Engineering properties of vertical cutoff walls consisting of reactive magnesia-activated slag and bentonite: workability, strength and hydraulic conductivity

Soil–cement–bentonite (SCB) vertical cutoff walls are commonly used to control the flow of contaminated groundwater at polluted sites. However, conventional backfill consisting of ordinary portland cement (OPC) is associated with a relatively high CO2 footprint. Potential chemical interactions between OPC and bentonite could also undermine the long-term durability of SCB materials. This paper proposes an innovative backfill material for cutoff walls that is composed of MgO-activated ground granulated blast furnace slag (GGBS), bentonite, and soil. The OPC–soil, OPC–bentonite–soil, and OPC–GGBS–bentonite–soil backfill materials are also tested for comparison purposes. The workability of fresh backfills and unconfined compressive strength of aged backfills are investigated. The hydraulic conductivities of aged backfills permeated with tap water, Na2SO4, and Pb–Zn solutions are assessed. The unconfined compressive strength and hydraulic conductivity of the proposed backfill permeated with tap water are in the range of 230–520 kPa and 1.1×10−10  to  6.3×10−10  m/s after 90 days of curing, respectively, depending on the mix composition. The hydraulic conductivity of the proposed MgO–GGBS–bentonite–soil backfill permeated with sodium sulfate (Na2SO4) or lead–zinc (Pb–Zn) solution is well below the commonly used limit, while the OPC–bentonite–soil backfill shows a significant loss in impermeability. Environmental and economic analyses indicate that, compared with conventional backfill made from OPC–bentonite–soil mixtures, the proposed backfill reduces CO2 emissions by approximately 84.7%–85.1% and costs by 15.3%–16.9%. The environmental and economic advantages will promote the use of MgO-activated GGBS–bentonite mixtures in cutoff walls and lead to their increased application in land remediation projects

Multiple positive solutions for second order impulsive boundary value problems in Banach spaces

By means of the fixed point index theory of strict set contraction operators, we establish new existence theorems on multiple positive solutions to a boundary value problem for second-order impulsive integro-differential equations with integral boundary conditions in a Banach space. Moreover, an application is given to illustrate the main result

A note on the fractional Cauchy problems with nonlocal initial conditions

AbstractOf concern is the Cauchy problems for fractional integro-differential equations with nonlocal initial conditions. Using a new strategy in terms of the compactness of the semigroup generated by the operator in the linear part and approximating technique, a new existence theorem for mild solutions is established. An application to a fractional partial integro-differential equation with a nonlocal initial condition is also considered