 28 days. These results suggested that the use of ground CCR and ground BA mixtures as a binder could reduce Portland cement consumption by up to 70% compared to conventional concrete that requires 300 kg/m³ of Portland cement to achieve the same compressive strength. In addition, the mechanical properties of the alternative concrete including compressive strength, splitting tensile strength, and elastic modulus were similar to that of conventional concrete.     

Alkali-aggregate behaviour of alkali-activated slag mortars: Effect of aggregate type

The alkali–silica reaction in waterglass-alkali-activated slag (waterglass-AAS) and ordinary Portland cement (OPC) mortars was evaluated using three types of (siliceous and calcareous) aggregates. The tests were conducted to the ASTM C1260-94 standard test method. The mortars were studied by volume stability, mechanical strength and Hg intrusion porosity. The ASR products were studied with XRD, FTIR and SEM/EDX techniques.According to the results obtained, under the test conditions applied in this study, waterglass-AAS mortars are stronger and more resistant to alkali-aggregate reactions than OPC mortars. When the mortars were made with a reactive siliceous aggregate, expansion was four times greater in the OPC than in the AAS material. When a reactive calcareous (dolomite) aggregate was used, no expansion was detected in any of the mortars after 14 days, although the characterization results showed that the dolomite had reacted and calcareous-alkali products (brucite) had in fact formed in both mortars. These reactive processes were more intense in OPC than in AAS mortars, probably due to the absence of portlandite in the latter. When the calcareous aggregate was non-reactive, no expansions were observed in any of the mortars, although a substantial rise was recorded in the mechanical strength of AAS mortars exposed to the most aggressive conditions (1 M NaOH and 80 °C).     

The effects of a hydrochloric acid pre-treatment on the physicochemical properties and pozzolanic performance of rice husk ash

This paper investigates the effects of acid normality (0.01–6 N HCl) and combustion retention time (0.25–16 hours) on the pozzolanic properties of pre-combustion acid-treated rice husk ash. The pozzolanic reactivity was quantified by adding ground ash to saturated Ca(OH)₂ solutions and monitoring the time-dependent electrical conductivity and pH of the solutions. Also, the strength activity of ashes from different processes was measured by testing the compressive strength of mortars. It was observed that acid treatment results in ashes with higher SiO₂ content, lower alkali and unburned carbon content, better grindability, and smaller particle size, in comparison with ash from non-acid treated husks. Acid leaching increased the lime reactivity of the ashes and decreased their sensitivity to prolonged combustion times. Further, acid treatment with 0.01 N HCl was found to be sufficient, as the use of stronger acids did not considerably improve the pozzolanic reactivity of rice husk ash.     

A study on the effect of nano silica on compressive strength of high volume fly ash mortars and concretes

This paper presents the effect of nano silica (NS) on the compressive strength of mortars and concretes containing different high volume fly ash (HVFA) contents ranging from 40% to 70% (by weight) as partial replacement of cement. The compressive strength of mortars is measured at 7 and 28 days and that for concretes is measured at 3, 7, 28, 56 and 90 days. The effects of NS in microstructure development and pozzolanic reaction of pastes containing above HVFA contents are also studied through backscattered electron (BSE) image and X-ray diffraction (XRD) analysis. Results show that among different NS contents ranging from 1% to 6%, cement mortar containing 2% NS exhibited highest 7 and 28 days compressive strength. This NS content (2%) is then added to the HVFA mortars and concretes and the results show that the addition of 2% NS improved the early age (7 days) compressive strength of mortars containing 40% and 50% fly ash by 5% and 7%, respectively. However, this improvement is not observed at high fly ash contents beyond 50%. On the other hand, all HVFA mortars exhibited improvement in 28 days compressive strength due to addition of 2% NS and the most significant improvement is noticed in mortars containing more than 50% fly ash. In HVFA concretes, the improvement of early age (3 days) compressive strength is also noticed due to addition of 2% NS. The BSE and XRD analysis results also support the above findings.     

Upgrading of low-grade gold ore samples for improved particle characterisation using Micro-CT and SEM/EDX

There is a considerable challenge in accurate characterisation of gold (Au) particles in low-grade plant ore mineral samples. This is particularly true for automated mineralogical tools such as X-ray micro-computed tomography (Micro-CT) and scanning electron microscopy (SEM), where the need for statistically meaningful numbers of particles requires many sections to be analysed. Whiles the Vertical Gas Stream (VGS) elutriator is suitable for coarse particle upgrading (i.e. >38 μm), the performance is poor for finer particles (i.e. <38 μm). Consequently, the system has been modified to Vertical Water Stream (VWS) elutriator using higher density fluid (i.e. water) to enable analysis of Au particles below 38 μm. In this work, the VGS system was used to upgrade Au particles in the ?53 + 38 μm size fraction (in rougher concentrate, rougher tailings, regrind mill discharge and regrind cyclone underflow) and the VWS system was used to upgrade Au particles in the ?38 μm size fraction of the regrind mill discharge sample. The VWS elutriator was calibrated using galena (specific gravity, S.G. of 7.58) and quartz (S.G. of 2.65) particles of <38 μm size as model minerals. From the calibration tests, partition curves as a function of particle size were generated. Using these measurements, theoretical partition curves for Au (S.G. of 19.3) have been calculated. The VWS concentrate was characterised using Micro-CT and compared with SEM coupled with energy dispersive X-ray (EDX) analysis of ?53 + 38 μm ore size fraction of the VGS concentrate of the four sample streams. The Micro-CT analysis of VWS Au concentrate showed that sufficient particles (Au) can be upgraded. SEM/EDX results indicate that regrind does not affect changes in free Au particle morphology, aspect ratio and frequency of shearing damage in the ?53 + 38 μm size fraction. Cyclone classification of the regrind mill discharge in the ?53 + 38 μm size fraction appears to perform surface cleaning by exposing obscuring silver (Ag) surfaces on Au particles in the mill discharge sample.     

Contribution of limestone to the hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements can be blended with mineral additions such as limestone for properties and cost optimization. This study investigates the contribution of limestone to the hydration of a commercial CSA clinker regarding the hydration kinetics, hydrate assemblage and compressive strength. Nine formulations were defined at M-values of 0, 1.1 and 2.1 (M = molar ratio of anhydrite to ye’elimite) without and with medium and high limestone contents.Calorimetric results indicate that limestone accelerates the hydration reaction especially at M = 1.1, probably due to the filler effect. The phase assemblages were calculated by thermodynamic modeling using Gibbs Energy Minimization Software (GEMS). With increasing limestone content the formation of ettringite and calcium monocarboaluminate is predicted at the expense of calcium monosulfoaluminate. With increasing M-value more ettringite is predicted at the expense of the monocarbonate and less calcite takes part in the hydration reactions.The modeled results compare well with the experimental data after 90 d of hydration, except that calcium hemicarboaluminate was found instead of monocarbonate, which is assumed to be due to kinetics considerations.The lowest compressive strength occurs in ternary formulations, whereas in the absence of calcium sulfate, strength is significantly higher.The results presented here indicate that in CSA cements, limestone accelerates early hydration kinetics, takes part in the hydration reactions at M < 2, and has a positive effect on strength development in systems without anhydrite.     

Preparation of nanocrystalline zinc carbonate and zinc oxide via solid-state reaction at room temperature

The precursor mixture was obtained by grinding ZnSO₄·7H₂O and NH₄HCO₃ with surfactant OP thoroughly at room temperature. Then soluble inorganic salts were removed by washing with water. After drying, the pure nanocrystalline ZnCO₃ was obtained. ZnO powder was obtained by one-step thermal decomposition of the ZnCO₃ at 400 °C for 1.5 h. Both the ZnCO₃ and the ZnO were characterized by TG/DTA, XRD and TEM. The particle size of the ZnCO₃ and the ZnO was found to be 50 nm and 20 nm, respectively. The smaller particle size of the ZnO suggests a fact that the crystals of the ZnCO₃ play a role in the self-crushing reaction.     

A study of the ash production behavior of spent limestone powders in CFBC

Spent limestone particles in a circulating fluidized bed combustor (CFBC) may show a bottom-ash-pro (BAP) behavior or a fly-ash-pro (FAP) behavior. In this study, two spent limestone particles showing the BAP behavior and two spent limestone particles showing the FAP behavior in a 125 MW CFBC are characterized based on their total pore volume and specific surface area before and after 800 °C calcination. Provided that the limestone primary fragmentation does not significantly affect the particle size distribution immediately after CFBC injection, the limestone particles having a relatively porous structure after 800 °C calcination show a BAP behavior in a CFBC.     

Effect of SO3 content and fineness on the rate of delayed ettringite formation in heat cured Portland cement mortars

This paper presents the findings of a long-term study on the expansion rate and microstructure of heat cured cement mortars. For this purpose, cements with different fineness and SO₃ contents were produced by using the same clinker. Different mortar specimens were prepared and subjected to heat curing. Length changes of specimens were measured within a period of 540 days. The microstructures of young (2 day after heat curing) and old (1.5 years after heat curing) specimens were also investigated by SEM and EDS analysis. The expansion rates and microstructures observed were compared with the control specimens.Results showed that, at the initial stages of testing (2–3 months), expansion rates of heat cured mortars prepared with finer cements were less than those prepared with coarser cements. However, in the long term, the rate of expansion of mortars prepared with finer cements exceeded the coarser ones’ expansion values. This result may be attributed to the different hydration characteristics and pore structure of heat cured mortars including cements of different fineness.     

Effect of grinding aids on the kinetics of fine grinding energy consumed of calcite powders by a stirred ball mill

An experimental investigation was carried out on the ultra-fine grinding of inorganic powders using a stirred ball mill. The power consumed in the grinding process was measured, and the comminution coefficient, K, in the grinding kinetics equation was examined, based on an analysis of the relationship between the experimental specific surface area and the particle-size distribution of ground products. The effect of grinding aids on the comminution coefficient, K, was also investigated. It was demonstrated that the grinding rate for calcite could be improved by the addition of grinding aids. When using grinding aids, K improved by 16.0% and 34.2% for 60 wt% and 70 wt% slurry concentrations, respectively. Thus grinding aids are very effective in the submicron range grinding process.