Studying the hydration kinetics and mechanical-microstructural properties of Portland cements made with and without dredged sediment: experimental and numerical approaches

This research focused on two objectives: (i) investigating the impacts of sediment substitution in the raw meal on the hydration and mechanical-microstructural properties of cement; (ii) assessing the reliability of CEMHYD3D code for modeling the properties of hydrated cement. The experimental results indicated that a maximum rate of sediment up to 7.55% had no impact on the formation of mineralogical phases of clinker, the hydration and mechanical-microstructural development of cement. The degree of hydration and strengths of cement made of sediment substitution were slightly higher than those of reference cement, whereas the critical diameter of pores of both hydrated cements was nearly identical. Comparing the modeling results with the experimental measurements showed good predictions for the degree of hydration, hydration heat as well as strength development. However, the formation of hemi-and mono-carboaluminate phases was not predicted in the model, and the porosity prediction was also limited to the capillary porosity

SURICATES : demonstration through pilots of sediment reuse for coastal defence or climate change mitigation

The SURICATES project is a research initiative funded by the European Union regional funds (INTERREG NWE), aimed at increasing the reuse of dredged sediments

Urban land planning: The role of a Master Plan in influencing local temperatures

Land use planning (LUP) is central for managing issues related to climatic variation in urban environments. However, Master Plans (MPs) usually do not include climatic aspects, and few studies have addressed climate change at the urban scale, especially in developing countries. This paper proposes a framework with ten categories for assessment of climatic variation in urban LUP. Each category comprises attributes that describe a complex of relationships in influencing local temperature variations. They are analyzed for the case of the Master Plan of Porto Alegre (MPPA), the Southernmost metropolis of Brazil. It is concluded that the MPPA is strongly grounded in climate-related land and zoning coordination, but exhibits weaknesses in building, cartographical and social aspects considered synergistically relevant for tackling problems related to urban climate variation. Furthermore, the MPPA does not contain provisions related to monitoring of local climate and greenhouse gases (GHG) emissions and it is ineffective for improving energy efficiency. Specific MPPA failures stemming from these weaknesses include: an increase of 21.79% in the city's urbanized area from 1986 to 2011 to accommodate a similar increase in population, with significant horizontal sprawl; average temperature rise of 0.392. °C from 1991-2000 to 2001-2010, with statistically significant increases in temperature found since 1931; significant vehicle traffic increases, especially since 2007. From these findings, it is possible to conclude that the MPPA does not offer answers to all the imbalances related to land use, and therefore gives insufficient support to tackle the issue of rising temperatures

Carbonation of a lime treated soil subjected to different curing conditions

International audienc

Experimental study of rockburst under true-triaxial gradient loading conditions

AC

Effect of Dewatering by the Addition of Flocculation Aid on Treated River Sediments for Valorization in Road Construction

Sediments produced from dredging are categorized as waste. The management of these materials is a worldwide problem. In the context of sustainable development, the traditional solutions such as, immersion, suspension and storage are controlled by national and international regulations. Simultaneously, there is a shortage of aggregates from quarries. It is for these reasons that the environmentalists are encouraged to increase the economically and ecologically responsible re-use of sediments. The aim of this work is to assess the applicability of dredged river sediments in road construction. After dredging the sediment contains a high amount of water. In order to obtain a rapid dewatering, the addition of an optimum dose of a flocculation aid has been proposed. The first part of this paper looks to evaluate the physical, geotechnical and environmental properties of the raw sediment and dehydrated sediment through addition of a flocculation aid. The second part focuses on the treatment of these materials by incorporating a hydraulic binder/lime and a granular corrector, in order to improve the mechanical properties of these sediments for use in sub-base construction and to evaluate the effect of these treatments on the dehydrated sediment. The obtained results show that the dehydrated sediment has no appreciable effect for valorization of river sediments and can be used in sub-base layer of the road construction. © 2016, Springer Science+Business Media Dordrecht

Elevated curing temperature-associated strength and mechanisms of reactive MgO-activated industrial by-products solidified soils

International audienceAlkali-activated industrial by-products (granulated blast furnace slag, Class F fly ash) by traditional alkali activator (such as NaOH and Na2SiO3) serves as a partial replacement for Portland cement in soil stabilization projects and suffers from environmental and technical problems. Reactive MgO–a greener and more practical alternative has recently emerged as a potential activator for slag and fly ash, but its micromechanisms of alkaline activation still need to be deeply investigated for strength improvement of soils. Hence, this study focuses on the strength and hydration properties of reactive MgO-slag and MgO-fly ash solidified soils, especially incorporating the impact of elevated curing temperature. Reactive MgO is proved to be excellent as a novel activator for activation of slag and fly ash, and their activating efficiency increases with elevated curing temperature that helps to remarkably enhance the compressive strength of soils. The major hydration products for reactive MgO-slag solidified soils, detected jointly by X-ray diffraction, scanning electron microscopy and thermogravimetric/differential thermogravimetric tests, are calcium silicate hydrate gels and hydrotalcite-like phases. The primary hydration products for MgO-fly ash solidified soils are magnesium silicate hydrate gels and Mg(OH)2. That is just the intrinsic reason why the microstructure of solidified soils becomes much denser and the mechanical behavior is significantly improved. The minor carbonate phases such as magnesium carbonate and/or calcite are also observed in reactive MgO-slag and MgO-fly ash solidified soils, depending on the period of exposure to air. The curing temperature and binder amount are proved to be the two major factors governing the hydration process of reactive MgO-slag and MgO-fly ash blends. A higher curing temperature and binder amount can generate more hydration products, but their chemical compositions such as accurate element ratios need to be investigated in the future study. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group

Strength, Permeability, and Micromechanisms of Industrial Residue Magnesium Oxychloride Cement Solidified Slurry

International audienceThe solidification of construction waste slurry draws much attention today due to the increasing awareness of environmental protection. Magnesium oxychloride cement (MOC) was first incorporated to solidify slurry in combination with industrial residue, which has the potential to be used as roadbed material. Three types of binding materials including MOC, industrial residue, and industrial residue modified MOC were proposed to evaluate their performance in the solidification of construction slurry with high water content. The unconfined compressive strength (UCS) and coefficient of permeability were investigated, taking into account factors including MOC content, molar ratio of MgO/MgCl2, mass ratio of MOC to industrial residue, industrial residue content, and curing time. The microstructure was identified to reveal the intrinsic mechanisms by scanning electron microscopy (SEM). The results showed that the mechanical behavior of solidified slurry was largely influenced by these factors, and the industrial residue proved effective in improving the strength and permeability of MOC solidified slurry by impeding the decomposition of phase 5 and phase 3 and absorbing a certain amount of water. The industrial residue modified MOC solidified slurry showed higher water resistance and a lower coefficient of permeability due to the generation of amorphous calcium silicate hydrate (C-S-H) gels, phase 5 and phase 3 that could form a much stronger interlocking network. © 2020 American Society of Civil Engineers

New software for the optimization of the formulation and the treatment of dredged sediments for utilization in civil engineering

International audiencePurpose: The objective of our work was to develop a software for the optimization of the processes of treatment and formulation of dredged sediments for utilization in civil engineering applications. The software proposes an optimal solution that meets the different technical and environmental requirements of sediment utilization at a lower cost. Materials and methods: The software development consisted of defining the technical and environmental constraints that the sediments must comply with to be used in one of the four applications targeted in this work: road technique, dikes, concrete, and agricultural spreading. Boundary values were determined according to the current national regulations (France, Belgium, the Netherlands, and the United Kingdom) for each type of application. The constraints were modeled by equations, and then introduced into the software. Economical aspects were also taken into account in the optimization process, with an assessment of costs related to dredging operations, natural materials, treatment, and transportation. In order to validate the computation model of the software, a simulation of the construction of a road based on three sediments was performed. Results and discussion: The aim of this work was to provide decision makers with simple and interactive software which will facilitate the management and the utilization of dredged sediments in civil engineering. The software proposed the mixture of three types of dredged sediments (30.29%) and sand (69.69%). The software also proposed treatments to reduce the organic matter content of the sediment and the amount of chemical elements that exceed the environmental thresholds defined by regulations. An estimate of the overall cost and of the detailed cost related to the sediment utilization was also proposed by the software. Conclusions: The presented software is a tool for optimizing the utilization and treatment of dredged sediments in civil engineering works. The technical and environmental constraints were modeled as well as the costs of each step of the sediment utilization. This allowed proposing the optimal solution that meets different technical and environmental requirements at a lower cost. The software has been tested during a road construction in Lille, France, and results confirmed the reliability of the solution proposed by the software. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature