Strength performance of mucky silty clay modified using early-age fly ash-based curing agent

Due to environmental pollution and resource waste in its production, environmentally friendly and economically efficient curing agents based on fly ash have been proposed to replace tradi-tional cement. However, such curing agents for the modified soil fail to meet the requirement of the early-age strength for foundation engineering due to the low activity of the fly ash. This paper investigates the strength performance of mucky silty clay curded by early-age strength fly ash -based curing agent (class-F fly ash, inorganic curing agent, and alkali activator account for 60%, 30% and 10% of the curing agent), featured with high early-age strength, through a series of laboratory tests. The results demonstrated that this agent completed most of the reactions within the first 7-day curing, and the early-age strength is higher than that of traditional fly ash modified soil (lime-fly ash modified soil). The 7-day modified soil UCS can reach 1.282 MPa with a 20% curing agent. In addition, with the increase of curing agent dosage, curing time, and confining pressure, the deviator stress of modified soil increases significantly. The cohesion and internal friction angle of modified soil increase with the increase of dosage and curing time, but compared with the increasing of cohesion, the internal friction angle of modified soil increases more slowly. The pores in the modified soil tend to change from large to tiny with the addition of a curing agent, and a great deal of gel state products have appeared in the pores of the modified soil. The improved early-age strength performance was attributed to quick hydration of the early-age strength fly ash-based curing agent, which generates a large amount of gel state hydration products and ettringite crystal to agglutinate the soil particles and fill the pores within the modified samples. The early-age strength fly ash-based curing agent still has high early-age strength performance in practical engineering applications. The 7-day UCS obtained from the field test can reach 83.8%-85.8% of the 28-day UCS.