Papers by Keyword: Void Content

Abstract: Pervious concrete is considered an advanced pavement material in terms of environmental benefits resulting from its basic feature - high water permeability. While natural aggregate is a standard component for permeable concrete production, the paper presents the potential of air-cooled blast furnace slag aggregate. The aggregate is specific for its open internal structure and at the same time high hardness and strength, which was assumed to be advantageous for this type of concrete. As permeable concrete is characterized by a specific structure and low amount of binder, it needs for optimization of kind and composition of aggregate, as well as the quantity and quality of the binder. In the experiment, following variables of composition were applied: a ratio of binder to aggregate b/a (0.28 and 0.36), a ratio of fine to coarse aggregate f/c (0.1, 0.2 and 0.3), and a set of blended cements. Experimental results point to the specific benefit of slag aggregate for permeable concrete production. The values of total porosity (30-38%) and permeability (4.6-17.5 mm/s) are higher than those recommended by most publications, as well as than those of concretes with natural aggregates. The compressive strength runs from 7.5 MPa to 15.0 MPa depending on the variables, while the effect of fine aggregate portion on both compressive strength and hydraulic conductivity is found to be much greater than that of the amount of binder. An important aspect is that, due to the nature of the aggregate, sufficient permeability is maintained even with higher proportion of fines. The range and variance values of the individual properties indicate that a change in the quality of the binder causes less variation in the results than a change in the composition of the mixtures.

Abstract: Additive Manufacturing (AM) is revolutionizing the manufacturing industry as various AM technologies continue to mature and more AM-compatible materials are being developed. Polyether ether ketone (PEEK) is one of the promising materials at the forefront of this technological revolution as efforts to enhance its application as a 3D-printing material are continuously being pursued. In this study, the effect of printing parameters on the void content of 3D-printed PEEK was examined using a non-destructive method, X-ray micro computed tomography (X-ray micro-CT). Of the fused filament fabrication (FFF) parameters considered, higher nozzle temperature and printing speed were seen to promote an increase in void content while higher build plate temperature reduces it. Void content has a direct effect on the mechanical and other properties of the manufactured material and therefore provides a link between the printing parameters and the expected mechanical performance of these materials. This study also highlights the importance of choosing the right printing parameters to ensure the quality of the manufactured PEEK.

Abstract: This research addresses the influence of various processing parameters on the post cure quality of carbon fibre composites. Four processing parameters were investigated in the study, in terms of their impact on void content and overall compressive strength. The first parameter distinguishes between laminates cured in a vacuum oven and those cured in an autoclave under high positive pressure. The second parameter describes the impact on voids of differing fibre architectures, comparing a unidirectional fibre structure to that of woven cloth. Thirdly, the influence of compaction during manufacture is analysed and lastly, variation in cure temperature was tested to determine its effect on final laminate quality. The quality of the cured laminate samples was assessed from visual inspection, and in terms of compressive strength and void fraction calculated by Micro-CT X-ray Tomography. The results show that autoclave-cured samples feature significant quality improvements in terms of void fraction and compressive strength when compared to oven-cured samples. Unidirectional laminates incur higher sensitivity to void inclusion than cloth laminates due to the influence of fibre wrinkling. Compaction has no effect on laminate strength; it does however reduce variability in certain cases. Temperature affects different fibre structures in different ways, these being highly dependent on curing method. Finally, it was discerned that curing by autoclave was the dominant processing parameter. Thus, regardless of other manufacturing techniques, the autoclave samples featured almost zero voids and were consequently of the highest quality.

Abstract: As a new kind of pavement material, the Open Graded Friction Course (called OGFC) has many advantages, and so is rapidly popularized in China recently. However, the performance of OGFC decreases with the utilization of road, such as the decrease in permeability, durability and so on. In the present study, the influence of the shape of coarse aggregate, which is the most important material in OGFC, on the performance of OGFC was investigated in laboratory. The shape of coarse aggregate is indicated by the bulk density and total 4 kinds of aggregates with different bulk density were produced artificially and tested in this study. When the shape of coarse aggregate changed, the wear resistance and dynamic stability of OGFC also changed lightly. The bulk density of aggregate has no serious influence on the void content, but has obvious influence on the permeability of OGFC. The shape of continuous void in horizontal cross-section becomes rounder when the aggregate with large bulk density is used. The rounder continuous void is benefit for the flowing of water, so the permeability of OGFC is improved.

Abstract: The microstructure (i.e., fibre volume fraction, void content, and fibre misalignment) of unidirectional carbon fibre-reinforced polymer (CFRP) composites was optimised by controlling several parameters during manufacture, namely: (i) compressive pressure (0.25~1.25 MPa, in steps of 0.25 MPa), (ii) vacuum pressure (−0.15, −0.20, −0.30, −0.45, and −0.65 MPa), and (iii) holding temperature (100~140 oC, in steps of 10 oC), applied during autoclave curing with the holding time being 30 minutes for all specimens. Optical micrographs captured from cross-sectional, through-the thickness areas, and in-plane areas of the resulting composites were evaluated and analysed in order to describe their microstructural characteristics.

Abstract: Eliminating common defects such as voids, bubbles and poor adhesion at interfaces will increase the quality of laminated sandwich composite structure. We are experimenting and analyzing the effect of mechanical vibrations applied to the curing system of composite materials production, particularly on minimizing void content. The range of frequency of vibrations covered was from 2Hz to 8kHz, for different period of vibrations. The composite laminates were made by hand lay-up using glass fibres and vinyl-ester resin, and examined under a microscope to determine types and quantity of defects. The results showed reduction in the number of bubbles (as well as in void content) at frequencies between 10Hz and 50Hz for 30 minutes of vibrations.