SGC Tests for Influence of Material Composition on Compaction Characteristic of Asphalt Mixtures
Compaction characteristic of the surface layer asphalt mixture (13-type gradation mixture) was studied using Superpave gyratory compactor (SGC) simulative compaction tests. Based on analysis of densification curve of gyratory compaction, influence rules of the contents of mineral aggregates of all sizes and asphalt on compaction characteristic of asphalt mixtures were obtained. SGC Tests show that, for the mixture with a bigger content of asphalt, its density increases faster, that there is an optimal amount of fine aggregates for optimal compaction and that an appropriate amount of mineral powder will improve workability of mixtures, but overmuch mineral powder will make mixtures dry and hard. Conclusions based on SGC tests can provide basis for how to adjust material composition for improving compaction performance of asphalt mixtures, and for the designed asphalt mixture, its compaction performance can be predicted through these conclusions, which also contributes to the choice of compaction schemes.
Effect of Flat and Elongated Coarse Aggregate on Field Compaction of Hot-Mix Asphalt
It has long been believed that coarse aggregates that have a flat and elongated (F&E) shape are detrimental to the properties of hot-mix asphalt. Several attempts have been made to establish a relationship between these aggregate particles and performance. It is believed that decreased performance may result from either aggregate breakage or less than optimum particle orientation. The question of mixture performance is set aside, and the focus is on the construction effects in asphalt mixtures with high percentages of F&E aggregate. Research shows that for a given gradation and aggregate type, increasing the percentage of F&E will increase the amount of aggregate breakdown. One focus is to determine if the same relationship between percentage of F&E particles and breakdown that has been documented in laboratory settings can be observed in the field. The other focus is on a comparison of the aggregate breakdown caused by the gyratory compactor with the aggregate breakdown in the field.
Transmission electron microscopy of lattice planes in human alveolar bone apatite crystals
SummaryPeriodic fringes corresponding to six different lattice planes have been observed in apatite crystals of human normal alveolar bone by transmission electron microscopy. Three of these sets of fringes have spacings less than 3.5 Å corresponding to the Scherzer resolution of the microscope used. The (0002) lattice plane of hydroxyapatite of 3.4 Å d-spacings, the
$$\left( {21\bar 11} \right)$$
 lattice plane with a d-spacing of 2.81 Å, and the
$$\left( {30\bar 30} \right)$$
 lattice plane with a d-spacing of 2.72 Å have been identified. The (0002) and
$$\left( {21\bar 21} \right)$$
 lattice planes have been observed for the first time in bone microcrystals. Some of the crystals studied were characterized by a mean width/thickness ratio of 6.91, typical of platelike habit, whereas observations of crystals aligned along the
$$\left\langle {1\bar 210} \right\rangle $$
 and
$$\left\langle {1\bar 211} \right\rangle $$
 directions showed a needlelike habit. The mean length of the bone apatite crystals was 470 Å. A dark line similar to the one observed in enamel and dentine crystals was also seen. The bone microcrystals observed have shown a high sensitivity to beam damage.