Abstract
As a kind of granular waste with complex composition and alkali corrosiveness, concrete slurry waste (CSW) has severe recycling limitations in the ordinary Portland cement (OPC). Considering this, a new type of geopolymer, prepared by granulated blast furnace slag/fly ash, concrete slurry waste, and powdered activators (sodium carbonate and different silicon sources including sodium metasilicate pentahydrate and silica fume), was adopted to conduct a comparative study with the OPC counterpart. In this study, the homogenized CSW was mixed in the OPC and geopolymer with a constant ratio of 50 wt%, respectively. Then the properties were studied in terms of the flowability, setting times, mechanical strengths, and microstructures. The results showed that better flowability (200 mm) could be achieved in the obtained geopolymer than in the OPC reference group (95 mm) by increasing the powdered activators. The setting time of the OPC was significantly shortened due to the addition of CSW. The strengths of geopolymer were supported by the produced C-A-S-H and carbonates, with less chemically bonded water than the hydration products in the reference group. The dominant size of pores in the hardened geopolymer was much smaller than that in the OPC group which was 80 nm. Silica fume could be the alternate of the sodium metasilicate pentahydrate and had an insignificant negative impact on the fresh and hardened properties and microstructures of the geopolymer when the incorporation rate was within 5%.
Highlights
As an energy-intensity industry, the production of ordinary Portland cement is accompanied by a massive amount of CO2 emission and has left a large amount of hardened or unhardened waste (Ali et al, 2011; Singh et al, 2015; Miller et al, 2016; Shen et al, 2017)
When the level of activators is fixed at 15%, and the SF incorporation rate kept at 0%, the flow diameters of GCSW gradually decrease from 192 to 165 mm with the increase of BFS, which can be attributed to the existence of CaO and rough morphology of BFS (Ismail and El-Hassan, 2018)
This paper showed an innovative way to recycle concrete slurry waste (CSW), and a comparative study was made between the GCSW and CCSW in terms of the flowability, setting times, mechanical strengths, and microstructures (XRD, FTIR, TG-DTG, and MIP)
Summary
As an energy-intensity industry, the production of ordinary Portland cement is accompanied by a massive amount of CO2 emission and has left a large amount of hardened or unhardened waste (Ali et al, 2011; Singh et al, 2015; Miller et al, 2016; Shen et al, 2017). The reuse of the unhardened waste generated from the concrete batching plant (CBP) in China is greatly restricted, especially for concrete slurry waste (CSW). Fly Ash-Slurry Based Geopolymer the incorporation of CSW into mortar or concrete is an efficient stabilization method in terms of the heavy metals’ leaching behavior (Audo et al, 2018). It is reasonable to consider CSW as aggregate or filler substitutes in concrete productions after dewatering, drying, crushing, and sieving. The relevant studies highlighted that the substitute rate should not exceed 30% because of its poor qualities (high porosity, weak adhesion of the old mortar, and low strength), which can cause the degradations of the workability, strengths, fire resistance, and durability The CSW may not be suitable to use in new concrete productions. A new cementitious system is desired to solve the disposal problem of the CSW
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