Study On The Origin Of Concretes Crack And Prevention Measure In Railway Engineering

The concretes crack is the prominent"common disease"and"frequently-occurring disease"in the railway engineering, is also one of quite thorny problems which puzzles the Department concerned for a long time. The research of origin and the prevention measures of concretes crack in the railway engineering is being at the elementary step in our country. Although in the application has made the good progress in certain actual projects, it profits from the overseas experience. This thesis is underway under such background. It studies the origin of concretes crack in the railway engineering, discusses the reaction mechanism, and studies measures of suppress- ing and patching.In this thesis, the origin of concretes crack is discusses deeply by making full investigations on the concretes crack situation in railway engineering, studies emphatically the mechanism, the cause and the harm of the crack by the alkali-aggregate Reaction. Discusses the method and measures to prevent and to suppress the alkali- aggregate response. The fast mortar-stick method is used in this thesis, The suppress effect of the mineral admixture and the inorganic admixture is studied by mensurating the expansion rate in stated age time(14d). The microcosmic functionary mechanism is analysed combining with the SEM testing measure. The result indicated that using mineral admixture and inorganic admixture in a right amount may suppress the sample's expansion made by alkali-aggregate reaction. And mixes in the quantity to be bigger, the function effect is more obvious. Considered synthesis factors, the quantity of fly ash mixes is 25%, the quantity of silica fume mixes is 20%, the quantity of lithium salt mixes is 0.1%, the quantity of polypropylene fiber mixes is 0.6 kg/m~3 are suitable.After a lot of experimental study and academic analysis, problems of the cement- based materials were solved effectively in this paper. A new grouting material which consists of VAE latex, rapid hardening sulphoaluminate cement and defined amount of additives, and its performances such as viscosity, groutability, setting time, shrinkage, water-resistance and so on were researched under different polymer/cement ratios. The microstructure of the cement-based grouting material modified by polymer was studied and the modification mechanism was analyzed. The optimum mixture ratio was confirmed by comparing the experiment results. The research indicates that performance indexes of the cement-based grouting material modified by polymer fulfill the requirements of projects. Using polymer modified cement-based grouting material to mend cracks not only improved water-resistance, but also reinforced the structure of the building. When the polymer/cement ratio is 10% or 15% , polymer modified cement-based grouting material shows good performances.In this paper, we also prepared a new cement mortar modified by polymer for mending cracks. The technology and performances such as mechanical properties, interface bond property, shrinkage, water-resistance and so on were studied, and the microstructure and porosity were researched, and the modification mechanism was discussed. The results indicate that performances of the mortar modified by polymer fulfill the requirements in practical engineering and the interface bonded very well. When the polymer/cement ratio is 10%, the additions of polycarboxylate acid superplasticizer, defoaming agent, and setting retarder are 0.7%, 0.5% and 1.5% respectively, the mortar modified by polymer shows good performance.