Additive manufacturing and digital fabrication bring new horizons to concrete and cement-based material construction. 3D printing inspired construction techniques that have recently been developed at ...laboratory scale for cement-based materials. This study aims to investigate the role of the structural build-up properties of cement-based materials in such a layer by layer construction technique. As construction progresses, the cement-based materials become harder with time. The mechanical strength of the cement-based materials must be sufficient to sustain the weight of the layers subsequently deposited. It follows that the comparison of the mechanical strength, which evolves with time (i.e. structural build-up), with the loading due to layers subsequently deposited, can be expected to provide the optimal rate of layer by layer construction. A theoretical framework has been developed to propose a method of optimization of the building rate, which is experimentally validated in a layer-wise built column.
•Using a fast setting binder, it is possible to print an earth-based mortar.•Alginate is an efficient binder to enables earth printing.•3D printing can make an earth-based material with compressive ...strength in the same order of conventional cob earth.•Young modulus and yield stress evolution of the material govern the maximum printing rate.
Due to its low environmental impact, earth construction has received much consideration in recent years. Nevertheless, its development remains limited due to low production rate. Recent developments have been made to improve earth-based materials mix-design and processing methods. Simultaneously, digitally based construction methods have been introduced in the field of construction especially for cement-based materials application. Among these new techniques, the so-called 3D printing by extrusion deposit has been the most intensively studied. In this study, we assess the possibility of adapting this technique to earth-based material. After making the earth’s rheological behaviour suitable for 3D printing, a laboratory-scale printing has been carried out and the printed samples have been mechanically tested.
Today, the extrusion-based 3D printing of concrete is a potential breakthrough technology for the construction industry. It is expected that 3D printing will reduce the cost of construction of civil ...engineering structures (removal of formwork) and lead to a significant reduction in time and improve working environment conditions. Following the use of this additive manufacturing layer-wise process, it is required to change the way concrete structures are designed and reinforced, especially for the parts of the structure under tension loads. Indeed, the extrusion-based concrete 3D printing process does not allow for the production of conventional reinforced concrete, and there is a need to develop other ways of compensating for the low mechanical performances of concrete, particularly in tension. In this study, the reinforcement of printed structures by using steel nails through the deposited layers of fresh concrete was investigated. Additionally, three-layer and 10-layer samples were reinforced with nails with varying inclination and spacing. The results show that inclined nails can be used to provide a flexural strengthening of the printing material in different directions.
•Reinforcement strategies for earth depends on the clay mineralogy.•Fibers, Particles packing optimization and alginate are efficient for kaolinite clay soils.•Woven fabrics act efficiently for all ...kinds of soils.•Coupling reinforcement strategies can lead to earth-based composites with high compressive strength (18.5 MPa).
Earth-based mortars are commonly reinforced with bio-based materials such as straw or biopolymers. The aim of this work is to identify reinforcements that are able to improve the mechanical strengths and the ductility of an earth-based matrix. We have also attempted to describe the mechanisms of reinforcement involved in such materials. Firstly, a kaolinite-based clay soil was mixed with sand to achieve earth-based mortars with the highest density at the dry state. For this material (kaolinite-based mortar), we have shown that, at the same water content, the compressive strength at the dry state only depends on the dry density of the sample whatever the forming process. Various quantities of fibers, fabrics and alginate were then used to reinforce the studied mortars (a kaolinite based mortar and a natural soil containing swelling clay sieved at 4 mm). We found that these reinforcements significantly increase the compressive strength of all tested samples containing kaolinite. A comparison between the two materials helps us to understand the reinforcement mechanisms for various fibers; it also demonstrates that natural fibers and woven fabrics enhance the mechanical behavior of earth mortars notably under a compressive load.
Due to its low environmental impact, earth construction has received much consideration in recent years. However, its development is limited by construction time as the strength of the material ...results from a slow drying stage and not by chemical setting. This means that using conventional rammed earth construction, it is not possible to strike the formwork the day after casting. In order to find another construction technique, many researchers have studied the behaviour of freshly made earth material using different types of admixtures that change the material’s rheology. Conventional dispersants used in the ceramic industry (such as sodium hexametaphosphate) or superplasticizers used in concrete are used to modify the fresh raw earth material. Moreover, earth materials are often described using empirical geotechnical parameters such as Proctor water content or plasticity index that are not directly linked to the material intrinsic behaviour. This paper has two simultaneous goals: the first one is to describe the rheology of kaolinite paste with and without dispersants and the second one is to link the “engineering” geotechnical parameters to the material’s rheology.
River sand is a non-renewable resource that is becoming more and more scarce. For concrete industry, it is important to use alternatives like manufactured crushed sand or recycled sand. This article ...deals with the effect of manufactured crushed sand variability on the consistency of mortars. Two basic formulations are tested: the first corresponds to the mortar contained in a reference concrete and the second corresponds to the equivalent concrete mortar of the same concrete. For these formulations, the shear yield stress is measured to evaluate the mortars rheology with different crushed sand contents (from 30 to 100% of the total sand content) and origins. Eight crushed sands and three river sands are tested in this study. The loose and dense packing behaviour of reconstituted sands are measured and are linked to physical characteristics of the sand (surface roughness, morphology, and particle size distribution). The shear yield stress of the mortars is then predicted from the computed loose packing using homogenisation model. This work can be seen as a step forward to master the large variability in crushed sand and its effect on mortars consistency and rheology.
Due to its low environmental impact, earth construction has received lot of consideration in recent years. Furthermore, in order to improve the quality of earth construction, there is a need for a ...better description and control of the earth consistency or rheology. Just as for concrete with the Abrams cone, there is need for a simple and robust test that is able to provide, under field conditions, the consistency of the earth and that has results that can be used to estimate the yield stress of a fine soil used for cob or adobe. Two types of field-oriented tests are optimized for field conditions: the first one is based on the cone penetration test as used for the determination of the Atterberg limits and the second one is the ball dropping test already used onsite to check the adequacy between the earth consistency and the construction process. Finally, an experimental validation carried out on two types of soil shows that the yield stresses computed from the field-oriented tests is in agreement with the yield stresses obtained in a conventional way using a vane rheometer.
Fresh cement paste permeability is a key parameter to understand the hydro-mechanical behavior of cement-based materials, i.e., rhelogical properties and static stability. However, its permeability ...measurement is not easy to assess. The porous medium is not rigid and tends to change due to hydration kinetics. Two measurement methods, with 70
mm and 20
mm initial height specimens respectively, are presented and compared in this paper. The first uses a basic cell of soil permeability measurement and consists of simultaneous consolidation and percolation tests. The second uses a displacement-controlled oedometer cell equipped with pore water pressure transducers, and consists in inducing consolidation to a given void ratio first and, consecutively, in accurately measuring the permeability. A good correlation of results is observed. A comparison with theoretical models confirms that, from one fitted parameter relative to particle characteristics, a relationship between permeability and void ratio can be established.
For perfect and homogeneous plastic materials, the extrusion stress and flow typology have previously been well described. However for firm pastes, during extrusion, liquid phase migration may appear ...leading to unsuccessful processing. Reviewed literature explains that there is a competition between the extrusion velocity and the liquid filtration velocity (or time).
The aim of this work is to develop a new model to predict the ram extrusion force of frictional plastic materials such as firm fresh cement-based materials or clay pastes. A quantitative one-dimensional model based on consolidation theory has been developed to predict the extrusion force and quantify liquid phase migration.
Model results are compared with experimental data from tests carried out on kaolin paste undergoing ram extrusion. Influences of extrusion rate, rheological parameters and filtration characteristics on extrusion load are investigated.
Display omitted
•Modelling the ram extrusion load of a firm paste undergoing drainage•Establishing a continuous transition from plastic to frictional plastic behaviour•Use of the consolidation theory to estimate the drainage rate•The modelling fits experimental tests performed on kaolin paste.
In this paper, to have control over geometry specifications of rectangular bar-shaped layers in a robotic concrete 3D printing process, a real-time vision-based control framework is developed and ...proposed. The proposed control system is able to set the layer-width by automatically adjusting the velocity of an industrial manipulator during the 3D printing process of concrete based materials relying on a vision system feedback. Initially, details related to the control system, vision and processing units, and robotic platform are discussed. In continue, technical descriptions related to the printhead design, conversion process from a digital 3D drawing model to numerical motion control commands of an industrial manipulator and building material used in this work are reported. The reliability and responsiveness of the developed system is then evaluated through experimental tests by printing several single bar-shaped layers with different wideness by means of an unique printhead geometry and also by printing two layers with the same dimension centrally above another. Overall, the high accuracy and responsiveness of the developed system demonstrate a great potential for real-time vision-based control of industrial manipulators for layer-width setting in concrete 3D printing applications.
PDF
