On the chemical durability of a metal-metalloid glass from the alloy (Fe,Cr)80(P,C,Si)20 in hardened Portland cement investigated by FT-IRRS, ESCA, and SEM/EDX

Composites of metal-metalloid glass fibres FIB-RAFLEX^TM (Fe,Cr)₈₀(P,C,Si)₂₀ with ordinary Portland cement (OPC) were prepared and used for an accelerated ageing procedure to study the cement paste-fibre interfaces which affect the mechanical behaviour of concrete composites. The role of the interface on the global behaviour of the concrete composite as a basis for the development of high-performance cementitious materials was studied on pulled out fibres by EDX, ESCA and by FTIR/RAMAN microspectroscopy. A Ca(OH)₂ rich layer is predominant for the surface of the reinforced cementitious material and represents the interface between aggregate and matrix. The interaction between aggregate and matrix is the reason for the strength of composites with this fibre in the highly alkaline environment of hydrating cements.     

Optimization of cementitious composite for heavyweight concrete preparation using conduction calorimetry

The present work investigates the hydration heat of different cement composites by means of conduction calorimetry to optimize the composition of binder in the design of heavyweight concrete as biological shielding. For this purpose, Portland cement CEM I 42.5 R was replaced by a different portion of supplementary cementitious materials (blast furnace slag, metakaolin, silica fume/limestone) at 75%, 65%, 60%, 55%, and 50% levels to obtain low hydration heat lower than 250 j g^?1. All ingredients were analyzed by energy dispersive X-ray fluorescence (EDXRF) and nuclear activation analysis (NAA) to assess the content of major elements and isotopes. A mixture of two high-density aggregates (barite and magnetite) was used to prepare three heavyweights concretes with compressive strength exceeding 45 MPa and bulk density ranging between 3400 and 3500 kg m^?3. After a short period of volume expansion (up to 4 h), a slight shrinkage (max. 0.3°/°°) has been observed. Also, thermophysical properties (thermal conductivity, volumetric specific heat, thermal diffusivity) and other properties were determined. The results showed that aggregate content and not binder is the main factor influencing the engineering properties of heavyweight concretes.

     

Study of the immobilization of226Ra

A study of the immobilization for²²⁶Ra waste has been carried out. Cement-based concrete was used as a matrix for the solidification of radium waste. The experimental results show that the cement mixture with water/cement between 0.46–0.54 has higher strengh (above 20 MPa), and the compressive strength was not reduced by addition of 1% barite or the radium waste (RaSO₄) into the concrete solid.Sponsored by the National Nuclear Corporation of China.     

Nanomaterials in Cementitious Composites: An Update

This review is an update about the addition of nanomaterials in cementitious composites in order to improve their performance. The most common used nanomaterials for cementitious materials are carbon nanotubes, nanocellulose, nanographene, graphene oxide, nanosilica and nanoTiO₂. All these nanomaterials can improve the physical, mechanical, thermal and electrical properties of cementitious composites, for example increase their compressive and tensile strength, accelerate hydration, decrease porosity and enhance fire resistance. Cement based materials have a very complex nanostructure consisting of hydration products, crystals, unhydrated cement particles and nanoporosity where traditional reinforcement, which is at the macro and micro scale, is not effective. Nanomaterials can reinforce the nanoscale, which wasn’t possible heretofore, enhancing the performance of the cementitious matrix.     

Ba0.6Sr0.4TiO3/聚偏氟乙烯-聚甲基丙烯酸甲酯复合材料的制备及其介电性能

采用流延热压工艺制备Ba_0.6Sr_0.4TiO₃(BST)/聚偏氟乙烯(PVDF)?聚甲基丙烯酸甲酯(PMMA)复合薄膜,研究了PMMA含量对复合材料微观组织结构和介电性能的影响规律。结果表明,BST相能够均匀分散在聚合物基体中,归因于PMMA与PVDF良好的相容性,2种聚合物之间的界面不分明;随着PMMA含量的增加,复合材料的介电常数先降低后升高,耐击穿强度和介电可调性先增加后减少。PMMA含量(体积分数)为15%的BST/PVDF?PMMA₁₅复合材料的综合性能最佳:介电常数为23.2,介电损耗为0.07,耐击穿强度为1412 kV·cm^-1,在550 kV·cm^-1偏压场下,介电可调性为26.2%。     

Thermal and microstructural characterization of compatibilized polystyrene/natural fillers composites

Composites of polystyrene (PS) with cellulose microfibres and oat particles, obtained by melt mixing, were examined. The compatibilization of the composites was carried out by addition of maleic anhydride-functionalized copolymers (SEBS-g-MA, PS-co-MA) and poly(ethylene glycol) to improve the fibre–matrix interfacial interactions. The plain components and their composites were characterised by FT-IR, DSC, TGA, SEM microscopy and mechanical tests. The properties of the various systems were analysed as a function of both fibre and compatibilizer amount. The compatibilized PS composites showed enhanced fibre dispersion and interfacial adhesion as a consequence of chemical interactions between the anhydride groups on the polymer chains and the hydroxyl groups on the fibres, as demonstrated by FT-IR spectroscopy. DSC analysis pointed out a neat increase of T _g of composites on addition of SEBS-g-MA, as compared to PS-co-MA. The thermal stability of composites was also influenced by the type and amount of fibres, as well as by the structure and concentration of compatibilizer. The effect of the reactive copolymers on the composites properties was accounted for on the basis of the polymer–polymer miscibility and chemical interactions at the matrix/filler interface.     

Enhanced photocatalytic activities of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> nanohybrids immobilized on cement-based materials for dye degradation

Using cement-based material as a matrix for photocatalytic hybrids is an important development for the large-scale application of photocatalytic technologies. In this work, photocatalytic activity of nanosized hybrids of TiO₂/SiO₂ (nano-TiO₂–SiO₂) for degradation of some organic dyes on cementitious materials was highlighted. For this purpose, an optimal inorganic sol–gel precursor was firstly applied to prepare the composites of nano-TiO₂–SiO₂ which was characterized by XRD, SEM and UV–Vis. Then, a thin layer was successfully coated on white Portland cement (WPC) blocks using a dipping process in a nano-TiO₂–SiO₂ solution. The effect of nano-TiO₂–SiO₂-coated WPC blocks on photocatalytic decomposition of three dyes, including Malachite green oxalate (MG), Methylene blue (MB) and Methyl orange (MO) were studied under UV irradiation and monitored by chemical oxygen demand tests. The results showed an increase in photocatalytic effects which depends on the structure and pH of the applied cement.     

金属有机框架材料对[Fe（HB（pz）3）2] 自旋转换行为的影响

通过在介孔结构金属有机框架材料MIL^-101（Cr）和MIL^-100（Al）的孔洞中合成自旋交叉化合物[Fe（HB（pz）₃）₂] 的方法,可以得到SCO@MOF复合物。通过红外光谱（FTIR）、粉末X射线衍射（PXRD）、原子吸收光谱（AAS）以及气体吸附-脱附等进行了进一步测试。通过变温磁测量对复合材料的温度诱导自旋转换行为的研究表明,复合材料的自旋转换行为发生改变甚至是消失了。复合材料的这一现象可以解释为[Fe（HB（pz）3）2] 在MOF主体材料的孔洞中形成了一种新的结晶相,且孔壁压力将会阻碍[Fe（HB（pz）₃）₂] 从低自旋态向高自旋态转变。不同SCO@MOF复合物得到了相似的自旋转换行为结果。这确认了当自旋交叉化合物在金属有机框架材料孔洞中形成时,MOFs材料的限制压力或基体效应对其自旋转换行为的影响显然是至关重要的。     

金属有机框架材料对[Fe(HB(pz)3)2]自旋转换行为的影响

通过在介孔结构金属有机框架材料MIL-101（Cr）和MIL-100（Al）的孔洞中合成自旋交叉化合物[Fe（HB（pz）₃）₂]的方法,可以得到SCO@MOF复合物。通过红外光谱（FTIR）、粉末X射线衍射（PXRD）、原子吸收光谱（AAS）以及气体吸附-脱附等进行了进一步测试。通过变温磁测量对复合材料的温度诱导自旋转换行为的研究表明,复合材料的自旋转换行为发生改变甚至是消失了。复合材料的这一现象可以解释为[Fe（HB（pz）₃）₂]在MOF主体材料的孔洞中形成了一种新的结晶相,且孔壁压力将会阻碍[Fe（HB（pz）₃）₂]从低自旋态向高自旋态转变。不同SCO@MOF复合物得到了相似的自旋转换行为结果。这确认了当自旋交叉化合物在金属有机框架材料孔洞中形成时,MOFs材料的限制压力或基体效应对其自旋转换行为的影响显然是至关重要的。     

Immobilization of Zn(II) in Portland cement pastes

The aim of this paper is to study the solidification/stabilization potential of cementitious matrices on the immobilization of Zn(II) before its disposal into the environment by determining the mechanisms of interaction between the Zn(II) ions and the binder. The results of structural and mineralogical characterization of cement pastes formed with different amounts of immobilized Zn(II) ions are presented and the study includes results from thermogravimetric analysis (TG), scanning electron microscopy, X-ray diffraction, and leaching performance. Zn(II) ions delay the hydration reaction of Portland cement due to the formation of mainly CaZn₂(OH)₆·2H₂O , as well as Zn₅(CO₃)₂(OH)₆, Zn(OH)₂, and ZnCO₃ in minor proportion. Correlations between total mass loss in TG analysis and leached Zn(II) ions in long-term curing pastes have been obtained. This result is important because in a preliminary approach from a TG on an early-aged cement paste containing Zn(II), it could be possible to perform an estimation of the amount of Zn(II) ions that could be leached, thus avoiding costly and time-consuming tests.     

Effects of surface modification of fumed silica on interfacial structures and mechanical properties of poly(vinyl chloride) composites

Poly(vinyl chloride) (PVC)-based composites were prepared by blending PVC with nano-SiO₂ particles, which were treated with dimethyl dichlorosilane (DMCS), γ-methylacryloxypropyl trimethoxy silane (KH570). The dispersion and interfacial compatibility of nano-SiO₂ particles in PVC matrix was characterized by SEM, which indicated that DDS had a better dispersion and compatibility than UTS but worse than KHS. The mechanical properties, processability and effective interfacial interaction of nano-SiO₂/PVC composites were studied. The nano-SiO₂ particles treated with KH570 or DMCS significantly reinforced and toughened the PVC composites. The maximum impact strength of PVC composites was achieved at a weight ratio of nano-SiO₂/PVC:4/100. The tensile yield stress increased with increasing the content of treated inorganic particles. The incorporation of untreated nano-SiO₂ particles adversely affected the tensile strength of the composite. Although the equilibrium torques of all nano-SiO₂/PVC composites were higher than that of pure PVC, the surface treatments did reduce the equilibrium torque. The interfacial interaction parameter, B, and interfacial immobility parameter, b, calculated respectively from tensile yield stress and loss module of nano-SiO₂/PVC composites, were employed to quantitatively characterize the effective interfacial interaction between the nano-SiO₂ particles and PVC matrix. It was demonstrated that the nano-SiO₂ particles treated with KH570 had stronger effective interface interaction with PVC matrix than those treated with DMCS, which also had stronger effective interface interaction than the untreated nano-SiO₂ particles.     

Physicochemical Characteristics of Styrene-Butadiene Latex- modified Mortar Composite vis-à-vis Preferential Interactions

The interaction between styrene-butadiene rubber (SBR) film and the ions from C₂S and C₃S hydration of Portland cement mortar composites has been evaluated by Fourier Transform Infrared Spectroscopy (FTIR), and the morphology of the composites characterized with scanning electron microscopy (SEM). The specimen used was cured for 28 days. FTIR spectrum supports the interaction of SBR with cement in the composite. Compressive strength, bulk density and water absorption properties of the cured composites were tested. Addition of SBR latex in Portland cement mortar increases the compressive strength and decreases the water absorption. Bulk density study revels interface formation in the composite. The role of the interface in relation to compressive strength of the composite has been discussed. A simple Matrix System model is shown to account composition dependence of bulk density.     

Chemistry for the design and better understanding of cement-based materials and composites

Macrodefect-free (MDF) materials are one example of “hot topics” in the field of cement-based materials and composites exerting new possibilities of the exploitation of added value. These are formed through cross-linking reactions of atoms at the interfaces of cement grains and functional polymers, when medium pressure and twin-rolling procedure are applied. The MDF-relevance of the system of Portland cement + polyphosphate is reported, together with optimal synthesis conditions and limiting rules. The chemistry knowledge about MDF materials has been shown critical for both procedure design and exploitation. Chemical shifts in both ²⁷Al and ³¹P MAS NMR spectra confirm Al(6)—O—P(4) cross-linking in virgin probes and indicate secondary hydrolysis during moisture uptake in domains free of cross-links. Thermogravimetric identification of the contents of hydrated and cross-linked phases in virgin and in moisture-attacked MDF probes displays that moisture uptake is accompanied by an increase in content of cementitious hydrates and CaCO₃. The key phenomena governing the moisture sensitivity/resistance are the density and compactness of interfacial Al(6)—O—P(4) cross-links vs. the access of the moist environment to the unreacted cement residue. The paper was presented at the 20 ICCBiC (International Conference on Coordination and Bioinorganic Chemistry) held on 5–10 June 2005 in Smolenice, Slovakia.     

Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites

Microscopic, mechanical, rheological and thermal tests were carried out in order to determine the recycling behaviour of PP/vegetal fibre composites. Different composites using hemp and sisal were characterized. All results were compared with PP-g-MA/hemp composites and PP/glass fibre composites.The results prove that mechanical properties are well conserved with the reprocessing of PP/vegetal fibre composites but that there is poor adhesion between the fibres and PP without any treatment. The addition of PP-g-MA shows an improvement of the bonding evidenced by MEB pictures. Vegetal fibres induce an increase in the percentage of crystallinity χ_c and in the crystallization temperature T_c which can be explained by the nucleating ability of the fibres improving crystallization of PP. The Newtonian viscosity η₀ decreases with cycles, indicating a decrease in molecular weight and chain scissions induced by reprocessing. The decrease of fibre length with reprocessing could be another reason for viscosity decrease.     

The use of thermal analysis in the approximate determination of the cement content in concrete

Thermal analysis was first used to investigate the pattern of dissociation of hydrated ordinary Portland cement. Portlandite (Ca(OH)₂) decomposes at about 500°C. This was confirmed by kinetic calculations. Thermal analysis was then performed to establish the effect of varying the cement content on the percent mass loss associated with the decomposition of Ca(OH)₂ in cement mortar cured for 28 days. An increasing relation was obtained. Standard concrete cubes were then prepared with cement contents ranging from 200 to 450 kg m^-3. The loss in mass on heating, up to 750°C, of concrete samples cured for 28 days was then related to the cement content in concrete. The relation obtained was tested for concrete cubes of known cement content and found to be in better agreement than the results obtained by conventional chemical analysis. This method can be used for an approximate determination of the cement content in concrete. This revised version was published online in July 2006 with corrections to the Cover Date.     

Poly‐(ε‐caprolactone) (PCL) and poly(hydroxy‐butyrate) (PHB) blends containing seaweed fibers: Morphology and thermal‐mechanical properties

Massive quantities of marine seaweed, Ulva armoricana are washed onto shores of many European countries and accumulates as waste. Attempts were made to utilize this renewable resource in hybrid composites by blending the algal biomass with biodegradable polymers such as poly(hydroxy‐butyrate) and poly‐(ε‐caprolactone). Compression‐molded films were developed and examined for their morphological, thermal and mechanical property. The Ulva fibers were well dispersed throughout the continous matrix exhibiting considerable cohesion with both polymers. Occasionally, regions with exposed fibres or aggregates were visible. About 50% algal content seemed to be an ideal concentration, thereafter, thermal stability was impacted. A progressive decrease in melting heat (ΔH_m) was observed with increased algal content as well as a decrease in the crystallinity of the polymer matrix due to the presence of the organic filler. The addition of algal fibres improved the Young modulus of the blends, creating a concomitant loss in percent elongation (El) and ultimate tensile strength. Fiber content above 40% impacted tensile property negatively and composites with over 70% fiber contents composites were too fragile. Data suggest that macro algae are compatible with both polymers and processable as fillers in hybrid blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Sulphate resistance and passivation ability of the mortar made from pozzolan cement with zeolite

Sulphate resistance and passivation ability of the mortars made from pozzolan cement of CEM IV/A (P) type according to European Standard EN 197-1 (zeolite blended cement with 60.82 mass% of PC clinker, 35.09 mass% of zeolite and 4.09 mass% of gypsum abbreviated as ZBC) and ordinary Portland cement (abbreviated as PC) are introduced. Resistance tests were performed in water and 5% sodium sulphate solution (both 20°C) for 720 days. The increased sulphate resistance of pozzolan cement relative to that of PC was found. The key quantitative insight into the hydrate phase behaviour is given by thermal analysis. This is due to pozzolanic reaction of zeolite with PC resulting in reduction of the formed Ca(OH)₂ opposite to the reference PC. Ability of pozzolan cements with 15 to 50 mass% of zeolite to protect steel against corrosion was verified in 20°C/85% RH-wet air within 180-day cure. Steel was not corroded in the mortars made with pozzolan cement containing up to 35 mass% of zeolite. Pozzolan cement of CEM IV/A (P) type containing 35 mass% of zeolite is a suitable cementitious material for concrete structures exposed to sulphate attack. Steel is protected against corrosion by this pozzolan cement in the same measure as the reference PC.     

Effect of heterogeneity on the quantitative determination of trace elements in concrete

Laser-induced breakdown spectroscopy has been used for quantitative measurement of trace elements, e.g. sulfur and chlorine, in concrete. Chloride and sulfate ions have a large effect on the durability of concrete structures, and quantitative measurement is important for condition assessment and quality assurance. Concrete is a highly heterogeneous material in composition and grain-size distribution, i.e. the spatial distribution of elements. Calibration plots were determined by use of laboratory-made reference samples consisting of pressings of cement powder, hydrated cement, cement mortar, and concrete, in which the heterogeneity of the material is increasing because of the aggregates. Coarse aggregate and cement paste are distinguishable by the intensity of the Ca spectral lines. More advanced evaluation is necessary to account for the effect of the fine aggregate. The three series of reference samples enable systematic study of the effects of heterogeneity on spectral intensity, signal fluctuation, uncertainty, and limits of detection. Spatially resolved measurements and many spectra enable statistical evaluation of the data. The heterogeneity has an effect on measurement of the sulfur and chlorine content, because both occur mainly in the cement matrix. Critical chloride concentrations are approximately 0.04% (m/m). The chlorine spectral line at 837.6 nm is evaluated. The natural sulfur content of concrete is approximately 0.1% (m/m). The spectral line at 921.3 nm is evaluated. One future application may be simultaneous determination of the amount of damaging trace elements and the cement content of the concrete.     

Sugarcane bagasse cellulose fibres and their hydrous niobium phosphate composites: synthesis and characterization by XPS,XRD and SEM

Cellulose fibres obtained from sugarcane bagasse were submitted to a purification process, which consisted of an acid hydrolysis for elimination of the major part of lignin and hemicellulose. This was followed by a delignification process carried out in two steps to yield crude cellulose (CCell) fibres in the first one and with a subsequent bleaching in order to yield bleached cellulose fibres (BCell). Composites of crude and bleached cellulose fibres with hydrous niobium phosphate, cell/NbOPO₄·nH₂O, were subsequently synthesized. Scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction characterization of the obtained materials showed CCell/NbOPO₄·nH₂O and BCell/NbOPO₄·nH₂O are real composites. The nature of the cellulose (CCell or BCell) has an important role on the composites obtained, namely on the niobium salt composition at the composite surface. The synthesis of membranes of both cellulose and mixed matrix cellulose/NbOPO₄·nH₂O was only possible when the bleached cellulose was used.     

Conductivity of composite materials based on Me2(WO4)3 and WO3 (Me = Sc,In)

Composites {Me₂(WO₄)₃ ? xWO₃} (Me = Sc, In) (x = 0.5–99%) are synthesized and characterized by XRD and electron microscopy methods and also by the density and specific surface measurements. Temperature dependences of the total conductivity of composites are measured. The contributions of σ_tot and σ_el are assessed by the $\sigma (a_{O_2 } )$ and EMF methods. The concentration dependences of conductivity and activation energy are plotted based on the σ_tot and σ_ion data. It is shown that (a) in the interval x = 0–30 vol % WO₃ (0–70 mol %), the conductivity is independent of composition and the ionic component prevails; (b) in the interval x = 60–94.5 vol % (90–99 mol %), the electron conductivity prevails and increases with the increase in x; (c) in the x interval of 30–60 vol % WO₃ (70–90 mol %), the conductivity is mixed, i.e., electron(n-type)-ionic; the latter region represents the transition interval from ionic to electron conductivity as x increases. These data are compared with the results obtained earlier for MeWO₄-WO₃ composites (Me = Ca, Sr, Ba). As regards the structural topology, the {Me₂(WO₄)₃ ? xWO₃} composites pertain to the randomly distributed type. It is shown that in contrast to {Me^IIWO₄ · xWO₃} composites, the composites under study do not form the nonautonomous interface phase with the high ionic conductivity. The possible reasons for the observed differences in the topology and the conduction type of composites based on MeWO₄ and Me₂(WO₄)₃ are analyzed.