Study On The Thermal Properties Of Concrete And The Technology Of Concrete Reuse

Waste concrete (WC) have brought into negative influences to environment. It is need for social sustaining development to make recycled concrete (RC) with WC broken as recycled aggregate. While the Old waste concrete is used as recycled concrete aggregate (RCA), the poor workability of fresh recycling concrete due to the high water adsorption of RCA makes its wide application limited. In the other hand, the fine aggregates of RCA smaller than 4.75mm, which were gotten by grinding and classification, were always abandoned as waste, because they were almost considered as no practical use as for the influence of the workability of fresh recycling concrete. In order to improve the quality of RCA, increase the recycling efficiency and overcome some flaws of RCA, the technology way of thermal grinding and vibration was used in this research work, by this way, we can separate the aggregates from hydrated gel components, get original state aggregates and heat activity concrete powders, eventually get high-quality original state aggregates and dry-mixed mortar by our suitable treatment.To get the optimal separation temperature, the Workhorse-1 thermal expansion instrument was conducted to measure the linear expansion values of different cement mortars and some normal aggregate. The results showed that the greatest divergence of thermal expansion between hardened cement paste and aggregate lied between 500 ℃ to 600℃ when the waste concrete was subjected to the elevated temperature. The high temperature mechanical test instrument was used to measure concrete strength changes under different temperature points from room temperature to 590℃. It was found that the concrete strength at 550℃ was just 10% to 14% of concrete strength at room temperature. At the same time, The hydrating and hardening performance of dehydrated cement pastes was also investigated to find out that the strength of rehydration products were the highest when the separated waste mortar were experienced to 600℃. In combination with these three factors and the crystal conversion temperature of SiO₂ around 573℃, the separation temperature of aggregate and hardened cement paste in the waste concrete was decided at 550℃. Atthis temperature, the structure of fine aggregate was still not destroyed.In progress, the processing of dry-mixed mortar with active power was investigated according to its activity. The results showed that both dehydrated cement pastes and calcined mortar behaved hydration and hardening ability, which was greatly affected by calcined temperature. Moreover, the original aggregates into the waste concrete can be obtained after subjected to the 550°C separation temperature. When preparing the C30 concrete with this part of separated aggregates, its workability and strength were the same as the C30 concrete with natural aggregates. A significative conclusion can be given that the separated aggregates from waste concrete can replace the whole natural aggregates applied into the concrete preparation. The XRD of dehydrated cement pastes at high temperatures showed that the main components were C2S and CaO and there were many kinds of noncrystal materials. All these active components lead to the re-hydrating and re-hardening performance. Its crystal phase and hydration ability were explored in this thesis. A new type of M5^M15 recycled dry-mixed mortar was made from activity concrete powders mixed with appropriate fly ash, phosphogypsum and a little cement.