Research on Low Temperature Fracturing of Asphalt Pavement

アスファルト舗装には様々な破壊現象があり，種々の研究が行われている。しかし，わだち掘れ現象以外のき裂現象で寒冷地に多く見られる外気温の低下により舗装体が収縮して横断方向に破壊する，いわゆる低温き裂に関する研究は多いが，主要な因子と現地との対応がとれていない。この理由は，低温き裂の発生原因が材料の性状，施工の条件，アスファルト舗装の構造の形式，環境条件など多岐にわたり，これら各々の条件がアスファルト混合物の性状を著しく変化させているためと考えられる。本研究は，寒冷地に多く見られるアスファルト舗装の低温き裂現象と使用アスファルトの性状およびその舗装構造について検討した。アスファルト舗装構造では複雑な材質の組合せを有する舗装構成と低温き裂との対応を求めるため，現場調査，室内実験および数値解析シミュレーションを行った。検討の結果，アスファルト舗装の低温き裂現象は，応力よりもひずみが支配的であり，アスファルト舗装は応力緩和現象を伴いながらあるひずみレベルを超えると破壊することが確認された。Various failures occur in asphalt pavements, and researches on these failures were carried out. Most of them were on rutting or fracturing phenomenon, but research on low temperature fracturing, which is very important in cold regions, have been insufficient, as of now. This is mainly due to the fact that circumstances make it extremely difficult to research, including factors, such as material properties, construction conditions, particular kind of structure involved in asphalt pavement, and the prevailing environment. Recently, the authors investigated the relation between low temperature cracking in asphalt pavement in cold regions, such as Hokkaido, and pavement structure with varying properties of asphalt mixture. These researches were carried out in construction fields, and the laboratory, performing simulation analysis of finite element method using visco-elastic program of hybrid type. The authors arrived at the following conclusions in this study: the low temperature fractures in asphalt pavements in cold region depends mainly upon the strain, more so than on the stress, in asphaltic mixture. The low temperature fracture may occur when strain in the asphalt pavement reaches a critical value accompanying relaxation of stress in asphaltic mixture