Evaluation of novel reactive MgO activated slag binder for the immobilisation of lead and zinc.

Although Portland cement is the most widely used binder in the stabilisation/solidification (S/S) processes, slag-based binders have gained significant attention recently due to their economic and environmental merits. In the present study, a novel binder, reactive MgO activated slag, is compared with hydrated lime activated slag in the immobilisation of lead and zinc. A series of lead or zinc-doped pastes and mortars were prepared with metal to binder ratio from 0.25% to 1%. The hydration products and microstructure were studied by X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The major hydration products were calcium silicate hydrate and hydrotalcite-like phases. The unconfined compressive strength was measured up to 160 d. Findings show that lead had a slight influence on the strength of MgO-slag paste while zinc reduced the strength significantly as its concentration increased. Leachate results using the TCLP tests revealed that the immobilisation degree was dependent on the pH and reactive MgO activated slag showed an increased pH buffering capacity, and thus improved the immobilisation efficiency compared to lime activated slag. It was proposed that zinc was mainly immobilised within the structure of the hydrotalcite-like phases or in the form of calcium zincate, while lead was primarily precipitated as the hydroxide. It is concluded, therefore, that reactive MgO activated slag can serve as clinker-free alternative binder in the S/S process.The authors are grateful to Cambridge Trust and China Scholarship Council (CSC) for their financial help of the PhD studentship for the first author.This is the accepted manuscript version. The final version is published by Chemosphere here: http://dx.doi.org/10.1016/j.chemosphere.2014.07.027

Three-year performance of in-situ mass stabilised contaminated site soils using MgO-bearing binders

This paper provides physical and chemical performances of mass stabilised organic and inorganic contaminated site soils using a new group of MgO-bearing binders over 3 years and evaluated the time-dependent performance during the 3 years. This study took place at a contaminated site in Castleford, UK in 2011, where MgO, ground granulated blastfurnace slag (GGBS) and Portland cement (PC) were mixed with the contaminated soils in a dry form using the ALLU mass mixing equipment. Soil cores were retrieved 40-day, 1-year and 3-year after the treatment. The core quality, strength, and the leaching properties were determined via physical observation, unconfined compressive strength (UCS) and batch leaching tests. After 3-year treatment, the UCS values of ALLU mixes were in the range of 50–250 kPa; the leachate concentrations of Cd, Pb, Cu and Zn (except Ni) in all mixes were lower than their drinking water standards; and the leachability of total organics was in the range of 10–105 mg/L. No apparent degradation of the mass stabilised materials after 3 years’ exposure to the field conditions was found. MgO-GGBS blends were found able to provide higher strength and less leachability of contaminants compared to PC and MgO-only mixes in mass stabilised soils

Three-year performance of in-situ solidified/stabilised soil using novel MgO-bearing binders.

A new group of MgO-bearing binders has been developed recently which showed improved sustainability and technical performance compared to Portland cement (PC). However, the application of these MgO-bearing binders in the Solidification/Stabilisation (S/S) techniques is very limited. This study investigates the three-year performance of a highly contaminated soil treated by in-situ S/S using MgO-bearing binders and PC. The core quality, strength, permeability and the leaching properties of the S/S materials were evaluated. The effects of binder composition, addition of inorgano-organo-clay (IOC) and the grout content on the properties of the 3-y S/S materials are discussed. It is found that although MgO alone provided negligible strength to the soil, it is superior in immobilising both inorganic and organic contaminants. Replacing MgO by ground granulated blast-furnace slag (GGBS) significantly enhanced the strength while also performed well in immobilising the contaminants. The improved pH buffering capacity was attributed to the low solubilities of brucite and hydrotalcite-like phases formed in the MgO-bearing binders, and was also the reason for the improved performance in stabilising contaminants. The addition of IOC slightly decreased the strength and the permeability of the S/S materials but inconsistent effect on the contaminant immobilisation was found depending on the binder composition. This study showed no degradation of the S/S materials after 3 y exposure to field conditions and has proved the applicability and the advantages of MgO-bearing binders over PC in S/S.The authors are grateful to the funding from EPSRC (Grant No.: NMZJ/116 RG60240) to support this research. The samples were all retreived from a field trial sponsored by EPSRC/TSB (Grant No.: TP/5/CON/6/I/H0304E).This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.chemosphere.2015.09.046 The data reported in this study can be accessed at: http://www.repository.cam.ac.uk/handle/1810/250325

Defining Niger Delta Soils – Are They Laterites?

This is the final published version. It was first published by IISTE at http://www.iiste.org/Journals/index.php/CER/article/view/22179.The ambiguity of the use of the term ‘laterite’ to generally classify tropical soils especially for engineering purposes needed to be addressed. An attempt was made to analyze the silica-sesquioxide ratio of some Niger Delta soils to establish whether these soils which are formed in the tropic are indeed laterites. This ratio is used because it is generally accepted as a parameter in the classification and specification of laterites and can be measured with some degree of accuracy in the laboratory. This study revealed that these soils (except the ferralsols) which were soft when wet and significantly hard when air-dried could not be called laterite soils because of the high silica-sesquioxide ratios. It is envisaged that this study would help the engineers in the region to have a better understanding of the soils which are erroneously acclaimed and handled as laterite soils

Development and Application of Novel Sodium Silicate Microcapsule-Based Self-Healing Oil Well Cement.

A majority of well integrity problems originate from cracks of oil well cement. To address the crack issues, bespoke sodium silicate microcapsules were used in this study for introducing autonomous crack healing ability to oil well cement under high-temperature service conditions at 80 °C. Two types of sodium silicate microcapsule, which differed in their polyurea shell properties, were first evaluated on their suitability for use under the high temperature of 80 °C in the wellbore. Both types of microcapsules showed good thermal stability and survivability during mixing. The microcapsules with a more rigid shell were chosen over microcapsule with a more rubbery shell for further tests on the self-healing efficiency since the former had much less negative effect on the oil well cement strength. It was found that oil well cement itself showed very little healing capability when cured at 80 °C, but the addition of the microcapsules significantly promoted its self-healing performance. After healing for 7 days at 80 °C, the microcapsule-containing cement pastes achieved crack depth reduction up to ~58%, sorptivity coefficient reduction up to ~76%, and flexural strength regain up to ~27%. The microstructure analysis further confirmed the stability of microcapsules and their self-healing reactions upon cracking in the high temperature oil well cement system. These results provide a promising perspective for the development of self-healing microcapsule-based oil well cements.Shell, Schlumberger Foundation Faculty for the Future, Cambridge Trust and EPSRC Resilient Materials for Life (RM4L) Programme Grant (EP/P02081X/1

Defining Niger Delta Soils: Are They Laterites?

The ambiguity of the use of the term ‘laterite’ to generally classify tropical soils especially for engineering purposes needed to be addressed. An attempt was made to analyze the silica-sesquioxide ratio of some Niger Delta soils to establish whether these soils which are formed in the tropic are indeed laterites. This ratio is used because it is generally accepted as a parameter in the classification and specification of laterites and can be measured with some degree of accuracy in the laboratory. This study revealed that these soils (except the ferralsols) which were soft when wet and significantly hard when air-dried could not be called laterite soils because of the high silica-sesquioxide ratios. It is envisaged that this study would help the engineers in the region to have a better understanding of the soils which are erroneously acclaimed and handled as laterite soils. Keywords: Laterite, Niger Delta soils, Silica-sesquioxide ratio

Performance of Magnesia-modified sodium carbonate-activated slag/fly ash concrete

Various innovative research in the cement industry is looking into improving its environmental sustainability. Sodium carbonate-activated slag/fly ash (NC-SF) binders has recently evolved as a potentially more sustainable binding materials than both Portland cement and conventional alkali activated materials such as sodium silicate and sodium hydroxide activated materials. The reaction mechanism and some microstructural properties of NC-SF cements have been a major area of research recently. However, very few studies have scaled up the investigation of these binders into concrete specimens. This paper, therefore, provides new insight into the strength development and the durability performance of NC-SF concrete and MgO-modified NC-SF concrete. Concrete testing included measurements of compressive strength, split tensile strength, water absorption, depth of carbonation, sulphate exposure, acid exposure and elevated-temperature exposure. Microstructure studies were conducted using Powder X-Ray diffraction (PXRD), Thermogravimetric analysis (TGA) and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR). It is concluded that NC-SF concrete mixes develop acceptable mechanical strength and demonstrate high resistance to sulphate attack. They also showed higher resistance to acid attack than the control mix based on sodium silicate-activated slag concrete. Here, emphasis is placed on the potential of developing NC-SF concrete with excellent performance and less complicated production methods as well as a low carbon footprint. It is also found that the use of reactive MgO enhanced the strength development of NC-SF concrete as well as its resistance to acid and carbonation.Yousef Jameel Foundatio

Time-dependent performance of soil mix technology stabilized/solidified contaminated site soils.

This paper presents the strength and leaching performance of stabilized/solidified organic and inorganic contaminated site soil as a function of time and the effectiveness of modified clays applied in this project. Field trials of deep soil mixing application of stabilization/solidification (S/S) were performed at a site in Castleford in 2011. A number of binders and addictives were applied in this project including Portland cement (PC), ground granulated blastfurnace slag (GGBS), pulverised fuel ash (PFA), MgO and modified clays. Field trial samples were subjected to unconfined compressive strength (UCS), BS CN 12457 batch leaching test and the extraction of total organics at 28 days and 1.5 years after treatment. The results of UCS test show that the average strength values of mixes increased from 0-3250 kPa at 28 days to 250-4250 kPa at 1.5 years curing time. The BS EN 12457 leachate concentrations of all metals were well below their drinking water standard, except Ni in some mixes exceed its drinking water standard at 0.02 mg/l, suggesting that due to varied nature of binders, not all of them have the same efficiency in treating contaminated soil. The average leachate concentrations of total organics were in the range of 20-160 mg/l at 28 days after treatment and reduced to 18-140 mg/l at 1.5 years. In addition, organo clay (OC)/inorgano-organo clay (IOC) slurries used in this field trial were found to have a negative effect on the strength development, but were very effective in immobilizing heavy metals. The study also illustrates that the surfactants used to modify bentonite in this field trail were not suitable for the major organic pollutants exist in the site soil in this project.This paper was written to support the SMiRT (soil mix remediation technology) project, the funding for which was supplied by the UK Technology Strategy Board with 16 industrial partners (Project TP/5/CON/6/I/H0304E). The project website is at http://www-g.eng.cam.ac.uk/smirt. The authors are grateful to Schlumberger Foundation for its financial help of the PhD studentship for the first author, and many thanks to the proofreading by Fei Jin and David O’Connor.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/doi:10.1016/j.jhazmat.2015.01.00

Self-Healing Concrete and Cementitious Materials

Concrete is one of the most used materials in the world with robust applications and increasing demand. Despite considerable advancement in concrete and cementitious materials over last centuries, infrastructure built in the present world with these materials, such as dams, roads, bridges, tunnels and buildings requires intensive repair and maintenance throughout its design life. Self-healing concrete and cementitious materials, which have the ability to recover after initial damage, have the potential to address these challenges. Self-healing technology in concrete and cementitious materials can mitigate the unnecessary repair and maintenance of built infrastructure as well as overall CO2 emission due to cement production. This chapter provides the state-of-the-art of self-healing concrete and cementitious materials, mainly focusing on autogenic or intrinsic self-healing using fibre, shrinkable polymers, minerals and supplementary cementitious materials, and autonomic self-healing using non-traditional concrete materials such as microscale to macroscale capsule as well as vascular systems with polymeric, mineral and bacterial agents

Self-healing of drying shrinkage cracks in cement-based materials incorporating reactive MgO

Excessive drying shrinkage is one of the major issues of concern for longevity and reduced strength performance of concrete structures. It can cause the formation of cracks in the concrete. This research aims to improve the autogenous self-healing capacity of traditional Portland cement (PC) systems, adding expansive minerals such as reactive magnesium oxide (MgO) in terms of drying shrinkage crack healing. Two different reactive grades (high “N50” and moderately high “92-200”) of MgO were added with PC. Cracks were induced in the samples with restraining end prisms through natural drying shrinkage over 28 days after casting. Samples were then cured under water for 28 and 56 days, and self-healing capacity was investigated in terms of mechanical strength recovery, crack sealing efficiency and improvement in durability. Finally, microstructures of the healing materials were investigated using FT-IR, XRD, and SEM-EDX. Overall N50 mixes show higher expansion and drying shrinkage compared to 92-200 mixes. Autogenous self-healing performance of the MgO containing samples were much higher compared to control (only PC) mixes. Cracks up to 500 μm were sealed in most MgO containing samples after 28 days. In the microstructural investigations, highly expansive Mg-rich hydro-carbonate bridges were found along with traditional calcium-based, self-healing compounds (calcite, portlandite, calcium silicate hydrates and ettringite).The support of the Islamic Development Bank (IDB) scholarship, collaborating with the Cambridge Commonwealth, European and International Trust (CCEIT) for the first author’s PhD research, is highly appreciated. The authors also thank Wai Yuk Lau for his assistance and suggestions in the shrinkage measuring experiments.This is the author accepted manuscript. The final version is available from the Institute of Physics via http://dx.doi.org/10.1088/0964-1726/25/8/08400