This article reviews the literature related to the performance of fiber reinforced concrete (FRC) in the context of the durability of concrete infrastructures. The durability of a concrete ...infrastructure is defined by its ability to sustain reliable levels of serviceability and structural integrity in environmental exposure which may be harsh without any major need for repair intervention throughout the design service life. Conventional concrete has relatively low tensile capacity and ductility, and thus is susceptible to cracking. Cracks are considered to be pathways for gases, liquids, and deleterious solutes entering the concrete, which lead to the early onset of deterioration processes in the concrete or reinforcing steel. Chloride aqueous solution may reach the embedded steel quickly after cracked regions are exposed to de-icing salt or spray in coastal regions, which de-passivates the protective film, whereby corrosion initiation occurs decades earlier than when chlorides would have to gradually ingress uncracked concrete covering the steel in the absence of cracks. Appropriate inclusion of steel or non-metallic fibers has been proven to increase both the tensile capacity and ductility of FRC. Many researchers have investigated durability enhancement by use of FRC. This paper reviews substantial evidence that the improved tensile characteristics of FRC used to construct infrastructure, improve its durability through mainly the fiber bridging and control of cracks. The evidence is based on both reported laboratory investigations under controlled conditions and the monitored performance of actual infrastructure constructed of FRC. The paper aims to help design engineers towards considering the use of FRC in real-life concrete infrastructures appropriately and more confidently.
Purpose
Three-dimensional printing of concrete (3DPC) has a potential for the rapid industrialization of the housing sector, with benefits of reduced construction time due to no formwork requirement, ...ease of construction of complex geometries, potential high construction quality and reduced waste. Required materials adaption for 3DPC is within reach, as concrete materials technology has reached the point where performance-based specification is possible by specialists. This paper aims to present an overview of the current status of 3DPC for construction, including existing printing methods and material properties required for robustness of 3DPC structures or structural elements.
Design/methodology/approach
This paper has presented an overview of three categories of 3DPC systems, namely, gantry, robotic and crane systems. Material compositions as well as fresh and hardened properties of mixes currently used for 3DPC have been elaborated.
Findings
This paper presents an overview of the state of the art of 3DPC systems and materials. Research needs, including reinforcement in the form of bars or fibres in the 3D printable cement-based materials, are also addressed.
Originality/value
The critical analysis of the 3D concrete printing system and materials described in this review paper is original.
•Influence of nanoparticles on the properties of cement-based materials is discussed.•Nanoparticles can significantly alter the hydration mechanism of cement paste.•Research needs are identified ...based on the gaps in the current state of knowledge.
This review paper intends to synthesise the data published in the literature on the uses of different types of nanomaterials in cementitious materials. According to ASTM, depending on types, the size of nanoparticles varies from 1 nm to 100 nm. Application of nanomaterials in different sectors has shown that the properties of conventional materials can be significantly improved when nanoparticles are included. The addition of nanoparticles in cementitious materials can act as a filler agent, producing a dense matrix and reduce the growth of micro pores. Some nanoparticles also help in the secondary reactions forming cement composite and contribute to the strength development. Moreover, this paper summarises the current knowledge of the microstructure, mechanical strength and durability of cementitious materials when incorporating different types of nanoparticles. In addition, research needs are identified based on the gaps in the current state of knowledge on using nanoparticles in cement-based construction materials.
While interest in 3D printing of concrete (3DCP) and structures has been growing, a major obstacle for implementation of 3DP construction method is the need for steel reinforcement and the challenges ...this presents to the 3DP process. Engineered Cementitious Composites (ECC), also known as Strain-hardening Cement-based Composites (SHCC), hold promise to attain structural integrity, durability, reliability and robustness without steel reinforcement. This article surveys the state of the art on 3DP research with ECC and suggests needed research to direct future development. Research in Asia, Europe and the United States has demonstrated printability and buildability of 3DP-ECC that exhibits characteristic tensile ductility of cast ECC. Nonetheless, a number of outstanding research areas are identified, including those associated with more sustainable mix-design, rheology control, microstructure, filament/filament interface weakness, and long-term durability. Resolution of these challenges will better position the research community to addressing full scale construction, print speed, and print quality.
Two of the main activities of RILEM Technical Committee 208-HFC Subcommittee 2 were the preparation and publication of the state-of-the-art report on durability of strain hardening cement-based ...composites (SHCC), and the performance of comparative laboratory testing on SHCC. In this paper the comparative mechanical tests are reported, as performed in laboratories of five participating institutions. The purpose was to investigate and compare the crack patterns in terms of crack widths and spacing, and subsequently to make recommendations for a suitable test setup and procedure towards characterizing cracking in this class of materials. Such standardized procedures are required for future systematic and objective research towards durability of these materials in their in-service conditions, i.e. their resistance to deterioration processes in the cracked state. Standardized test procedures are also required for durability testing and guidelines for structural design with SHCC, which is the focus of follow-up committee activity in TC 240-FDS.
•A novel method to improve the interlayer adhesion is proposed.•The interlayer bond strength was improved by 78 % for the control.•The method improved interlayer bond at 10-minute passtime beyond the ...control by 9%•From microstructural analysis the material in the interlayer is altered.
For 3D printable concrete, lack of interlayer adhesion (IA) is an important consideration. This paper presents an experimental study to investigate a novel method to mitigate lack of IA by enhancing the interlayer bond strength through induced thermo-hydrokinetics. Thermo-hydrokinetics in this study describe the motions of heated fluids and/or the forces which produce or affect such motions. Thermo-hydrokinetics were induced by steaming the interlayer region of a substrate right before placement of a fresh filament layer. The method is applied at 3 different pass times; typical pass time for the arbitrarily selected object for printing, 5 min, and 10 min. A control for each pass time, on which thermo-hydrokinetics were not induced is also obtained. Direct tensile tests are performed to quantify the interlayer bond strength (IBS) of printed specimens. The experimental results show that inducing thermo-hydrokinetics in the interlayer region, even with increasing pass times, is beneficial for the tensile performance of the printed specimen. Steamed tensile specimens showed superior mechanical performance, achieving a 28-day overall mean IBS value of 2.8 MPa, which was a 78 % increase from that of non-steamed tensile specimens. The strength development of the specimens was also quantified, and it was shown that the rate of strength development for the steamed regime specimens was greater than that of the non-steamed regime. Furthermore, scanning electron microscope images provided information into the material in the interlayer region, illustrating that induced thermo-hydrokinetics altered the material in the interlayer region.
Durability of reinforced concrete (RC) is influenced by cracks, providing paths for ingress of corrosion agents and early corrosion initiation. The corrosion propagation stage has in recent years ...been the focus of investigation, however, mainly focused on a single crack and reinforcement bar. This study focuses on chloride‐induced corrosion in three reinforcement layouts with a single or two transverse cracks kept at a constant crack width in flexure. The 27 beams were subjected to cyclic ponding with chloride aqueous solution for 36 weeks, and corrosion rate and potential measured weekly. The results indicate that the corrosion rate of RC members is influenced by crack spacing and reinforcement quantity. In current practice, corrosion initiation indicates end of service life. However, corrosion initiation is quick in cracked regions. It is proposed here to base the residual structural service life on the corrosion rate in the propagation phase, and a limit state of a threshold loss of reinforcing steel. In addition, crack spacing and reinforcement density are to be considered in the prediction of residual service life.
This article focuses on the specifics in characterizing the properties of additively manufactured, cement-based materials in their hardening and hardened states. Such characterization is required for ...the material development, structural design, and quality control of both printable material and 3D-printed elements. The related challenges are associated with the printed material's layered structure, which results in higher degrees of anisotropy and inhomogeneity in comparison to conventionally cast concrete. Thus, in the production of test specimens, the particularities of the real-scale 3D-printing process must be considered. Here a distinction is made between the production of samples for material testing prior to or parallel to actual application and those extracted from full-scale elements. Specifics of destructive testing are analyzed with emphasis on mechanical characteristics, while the discussion of non-destructive testing mainly addresses the geometry of the deposited layers and printed elements, measuring deformations, and finding such defects as voids and gaps. Finally, approaches required for developing/adapting guidelines and standards for testing of 3D-printed, cement-based materials are discussed.
Strain-hardening cement-based composites were named after their ability to resist increased tensile force after crack formation, over a significant tensile deformation range. The increased resistance ...is achieved through effective crack bridging by fibres, across multiple cracks of widths in the micro-range. Whether these small crack widths are maintained under sustained, cyclic or other load paths, and whether the crack width limitation translates into durability through retardation of moisture, gas and other deleterious matter ingress, are scrutinised in this paper by evaluation of test results from several laboratories internationally. This contribution is a short version of the State-of-the-Art report by RILEM TC 208-HFC, Subcommittee 2: Durability, developed during the committee life 2005–2009.
An alternative to Portland cement concrete is metakaolin (MK)-based digitally fabricated geopolymer concrete. However, global adoption is sparse due to the prolonged setting time of a two-part ...geopolymer concrete (GPC) system and the uncertain long-term durability properties. The durability and pore structure of the MK-based 3DPGPC (M1) and slag-modified MK-based 3DPGPC (M2) are examined and juxtaposed with mould-cast specimens. Firstly, the fresh properties, rheological behaviour, compressive and flexural strength of 3DPGPC and cast specimens were characterised. Thereafter, the durability and pore structure are investigated by examining the drying shrinkage, water absorption, capillary and gel porosity, and oxygen permeability index (OPI) and X-ray computed tomography (X-CT) analysis. A 5% slag inclusion reduced workability and final setting time from 17 hours in M1 to 4 hours in M2. Also, slag inclusion increased the initial static and dynamic yield stresses by 0.1 and 2%, respectively, resulting in an increase in buildability from 27 of 42 layers. At the 28-day curing age, the average compressive strength of M2–3DPGPC is 11 and 21% higher than M1–3DPGPC in D1 and D3 specimens, while the flexural strength is 33 and 28% higher, respectively. Drying shrinkage and water absorption are mitigated with slag inclusion, and the OPI compares with OPC concrete. Specimens cored along the printing direction (D3) are less permeable compared to disc specimens’ core in the perpendicular to the printing direction (D1). The M1 and M2–3DPGPC specimens contain lower average CT scan macro pores of 2.98 and 1.81% in comparison to the mould-cast specimens having 4.48 and 4.07%. The porosity is position-dependent in 3DPGPC due to the presence of more voids at the interlayer region. 3DPGPC specimens depicted a more compact pore structure in the range of 0.1–1.7 mm, whereas pores in mould-cast are in the range of 0.1–2.5 mm. The durability index tests indicate that 3DPGPC is a potentially durable material.
•Early age time-dependent strain of 3D printed geopolymer concrete is anisotropic.•Capillary and gel porosity of 3DPGPC is significantly reduced by 5% slag replacement of precursor by mass•Anisotropy in oxygen permeability of 3DPGPC is significantly reduced by 5% slag replacement of precursor by mass.•Slag inclusion in 3DPGPC reduces macro porosity observed by X-ray CT and significantly increases compressive strength.
PDF
