Autogenous Shrinkage Of Ultra-high Performance Concrete Research Articles

Autogenous shrinkage prediction models and microstructure of UHPC with single or binary addition of an expansive agent and steel fibers

The low water/binder ratio of ultra-high performance concrete (UHPC) often results in its high autogenous shrinkage. Our study explored the effect of the single or binary addition of a CaO-based expansive agent (CEA) and steel fibers on flowability, compressive strength, flexural strength, microstructure, and autogenous shrinkage of UHPC. X-ray diffraction (XRD), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were applied to reveal the effects of CEA and steel fibers on hydration products and microstructure characteristics of UHPC. Experimental results show that the autogenous shrinkage of UHPC decreased markedly with the single or binary addition of CEA and steel fibers. Relative to the control group, autogenous shrinkage of UHPC with 2.5% dosage of single steel fibers, 6% dosage of single CEA, and binary addition of 2.5% steel fibers and 6% CEA decreased 17.8%, 10.9%, and 30.8% at 180 days, respectively. Steel fibers could enhance the mechanical performance of UHPC; nevertheless, they would decrease the flowability of UHPC. Meanwhile, the addition of CEA in the UHPC mixture not only maintained the mechanical properties and flowability but also decreased the autogenous shrinkage. Diffraction peak intensity and endothermic peak of Ca(OH)2 and the pore volume of 10–50 nm diminished with the content of CEA; however, that of C-S-H gel and ettringite increased. The prediction accuracy of nine shrinkage models (FHWA model, Lee model, Yoo model, JSCE model, B4 model, JonassonH model, Eurocode 2 model, CEB model, and DilgerW model) is analyzed with RE, Rnew2, and autogenous shrinkage of UHPC in this paper.

Retraction: “Effect of Crushed Granite, Superabsorbent Polymer, and Expansive Agent on the Workability, Compressive Properties, and Autogenous Shrinkage of Ultrahigh-Performance Concrete”

Retraction: “Effect of Crushed Granite, Superabsorbent Polymer, and Expansive Agent on the Workability, Compressive Properties, and Autogenous Shrinkage of Ultrahigh-Performance Concrete”

Development of low-carbon and cost-effective ultra-high performance concrete using carbonated recycled fine aggregate

This paper studied the influence of carbonated recycled fine aggregate (RFA) on mechanical and microstructural performance of ultra-high performance concrete (UHPC), aiming to develop a low-carbon and cost-effective UHPC. This includes the changes in strength, hydration kinetics, RFA-to-paste interfacial microstructure, and pore structure with the use of carbonated RFA. The environmental and economic effect of using carbonated RFA in UHPC is evaluated. The RFA content was investigated at 0–30%, by mass of total sand. Experimental results showed that a reduction greater than 10% in crushing index and water absorption of RFA was achieved by carbonation. The increase of carbonated RFA content from 0 to 30% led to 45% reduction in autogenous shrinkage of UHPC. The use of 20% uncarbonated RFA resulted in 12% and 10% reduction in 28-d compressive and flexural strengths, respectively, while such use of carbonated RFA can secure similar 28-d compressive and flexural strengths compared to those without RFA. Despite the reduced cement hydration, the use of carbonated RFA can secure a denser RFA-to-paste interfacial microstructure and refine the pore structure of UHPC compared to those made with uncarbonated RFA, given the chemical bonding and nucleation effect of carbonated RFA. Moreover, the use of 20% carbonated RFA can enable 5% decrease in the Global Warming Potential value evaluated by life cycle assessment compared to that without RFA. Such use of RFA led to a decrease greater than 15% in UHPC cost. This indicated the low-carbon and cost-effective characteristics of the developed UHPC made with carbonated RFA.

Retracted: Effect of Crushed Granite, Superabsorbent Polymer, and Expansive Agent on the Workability, Compressive Properties, and Autogenous Shrinkage of Ultrahigh-Performance Concrete

Retracted: Effect of Crushed Granite, Superabsorbent Polymer, and Expansive Agent on the Workability, Compressive Properties, and Autogenous Shrinkage of Ultrahigh-Performance Concrete

Using sol-gel deposition of nanosilica to enhance interface bonding between sisal fiber and ultra-high performance concrete

A new idea of using sol-gel method deposition of nanosilica on sisal fibers for improving the interface bonding with ultra-high performance concrete (UHPC) was suggested in this study. The change in surface microstructure, chemical groups, surface roughness, thermal degradation process, phase composition, and tensile strength of modified sisal fiber were characterized. Moreover, the fiber modification on early hydration, bond performance, mechanical performance, and autogenous shrinkage of UHPC was further explored. The results showed that nanosilica was successfully coated on sisal fibers, and these nanosilica particles accelerate the early hydration of mixtures. The bond strength (pullout energy) was increased by 28.0% (40.8%) by nanosilica deposition. Consequently, the flexural strength and toughness of UHPC incorporating nanosilica-modified sisal fibers were 9.8% and 40.5% higher than those of untreated sisal fibers reinforced UHPC. Furthermore, the shrinkage-reducing effect of sisal fibers after deposition of nanosilica was increased by 11.5% compared with the untreated fibers. Therefore, nanosilica deposition is a promising method for enhancing the bond performance between plant fiber and UHPC matrix.

Effects of seawater on UHPC: Macro and microstructure properties

Due to the shortage of fresh water, the use of seawater in concrete production could alleviate the demand for the limited resource. To promote the use of seawater in ultra-high-performance concrete (UHPC), the effects of seawater on the hardening process and the corresponding relationship between the macroscopic performance and hydration, pozzolanic reaction, and microstructure of hydration products were investigated. Earlier setting times, higher early but lower later compressive strength and higher shrinkage of UHPC were observed. The modified performance was not only attributed to the presence of seawater accelerating the early hydration but also due to the change of microstructure and C-S-H structure. Better early strength and exacerbated shrinkage were associated with the slightly reduced porosity but refined pore structure, while lower later-age compressive strength in the seawater group was related to coarser microstructure and shorter mean chain length (MCL) and lower polymerisation of C-S-H. In addition, the pozzolanic reactivity of silica fume was enhanced, which would also contribute to the increased early compressive strength and exacerbated shrinkage of UHPC. It should be noted that no Friedel’s salt and brucite were observed in the seawater UHPC. Moreover, although the incorporation of fly ash (PFA) was able to compensate for the adverse effects of seawater on compressive strength and autogenous shrinkage of UHPC, the exacerbated drying shrinkage was still a concern even when fly ash was present.

Utilization of natural sisal fibers to manufacture eco-friendly ultra-high performance concrete with low autogenous shrinkage

This study aims to explore a new method to reduce autogenous shrinkage of ultra-high performance concrete (UHPC) by incorporating natural sisal fibers. The water absorption and desorption behavior of sisal fibers were firstly determined. Then, flowability, setting time, hydration heat, autogenous shrinkage, internal relative humidity, mechanical properties, fiber distribution, hydration performance, and microstructure of UHPC mixtures incorporating various volume content of sisal fibers were evaluated. The results show that sisal fibers can release the absorbed water with decreasing relative humidity in UHPC specimens. The addition of sisal fibers can restraint the cement hydration process and delay the setting times. The 7 days autogenous shrinkage of UHPC was reduced by 71.4% by adding 1.5 vol% sisal fiber due to the internal curing and reinforcing effect induced by sisal fibers. Incorporating sisal fibers can promote late hydration of UHPC, so the 28 days compressive strength was reduced by only 7.7%∼8.2%. Moreover, the obvious gap between sisal fiber and concrete can be observed from the backscattered electron images, which is caused by the contraction of sisal fiber after releasing water. Finally, the environmental and cost evaluation shows that the use of renewable sisal fiber as a shrinkage-reducing material can reduce the production cost and carbon footprint of UHPC, so it is of great significance to the sustainable production of UHPC.

Effects of SAP characteristics on internal curing of UHPC matrix

Superabsorbent polymer (SAP) is an effective internal curing agent, and its efficiency is highly dependent on its physical and chemical characteristics. This study investigates the effect of molecular structure, size, content and pre-treatment of SAP on its performance as an internal curing agent in ultra-high performance concrete (UHPC) through the measurement of internal relative humidity, heat of hydration evolution, autogenous shrinkage, and compressive strength. Two types of SAP (ionic and non-ionic) at three contents of 0.2%, 0.4%, and 0.6% were used at the dry state. The ionic SAP was used in two sizes of 471.3 and 95.1 μm to study the effect of SAP size on the efficiency of internal curing. On the other hand, selected ionic SAPs were prewetted by additional water before mixing (0.4% by mass). Results showed that non-ionic small particle size SAP exhibited a higher restraining effect on autogenous shrinkage. The incorporation of SAP can significantly increase the cumulative heat after 15 h, and thus increase the degree of hydration of cementitious materials in UHPC. However, the investigated SAP characteristics showed no significant effect on the cumulative heat of hydration within the tested period of 72 h. The addition of pre-wetted SAP increased the autogenous shrinkage and delayed the hydration, compared to the dry SAP particles with additional water. Finally, the autogenous shrinkage of UHPC was fitted with several published prediction models, and an optimized model was proposed to predict autogenous shrinkage with respect to internal relative humidity and heat of hydration.

Effect of Natural Zeolite on Mechanical Properties and Autogenous Shrinkage of Ultrahigh-Performance Concrete

AbstractIn this study, different percentages of silicafume (SF) were replaced with natural zeolite (NZ) (25%, 50%, 75%, and 100%), in order to mitigate autogenous shrinkage of ultrahigh-performance...

Effect of graphite nanoplatelets and carbon nanofibers on rheology, hydration, shrinkage, mechanical properties, and microstructure of UHPC

This study evaluates the effects of two types of graphite nanoplatelet (GNP-C and GNP-M) and one type of carbon nanofiber (CNF) on rheological properties, hydration kinetics, autogenous shrinkage, and pore structure of ultra-high-performance concrete (UHPC). The dispersion method was optimized to secure uniform dispersion of the nanomaterials in the UHPC. The plastic viscosity decreased with the nanomaterials content as the content was increased from 0 to 0.05%. As the nanomaterials content increased from 0 to 0.3%, the duration of induction period was extended by the addition of CNF, but shortened by use of GNP-C or GNP-M; cumulative hydration heat release was increased by introduction of nanomaterials; the autogenous shrinkage of UHPC with CNF, GNP-C, and GNP-M was increased by 30%, 20%, and 20%, respectively. The use of 0.3% CNFs reduced the total porosity of the UHPC by approximately 35%, indicating that the presence of CNFs refined the microstructure of UHPC.

Effects of saturated lightweight sand content on key characteristics of ultra-high-performance concrete

In this study, 0 to 75% volume of river sand was replaced by an equivalent amount of pre-saturated lightweight sand (LWS) to enhance mechanical properties and reduce autogenous shrinkage of ultra-high-performance concrete (UHPC). The use of LWS is demonstrated to effectively decelerate and reduce the drop in internal relative humidity and autogenous shrinkage of UHPC. Isothermal calorimetry and thermal gravimetry results showed that the use of LWS promoted cement hydration degree after 28d of hydration. Mercury intrusion porosimetry and scanning electron microscope analyses revealed that the porosity was decreased and interface properties between sand and cement matrix is enhanced by use of LWS up to 25%. The optimum replacement ratio of LWS to river sand was found to be 25%, which resulted in the highest compressive strength (168MPa at 91d), flexural strength (24MPa at 28d), and autogenous shrinkage limited to 365μm/m at 28d.

Effectiveness of Saturated Coral Aggregate and Shrinkage Reducing Admixture on the Autogenous Shrinkage of Ultrahigh Performance Concrete

The use of saturated coral aggregate (SCA) as practical replacement of quartz sand has been shown to effectively mitigate the autogenous shrinkage in ultrahigh performance concrete (UHPC). The autogenous deformation, the compressive strength, the flexural strength, and the hydration property development of paste with different shrinkage means were tested. Three different methods were evaluated to mitigate the autogenous shrinkage: SCA, shrinkage reducing admixture (SRA), and the mixture of SCA and SRA (SRA-SCA). It was found that SCA and SRA have all the effective ways to reduce the shrinkage deformation, and SRA-SCA was the most effective in mitigating the shrinkage. The autogenous shrinkage of UHPC was restrained, when the SCA dosage was 44%, the SRA dosage was 0.8%, the SCA content was 26%, the SRA dosage was 2.4%, the SCA content was 18%, the SRA content was 2.4%, or the SCA dosage was 26%. The mechanical properties were deteriorated by the addition of SCA, while the compressive strength was still higher than 90 MPa at 28 days even though the replacement ratio of SCA was up to 50%. Furthermore, internal curing by means of SCA was proved to be a successful way to mitigate autogenous shrinkage, after the tests.

Influence of Nanolimestone on the Hydration, Mechanical Strength, and Autogenous Shrinkage of Ultrahigh-Performance Concrete

AbstractThe influence of nanolimestone/nanoCaCo3 (NC) on the properties of ultrahigh-performance concrete (UHPC) cured at standard and heat conditions was experimentally investigated. The NC was used at ratios of 1, 2, and 3% as partial mass replacement for cement. Incorporating NC accelerated the hydration reactions of UHPC because of the nucleation effect. On the mechanical properties aspect, a threshold value of the NC content was found so that the compressive, flexural strengths, and flexural to compressive strength ratio of the UHPC were found to increase as the NC content increased towards the threshold content, and then to decrease with the increase of NC contents when the threshold was surpassed. Conversely, replacing cement with NC decreased flowability and increased the amount of autogenous shrinkage of the UHPC. While the NC accelerated the cement hydration process, it also acted as an effective filling material, resulting in enhanced mechanical properties and denser microstructure compared wit...

Mechanical Properties and Durability of Ultra-High Performance Concrete Incorporating Coarse Aggregate

Ultra-high performance concrete (UHPC) incorporating coarse aggregate was prepared with common raw materials. Fresh concrete had excellent good workability with slump of 265 mm and slump spread of 673 mm. Compressive strength of UHPC at 56 d reached 150 MPa. However, UHPC exhibited high brittleness in terms of spalling failure which occurred during compression loading.The ratio of splitting tensile strength to compressive strength of about 1/18 and the ratio of flexural strength to compressive strength of about 1/14 at 56 d were also associated with the brittleness of UHPC in this research. Mineral admixtures and fluidity of fresh concrete influenced compressive strength of UHPC significantly. Moreover, UHPC had excellent permeation-related durability but considerable shrinkage. Autogenous shrinkage of UHPC was less than half of free shrinkage, for which the reason is unknown and needs further research.

Evaluation of Setting Time in Ultra High Performance Concrete

Ultra high performance concrete (UHPC), characterized by a high strength and high ductility, is also subjected to large shrinkage due to its low water-to-binder ratio and its large content in high fineness materials. The large amount of autogenous shrinkage of UHPC can induce crack on structural member when it was restrained with reinforcement and form. However, shrinkage of UHPC in plastic state is not generating confining stress, which is the main cause of initial crack. Normally, the setting time in concrete is an index to distinguish shrinkage which occur confining stress or not. An estimation of setting time is conducted in compliance with ASTM C 403 till now however, that test standard reveals error of results due to discordance of test condition as following with concrete type. This study therefore evaluated setting time of UHPC through the modified test method which was proposed by KICT. Test results and analyses proved a discrepancy of setting time between ASTM and proposed method. The proposed method put faith in evaluation of setting time in accordance with UHPC.

The Influence of Chemical Admixtures on the Autogenous Shrinkage Ultra-High Performance Concrete

Ultra-high performance concrete (UHPC) is a material developing remarkable performance with compressive strength of about 200 MPa and flexural strength of approximately 30 MPa on which research is actively conducted today. However, UHPC is also characterized by a mixing composed of a high specific quantity of binder that is a W/B ratio of about 0.2, which requires to examine the effects of the autogenous shrinkage. Accordingly, this study investigates the effects of the use of expansive additive and water reducing agent on the autogenous shrinkage of UHPC at early age. To that goal, autogenous shrinkage test and ultrasonic pulse velocity (UPV) monitoring are conducted for a mixing of UHPC using expansive additive and shrinkage reducing agent. The experimental results reveal that the autogenous shrinkage of UHPC reduces by 24% for a mix of UHPC adopting both 7.5% of expansive additive and 1% of shrinkage reducing agent compared to the mix without admixture. Furthermore, this mix is seen to compensate the autogenous shrinkage occurring at early age when UHPC develops its largest stiffness in view of the UPV evolution curve. At that time, the shrinkage stress seems to be extremely softened.