Compressive strength and durability properties of ceramic wastes based concrete

This paper presents an experimental study on the properties and on the durability of concrete containing ceramic wastes. Several concrete mixes possessing a target mean compressive strength of 30 MPa were prepared with 20% cement replacement by ceramic powder (W/B = 0.6). A concrete mix with ceramic sand and granite aggregates were also prepared as well as a concrete mix with natural sand and coarse ceramic aggregates (W/B = 0.5). The mechanical and durability performance of ceramic waste based concrete are assessed by means of mechanical tests, water performance, permeability, chloride diffusion and also accelerated aging tests. Results show that concrete with partial cement replacement by ceramic powder although it has minor strength loss possess increase durability performance. Results also shows that concrete mixtures with ceramic aggregates perform better than the control concrete mixtures concerning compressive strength, capillarity water absorption, oxygen permeability and chloride diffusion. The replacement of cement and aggregates in concrete by ceramic wastes will have major environmental benefits.     

Compressive strength and electrical properties of concrete with white Portland cement and blast-furnace slag

Electrical resistivity is an important characteristic of concrete because it allows evaluation of the accessibility of aggressive agents prior to the beginning of the corrosive process and estimation of the corrosion propagation. This study investigated the apparent electrical resistivity of concrete mixes with white Portland cement and with and without blast-furnace slag using Wenner’s four-electrode method. The compressive strength of concrete cylinders and the electrical conductivity of the pore solution were tested. Examined slag contents were 50% and 70% by mass and the results were compared to reference mixtures of 100% white Portland cement and 100% grey Portland cement, as well as to mixtures with equal percentages of slag and grey Portland cement. Larger amounts of slag resulted in increased electrical resistivity and decreases in the electrical conductivity of the pore solution, when compared to the reference concretes. The mixture made of 50% slag and 50% white Portland cement showed, on average, compressive resistance levels between 35 MPa and 60 MPa, electrical resistivity values that were approximately five times greater, costs that were 14.6% less per m³, and whiteness similar to the reference concrete. These results indicate that white Portland cement can be partially substituted by blast-furnace slag.     

Development of the stiffness damage test (SDT) for characterisation of thermally loaded concrete

This paper describes the use of the Stiffness Damage Test (SDT) technique for quantifying the degree of deterioration experienced by thermally loaded concretes. The applicability of the SDT for assessing temperature damaged concrete has been experimentally investigated and analysed. Results have shown the SDT parameters to be sensitive to the influences of test age, the level of temperature exposure and the degree of damage caused by that exposure. A strong and consistent degree of correlation between the results obtained from the SDT and the standard test measurements (compressive strength, static modulus and ultrasonic pulse velocity) has been found. The use of the SDT as a tool for detecting pre-damage and the development of microcracking in concrete specimens subjected to compressive loading have been confirmed by Acoustic Emission (AE) test techniques.     

Effects of different nanomaterials on hardening and performance of ultra-high strength concrete (UHSC)

Nanomaterials have attracted much interest in cement-based materials during the past decade. In this study, the effects of different nano-CaCO₃ and nano-SiO₂ contents on flowability, heat of hydration, mechanical properties, phase change, and pore structure of ultra-high strength concrete (UHSC) were investigated. The dosages of nano-CaCO₃ were 0, 1.6%, 3.2%, 4.8%, and 6.4%, by the mass of cementitious materials, while the dosages of nano-SiO₂ were 0, 0.5%, 1.0%, 1.5%, and 2%. The results indicated that both nano-CaCO₃ and nano-SiO₂ decreased the flowability and increased the heat of hydration with the increase of their contents. The optimal dosages to enhance compressive and flexural strengths were 1.6%–4.8% for the nano-CaCO₃ and 0.5%–1.5% for the nano-SiO₂. Although compressive and flexural strengths were comparable for the two nanomaterials after 28 d, their strength development tendencies with age were different. UHSC mixtures with nano-SiO₂ showed continuous and sharp increase in strength with age up to 7 d, while those with nano-CaCO₃ showed almost constant strength between 3 and 7 d, but sharp increase thereafter. Thermal gravimetry (TG) analysis demonstrated that the calcium hydroxide (CH) content in UHSC samples decreased significantly with the increase of nano-SiO₂ content, but remained almost constant for those with nano-CaCO₃. Mercury intrusion porosimetry (MIP) results showed that both porosity and critical pore size decreased with the increase of hydration time as well as the increase of nanoparticles content to an optimal threshold, beyond which porosity decreased. The difference between them was that nano-CaCO₃ mainly reacted with C₃A to form carboaluminates, while nano-SiO₂ reacted with Ca(OH)₂ to form CSH. Both nano-CaCO₃ and nano-SiO₂ demonstrated nucleation and filling effects and resulted in less porous and more homogeneous structure.     

Synthesis and crystal structure of double Ln(III) malonates with Co(NH3) 6 3+ in the outer sphere

Double Ln(III) malonates of two different compositions crystallize from malonate solutions containing [Co(NH₃)₆]³⁺ ions. Lanthanides of the beginning of the series form compounds of the composition [Co(NH₃)₆][Ln(mal)₂]₃·6H₂O (I) (Ln = La, Ce, Pr, Nd; mal = C₃H₂O^2?), and those of the end of the series form compounds of the composition [Co(NH₃)₆]₂[Ln₃(mal)₇(Hmal)(H₂O)₄]·nH₂O (II) (Ln = Tb, Ho, Er, Tm). Structure I is based on trimeric anionic complexes [Ln₃(mal)₆]^3? linked with each other to form a branched 3D network with [Co(NH₃)₆]³⁺ cations and water molecules accommodated in large voids. The coordination mode of malonate ions in I with the coordination capacity equal to 5 was unknown previously for lanthanide malonate compounds. The Ln(1) atom has the maximum possible for malonate compounds coordination number (CN) 12, and the Ln(2) atom has CN 9. The structure of II consists of anionic chains [Ln₃(mal)₇(Hmal)(H₂O)₄] _n ^3? between which the [Co(NH₃)6]₃₊ cations and water molecules are arranged. One independent malonate ion in the structure is coordinated in the bidentate chelate fashion to the Ln(1) atom, and the other independent chelate-bridging ligand is coordinated in the bidentate fashion to the Ln(2) atom and in the monodentate fashion to the Ln(1) atom. As a result, tetrameric fragments linked in anionic chains are formed in the structure of II. The Ln(1) and Ln(2) atoms have CN 8.     

The influence of poly(acrylic acid) molar mass and concentration on the properties of polyalkenoate cements Part I Compressive strength

The influence of poly(acrylic acid), PAA molar mass, concentration and glass volume fraction were investigated on the compressive strength of polyalkenoate cements after ageing for 1, 7 and 28 days in water at 37°C. The compressive strength increased with the molar mass of the polyacid. The increase in compressive strength with molar mass was greater at higher PAA concentrations. Increasing the polyacid concentration generally increased the compressive strength, until PAA concentrations greater than 50% m/m were achieved. Increasing the glass volume fraction had little influence on the compressive strength of cements made with low PAA concentrations, however the compressive strength increased with glass volume fraction for cements that had a high PAA concentration. Increasing the ageing time of the cement prior to testing generally resulted in an increase in compressive strength. However the influence of ageing time was greater in cements made with high PAA concentrations.     

Preparation and properties of poly(urea–formaldehyde) microcapsules filled with epoxy resins

The poly(urea–formaldehyde) (PUF) microcapsules filled with epoxy resins have potential for self-healing or toughening polymeric composites. A series of PUF microcapsules containing epoxy resins were synthesized by selecting different process parameters including surfactant type, surfactant concentration, adjusting time for pH value and heating rate. The effects of process parameters on the size and surface morphology of microcapsules were discussed. The storage stability, solvent resistance and the mechanical strength of microcapsules were investigated. The morphology of microcapsules was observed using scanning electron microscopy (SEM) and optical microscopy (OM). The results indicate that the formation of microcapsules is affected by the surfactant type. The size of microcapsules can be controlled by the surfactant concentration. The surface morphology of microcapsules can be adjusted by the surfactant concentration, the adjusting time for pH and the heating rate. The microcapsules prepared by using surfactant sodium dodecylbenzene sulfonate (SDBS) show good storage stability, excellent solvent resistance and appropriate mechanical strength.     

Determination of the bilinear stress‐crack opening curve for normal‐ and high‐strength concrete

An improved version of the method proposed to ACI committee 446 and to RILEM TC 187‐SOC to determine the fracture parameters of concrete is applied in this study to several mixtures of normal and high‐strength concretes. The results are processed with a C++ program developed by the authors to automatise the mathematical operations required to obtain the bilinear softening curve of concrete from the experimental results. Numerical simulations of the tests are also carried out using finite elements with an embedded cohesive crack. The comparison between numerical and experimental results confirms that the experimental and numerical procedures are appropiate for normal‐strength concretes and high‐strength concretes.     

Properties of electrospun CdS and CdSe filled poly(methyl methacrylate) (PMMA) nanofibres

Electrospinning technique was used to fabricate poly(methyl methacrylate) (PMMA) fibres incorporating CdS and CdSe quantum dots (nanoparticles). Different nanoparticle loadings (2, 5 and 10 wt% with respect to PMMA) were used and the effect of the quantum dots on the properties of the fibres was studied. The optical properties of the hybrid composite fibres were investigated by photoluminescence and UV-vis spectrophotometry. Scanning electron microscopy (SEM), X-ray diffraction and FTIR spectrophotometry were also used to investigate the morphology and structure of the fibres. The optical studies showed that the size-tunable optical properties can be achieved in the polymer fibres by addition of quantum dots. SEM images showed that the morphologies of the fibres were dependent on the added amounts of quantum dots. A spiral type of morphology was observed with an increase in the concentration of CdS and CdSe nanoparticles. Less beaded structures and bigger diameter fibres were obtained at higher quantum dot concentrations. X-ray diffractometry detected the amorphous peaks of the polymer and even after the quantum dots were added and the FTIR analysis shows that there was no considerable interaction between the quantum dots and the polymer fibres at low concentration of quantum dots however at higher concentrations some interactions were observed which shows that QDs were present on the surfaces of the fibres.     

Synthesis and characterization of Fe(III)-silicate precipitation tubes

Fe(III)-silicate precipitation tubes synthesized through “silica garden” route have been characterized using a number of analytical techniques including X-ray diffraction, infrared spectroscopy, atomic force microscopy, scanning and transmission electron microscopy. These tubes are brittle and amorphous and are hierarchically built from smaller tubes of 5-10 nm diameters. They remain amorphous at least up to 650 °C. Crystobalite and hematite are the major phases present in Fe(III)-silicate tubes heated at 850 °C. Morphology and chemical compositions at the external and internal walls of these tubes are remarkably different. These tubes are porous with high BET surface area of 291.2 m²/g. Fe(III)-silicate tubes contain significant amount of physically and chemically bound moisture. They show promise as an adsorbent for Pb(II), Zn(II), and Cr(III) in aqueous medium.     

Characterization and bond strength of electrolytic HA/TiO<Subscript>2</Subscript> double layers for orthopaedic applications

Insufficient bonding of juxtaposed bone to an orthopaedic/dental implant could be caused by material surface properties that do not support new bone growth. For this reason, fabrication of biomaterials surface properties, which support osteointegration, should be one of the key objectives in the design of the next generation of orthopaedic/dental implants. Titanium and titanium alloy have been widely used in several bioimplant applications, but when implanted into the human body, these still contain some disadvantages, such as poor osteointegration (forming a fibrous capsule), wear debris and metal ion release, which often lead to clinical failure. Electrolytic hydroxyapatite/titanium dioxide (HA/TiO₂) double layers were successfully deposited on titanium substrates in TiCl₄ solution and subsequently in the mixed solution of Ca(NO₃)₂ and NH₄H₂PO₄, respectively. After annealing at 300∘C for 1 h in the air, the coated specimens were evaluated by dynamic cyclic polarization tests, immersion tests, tensile tests, surface morphology observations, XRD analyses and cells culture. The adhesion strength of the HA coating were improved by the intermediate coating of TiO₂ from 11.3 to 46.7 MPa. From cell culture and immersion test results, the HA/TiO₂ coated specimens promoted not only cells differentiation, but also appeared more bioactive while maintaining non-toxicity.     

Preparation of Sm-doped ceria (SDC) nanowires and tubes by gas–liquid co-precipitation at room temperature

Sm-doped cerium dioxide (SDC) with fcc structure was formed using a gas–liquid chemical co-precipitation process at room temperature. Morphology and structure of the as-prepared samples were characterized using TG, XRD, TEM, HRTEM and SAED techniques. Under our specific experimental conditions, two kinds of 1D nano-structures SDC have been mainly obtained. SDC nanowires are 0.3–1.2 μm in lengths and 5–20 nm in diameters. SDC nanotubes have outer diameters in 10–40 nm with lengths up to 2 μm. The as-prepared SDC shows very strong UV absorption ability and the maximum absorption peak redshifts compared with that of SDC nanoparticles.     

Thermal and mechanical properties of poly(ether ester)-based thermoplastic elastomer composites filled with TiO<Subscript>2</Subscript> nanoparticles

Poly(butylene terephthalate)-block-poly(tetramethylene glycol) (PBT-PTMG)-based thermoplastic elastomer (TPE) was filled with nano TiO₂ particles by direct melt blending. The particle content in matrix was varied from 1.3 to 4.9 vol.%. The samples were characterized using SEM, μCT, DSC, TGA, DMTA and tensile test. SEM examination shows strong interfacial interactions between TPE matrix and TiO₂ particles due to formation of chemical bonds. The incorporation of TiO₂ particles increases overall the thermal properties of soft and hard segments such as the glass transition temperature, the melting temperature, and the thermal stability of material. The tensile properties of TPE are also significantly improved indicated by increased tensile strength and modulus. Increasing particle content leads to increased mechanical properties and thermal stability of composites.     

Synthesis of new crystalline Pu(V) compounds from solutions: I. Structure and characteristics of a double Pu(V) phthalate with [Co(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>]<Superscript>3+</Superscript> in the outer sphere

The conditions of synthesis of Pu(V) phthalates by conversion of Pu(VI) into the pentavalent state with addition of H₂O₂ in the presence of excess of phthalate ions (L) were determined. Subsequent addition of [Co(NH₃)₆]Cl₃ allowed isolation of crystalline [Co(NH₃)₆][PuO₂L₂]2H₂O isostructural with [Co(NH₃)₆][NpO₂L₂]2H₂O studied previously. The thermal behavior and IR spectra of both compounds were studied.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 516–520.Original Russian Text Copyright © 2004 by Krot, Bessonov, Grigorev, Charushnikova, Makarenkov.     

Comparison of compressive and splitting tensile strength of autoclaved aerated concrete (AAC) containing water hyacinth and polypropylene fibre subjected to elevated temperatures

This paper described the results of an extensive experimental study on the comparative between compressive and splitting tensile behavior of autoclaved aerated concrete (AAC) containing water hyacinth fibre (WHF) with AAC mixed with polypropylene (PP) fibre. The specimens of AAC-WHF and the AAC-PP were subjected to elevated temperatures (100, 200, 400, 800 and 1000 °C). Test results indicated that an optimum water hyacinth and PP fibre dosage was at 0.5 and 0.75 % by volume respectively. The maximum residual in compressive strength and the splitting tensile strength of AAC-WHF and AAC-PP were 0.43 and 0.16 N/mm² and 0.51 and 0.18 N/mm² respectively. In addition, the loss in residual strength of AAC mixed PP fibre was slower than AAC mixed WHF. The splitting tensile strength of AACs was more sensitive to high temperatures than the compressive strength. A severe strength loss was observed for all of the AAC after exposure to 800 °C. Based on the test results, it can be concluded that the addition of PP fibers can significantly promote the residue mechanical properties of AAC during heating.     

Facile preparation and thermal degradation studies of graphite nanoplatelets (GNPs) filled thermoplastic polyurethane (TPU) nanocomposites

A facile method with the advantage of using only one single solvent throughout the whole processing was introduced to prepare graphite nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) nanocomposites. Morphological studies showed that the employed method could provide the uniform dispersion of GNPs in the TPU matrix. Storage modulus of the nanocomposites was increased with increasing GNP content, and the improvement was more obvious at temperatures below the glass transition temperature (T_g) of TPU. For the nanocomposite that contains 3.9 vol% (the maximum loading employed in this study) of GNP, it still showed a long elongation at break of over 600%. Thermogravimetric analysis (TGA) showed that the incorporation of GNPs could improve the thermal stability of the nanocomposites. In addition, cone calorimetry results showed that the GNPs could act as intumescent flame retardant and significantly reduced the heat release rate (HRR), thus improved the flame retardancy of the TPU matrix.     

Synthesis and properties of a copper(I) cobalt(II) double sulfite

The Pourbaix diagrams of the Cu–H₂SO₄–H₂O and Co–H₂SO₄–H₂O systems have been refined and the stability regions of sulfite phases in the diagrams have been identified. Phase diagrams of copper(I) copper( II) and copper(I) cobalt(II) double sulfites have been mapped out. The double sulfites Cu₂SO₃ · СuSO₃ and Cu₂SO₃ · СoSO₃ have been isolated from an aqueous solution saturated with sulfur dioxide. We have obtained electron paramagnetic resonance spectra of the double sulfite Cu₂SO₃ · СoSO₃ and characterized it by X-ray diffraction, IR spectroscopy, particle size analysis, and thermogravimetry. A foundation has been laid for the thermodynamic prediction of the synthesis of the Cu₂SO₃ · MSO₃ (M = Cu, Co) double sulfites.     

Recombination instability and double S-switching in <Emphasis Type="Italic">p</Emphasis>-Ge(Au)

We report on the experimental investigation of p-Ge(Au) samples and compare the results qualitatively to a one-dimensional theoretical model describing the recombination instability of current in gold-compensated germanium in a two-parameter (voltage-emission) space. Experiments showed the existence of three regimes of the system functioning in the parametric space. The second S-switching region was found on the current-voltage characteristic, which is probably related to a noise-induced nonequilibrium phase transition.     

Preparation and properties of poly(propylene-g-maleic anhydride) filled with expanded graphite oxide

Poly(propylene-g-maleic anhydride) (PPMA) layered expanded graphite oxide (EGO) (PPMA–EGO) composites were prepared by melt dispersion in an internal shear mixer. EGO influenced crystalline structure, thermal and dynamic thermomechanical properties of PPMA–EGO composites. Wide-angle X-ray diffraction revealed no change in d spacing of EGO. Crystallization temperature increased, due to heterogeneous nucleation by EGO. Thermogravimetry demonstrated enhanced thermal stability, due to thermal insulation, adsorption of PPMA degradation products and a tortuous path for escaping vapors. Dynamic mechanical analysis showed that the EGO in PPMA matrix provided modulus reinforcement and increased glass transition temperature. These enhancements were attributed to interactions and potentially bond formation between EGO and the maleic anhydride of PPMA. Electrical conductivity of PPMA–EGO increased at 3 %·W/W of EGO indicating a percolation threshold that can lead to semi-conductor application.     

Measurement of concrete strength using the emission intensity ratio between Ca(II) 396.8 nm and Ca(I) 422.6 nm in a Nd:YAG laser-induced plasma

An experiment to investigate the potential of a laser-induced plasma method for determining concrete compressive strength was conducted by focusing a Nd:YAG laser on concrete samples with different degrees of compressive strength. This technique was developed in light of the role of the shock wave in the generation of a laser-induced plasma. It was found that the speed of the shock front depends on the hardness of the sample. It was also found that a positive relationship exists between the speed of the shock front and the ionization rate of the ablated atoms. Hence, the ratio of the intensity between the Ca(II) 396.8 nm and Ca(I) 422.6 nm emission lines detected from the laser-induced plasma can be used to examine the hardness of the material. In fact, it was observed that the ratio changes with respect to the change in the concrete compressive strength. The findings also show that the ratio increases with time after the cement is mixed with water.