Abstract
Recycled aggregates have high water absorption and crushing index. In order to improve the properties of recycled aggregates in concrete production, various treatments were used to modify the aggregates. In recent years, bio-deposition as a new treatment method of recycled aggregates was environmentally friendly. An improved method of bio-deposition was implemented to modify the properties of recycled mortar aggregates (RMA). O-bio-deposition is based on aerobic bacteria induced CaCO3 precipitation by respiration by varying the distance between the RMA and the bottom of the container and by adding an oxygen release compound to the culture solution that contains bacteria to promote the induction of CaCO3. First, the physical properties, including water absorption, crushing value, and apparent density, of the coarse RMA under different treatment methods were determined, and an o-bio-deposition treatment method was obtained. The fine RMA was treated and compared with the untreated RMA. Concretes were then prepared from the treated coarse RMA, and compressive strength and slump were determined. In addition, the effect of the o-bio-deposition treatment on the RMA surface and the micro-cracks of concretes were observed by scanning electron microscopy (SEM). It was found that the water absorption and crushing index of the coarse RMA treated by o-bio-deposition were reduced by 40.38 and 19.76% compared with untreated RMA, respectively. Regarding the concrete, the slump and the compressive strength (28 d) of concrete were increased by 115% and 25.3%, respectively compared with the untreated concrete.
Highlights
In China, with the rapid development of the construction industry, the amount of construction and demolition (C&D) waste produced increases
The results showed that the properties of the coarse recycled mortar aggregates (RMA) were significantly improved by adding CaO2 solution to the bacterial solution and changing the immersion position of the coarse RMA compared to the traditional bio-deposition method
When the same concentration of CaO2 was added to the culture solution, the modification of the properties of the coarse RMA were optimum in the middle of the immersion position; at the same immersion position, the water absorption and the crushing index of the aggregate first decreased and increased with the concentration of CaO2, and the apparent density increased first and decreased when the concentration of CaO2 was 15 g/L
Summary
In China, with the rapid development of the construction industry, the amount of construction and demolition (C&D) waste produced increases. From the perspective of sustainable development, recycling waste concrete to produce recycled concrete aggregate (RCA) can effectively reduce harm to the environment [2,3]. The attached mortar on the surface of recycled aggregates leads to higher water absorption and crushing value of RCA [4,5,6,7]. The compressive strength and durability of recycled aggregate concrete (RAC) prepared with RCA were negatively affected. [7,9,10,11,12,13,14]; the compressive strength of RAC for 100% aggregates replaced by RCA can decrease by about 30% compared to concrete made with NA [5,8].
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