The engineering properties and reaction mechanism of MgO-activated slag cement-clayey sand-bentonite (MSB) cutoff wall backfills

Wu, Hejun; Jin, Fei; Zhou, Annan; Du, Yao

doi:10.1016/j.conbuildmat.2020.121890

Cited by 18 publications

(19 citation statements)

References 34 publications

(28 reference statements)

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“…The concretes were significantly efficient regarding durability and mechanical resistances; on the other hand, it was highlighted as a good response to the environmental problem. Wu et al [18] made a mixed compound based on reactive MgO, blast furnace grinded granulated slag, bentonite and clay sand to improve soils. Bentonites are currently being used successfully to make high activity radioactive waste inert, in the form of a paste fabricated from grains, particulates and bentonite dust [19].…”

Section: Introductionmentioning

confidence: 99%

Bentonites in Southern Spain. Characterization and Applications

Costafreda¹,

Martín²

2021

Crystals

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The objective of this work was to investigate and demonstrate the pozzolanic properties of the bentonites found at the San José–Los Escullos deposit, located in the southeast of the Iberian Peninsula, to be used in the manufacturing of more durable and environmentally compatible pozzolanic cements, mortars and concretes. These bentonites are mainly composed of smectites, with montmorillonite as the main clay mineral. They were formed by the hydrothermal alteration of tuffs, volcanic glasses, dacites, rhyolites and andesites. For this research, samples were taken from outcrops on the south, north and west side of the San José–Los Escullos deposit, and in the Los Trancos deposit located 19.3 km to the northeast. All samples consisted of bentonites, except for a zeolite sample taken from the northern flank of the San José–Los Escullos deposit, which was used to contrast and compare the behaviour of bentonite in some of the analyses that were done. An investigation of the mineralogical, petrological, chemical and thermogravimetric characteristics of the samples was carried out using various methods, such as XRD, OA (Oriented aggregates), TGA, XRF, SEM and thin section petrography (TSP). In addition, a chemical analysis of pozzolanicity (CAP) was done at 8 and 15 days to determine the pozzolanic capacity of the samples. XRD, XRF, SEM and TSP studies showed that these bentonites have a complex mineralogical constitution, composed mainly of smectites of the montmorillonite variety, as well as halloysite, illite, vermiculite, biotite, muscovite, kaolinite, chlorite, mordenite, feldspar, pyroxene, amphibole, calcite, volcanic glass and quartz. Thermogravimetric analysis (TGA) established the thermal stability of the bentonites studied at above 800 °C. Chemical analysis of pozzolanicity (CAP) confirmed the pozzolanic character of the bentonites, exhibited in their reactive behaviour with Ca(OH)2. The pozzolanic reactivity increased significantly from 8 to 15 days. These results show that the materials studied can be used as quality pozzolans for the manufacture of pozzolanic cements, mortars and concretes.

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Section: Introductionmentioning

confidence: 99%

Bentonites in Southern Spain. Characterization and Applications

Costafreda¹,

Martín²

2021

Crystals

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“…The main hydration products of MgO-activated GGBS are calcium silicate hydrate (C-S-H) and hydrotalcite (HT), which are flocculated hydration that fill the pores between soil particles and improve the impermeability as shown in Fig. 11 [19,52,55]. Although these hydration products will increase the strength of the cutoff wall soil with the increase of ages [23,56], there is no significant strength increment that can be reflected by q t and f s in CPTU test because the age is only 3 days.…”

Section: Comparison With Soil Classification Based On Soil Behavior Typementioning

confidence: 99%

Quantitative identification of cutoff wall construction defects using Bayesian approach based on excess pore water pressure

Cai

Liu

et al. 2021

Acta Geotech.

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Cutoff wall has been widely used as a barrier to prevent the migration of contaminants in aquifers. Hydraulic impermeability and homogeneity should be ensured before operation. The difficulties in the rapid evaluation of newly constructed cutoff wall lie in high-quality sampling and time-consuming laboratory testing. In this study, piezocone penetration test is used to evaluate the barrier performance of a newly built cutoff wall. A Bayesian approach combined with genetic algorithm is adopted. The weak layers of cutoff wall are identified using excess pore water pressure data. The causes of impermeability defect are quantitatively characterized through optimized model parameters. Then, through comparison with the results of traditional soil behavior type based classification method, it points out the inapplicability of traditional method to evaluate the goodness of cutoff wall. Finally, the continuous horizontal hydraulic permeability profile is assessed by combining pore water pressure dissipation tests with adopted Bayesian approach. Results show that adopted Bayesian approach using excess pore water pressure can properly identify the weak layers of the newly built cutoff wall and reflect the causes. The analysis results can be used as guiding information for making remediation plans.

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“…Recently, Wu et al [8,15,16], Fu et al [17], and Ni [18] developed an MSBS backfill with the merits of lower hydraulic conductivity, superior chemical compatibility, and greater environmental friendliness compared to the conventional backfills consisting of sand and cement, sand and cement-activated slag regardless of bentonite inclusion. The MSBS backfill consisted of reactive MgO, GGBS, conventional bentonite, and sand.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, magnesium could be released from the hydrated MgO. The pH of the hydrated MgOactivated GGBS system is alkaline (10.1~10.8) [16]. The presence of multi-valent cations and alkane conditions in the MSBS backfill pore fluid may impose a negative impact on the hydration of the bentonite and mitigate its pore filling and "sand-coating" effects and maintenance of relatively low hydraulic conductivity [8].…”

Section: Introductionmentioning

confidence: 99%

“…Ni [18] found that increasing the contents of MgO and CB would reduce the hydraulic conductivity of MSBS backfills permeated with synthetic landfill leachate. On the other hand, Wu et al [8,16] and Ni [18] indicated that increasing CB content yielded a decrease in the unconfined compressive strength of MSBS backfills. Moreover, the employment of MSBS backfill resulted in cost savings of approximately 15.33~16.9% and a reduction in CO 2 emissions of 84.7~85.1% compared to the conventional Ordinary Portlant cement-based backfills [8].…”

Section: Introductionmentioning

confidence: 99%

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Engineering Properties of Novel Vertical Cutoff Wall Backfills Composed of Alkali-Activated Slag, Polymer-Amended Bentonite and Sand

Jiang

Shi

et al. 2023

Polymers

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The workability, hydraulic conductivity, and mechanical properties are essential to contaminant containment performance of cementitious backfills in vertical cutoff walls at contaminated sites. This study aims to investigate the engineering properties of a novel vertical cutoff wall backfill composed of reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS), sodium-activated calcium bentonite amended with polyacrylamide cellulose (PAC), and clean sand (referred to as MSBS-PAC). Backfills composed of MgO-activated GGBS, sodium-activated calcium bentonite, and clean sand (referred to as MSBS) were also tested for comparison purposes. A series of tests were conducted which included slump test, flexible-wall hydraulic conductivity test, and unconfined compression test. The pore size distributions of two types of backfills were investigated via the nuclear magnetic resonance (NMR) technique. The results showed the moisture content corresponding to the target slump height was higher for MSBS-PAC backfill than that for MSBS backfill. The MSBS-PAC backfill possessed lower pH, dry density, and higher void ratio at different standard curing times as compared to MSBS backfill. The unconfined compressive strength and strain at failure of the MSBS-PAC backfill were noticeable lower than those of the MSBS backfill. In contrast, the hydraulic conductivity of MSBS-PAC backfill was approximately one order of magnitude lower than that of the MSBS backfill, which was less than 10−9 m/s after 28-day and 90-day curing. Lower hydraulic conductivity of MSBS-PAC backfill was attributed to the improvement of pore structure and pore fluid environment by PAC amendment.

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The engineering properties and reaction mechanism of MgO-activated slag cement-clayey sand-bentonite (MSB) cutoff wall backfills

Cited by 18 publications

References 34 publications

Bentonites in Southern Spain. Characterization and Applications

Bentonites in Southern Spain. Characterization and Applications

Quantitative identification of cutoff wall construction defects using Bayesian approach based on excess pore water pressure

Engineering Properties of Novel Vertical Cutoff Wall Backfills Composed of Alkali-Activated Slag, Polymer-Amended Bentonite and Sand

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