Effect of Binder Concentration and Method of Addition on Granule Growth in a High Intensity Mixer

A model system consisting of microcrystalline cellulose and povidone was used to study the effect of binder concentration and method of addition on granule growth in a high intensity mixer. The methods of binder addition include blending the dry binder with the excipient prior to granulating with water and granulation of the excipient with an aqueous solution of the binder. When the binder was dry-mixed with excipient prior to wetting, a good correlation was obtained between granule size and binder level. The growth of granules prepared by this method also appears to be related to the mechanical “resistance” encountered by the mixing blade during wet massing. In general, granules prepared by the addition of aqueous binder solutions are smaller than granules prepared with corresponding concentrations of dry binder and demonstrate a lesser degree of granule growth with respect to increasing binder level. For the wet addition method, the mechanical resistance was found to be essentially constant with respect to binder level.     

An experimental study on optimum usage of GGBS for the compressive strength of concrete

This paper presents a laboratory investigation on optimum level of ground granulated blast-furnace slag (GGBS) on the compressive strength of concrete. GGBS was added according to the partial replacement method in all mixtures. A total of 32 mixtures were prepared in four groups according to their binder content. Eight mixes were prepared as control mixtures with 175, 210, 245 and 280 kg/m³ cement content in order to calculate the Bolomey and Féret coefficients (K_B, K_F). For each group 175, 210, 245 and 280 kg/m³ dosages were determined as initial dosages, which were obtained by removing 30 percent of the cement content of control concretes with 250, 300, 350, and 400 kg/m³ dosages. Test concretes were obtained by adding GGBS to concretes in an amount equivalent to approximately 0%, 15%, 30%, 50%, 70%, 90% and 110% of cement contents of control concretes with 250, 300, 350 and 400 kg/m³ dosages. All specimens were moist cured for 7, 14, 28, 63, 119, 180 and 365 days before compressive strength testing.The test results proved that the compressive strength of concrete mixtures containing GGBS increases as the amount of GGBS increase. After an optimum point, at around 55% of the total binder content, the addition of GGBS does not improve the compressive strength. This can be explained by the presence of unreacted GGBS, acting as a filler material in the paste.     

Preparation of Ultra-High Performance Concrete with common technology and materials

The technology development of concrete and demand for high strength construction materials give momentum to the development of Ultra-High Performance Concrete (UHPC). Current UHPC preparation methods require costly materials and relatively sophisticated technology. To overcome these weaknesses, this paper focused on the preparation of UHPC with common technology and ordinary raw materials. Influence of binder content, water/binder ratio, ground granulated blastfurnace slag (GGBS) content, and limestone powder (LP) replacement on fluidity and compressive strength of concrete were researched, respectively. The test results show that the addition of superplasticizer and fine mineral additives enabled the UHPC to be produced at an extremely low water/binder ratio of 0.14-0.18, achieving excellent workability with a maximum slump of 268 mm and compressive strengths of 175.8 MPa at 90 d and 182.9 MPa at 365 d.     

早龄期复合胶凝材料的裂纹扩展阻力分析

研究了不同组成的复合胶凝材料硬化浆体(硅酸盐水泥,硅酸盐水泥 粉煤灰,硅酸盐水泥 矿渣,硅酸盐水泥 硅灰,硅酸盐水泥 硅灰 粉煤灰)早龄期时裂纹扩展阻力的发展,探讨了粉煤灰掺量对裂纹扩展阻力的影响.结果表明:早龄期时,在相同水胶比条件下,掺加硅灰使胶凝材料体系裂纹扩展阻力明显降低,在低水胶比条件下,掺加一定量的粉煤灰能够明显增加体系的裂纹扩展阻力,掺加20%的粉煤灰能使胶凝材料具有较高的裂纹扩展阻力.     

Effect of Binder Concentration and Method of Addition on Granule Growth in a High Intensity Mixer

Abstract

A model system consisting of microcrystalline cellulose and povidone was used to study the effect of binder concentration and method of addition on granule growth in a high intensity mixer. The methods of binder addition include blending the dry binder with the excipient prior to granulating with water and granulation of the excipient with an aqueous solution of the binder. When the binder was dry-mixed with excipient prior to wetting, a good correlation was obtained between granule size and binder level. The growth of granules prepared by this method also appears to be related to the mechanical “resistance” encountered by the mixing blade during wet massing. In general, granules prepared by the addition of aqueous binder solutions are smaller than granules prepared with corresponding concentrations of dry binder and demonstrate a lesser degree of granule growth with respect to increasing binder level. For the wet addition method, the mechanical resistance was found to be essentially constant with respect to binder level.     

Physical properties and reactivity of pozzolans,and their influence on the properties of lime–pozzolan pastes

This paper studies how pozzolan properties including particle size, specific surface, chemical and mineral composition, amorphousness and water demand, affect their reactivity as well as the strength of lime–pozzolan pastes. Reactivity was evaluated with chemical, mechanical and mineralogical methods. A number of artificial pozzolans were investigated including Ground Granulated Blastfurnace Slag (GGBS); Leca; Pulverised Fuel Ash (PFA); Calcined Clay (Metastar); Microsilica (MS); Rice Husk Ash (RHA); Red Brick Dust (RBD); Tile and Yellow Brick Dust (YBD). The paper concludes that the pozzolan’s specific surface has a much greater influence on the water demand of the paste than its particle size or the lime:pozzolan ratio. It was evidenced that each pozzolan has a particular water demand for a given workability that increased with its specific surface; and that the replacement of lime by pozzolan lowers the water demand of the paste except for Metastar, on account of its greater fineness and specific surface. There is a good correlation between the chemical and physical activity indices and the rate of portlandite consumption. These evidenced that the most amorphous pozzolans (Metastar, GGBS, RHA and MS) are the most active. Finally, it also appears from the results, that the amount of lime combined by reactive crystalline phases in the pozzolans is insignificant when compared to that bound by their amorphous fraction. The paper concludes that amorphousness determines pozzolan reactivity to a much greater extent than any other pozzolan property. It also concludes that the specific surface area of the pozzolan governs the water demand of the paste, while amorphousness largely determines the strength of the paste. In contrast, the chemical composition of the pozzolan is not instrumental as a variable affecting neither pozzolan reactivity nor the strength of the paste.     

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO–GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.     

Dispersion kinetics of carbon black for the application in lithium-ion batteries

For production of electrodes for lithium-ion batteries, conductive carbon black (CB) has to be dispersed within the anode and cathode slurry. A sufficient dispersing degree has to be reached in order to ensure the formation of an adequate conductive network within the electrodes. As intermediate product, CB is dispersed in binder solution, prior to addition of active materials. As binder system on anode side carboxymethylcellulose in water is used, whereas on cathode side polyvinylidene fluoride in N-Methyl-2-pyrrolidone is applied. The conductive carbon slurry facilitates the characterization of the slurry properties, based on changes of CB. The structure and amount of conductive carbon black influences the slurry properties decisively. Viscosity increases with increasing CB content, which affects the shear stress within the mixing process. Rheological properties and particle size distributions are investigated over time while dispersing CB with various tip speeds in a dissolver. Dispersion kinetics are described on behalf of an existing model for tip speed variations. Based on the investigations of rheological changes due to varying amount of CB, an extended model enclosing the CB concentration as variable was developed. Using the extended model, particle sizes for new process parameters can be predicted.     

Characterization of porous silicon nitride ceramics using bentonite as binder and sintering additive

The effect of bentonite addition on extrusion behavior, open porosity, microstructure, and mechanical properties was investigated. The results showed that paste with an appropriate amount of bentonite had a good extrusion behavior. The resultant microstructures consisted of rod-like silicon nitride grains and some intergranular amorphous phase. Furthermore, superior mechanical properties were obtained. Using cheap but effective bentonite as inorganic binder as well as sintering aid is a promising eco-friendly preparation route for cost-effective porous silicon nitride ceramics.     

磨细矿渣改性超细水泥耐久性及收缩性能研究

以超细水泥、磨细矿渣及其它外加剂制备了水泥混凝土路面裂缝灌浆材料,研究了该类材料的耐久性能和收缩性能,并通过热分析及微观形貌的观测分析揭示了材料耐久性的改性机理.研究表明磨细矿渣能通过二次火山灰作用使材料微观结构密实,并且大大减少不利于耐腐蚀的氢氧化钙晶体,改善灌浆材料的耐久性,适当掺量时能减小收缩量.     

Biocatalytic carbon paste sensors based on a mediator pasting liquid

The preparation and advantages of a new generation of carbon paste enzyme electrodes where the redox mediator acts also as the pasting liquid are described. The mediator pasting liquid concept is illustrated for amperometric biosensing of glucose in connection with either the tert-pentylferrocene or n-butylferrocene mediator/binder along with the glucose oxidase enzyme. The attractive performance and advantages of the new device is indicated from comparison to a conventional carbon paste biosensor using a mineral oil binder and the dimethylferrocene electron acceptor. The simplified preparation of the biosensor is coupled with a greatly improved sensitivity and an extended linear range. The mediator pasting liquid imparts high thermal stability onto the embedded enzyme and leads to good resistance to oxygen effects. Owing to the huge mediator reservoir, stability problems associated with the leaching of the mediator are greatly reduced. The fundamental aspects of the electrode behavior have been examined first in the absence of the enzyme. Variables affecting the performance of the new carbon paste biosensor have been investigated and optimized. Such use of the electron acceptor as a binder as well as the mediator offers considerable promise for the biosensing of numerous analytes of clinical and environmental significance.     

Structuring of particles in concentrated pastes: a source of defects in powder processed materials

Abstract

Pastes made by mixing particles into liquids are of great use in the materials and processing industries. The dependence of paste products on the composition and treatment of the particle dispersions has not beenfully understood. For example, defects seem toform during the preparation of a paste, making the end product far weaker than expected. Therefore, it should be possible to improve paste products significantly by understanding the genesis and removal of these defects, then optimising the proc;ess to remove flaws. Some flaws, such as bubbles or agglomerates, can be removed by adding surfactants and shearing to give remarkable improvements in structure and properties of cements or ceramics. But there may be other more fundamental sources of flaw genesis in pastes. One such mechanism of flaw formation is the disorder-order transition which is known to occur as particles are concentrated in a fluid. Another new possibility is that adhesion of particles within the paste causes the growth of large multiplets which act as nuclei for defects as the paste is compacted. The measurement and interpretation of such phenomena are discussed.     

Prediction of compressive strength and optimization of mixture proportioning in ternary cementitious systems

This paper discussed the application of the method of the simplex-lattice design for predicting the properties of cement-based composites. On the basis of the compressive strength, its use was demonstrated on ternary paste systems composed of cement, silica fume and fly ash with constant water to binder ratio and a mass fraction of mineral admixtures not exceeding 30%. The regression model between compressive strength of paste and binder proportion was built up. The F-test method was utilized for validation of the regression model. The nonlinear programming system with upper and lower bound was solved. This allowed assessment of optimum mixture proportions and corresponding maximum compressive strength. It was shown that: (1) the 3rd-order regression model constructed by using the simplex-lattice design method could accurately predict the compressive strength in ternary paste system made of cement, silica fume and fly ash (the total mass fraction of all mineral admixtures was up to 30%); (2) to solve the nonlinear programming with the constraints of upper and lower bound played an important role in getting the optimum compressive strength and its corresponding mixture proportion at different ages; (3) the combination of the simplex-lattice design method and the optimization theory could be valuable tool for optimization of cement-based composites' properties.     

Effect of manufacturing process on the mechanisms and mechanical properties of fly ash-based geopolymer in ambient curing temperature

The manufacturing process of geopolymer cement generally uses alkaline solutions mixed with alumina-silicate prime materials to form a cement paste. Other factors may be set up for the designated experiment, e.g., material constituents, activator’s concentration and curing regimes. One of the latent factors influencing the properties of geopolymer, which has received less attention, is a mixing method. General mixing and separate mixing processes, which have been previously studied, were synthesized as controlled procedures and compared with another alternative new mixing method called the pre-dry mixing process. The results have shown that the pre-dry mixing process provided high potential heat liberation, which could prove beneficial for curing purposes. It is confirmed that the proper mixing order leads to better results, especially for any of the alkaline-activated cementitious binders. With more practicality in field application, by just adding water, this process could be developed and applied in ambient temperatures.     

新型聚合物水泥胶浆界面剂粘结性能及作用机理研究

采用新型聚合物水泥胶浆作为界面剂以提高新旧混凝土之间的粘结性能,通过拉拔粘结强度与劈裂抗拉粘结强度实验对5种不同类型的聚合物水泥胶浆界面剂的粘结性能进行了测试,并利用扫描电镜(SEM)分析研究了丁苯聚合物水泥胶浆的界面增强机理。实验结果表明,5种聚合物乳液中,丁苯聚合物水泥胶浆具有较好的拉拔粘结性能,当优选m(水泥)∶m(DB-1乳液)=3∶2时,其7d、28d拉拔粘结强度分别达到1.83MPa、2.41MPa,相比水泥净浆空白样分别提高了144%、96%;在劈裂抗拉粘结强度方面,水平方向浇筑时劈裂抗拉粘结强度相对较高,当聚合物水泥胶浆的优选m(水泥)∶m(DB-1乳液)=3∶2,水平浇筑时其28d劈拉粘结强度达到2.96MPa,明显高于不掺界面剂的试样以及掺加其它配比界面剂的混凝土试样;经过微观测试分析,丁苯DB-1聚合物水泥砂浆内部界面过渡区(ITZ)相比空白样明显致密,表明丁苯聚合物的加入有效填充了水泥基材料内部的宏观与微观缺陷,提高了界面过渡区的密实程度。     

Superfine cement for improving packing density, rheology and strength of cement paste

Superfine cement is a cement ground to a much higher fineness than ordinary cement. The addition of a small quantity of superfine cement to fill into the voids of ordinary cement can improve the packing density of the cement and thereby reduce the amount of mixing water needed to fill the voids. In this study, the effects of superfine cement on the packing density of cement (directly measured by a wet packing test), the water film thickness of cement paste (taken as the excess water to solid surface area ratio), and the flowability, rheology and strength of cement paste were investigated. The results showed that the addition of 10% to 20% superfine cement can significantly increase the packing density of the cement and the water film thickness of the cement paste. Such increases in packing density and water film thickness would then improve the flowability, rheology and strength of the cement paste. Hence, superfine cement is an effective cementitious filler for improving cement performance.     

A method developed to quantify lime and gypsum consumed by mineral additions

This paper presents an original method developed to quantify the reactivity of mineral additions based on the measurement of the lime (CaO) and gypsum (CaSO₄, 2H₂O) consumed by mineral additions in a paste. Three mineral additions were tested: a Siliceous Filler (SF), a natural pozzolan (Poz) and a Wastepaper Sludge Ash (WSA). The results obtained on SF, considered as a reference, show the efficiency of this method. Its application to Poz and WSA permits the quantity of lime and gypsum consumed by these additions to be evaluated and, thus, the amount of each component to be optimized in Hydraulic Road Binders.     

Plastic shrinkage cracking of concrete incorporating mineral admixtures and its mitigation

In recent years, there has been a rapid increase in the use of mineral admixtures for high performance and durable concrete. Plastic shrinkage cracking in such concretes is a serious concern in large surface area/volume applications. The present study has two objectives: firstly, to investigate the influence of incorporating fly ash and granulated blast furnace slag (GGBS) on the susceptibility to such cracking; and secondly, to assess the techniques, such as fibre and shrinkage reducing admixture (SRA) addition, and spraying of curing compounds, to mitigate the cracking. The results indicate that replacement of ordinary Portland cement (OPC) with fly ash and GGBS increases the possibility of plastic shrinkage cracking significantly, with higher severity as the replacement level increases; 30% replacement of OPC with fly ash and GGBS doubled and quadrupled the crack area, respectively, mainly due to higher binder finesses, and the delay of setting and strength gain. Among the fibres tested, polypropylene and polyester fibres, at the recommended dosages of about 0.9 kg/m³, completely eliminated cracking in the most affected concrete (i.e., with 30% GGBS) while the dosages of the polyacrylonitrile and glass fibres had to be increased to provide a higher volume fraction. Two glycol-based SRAs, and two curing compounds based on acrylic resin and methacrylate mitigated cracking by significantly reducing evaporation from the surface of concrete.     

Fabrication of mesoporous calcium silicate/calcium phosphate cement scaffolds with high mechanical strength by freeform fabrication system with micro-droplet jetting

In this study, we explored the feasibility of fabrication bioactive mesoporous calcium silicate/calcium phosphate cements (MCS/CPC) scaffolds with high mechanical strength by Freeform Fabrication System with Micro-Droplet Jetting. After preparation of ordered mesoporous calcium silicate (MCS) powder, ready-to-use MCS/CPC paste was formed by mixing calcium phosphate cement (CPC) powder and MCS powder with the binder polyvinyl alcohol (PVA) aqueous solution at a certain ratio of powder to liquid. MCS/CPC scaffolds with various architectures, pore sizes, and interconnectivity were then directly printed at room temperature using MCS/CPC paste. The mechanical strength, apatite formation, degradation rate, and cytocompatibility of the composite scaffolds were systematically investigated. The results showed that MCS/CPC paste exhibited outstanding printability to form MCS/CPC scaffolds. The hybrid MCS/CPC scaffolds with predefined pore size of 350 μm showed fast degradation rate, high mechanical strength, and good cytocompatibility. It was indicated that the hybrid MCS/CPC scaffolds might be a promising candidate for critical bone defect repair.     

Assessing the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste

This study assesses the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste. rice husk ash (RHA), palm oil fuel ash (POFA) and river sand (RS) were ground to obtain two finenesses: one was the same size as the cement, and the other was smaller than the cement. Type I Portland cement was replaced by RHA, POFA and RS at 0%, 10%, 20%, 30% and 40% by weight of binder. A water to binder ratio (W/B) of 0.35 was used for all blended cement paste mixes. The percentages of amorphous materials and the compressive strength of the pastes due to the hydration reaction, filler effect and pozzolanic reaction were investigated. The results showed that ground rice husk ash and ground palm oil fuel ash were composed of amorphous silica material. The compressive strength of the pastes due to the hydration reaction decreased with decreasing cement content. The compressive strength of the pastes due to the filler effect increased with increasing cement replacement. The compressive strengths of the pastes due to the pozzolanic reaction were nonlinear and were fit with nonlinear isotherms that increased with increasing fineness of RHA and POFA, cement replacement rate and age of the paste. In addition, the model that was proposed to predict the percentage compressive strength of the blended cement pastes on the basis of the age of the paste and the percentage replacement with biomass ash was in good agreement with the experimental results. The optimum replacement level of rice husk ash and palm oil fuel ash in pastes was 30% by weight of binder; this replacement percentage resulted in good compressive strengths.