Strength and drying shrinkage of slag paste activated by sodium carbonate and reactive MgO

This paper investigates the potential of combining Na2CO3 and reactive MgO as a sustainable activator for ground granulated blastfurnace slag. Two very different reactivity MgOs were added at 5–10 % and the Na2CO3 content varied from 4% to 8% by the weight of slag. The strength and drying shrinkage of the activated slag pastes were tested up to 90 d. It was found that the optimum reactive MgO addition was 5% regardless of the MgO type and Na2CO3 content. MgO with the higher reactivity significantly increased the early strength of the paste but had almost no effect on the strength at 90 d. On the other hand, the effect of the lower reactivity MgO on the strength was more profound at later ages and low Na2CO3 dosage. In terms of drying shrinkage, increasing the Na2CO3 content from 4% to 6% caused a remarkable decrease of drying shrinkage while increasing it from 6% to 8% had negligible effect. X-ray diffraction and thermogravimetric analysis revealed that the major hydration products were calcium silicate hydrate gel and hydrotalcite-like phases, similar to those in conventional alkali-activated slag cements. There was also a large quantity of calcite formed especially in the 8% Na2CO3 pastes due to causticisation. It was concluded that the combination of reactive MgO and Na2CO3 could serve as a potential sustainable activator for slags.The first author is grateful to Cambridge Trust and China Scholarship Council (CSC) for sponsoring his Ph.D. studentship.This is the accepted manuscript for a paper published in Construction and Building Materials, Volume 81, 15 April 2015, Pages 58–65, doi:10.1016/j.conbuildmat.2015.01.08

The role of brucite, ground granulated blastfurnace slag, and magnesium silicates in the carbonation and performance of MgO cements

This study focuses on the enhancement of the technical and environmental performance of MgO cements through the inclusion of brucite, GGBS, talc and serpentine as partial MgO substitutes in concrete blocks. The influence of these additives on the microstructure, hydration, carbonation, and mechanical performance of blocks cured under natural and elevated CO2 conditions is presented. An optimum replacement level was determined for each composition via unconfined compressive strength (UCS), scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and acid digestion. Mixes subjected to accelerated carbonation indicated up to 100% carbonation in 7 days. Results highlight the suitability of each additive in replacing MgO without compromising performance.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.conbuildmat.2015.07.10

Characterisation of reactive magnesia and sodium carbonate-activated fly ash/slag paste blends

A system of alkali-activated fly ash (FA)/slag (AAFS) mixtures as a clinkerless cement was investigated with different dosages of Na2CO3, as a sustainable activator. The effect of incorporating various proportions of reactive magnesia (MgO) was also examined. Mechanical, mineralogical, and microstructural characterisation of the cement pastes was carried out using the unconfined compressive strength, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy and scanning electron microscopy. It was found that the strength of Na2CO3 activated FA/slag mixtures generally increased with time and the Na2CO3 dosage. The hydration products were mainly C–(N)–A–S–H gel of low-crystallinity, which is rich in Al and may have included Na in its structure, and hydrotalcite-like phases. Adding reactive MgO in the mixes showed an accelerating effect on the hydration rate as suggested by the isothermal calorimetry data. Additionally, findings revealed variations on the strength of the pastes and the chemical compositions of the hydration products by introducing reactive MgO into the mixtures.The financial support of the PhD scholarship for the first author from the Yousef Jameel Foundation and Cambridge Overseas Trust are gratefully acknowledged.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.conbuildmat.2015.06.01

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO–GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.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 manuascript for a paper published in Cement and Concrete Composites, Volume 57, March 2015, Pages 8–16, doi:10.1016/j.cemconcomp.2014.10.00

Effects of sewage sludge on heavy metal accumulation in soil and plants and on crop productivity in Aleppo governorate

Sewage sludgeHeavy metalsCrop productionCropsOrganic matterSoil

Comparative Analysis of Cement and Lateralite on the Engineering Properties of Niger Delta Soils for Pavement Construction

This is the final published version. It first appeared at http://sciencedomain.org/abstract/9224.This study investigated the effect of cement and lateralite in improving some engineering properties of Niger Delta soils, classified as clayey soil, silty/clayey sand, and fine sand. Cement had very good effect in reducing the plasticity of the clayey soil and the silty/clayey sand but increased the plasticity of the fine sand, and all the samples had increased soaked CBR and UCS at 28 days especially with 6% and 8% cement contents. 14% lateralite content had the best effect on the silty/clayey sand in reducing the plasticity and increasing both the CBR and UCS. However, no positive effect on the plasticity indices was noticed for the clayey soil and the fine sand, but appreciable increases in their unsoaked and soaked CBR and UCS at 28 days curing. The applications of cement (6% and 8%) and 14% lateralite would make the stabilized soils applicable as sub-base and base materials.The sponsorship of the PhD program of the first author by Schlumberger Faculty for the Future Foundation at the University of Cambridge, United Kingdom and the funding by Cambridge- Africa Alborada Scheme of this study which formed part of the PhD research are acknowledged

Deformation and mechanical properties of the expansive cements produced by inter-grinding cement clinker and MgOs with various reactivities

Magnesia (MgO) either intrinsically contained in cement clinker or prepared separately as expansive additive has been used to compensate for the shrinkage of cementitious materials. In this study, for improving the homogenous distribution of MgOs, the cement clinker was inter-ground with MgO expansive additives with various reactivities ranging from 50 to 400 s to prepare series of expansive Portland cements and blended cements with incorporation of slag and fly ash. The deformations and mechanical properties of the expansive cements were investigated. Results showed that the expansive cements containing more reactive MgOs produced more rapid expansion under sealed condition or water curing, leading to effective autogenous shrinkage compensations at early age. The reactivities of MgOs caused insignificant influences on the mechanical strengths of expansive cements. The blended cements had lower strengths at early age but higher strengths than that of the corresponding Portland cements at late age due to the pozzolanic reaction.The financial support from the Royal Academy of Engineering UK/China, India Exchange, The National Key Technology R&D Program (2011BAE27B01-1), Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and National Natural Science Foundation of China (51461135003) are acknowledged.This is the accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0950061815000914#

Smart biomimetic construction materials for next generation infrastructure

The resilience of building and civil engineering structures is typically associated with the design of individual elements such that they have sufficient capacity or potential to react in an appropriate manner to adverse events. Traditionally this has been achieved by using ‘robust’ design procedures that focus on defining safety factors for individual adverse events and providing redundancy. As such, construction materials are designed to meet a prescribed specification; material degradation is viewed as inevitable and mitigation necessitates expensive maintenance regimes; ~£40 billion/year is spent in the UK on repair and maintenance of existing, mainly concrete, structures. More recently, based on a better understanding and knowledge of microbiological systems, materials that have the ability to adapt and respond to their environment have been developed. This fundamental change has the potential to facilitate the creation of a wide range of ‘smart’ materials and intelligent structures, including both autogenous and autonomic self‐healing materials and adaptable, self‐sensing and self‐repairing structures, which can transform our infrastructure by embedding resilience in the materials and components of these structures so that rather than being defined by individual events, they can evolve over their lifespan. We therefore advocate that next generation infrastructure will include next generation infrastructure materials based on smart biomimetic construction materials. This paper presents details of the national consortium that is leading international efforts in the development of those next generation infrastructure materials. It presents details of the work done to date, over the past three years, as part of the EPSRC funded project Materials for Life and the plans for work to be done over the next five years as part of a follow-on Programme grant: Resilient Materials for Life

Comparison of reactive magnesia- and carbide slag-activated ground granulated blastfurnace slag and Portland cement for stabilisation of a natural soil

In this study, reactive magnesia (MgO)- and carbide slag (CS)-activated ground granulated blastfurnace slag (GGBS) were used to stabilise a natural soil in comparison to Portland cement (PC). X-ray diffraction (XRD), scanning electron microscopy (SEM) and unconfined compressive strength (UCS) test were employed to investigate the microstructural and mechanical properties of stabilised soils. The results indicated that the main hydration products of CS-GGBS stabilised soil included calcium silicate hydrates (CSH), calcium aluminate hydrates (CAH) and ettringite. For MgO-GGBS stabilised soils, CSH was the only hydration product detected. These hydration products had different microstructure and binding ablility, affecting the strength of stabilised soils. There was an optimum MgO or CS content, in a range of 10-20%, for yielding the highest UCS of MG-GGBS or CS-GGBS stabilised soil at the same age. The 90-day UCS of the optimum MgO-GGBS and CS-GGBS stabilised soils was 3.0-3.2 and 2.4-3.2 times that of the PC stabilised soil, respectively.The authors appreciate the funding provided by National Natural Science Foundation of China (41330641) and Jiangsu Province (BY2014120).This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S0169131715001325

Mechanical and hydration properties of ground granulated blastfurnace slag pastes activated with MgO-CaO mixtures

Since alkali-activated slag using conventional activators suffers from economical and technical problems, other alternative activators should be explored. This paper reports the results of an investigation into the activation of ground granulated blastfurnace slag by using 10% (by weight) reactive MgO, CaO and their mixtures with various ratios. The mechanical and hydration properties of pastes were examined up to 90 days. It was found that the strength of slag pastes activated with MgO–CaO mixtures decreased with the increasing ratio of MgO to CaO in the early age while a much steeper strength gain was observed in pastes with MgO/CaO higher than 19/1 after 28 days and longer. The addition of small amount of CaO in MgO can greatly accelerate the hydration of slag in the early age by increasing the pH of pore solution. However, pastes showed small difference in strength development at each period when MgO/CaO was less than 1. The main hydration products, analysed by XRD, TGA and SEM/EDS, were C–S–H and hydrotalcite-like phases. While CaO accelerated the formation of C–S–H in the early age, MgO induced more amount of hydrotalcite-like phases, which notably enhanced the strength of slag pastes with high MgO content after 28 days and longer. Calcite, portlandite and residual MgO were also observed, depending on the MgO/CaO ratio and the hydration time. This work indicated that the replacement of MgO by CaO can make the application of reactive MgO in slag activation more economical.The work presented in this paper was carried out at Department of Engineering, University of Cambridge, where the first author was a visiting researcher. The visit was funded by the China Scholarship Council and the Scientific Research Foundation of the Graduate School of Nanjing University (No.2012CL11). The financial support for the PhD studentship of the second author from the Cambridge Trust and China Scholarship Council was also very much appreciated.This is the accepted manuscript version. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0950061814007569