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Abstract
Most areas of Caofeidian (Tangshan Caofeidian New District in Hebei Province, China) were formed by land reclamation, where the dredger fill has a high water content and a high salt content. The solidification of Caofeidian’s dredger fill is difficult because of salinisation, as well as environmental and economic factors. This article proposes a composite slag solidifying agent. The optimal proportion of various additives was determined by an unconfined compression test and orthogonal design. Next, a microanalysis was carried out by SEM and XRD tests to characterise the solidification mechanism of the composite slag solidifying agent. The results reveal that the composite slag solidifying agent can substantially improve the unconfined compressive strength of Caofeidian’s saline dredger fill by imparting a good microstructure: a compact overall structure was obtained and few voids were observed in the solidified soil. The optimal proportion was determined as 10% slag + 1.0% quicklime + 0.8% sodium silicate + 1.5% gypsum powder. In addition, the composite slag solidifying agent can effectively reduce the content of soluble salts in saline dredger fill and substantially improve the engineering characteristics of solidified soil.
Highlights
Most areas of Caofeidian (Tangshan Caofeidian New District in Hebei Province, China) were formed by land reclamation
It can be stated that the strength first increased and decreased with the increase in quicklime content: the strength increased for quicklime content between 0% and 1% and decreased for quicklime content higher than 1%
calcium aluminate hydrate (CAH) can combine with SO42− and Cl− in the soil to form calcium aluminate chloride sulphate hydrate, which can effectively reduce the content of soluble salts in saline dredger fill and substantially improve the engineering characteristics of solidified soil
Summary
Most areas of Caofeidian (Tangshan Caofeidian New District in Hebei Province, China) were formed by land reclamation. Certain new solidifying materials have been examined by a few researchers: Bell investigated the use of lime-combined PFA (pulverised fuel ash) and cement-combined PFA to solidify clay soil [12]. X-ray diffraction (XRD), scanning electron microscopy (SEM), and other microscopic test methods have been applied in different research studies to clarify the mechanism of saline soil solidification and to select good solidifying agents. Composite solidifying agents containing industrial waste and other cementing materials have a better solidifying effect on saline soil. In the present study, a composite solidifying agent (slag is used as the main solidifying agent and sodium silicate, quicklime, and gypsum powder are used as additives) is proposed to improve the strength of the Caofeidian saline dredger fill. Based on the site survey (20 m depth), it can be stated that it mainly contains silty sand, silt, and silty clay layers formed by quaternary Holocene sedimentary layers (Q4m), except the surface dredge fill (Q4ml)
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