In this paper, the basic damage mechanisms and the primary reasons for the property
fluctuation of recycled aggregate concrete are investigated experimentally. By a comprehensive
literature study and systematic laboratory tests, the interactions between the old and the new interfaces
in recycled aggregate concrete are analyzed. In particular, the damage initiation and evolution
mechanisms on the old and the new interfaces are studied in details. The essential factors affecting the
fluctuation and its extent are investigated from the point of view of material sciences. The present
results imply that the qualitative and quantitative changes of the old and the new interfaces during the
loading process induce a notable fluctuation of the mechanical and the physical properties of recycled
aggregate concrete. To reduce the fluctuation and improve the mechanical properties of the recycled
aggregate concrete, effective controlling and processing measures are suggested and discussed.
The calcium hydroxide (Ca(OH)2) content is one of the main indices of cement hydration degree. In order to accurately determine the calcium hydroxide content of ethylene and vinyl acetate (EVA) copolymer-modified cement paste, a dual atmosphere thermogravimetric method (first in an oxidizing atmosphere and then in an inert atmosphere) was used to track the mass loss and change in enthalpy by TG-DSC (simultaneous thermogravimetry and differential scanning calorimetry). The results showed that using the dual atmosphere thermogravimetric method, the source of mass loss can be distinguished. The exothermic peaks in an oxidizing atmosphere show the oxidation reactions of EVA, while the endothermic peak in an inert atmosphere is due to the pyrolysis reaction of EVA and the decomposition of the calcium hydroxide. The influence of EVA on cement hydration was investigated. The results showed that the polymer powder can be dispersed in water, forming a kind of composite membrane. The test method of dual atmosphere thermogravimetry to measure the calcium hydroxide content of polymer-modified cement pastes is more accurate and convenient than those previously applied.
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