Effects of Water Immersion on the Adhesion between Adhesive Layer and Concrete Block

The effectiveness of load transfer in the CFRP-adhesive-concrete system highly relies on the integrity of the interfacial bond between adhesive layer and concrete. In the present paper, the effects of water immersion on the mode I fracture energy of the adhesion between CFRP adhesive and concrete were investigated experimentally and numerically. Four-point bending test was conducted to measure the mode I fracture energy of the interfacial layer between adhesive and concrete. The moisture content distribution and the hygrothermal stress were determined by using the finite element method (FEM). The mode I fracture energy was found decreasing with increasing immersion time. The difference between the mode I fracture energy at 2 weeks and 4 weeks is rare. The failure mode of the four-point bending test specimen shifts from concrete failure to interfacial debonding. The moisture content at the adhesive/concrete interface reaches equilibrium after 2 weeks of water immersion. The hygrothermal stress between adhesive and concrete is smaller than the tensile strength of concrete. Deterioration of the physical bond leads to the degradation of bonding strength. The reduction of the mode I fracture energy is more severe than that of the mode II fracture energy.

Distribution of insect galls in xeric and mesic habitats of Floresta Nacional de Silvânia, Brazil

ABSTRACT We investigated the insect gall distribution along savanna (xeric) and forest (mesic) vegetation in the Floresta Nacional de Silvânia, Goiás, Brazil. We tested if the insect gall diversity is higher in the xeric vegetation than in the mesic vegetation, as predicted by the hygrothermal stress hypothesis. The insect gall fauna was surveyed between December 2009 and June 2010 in two transects established each vegetation type. In total we found 186 insect gall morphotypes, distributed on 35 botanical families and 61 plant species. Cecidomyiidae (Diptera) induced the most insect galls (34.1%), and the plant family Fabaceae had the greatest richness of insect gall morphotypes (18). We recorded 99 insect gall morphotypes in the forest and 87 morphotypes in the savanna vegetation, being that none insect gall morphotype occurred in both habitats. We found that the insect gall richness and abundance did not differ between forest and savanna transects. On the other hand, the estimated insect gall richness was higher in the forest than in the savanna. Our findings contrary the hygrothermal stress hypothesis possibly because forest habitats have higher plant architecture complexity and occurrence of super-host taxa than the savanna habitats.

Analysis of Local Moisture Increase of Timber Constructions on Ice Arena Roof

Timber is one of the most used materials for roofing of ice arena because of its very good mechanical properties and low weight. High relative humidity of internal air, low temperature and ice rink presence, which cause fall of surface temperatures of constructions under the dew point due to radiation, are risky factors not only from structural point of view, when load bearing capacity of construction in time is reduced, but also from the view point of bio corrosion. Specific hygrothermal microclimate, different from air parameters in the ice arena, is formatted close to the individual members of roof construction. Newly developed mathematical and physical model using CFD simulation is used for simulation of hygrothermal stress in chosen part of the ice arena roof construction, which substantially affects quality, utility properties and life time of timber roof components. Results are compared with experiments in specific ice rink.