Sintering mechanism of blast furnace slag–kaolin ceramics

A general ceramics processing scheme by cold uniaxial pressing and conventional sintering process have been used to prepare ceramics from mixtures of blast furnace slag (BFS) and kaolin (10%, 30% and 50% kaolin). The properties of the ceramics were studied by measuring linear shrinkage, bulk density, apparent porosity and mechanical properties of samples heated at temperatures from 800 °C to 1100 °C. The formed crystalline phases were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Slag melt formed at relatively low temperatures (800–900 °C) modified the sintering process to liquid phase sintering mechanism. Combination of BFS with 10% kaolin gave the highest mechanical properties, densification and shrinkage at relatively low firing temperatures. The crystalline phases were identified as gehlenite (Ca₂Al₂SiO₇) in both BFS and BFS with 10% kaolin samples. Anorthite (CaAl₂Si₂O₈) phase increased with increasing kaolin contents. In the case of kaolin-rich mixtures (30% and 50% kaolin), increased expansion took place during firing at temperatures in the range 800–1000 °C. This effect could be attributed to the entrapment of released gases.     

Thermal activation of ordinary Portland cement–slag mortars

Thirty one mix proportions of ordinary Portland cement (OPC)–slag mortars (OSM) used to study the effects of temperature on early and ultimate strengths. Three levels of slag (0%, 40%, and 50%) and different temperatures were used; it was found that 50% is the optimum level and 60 °C with 20 h duration is also optimum. The maximum strengths obtained of optimum mortar, at 3 and 7 days, for specimens cured in the air, are 55.00 and 62.00 MPa, respectively. These strength levels are 64.50% and 66.50% greater than those without heating. The results show for 0 and 2 h heating time, the strength of specimens cured in the water are greater than those cured in the air, but for 4–26 h, this statement is reversed. This is a novelty, is very important in the precast industry and has many advantages for arid regions to overcome curing of concrete structures.     

Evolution of alkaline activated ground blast furnace slag–ultrafine palm oil fuel ash based concrete

The two locally available pozzolanic solid wastes (PMs) – ultrafine palm oil fuel ash (UPOFA) and ground blast furnace slag (GBFS) – have been used as base materials to develop high alkaline activated strength concrete. The samples were prepared with combined aggregate modulus of 3.66 and at constant GBFS/PM that varied from 0 to 0.3. The combined alkaline activators (CAA) (Na₂SiO₃ and NaOH) to PMs ratios (CAA/PMs), temperature and curing durations also varied as 0.45–0.55, 25–90 °C, and 6–24 h, respectively. The findings revealed that the strength at 3-day and 28-day were 69.13 and 71.2 MPa, respectively and the respective optimum GBFS/PM, CAA/PM, temperature and curing duration are 0.2, 0.5, 60 °C and 24 h. GBFS was found to contribute to the soluble Ca, heterogeneity, and amorphousity of the product. This eventually facilitated the formation of suspected calcium-silicate-hydrate and the geopolymer products of Ca/Na-aluminosilicate-hydrate (C/NASH) that enhanced the compressive-strength results.     

A study on burden distribution of blast furnace with a bell‐less top

Abstract

The so‐called coke layer collapse phenomenon was observed on a blast furnace top model which was 1/4‐scale of No. 2 blast furnace of China Steel. A simulation program based on the Bishop simplified method of soil mechanics and the material balance was developed to identify the collapse occurrence and to predict the burden distribution after the collapse. A close agreement between the experimental results and the prediction of simulation program was found.     

Carbothermal formation and microstrutural evolution of α′-Sialon–AlN–BN powders from boron-rich blast furnace slag

Boron-rich blast furnace slag of low activity is one of the major products created during the separation of iron and boron from ludwigite in a blast furnace process, and the high-efficiency utilisation of its is of great importance to the Chinese boron industry. This paper proposes one new application process to synthesize α′-Sialon–AlN–BN powders by a carbothermal reduction–nitridation method using boron-rich blast furnace slag as the staring material and describes a series of experimental studies that were performed to elucidate the mechanism of phase formation and microstructure evolution during CRN. The experimental results revealed that the phase compositions and microstructures of the synthesized products were greatly affected by the initial compositions ((Ca,Mg)_xSi_12–3xAl_3xO_xN_16–x), x = 0.3–1.8), temperature and holding time. With the compositions shifting from values of x of 0.3–1.8, the relative amount of α′-Sialon, AlN and BN increased gradually, and the amount of α′-Sialon reached a maximum at a value of x of 1.4. The optimal condition for powder synthesis was a temperature of 1480 °C with a holding time of 8 h, under which the crystalline phases included α′-Sialon, AlN, BN and less SiC. More elongated α′-Sialon grains were observed at higher x values and temperatures. During the CRN process, MgAl₂O₄, Mg₂SiO₄, Ca₂Al₂SiO₇, MgSiN₂, β′-Sialon and 27R appeared sequentially as intermediate products. The volatilisation of SiO gas and magnesium vapour resulted in additional weight loss of the samples, which was aggravated with increases in the synthesis temperature and holding time.     

Microstructural properties of lithium-added cement mortars subjected to alkali–silica reactions

Little comparative research has been done on the efficiency of lithium additives to reduce the alkali–silica reaction (ASR) expansion. To reduce the ASR effects of reactive aggregate, different mortar bars were obtained by adding lithium additives (Li₂SO₄, LiNO₃, Li₂CO₃, LiBr and LiF) to the mixing water by the following mass percentages of cement: 0%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3%. The ASR expansions of the mortar bars at 2, 7 and 14 days were identified according to ASTM C 1260-14. The morphology of the specimens subject to the ASR effect was analysed using a scanning electron microscope, and their chemical composition was analysed by electron dispersion spectroscopy. Among all specimens, the lowest level of 14-day ASR expansion was obtained in mortar bars with 3% Li₂CO₃ additive.     

Investigation of freeze–thaw effects on mechanical properties of fiber reinforced cement mortars

Fibers are used for improving some properties of conventional concrete (which is a brittle material) such as tensile strength, abrasion resistance, absorption and crack control. This study investigates the usability of fibers against the harmful effects of freeze–thaw cycles on cement mortars. For this objective, five different types of fibers, i.e., Polypropylene (PP), Carbon (CF), Aramid (AR), Glass (GF) and Poly vinyl alcohol (PVA) in four different ratios (0.0%, 0.4%, 0.8% and 1.2%) were added to cement mortars along with an amount of air agent. These samples were then subjected to five different freeze–thaw cycles (0, 25, 50, 75 and 100). Thus, mechanical behaviors were investigated under freeze–thaw effects.The most important results of the study are summarized; the fibers increase flexural strength and deflection ability of the samples while decreasing compressive strength, dynamic modulus of elasticity and specific mass. The highest flexural strength was obtained with a 1.2% addition of CF fiber for the samples in normal conditions. The mechanical properties of the samples subjected to repetitive freeze–thaw cycles were also investigated; the best flexural strength was provided with 1.2% CF addition, while the highest dynamic modulus of elasticity was obtained with a 1.2% PP addition.     

Adhesive and cohesive properties of glue cement mortars with addition of organic–mineral modifiers

The paper deals with results of experimental research on cement glue mortars containing non-milled fly ash and organic–mineral modifiers are given. The organic–mineral modifiers (OMM) include finely dispersed additives like microsilica or milled fly ash and organic substances (naphthalene formaldehyde superplasticizers and redispersed polymers). Glue cement mortars, modified by OMM additives allow reducing Portland cement consumption, stabilizing and improving the mortars’ properties, especially their adhesive and cohesive strength. The influence of the modifier compositions on the strength parameters of mortars for masonry stone walls, facing by ceramic tiles or gluing heat isolation materials was studied. The experimental results show that as the silica additives dispersion is higher the positive effect on adhesive and cohesive strength increases. Optimal content of modifiers in mortars is obtained.     

A multi-phase kinetic model to simulate hydration of slag–cement blends

Ground granulated blast furnace slag, which shows cementitious behavior (latent hydraulic activity) and pozzolanic characteristics (reaction with lime), has been widely used as a mineral admixture in normal and high strength concretes. Hydration of slag–blended cement is much more complex than that of ordinary Portland cement because of the mutual interactions between the cement hydration and the slag reaction. This paper presents a kinetic hydration model for cement–slag blends. The proposed model analyzes the slag reaction separate from cement hydration by considering the production of calcium hydroxide in cement hydration and its consumption in slag reactions. The amount of free water and the amount of calcium hydroxide left in the system were adopted as the control indicators for determining the slag reaction. Using the proposed model, the reaction ratio of slag can be evaluated as a function of curing age, considering the influences of the water to binder ratio, the slag replacement ratio and the curing temperature. Furthermore, the amount of chemically-bound water (self-cementing properties), calcium hydroxide (pozzolanic capabilities), and the heat released from hydration are evaluated by determining the contributions from both the cement hydration and the slag reaction. The evaluated results show good accordance with the experimental results.     

Compressive strength development of binary and ternary lime–pozzolan mortars

This study considers the compressive strength development of broad range of hydraulic lime mortars prepared with a range of commercially available alumino-silicate by-products and modern pozzolanic additions. Specifically this paper considers the effect of mineral addition selection, binary and ternary combinations, pozzolan content and the effect of curing conditions on the compressive strength development of hydraulic lime based mortars. The study was undertaken as the initial phase of a broader investigation considering the feasibility of producing modern, sustainable hydraulic lime–pozzolan concretes with comparable strengths to Portland cement based concretes. The aim of the initial phase was to identify a small number of additions, and combinations thereof, which would result in a structural strength lime–concrete when scaled up from mortars to concretes.In the absence of a definitive source of information on the mechanical properties of hydraulic-lime mortars prepared with binary and ternary combinations of alumino-silicate by-products, 22 combinations consisting of Natural Hydraulic Lime (NHL5) and a range of possible additions, identified from historical and current practice, were prepared. The results have shown that combining an eminently-hydraulic NHL5 with silica fume and ground granulated blastfurnace slag can produce mortars with a 28-day compressive cube strength of around 28 N/mm², at a water-to-binder (w/b) ratio of 0.5. This is eight times the strength of an equivalent mortar prepared with NHL5 alone and broadly speaking comparable with that of low-heat cementitious mortars. The contribution of the pozzolanic reaction to the strength of hydraulic lime mortars is discussed for a range of alumina-silicious materials and combinations thereof.     

Decalcification of activated paper sludge – Fly ash-Portland cement blended pastes in pure water

Decalcification in pure water of ternary Portland cement (TPC) pastes, containing thermally activated paper sludge and fly ash, has been evaluated from the leaching of Ca²⁺ in pure water at the temperature of 20 °C during 90 days. Monitoring of calcium loss showed that the leaching kinetics are controlled by diffusion. The degradation of the material over time is estimated from the calcium effective diffusivity. A similar study of plain ordinary Portland cement (OPC) pastes was carried out for comparison. The results showed lower effective diffusion coefficients of calcium in the case of the TPC pastes. This behaviour is related to its microstructure, which is denser than that of OPC as a result of the pozzolanic activity of both additions.     

Shrinkage and Strength of Capillary‐Porous Colloidal Materials

The processes of shrinking of capillaryporous colloidal bodies under the action of capillaryosmotic pressures have been investigated. The mechanisms of densification and strengthening of a material in the drying process have been considered. An equation relating the material's strength to its density, which agrees with experiment, is proposed.     

Photocatalytic activity of nanostructured TiO2‐modified white cement

In this study, the photocatalysis of Alphazurine FG as a model water pollutant, by white Portland cement samples modified with different TiO₂ nanomaterials (TiO₂ in the form of Degussa P25, Millennium PC500, Millennium PC105 and anatase-Merck), was investigated. The pseudo first-order rate constants of Alphazurine FG photocatalysis were compared with the degradation rate by unmodified cement sample. A significant enhancement of the photocatalytic activity due to the addition of TiO₂ nanomaterials in the form of Degussa P25 to Portland cement was observed. The crystalline phase, average crystalline size and surface area of the photocatalyst were found to have a significant influence on the photocatalytic activity of the nanostructured TiO₂-modified cement samples. The photocatalysis of Alphazurine FG in the presence of TiO₂–P25/cement was experimentally studied through changing the UV light intensity and initial dye concentration. The electrical energy consumption of Alphazurine FG photocatalysis was estimated at different initial dye concentrations. The results open important perspective applications in the field of eco-friendly construction applications.     

Statistical analysis for freeze–thaw resistance of cement mortars containing marble dust and glass fiber

This paper investigated the usability of marble dust and glass fiber against the harmful effects of freeze–thaw (FT) cycles on cement mortars as experimentally and statistically. To this end, the cement mortar specimens containing marble dust (0%, 20%, 40% and 50% by volume) and glass fiber (0 kg/m³, 0.25 kg/m³, 0.50 kg/m³, 0.75 kg/m³) were prepared. The compressive and flexural strengths of the specimens were determined after being exposed to FT cycles. In order to reduce the numbers of experiments, an L₁₆ (4² × 2¹) Taguchi orthogonal array was adopted to the study. Amounts of glass fiber, percentages of marble dust and cycles of freeze–thaw, were changed to explore their effects on the compressive and flexural strengths of the mortar specimens. Statistically effects of the factors were also determined by using analysis of variance (ANOVA) method. Finally, experimental findings were compared with statistical results and a good agreement between them was achieved.     

Effects of thermal and mechanical activation methods on compressive strength of ordinary Portland cement–slag mortar

Activation methods and curing regimes have crucial effects on the strength of mortars and concretes. The objective of this investigation is to examine the early and later compressive strength of activated ordinary Portland cement (OPC)–ground granulated blast-furnace slag (GGBFS) mortars and identify the most effective activation technique. The methods of activation used were thermal, mechanical and thermal–mechanical combined. Two curing regimes were adopted and five groups of mortars were prepared. It was observed that OPC–GGBFS mortars have greater sensitivity to OPC mortars against the curing regimes. However, the study revealed that there was no particular activation method which when used gave the best results for both early and later strengths and did not cause strength loss. It also proved that the most effective activation method for early strength is a combination of both the thermal and mechanical, while for later strengths, none of the activation methods was recommended.     

Evaluation of the compressive strength and Cl− content of the blast furnace slag-soda sludge-based cementitious material using machine-learning approaches

Clean Technologies and Environmental Policy - Solid waste-based cementitious material is friendly to the environment. The machine-learning technique brings the advantage of high efficiency to the...     

The hydration and microstructure of ultra high-strength concrete with cement–silica fume–slag binder

This study investigated the flowability, compressive strength, heat of hydration, porosity and calcium hydroxide content of ultra-high-strength concrete (UHSC) with cement–silica fume–slag binder at 20 °C. The composition of the binder was designed using seven-batch factorial design method. The relationships between the binder composition and the properties were expressed in contours. Results showed that proper silica fume content could improve the flowability and compressive strength of UHSC, reduce the porosity and calcium hydroxide content of UHSC. Slag reduced the flowability, compressive strength, porosity, and calcium hydroxide content of UHSC to certain extent. The silica fume and slag demonstrated positive synergistic effects on the flowability and 3 d compressive strength, but have negative synergistic effects on the total heat of hydration, hydration heat when the time is infinitely long(P₀), 56 d compressive strength, porosity and calcium hydroxide content of UHSC.     

Investigation of the Strength and Elastic Properties of Glass‐Ceramic of a Lithium Alumosilicate Composition

This paper presents the results of investigations of the strength and elastic properties of the glassceramic obtained by novel technology with the use of the method of casting blanks from highdensity aqueous suspensions of lithium alumosilicate glass into porous moulds followed by their sintering and crystallization under combined conditions of thermal treatment. Comparison of the properties of the proposed glassceramic with the properties of the glassceramics obtained by conventional technology enabled us to gain a better insight into its potentialities and provide the necessary information for calculating the structural strength.     

The effect of processed fly ashes on the durability and the corrosion of steel rebars embedded in cement–modified fly ash mortars

This paper deals with the study of corrosion level of reinforcing steel bars embedded in Portland cement mortars containing different types of fly ash. Fly ashes used were obtained by physico-chemical treatments of an original F class fly ash to modify their magnetic properties and reduce their particle size. An original fly ash (T0) and three types of modified ashes were tested according to treatment duration and magnetic properties (T60, ground fly ash; TNM, non-magnetic fraction; TM, magnetic fraction). Corrosion tests on reinforced mortar specimens with and without different types of fly ashes, cured at 40 °C, and under accelerated carbonation conditions and seawater immersion, have been performed in order to obtain conclusions on durability. From the corrosion point of view the addition of TNM in mortars showed to be much more effective than addition of the original T0 fly ash.