Influence of super⁃absorbent polymer on properties of alkali⁃activated foamed concrete

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Influence of super⁃absorbent polymer on properties of alkali⁃activated foamed concrete

Journal Title: China Powder Science and Technology - Year 2024, Vol 30, Issue 5

Abstract

Objective Using recycled concrete powder as an auxiliary cementing material to partially replace slag in the preparation of alkali-activated foamed concrete helps reduce costs and address the problem of air pollution caused by construction waste crushing dust. However， a higher amount of recycled fine powder usually reduces the performance of concrete. To improve the properties of alkali-activated foamed concrete with recycled micropowder and slag as the main raw materials， internal curing method was considered. The influence of superabsorbent polymer （SAP） on the properties of alkali-activated foamed concrete was studied in the paper. Methods The experiment evaluated the influence of SAP on the fluidity， water absorption rate， setting time， thermal conductivity， pore structure， and strength of alkali-activated foamed concrete by adjusting the mass concentration and dosage of SAP pre-absorbed with NaOH solution. Using alkali-activated foamed concrete without SAP as the control group， the study explored the influence of different SAP dosages （0.05%， 0.10%， 0.15%， 0.2%） on the performance of alkali-activated foamed concrete with recycled micropowder and slag as the main raw materials， when SAP was pre-absorbed with 0%， 0.4%， and 0.9% NaOH solution. The mechanism by which SAP affects the performance of alkali-activated foamed concrete was investigated by electron microscopy and infrared spectroscopy analysis. Results and Discussion The study on the viability of alkali-activated foamed concrete showed that SAP significantly affected the fluidity of the concrete. With the increase of SAP content， its fluidity showed a general trend of decreasing. The influence of SAP-Water on fluidity was the largest. The water absorption rate of alkali-activated foamed concrete increased gradually with the increase in SAP content. When the content of SAP-Water increased from 0.05% to 0.2%， the water absorption rate increased from 46.7% to 53.5%. Regardless of the mass concentration of NaOH solution added to SAP beforehand， the setting time of alkali-activated foamed concrete was shorter that of the control group. It initially decreased and then increased with the increase in SAP-Water content， but gradually decreased with the increase in SAP-0.4% NaOH or SAP-0.9% NaOH content. In addition， SAP significantly influenced the thermal conductivity of alkali-activated foamed concrete. With the increase in SAP-Water and SAP-0.4% NaOH content and the decrease of the mass concentration of NaOH solution pre-absorbed by SAP， the thermal conductivity of alkali-activated foamed concrete decreased， which was related to the changes in pore structure. Pore structure analysis showed that SAP not only increased the porosity of the concrete， but also changed its porosity distribution. Among them， SAP-Water increased the porosity of the concrete most significantly. When the content of SAP-Water increased from 0% to 0.2%， the porosity of the specimen increased from 64.8% to 67.9%， an increase of 4.8%. SAP-Water and SAP-0.4% NaOH increased the proportion of pores larger than 550μm in alkali-activated foamed concrete， while SAP-0.9% NaOH increased the proportion of pores smaller than 250μm. Microscopic analysis of the pore structure showed that pre-absorbed SAP-0.4% NaOH improved the pore wall products， reduced internal defects， and improved the material's pore structure. Mechanical property test showed that adding an appropriate amount of SAP significantly improved the compressive and flexural strength of alkali-activated foamed concrete. With the increase in SAP-Water and SAP-0.4% NaOH dosage， the compressive strength of the concrete initially increased and then decreased. Microscopic analysis showed that SAP did not produce new hydration products but changed its hydration degree and microstructure. SAP promoted the formation of C-A-S-H gel， improving material compactness. SAP pre-absorbed with 0.4% NaOH solution not only improved the pore structure of the specimen， but also deepened the hydration degree of the matrix， enhancing the mechanical properties of the specimen. When the dosage was 0.1%， the 28-day compressive strength of the specimen reached 4.94 MPa， and the flexural strength was 17.5% higher than the control group. When the dosage of SAP exceeded the optimal value， excess SAP introduced additional pores in the matrix of alkali-activated foamed concrete， thereby reducing material compactness and consequently its strength. Conclusion Pre-absorbed SAP with NaOH solution， serving as an internal curing agent， significantly enhances the hydration degree and pore structure of alkali-activated foamed concrete that incorporates recycled concrete powder. This improvement in microstructure contributes to better viability and increases the strength of the concrete. The proposed method provides a new approach to improving the properties of alkali-activated foamed concrete materials mixed with recycled micropowder.

Authors and Affiliations

Weiwei HAO, Shuxiang ZHANG, Yingdong MAI, Chao MAO, Mingjie MAO

Keywords

EP ID EP749287
DOI 10.13732/j.issn.1008-5548.2024.05.007
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