Skid Resistance of Asphalt Concrete based on Mixture and Aggregate Characteristics: Predictive Model Development for Thailand

This research aims to produce a new predictive model of skid resistance in asphalt concrete, with a particular focus on Thailand. Skid resistance in road pavements is an inherent safety factor affecting vehicle users. Thus improvements in this area will greatly enhance road network safety in Thailand. A skid resistance predictive model, based upon the essential aggregate and mixture characteristics that significantly relate to the skid resistance values of asphalt concrete was developed. In this study, three types of aggregate (limestone, granite and basalt) were collected. These aggregates, obtained from 14 provinces in Thailand were representative of all of Thailand’s aggregates. Petrographic Analysis, Gradation tests, Aggregate Impact tests (AIV), Aggregate Crushing tests (ACV), the Los Angeles Abrasion (LA) test, Soundness tests, Polishing Stone tests (PSV) and the British Pendulum Test (BPT), along with the standard mix design were performed. These procedures determined all the essential characteristics in the mixtures and aggregates of asphalt concrete. The results of the research demonstrate that some aggregate characteristics are statistically significant in their relationship to the skid resistance values of asphalt concrete mixtures. These findings will be embraced in the preventive scheme under the strategic road safety management of the Department of Rural Roads, Thailand

Antibiotic production and biocontrol activity by Bacillus subtilis CL27 and Bacillus pumilus CL45.

Bacillus subtilis CL27 and B. pumilus CL45 showed similar activity against Botrytis cinerea in in vitro plate assays. In a seedling bioassay, however, B. subtilis CL27 had activity similar to a commercial fungicide while B. pumilus CL45 failed completely to prevent seedling damping-off caused by Bot. cinerea. Antibiotic production by the two Bacillus strains was found to depend on the growth substrate and highest antibiotic production was found on media based on homogenized cabbage tissue. Antibiotic activity was found to depend on the pH and nutrient concentration in the assay medium. Antifungal antibiotics produced by B. subtilis CL27 and B. pumilus CL45 in different fermentation media were separated by thin layer chromatography. As suspected from the activity spectrum, three antibiotics (one with activity against Alternaria brassicicola, one with activity against Botrytis cinerea and one with activity against both fungi) could be detected in the fermentation broth of CL27, but only one in the fermentation broth of CL45. The two antibiotics produced by strain CL27 with activity against A. brassicicola were identified as peptides since their bands on the TLC plates developed a green to blue/green colour after treatment with 4,4'-tetramethyldiamino-diphenylmethane (TDM) reagent. The third antibiotics produced by strain CL27 and antibiotic produced by CL45 had a similar Rf-value and appeared not to be peptides based on the reaction with TDM. However, they showed a slightly different activity spectrum when tested against a range of different fungi. Antibiotic production was clearly indicated as the mode of action of in vivo biocontrol by strain CL27 against damping off caused by Bot. cinerea of Astilbe micro-plants, because a u.v.-induced antibiotic negative mutant strain CL27b showed no activity in seedling bioassays in vivo. Also the mutant strain CL27a which produced the two peptide antibiotics but had lost the ability to produce the non-peptide antibiotic, showed greatly reduced in vivo activity