Concrete Mixtures Research Articles

Self-Compacting Mixtures of Fair-Faced Concrete Based on GGBFS and a Multicomponent Chemical Admixture—Technological and Rheological Properties

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture.

Rheological Characteristics of Concrete Mixtures Modified with Urease Additives

Statement of the problem. Rheological characteristics of concrete samples made with the use of various bioadditives are studied. Results. The results of experimental studies of the rheological properties of concrete, taking into account the effect of dietary supplements based on the following strains of bacteria B.subtilis, Ps.aeruginosa, with urease activity, are presented. Conclusions. The values of the cone sediment of concrete mixtures made using various grades of Portland cement were obtained, the values of conditional viscosity were also established, and the limiting shear stress and compressive strength of the obtained concrete cube samples made using urease bioadditives were determined. It was found that the use of dietary supplements leads to a decrease in the conditional viscosity of the mixture by 2 times, as well as to an increase in compressive strength by at least 15 %. Thus, it has been established that bioadditives improve the quality of the bond between the components of concrete, making it more durable and resistant to loads, as well as its rheological characteristics.

Polypropylene Fiber as a Factor of Reduction of the Total Shrinkage Strain of Expanded Clay Concrete

Statement of the problem. The article presents the development features of the total shrinkage strain of expanded clay concrete, expanded clay fiber-reinforced concrete, expanded clay steel-reinforced concrete, and expanded clay fiber-steel-reinforced concrete. According to the analytical review, the shrinkage strain decrease as a result of the fibers adding was noted by the researchers without analyzing the reason for the phenomenon. Therefore the purpose of the study is to establish the reason for the decrease of the shrinkage strain of expanded clay concrete with the addition of polypropylene fibers. Results. It has been confirmed that the polypropylene fiber addition reduces the total shrinkage strain of expanded clay concrete by 29—34 % on the 120th day with the volume content of fibers of 0.36 %. Empirical dependences of deformations compatibility for expanded clay fiber-reinforced concrete and expanded clay fiber-steel-reinforced concrete are set forth. Conclusions. It has been experimentally established that fiber is a significant factor on the first days of the concrete mixture hardening, when the elastic modulus of the fiber is greater than or equal to the elastic modulus of the cement stone. Fibers act as a bond and affect the redistribution of shrinkage stresses within the composite, thus reducing the values of the total shrinkage strain.

Optimizing sustainable concrete mixes with recycled aggregate and Portland slag cement for reducing environmental impact

Optimizing sustainable concrete mixes with recycled aggregate and Portland slag cement for reducing environmental impact

Self-Healing and Mechanical Behaviour of Fibre-Reinforced Ultra-High-Performance Concrete Incorporating Superabsorbent Polymer Under Repeated and Sustained Loadings

This study investigated the mechanical responses and self-healing capability of incorporating superabsorbent polymer (SAP) particles in Fibre-Reinforced Ultra-High-Performance Concrete (UHPC) mixes under repetitive flexural and sustained tensile loadings. UHPC with SAP addition of 0.3% and 0.4% of the binder ratio were studied along with a control UHPC mix. The methodology included investigating the mechanical properties of these mixes under ambient, water, and 100% of relative humidity (RH) curing conditions. In addition, the mechanical performance of ambient-, water-, and 100% RH-cured prismatic specimens (100 mm × 100 mm × 500 mm) under repeated load was studied under the same curing conditions. Prismatic specimens (75 mm × 75 mm × 500 mm) were kept under cure conditions of wet and dry cycles with applied tensile load for 28 days for the sustained tensile load. The results showed that incorporating SAP into UHPC enhances the elastic modulus, flexural strength, and tensile strength. Also, mixes with SAP have exhibited compressive strength above 120 MPa after 90 days. Furthermore, the load recovery of the prisms under repetitive flexural load and prisms under sustained tensile loading demonstrated the self-healing efficiency of SAP incorporated into the UHPC mixes higher than the control mix specimens.

Flexural behavior of UHPC wet joints for precast bridge deck panels

Over the past decade or so, ultra-high performance concrete (UHPC) has been increasingly used for wet joints of bridge deck panels (BDPs) in bridge superstructures. To evaluate the flexural performance of UHPC wet joints for precast bridge deck panels, a total of seven BDPs were designed, including one monolithic cast-in-place bridge deck panel (MCIPBDP), one precast bridge deck panel (PBDP) with NC wet joints, and five precast bridge deck panels (PBDPs) with UHPC wet joints. The design parameters included reinforcement types (straight bars and U-bars), U-bar lap details (contact lap splice and non-contact lap splice), filling materials (UHPC and NC), and joint widths (150 mm, 200 mm, 250 mm, and 500 mm). Three-point bending tests were performed to evaluate the flexural performance based on the failure mode, load-deflection curve, cracking width in the wet joint region, and stiffness degradation. The experimental results showed that it is feasible to replace 500-mm-width NC wet joints with 200-mm-width UHPC wet joints for PBDPs with U-bars. UHPC wet joints, with a width of 250 mm, effectively prevented straight bars from slipping. As the width of UHPC wet joints decreased, the failure mode shifted from shear failure to bending failure. In addition, the cohesion-friction hybrid model was proposed to simulate the behavior of joint interfaces. The FE analysis results demonstrated that the FE model and modeling method have high accuracy and general applicability. Finally, the flexural capacity calculation formula was developed according to the strut-and-tie model. The theoretical calculation results were in good agreement with test results.

Performance of Molasses Waste as a Cement Replacement to Study Concrete Compressive Strength

To reduce the negative environmental impact of cement production and preserve natural resources, an experimental investigation was conducted to study the performance of concrete specimens at different curing ages and to determine the compressive strength of these specimens by replacing cement with molasses. Experimentation was carried out on the concrete specimens at a temperature range of 25 °C to 30 °C; six specimens were cast for each replacement ratio, except for 0.75% wt. of cement (86.55 g) and 1% wt. of cement (113.6 g), where five samples were considered for each ratio. The average 28-day compressive strength of the conventional concrete specimens came out to be 29 MPa, but increased to 40 MPa with the addition of 0.25% wt. of cement molasses (28.85 g). It was observed that as the percentage of molasses waste in the concrete mix was further increased by replacing the cement, the compressive strength of the concrete specimens increased gradually and then significantly decreased. The findings shed light on the prospect of using molasses waste instead of cement in the concrete mix. Also, it is worth mentioning that about 30% of the cost–benefit was obtained with reference to that of conventional admixtures available in the market for the production of concrete. However, it is notable that a long-term durability study needs to be conducted before making it viable. This work not only addresses a sustainable and innovative method of waste management (SDG12), but also contributes to low carbon emissions (SDG13). The novelty of this work lies in the fact that no such kind of study has been conducted in Pakistan so far, in addition to the very limited international literature available, and, in particular, no evidence on the compressive strength results at higher molasses dosages, i.e., 1% wt. of cement (113.6 g) and 2% wt. of cement (230.8 g).

Experimental studies on strength and workability of mineral admixture modified cement-based fibre-reinforced self-compacting concrete

ABSTRACT Mineral admixtures such as fly ash (FA), ground granulated blast furnace slag (GGBS), metakaolin (MK), and silica fumes (SF) derived from industries are often referred to as secondary cementitious materials, as partial replacements for cement. Also, the use of fibres significantly enhances the flexural behaviour of concrete. Various kinds of literature highlight the performance of concrete with one or two types of admixtures. In this study, an attempt is made to explore the effect of the use of more than two admixtures viz. FA, GGBS and MK as a partial replacement to cement and fibrofor fibre (FF) on workability and strength properties of based Fibre-Reinforced Self-Compacting Concrete (FRSCC). The FF in Self-Compacting Concrete (SCC) is varied from 1.0 to 2.0 kg/cum. The SCC samples are tested for three curing durations. Based on the experimental investigations, the workability of all the mixes is found to be within the EFNARC limits. The variation in the compressive strength of SCC for various fibre dosages is within 10%, after 28 days of the curing period. It is noted that A-10 mix with fibre dosage of 1.0 Kg/cum yielded the highest compressive, split tensile, and flexural strengths after 56 days of curing, as compared to that of all other variations including conventional SCC mix.

Experimental, analytical, and numerical investigation on flexural behavior of the gradient UHPC-NC composite beams

To enhance the deformation resistance of concrete beams, the flexural behavior of eight gradient ultra-high performance concrete (UHPC)-normal concrete (NC) composite beams was experimentally studied. The effects of different gradients and fiber types on the deflection of the gradient UHPC-NC composite beams were investigated, and a deflection calculation method for the composite beams was proposed. Finally, numerical simulations were conducted on the basis of the cohesion models. Results indicate that the gradient UHPC design significantly improves both the loading-bearing and deformation capacity of the composite beams. The cracking load of the gradient composite beams with steel fiber-UHPC at the bottom layer is much higher than that of the beams with basalt fiber-UHPC, and the number of cracks in the pure bending section of the beams with steel fiber-UHPC at the bottom layer is remarkably less than that of the beams with basalt fiber-UHPC at the bottom layer. However, their ultimate capacities were comparable, indicating that steel fibers can effectively improve the fracture toughness of UHPC. The predicted deflection of the gradient UHPC-NC composite beams agrees well with the test results, indicating the accuracy of the proposed deflection model. The bearing capacity and deflection obtained from the numerical simulation also align well with the test results.

Fresh, hardened properties and microstructural analysis on the effect of NaOH molarities of industrial by-products based self-compacting geopolymer concrete

AbstractThe sodium hydroxide (NaOH) molarity in Self-compacting geopolymer concrete (SCGC) is essential for activating the precursor and aggregate to develop strength, workability, and microstructure. In this study, SCGC mixes prepared with 50% fly ash (FA) and 50% ground granulated blast furnace slag (GGBS) to investigate fresh and hardened properties with NaOH molarities (M) ranges from 8 to 16, the ratio of Na2SiO3 to NaOH kept constant at 2.5 and ratio of alkaline solution to the binder at 0.45 with 2% SP for the polymerization process. SCGC workability studies indicate the NaOH concentration increased, the slump flow decreased, and 14 M was the optimum molarity. The compressive, split tensile, and flexural strength results showed 39.4 MPa, 4.72 MPa, and 5.91 MPa at 28 days. The C–S–H gel enhanced the strength qualities studied from Fourier transform infrared spectroscopy. The scanning electron microscope showed microstructural densification of the entire system, which improved with the NaOH concentration, and the strength increased with the degree of polymerization and polycondensation. Hence, based on workability, the optimized NaOH concentration is 14 M with binder contents of FA (50%) and GGBS (50%). This study helps to improve the microstructure and strength properties with potential cost implications of SCGC.

Exploring Ultimate Flexural Strengths of Ultra-High-Performance Concrete (UHPC) Samples through Experimental Analysis in Comparison with Ordinary Concrete Structures

Exploring Ultimate Flexural Strengths of Ultra-High-Performance Concrete (UHPC) Samples through Experimental Analysis in Comparison with Ordinary Concrete Structures

Enhancing the Mechanical Properties of Ultra-High-Performance Concrete (UHPC) Through Silica Sand Replacement with Steel Slag

In modern construction, increasing the sustainability of materials without sacrificing performance is crucial. Ultra-High-Performance Concrete (UHPC) is known for its exceptional strength and durability. However, incorporating waste and optimizing the mix is still a key focus. The main goal of this article is to evaluate the enhancement of the mechanical properties of UHPC by replacing silica sand with steel slag at various percentages (25%, 50%, 75%, and 100%). With this purpose, we measured the compressive, tensile, and flexural strengths, as well as relative density and water absorption. It was found that the best mechanical performance of UHPC occurs at 50% replacement, exhibiting a maximum compressive strength of 126 MPa (+13.5%), a bending strength of 11.6 MPa (+20.8%), and a tensile strength of 7.2 MPa (+6.5%). Moreover, for the same steel slag replacement, 5.1% decrease in the CO2 eq. emissions was found. However, exceeding the 50% threshold led to a deterioration of UHPC’s mechanical properties, and the SEM images revealed that this was mainly caused by the weakened bond between the cement matrix and the aggregates. Thus, it was concluded that the use of steel slag may significantly improve the structural integrity of UHPC when the adequate replacement percentage is adopted (around 50%), being a viable alternative to traditional aggregates that also has environmental advantages (e.g., reduced carbon emissions).

Effect of Using Fine Volcanic Ash Instead of Crushed Basalt Filler in Hot Mix Asphalt

Numerous studies over the years have demonstrated the significance and impact of filler in influencing the physical and mechanical properties of Hot Mix Asphalts (HMAs). To overcome such issues, as environmentally friendly alternatives, several different materials for construction have been proposed. This led to an investigation into the potential use of fine volcanic ash (FVA) as a hot mix asphalt filler alternative. In order to prepare bituminous concrete mix sample with conventional basalt filler (BF) as control mix. The Marshall Mix design approach was used to calculate the effective bitumen content. A total of 15 bituminous concrete mix specimens with bitumen content of 4%, 4.5%, 5%, 5.5%, and 6% were created, and the optimum asphalt content was 5.24 %. The impacts of five different (FVA) samples with filler contents of 15%, 30%, 45%, and 60% by weight were compared with respect to bituminous concrete performance. The Marshall stability of a total of 30 samples with varying amounts of (FVA) were investigated. The outcomes were compared with a conventional bituminous concrete mixture. The results showed that fine volcanic ash may substitute 30% of the basalt filler at a bitumen content of 5.24%, 13.84 KN Marshall stability value, 4.0% air voids, 74.77% VFB, 2.380 g/cm3 bulk density and 3.54 mm flow. Therefore, the combination of 30% Fine Volcanic Ash by weight of Basalt Filler satisfies the ASTM Specifications, while the remaining VA content satisfies the basic requirements of the ASTM Specifications.

What is the embodied CO2 cost of getting building design wrong?

Today, carbon and cost-efficient construction are well matched. However, in the future, as steel production is increasingly done from recycled scrap in electric arc furnaces (EAFs) and concrete mix design is improved, the current balance of CO[Formula: see text] impacts and costs can be altered. When this happens, structural designers need to update their design strategies, and incentives must be put in place to retain the alignment between environmental impact and cost. Here, I assess the potential of carbon taxation to improve the structural design. I also assess the discrepancy in embodied carbon outcomes if construction costs remain constant, but the embodied carbon of materials is varied. Finally, I look at the effect of an early-stage design tool, PANDA, on embodied carbon outcomes of real projects. I find that carbon taxes need to be extremely high to have an effect, and that this effect is limited to certain types of frames. Embodied carbon in construction can become disconnected from costs if the embodied carbon of materials varies heterogeneously. Finally, novel design tools can help designers substantially improve the embodied carbon of their design. This happens despite the absence of a significant monetary incentive to that effect.This article is part of the discussion meeting issue 'Sustainable metals: science and systems'.

Dynamic shear strength of precast connection with UHPC-based and traditional grouted sleeves: Test, simulation, and analytical formulas

Dynamic shear strength is critical for ensuring the integrity of prefabricated structures with grouted sleeve connections under dynamic loads such as impacts and earthquakes. However, studies have yet to be conducted to clarify the dynamic shear strength of grouted sleeve connections for designs. To this end, this study systematically investigated the dynamic shear behavior of precast connection with grouted sleeves through physical experiments, numerical simulations, and theoretical analysis. Drop hammer impact tests were performed on nine precast connection specimens that differ in amounts of impact energy, axial loads, rebar ratios, and grouting materials. Experimental data indicated that the dynamic shear performance of the ultra-high-performance concrete (UHPC)-based connections is superior to that of traditional grouted sleeve connections. The impact-induced displacement of a grouted sleeve connection is very sensitive to the amount of impact energy. Detailed finite element (FE) models were further developed to examine the dynamic shear strength of precast connections. Good agreements are observed between the numerical results and experimental data, demonstrating the rationality of the developed FE modeling method. It was found that the dynamic shear strengths of grouted sleeve connections are more sensitive to axial load levels and concrete strength grades than rebar ratios. Based on extensive simulation results obtained from the validated modeling method, the analytical formulas were proposed to predict the dynamic increase factor (DIF) and shear strength of precast connections. The analytical results predicted by the proposed formulas agree well with the FE results, demonstrating the applicability of the proposed formulas.

Effects of Superabsorbent Polymer and Natural Zeolite on Shrinkage, Mechanical Properties, and Porosity in Ultra-High Performance Concretes

The low water-to-binder ratio of ultra-high performance concrete (UHPC) often causes shrinkage and cracking due to early-age self-desiccation. This leads to significant initial dimensional instability, which may compromise structural integrity. As a promising solution, internal curing agents such as superabsorbent polymers (SAP) and natural zeolite have the potential to mitigate shrinkage and achieve self-stressing properties. This research aims to provide a comprehensive comparison between SAP and zeolite's effects within a consistent UHPC formulation. Six UHPC mixtures (including the reference mixture) were designed: three with SAP dosages of 0.2%, 0.4%, and 0.6% by cement mass, and two with zeolite replacing silica fume at 25% and 50% by mass. Various testing methods, including autogenous and drying shrinkage assessment, heat of hydration and thermogravimetric analysis, compressive strength evaluation, mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), were employed to assess the mixtures at different stages of curing. The result reveals that the incorporation of SAP and zeolite in the mixtures significantly reduces UHPC's early-age autogenous shrinkage. Moreover, SAP and zeolite additions impact mechanical properties, demonstrating that a balance between shrinkage control and compressive strength can be reached, through an optimization of the additions to achieve the desired performance. Microstructural analysis through MIP and NMR reveals increased overall porosity of the UHPC with SAP and zeolite, suggesting that low-field NMR can be a valuable tool for complementing conventional test methods. The outcome of this study provided valuable insights into optimizing the balance between durability and mechanical performance, paving the way for more sustainable and cost-effective applications of UHPC in modern construction practices.

Experimental study on the static properties of bamboo fiber reinforced Ultra-High Performance Concrete (UHPC)

Bamboo fiber, as a natural and sustainable material, offers low cost, high strength, and environmental benefits, showing significant potential in composite material reinforcement. This study investigates the effects of bamboo fiber on the static properties of ultra-high performance concrete (UHPC) through experimental research. Different fiber lengths (6mm, 12mm, 18mm) and volume contents (0.5%, 1.0%, 1.5%, 2.0%) were examined for their impact on the workability, mechanical properties, and pore/void structure of UHPC. The results demonstrate that while bamboo fiber incorporation reduces workability, it significantly enhances compressive and flexural strengths. Specifically, a 21.9% increase in compressive strength was achieved with 18mm fibers at 1.0% content, and a 40.5% increase in flexural strength was observed with 18mm fibers at 1.5% content. Mercury intrusion porosimetry (MIP) and computed tomography (CT) revealed that longer fibers contribute to the formation of larger pores, affecting the void structure. Moreover, bamboo fibers degrade over time in alkaline environments, with a 5% reduction in tensile strength after 28 days, but the crystallinity of the cellulose has increased. Based on the experimental results, 12mm bamboo fibers at 1.0-1.5% content provide the best balance of strength enhancement and workability, making them a promising reinforcement material for UHPC.

Influence of the graphene oxide-coated steel fiber on the microstructure optimization of UHPC

Benefiting from its superior mechanical properties, large specific surface area and abundant oxygen-containing functional groups, graphene oxide (GO) can generate nucleation and pore-infilling effects to optimize the microstructure of the cementitious composites, thus reinforcing the mechanical performance and durability of cement-based materials. However, due to the dispersion issues and relatively high cost, the widespread use of GO in the cement industry has not yet been realized. In the present study, we applied three different methods to coat industrial GO nanosheets on the steel fiber’s surface and reinforce the UHPC microstructure. The proposed coating method effectively disperses GO within the ultra-high-performance concrete (UHPC) matrix and targets its enhancement effects on the interfacial transition zone (ITZ), which has the weakest pore structure in UHPC. The result presents that the three-step dip method of GO coating on the steel fiber demonstrates higher effectiveness in reinforcing the microstructure of UHPC, the porosity of the matrix is 1.88 %, with a relative decrease of 37.1 ∼ 60.3 %. In addition, the average distance of ITZ after GO enhanced UHPC is about 3.7 µm, about 37.3 %-68.1 % shorter, and the ITZ porosity is 3.8 %, which is 15.6 %-65.5 % lower. With the assistance of the metal intrusion technique, backscattered electron characterization and deep learning-based analysis, the pore structure features of UHPC were extracted with a classification recognition accuracy of 88.5 %, and the pore intrusion volume inside the characteristic region of the UHPC matrix increased by 1.89–2.14 times. The extraction characteristics illustrated that the GO strengthening on steel fibers was more effective in ITZ, with an optimization efficiency of about 8.1 % higher than in other regions. We expect that the findings of this study could provide deep insights into GO modification for cementitious composite reinforcement applications and open new pathways for affordable alternatives to nano-enhanced composites.

Developing ultra-high performance concrete with different strength grade based on mix proportion sensitivity factor analysis

Abstract Owing to the excellent strength and durability, ultra-high-performance concrete (UHPC) has been used for fabricating large-scale and important infrastructures. However, mix proportion of UHPC is still the core factor influencing its workability, strength, cost and energy resource consumption. Based on this, the amount of cementitious materials, water-binder ratio, and the content of steel fibers were matched to obtain UHPC with required workability and strength according to three-factor five-level orthogonal range analysis considering the interaction of these three parameters. Experimental results show that the water-binder ratio and steel fiber content is the primary factor to guarantee the fluidity/compressive and flexural strength of UHPC, respectively. For developing UHPC with compressive strength grade of 150 MPa and flexural strength higher than 50 MPa, the amount of cementitious materials (including cement, silica fume, cenosphere, and fly ash) and the content of steel fibers should be higher than 1000 kg m−3 and 2.5 vol.%, and the corresponding water-binder ratio is equal to 0.16. When the aim is to fabricate UHPC with compressive strength grade of 120 MPa and flexural strength higher than 40 MPa, the water-binder ratio can be increased but should be lower than 0.20 with the increasing amount of cementitious material, and the volume fraction of steel fibers should be higher than 1.5 vol.%. High steel fiber content and water-binder ratio all easily coarsens the microstructure and pore structure of UHPC, and this phenomenon cannot be compensated by using high amount of cementitious materials. It should be adjusting the matching degree of amount of cementitious materials and water-binder ratio to obtain a slurry with appropriate fluidity and cohesiveness, and then content of steel fibers can be selected to perform without adverse effects.

Bond-slip Behavior of Lapped Sand-Coated Deformed GFRP Rebars in UHPC under Double-Row Splice Test

Novel Ultra-High-Performance-Concrete (UHPC) structures reinforced with Fiber-Reinforced Polymer (FRP) rebars are promising candidates for applications in important infrastructures under exposed environments where normal concrete and steel rebars may falter. This paper aims to assess the bond-slip behavior between lapped sand-coated deformed Glass FRP (GFRP) rebars and UHPC using double-row splice tests, with parameters including bar diameter, splice length and lap clearance. Failure modes including the pullout of GFRP rebars and the splitting of UHPC were identified. For cases of pullout failure, the average bond strengths in samples with splice lengths of 5db were reduced by 17.6-22.1% compared to those of 2.5db. Increasing the lap clearance from 0 to 1db and 2db led to 11.1% and 30.2% increases in average bond strengths. Furthermore, average bond-slip models for lapped sand-coated deformed GFRP rebars in UHPC were developed. The predicted curves matched the experimental ones, showing errors within 20% for both average bond stresses and slips. When the cover is not less than 2db, the splice length is recommended to be at least 15db for sand-coated deformed GFRP rebars with diameters of 10mm to 16mm in UHPC, approximately 1.25 times the corresponding development length proposed by the existing research.