Shrinkage Reducing Agent Research Articles

Effect of shrinkage-mitigating additive and curing condition on flexural and fracture behavior of ultra-high-performance concrete (UHPC) unnotched beam

The study aims to examine how the flexural and fracture behavior of UHPC is impacted when shrinkage is mitigated by adding shrinkage-mitigating additives. Furthermore, due to the consistent use of UHPC for structural repair and reinforcement throughout the year, including emergency construction in winter, it is necessary to carry out construction operations in winter conditions. Thus, this study adopts the natural cold curing condition of UHPC specimens to mimic real-world outdoor construction settings, while also using the standard curing condition as a comparison. The bending test was performed on three different types of UHPC materials: material 1 without a shrinkage-reducing agent (SRA) or expansive agent (EA), material 2 with 1 % SRA, and material 3 with 1 % SRA and 7.5 % EA. Fracture and flexural behavior of UHPC beams were studied, and Spearman's correlation between shrinkage and flexural/fracture toughness was evaluated. The study revealed that adding SRA/EA decreased the mean flexural tensile strength of specimens cured in standard conditions. Additionally, specimens cured in natural conditions showed less flexural tensile strength when SRA/EA was added. Furthermore, when compared to material 1, the addition of SRA and EA greatly reduced the fracture energy of UHPC, resulting in reductions of 21.9 % and 26.6 %, respectively, for materials 2 and 3. The fracture toughness showed a modest correlation with the shrinkage behavior, and the fracture energy exhibited a high association with the shrinkage behavior. The research findings can provide references for UHPC applications in natural winter conditions when the material contains shrinkage-mitigating additives.

Effects of cooking oil on the shrinkage-reducing of high-strength concrete

Autogenous shrinkage is a serious problem for high-strength concrete, which may lead to early-age cracking. Shrinkage-reducing agents are typically used to mitigate the autogenous shrinkage of concrete. However, some negative effects, such as unstable workability and the reduction of compressive strength, will be caused. In this study, emulsified or plain cooking oil is used as a shrinkage-reducing agent in low water-binder ratio concrete. Deformational behaviours of concrete with cooking oil and normal commercially available shrinkage-reducing agent are investigated. Experimental results show that the utilization of cooking oil could significantly reduce the autogenous shrinkage of high-strength concrete due to the reduction of surface tension. Additionally, emulsified cooking oil is better than normal shrinkage-reducing agents and plain cooking oil in many aspects of the concrete. Micro-structure of the concrete with different shrinkage-reducing agents is also observed. Emulsified cooking oil is considered a promising admixture for the mitigation of autogenous shrinkage of high-strength concrete.

Early-Age Shrinkage Stress of Alkali-Activated Cement-Free Mortar Using Shrinkage Reducing Agent and Expansive Additive

Cement-free concrete has a superior physical performance, such as in its strength and durability, compared to OPC concrete; however, it has the disadvantage of large shrinkage. Large shrinkage can cause cracks due to shrinkage stress in the long term. In this study, a shrinkage reducing agent (SRA) was used to reduce the shrinkage of cement-free mortar; its content was increased from 0.0 to 1.5%. For an SRA content of 1.0%, a calcium sulfoaluminate (CSA) expansive additive (EA) (2.5, 5.0, and 7.5%) was added. To calculate the shrinkage stress of cement-free mortar using the SRA and EA, the compressive strength, elastic modulus, and total and autogenous shrinkage were measured. The unit shrinkage stress of cement-free mortar was obtained by multiplying the elastic modulus by the length change and accumulated to obtain the shrinkage stress acting on the mortar according to the age. The shrinkage stress of cement-free mortar showed different tendencies as the age increased. At early ages, the shrinkage rate of the mortar occupied a large proportion of the shrinkage stress. In the long term, the shrinkage stress was significantly affected by the elastic modulus. As a result, SRA was found to be effective in reducing the shrinkage stress by decreasing both the elastic modulus and shrinkage. However, EA increased the shrinkage stress over the long term due to an increase in the elastic modulus even though it compensated for early-ages shrinkage.

High-Performance Materials Improve the Early Shrinkage, Early Cracking, Strength, Impermeability, and Microstructure of Manufactured Sand Concrete

The poor early shrinkage and cracking performances of manufactured sand concrete, waste powder concrete, and recycled aggregate concrete are the main difficulties in engineering applications. To solve these problems, early shrinkage and cracking, strength, and impermeability tests were performed on high-volume stone powder manufactured sand concrete mixed with fly ash and slag powder (FS), a shrinkage-reducing agent (SRA), polyvinyl alcohol (PVA) fibers, and a superabsorbent polymer (SAP). Furthermore, the microstructures and pore structures of these concretes were revealed using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results showed that the mixture of FS, SRA, PVA fibers, and SAP could effectively inhibit the shrinkage strain and cracking area of the concrete. The effect of the SAP on reducing the early shrinkage of the concrete is the greatest, and the shrinkage strain can be reduced by 76.49%. The PVA fibers had the most obvious effect on inhibiting the early cracking of the concrete, and the total cracking area was reduced by 66.91%. Significantly, the incorporation of the FS can improve the particle gradation and the pore structure and improve its compactness. The PVA fibers not only provide good carriers for cement-based materials but also enhance the bonding force between the particles inside the concrete, filling the pores inside the concrete, inhibiting the loss of water, and reducing the generation of internal microcracks. The FS and PVA can reduce the shrinkage and cracking risk and improve the strength and impermeability of the concrete. Although the SRA and SAP can reduce the shrinkage and cracking risks, it will lead to a significant decrease in the later strength and impermeability. The main reason is that the SRA leads to an increase in micropores in the matrix and microcracks near the aggregate, which are not conducive to the development of the strength and penetration resistance of the MS. Similarly, the SAP can promote the rapid formation of ettringite (Aft) at an early age and improve the early shrinkage, early cracking, and early strength of the concrete. However, with an increase in age, the residual pores, after SAP dehydration, will cause the deterioration of the concrete pore structure, resulting in the deterioration of the strength and impermeability.

Preparation and performance analysis of polycarboxylate superplasticizer modified with fluorine-containing monomer and silicon dioxide nanoparticles

With the development of technology, the performance requirements for building materials in the modern construction industry are increasing. Nanomaterials and polycarboxylate superplasticizers (PCE) have good applicability in this field. Therefore, we develop a composite material by incorporating a fluorocarbon surfactant (FS) as a shrinkage-reducing agent into the PCE and modifying it with silicon dioxide nanoparticles (nano-SiO2) (SiO2-FS-PCE). Moreover, we investigate the preparation, dispersity, flowability, rheological properties, adsorption performance, and microstructure of the SiO2-FS-PCE composite. We observe that introducing an appropriate concentration of fluorine-containing monomer can effectively reduce surface tension in the solution and inhibit the shrinkage of the slurry. The rheological properties of the SiO2-FS-PCE1 slurry decrease significantly with time. When the dosage of nano-SiO2 exceeds 20%, the silicon hydroxyl groups on the material’s surface tend to polymerize, which affects the adsorption and dispersion of the superplasticizer, thereby reducing its fluidity. As the dosage of nano-SiO2 increases, there is a trend of increasing friction of SiO2-FS-PCE, followed by a decrease. This change is closely related to changes in the adsorption and morphology of SiO2-FS-PCE, providing higher adsorption sites than other materials. In conclusion, these findings provide insights for a deeper understanding of the synthesis and properties of nanocomposite materials, thereby offering a theoretical basis for further optimization of their preparation and performance.

Synthesis, performance and mechanism of novel polymer-type shrinkage reducing agents for cement-based materials

Simplifying the synthesis process and preparing a new type of shrinkage reducing agent (SRA) with a low dosage and high efficiency are beneficial for promoting the development of SRA and its application in cement-based materials. This study aims to synthesize three novel polymer-type SRAs with diverse structures through free radical copolymerization and to investigate their performance and working mechanisms in cement-based materials. Results clearly showed that the three synthesized SRAs reduced the surface tension of pore solution, and increased the flowability of cement paste. The SRAs-1 with butyl resulted in higher flowability of cement paste due to lower surface tension. Their addition at a low dosage of 0.5% by cement mass effectively mitigated the shrinkage of cement mortar. Among the three, SRAs-1 with butyl exhibited a higher capability of reducing drying shrinkage due to lower surface tension, lower porosity in the range of 2.5–50 nm, and lower total porosity.

Sustainable Use of Gum Acacia as a Biopolymeric Additive in Ultra‐High Performance Concrete

The main objective of this research is to analyze whether biopolymer (gum acacia) can be used as an admixture for ultra‐high performance concrete (UHPC) and to elucidate the strength, durability, microstructure, and transport properties of biopolymer (gum acacia) incorporated UHPC mixes in combination with the shrinkage reducing agent (SRA). The mechanical, thermal, and durability aspects of UHPC were studied at different ages and curing conditions by adding gum acacia in combination with the SRA. After 28 days under hybrid curing, the compressive strength increased by 22.19% and the flexural strength increased by 41.59% for 1% biopolymer addition. The highest strength and durability were obtained using the hybrid curing procedure using superplasticizer and gum acacia biopolymer at a water‐binder ratio of 0.35. With an improved microstructure, the results revealed improved hydration and durability as revealed through the scanning electron microscopic (SEM) images. The SEM photographs of the concrete showed more polymorphic patterns and crystals overall relative to the UHPC with SRA, while exhibiting little to no microfractures. Through adjustment of the biopolymer proportion and adoption of a suitable curing method, this research presents a new strategy for addressing the negative impact produced by the usage of SRA in UHPC.

Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete

Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete

Study on the Influence of Shrinkage-Reducing Materials on the Volume Stability of Shotcrete with a Fluorine-Containing Alkali-Free Accelerator.

In contrast to ordinary concrete, shotcrete exhibits greater shrinkage deformation. The utilization of an aluminum fluoride alkali-free accelerator (AF) is prevalent in tunnel engineering, attributed to its economical nature and fast setting and hardening. Currently, there is a dearth of research on the volume stability of aluminum fluoride accelerators, and no relevant studies have been conducted on the application of shrinkage-reducing materials in shotcrete using an aluminum fluoride accelerator. With the use of an aluminum fluoride accelerator, the early strength of shotcrete is reduced, and the addition of a shrinkage-reducing agent (SRA) and super-absorbent polymer (SAP) can also lead to a further reduction in the early strength of concrete. Therefore, this study aims to investigate the influence of these two shrinkage-reducing materials (SRA and SAP) on the workability and mechanical properties of shotcrete. The primary focus of this research is to determine the better compensation effect of the two shrinkage-reducing materials. To accomplish this, the study focuses on assessing the setting time, compressive strength, and volume stability of shotcrete that has been mixed with an aluminum fluoride accelerator using SRA and SAP. Additionally, we also aim to explore the hydration and shrinkage compensation mechanism of these shrinkage-reducing materials on shotcrete by conducting a microscopic test analysis.

Effects of shrinkage reducing admixture and internal curing agent on shrinkage and creep of high performance concrete

The shrinkage and creep behavior of track beam concrete have the significant influence on the stability and safety of train operation. While superabsorbent polymer (SAP) and shrinkage reducing agent (SRA) are two commonly used admixtures in such high-performance concrete. So, the shrinkage and creep behavior of concrete with SRA or SAP were studied in this paper. Moreover, The microstructure of the interfacial transition zone (ITZ) observed by the scanning electron microscope (SEM) was discussed for the improvement of the mechanical properties of the concrete after the creep test. The experimental results indicate that SRA has a positive effect on reducing the shrinkage and creep deformation of concrete, and it is beneficial to the improvement of long-term strength and elastic modulus with little influence on creep recovery. In contrast, SAP reduces shrinkage, but increases the creep of concrete with less creep recovery and higher residual stress. Meanwhile, the fib 2010 model was revised to improve the ability to predict the creep of concrete containing SAP and other admixtures. Besides, it was found concrete after creep test has better mechanical properties, and the improvement of sample with SAP is the most obvious. The analyses of SEM also conformed that the concrete after creep test has a higher degree of hydration, and the denser ITZ microstructure.

Drying shrinkage behavior of cement mortar under low vacuum conditions

In this work, the time-dependent drying shrinkage behaviors of cement mortar under low vacuum and standard drying conditions were tested and compared, in which the specimens were prepared based on various mixtures. Also, a series of microscopic tests were conducted to investigate the hydration and microstructure of the prepared specimens, and thus, to explain the drying shrinkage behavior of different specimens. The results showed that compared with standard drying condition, the specimens under the low vacuum condition exhibited higher drying shrinkage and mass loss, but lower sensitivity of drying shrinkage to mass loss. Under both conditions, the incorporation of fly ash and silica fume or shrinkage-reducing agent could greatly decrease the drying shrinkage, with the better performance identified in the case of fly ash and shrinkage-reducing agent; while the addition of sulphoaluminate cement had no inhibiting effect on the drying shrinkage deformation. Although the specimen solely based on sulphoaluminate cement showed the lowest drying shrinkage under standard drying condition, it exhibited greater drying shrinkage than the Portland cement specimens under low vacuum conditions. The microscopic test results suggested that low vacuum treatment could decrease the hydration degree while the decomposition of ettringite in the sulphoaluminate cement could be observed under low vacuum conditions. Besides, the gel pore volume fractions decreased while the cumulative total pore volume increased after low vacuum treatment, which resulted in a loose and porous microstructure with high vulnerability to drying shrinkage.

Impact of High-Performance Expansion and Shrinkage-Reducing Agents on the Mechanical Properties and Shrinkage Compensation of High-Strength Concrete

A large number of binder ingredients such as cement and active mineral admixtures are used in the preparation of high-strength concrete, and the water:binder ratio is extremely low. This leads to a large amount of shrinkage of concrete at the early stage of curing, which poses a great threat to the safety and durability of the structure. To solve the cracking problem of high-strength concrete induced by high shrinkage, we choose to change the admixture to solve it. In this study, a high-performance expansion agent (HPEA) and shrinkage-reducing agent, which are currently studied in a small number, were selected by changing the way of admixture, and their effects on the strength and shrinkage of high-strength concrete were compared and analyzed. The results show that the addition of a HPEA is beneficial to the compressive strength of concrete and sufficient expansion can be obtained by using a high amount of HPEA, but there is an excessive and delayed expansion to produce cracks in the later stage. A shrinkage-reducing agent plays an adverse role in the development of concrete strength, but it performs better in inhibiting shrinkage. The combination of a HPEA and shrinkage reducing agent can largely avoid the formation of cracks, and the two have a certain synergy. The main reason is that a HPEA compensates for some of the negative effects of a shrinkage-reducing agent on concrete strength, and the shrinkage-reducing agent further strengthens the inhibition effect of a HPEA on concrete shrinkage, and to some extent avoids the risk of cracks caused by delayed expansion caused by admixture problems.

Concrete Shrinkage Analysis with Quicklime, Microfibers, and SRA Admixtures

This research explores the effect of various humidity conditions and the efficiency of shrinkage-reducing admixtures on the free shrinkage strain of ordinary Portland cement (OPC) concrete and its mechanical properties. An OPC concrete C30/37 mixture was replenished with 5% of quicklime and 2% of organic-compound-based liquid shrinkage-reducing agent (SRA). The investigation revealed that a combination of quicklime and SRA led to the highest reduction in concrete shrinkage strain. Polypropylene microfiber addition was not so effective in reducing the concrete shrinkage as the previous two additives did. The prediction of concrete shrinkage without quicklime additive was performed according to EC2 and B4 model methods, and the obtained results were compared with the experimental ones. The B4 model evaluates the parameters more than the EC2 model does and, therefore, was modified to calculate the concrete shrinkage for the case of variable humidity and to evaluate the effect of quicklime additive. The experimental shrinkage curve that best coincides with the theoretical one was that obtained by the modified B4 model.

Research on behavior mechanism and performance of concrete shrinkage reducing agent

The research on the function and mechanism of shrinkage reducing agent shows that shrinkage reducing agents can greatly reduce the shrinkage rate of concrete without adversely affecting the mechanical properties of concrete. The mechanism of the shrinkage-reducing agent was tested and analyzed from the water evaporation rate of the solution and the surface tension of the solution. The results showed that the addition of the shrinkage reducing agent could significantly reduce the surface tension of the aqueous solution, and had little effect on the evaporation rate of the water on the surface of the aqueous solution; the surface tension test shows that the mechanism of shrinkage reducing agent reducing drying shrinkage is mainly to reduce the surface tension of pore solution; the analysis from the water evaporation rate test shows that shrinkage reducing agent has no significant effect on water evaporation inhibition, and inhibiting concrete moisture evaporation is not the most commonly used shrinkage reducing agent reduction mechanism.

Preparation and Experimental Investigations of Low-Shrinkage Commercial Concrete for Tunnel Annular Secondary Lining Engineering

Secondary lining concrete is frequently used in underground tunnels. Due to the internal restriction of the annular concrete segment, micro-cracks may be caused by temperature stress and volume deformation, thus affecting the safe transportation of the tunnel. The purpose of this study is to provide a concrete experimental basis with low hydration heat and low shrinkage for tunnel engineering with different construction requirements. Different amounts of expansion agent (EA), shrinkage-reducing agent (SRA), and superabsorbent polymer (SAP) were considered in commercial concrete. It was found that EA elevated the degree of hydration and the hydration exothermic rate, while SRA and SAP showed the opposite regularity. SRA has the optimum shrinkage reduction performance with a 79% reduction in shrinkage, but the strength decreases significantly compared to EA and SAP groups. The effect of the combination of different shrinkage reducing components in commercial concrete is instructive for the hydration rate and shrinkage compensation in secondary lining engineering.

Mitigation on the shrinkage properties of ultra-high strength concrete via using porous coral sand and shrinkage reducing agent

This work used porous coral sand aggregate (PCSA) and shrinkage reducing agent (SRA) in hybrid systems in order to compensate high shrinkage of ultra-high strength concrete (UHSC). Accordingly, the flowability, setting times, mechanical properties autogenous shrinkage and drying shrinkage of UHSC incorporating PCSA and SRA were studied. Moreover, Scanning electron microscopy (SEM) and Mercury intrusion porosimeter (MIP) were used to characteristic the microstructure development. The results showed that pretreated PCSA improved the fluidity and compensate the autogenous and drying shrinkage, while it decreased the compressive strength of UHSC. The addition of SRA exhibited similar trend. The hybrid system of PCSA and SRA were beneficial to the fluidity and compensated the autogenous and drying shrinkage significantly, whereas it had slightly adverse effect on the compressive strength of UHSC. It was also found that, due to the synergistic effects of internal curing by PCSA and reduction effect by SRA, the dense microstructure and increased of the distribution of large capillary pores in UHSC were effectively mitigation on the autogenous shrinkage. Overall, the specimens with 45% PCSA and 1.0% SRA had the minimum autogenous and drying shrinkage.

Solving shrinkage problem of ultra-high-performance concrete by a combined use of expansive agent, super absorbent polymer, and shrinkage-reducing agent

To solve the cracking and interface debonding problems of ultra-high-performance concrete (UHPC) induced by high shrinkage in confined spaces or under strongly restrained conditions, a series of laboratory experiments was performed to evaluate the use of a CaO-based expansive agent (EA) in combination with a super absorbent polymer (SAP) and/or a shrinkage-reducing agent (SRA) to obtain expansive UHPC. The mechanisms underlying these techniques were also investigated. The test results showed that sufficient expansion was obtained by using a high dosage of CaO-based EA in UHPC, but the samples exhibited cracks owing to excessive and delayed expansion. The addition of SAP significantly enhanced the expansion effect of EA in UHPC. Autogenous shrinkage after 3 d and drying shrinkage within 180 d were effectively reduced by using SRA. Moreover, expansive UHPC was achieved by the combined use of EA, SAP, and SRA, in which excessive and delayed expansion was avoided. This was mainly attributed to i) increased initial expansion by using SAP for the reaction of CaO-based EA and ii) reduced later-age autogenous and drying shrinkage by adding SRA.

Improving mechanical properties and shrinkage cracking characteristics of soft clay in deep soil mixing

Deep soil mixing is a ground improvement method that enhances the characteristics of soft soils by mechanically mixing the soil with cementitious binders such as cement and fly ash (FA). The objective of this paper is to investigation the post-treatment mechanical properties and shrinkage cracking characteristics of soft Bangkok clays treated with ordinary Portland cement (OPC) and FA. Unconfined compressive strength, modulus of elasticity, and shrinkage cracking after 7 and 28 days of mixture curing were measured. The effects of wet/dry cycling on the durability of mixtures were examined. Microstructures of treated soft clays were examined using scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) techniques. Test results showed that strength and stiffness improvements of stabilised soft clays increased with OPC content but decreased with FA content, while the extent of sample shrinkage decreased with increasing FA content. Based on these results, we propose the preliminary guideline of applying 15% replacement of OPC with FA to obtain the optimal mixture ratios that allows FA to act as a shrinkage-reducing agent for deep soil mixing purposes. By adding OPC and 15% FA at a binder-per-water ratio (B/wc) of 0.4, the stabilised soft clay satisfied both strength and shrinkage cracking criteria for deep soil mixing purposes. SEM/EDX analyses further supported these experiment results. In addition, correlations between the mechanical properties and the chemical compositions of stabilised soft clay were derived and presented.

Mechanical performance and autogenous and drying shrinkage of MgO-based recycled aggregate high-performance concrete

The high strength and durability of high-performance concrete (HPC) may be significantly reduced by shrinkage cracking. The use of reactive magnesium oxide (MgO) can reduce shrinkage of cement-based materials due to its expansive properties. This study intends to analyse the validity of MgO as shrinkage-reducing agent in recycled aggregate HPC. To do so, ten HPC mixes with 0%, 25%, and 100% of both early-age (7-days air curing) and matured (6-month air curing) RA were produced. In half of the mixes, 10% ordinary Portland cement was replaced with MgO. The use of MgO slightly worsened the mechanical behaviour of HPC, especially when combined with large amounts of RA. On the other hand, the expansion of MgO fully offset the autogenous shrinkage of HPC and reduced total shrinkage by around 20–40%. Water storage of RA, and its deferred release over time, produced a more efficient hydration of MgO, which in turn led to a further reduction of autogenous shrinkage. However, the increase of drying shrinkage caused by RA was greater than this decrease of autogenous shrinkage due to MgO, so the higher the RA content of HPC the lower the total shrinkage reduction when adding MgO. Thus, the decrease of total shrinkage caused by MgO was compensated by the shrinkage increase because of RA when adding amounts above 35% early-age RA and 42% matured RA. Therefore, despite the suitability of MgO as shrinkage-reducing agent in recycled aggregate HPC, its effectiveness was reduced with increasing amounts of RA.

Effect of polyethylene glycol on chloride binding in mortar

As a widely used chemical admixture, polyethylene glycol (PEG) is often added to concrete as a self-curing or shrinkage-reducing agent. PEG with a low molecular mass can inhibit the corrosion of chloride by increasing the viscosity of the pore solution. The chloride binding capacity of the cement matrix significantly affects the service life of reinforced concrete owing to its high correlation with the concentration of free chloride. However, the influence of PEG on the chloride binding capacity of cement-based materials remains unclear. Through chloride concentration profiles, the assessment of solid phase content based on the TGA/XRD/reference intensity ratio method, and SEM morphology analysis, this study reveals the influence of PEG on chloride binding in mortar. The addition of PEG significantly reduced the chloride binding capacity of the cement matrix. Complexing Ca2+ on the surface of calcium silicate hydrate (C-S-H), to occupy the adsorption sites of chloride, reduces the physical adsorption capacity and the chemical binding ability of the matrix by inhibiting the conversion of ettringite (AFt) to monosulfoaluminate (AFm). Moreover, the addition of PEG spheroidizes C-S-H and reduces its particle size, leading to loose packing of C-S-H in the mortar. Thus, the findings of this study suggest that when PEG is used in cementitious materials, caution and corresponding measures are needed to optimize its impact on durability.