Shrinkage Mitigation Research Articles

Flexural post-cracking performance of macro synthetic fiber reinforced super workable concrete influenced by shrinkage-reducing admixture

Most literature has focused on the effect of shrinkage-reducing admixture (SRA) in shrinkage mitigation resistance of concrete. This study aims to examine the impact of SRA on the efficiency of macro synthetic fibers (MSF) in enhancing the flexural post-cracking behavior of fiber-reinforced super workable concrete (FR-SWC). A comparative analysis of the influence of fiber combinations on the flexural post-cracking behavior of beams is also included. Results showed that a higher dosage of SRA, particularly at 5 % by mass of binder, had a noticeable negative impact on flexural post-cracking performance of beams while exhibiting positive effect on workability and shrinkage reduction. However, incorporating low dosages of SRA (1.25 % by mass of binder) did not have a significant impact on the ability of MSF. This was attributed to the reduction of the MSF-matrix bond strength caused by a significant delay in cement hydration. The characteristics of selected MSF type, including length and surface roughness had a positive effect on the post-cracking performance of FR-SWC, regardless of SRA dosage. The notched beams made with 100 % MSFA outperformed those made with fiber combination of 25 % MSFA and 75 % MSFB. Beams made with 100 % MSFA showed 55 % higher residual flexural tensile strength, 49 % higher equivalent flexural tensile strength, 50 % higher fracture energy, and 35 % higher equivalent flexural strength ratio compared to beams made with fiber combination of 25 % MSFA and 75 % MSFB. Therefore, the negative effect of SRA on the flexural-post cracking behavior can be partial compensated by adjusting MSF content and combinations.

3d Mapping Of Stiffness Evolution Of Hardening Concrete With Saps Using Elastic Wave Tomography

Phenomena occurring during the delicate phase of concrete curing can have a strong influence on the final mechanical properties. Therefore, monitoring the changes during hydration can provide meaningful information on the material properties. Lately, non-destructive techniques have received great attention for monitoring earlyage concrete. This paper aims to assess the ultrasonic velocity and stiffness development of hardening concrete during various curing stages using the Elastic Wave Tomography (EWT) technique. The monitoring of the curing process starts as soon as seven hours after casting and lasts up to seventy hours. A three-dimensional (3D) wave velocity map is created, and conventional concrete is compared to concrete containing SuperAbsorbent Polymers (SAPs), a novel admixture used for shrinkage mitigation by providing internal curing in the cementitious matrix. However, SAPs have been proven to reduce compressive strength when added to concrete, due to the increased porosity they induce. This porosity may also result in the reduction of the wave velocity. However, the internal curing provided by the SAPs can promote the formation of new hydration products in the matrix and thus (partly) compensate for the strength loss making the uniformity of the internal curing another important point of concern. EWT can provide global information on the homogeneity of the influence of the SAPs in the cementitious matrix as opposed to the wave velocity of a single wave path that is usually examined in practice. In addition, the determination of the early-age stiffness evolution can be connected to the final mechanical properties of the material. The dynamic Young’s Modulus is calculated and compared to the static Young’s modulus at 28 days. Predictions towards the static Young’s modulus are also made, showing good agreement.

Exploring the role of SAP chemical composition in the internal curing of high-performance cementitious materials

This study investigates the impact of the chemical composition of superabsorbent polymers (SAPs) on their effectiveness in internal curing within high-performance cementitious materials. Although the use of commercial SAPs in cementitious systems has been widely researched, there is still no consensus on how different SAP structures influence material properties. For the first time, this research employs photoinitiated free radical polymerization technology to synthesize three structurally distinct SAPs: SAP with sulfonic acid groups (PAMPS), SAP with amide groups (PAM), and SAP with carboxyl groups (PAAs). The effects of these SAPs on the cement hydration process and microstructure were examined by analyzing their water absorption behavior in cement filtrate. The residual cation content on the SAP surface was evaluated using EDS, while XRD and TGA were used to study how SAP structure affects cement hydration products. Furthermore, the impact of these SAPs on the strength and autogenous shrinkage of the material was investigated. The results indicate that PAMPS, with its sulfonic acid groups, exhibited stable water absorption performance in the alkaline cement environment, promoting hydration reactions and increasing the formation of needle-shaped C-S-H. This stability contributed to mitigating the negative effects on mechanical properties. While the inclusion of SAPs generally reduced the strength of the cement matrix, PAMPS was the most effective in mitigating autogenous shrinkage, achieving a shrinkage mitigation efficiency of 86 %. These findings highlight the importance of SAP chemical structure in influencing cement hydration and material performance, offering insights for the development of effective internal curing agents to enhance high-performance concrete.

Shrinkage behaviour of high-strength concrete plates reinforced with carbon textile reinforcement

Carbon textile reinforcement is a relatively new type of CFRP reinforcement which, when utilized with high-strength concrete, leads to the production of ultra-thin free-form concrete shells. However, such reinforcement usually suffers from weak resistance to compressive stresses, while high-strength concrete is susceptible to high shrinkage rates. This combination may lead to a boor shrinkage behaviour, and thus an excessive shrinkage-related craking. Therefore, this paper aims to study the shrinkage behaviour of high-strength concrete plates reinforced with carbon textile reinforcement. Additionally, the utilization of shrinkage-compensating concrete as a possible shrinkage mitigation method was also investigated. For this aim, twelve concrete plates of dimensions 500 mm × 150 mm x 30 mm were cast. The shrinkage and expansion behaviour of the specimens were monitored for six months using the distributed fibre optic sensor (DFOS) technology, and then all the specimens were tested till failure under a direct tension test. The results have revealed that the existence of textile reinforcement does not provide any significant resistance to the negative strains generated from the shrinkage of concrete, which, for restrained concrete plates, leads to the formulation of wide cracks. On the other hand, the utilization of shrinkage-compensating concrete not only eliminates the formulation of shrinkage-related cracks but also reduces the crack’s width resulting from the loading process by up to 35 % during all stages of loading as illustrated by the fibre optic sensors measurements. Additionally, shrinkage-compensating concrete exhibits a slightly higher compressive strength than normal concrete.

Enhancement of concrete performance and sustainability through incorporation of diverse waste carpet fibres

Carpet fibres have demonstrated the potential to mitigate early-age cracking and improve tensile properties in concrete. However, a detailed analysis of the varied types of standard carpet fibres in reinforced concrete has been lacking. This study aims to bridge this gap by investigating the performance of concrete reinforced with widely used waste carpet fibres, namely Nylon, Polypropylene, Polytrimethylene terephthalate, and Polyester. The study employs fibres at 0.3 % and 0.5 % volume fractions with a 12 mm length. The research examines mechanical properties, shrinkage and cracking behaviour, pore structure, microstructure, and the ITZ. Results show that 0.3 % fibre volume yielded optimal performance based on GRA analysis. All fibre types reduced shrinkage compared to the control with no fibres. Nylon T1 at 0.3 % achieved a 22.3 % reduction at 90 days. Furthermore, fibre inclusion enhanced flexural and splitting tensile strengths up to 12 % and 39 % respectively due to fibre bridging, pore refinement, and reduced porosity. Notably, individual fibre mechanical properties influenced concrete performance significantly. Hydrophilic fibres exhibited a thinner 10 µm ITZ compared to 15 µm for hydrophobic fibres, contributing to denser interfacial regions and improved bonding. This study demonstrates the potential of carpet fibre-reinforced concrete as a sustainable solution, offering enhanced mechanical properties, shrinkage mitigation, and effective utilization of carpet waste, addressing critical issues in construction and waste management sectors.

Rheology control and shrinkage mitigation of 3D printed geopolymer concrete using nanocellulose and magnesium oxide

3D printing concrete (3DPC) is an emerging technology that produces concrete using digital method and has revolutionized the traditional labor-intensive construction mode. However, the free formwork printing and layer-by-layer production of 3DPC induce severe shrinkage and plastic cracking during the early ages, especially for the geopolymer based materials. This research utilizes the nano-fibrillated cellulose (NFC) with the combination of magnesium oxides expansive agent (MEA) to mitigate the plastic and drying shrinkage of 3D printing geopolymer concrete (3DPGC), while optimizing its rheological behavior. The results show that after modification with proper dosages of NFC and MEA, 3DPGC showed reduced plastic and drying shrinkage at early ages, with improved printability, buildability, and mechanical strength. The underlying role of NFC and MEA on the performance of 3DPGC was thoroughly analyzed with rheometry, calorimetry, scanning electron microscopy, and internal humidity test. The water retention ability of nanocellulose can provide more moisture at early ages, thus mitigating cracking, while MEA can compromise the drying shrinkage at later ages. The contribution of the study shed light on the application of nanocellulose and MgO to increase the volume stability and mechanical performance of 3D printing geopolymer concrete.

Drying shrinkage mitigation of alkali-activated blast furnace slag-copper slag by polyether-based shrinkage reducing admixture and MgO-based expansion agent

Volume stability is a critical challenge for the practical applications of alkali-activated materials. To mitigate the drying shrinkage of alkali-activated blast furnace slag-copper slag (AAS-CS), different contents of polyether-based shrinkage reducing admixture (PSRA) and MgO-based expansion agent (MEA) are used in this study. The effects of PSRA and MEA on the hydration process, mechanical property and drying shrinkage are investigated. Meanwhile, the mechanisms for drying shrinkage compensation of PSRA and MEA are deeply analyzed by nuclear magnetic resonance (NMR), Fourier transform infrared spectrum (FTIR), thermogravimetry and differential scanning calorimetry (TGA/DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). Results show that the drying shrinkage rate and the compressive strength of AAS-CS gradually decrease with the PSRA content increases from 0 to 2.0 wt%. This is mainly attributed to the coarser pore size and the lower surface tension caused by PSRA. When the content of MEA is 4.0 wt%, AAS-CS exhibits the lower drying shrinkage rate and the higher compressive strength in comparison with the reference sample. The addition of MEA promotes the formation of hydrotalcite (Ht). As an expansive product, an appropriate amount of Ht can exert the filling effect and the shrinkage compensating effect.

Continuous monitoring of the moisture, shrinkage, and carbonation effects on foam concrete performance

The carbonation of conventional concrete is a slow process that generally affects exposed surfaces, however, this reaction is significantly facilitated in foam concrete because of its highly cellularized cementitious matrix. Coupled with the rapid moisture loss, foam concrete tends to exhibit drastic compositional, dimensional, and mechanical changes over a short period of time, highly contingent on environmental conditions. In this study, we investigated the change in the shrinkage, resonant frequency, compressive strength, and carbonation degree of foam concrete at various density levels (2.0, 1.0, and 0.6 g/cm3), under 50% and 100% relative humidity conditions, over 84 days. Under each condition, a physical and a chemical approach (sand and shrinkage-reducing admixture, respectively) were compared to determine the most suitable shrinkage mitigation. The results show that foam concrete undergoes intensive shrinkage within a couple of days when exposed to ambient conditions, with higher values present for the lower density levels. While both mitigation approaches effectively restrain shrinkage of the 1.0 g/cm3 samples, the physical-based shrinkage mitigation can cause marked foam degradation to the 0.6 g/cm3 samples. Additionally, results indicate that, due to rapid carbonation of both Ca(OH)2 and C–S–H, substantial CO2 uptake can take place in foam concrete within 84 days.

Internal curing with superabsorbent polymer modified by nano SiO2: Shrinkage mitigation and microstructure refinement

The existing commercial superabsorbent polymer (SAP) products have the intrinsic defects of low internal curing efficiency and weakening strength. In this paper, a novel type of organic-inorganic composite SAP (SAPN) modified by nano SiO2 was designed and synthesized. The absorption-desorption kinetics of SAP-N in alkali pore solution were measured to evaluate the structural stability and water retention capacity. The water transport process and distribution of SAP-N in cement pastes were studied using 1H NMR and X-ray computed tomography. In addition, the effect of SAP-N on the autogenous shrinkage, microstructure, and compressive strength of cement pastes was investigated. The research results demonstrated that the incorporation of nano SiO2 could enhance the absorption capacity of SAP in pore solution. The water retention capacity of SAP-N was increased by over 50 % compared to commercial SAPC, despite the dissolution of a proportion of nano SiO2. SAP-N exhibited a low agglomeration degree but a high effective utilization rate of internal curing water in cement pastes, and thus mitigated effectively the self-desiccation and autogenous shrinkage. The hydration degree of cement pastes internally cured with SAP-N was significantly enhanced owing to the pozzolanic effect of nano SiO2, which enabled the in-situ repair of residual voids and reduced capillary pore size, thus improving the long-term compressive strength.

Early-age shrinkage assessment of cementitious materials: A critical review

With the advent of formwork-free construction technologies like 3D concrete printing, evaluating early-age shrinkage in cementitious materials has become more critical. This paper reviews different test methods for assessing early-age shrinkage. These methods are classified as contact-based, which includes measurement systems that must remain in physical contact with the test specimen or embedded sensors placed inside the fresh concrete, and non-contact-based, which includes optical-based approaches either using white light (digital image correlation) or laser beams. The working principles, advantages, and challenges of the techniques, particularly while handling fresh concrete are discussed. The different mechanisms contributing to early-age shrinkage are reviewed and the common shrinkage mitigation strategies are also pointed out.

The role of carbon nanotubes to reduce autogenous shrinkage of cement paste at different ages

The effects of carbon nanotubes (CNTs) on autogenous shrinkage of cement paste were explored. The additions of CNTs were 0.025%–0.125% of cement by mass. Results showed that the autogenous shrinkage of cement paste with 0.05% CNTs was lowest, 22.1% lower than PC. The autogenous shrinkages of CNTs blended cements were predicted based on the poroelastic model and poroviscoelastic model, respectively. The root mean square error (RMSE) of autogenous shrinkage prediction based on poroelastic model was 3 times higher than that of poroviscoelastic model, which indicated that poroviscoelastic model was more appropriate for predicting the autogenous shrinkage of CNTs-cement paste. The role of CNTs on shrinkage mitigation were analyzed by combination with microscopic tests and prediction results. Results indicated that CNTs possess distinctive mitigation effects at different curing ages, which were related to the CNTs contents.

Mitigation of autogenous shrinkage of alkali-activated slag mortar by stearate salts

The autogenous shrinkage of the stearates-modified alkali-activated slag (AAS) mortar was investigated in this study. The experimental results suggested that the maximum reduction (25 %) of autogenous shrinkage of AAS can be achieved by adding 0.5 wt% calcium stearate, while potassium stearate and sodium stearate seem less effective in decreasing shrinkage. According to the results obtained, the mechanisms of shrinkage mitigation are mainly associated with the retardation of hydration, the coarsening of pore structure, and the increased contact angle. It is estimated that the capillary pressure of pores was reduced by 30 % ∼ 60 % when stearates were used. However, the elastic modulus of AAS was reduced by 20 % due to the bubble-stabilizing effect of stearates, especially at higher dosages, which would partially offset its decreasing effects on autogenous shrinkage. It is also found that the traditional physical model could be used to predict the autogenous shrinkage of plain and modified AAS samples, provided the effect of both elastic and creep parts is considered.

Early-age deformation of hydrophobized metakaolin-based geopolymers

This study presents a novel strategy to simultaneously mitigate the early-age shrinkage and achieve hydrophobization of metakaolin-based geopolymer (MKG) pastes through the incorporation of organic admixtures including polydimethylsiloxane (PDMS) and sodium methylsilicate (SMS). The pore structure, wettability, moisture/water adsorption capacity, and internal moisture distribution are investigated through different techniques including MIP and LF-NMR. Results indicate that the autogenous shrinkage of MKG paste is reduced by 91.2 % and 41.6 % when adding 5 % PDMS and replacing with 20 % SMS, and the water contact angle increases to approximately 130° and 140°, respectively. The addition of organic admixtures significantly reduces the moisture adsorption and surface tension of the MKG matrix, and thus internal water tends to be transported into larger pores, leading to less liquid-vapor meniscus and lower capillary stress. Moreover, an underlying mechanism is proposed to explain the shrinkage mitigation of hydrophobized MKG paste, accounting for the moisture transfer tendency and internal stress distribution.

Microstructure refinement and shrinkage mitigation of alkali-activated slag paste by superabsorbent polymer

This paper investigates the effects of superabsorbent polymer (SAP) dosage, particle size, addition method, and absorption status on the properties and microstructure of alkali-activated slag (AAS) pastes. The results show that incorporating SAP can mitigate the autogenous shrinkage and short-term drying shrinkage of the AAS pastes, mainly depending on the SAP dosage and size. The release of activator can promote the geopolymerisation around the SAP particles, which improves the local micro-hardness of the pastes and reduces the amount of capillary pores. This consequently densifies the microstructure around the SAP particles and mitigates the shrinkage of the AAS pastes. The large SAP particles are found to release activator to a farther distance than the small ones, which is more effective in mitigating the autogenous shrinkage. The promoted conversion from mesopores to gel pores in the paste with large SAP is also beneficial to reducing the driving force of autogenous shrinkage. By contrast, the addition method and absorption status of SAP particles have marginal impacts on the autogenous shrinkage as the released activators travel a similar distance within the AAS pastes. Moreover, adding SAP particles increases the number of gel pores and macropores regardless of their size or absorption status, leading to an increased long-term drying shrinkage and a weakened mechanical property of the AAS paste. Overall, the findings of this study can guide the mix design and preparation of AAS materials with SAP.

Mechanisms of recycled fine brick aggregate in autogenous shrinkage mitigation, mechanical properties enhancement and microstructure improvement of alkali-activated slag-fly ash mortar

This study provides a profound comprehension of the influence of recycled fine brick aggregate (RFBA) as internal curing agent on autogenous shrinkage, mechanical properties and microstructure in the alkali-activated slag/fly ash (AASF) system. Specifically, the effects of RFBA on the setting time, flowability, compressive strength, flexural strength, autogenous shrinkage, and microstructure of AASF were investigated. The utilization of RFBA dramatically mitigates the autogenous shrinkage with an increase in compressive strength. As well as self-desiccation, the reduction of steric-hydration force and the structural incorporation of alkali cations in C-A-S-H are turned out to generate an enormous amount of autogenous shrinkage in AASF. In addition, it can be observed by the Nitrogen absorption test that the total pore volume is declined, and the pore structure is coarser with RFBA involved. Further, the phase composition acquired by X-ray diffraction (XRD) illustrates that the RFBA applied in AASF does not influence the type of reaction products but affects the quantity especially C-S-H and C-A-S-H gels. As Fourier transform infrared spectroscopy (FTIR) demonstrated, the polymerization degree of C-A-S-H gel is increased with the AASF containing of RFBA, and the chain length elongation of C-A-S-H is decreased.

Mechanical strength, shrinkage, and porosity of mortar reinforced with areca nut husk fibers

Cement-based materials perform well in compression but poorly in tension due to their brittleness. They also exhibit shrinkage cracking over time, which can be mitigated by incorporating fibers. Areca nut husk fiber (AHF) is agricultural waste, which is eco-friendly, light in weight, renewable, offers higher corrosion protection, and is a sustainable construction material. A novel application of AHF in a cement-based material has been undertaken. The effect of incorporating AHF (0%, 0.25%, 0.50%, 0.75%, and 1.0% by volume of mortar) on the properties of mortar was investigated. Workability, mechanical strength (compressive, tensile, and flexural), shrinkage, and porosity tests were performed. The results were compared to those obtained with jute and coir fiber mortars, as no data on mortar/concrete containing AHF have been reported. The mechanical strength of the mortar was increased at an AHF content of 0.5%. Beyond this level, the strength declined but was not lower than that of the control mix (0% AHF). Furthermore, significant shrinkage mitigation was observed with an increase in the AHF percentage. The porosity of the mortar increased with an increase in the content of AHF. This study reveals that 0.5% AHF can be used in mortar, given its excellent performance among all mixes.

Repurposing of blended fabric waste for sustainable cement-based composite: Mechanical and microstructural performance

In this study, the strength properties, shrinkage and microstructures of mortar incorporating blended fabric fibres were characterised via X-ray micro CT and nanoindentation. Three different hybrid recycled fabric fibres, namely Kevlar/Nomex, Kevlar/Nylon and Nomex/Nylon fibres were investigated at three different blend ratios (2:1, 1:1, and 1:2). The fibre content was maintained at 0.3 % for all mixes. The findings indicated that the optimum blend ratio for hybrid fabric fibres is 1:1. At this optimum fibre blend ratio, an enhancement by 2.7 %, 4.8 % and 5.9 % in compressive strength, together with 9.8 %, 12 % and 13.4 % in flexural strength of mortar are recorded, corresponding to the inclusion of hybrid Nomex/Nylon, Kevlar/Nomex and Kevlar/Nylon fibres respectively. Kevlar/Nomex fibres display no effect in drying shrinkage mitigation, irrespective of blend ratios. In contrast, Kevlar/Nylon and Nomex/Nylon fibres result in reducing 180-day shrinkage rates by up to 13.9 % and 11 % respectively. The hybrid fabric fibres were found to refine the pore network, especially the highly hydrophilic Kevlar/Nomex fibres. Also, an increase in curing days from 7 to 90 days densifies the microstructure near the fibre-matrix interface due to the growth of hydration products (LD/HD CSH and CH). These research findings can open the pathway for utilising textile waste in landfill as reinforcing members for cementitious matrices toward sustainable building and construction.

A novel apparatus and method for lab-scale study of wellbore integrity using CT imaging and analysis

Well drilling, completions, stimulation, and enhanced oil recovery operations induce downhole conditions that may negatively impact the integrity of the annular seal and consequently hinder zonal isolation. Thus, the ability to accurately quantify the evolution of the annular seal in response to the prevailing downhole environment is critical for the optimal design of the annular barrier for the life of a well. Thanks to increased accessibility and recent advancements in computing power and techniques, X-ray computed tomography has gained popularity as a non-destructive analysis method in materials science and geomechanics due to its ability to reveal details about the interior volume of objects in real-time without physical disassembly.Therefore, in this study, a novel apparatus is presented for the construction of a lab-scale wellbore, with the purpose of simulating downhole processes while simultaneously monitoring wellbore elements of interest in real-time via x-ray computed tomography. The benefits of this novel setup for wellbore integrity are demonstrated via applications to two test cases: the mechanical evolution of annular cement under stresses induced by cyclic water injection as a function of the mechanical properties of the cased and cemented wellbore system; the evaluation of nano magnesium oxide performance as an additive for autogenous shrinkage mitigation in annular cement.The results of the studies presented illustrate the benefits of combining x-ray computed tomography with lab-scale wellbore process simulations. The results of the cyclic water injection study suggest that residual strain in the cement is the major factor in annular seal degradation under cyclic downhole pressure fluctuations. Nano magnesium oxide is also shown to be very effective in preventing autogenous shrinkage of Class H cement. However, more study is required to characterize its effectiveness in a wider range of cement formulations. Finally, suggestions are offered on how to improve the experimental procedure presented while future potential applications of the apparatus are discussed.

Shrinkage mitigation of metakaolin-based geopolymer activated by sodium silicate solution

Geopolymers seem to be a good alternative to ordinary Portland cement to reduce the carbon footprint of the construction industry. However, their durability over time is still a subject of discussion. One of the major problems blocking their marketing is shrinkage, which can induce excessive cracking and circulation of aggressive agents. The aim of this study is to evaluate the autogenous deformation and desiccation shrinkage of a metakaolin-based geopolymer activated with sodium silicate solution. Several shrinkage measurement methods are used and criticized. Then, twenty-two formulas were tested to reduce shrinkage: varying the cure or the environmental conditions, changing the water-to-binder ratio, adding filler or fibres, incorporating chemical admixtures (plasticizers, water repellents, water retainers) or using curing products. Coupled with these results, showing a shrinkage reduction reaching 35 %, a model was developed to explain the involved mechanisms specific to geopolymers. It might offer prospects for improving the durability of geopolymers.

Effect of overlay thickness, fiber volume, and shrinkage mitigation on flexural behavior of thin bonded ultra-high-performance concrete overlay slab

This study investigated the flexural performance of 10 reinforced concrete slabs rehabilitated using thin ultra-high-performance concrete (UHPC) bonded overlay. The performance was compared to two slabs repaired using latex-modified concrete (LMC) that is widely used for bridge deck rehabilitation. Test parameters included the overlay thickness (25, 38, and 50 mm), fiber volume (2% and 3.25%), and shrinkage mitigation methods for the UHPC. The overlay slab specimens were stored outdoor for 30 months before conducting the four-point bending test. Experimental results indicated that the overlay slabs exhibited flexural failure pattern with yield of reinforcing steel, concrete crushing of the reinforced concrete substrate, and multiple cracks in the overlay. The use of UHPC thin bonded overlay enhanced cracking load by 295%–395% and flexural capacity by 35%–75% compared to the LMC overlay slabs. The maximum crack width of UHPC overlay slabs at the stage of the yield of reinforcement was less than 0.1 mm compared to 0.25–0.3 mm for the LMC overlay slabs. No slip occurred at the interface between the UHPC overlay and substrate, whereas the slip initiated following LMC overlay cracking. The increase of overlay thickness from 25 to 50 mm and fiber volume from 2% to 3.25% enhanced the flexural load capacity of the UHPC overlay slabs by 30%–40% and 10%–25%, respectively. These two strategies also reduced crack opening and propagation before the yield of reinforcing steel. The use of pre-saturated lightweight sand and CaO-based expansive agent was effective in mitigating autogenous and drying shrinkage without significantly influencing the flexural capacity of UHPC overlay slab.