•Review of investigations on recycled aggregate concretes (RAC).•Techniques of demolition, recycling and pre-treatment of aggregates.•Review on mechanical properties and durability of RAC.•Structural ...and fire resistances of reinforced RAC structures.
In the context of a circular economy, the recycling becomes more than more important. In the construction industry, the wastes from the destructions of old structures are significant. The recycling of the old concretes can contribute to reduce the extraction of the new natural resources (gravel, sand) and to reduce the waste deposit areas. Numerous studies have already been performed to investigate different aspects of recycled aggregate concretes (RAC). Several publications have also done the detailed reviews on certain topics of RAC (such as mechanical properties, mix proportioning); however, still few articles have done the global synthesis on different aspects of RAC. This paper presents a rapid state-of-the-art of numerous topics related to RAC: from the recycling techniques of old-concrete-aggregates, the mix proportioning, the mechanical properties, the durability, the structural behavior and the fire resistance. The number of existing studies synthesized is relatively important (about 170 publications). The aim of the present paper is to provide a rapid overview about existing scientific investigations on RAC, which can offer a good guidance to researchers and engineers who are entering to this area.
•Compressive strength, elastic modulus and Poisson’s ratio were determined.•Influence of water on the mechanical characteristics of earthen material.•Variations of mechanical characteristics ...following suction.•A slight increase in water content (<4% by weight) is not followed by sudden drop in strength.•Interpretations at the microscopic level are presented for sandy, clayey and stabilised soil.
In this paper, influence of moisture content on the mechanical characteristics of rammed-earth has been studied. Samples from different soils (sandy, clayey, stabilised) were manufactured and tested in unconfined compression at several moisture contents. Compressive strength, elastic modulus and Poisson's ratio were determined. A simplified method to measure the suction within rammed earth samples has been developed and validated. The variation of mechanical characteristics related to moisture content and suction are presented. This paper shows that a slight increase in the moisture content of dry rammed-earth is not followed by sudden drop in wall strength. Qualitative explanations at the nano-scale are presented.
The need for a vast quantity of new buildings to address the increase in population and living standards is opposed to the need for tackling global warming and the decline in biodiversity. To ...overcome this twofold challenge, there is a need to move towards a more circular economy by widely using a combination of alternative low-carbon construction materials, alternative technologies and practices. Soils or earth were widely used by builders before World War II, as a primary resource to manufacture materials and structures of vernacular architecture. Centuries of empirical practices have led to a variety of techniques to implement earth, known as rammed earth, cob and adobe masonry among others. Earth refers to local soil with a variable composition but at least containing a small percentage of clay that would simply solidify by drying without any baking. This paper discusses why and how earth naturally embeds high-tech properties for sustainable construction. Then the potential of earth to contribute to addressing the global challenge of modern architecture and the need to re-think building practices is also explored. The current obstacles against the development of earthen architecture are examined through a survey of current earth building practitioners in Western Europe. A literature review revealed that, surprisingly, only technical barriers are being addressed by the scientific community; two-thirds of the actual barriers identified by the interviewees are not within the technical field and are almost entirely neglected in the scientific literature, which may explain why earthen architecture is still a niche market despite embodying all the attributes of the best construction material to tackle the current climate and economic crisis.
This article is part of the theme issue ‘The role of soils in delivering Nature's Contributions to People’.
•Mechanical and microstructure properties of FA-GGBS-HMNS based GPC are investigated.•Addition of HMNS in FA-GGBS based GPC can enhance the intermolecular bonding of GPC matrix.•Mechanical properties ...are improved when HMNS is added in FA-GGBS based GPC cured at ambient conditions.•SEM analysis showed that FA-GGBS-HMNS based GPC is highly compacted, with a dense matrix and fewer pores.
This paper presents an experimental investigation on the mechanical properties and microstructure of geopolymer concrete mixed using class F fly ash (FA), ground granulated blast-furnace slag (GGBS) and high-magnesium nickel slag (HMNS). An optimal combination of FA, GGBS and HMNS was determined using the compressive strength tests of geopolymer (GP) pastes mixed with various different replacements of FA with GGBS and/or HMNS. It was found that the replacement of FA with 20% of GGBS and 10% of HMNS in GP concrete increases the 28-day compressive strength by 100% and the 28-day splitting tensile strength by 58%. The microstructure analysis of the GP concrete using SEM, XRD, and FTIR showed the formation of aluminosilicate amorphous phase in a three-dimensional network. The SEM images revealed a fully compact and cohesive geopolymer matrix, which explains the reason why the mechanical properties of the FA based GP concrete with both GGBS and HMNS are improved.
Ordinary cement concrete is a popular material with numerous advantages when compared to other construction materials; however, ordinary concrete is also criticized from the public point of view due ...to the CO
emission (during the cement manufacture) and the consumption of natural resources (for the aggregates). In the context of sustainable development and circular economy, the recycling of materials and the use of alternative binders which have less environmental impacts than cement are challenges for the construction sector. This paper presents a study on non-conventional concrete using recycled aggregates and alkali-activated binder. The specimens were prepared from low calcium fly ash (FA, an industrial by-product), sodium silicate solution, sodium hydroxide solution, fine aggregate from river sand, and recycled coarse aggregate. First, influences of different factors were investigated: the ratio between alkaline activated solution (AAS) and FA, and the curing temperature and the lignosulfonate superplasticizer. The interfacial transition zone of geopolymer recycled aggregate concrete (GRAC) was evaluated by microscopic analyses. Then, two empirical models, which are the modified versions of Feret's and De Larrard's models, respectively, for cement concretes, were investigated for the prediction of GRAC compressive strength; the parameters of these models were identified. The results showed the positive behaviour of GRAC investigated and the relevancy of the models proposed.
•Flood susceptibility was derived through IOE, FAHP, FAHP-IOE, SVM and SVM-IOE models.•205 flood pixels were the dependent variable into stand-alone and ensemble models.•Between 13% and 20% of the ...study area has a high and very high flood susceptibility.•SVM-IOE was the most performant model.
The global warming and climate changes determined a considerable increase in the frequency of floods and their related damages. Therefore, the high accuracy prediction of flood susceptible areas plays a key role in flood warnings and risk reduction. The main objective of this study is to propose novel hybridizations of fuzzy Analytical Hierarchy Process (FAHP), Index of Entropy (IoE), and Support Vector Machine (SVM) for predicting the areas susceptible to floods. Buzău river catchment (Romania) was the area on which the present study was focused. In this regard, a database with 205 flooded locations, 205 non-flood locations and 12 flood predictors was established and used to train and validate the flood susceptibility models. The performance of the proposed models was evaluated using the Receiver Operating Characteristic (ROC) Curve and statistical metrics. The results show that all the hybrid models have a high prediction performance and outperform the stand-alone models. Among them, the SVM-IoE model (AUC = 0.979) has the highest performance, followed by the FAHP-IoE (AUC = 0.97), IoE (AUC = 0.969), SVM (AUC = 0.966) and FAHP (AUC = 0.947). These results highlight a very high efficiency of all the applied models. The application of the models mentioned above revealed that a percentage between 12.5% (FPIIoE) and 21.2% (FPIFAHP) of the study area is characterized by high and very high exposure to these hydrological hazards.
•Experimental studies with horizontal loading tests.•Four walls with two height/length ratios were built and tested.•Application of the pushover method to assess the seismic performance of rammed ...earth structures.•The seismic performance was evaluated following Eurocode 8, in different conditions (seismicity zones and soil types).
Rammed earth (RE) construction is attracting renewed interest throughout the world thanks to its sustainable characteristics: very low embodied energy, advantageous living comfort due to substantial thermal inertia, good natural moisture buffering and an attractive appearance. This is why several studies have recently been conducted to investigate RE. However, there have not yet been sufficient studies on the seismic performance of RE buildings. This paper presents an experimental study on the static nonlinear pushover method and its application to the seismic performance of RE structures. Several walls with different height/length ratios were built and tested to obtain nonlinear shear force–displacement curves. By transposing these shear force-displacement curves to an acceleration–displacement system and using the standard spectra presented in Eurocode 8, the performance points were determined, making it possible to assess the seismic performance of the walls studied in different conditions (seismicity zones and soil types).
•DEM to investigate the in-plane seismic behaviour of rammed-earth walls.•A real earthquake excitation was applied to the model.•Excitation was scaled at different amplitudes to assess the ...damages.•For excitations lower than 2.3 m/s2, rammed-earth walls had satisfying performance.
Rammed earth (RE) is a construction material which is manufactured by compacting the soil within a formwork, in superimposed layers. RE is attracting scientific studies because of its sustainable properties: a very low embodied energy and an advantageous living comfort due to a particular benefic hygro-thermal behaviour. Numerous studies have been conducted to investigate RE material and RE structures, however, a lack of knowledge on the seismic performance of RE buildings is noticed. This paper presents an advanced numerical study to investigate the in-plane seismic behaviour of RE walls. First, a numerical model of an in-situ RE wall was constructed by using discrete element modelling (DEM). The relevancy of the numerical model was verified by comparing dynamic properties of the model with that measured on the in-situ wall. Then, a real earthquake excitation was applied to the model, in order to evaluate the seismic performance of the RE wall studied. This is the first time, to our knowledge, that a dynamic discrete explicite analysis was performed for a RE wall. The excitation was scaled at different amplitudes to assess the damages following different earthquake intensities. The results showed that for seismic excitations lower than 2.3 m/s2, RE walls studied had satisfying in-plane earthquake performance.
The construction industry is one of the sectors which have significant impacts on the environment. The research on sustainable materials is a demand of society. This paper presents an investigation ...on the use of fly ash (FA) geopolymer binder for the production of unburnt bricks. First, an optimisation process for the ratio of alkaline activator solution (AAS) and FA was performed. The blocks were obtained by compressing the materials in a mould by hand, similar to the traditional technique of the adobes. Different ratios of AAS in the blocks were investigated: 6%, 8%, 12% and 20% by mass, respectively. Two curing temperatures were tested: ambient temperature and at 60 °C. Then, different properties of the blocks were determined: flexural tensile strength, compressive strengths (in the quasi-dry state and in the saturated state), water absorption. The techniques of Fourier Transform Infrared (FTIR) and Scanning Electron Microscope (SEM) were also used for the analyses of the results obtained. The results showed that the blocks with 20% AAS had highest compressive strengths with an average of 24 MPa at 28 days, while the recommended AAS amount for both technical and economical points of view was 8%, with a mean compressive strength of 13 MPa at 28 days. The ratio between the saturated compressive strength on the quasi-dry compressive strength was higher than 0.5, which satisfied the current exigencies from the standards. These exploratory results are important for practice applications of this type of blocks.
Thermal conductivity measurement.
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•The hygrothermal properties of bamboo particles are studied.•Novel binders from natural resources are used for building bio-insulation ...materials.•Influence of high relative humidity on durability of bamboo particles is investigated.•Thermal insulation of bio-materials is evaluated under different humidity conditions.
Bio-insulating materials are well known to reduce the environmental impact of constructions and are able to regulate the indoor temperature and humidity of buildings. This study investigates the influence of high-absorbing bio-glues based on a protein and lignin compound on moisture transfer and storage as well as on thermal performance of bamboo particleboards. The investigations are based on the moisture buffer value, vapor permeability, isothermal vapor sorption and thermal conductivity. Simultaneously, the mechanical properties and mold growth of these materials, manufactured for the study, are also investigated. The results demonstrate excellent moisture buffer capacity, from 2.13 to 3.26 g/(m2·%RH). The vapor sorption isotherm results exhibit the materials’ high moisture storage, and the vapor permeability behaves like commercial bio-insulating materials. The thermal conductivity of particleboards shows a low value, in accordance with their density and variation in moisture content. In addition, the results indicate mold appearance on the surfaces of specimens after 14 days exposure to 84% relative humidity. Moreover, a comparison of the hygrothermal characterizations between bamboo particleboards and fiberboards (Nguyen et al., 2017) is carefully made to highlight the exceptional features of those bio-boards.
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