Study on Shrinkage in Alkali-Activated Slag-Fly Ash Cementitious Materials

Area of Science:

• Materials Science
• Civil Engineering
• Sustainable Construction

Background:

• Traditional silicate cement production generates significant CO2, necessitating eco-friendly alternatives.
• Alkali-activated slag cement (AASC) presents a sustainable option with low carbon emissions and waste utilization.
• AASC exhibits superior properties but can suffer from increased shrinkage compared to conventional concrete.

Purpose of the Study:

• To investigate the impact of fly ash and fine sand content on the dry and autogenous shrinkage of AASC.
• To analyze the relationship between pore structure changes and shrinkage behavior in AASC.
• To identify optimal additive levels for mitigating AASC shrinkage.

Main Methods:

• Utilized slag powder and sodium silicate (water glass) as primary materials.
• Incorporated varying percentages of fly ash and fine sand into AASC mixtures.
• Measured dry shrinkage and autogenous shrinkage, correlating with pore structure analysis.

Main Results:

• Adding fly ash and fine sand effectively reduced both drying and autogenous shrinkage in AASC.
• Increased additive content led to decreased shrinkage but also a reduction in mechanical strength.
• At 60% fly ash, drying shrinkage decreased by ~30% and autogenous shrinkage by ~24%.
• At 40% fine sand, drying shrinkage decreased by ~14% and autogenous shrinkage by ~4%.

Conclusions:

• Fly ash and fine sand are effective in reducing AASC shrinkage, with fly ash showing a more significant impact.
• A trade-off exists between shrinkage reduction and mechanical strength in AASC formulations.
• Optimizing fly ash and fine sand content is crucial for developing high-performance, low-shrinkage AASC.