The view towards a sustainable bioeconomy is increasing the interest of using renewable natural resources in the production of composites. Until now, the production of sustainable composites has been mainly examined from the point of view of material composition and structure, by replacing petroleum-based components with those that are obtained from renewable resources known as natural fiber composites (NFCs). The usefulness of newly acquired materials is mostly evaluated considering their performance and economic costs, whereas the aspect of environmental protection is underestimated. The impact of composites that are made from renewable resources is examined within the two parts of this study—the first part compares different nitrogen (N) fertilization scenarios for plant origin (hemp and flax) fibers. When compared, hemp crops show higher CO2 accumulation, (−1.57 kg CO2 eq) than flax (−1.27 kg CO2 eq). In addition, the environmental impact of both fiber types is compared to polyamide composites, one of the traditionally used materials in the automotive industry in the second part of this study. According to the conducted life cycle assessment, Flax/PLA emits 1.19 kg CO2 eq per 1 kg composite, Hemp/PLA 1.7 kg CO2 eq per 1 kg composite, and PA66/GF 9.14 kg CO2 eq per 1 kg composite. After the comparison, it was concluded that bio-based composites are able to ensure lower CO2 emissions, because CO2 is accumulated and stored in the fibers, however the traditionally used composites are able to provide a lower impact in other environmental categories.

Hempcrete is a bio-based self-bearing envelope and thermal insulation building material that is becoming more popular nowadays and has a low environmental impact, especially CO2 emissions. This study looks for solutions for hempcrete printing using a custom-built gantry type 3D printer typically used for concrete 3D printing. Preliminary research shows that hempcrete can be printed at a relatively low density of 660 kg/m3 and achieve an adequate buildability and compressive strength for printing individual wall elements. At this density, hempcrete has a thermal conductivity of 0.133 W/(m·K), unable to provide the adequate thermal resistance at average wall thickness, so high-density hempcrete should be printed as an outer wall shell (similar to Contour Crafting) and the middle filled with lower density thermal insulation hempcrete. By calculating the CO2 emissions of such printed 400–620 mm thick walls, it was found that they absorb from 1.21 to 16.7 kg of CO2 per m2, thus, such material could reduce the negative environmental impact of the construction industry while improving its productivity through 3D printing.

Three-dimensional concrete printing (3DCP) is becoming more common in the construction industry nowadays; however, the aspect of durability of printed concrete is not well-studied yet. Frost resistance is a very important factor for durability of concrete structures located in northern regions. Since air-entraining agents (AEAs) are widely used in conventional concrete, this paper focuses on exploring the potential of using AEAs in 3D concrete as well—the main objective is to determine how it affects fresh and hardened properties, including frost resistance of 3D concrete. Three different mixes were printed and cast—the dry mix consisted of ordinary Portland cement (OPC), limestone filler (LF), sand, as well as viscosity modifying agent (VMA) and superplasticizer (SP). Two mixes contained different amounts of AEA, the third one was used as reference. First, fresh state properties were tested—air content, density, and mini cone flow test. Second, 28-day compressive and flexural strength tests were carried out; bulk and particle densities were also determined. Next, both cast and printed concrete samples were subject to freeze–thaw cycles according to provisions of CEN/TS 12390-9, mass loss due to surface scaling was determined for each sample. As a result, printed concrete samples containing AEA in the amount of 0.06% of binder mass showed the highest frost resistance—addition of AEA decreased both flexural and compressive strength of this printed concrete mix by 30–40%. To conclude, the obtained results give an insight of how addition of AEA to printed concrete mix affects its properties both in long and short term. Further research of certain aspects, for instance, the air void system and pore distribution is needed to gain a deeper understanding on how to increase durability of 3D concrete.

3DCP is becoming more common in the construction industry nowadays, however, the aspects of durability of printed concrete are not well-studied yet. This paper focuses on determining how frost-thaw cycles affect printed concrete samples, compared to cast samples of the same concrete mix and whether the conventional concrete frost resistance tests can be applied for 3D printed concrete samples. Two different concrete mixes were both printed and cast – first one was a ready-made mix provided by a dry concrete mix manufacturer and was used for reference, whereas the other mix was prepared at the lab. First, 7 and 28-day compressive and flexural strength as well as density were determined to establish the difference between mechanical and material properties of both printed and cast concrete samples that were intended to be used for frost resistance testing according to standard CEN 12390-9. Next, both printed and cast samples of both mixes were subject to a total of 56 freeze-thaw cycles while submerged in NaCl solution, allowing to determine mass loss of each sample after N frost cycles. To conclude, the obtained results enable the authors to evaluate how 3D printing affects concrete resistance to frost/thaw cycles compared to conventionally cast concrete as well as the possible causes for this. Further research is needed to improve both the design mix of concrete as well as the printing and testing methodology of frost resistance of 3D printed concrete which would possibly lead to its increased use in exposed outdoor structures in northern regions.