One of the considerable challenges in the design of cementitious mixtures for additive manufacturing/three-dimensional (3D) printing applications is achieving both suitable fresh properties and ...significant mechanical strengths. This paper presents the use of graphene oxide (GO) as a promising nano reinforcement material with the potential to improve the printing feasibility and quality of a 3D printed cementitious matrix. Additionally, in this study, a viscosity modifying agent (VMA) was employed as a chemical additive to attain the required consistency and flow. The printed mixture was fabricated using various cementitious materials and waste materials. This study investigated the impact of GO and VMA on the enhancement of the 3D printing of cementitious composites through several tests. A flow test was conducted using the flow table test. The results showed a high fluidity and practical consistency, which are essential for nozzle pumping and accurateness in printed shapes. Furthermore, the bleeding test showed minimal bleeding up to hardening, and a considerable self-cleaning ability was noted during handling when conducting examinations of fresh properties. For hardened properties, the mechanical strengths were exceptionally high, especially at early ages, which is crucial for the stability of sequence layers of printed composites. The tensile strengths were 3.77, 10.5, 13.35, and 18.83 MPa at 1, 3, 7, and 28 days, respectively, and the compressive strengths were 25.1, 68.4, 85.6, and 125.4 MPa at 1, 3, 7, and 28 days, respectively. The test results showed the effectiveness of the fabricated cementitious mixture design method for meeting the requirements for 3D concrete printing applications.
•NSM FRP strengthening of beams by cement-based adhesives under fatigue loading has not been studied.•Cement-based adhesive (IHSSC-CA) is easier to use during NSM CFRP application than epoxy.•Fatigue ...load range and frequency were designed to simulate service load conditions.•Results show better composite action between NSM CFRP and concrete by using IHSSC-CA.•A damage accumulation model of RC beams under fatigue loading is also proposed.
In this study, the flexural performance and effectiveness of the use of innovative high-strength self-compacting non-polymer cementitious adhesive (IHSSC-CA) for the strengthening and repair of reinforced concrete (RC) beams using the near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) technique under fatigue loading was investigated, with the purpose of improving the serviceability of these RC beams. Cementitious materials with graphene oxide were used to produce the IHSSC-CA. The effect of fatigue loading on the behaviour of all tested beams was assessed by monitoring the deflection, crack widths and strain in concrete, steel reinforcement and CFRP strips during fatigue loading. An analytical model is also proposed to predict the cumulative damage-fatigue life relationship. The test results show that using cement-based adhesive (IHSSC-CA) could represent an excellent alternative to epoxy adhesive, as it improves the serviceability of NSM CFRP-strengthened and repaired RC members. Moreover, the proposed damage accumulation-fatigue life model shows good agreement with the experimental results and can be used in the design of RC members strengthened and repaired with NSM CFRP using IHSSC-CA and epoxy adhesives.
•IHSSC-CA is easier to use during NSM CFRP application than polymer cement and epoxy adhesives.•Physical, pore structure and 3D-laser profilometery analysis showed the effectiveness of ...IHSSC-CA.•IHSSC-CA has better composite action between NSM CFRP and concrete than the other adhesives.
Efficient transfer of load between concrete substrate and fibre reinforced polymer (FRP) by the bonding agent is the key factor in any FRP strengthening system. An innovative high-strength self-compacting non-polymer cementitious adhesive (IHSSC-CA) was recently developed by the authors and has been used in a number of studies. Graphene oxide and cementitious materials are used to synthesise the new adhesive. The successful implementation of IHSSC-CA significantly increases carbon FRP (CFRP) strip utilization and the load-bearing capacity of the near-surface mounted (NSM) CFRP strengthening system. A number of tests were used to inspect the interfacial zone in the bonding area of NSM CFRP strips, including physical examination, pore structure analysis, and three-dimensional laser profilometery analysis. It was deduced from the physical inspection of NSM CFRP specimens made with IHSSC-CA that a smooth surface for load transfer was found in the CFRP strip without stress concentrations in some local regions. A smooth surface of the adhesive layer is very important for preventing localized brittle failure in the concrete. The pore structure analysis also confirmed that IHSSC-CA has better composite action between NSM CFRP strips and concrete substrate than the other adhesives, resulting in the NSM CFRP specimens made with IHSSC-CA sustaining a greater load. Finally, the results of three-dimensional laser profilometery revealed a greater degree of roughness and less deformation on the surface of the CFRP strip when IHSSC-CA was used, compared to other adhesives.
•NSM CFRP strip was modelled efficiently as embedded reinforcement in cement adhesive.•Developed FE models are able to simulate the experimental aspects accurately.•Developed FE models can be used in ...the design of NSM CFRP-strengthened RC members.
The use of near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) is a promising technique for strengthening deficient reinforced concrete members. In order to shed further light on this technique, the finite element method (FEM) was used to simulate the bond behaviour between NSM CFRP strips and concrete substrate with cement-based adhesive in single-lap shear tests. Non-linear FEM software ATENA 3-D was used in this study. The developed numerical models can predict the experimental aspects reasonably well and can be used in the design of reinforced concrete members strengthened with NSM CFRP strips.
•NSM FRP system has gained considerable popularity worldwide.•This paper reviews current research on concrete members retrofitted by NSM FRP system.•The review focuses on the bond characteristics ...between NSM FRP, adhesive and concrete.
The use of fibre reinforced polymer (FRP) in civil construction applications with near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. The response of concrete structural members rehabilitated using FRP with externally-bonded (EB) method under monotonic and fatigue loading has been well reported. On the other hand, the monotonic and fatigue response of NSM FRP-rehabilitated concrete structures is less known. This paper reviews current research on concrete members retrofitted by NSM FRP system and exposed to monotonic and fatigue loading. It provides an outline of FRP composites and the fatigue behaviour of concrete, steel and FRP materials. In addition, the review focuses on the bond characteristics between NSM FRP, adhesive and concrete substrate, and on the flexure behaviour of NSM FRP-strengthened and repaired reinforced concrete (RC) beams. Furthermore, the paper reviews the failure modes, factors affecting NSM FRP systems, guidelines and codes for the use of FRP in concrete structures, damage accumulation and residual strength, stress limits in steel reinforcement, and the limitations of using epoxy and polymer-based cementitious adhesives for the strengthening of concrete members.
•IHSSC-CA is easier to use for NSM CFRP application than epoxy and polymer cement adhesives.•IHSSC-CA shows better composite action with concrete and CFRP than polymer cement and epoxy adhesives.•The ...results confirm the effectiveness of using IHSSC-CA to improve the NSM CFRP technique.•An analytical model is proposed to predict the ultimate pull-out force (bond strength).
Concrete structures are normally strengthened using fibre reinforced polymer (FRP) with epoxy adhesives and polymer cementitious mortars. Epoxy adhesives have significant issues, such as the release of toxic fumes throughout curing, loss of strength and stiffness when exposed to hot temperatures, and low permeability and weakness to UV radiation. In the case of polymer cementitious adhesives, their properties are adversely affected by hydrothermal conditions. An innovative high-strength self-compacting non-polymer cementitious adhesive (IHSSC-CA) has recently been developed by the authors which uses graphene oxide and cementitious materials. This paper presents the bond response of carbon FRP strips bonded to concrete substrate using near-surface mounted (NSM) technique with IHSSC-CA, epoxy and polymer cement-based adhesives using direct pull-out tests. The behaviour of each adhesive is presented and compared and the local bond-slip relationship is calculated. Finally, an analytical model is proposed to predict the ultimate pull-out force (bond strength). The results of this study confirm the effectiveness of using IHSSC-CA to improve the bond strength, stiffness, CFRP strip utilisation, ductility and residual strength of NSM CFRP system. Moreover, the proposed analytical model can simulate experimental conditions reasonably well.
This paper presents the results of an experimental study of near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP)-repaired and strengthened reinforced concrete (RC) beams with innovative ...high-strength self-compacting cementitious adhesive (IHSSC-CA), with the particular objective of improving the ductility. Graphene oxide and cementitious materials were used to synthesise the IHSSC-CA. An analytical model is developed to predict the maximum tensile strain in NSM CFRP strips based on the experimental results. ACI 440.2R-08 guide was used to calculate the ultimate flexural capacity of the tested specimens based on the predicted tensile strain in NSM CFRP strips. The test results confirm the effectiveness of using IHSSC-CA to improve the flexural strength, CFRP strip utilisation, stiffness, residual strength and ductility of RC beams repaired and strengthened with NSM CFRP strips. Moreover, the statistical model proposed to predict the maximum tensile strain in CFRP strips has good agreement with the experimental results and can be used in the design of NSM CFRP-repaired and strengthened RC members with cement-based (IHSSC-CA) and epoxy adhesives. Furthermore, the ultimate flexural capacity of the repaired and strengthened RC beams using NSM CFRP strips with cement-based (IHSSC-CA) and epoxy adhesives can be predicted adequately using the ACI 440.2R-08.
The efficiency of strengthening reinforced concrete (RC) structures using the near-surface mounted (NSM) fibre reinforced polymer (FRP) technique depends on the bond between the NSM FRP and the ...concrete substrate. This paper presents the results of an experimental study of NSM carbon FRP strips bonded to concrete substrate with innovative high-strength self-compacting cementitious adhesive (IHSSC-CA) under fatigue loading using single-lap shear tests. Graphene oxide and cementitious materials were used to synthesise the IHSSC-CA. The test variables were: CFRP strip dimensions (1.4×10mm, 1.4×20mm) and CFRP strip surface conditions (smooth, rough). 61 specimens were tested under different fatigue load ranges to develop the load range (LR)-fatigue life (N) relationships. Finally, equations were developed to predict fatigue lives based on the experimental results. It was found that the rough surface CFRP strips 1.4×20mm in dimensions showed the best fatigue life under different fatigue load levels. Moreover, the test results confirm the effectiveness of using IHSSC-CA to bond NSM CFRP strips to the concrete substrate. Furthermore, the proposed equations can predict fatigue life reasonably well and can be used in the design of NSM CFRP-strengthened RC members.
This paper presents the residual strength of reinforced concrete (RC) beams strengthened and repaired by using near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) with innovative ...high-strength self-compacting non-polymer cementitious adhesive (IHSSC-CA) and epoxy adhesive after being subjected to fatigue loading. Cementitious materials and graphene oxide were used to synthesise the IHSSC-CA. Ten full-scale beams were manufactured and tested under four-point loading with different loading histories. Five beams were tested under monotonic loading up to failure, and another five beams were then tested under fatigue loading at service load levels up to failure or 3 million cycles, whichever happened first. The fatigue load range and frequency used in this study for testing the beams were designed to simulate the typical fatigue loading and frequency of an actual RC bridge girder under service loading conditions. The effect of fatigue loading was determined by comparing the performance of beams before and after fatigue loading. Finally, 3-D laser profilometry analyses was used to study the deformation of the CFRP strips after fatigue loading. The findings confirm the effectiveness of using IHSSC-CA to strengthen and repair RC beams with NSM CFRP system.
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