The use of mathematical modelling in the composition of a composite material

The paper treats the use of modelling of the mixture proportioning of a new composite material (CM) on the basis of combined utilization of secondary industrial by-products [V. Petkova, Composition of Heavy Strength Concrete, Patent Ser. B No. 60100, 03.10.19094, Bulgaria]. A three-parameter polynomial model is used for the determination of the amount of the composite components cement, active additive and granulated blast-furnace slag. It is shown that using this approach, the component's influence on the changes of compressive strength in the course of up to one-year hardening of the composite can be evaluated.     

High-percentage replacement of cement with fly ash for reinforced concrete pipe

Fly ash is commonly used as a substitute for cement within concrete in various applications. Manufacturers of reinforced concrete products commonly limit the quantity of fly ash used to 25% or less by weight. Test cylinders with varying percentages of Class C (25-65%) and Class F (25-75%) fly ash and a water-reducing admixture (WRA) were created under field manufacturing conditions and tested for 7-day compressive strength. Seven-day compressive strength for the concrete/fly ash/WRA was found to be highest when the concrete mix included approximately 35% Class C or 25% Class F fly ash. However, substitution ratios of up to 65% Class C or 40% Class F fly ash for cement met or exceeded American Society for Testing and Materials (ASTM) strength requirements for manufacture of Class I, II and III reinforced concrete pipe (RCP).     

The effect of fly ash and limestone fillers on the viscosity and compressive strength of self-compacting repair mortars

Today, self-compacting mortars are preferred for repair purposes due to the application easiness and mechanical advantages. However, for self-compactability, the paste phase must meet some certain criteria at fresh state. The cement as well as the ingredients of the paste, powders with cementitious, pozzolanic or inert nature and plasticizing chemical admixtures should be carefully chosen in order to obtain a suitable paste composition to enrich the granular skeleton of the mix. The physical properties of powders (shape, surface morphology, fineness, particle size distribution, particle packing) and physico-chemical (time-dependent hydration reactions, zeta potentials) interactions between cement powder and plasticizer should be taken into consideration. All these parameters affect the performance of fresh paste in different manners. There is no universally accepted agreement on the effect of these factors due to the complexity of combined action; thus, it is hard to make a generalization.This study deals with the selection of amount and type of powders from the viewpoint of fresh state rheology and mechanical performance. The influence of powder materials on self-compactability, viscosity and strength were compared with a properly designed set of test methods (the mini-slump, V-funnel tests, viscosity measurements and compressive strength tests). It may be advised that, for each cement-powder-plasticizer mixture, a series of test methods can be used to determine the optimum content and type of materials for a specified workability.     

Polymer microsphere embedded Si/graphite composite anode material for lithium rechargeable battery

Si/graphite composite materials embedded with polymer microsphere as an elastic inactive phase were prepared by high-energy mechanical milling and investigated as a high capacity anode material for lithium rechargeable battery. Improved capacity retention was achieved with the composite. In situ measurement of the electrode thickness revealed that the swelling of the electrode became smaller with the increase of polymer microsphere content. It is believed that polymer microsphere played a buffering role of accommodating the mechanical strains induced by silicon expansion during lithiation, resulting in the suppression of the volume expansion of the electrode, which improved the cycle performance of the electrode.     

Bending and compressive behaviours of a new cement composite

The Laboratoire Central des Ponts et Chaussées (LCPC) has recently developed and patented a new cement composite, the CEMTEC_multiscale, which is stress hardening in tension and has a very high uniaxial tensile strength, more than 20 MPa. This paper is about the determination of the compressive and bending behaviors of the CEMTEC_multiscale used in the frame of ribbed slabs.The principal results obtained are the following:

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the characteristic modulus of rupture is equal to 42 MPa for the “slab” function;

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the characteristic modulus of rupture is equal to 48 MPa for the “rib” function;

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the ultimate tensile strain is around 5 10⁻³;

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the characteristic strength and ultimate strain in compression are equal to 205 MPa and 4 10⁻³, respectively; and

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the Young modulus is equal to 55 GPa and the Poisson coefficient is equal to .21.

     

On the mechanism of strength enhancement of cement paste and mortar with triisopropanolamine

Recent work on the strength-enhancing mechanism of triisopropanolamine (TIPA) suggested that TIPA enhances the mechanical properties of mortar and concrete by acting on the interfacial transition zone (ITZ) between paste and sand or aggregate rather than improving the properties of the hydrated binder. This paper presents compressive strength data for 10 Portland cements tested as cement paste as well as two different kinds of mortar after 28 days hydration, so that these two mechanisms could be compared directly. The average strength improvement with TIPA was 10% in the hydrated portland cement paste and 9% in the mortar, clearly showing that the strength enhancement is not dependent on an ITZ mechanism.     

Compressive strength and preliminary in vitro evaluation of gypsum and gypsum–polymer composites in protein-free SBF at 37 °C

Gypsum is a bioresorbable material that has been used in many applications such as tissue regeneration. Mechanical properties of gypsum have limited its applications to non-load bearing sites. The current study aimed at studying the compressive strength and behaviour of gypsum–polymer composites in protein-free simulated body fluids (SBF). Polymers studied were poly(vinyl alcohol) (PVA) and its copolymers with vinyl acetate and itaconic acid in addition to vinyl acetate and vinyl chloride. Composites with the highest compressive strength results were chosen for the preliminary in vitro evaluation in protein-free SBF solutions. Changes in the concentrations of Ca²⁺ and PO₄³⁻ ions, weight loss and morphology of the solid samples were monitored after soaking them in SBF and 1.5 SBF solutions. Results showed resorption of gypsum, concurrently with deposition of apatite in all composites, including polymer-free gypsum. Mechanical integrities of all samples were maintained, suggesting their stabilities when used as bone cements.     

Development of rapid-set high-strength cement using statistical experimental design

Many applications like aircraft runway, busy roads, highway or motorways, water tank repair, etc. demand a cement that sets fast and gains the required strength in a few hours. Though there are few cements available to meet the requirements given above, most of them are very costly, like magnesium phosphate cement, jet cement, geopolymeric cement, etc. So, an attempt has been made to make cost-effective rapid-set high-strength cement having initial setting time of ∼15 min, final setting time of ∼30 min, 4 h cold compressive strength (CCS) of ∼12 MPa (minimum), 8 h CCS of ∼24 MPa and 1 day CCS of ∼40 MPa for the neat cement. The experiments were designed using orthogonal array technique in L₉ array with three factors, namely OPC/high-alumina cement/anhydrous calcium sulphate, fineness of the cement, and type of additives, at three levels each. The responses studied are initial setting time, final setting time, and CCS after 4, 8, and 24 h curing. The response data were analysed using analysis of variance (ANOVA) technique with a software package, ANOVA by Taguchi Method (ATM). In the case of setting time, fineness of the cement and OPC/HAC/anhydrous calcium sulphate ratio plays a significant role. Additive type and the OPC/HAC/anhydrous calcium sulphate are significant factors affecting the CCS at different ages. The confirmatory trial results clearly indicate that the setting time and CCS at different ages targeted were achieved using design of experiments.     

The effect of excessive steam curing on Portland composite cement concrete

Steam curing at atmospheric pressure is an important technique for obtaining high early strength values in precast concrete production. Cement type, as well as curing period and temperature, is an important parameter in the steam-curing process. PC42.5 is the type of cement that is most commonly used in Turkish precast concrete plants. Its behavior is well known. Nowadays, the production of composite cements is becoming more popular every other day due to its advantages. The object of this study was to determine the properties of this relatively new binder comparatively with conventional PC42.5 under steam curing. For this purpose, 15-cm concrete cubes were prepared with a water/cement ratio (W/C) of 0.44 and were subjected to steam curing for five different curing periods of 4, 8, 16, 24 and 36 h under curing temperatures of 65 and 85 °C. Cement dosage was kept constant (400 kg/m³) for all specimens. The variation of compressive strength values and maturity for each condition has been presented comparatively within this study. Test results indicated that Portland composite cement (PKC/A42.5) can be used in place of PC42.5 for steam curing at atmospheric pressure in precast concrete production. However, in case of early high strength demand for early demolding purposes, curing temperature should be increased to 85 °C for PKC/A42.5 cement concretes.     

Compressive strength and impact resistance of Al2O3/Al composite structures fabricated by digital light processing

The combination of multi-materials is an alternative way to meet the diverse requirements for various applications. However, the processing difficulty especially in ceramic forming limited the structural innovations. In this paper, a combined methods of ceramic digital light processing (DLP) and metal infiltration is proposed to fabricate the Al₂O₃/Al composite structures with controllable ceramic skeletons. The interfacial, compressive and impact resistance properties were studied. The results showed that the Al₂O₃ grains were closely bonded, and no destructive defects occurred at the interface between Al₂O₃ and Al. The energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) results showed that the formation of protective phases contributed to the improvement of bonding strength. The compressive tests showed that the composite structures had better capabilities to absorb and resist the applied loads compared with Al structures. Finally, the impact resistance of the structures was discussed, the finite element analysis and the experimental results showed that the composite structures had advantages in dissipating the energy of incident objects and reducing the penetration depth. Based on these results, the damage model of Al₂O₃/Al structures was established, and the roles of different materials were revealed.     

On the presence of a critical shell volume fraction leading to pseudo-pure droplet behavior in composite droplet polymer blends

During melt mixing a ternary blend system comprised of a high density polyethylene matrix containing dispersed polystyrene and poly(methyl-methacrylate) spontaneously forms a composite droplet structure where the PS encapsulates the PMMA. This study demonstrates that the PS/PMMA composite droplet exhibits pure PS droplet behavior at a critical volume fraction of encapsulating phase (PS:PMMA∼0.6:0.4). This critical volume fraction is shown to be independent of the overall dispersed phase concentration, shell thickness or dispersed phase size. Furthermore, the effect is observed even though the PMMA is significantly more viscous than the encapsulating PS phase. Interfacial slip as well as the maintenance of a complete PS shell during deformation are proposed as being important factors related to this behavior. The blends were prepared via melt mixing using an internal mixer and the morphology was examined by electron microscopy.     

莫来石—高硅氧玻璃复相材料的研制

研究了莫来石-高硅氧玻璃复相材料的相组成、显微结构、性能及应用。从相图出发，探讨了该复相材料的制备工艺和几种不同添加剂对制备该复相材料的影响。结果表明，含K2O化合物或矿物为较理想的助熔剂，以高钾矿物为添加剂，以高岭土为原料，制备了不含方石英和刚玉、莫来石含量在55％～60％的莫来石-高硅氧玻璃复相材料，该复相材料的体积密度为2．56g·cm－3，耐火库为1750～1770℃，室温至1300℃的热膨胀系数为4．2×10－6K－1。     

Alternative calcium-sulfate-bearing materials as cement retarders: Part II. FGD gypsum

The aim of this paper is to investigate the possible displacement of natural gypsum (CaSO₄·2H₂O) in cement with an alternative setting retarder, such as the industrial by-product derived from flue gas desulfurization process called FGD gypsum. These calcium-sulfate-bearing materials (CSBM), alone or in mixtures, were ground with clinker both in laboratory and industrial scale to examine their influence on the physical and mechanical properties of cement, as well as on the industrial production line of cement. From the present work, it is extracted that the use of mixtures of sulfate-bearing materials with gypsum seems to be advantageous for the actual control of setting time. The addition of FGD gypsum increases setting time without affecting compressive strength profile. During the industrial trial, the formation of hemihydrate form of calcium sulfate dihydrate has a profound regulatory effect on the setting and strength performance of the cement partially replaced with FGD gypsum.     

The Efficiency of Cellulosic Fillers in Common Thermoplastics. Part 1. Filling without Processing Aids or Coupling Agents

Abstract

The paper reports on the processing and properties of composites consisting of thermoplastics and cellulose-based fillers. The plastics used were HDPE, PP, PS, SB, PA 6, and PA 12; the fillers were wood flour (white spruce), cellulose flour (bleached sulphate, pine) and cellulose fibre (bleached sulphate, birch). The mixtures were homogenized (kneader, alternatively single-screw extruder) before being injection moulded into tensile test bars. The modulus increased with the filler content, while the yield and breaking stress remained relatively unaffected. For HDPE, SB, and PA 12 a moderate increase in the strength level was noted. The extension at rupture and the impact strength fell sharply when the filler content was increased. The compounding method had no influence on the modulus. Kneader compounding, producing a higher homogeneity, gave in general higher strength and impact values than compounding in a single-screw extruder. The temperature dependence of the modulus was highly reduced, as was also the mould shrinkage. At processing temperatures in excess of 200°C, severe discolouration was noted.

Cellulosic fillers may be regarded as low-reinforcing fillers comparable to untreated mineral products such as calcium carbonate. On the other hand, the materials used here have the advantage of a substantially lower density.     

聚合物基纳米无机复合材料的最新研究进展

聚合物基纳米无机复合材料是一种性能优异的新型复合材料,已成为材料科学的新热点。本文综述了此种材料的特性、制备方法及应用,并概述了聚合物基纳米无机复合材料的发展前景及发展过程中应注意的问题。     

气凝胶复合材料的研究进展

气凝胶材料是一种质轻、低密的多孔材料,对其研究较多。它具有良好的发展前景和巨大的科研价值。通过介绍高分子气凝胶、碳气凝胶等复合材料的制备方法,阐述了结构与性能的关系,并对气凝胶材料未来的发展作了展望。     

高分子复合生物材料的研究进展

本文综述了近年来用于骨修复的各类高分子复合生物材料的研究状况,并从力学性能的改善和降解速率的可调性等角度,总结了高分子复合生物材料与单一组分的材料相比在生物医用领域应用中所表现出的综合使用性能的优越性,提出将与人骨中磷灰石微晶类似的无机纳米粒子与具有降解性能的有机生物材料进行复合,能够得到具有优越骨修复性能的新型骨生物材料。     

Structural properties of sepiolite-reinforced cement composite

The structural properties and optimum blend ratios of sepiolite-reinforced cement composites are investigated. It is shown that the addition of 10% sepiolite (a natural clay mineral) fibers enhances the mechanical and physical properties of the mortar. In comparison to the ordinary Portland cement mix, improvements of 3.5%, 6.2% and 7.7% in compressive strength and 12.7%, 5.7% and 6.3% in bending strength values were respectively obtained for 2, 7 and 28 days. Based on the scanning electron microscope pictures, this enhancement is attributed to the modification of the rheology of the mortar through sepiolite fibers inducing a network structure within the cement matrix.     

Modeling properties of nylon 6/clay nanocomposites using composite theories

The reinforcement of nylon 6 by layered aluminosilicates (LAS) and glass fibers was examined using the composite theories of Halpin-Tsai and Mori-Tanaka. Theoretical comparisons show that exfoliated LAS offer superior reinforcement to glass fibers owing to the filler's high modulus, high aspect ratio, and its ability to reinforce in two directions. The effect of incomplete exfoliation of simple stacks of LAS on nanocomposite modulus was also examined. Increasing the number of platelets per stack and the gallery spacing between platelets results in a dramatic decrease in reinforcing efficiency. The predictions were benchmarked against experimental data for nylon 6 nanocomposites based on organically modified montmorillonite and glass fibers. The quantitative determination of the morphology of the nanocomposites is non-trivial due to the large distribution of filler shapes and sizes present. Thus, a detailed experimental procedure for determining the aspect ratio of the nanocomposites is reported. The composite theories satisfactorily capture the stiffness behavior of both types of composites. Furthermore, experimental heat distortion temperatures and those predicted from modeling the dynamic mechanical properties of nanocomposites are in reasonable agreement.