Performance Evaluation of Novel Chemical Activators for Soil Stabilization by Activated Slag

Poorly graded sandy soil could cause numerous geotechnical problems in large areas across the world. Weak soils have insufficient bearing capacity and this may be the cause of many issues in roads infrastructure, embankments, buildings foundation, and other geotechnical projects. Stabilizing the soil by chemical stabilizers like ordinary Portland cement (OPC) is one of the most conventional methods for enhancing the engineering proprieties of soil, usually by different percentages of binder/soil ratio. Some environmental and economical issues of utilizing OPC as binder are the serious concern of researches during few decades. Alkali-activated materials (AAM), with lower destructive impact on environment and more economical profits, have been one of the attractive materials as a new generation of binders recently. These materials can be utilize in different geotechnical applications such as: soil stabilizing, different kinds of mixing method, and grouting. The current study has aimed to evaluate the mechanical and durability properties of stabilized sandy soil by AAM, the used slag for AAM binder is Ground Granulated Blast furnace Slag (GGBS) and the slag is activated by different kinds of novel alkali activators. The activators are combination of Na2SiO3 and NaOH, Na2CO3 and Ca(OH)2, and Na2SO4 and Ca(OH)2; namely, Ac1, Ac2, and Ac3, respectively. In order to evaluate mechanical properties of stabilized soil samples, unconfined compressive strength (UCS) test, and to investigate the durability properties of stabilized soil samples, freezing-thawing cycles are applied to specimens. Additionally, scanning electron microscopy (SEM) test are implemented on Ac2- and Ac3-based stabilized samples to investigate the morphological aspects of stabilized soil. Studied parameters of this study are the effect of curing time on mechanical behavior of stabilized soil samples, and the effect of types of activator on mechanical and durability properties (volume changes and soil-cement losses) of stabilized soil samples. Curing time of 14, 28, and 90 days are considered for UCS test, and 28 days are considered for freezing-thawing cycles durability test. The amount of binder for soil stabilization is considered in a constant value of 5 wt.% of dry soil for UCS and freezing-thawing tests. The 90-day UCS value for OPC-based stabilized sample is 0.75 MPa, for As1-based stabilized sample is 2.63 MPa, for As2-based stabilized sample is 2.28 MPa, and for As3-based stabilized sample is 4.5 MPa. As seen, AAM-based stabilized soil samples show greater UCS value in the same binder/soil ratio and curing time. As3 showed the most effective activator with higher UCS value as a soil stabilizer. In the test of freezing-thawing, except As2-based stabilized sample, other samples survived all 12 cycles. As2-based soil stabilized sample only survived 7 cycles of freezing and thawing. The most amount of volume changes for OPC-based stabilized soil is 12.82% for 12 cycles, while this amount is 6.65% for As2-based stabilized soil for 7 cycles. As1- and As3-based stabilized soil have showed fairly stable volume changes; i.e. with the most amounts of volume changes of 5.93% and 4.17% for 12 cycles. This results show AAM-based stabilized samples are more soundness than OPC-based stabilized samples and are more stable during volume changes.