دانلود رایگان مقاله انگلیسی تاثیر یخ خشک بر عملکرد سیمان پرتلند و مکانیزم آن - الزویر 2018

abstract

This study reports on the effect of dry ice on the hydration and hardening behavior of Portland cement. Dry ice was directly added to fresh Portland cement paste, with its dosage fixed at 0 wt%, 0.3 wt%, 0.6 wt %, 0.9 wt%, 1.2 wt% and 1.5 wt%. Results showed that dry ice had little effect on the standard consistency and setting time of cement paste when its dosage was less than 0.9 wt%, but otherwise the standard consistency as well as the setting time was increased. The compressive strength of the paste at 7 days increased slightly when the dosage of dry ice was less than 0.9 wt%, but the compressive strength was reduced with the addition of 0.9 wt% to 1.5 wt% dry ice. For the compressive strength at 28 days, the cement paste with 0.6 wt% dry ice showed the greatest value, being increased by 30.9% compared to the control cement paste, and the compressive strength of the samples with dry ice was all higher than that of the control. In addition, hydration heat, XRD, DTA-TG and SEM results showed that the incorporation of dry ice retarded the early hydration of Portland cement, improved its later hydration, and optimized the hardened structure of the cement paste. These results can provide a reference for the future application of dry ice in Portland cement-based materials.

Conclusions

Dry ice was incorporated at 0 wt%, 0.3 wt%, 0.6 wt%, 0.9 wt%, 1.2 wt%, and 1.5 wt% by weight of Portland cement, the effect of dry ice on the standard consistency, setting time, compressive strength, hydration-hardening process and product of Portland cement were studied. Main conclusions are as follows:

(1) With the increase of dry ice content, the standard consistency of Portland cement first decreases but then increases, reaching its smallest value at 0.6 wt%. Similarly, with the increase of dry ice dosage, the patterns of the initial and final setting are similar to that of standard consistency. When the dosage of dry ice is 0.6 wt%, the setting time is at its lowest value: the initial setting time decreases by 12.3%, and the final setting time reduces by 17.4% compared to the control cement paste.

(2) The influence of dry ice on compressive strength at 7 days is subtle when its dosage is less than 0.9 wt%, and the compressive strength at 28 days drops notably when its dosage is more than 0.9 wt%. With the increase of dry ice content, the compressive strength of cement paste at 28 days first increases and then decreases. Compared to the control sample, the compressive strength at 28 days increases by 30.9% when its dosage is 0.6 wt%, and the compressive strength of the cement pastes at the given dosage of dry ice is higher than that of the control sample.

(3) The results of hydration heat analysis, XRD, and DTA-TG show that the incorporation of dry ice has a retarding effect on the early hydration of Portland cement, however, dry ice improves its later hydration. The SEM results of show that dry ice could change the morphology of AFt and optimize the hardened structure of cement paste.