Valorized deinking paper residue as fill material for geotechnical structures

This study introduces a novel geotechnical composite material comprising two types of fill material sourced from the paper industry—deinking paper sludge ash (DPSA) and deinking paper sludge (DPS). Five composites with different DPSA and DPS contents were investigated. Two composites were selected for further analyses. The technology and procedure for composite installation were implemented in field tests. The composites with 80% and 70% DPSA exhibited the elasticity required to withstand minor landslide slip deformations, in addition to achieving sufficiently high values of uniaxial compressive strength. The composites had a low maximum dry density value, which led to fewer settlements in the entire support structure. The enhanced shear characteristics can enable the construction of a thinner retaining wall. The delay between preparation and installation of the composites was further investigated. The field tests confirmed that the composites with 80% and 70% DPSA can be installed on the construction site 4 h and even 24 h after mixing. In 2018, a retaining wall structure with 70% DPSA and 30% DPS was successfully implemented near a railway line using conventional technology as followed-up research to the herein presented study. Results have been derived from work performed in the scope of the H2020 Paperchain project in which novel circular economy models centered on the valorization of the waste streams generated by the pulp and paper industry as secondary raw material for several resource-intensive sectors, including the construction sector, have been developed. Environmental benefits are savings in natural raw materials, reduction of landfill disposal as well as CO2 emission reduction.

Substitute Building Materials in Geogrid-Reinforced Soil Structures

The feasibility of substitute building materials (SBMs) in engineering applications was investigated within the project. A geogrid-reinforced soil structure (GRSS) was built using SBM as the fill material as well as vegetated soil for facing and on top of the construction. Four different SBMs were used as fill material, namely blast furnace slag (BFS), electric furnace slag (EFS), track ballast (TB), and recycled concrete (RC). For the vegetated soil facing, a mixture of either recycled brick (RB) material or crushed lightweight concrete (LC) mixed with organic soil was used. The soil mechanical and chemical parameters for all materials were determined and assessed. In the next step, a GRSS was built as a pilot application consisting of three geogrid layers with a total height of 1.5 m and a slope angle of 60°. The results of the soil mechanical tests indicate that the used fill materials are similar or even better than primary materials, such as gravel. The results of the chemical tests show that some materials are qualified to be used in engineering constructions without or with minor restrictions. Other materials need a special sealing layer to prevent the material from leakage. The vegetation on the mixed SBM material grew successfully. Several ruderal and pioneer plants could be found even in the first year of the construction. The porous material (RB and LC) provide additional water storage capacity for plants especially during summer and/or heat periods. With regard to the results of the chemical analyses of the greening layers, they are usable under restricted conditions. Here special treatment is necessary. Finally, it can be stated that SBMs are feasible in GRSS, particularly as fill material but also as a mixture for the greenable soil.

Characterization of TBM Muck for Construction Applications

This paper investigates the potential utilization of the Tunnel Boring Machine (TBM) muck generated from Doha’s Metro Gold Line in different construction applications. The properties of the raw TBM muck were studied, and the results were compared to the specifications of Qatari Construction Standards (QCS 2014) of concrete aggregates, fill material under buildings and road subgrades. Compared to the requirements of concrete aggregates, the results indicated that the gradation of the raw TBM muck does not comply with the QCS 2014 requirements, and hence, sieving and screening may be essential. Moreover, the tests’ results showed that the properties of the muck meet the requirements of the concrete coarse aggregates, except for the water absorption, loss by magnesium sulphate soundness, loss by Los Angeles abrasion and the acid-soluble sulphate. As fill material under buildings or road subgrades, the gradation of the TBM muck complies with the QCS 2014 requirements, while the liquid limit and plasticity index are higher than the QCS 2014 permissible limits. Additionally, the morphological structure and the elemental composition of the raw TBM muck were determined by employing Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX), respectively. Digital images were also taken at larger scale to draw a full picture of the TBM muck morphology. A mixture of rough-rounded to angular-elongated shaped particles with relatively large voids could be observed. The EDX analysis demonstrated the presence of silicon (Si) as the predominant component of the muck, which may alter the Coefficient of Thermal Expansion (CTE) values for mixtures prepared using TBM muck. Hence, further investigations should be performed on the mechanical and thermal properties of mixtures containing TBM muck as aggregates’ replacement, and further work should be directed toward this end.

THE PROPOSED GEOBEADS ADDITION AS LIGHTWEIGHT FILL MATERIAL

The study aimed to develop an alternative material for dam and road embankments, especially in the area with soft soil, using Geobeads. There are many problems constructing embankments on soft soil, such as low bearing capacity, excessive and differential settlement, and slope stability. The subgrade must be stable to resist the weight of the fill construction and upper structure. The lightweight fill material is commonly used as an alternative to reduce the excessive and differential settlements by reducing the weight of landfills on the soft soil subgrade. In this study, the laboratory test was conducted to investigate the influence of Geobeads (GB) additions as lightweight fill material both as the dam embankment and the road embankment. This study aims to find a combination of GB, sand, and cement to fulfill the standard as an embankment material. Investigation of physical and mechanical properties represented that light embankment can be an alternative on soft soil. The Indonesia National Standard, 8062:2015, and the General Specifications for Road and Bridge Construction Work were guidelines for embankment cases. The falling head test executes the permeability coefficient. The CBR test was conducted based on ASTM D1883. The specimen has varied the percentage of EPS addition (20%, 30%, 40%) with 14 days of curing time. Based on the test results, both the permeability coefficient value and the CBR value decreased along with the increase in the percentage of EPS, where the coefficient of permeability (k) of the specimens around 10-5 cm/s and the lowest CBR at 40% GB was 30.02% which is the range still used as embankment material.

Tests of Strength Parameters of Hydro-Mixtures Based on Ashes from a Fluidized Bed Boiler in the In-Situ Approach

The paper presents the practical use of a solidifying hydro-mixture based on ashes from fluidized bed boilers under hard coal mine conditions for filling an incline connecting the headgate and tailgate of a longwall running along the strike with roof caving. The reason for filling the incline with a material of preset strength parameters was to minimize the methane hazard in the extracted coal seam. Due to a great demand for fill material, which translates into economic considerations, the option of applying fine-fraction waste material was selected. Preliminary laboratory tests of the physical and mechanical properties of hydro-mixtures based on ash obtained from a fluidized bed boiler of a power plant, allowed us to select a specific hydro-mixture meeting the requirements. After 95 days, the incline filled with the proposed hydro-mixture was subjected to exploitation along with the advance of longwall working. This enabled the in-situ collection of a number of fill material samples from various places along the entire length of the incline. Then their strength was tested and the results compared with the obtained test results of identical material seasoned under laboratory conditions. The obtained results constitute a unique research material since it is practically impossible to verify the laboratory-determined strength parameters of the solidifying fine-fraction hydro-mixtures under in-situ conditions. Thsis results mainly from the lack of technical capabilities and poor access to the places where fine-fraction hydro-mixtures are applied, mostly abandoned cavings or parts of workings separated by dams.