دانلود رایگان مقاله انگلیسی بازیافت به کیفیت بهتر از جنس اولیه دی اکسید کربن برای بهبود استحکام مکانیکی سیمان پورتلند - الزویر 2018

Abstract

To reduce environmental pollution induced by the production of Portland cement and sequestrate greenhouse gas, a novel approach was developed to manufacture nano-calcium carbonate (nano-CaCO3) suspension by upcycling carbon dioxide. The influence of this nano-CaCO3 suspension on basic performances of Portland cement paste was experimentally evaluated and related mechanisms were demonstrated by isothermal heat conduction calorimeter (TAM Air), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimeter (MIP), scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements. Experimental results showed that the manufactured CaCO3 presented spherical and cubic shapes with size of 20 to 50 nm. This CO2 upcycling method can improve compressive strength of cement paste by 5.8~9.9% at ages of 3 to 56 days and significantly reduce the initial and final setting times. The introduction of CO2 in form of nano-CaCO3 accelerated the early age hydration of Portland cement and refined the pore structure. Around 0.4~2.4 kg of CO2 can be recycled by every ton of Portland cement while the usage efficiency 22 of cement was evidently improved. Therefore, both capture and solidification of carbon dioxide and 23 carbon footprint reduction of cement industry can be simultaneously achieved by this technology.

Conclusions

Based on the above experimental results, the following conclusions can be obtained. (1) A novel method was developed to upcycle CO2 for manufacturing nano-CaCO3 suspension by injecting CO2 into Ca(OH)2 solution. The produced CaCO3 presented spherical and cubic particles with size of 20 to 50 nm. (2) The manufactured nano-CaCO3 suspension increased the 3d, 7d, 28d and 56d compressive  strength by 2.8~5.8%, 2.0~9.9%, 3.4~7.2% and 3.5~7.6% respectively. The initial and final setting times were reduced by 8.89%~30.22% and 7.89%~19.08% respectively. (3) The early age hydration of Portland cement was accelerated by the nano-CaCO3 suspension, resulting in the increased hydration heat release and more formation of Ca(OH)2 in hardened cement 366 paste. (4) With introduction of the nano-CaCO3 suspension, the porosity was reduced and the pore 368 structure was refined for the hardened cement pastes. (5) Each ton of Portland cement absorbed around 0.4~2.4 kg of CO2 while the usage efficiency of cement was improved by around 3.4~7.2%. Therefore, this upcycling method has a great environmental potential being attributed to both the capture and solidification of carbon dioxide and the carbon footprint reduction of cement industry.