Influence of aggregates on chloride diffusion coefficient into mortar

In order to determine the influence of aggregates on chloride ion ingress, mortar specimens were cast with different aggregate size distribution and the same aggregate volume content. One side of the specimen was in contact with alkaline solution containing sodium chloride. The process of chloride ingress is due to diffusion. The effect of the interfacial transition zone (ITZ) around aggregate and of the tortuosity due to aggregates have been taken into account for interpreting the experimental data obtained. These two competing effects have been quantified by using the theory of composite materials. It appears that the diffusion coefficient varies as a function of the ITZ volume content and of the tortuosity.     

Thermotropic liquid crystalline polymer (Rodrun LC5000)/polypropylene in situ composite films: rheology, morphology, molecular orientation and tensile properties

In situ composite films were prepared by a two-step method. First, polypropylene and thermotropic liquid crystalline polymer (TLCP), Rodrun LC5000 (80 mol% p-hydroxy benzoic acid (HBA)/20 mol% polyethylene terephthalate (PET)), were melt blended in a twin-screw extruder and then fabricated by extrusion through a mini-extruder as cast film. Rheological behavior of the blends, morphology of the extruded strands and films, and tensile properties of the in situ composite films were investigated. Rheological behavior of the blends at 295 °C studied using a plate-and-plate rheometer revealed a substantial reduction of the complex viscosity with increasing TLCP content, and all specimens exhibited shear thinning behavior. Over the angular frequency range of 0.6-200 rad/s, the viscosity ratio (dispersed phase to matrix phase) was found to be very low, in the range of 0.03-0.07. Morphologies of the fracture surfaces of the blend extrudates and the film surfaces etched in permanganic solution were investigated by scanning electron microscope (SEM). The TLCP droplets in the extruded strands were seen with a progressive deformation into fibrillar structure when TLCP content was increased up to 30 wt%. In the extruded films, TLCP fibrils with increasing aspect ratio (length to width) were observed with increasing TLCP concentration. Orientation functions of each component were determined by X-ray diffraction using a novel separation technique. It was observed that the Young's modulus in machine direction of the extruded film was greatly improved with increasing TLCP loading, due to the increase in fiber aspect ratio and also molecular orientation.     

A study of global vs. local properties for maleic anhydride modified polypropylene nanocomposites

Nanoindentation of organomodified clay filled maleated polypropylene (MAPP) was investigated. The study aims to identify the relative increase in local stiffness in comparison to the increase in mechanical properties of the bulk in polypropylene-based nanocomposites. Such a study allows one to assess confined material property in addition to increased filler volume at the local scale. A mixture of highly intercalated and well exfoliated clay structures, when dispersed in MAPP matrix, was observed under transmission electron microscopy. The degree of exfoliation was found to increase with clay loading, which was attributed to the higher viscosity and mechanical shear forces during melt compounding. Instrumented indentation was performed on (1) clay aggregate supported by MAPP matrix, (2) clay-matrix boundary, and (3) the MAPP matrix. The clay aggregated region generally showed higher stiffness as compared to the matrix. And, the relative increase in indentation stiffness is substantially higher than the relative increase in tensile and compressive stiffnesses for clay reinforced systems. Polymer chain confinement and topological constraint appeared to be operative to enhance local stiffness in the clay aggregated region. Good correlation was, however, obtained between the change in macroscopic stiffness and the change in highly local indentation stiffness as a result of clay reinforcement.     

动态硫化EPDM/PP热塑性弹性体的研究进展

阐述了EPDM/PP共混型热塑性弹性体的发展历史、微观结构、性能、硫化体系、制备工艺、加工设备及研究展望。     

聚丙烯接枝改性及其接枝物的应用

对聚丙烯接枝的几种方法、单体和引发剂的选择及接枝物的表征作了简要的介绍；并介绍聚丙烯接枝物的应用情况。     

Preparation and characterization of polypropylene/layered silicate nanocomposites using an antioxidant

Polypropylene (PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine (C18-MMT) and antioxidant, to investigate the role of antioxidant. TEM and X-ray scattering results confirmed the intercalated state of silicates in PP/layered silicate nanocomposites with antioxidant. In rheological and mechanical study, the nanocomposites with antioxidant showed higher properties than those of the unfilled PP. The nanocomposite with 5 wt% C18-MMT and 0.5 phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher storage modulus than the unfilled PP. However, PP/C18-MMT without antioxidant showed lower rheological values owing to the thermal decomposition of PP and the poor compatibility between PP and C18-MMT. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT. According to the real time X-ray diffraction, the nanocomposite showed the weak ordering of PP crystals than the unfilled PP in the load-extension plateau region of elongation.     

Damage evolution analysis in mortar, during compressive loading using acoustic emission and X-ray tomography: Effects of the sand/cement ratio

This paper explores the use of acoustic emission (AE) and X-ray tomography to identify the mechanisms of damage and the fracture process during compressive loading on concrete specimens. Three-dimensional (3D) X-ray tomography image analysis was used to observe defects of virgin mortar specimen under different compressive loads. Cumulative AE events were used to evaluate damage process in real time according to the sand/cement ratio. This work shows that AE and X-ray tomography are complementary nondestructive methods to measure, characterise and locate damage sites in mortar. The effect of the sand proportion on damage and fracture behaviour is studied, in relation with the microstructure of the material.     

Exploring the effect of dry premixing of sand and cement on the mechanical properties of mortar

A spout-fluid bed device was developed for dry premixing sand and cement to produce mortar. The goal of the work was to explore the efficacy of a new method for dispersing cement in sand to produce a mortar with better mechanical and physical properties. This strategy was found to work best at high sand/cement ratios, indicating that the dry premixing is more effective as the cement content is reduced and that it may be possible to produce commercially acceptable mortars with a lower cement content. Other properties of the mortar are also positively affected, including a decrease in the shrinkage and an increase in the workability.     

Application of an interpenetrating network model to the solid deformation of a quenched isotactic polypropylene film

The molecular orientation and deformation mechanisms of a quenched isotactic polypropylene (iPP) film deformed at temperatures between 303 K and the melting point are studied. At draw temperature T_E less than 400 K where the degree of crystallinity does not change markedly, a linear relationship between molecular orientations of the crystalline and the amorphous phases is revealed and the slope is estimated about 1.82. The interpenetrating network (IPN) model, that takes into account the plastic response of the crystalline (C) network formed by a small portion of crystallites adhered through intercrystalline links and the pseudo-affine deformation of the crystallite enhanced amorphous matrix (CEAM) network, is able to account for inhomogeneous deformation behavior on the mesoscale accompanied with the localized necking in this T_E range. Meanwhile, the initial Young's modulus and the true yield stress exerted by the deformation of the rigid C network exhibit the Arrhenius type of dependence on T_E. The apparent shear modulus of the CEAM network as a function of T_E is discussed in relation to variations in numbers and average molecular weights of the crystalline and the amorphous sequences being manifested by small consecutive endothermic and exothermic peaks in the DSC curve. The IPN model becomes invalid for deformations above T_E=400 K where morphological changes are induced due to melting of crystallites as proved from the DSC measurement.     

Alkali silica reactivity of agglomerated silica fume

It is commonly accepted that replacement of a portion of cement in mortar or concrete with well-dispersed silica fume reduces expansion caused by alkali silica reaction. Recently there has been much discussion that large, agglomerated particles of silica fume may actually act as alkali silica reactive aggregates, thereby increasing expansion rather than reducing it. The data in the literature, from both field and laboratory studies, are inconsistent. This prompted an extensive laboratory investigation into the alkali silica reactivity of silica fume. Results from accelerated expansion testing and microscopic investigations are presented. It was seen that some agglomerated silica fumes participate in ASR while others do not. Factors determining the reactivity of silica fume agglomerates are suggested.