The friction of polymers under hydrostatic pressure

This paper reports data on the effect of hydrostatic gas pressure on the coefficient of sliding friction of several polymers. In general increasing the pressure causes a reduction in the observed coefficient of friction. Two simple friction models are used in an attempt to explain the data. Neither is completely satisfactory. However there appears to be a good empirical correlation between the observed friction and the low strain value of the dynamic loss modulus.     

Interfacial phenomena in steel fibre reinforced cement II: Pull-out behaviour of steel wires

This paper describes a study of the processes involved at and near the steel-matrix interface when an embedded steel wire is pulled out of a cement paste or mortar matrix. Prior to debonding, shrinkage leads to micro-cracking of the matrix which in turn reduces the stress transfer at the interface. The behaviour after debonding, which constitutes the major part of the study, is again markedly non-linear. This arises from compaction of the cement paste in the vicinity of the wire and is produced by the pull-out process itself. The compaction is more marked with rougher wires and occurs to a greater degree with cement paste than with mortars.     

Determination of the vapor pressures of select polychlorinated dibenzo-p-dioxins and dibenzofurans at 75-275 °C

Vapor pressures were determined for several polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) at 75-275 °C, extending the available literature data to more relevant temperature regions and providing the first experimental data for 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-TriCD). A modification of the effusion technique, based upon controlling the diffusion of the target compound and subsequent high resolution gas chromatography/low resolution mass spectrometry (HRGC/LRMS) analysis, was proven comparable to other accepted methods for determining the vapor pressures of semi-volatile organic compounds (SVOCs). Vapor pressures for octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) were in excellent agreement with those reported in literature. The application of the current method for the vapor pressure determinations of eight polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/PCDFs) in the extended temperature range (up to 275 °C) is reported. The extension of the vapor pressures to such temperatures, unprecedented for the PCDDs/Fs, is important for vapor-particle partitioning modeling in regions relevant to PCDD/F formation and control. Estimates for the melting temperatures and enthalpies of sublimation and vaporization are also reported, the latter for which no experimentally determined values have been found in the literature. The use of the method to deliver reproducible, trace concentrations (ppt-ppb) of targets was applied to the calibration of the jet-REMPI/TOFMS as an online detector for low chlorinated PCDDs/Fs.     

Adhesives in construction: A contractor's viewpoint

The development of epoxy- and polyester-based adhesives has dramatically widened the scope of adhesive bonding in the civil engineering industry but the technology of the adhesives used has often been more appropriate to the workshop than to the construction site. There is a need for the suppliers of structural adhesives to recognize this and to develop compositions and application techniques more amenable to site use. It is equally necessary for the construction industry to make more effort to understand these materials, to take advantage of their outstanding properties, and hence to use them successfully for the construction and repair of concrete structures.