ZHANG Caili^1，2，WANG Ben³，YU Yanlong¹，ZHANG Chongxi¹，MENG Qingying⁴，GONG Fangyuan^1，2

（1. College of Civil Engineering and Transportation， Hebei University of Technology， Tianjin 300401， China；2. Tianjin Traffic Engineering Green Material Technology Engineering Center， Tianjin 300401， China；3. Heilongjiang Longgao Highway Maintenance Engineering Co. ， Ltd. ， Harbin 150000， China；4. Tianjin Kaimande Engineering Technology Co. ， Ltd. ， Tianjin 300450， China）

Abstract

Objective To enhance the utilization efficiency of steel slag solid waste， a method is devised to prepare steel slag powder-cement foam lightweight soil by substituting a portion of cement with steel slag. The road performance of foamed lightweight soil is then analyzed upon the incorporation of steel slag powder to develop economically viable， high-performance foamed lightweight soil.

Methods The PO42. 5 ordinary Portland cement and steel slag micro-powder were used as the main materials， complemented by sodium carbonate and triethanolamine agents， along with a composite foaming agent for preparation. During the experimental process， materials were weighed using an electronic balance and then mixed in a blender according to the designed proportions. Subsequently， diluted foaming agent was added to water to generate fine and dense foam. The foam was thoroughly mixed with the steel slag micro-powder-cement slurry and poured into cubic molds， followed by surface leveling. Regarding performance testing， standards were referenced for determining flowability， water absorption rate， water stability， and freeze-thaw stability. Additionally， settlement distance and compressive strength tests were conducted to measure the settlement and compressive strength of specimens at different ages. Furthermore， an anti-sulfate corrosion test was performed by immersing specimens in solutions of varying sulfate concentrations to assess changes in compressive strength over time. This work investigated the impact of varying steel slag powder content （40% to 70%）， water-cement ratio （0. 60 to 0. 75）， wet density grade （600 kg/m³ to 900 kg/m³）， and curing time on the flow value， water absorption， settlement distance， compressive strength， water stability，freeze-thaw stability， and sulfate corrosion resistance of foamed lightweight soil.

Results and Discussion As the steel slag powder content increases， the water absorption rate and flow value of steel slag powder-cement foam lightweight soil gradually increase. Simultaneously， the subsidence distance increases with the rise in water-cement ratio. The compressive strength initially increases and then decreases with the elevation of the water-cement ratio. This behavior is attributed to water's pivotal role as a raw material in facilitating the hydration reaction between steel slag powder and cement. Insufficient water content at low water-cement ratios impedes full hydration of the slurry material， causing agglomeration of steel slag powder and cement particles. Consequently， the generated hydration products inadequately fill the pores or adhere to the pore wall， resulting in reduced compressive strength of the specimen. At a water-cement ratio of 0. 7， the compressive strength at 28 days reaches its peak value of 0. 9 MPa， satisfying the specification requirements.

  At the same age， an increase in steel slag powder content leads to a significant decrease in the compressive strength of the specimens. This decline occurs because the gradual replacement of cement by steel slag powder results in a reduction of material actively participating in the overall reaction， leading to decreased hydration product formation and a looser structure.

  Furthermore， with an increase in steel slag powder content， steel slag powder-cement foam lightweight soil exhibits an upward trend， accompanied by a decrease in settlement distance. This phenomenon arises from the addition of an activator to enhance the activity of steel slag，promoting synergistic reactions with cement that rapidly elevate the early strength of steel slag powder-cement foam lightweight soil. This acceleration of the hydration reaction rate consequently reduces the settlement distance. Notably， the content of steel slag powder has minimal impact on the fluidity of steel slag powder-cement foam lightweight soil.

  The wet density grade exerts a significant influence on the compressive strength and flow value of steel slag powder-cement foam lightweight soil. With an increase in wet density grade， there is a notable improvement in compressive strength and flow value， accompanied by a reduction in water absorption rate. This enhancement is attributed to the increased proportion of cement and steel slag powder， resulting in reduced foam content and fewer pores. Concurrently， the subsidence distance exhibits an increasing trend with the rise in wet density grade due to decreased foam content， leading to slurry thinning and increased setting time.

  Steel slag powder-cement foam lightweight soil demonstrates favorable water stability and freeze-thaw stability. Although the dry-wet cycle diminishes the compressive strength of steel slag powder-cement foam lightweight soil， the strength loss is minimal. Similarly， the compressive strength of the specimen decreases under the influence of freeze-thaw cycles， with insignificant strength loss.

  For specimens with a steel slag powder content of 50%， water-cement ratio of 0. 70， and wet density grade of 600 kg/m³，the compressive strength in 5%，10%， and 15% sodium sulfate solutions is measured at 0. 76 MPa，0. 79 MPa， and 0. 83 MPa，respectively. Compared to the 7-day compressive strength of the G2 test group， these values represent an increase of 11. 76%，16. 18%， and 22. 05%， respectively. However， at the age of 28 days， the compressive strength remains unchanged when the concentration of sodium sulfate solution is 15%. Beyond 60 days， a significant decrease in compressive strength occurs，indicating excessive generation of ettringite crystals filling the pores and causing internal stress-induced cracking. When the stress surpasses the ultimate tensile stress of cement-steel slag powder foamed lightweight soil， plastic deformation occurs， leading to surface peeling.

Conclusion The incorporation of steel slag powder and alkaline activator proves to be an effective strategy in enhancing the utilization efficiency of steel slag. The mechanical properties of 50% high volume steel slag powder-cement foam lightweight soil are guaranteed.

Keywords：foam lightweight soil； steel slag powder； physical property； mechanical property； durability

DOI：10.13732/j.issn.1008-5548.2024.03.005