Deterioration Characteristics of Cement-Fly Ash Paste under Strong Ultraviolet Radiation and Low Temperature Conditions

The pastes containing different dosages of fly ash were taken into ultraviolet radiation and low temperature freeze condition simultaneously(URL) for 30 days and only ultraviolet radiation condition(UR) for 30 days after standard curing, so as to investigate the influences of the conditions on the deterioration characteristics of the pastes. Microscopic test methods, such as XRD, TG-DTA and SEM, were used to study the UR effect on the deterioration process of hardened paste. The results show that the deterioration tests, such as URL and UR, inhibit the common development of paste strength, especially after the standard curing age of 360 days. With the increase of fly ash dosage, from 0 to 50%, the reference value decreases, especially at early age. While at the later age, i e, 180 and 360 days, the paste strength cured for 30 days under URL and UR conditions all increase to different extent and the strength is slightly affected very low, especially for the paste containing 25% fly ash. From XRD results, URL and UR dispositions do not influence the hydration product kinds but the amount, especially Ca(OH)2 and CaCO3. Deterioration experiments can decrease the diffraction peak of Ca(OH)2 sharply, and increase that of CaCO3 rapidly, especially under only ultraviolet radiation. From TG-DTA and SEM results, with the increase of curing age, the content of Ca(OH)2 decreases and that of CaCO3 increases. The Ca(OH)2 content of paste under continuous UR curing for 30 days is less than that under URL curing for 30 days, which indicates that UR has more negative effects on the pastes than URL.