Use of Hemp Fibres in 3D Printed Concrete

The use of fibres as reinforcement of 3D printed concrete is widely known and applicable in many situations. However, most of the applied fibres are not produced from renewable resources. Natural fibres are commonly considered as an ecological alternative for these fibres. In order to contribute to improvement of the sustainability of 3D printed concrete, natural fibres such as hemp can replace these synthetic fibres. The objective of this study is therefore to study the possibilities of adding hemp fibres for 3D printing purposes. Due to the comparable properties of hemp and synthetic fibres, natural fibres tend to be suitable for printing purposes. Mixes are made at laboratory scale using batches of 1 – 3 kg. The study examines the effect of adding hemp fibres for the mechanical and fresh state properties of hemp-based concrete. Mechanical properties from bending tests and direct tensile tests show comparable properties of mortars containing hemp fibres and mortars containing synthetic fibres. The fresh state behaviour of the designed concrete mix showed promising and comparable results for a mix based on 0.5wt% of hemp fibres. One of the major issues regarding the use of natural fibres is the irregularity and high water uptake of the fibres. Due to its high hydrophilicity natural hemp fibres take up much water and can therefore degrade. For this study the effect of water uptake did not have much influence on the mixing and printing purposes. By printing a wall element on laboratory scale the use of hemp fibre-reinforced 3D concrete is validated.

Use of recycled aggregates from civil construction in self-compacting mortar

abstract: The utilization of wastes from demolition in civil construction in self compacting concrete (SCM) has the potential to reduce both the environmental impact and financial cost. In this context, this article aims to verify the behavior of the incorporation of recycled aggregates of civil construction in the mix designs of self-compacting mortar (SCM) in replacing cement, presenting as an interesting alternative to natural raw materials. This study used the EMMA® software to optimize the choice of percentages of fine recycled aggregates when replacing cement. The proportions chosen were 0%, 5%, 15%, and 25%, through the analysis of the granular packing curve of the respective mix designs. The proportion of 0% has in its composition cement, metakaolin, sand, superplasticizer (SP) and water. The parameters obtained, through tests in the fresh state of the mini-slump and mini-funnel V, certified the samples as SCM. The compressive strength and flexural tensile strength tests in the hardened state demonstrated a reduction in mechanical properties of the material with cement replacement. It is concluded that the waste used brick and ceramic can be added in replacement to the cement in SCM without significant loss of properties in the fresh and hardened state.

Recycled PET Sand for Cementitious Mortar

Cementitious materials cause a great impact on the environment due to the calcination of clinker and the extraction of non-renewable mineral resources. In this work, the replacement of quartz sand from the river by PET sand was evaluated at levels of 10%, 20%, and 30%. Tests were performed in the fresh state through consistency, air retention, density, and incorporated air and in the hardened state for compressive strength, flexural strength, density, capillarity, and water absorption. The results show that PET sand is viable in contents of up to 10%, improving the mechanical properties of the mortar and without compromising its workability and incorporated air properties. Above that level, the loss of properties is very excessive, mainly of workability and incorporated air. The incorporated air of the 30% composition, for example, reaches 24%, an excessive value that impacts the properties of the hardened state, making it impossible to use the material at levels greater than 20%. It is concluded that the use of recycled PET sand is a possibility that contributes to sustainable development, as it reduces the extraction of quartz sand from the river, a non-renewable mineral resource.

ESTUDO DE VIABILIDADE TÉCNICA DA APLICAÇÃO DA ESCÓRIA GRANULADA DE ALTO-FORNO EM SUBSTITUIÇÃO AO AGREGADO MIÚDO NA COMPOSIÇÃO DO CONCRETO

The macro sector of the civil construction industry is a major consumer of natural resources and it generates impacts, identified as social, environmental or economic, and it is necessary to develop studies that aim to rationalize this raw materials consumption and reduce the impacts generated. Since some resources used in the sector are finite, this work’s main objective is to make the concrete more ecological by replacing part of the fine aggregate of its composition for granulated slag from the blast furnace, reducing the need for sand extraction. For this study, tests were carried out with the co-product and with the fine aggregate, evaluating the properties of the concrete in the fresh and hardened states in three mixture types, the first being a reference, the second with 30% replacement and the third with 60% replacement of fine aggregate with slag. Based on the results obtained, it is noted that the granulated blast furnace slag has more similar characteristics to the sand’s; in the fresh state, the concrete showed a similar result in the three mix types; in the hardened state, it was observed that the performance of the concrete in axial compression was satisfactory; while in flexion traction the two proposed mixtures with substitution presented an unsatisfactory result.

Study of the Extraction Efficiency of Cathode Material and Its Structural Stability after Extraction

Extraction of the cathode material from disassembled Samsung 18650 cell with LiCoO2 (LCO) chemistry was performed. The effect of dissolving with industrially used organic solvents is compared with the effect of selected ecological options. In successfully separated powders were studied structural changes as a function of aging and storage time. Ex-situ X-ray diffraction analysis was used for observation of differences between materials separated from cell in a fresh state and aged cell. Phase transition happening in the LiCoO2 material during cycling of the battery but also when in contact with air are discussed. Shift of the main peak (0 0 3) and (1 0 4) for the aged cathode material are displayed and discussed.

Early-age creep behaviour of 3D printable mortars: Experimental characterisation and analytical modelling

The construction sector is experiencing significant technological innovations with digitalisation tools and automated construction techniques, such as additive manufacturing. Additive manufacturing utilising cement-based materials can potentially remove the technological/economic barriers associated with innovative architectural/structural shapes which are not suitable for conventional formworks adopted for concrete material. However, in the “free-form” digital fabrication with concrete, the mechanical properties prediction of the material in the fresh state is essential for controlling both the element deformations and overall stability during printing. In this paper, the authors explore the critical aspects related to the determination of the early-age creep properties of a 3D printable cement-based material, particularly investigating such a behaviour at different resting times. The experimental results are used to calibrate the Burgers’ analytical model to consider both the elastic and the viscous response of the 3D printable mortar investigated in the fresh state. The visco-elastic model is validated by comparing the analytical total strain vs time curve with the corresponding experimental counterpart replicating the layer-by-layer stacking process in the 3D concrete printing process. It was found that the Burgers’ model represents a valuable numerical approach to evaluate the overall accumulation of layer deformation of a 3D printed element, since it is capable of taking into account the time dependency due to the time gap and the variable material stiffness over the process time.

Properties of Fibre-Reinforced High-Strength Concrete with Nano-Silica and Silica Fume

This study intends to assess the influence of steel fibres (SF) and polypropylene fibres (PPF) on the hardened and fresh state properties of high-strength concrete (HSC). For this purpose, 99 concrete mixes were designed and applied. SF and PPF were used at six-volume replacement contents of 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%. Moreover, nano-silica (NS) was used at three contents, 0%, 1% and 2%, and silica fume powder (SP) was also used at three weight ratios (0%, 5% and 10%). The slump, compressive and tensile strength, elasticity modulus, water absorption and the electric resistivity of concrete specimens were examined. The results showed that using 1% NS and 10% SP together with 0.5% PPF improved the compressive strength of HSC by about 123%; however, the effect of SF on tensile strength is more significant and adding 0.5% SF with both 2% NS and 10% SP increased the tensile strength by 104%. Moreover, increasing the SF content reduces the electric resistivity while using PPF improves this property especially when 1% NS was employed, and it was enhanced by about 68% when 0.5% SF and 1% NS were utilized with 10% SP.

Comparison of Properties of 3D-Printed Mortar in Air vs. Underwater

Research and technological advancements in 3D concrete printing (3DCP) have led to the idea of applying it to offshore construction. The effect of gravity is reduced underwater, which can have a positive effect on 3DCP. For basic verification of this idea, this study printed and additively manufactured specimens with the same mortar mixture in air and underwater and evaluated properties in the fresh state and the hardened state. The mechanical properties were evaluated using the specimens produced by direct casting to the mold and specimens produced by extracting from the additive part through coring and cutting. The results of the experiment show that underwater 3D printing required a greater amount of printing output than in-air 3D printing for a good print quality, and buildability was improved underwater compared to that in air. In the case of the specimen layered underwater, the density and compressive strength decreased compared to the specimen layered in air. Because there are almost no effects of moisture evaporation and bleeding in water, the interlayer bond strength of the specimen printed underwater was somewhat larger than that printed in air, while there was no effect of the deposition time interval underwater.

Fresh State, Rheological and Microstructural Characteristics of Alkali-Activated Mortars Developed Using Novel Dry Mixing Technique under Ambient Conditions

Ambient cured alkali-activated mortars (AAMs) are developed through the activation of supplementary cementitious materials (SCMs) by powder form reagents with silica sand using a novel dry-mixing method. The fresh state, rheological, compressive strength and microstructural characteristics of eight AAM mixes are comprehensively investigated. The effects of binary/ternary combinations/proportions of SCMs, different combinations/dosages of powder form reagents and the fundamental chemical ratios (SiO2/Al2O3, Na2O/SiO2, CaO/SiO2 and Na2O/Al2O3) present in the precursors and the reagents are investigated. The AAM mixes obtained compressive strengths ranging from 34 to 42.6 MPa with initial and final setting times between 122 and 458 min and 215 and 483 min, respectively. The yield stress and viscosity of the mixes decreased with the increase in the slump flow spread. All the mixes demonstrated pseudoplastic behavior. The microstructural analysis revealed the formation of more longer polymeric chains comprising Si-Al linkages in N-C-A-S-H/N-A-S-H gels for reagent one (calcium hydroxide:sodium metasilicate = 1:2.5) mixes, which resulted in a lower slump flow, higher yield stress, higher plastic viscosity and quicker setting times compared to their reagent two (calcium hydroxide:sodium sulfate = 2.5:1) counterparts.