Quantitative Analysis of the Calcium Hydroxide Content of EVA-Modified Cement Paste Based on TG-DSC in a Dual Atmosphere.

Abstract

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.