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A numerical simulation of the test beam was carried out with Abaqus and compared with test data to ensure that the modeling method is accurate. An analysis of the effects of the angle between the U-hoop and horizontal direction, the pre-crack height, the pre-crack spacing, and the strength of the geopolymer adhesive on the cracking load and ultimate load of the reinforced beam is presented.

Load tests and finite element simulations were conducted on carbon fiber reinforced polymer-reinforced concrete beams bonded with geopolymer adhesive. The bond-slip effect of geopolymer adhesive was taken into account in the model. The flexural performances, the flexural load capacities, the deformation capacities, and the damage characteristics of the beams were observed, and the numerical simulation results were in good agreement with the experimental results. An analysis of parametric sensitivity was performed using finite element simulation to investigate the effects of different angles between U-hoop and horizontal direction, pre-crack heights, pre-crack spacing, and strength of geopolymer adhesive on cracking load and ultimate load.

Under the same conditions, the higher the height of the pre-crack, the lower the bearing capacity; increasing the pre-crack spacing can delay cracking, but reduce ultimate load. By increasing the strength of the geopolymer adhesive, the flexural resistance of the beam is improved, and crack development is also delayed; the angle between the u-hoop and horizontal direction does not affect the cracking of reinforced beams; a horizontal u-hoop has a better effect than an oblique u-hoop, and 60° is the ideal angle between the u-hoop and horizontal direction for better reinforcement.

According to the experimental study in this paper, Abaqus was used to simulate the strength of different angles between U-hoop and horizontal direction, pre-crack heights, pre-crack spacings, and geopolymer adhesives, and the angles' effects on the cracking load and load carrying capacity of test beams were discussed. Since no actual tests are required, the method is economical. This paper offers data support for the promotion and application of environmentally friendly reinforcement technology, contributes to environmental protection, and develops a new method for reinforcing reinforced concrete beams and a new concept for finite element simulations.

In this paper, the effects of geopolymer adhesive, the number of CFRP layers and the width of pre-crack on the flexural performance of reinforced concrete beams strengthened with CFRP were studied, and the flexural capacity of strengthened beams was calculated theoretically.

Reinforced concrete beams were strengthened with CFRP by geopolymer adhesive, and flexural load tests were conducted to observe the reinforcement effect. Based on the method of calculating the flexural capacity of reinforced concrete beams, a theoretical calculation model on the flexural capacity of reinforced concrete beams strengthened with geopolymer adhesive bonded CFRP was established.

The test data shown the flexural capacity of epoxy resin adhesive CFRP strengthened reinforced concrete beams is 7.76% higher than that geopolymer adhesive is used. The flexural capacity of reinforced concrete beams strengthened with three layers of CFRP is 1.86% higher than that two layers are adopted. The mean ratio of the test data and the calculation results of the flexural capacity is 0.973, and the mean square error is 0.008. It can be seen that the test data are in good agreement with the theoretical value.

This paper provides data support for the popularization and application of the new environment-friendly reinforcement technology, contributes to the cause of environmental protection, and provides a new method for strengthening reinforced concrete beams.

The effects of carbon fiber reinforced polymer (CFRP) reinforcement form, adhesive type and pre-crack width on failure mode, shear capacity, deflection response, CFRP strain response and crack patterns of strengthened specimens were investigated.

This paper presents a geopolymer adhesive that matches the performance requirements of CFRP adhesive, which is applied to pre-cracked beams reinforced with CFRP strips.

For specimens with varying structural properties, two failure modes, the CFRP-concrete interface substrate failure and the fracture failure of CFRP, are observed. Moreover, the shear capacity, ultimate deflection and bending stiffness of the U-shaped CFRP-strengthened beams are enhanced in comparison to the complete-wrapping CFRP-strengthened beams. With an increase in pre-crack width, the increase in shear capacity of RC beams shear-strengthened with CFRP strips is less than that of non-cracked beams, resulting in a limited influence on the stiffness of CFRP-strengthened beams. The comparison of experimental results showed that the proposed finite element model (FEM) effectively evaluated the mechanical characteristics of CFRP-strengthened RC beams.

Taking into consideration the reinforcement effect and the concept of environmental protection, the geopolymer adhesive reinforcement scheme is preferable to applying epoxy resin to the CFRP-strengthened RC beams.

The effects of failure mode and strain conditions of CFRP, concrete and stirrups on the shear capacity of reinforced beams bonded by geopolymer and epoxy are studied. In addition, a prediction model of the ultimate bearing capacity of CFRP-shear-strengthened beams is proposed, which considers adhesive performance parameters adhesive performance parameter ßE and FRP width parameter ßw.

This paper presents an experimental study on ultimate bearing capacity of CFRP-shear-strengthened pre-cracked beams with geopolymer and epoxy resin, which considers parameters such as impregnated adhesives types and CFRP-strengthened scheme.

The failure modes of CFRP-strengthened beams bonded by geopolymer are the combination of the CFRP-concrete interface substrate failure and fracture failure of CFRP, and that of epoxy is the local substrate failures with small area. The ultimate load of CFRP-strengthened beams is directly affected by the failure modes. The ultimate bearing capacity of CFRP-strengthened beams with geopolymer is 91.4% of that of epoxy resin. Compared with ultimate bearing capacity of CFRP-strengthened beams with U-shaped, that of complete-wrapping increases by 2.5%. Moreover, the stirrup peak strain is reduced by more than 30% in CFRP-strengthened beams bonded with geopolymer and epoxy resin in comparison with the unstrengthened beam. The existing prediction model cannot accurately predict the CFRP shear capacity contribution of strengthened beams with different CFRP-strengthened schemes and adhesive properties. The estimated results are much lower than the test data, and the deviation is much larger than 20%.

Geopolymer alternative to epoxy as an adhesive is feasible and effective for CFRP reinforcement. Furthermore, the accuracy is improved by introducing parameters about adhesive properties based on the existing prediction model. The estimated results are in excellent agreement with the test data, and the deviation is controlled within −12.80%, and the model is suitable for predicting the shear capacity of FRP-strengthened beams with ßf = 90° in shear capacity database.

This paper aims to present performance comparison of fiber sheet-strengthened reinforced concrete (RC) beams bonded with geopolymer and epoxy resin under ambient and fire conditions.

This study presents experimental results of bending tests at ambient temperature and fire resistance tests on two control beams and eight fiber sheet-strengthened RC beams. The test variables include fiber sheet type (carbon fiber [CF] and basalt fiber [BF] sheet), number of layers of fiber sheet (one and two layers) and adhesive agent type (geopolymers and epoxy resin). Data generated from these tests were used to evaluate and compare the strengthening effectiveness of CF-reinforced polymer (CFRP) and CF-reinforced geopolymer (CFRG) at ambient temperature and under fire exposure conditions.

Test results clearly show that the CFRG system can provide good strengthening effectiveness on RC beams at ambient temperature, as the CFRP system, owing to excellent bond properties of geopolymers. Although geopolymers possess better bonding properties at high temperature than organic matrix, the strengthened beams bonded with geopolymer do not exhibit better fire resistance than that those bonded with epoxy resin, owing to early falling-off of fire insulation. Thus, in CFRG-strengthened beams, relevant measures are to be taken to minimize falling-off of fire insulation to achieve good fire resistance.

The presented results are from unique fire tests and provide valuable insight (and information) on the performance of fiber sheet-strengthened RC beams bonded with geopolymer and epoxy resin under ambient and fire conditions.

In this paper, to obtain shear and bending performance of carbon fiber-reinforced polymer (CFRP)-strengthened beams bonded by geopolymers, the effects of impregnated adhesive types, strengthened scheme, CFRP layer and pre-cracked width are investigated, and the performance of CFRP-strengthened beams is validated by the establishment of Finite Element Models (FEMs).

In this paper, static loading test and finite element analysis of epoxy-CFRP-strengthened (ECS) and geopolymer-CFRP-strengthened (GCS) were carried out, and the bearing capacity and stiffness were compared, the results show that GCS reinforced concrete (RC) beam is feasible and effective.

The bearing capacity, crack distribution and development, load–deflection curves of GCS RC beams with different pre-crack widths were investigated. The reinforcement effect of geopolymer achieves the same as epoxy, effectively improving the ultimate bearing capacity of the beam, with a maximum increase rate of 28.9%. The failure mode of CFRP is broken in the yield failure stage of GCS RC beam with reasonable strengthening form, and the utilization rate of CFRP is improved. CFRP-strengthened layers, pre-cracked widths significantly affect the mechanical properties, and deformation properties of the strengthened beams.

Compared with ECS RC beams, the bearing capacity and stiffness of GCS RC beams are similar to or even better, indicating that GCS RC beam is feasible and effective. It is a new method for CFRP-strengthened beams, which not only conforms to the concept of national ecological civilization construction, but also provides an economical, environmentally friendly and excellent performance solution for structural reinforcement.

This study aimed to review various existing methods for improving the quality of recycled concrete aggregates (RCAs) as a possible substitution for natural aggregates (NAs) in concrete. It is vital as the old paste attached to the RCA weakens its structure. It is due to the porous structure of the RCA with cracks, weakening the interfacial transition zone (ITZ) between the RCA and binding material, negatively impacting the concrete's properties. To this end, various methods for reinforcement of the RCA, cleaning the RCA's old paste and enhancing the quality of the RCA-based concrete without RCA modification are studied in terms of environmental effects, cost and technical matters. Furthermore, this research sought to identify gaps in knowledge and future research directions.

The review of the relevant journal papers revealed that various methods exist for improving the properties of RCAs and RCA-based concrete. A decision matrix was developed and implemented for ranking these techniques based on environmental, economic and technical criteria.

The identified methods for reinforcement of the RCA include accelerated carbonation, bio deposition, soaking in polymer emulsions, soaking in waterproofing admixture, soaking in sodium silicate, soaking in nanoparticles and coating with geopolymer slurry. Moreover, cleaning the RCA's old paste is possible using acid, water, heating, thermal and mechanical treatment, thermo-mechanical and electro-dynamic treatment. Added to these treatment techniques, using RCA in saturated surface dry (SSD) mixing approaches and adding fibres or pozzolana enhance the quality of the RCA-based concrete without RCA modification. The study ranked these techniques based on environmental, economic and technical criteria. Ultimately, adding fibres, pozzolana and coating RCA with geopolymer slurry were introduced as the best techniques based on the nominated criteria.

The study supported the need for better knowledge regarding the existing treatment techniques for RCA improvement. The outcomes of this research offer an understanding of each RCA enrichment technique's importance in environmental, economic and technical criteria.

The practicality of the RCA treatment techniques is based on economic, environmental and technical specifications for rating the existing treatment techniques.

The present work focuses on evaluating the physical and mechanical characteristics of geopolymer concrete (GPC) by replacing the sodium silicate waste (SSW) in place of traditional river sand. The aim is to create eco-friendly concrete that mitigates the depletion of conventional river sand and conserves natural resources. Additionally, the study seeks to explore how the moisture content of filler materials affects the performance of GPC.

SSW obtained from the sodium silicate industry was used as filler material in the production of GPC, which was cured at ambient temperature. Instead of the typical conventional river sand, SSW was substituted at 25 and 50% of its weight. Three distinct moisture conditions were applied to both river sand and SSW. These conditions were classified as oven dry (OD), air dry (AD) and saturated surface dry (SSD).

As the proportion of SSW increased, there was a decrease in the slump of the GPC. The setting time was significantly affected by the higher percentage of SSW. The presence of angular-shaped SSW particles notably improved the compressive strength of GPC when replacing a portion of the river sand with SSW. When exposed to elevated temperatures, the performance of the GPC with SSW exhibited similar behavior to that of the mix containing conventional river sand, but it demonstrated a lower residual strength following exposure to elevated temperatures.

Exploring the possible utilization of SSW as a substitute for river sand in GPC, and its effects on the performance of the proposed mix. Analyzing, how varying moisture conditions affect the performance of GPC containing SSW. Evaluating the response of the GPC with SSW exposed to elevated temperatures in contrast to conventional river sand.

Despite the dramatic increase in construction toward additive manufacturing, several challenges are faced using natural materials such as Earth and salt compared to the most market-useable materials in 3D printing as concrete which consumes high carbon emission.

Characterization and mechanical tests were conducted on 19 samples for three natural binders in dry and wet tests to mimic the additive manufacturing process in order to reach an efficient extrudable and printable mixture that fits the 3D printer.

Upon testing compressive strength against grain size, compaction, cohesion, shape, heat and water content, X-Salt was shown to record high compressive strength of 9.5 MPa. This is equivalent to old Karshif and fire bricks and surpasses both rammed Earth and new Karshif. Material flow analysis for X-Salt assessing energy usage showed that only 10% recycled waste was produced by the end of the life cycle compared to salt.

Findings are expected to upscale the use of 3D salt printing in on-site and off-site architectural applications.

Findings contribute to attempts to resolve challenges related to vernacular architecture using 3D salt printing with sufficient stability.

Benefits include recyclability and minimum environmental impact. Social aspects related to technology integration remain however for further research.

This paper expands the use of Karshif, a salt-based traditional building material in Egypt's desert by using X-Salt, a salt-base and natural adhesive, and investigating its printability by testing its mechanical properties to reach a cleaner and low-cost sustainable 3D printed mixture.

The purpose of this paper is to review research studies on process optimisation and machine development that lead to the enhancement of final products in various aspects of the fused deposition modelling (FDM) process.

An overview of the literature, focussing on process parameters, machine developments and material characterisations. This study investigates recent research studies that studied FDM capabilities in printing a vast range of materials from thermoplastics to metal alloys.

FDM is one of the most common techniques in additive manufacturing (AM) processes. Many parameters in this technology have effects on three-dimensional printed products. Therefore, it is necessary to obtain the optimum elements, for example, build orientation, layer thickness, nozzle diameter, infill pattern and bed temperature. By selecting a proper variable range of parameters, the layers adhere strongly and building end-use products of high quality are achievable. A vast range of materials and their properties from polymers to composite-based polymers are presented. Novel techniques to print metal alloys and composites are examined to increase the productivity of the FDM process. Additionally, defects such as shrinkage and warpage are discussed to eliminate the system’s limitations and improve the quality of final products. Multi-axis and mobile machines brought enhancements throughout the process to eliminate obstacles such as staircase defects in the conventional FDM process. In brief, recent developments were identified and a summary of major improvements was discussed in this study for future research.

This paper is an overview that provides information about research and developments in FDM. This review focusses on process optimisation and obstacles in printing polymers, composites, geopolymers and novel materials. Therefore, machine characteristics were examined to find out the accessibility of printing novel materials for different applications.