Autogenous Shrinkage Of High-performance Concrete Research Articles

Preparation and properties of porous rice husk ash for internal curing of high performance cement pastes

To address the challenges posed by significant autogenous shrinkage in high-performance concrete and mitigate the adverse effects of conventional internal curing materials on its mechanical properties, this study explored the potential use of rice husk ash (RHA) as internal curing materials. The research investigated the impact of combustion regime (combustion temperature and dwelling time) and the milling process on the microstructure and physical-chemical properties of RHA. Moreover, the effect of RHA on autogenous shrinkage, compressive strength, and microstructure in cement pastes were also reported. Experimental results demonstrated that the combustion regime and milling time could significantly affect the pore structure, particle size and pozzolanic activity of RHA. RHA had good potential for internal curing when it was burned at 600°C for 1 h and milled for 15–30 min. RHA released the entrained water after 12 h to slow down the depletion of free water, and thus inhibited the development of self-drying and autogenous shrinkage. The 168 h shrinkage was reduced by 56.8 %, 62 %, and 51.8 %, respectively when the milling time increased to 30 min. Moreover, the addition of RHA with a smaller particle size could refine the microstructure of matrix and enhance the compressive strength due to its higher pozzolanic activity. These findings suggest promising applications for RHA as an effective internal curing material in high-performance cementitious materials.

Evaluation of mechanical properties and environmental impact of using limestone powder in high-performance concrete

In this study, various dosages of limestone (LS) powder (10, 15 and 20%) of varying fineness were used as a replacement for cement to investigate its influence on the selected properties of high-performance concrete (HPC). The efficiency factor and carbon dioxide (CO2) equivalent emissions were evaluated for life cycle assessment of HPC mixtures containing LS powder. The workability, compressive, split tensile and flexural strength, semi-adiabatic temperature rise and autogenous shrinkage of HPC were investigated. The results indicated that workability and density were enhanced by replacing cement with fine and intermediate LS powder in comparison with coarse LS powder. The compressive, split tensile and flexural strengths were all reduced by increasing the replacement level of fine, intermediate and coarse LS powder at all curing ages. Furthermore, higher temperature peaks and high autogenous shrinkage were observed in fine LS mixtures due to the nucleation effect and the accelerating hydration reaction of fine LS particles. The highest efficiency factor and highest reduction in carbon dioxide equivalent emissions was observed in the mixtures containing 20% coarse LS powder followed by the intermediate LS powder. This research work may help in understanding the role of varying finenesses of LS powder as a viable material in high-performance-based composites.

Influence of Fineness of Wheat Straw Ash on Autogenous Shrinkage and Mechanical Properties of Green Concrete

This study investigates the effectiveness of an agricultural by-product wheat straw ash (WSA) as an internal curing agent in reducing the autogenous shrinkage of high-performance concrete (HPC). After incineration under different controlled time–temperature conditions, grinding and sieving were performed to obtain two different grades of fine WSA (F-WSA) and superfine WSA (SF-WSA). Subsequently, material characterization tests were carried out, followed by tests for mechanical properties and autogenous shrinkage potential of concrete incorporating 10% and 20% F-WSA and SF-WSA as a partial replacement of cement. The results demonstrated slightly higher compressive and tensile strength of concrete containing SF-WSA compared to control, whereas concrete with F-WSA demonstrated comparable strength results to that of the control concrete. Moreover, a significant reduction in 7 days’ autogenous shrinkage was observed in concrete containing 10% and 20% F-WSA by 42% and 25% compared to that of control concrete, respectively. This reduction in autogenous shrinkage increased further to 57% and 40% for concrete with 10% and 20% SF-WSA, respectively. The results of microstructural investigations on paste samples such as FTIR, TGA, and N2 adsorption analyses revealed a more refined and compact microstructure of paste samples with increasing fineness of WSA due to the formation of a more densified C-S-H phase. The improvement of the microstructure is attributable to the improved pozzolanic properties of SF-WSA compared with F-WSA.

Effectiveness of treated flax fibers in improving the early age behavior of high-performance concrete

In recent years, ecoefficiency incentives have recently attracted growing research attention towards the valorization of natural fibers in cement systems. Specific attractive features of natural fibers include cost-effectiveness, abundance, renewability, and non-toxicity while providing several functionalities to concrete such as volumetric stability, strength enhancement, and crack control. This study is aimed at leveraging the hydrophilicity, hygroscopicity, and bridging capacity of flax fibers to design high-performance concrete (HPC) with controlled autogenous shrinkage. The effect of raw fibers and that of alkali-treated fibers on autogenous shrinkage of HPC and its fresh and mechanical properties were investigated and compared to the effect of shrinkage reducing admixture (SRA) and expanded shale lightweight aggregate (LWA). Results show that while SRA was found efficient in reducing autogenous shrinkage at 7 days (64% lower), this option adversely affected mixture flowability and mechanical performance (particularly flexural capacity). Similarly, LWA reduced autogenous shrinkage (by 36%) but without a noticeable effect on mechanical performance. Interestingly, the use of alkali-treated fibers allowed obtaining an HPC mixture with reduced autogenous shrinkage (26% lower) while maintaining improved flowability, compressive strength, and flexural capacity (up to 17% increase). Therefore, alkali-treated flax fibers can be viewed as a viable tool for mitigating autogenous shrinkage, thereby offering a green alternative promoting the sustainability of the built environment.

Microstructure and shrinkage behavior of high-performance concrete containing supplementary cementitious materials

This paper investigated the influence of supplementary cementitious materials (SCM, including fly ash (FA), ground granulated blast-furnace slag (GGBS), metakaolin (MK)) on the microstructure and shrinkage behavior of high-performance concrete (HPC). The prediction accuracy of some typical shrinkage models and the correction factor kSCM were evaluated with statistical parameters RE and R2new. After analysis of shrinkage models, the kSCM*B4 model and kSCM*CEB were more suitable for the drying shrinkage and autogenous shrinkage of HPC, respectively. Although the activities of FA, GGBS, and MK were different, SCM were helpful to form a dense interfacial transition zone (ITZ) microstructure. To analyze comprehensively the effect of single or binary addition of SCM on its shrinkage properties, XRD, SEM, slump and compressive strength experiments of HPC were carried out. The diffraction peaks of Ca(OH)2 decreased with the content of FA and GGBS. The setting time of HPC was prolonged with the content of SCM. Both the decrease of FA and the increase of GGBS and MK could enhance the compressive strength of HPC. Drying shrinkage decreased with the content of FA, GGBS, and MK thanks to the refined microstructure with SCM. Autogenous shrinkage decreased remarkably with the content of FA and GGBS, however, that of MK was opposite. For the same total content of SCM, effects of binary addition of FA and MK, FA, and GGBS on the shrinkage behavior of HPC were more markedly than that of single FA. The drying shrinkage of HPC with single MK was slightly less than that with single GGBS, however, the autogenous shrinkage of HPC with single MK was significantly more than that with single GGBS.

Effects of pre-soaked zeolite and CaO-based expansive agent on mechanical properties and autogenous deformation of early-age concrete

High-performance concrete (HPC) is prone to cracking at an early age due to the large autogenous shrinkage (AS), which severely weakens the durability of the concrete structure. CaO-based expansive agent (CEA) is widely utilized to compensate for the AS of HPC, but CEA cannot achieve its potential expansion in HPC due to a low water to binder ratio, resulting in an incomplete hydration, and a sharp and substantial retraction after initial expansion. Pre-soaked zeolite can be introduced as internal curing (IC) agent to reduce the AS of HPC owing to the IC water released from zeolite. According to the AS-reduction mechanism of CEA and zeolite, a synergistic mechanism can be achieved by the combination use of CEA and zeolite in HPC. However, a comprehensive understanding of the effects of the combination use of zeolite and CEA on the mechanical properties and autogenous deformation of concrete is still lacking. Therefore, the influence of zeolite and CEA addition on mechanical properties and autogenous deformation were investigated experimentally. The investigation results showed that the zeolite addition weakened the mechanical properties of concrete while the CEA addition had the opposite effect. The internal relative humidity in concrete was significantly improved with zeolite and CEA incorporation. The IC water released from zeolite could not only enhance the expansion efficiency at an early age but also greatly reduce the retraction at the later age. The results exhibited an obvious synergistic mechanism with the combination use of zeolite and CEA on AS mitigation, which is of great benefit in AS-induced cracking control.

The Use of Superabsorbent Polymers in High Performance Concrete to Mitigate Autogenous Shrinkage in a Large-Scale Demonstrator

High performance concrete (HPC) is a high strength concrete that undergoes a lot of early-age autogenous shrinkage (AS). If shrinkage is restrained, then micro-cracks arise and threaten the durability of the structure. Superabsorbent polymers (SAPs) can reduce/mitigate the autogenous shrinkage, due to their promising application as internal curing agents. In this paper, large-scale demonstrators were built to investigate the efficiency of SAPs to mitigate autogenous shrinkage in HPC. For this purpose, different measurement techniques were used like embedded fiber optic sensors and demountable mechanical strain gauges, complemented by AS measurements in corrugated tubes and restrained ring tests. The SAP wall showed an AS reduction of 22%, 54%, and 60% at the bottom, middle, and top, respectively, as recorded by the sensors (in comparison with the reference wall (REF)). In the corrugated tubes, mitigation of AS was shown in the SAP mixture, and under restrained conditions, in the ring test, the reference mixture cracked after two days, while the SAP mixture had not cracked at the end of the measurement period (20 days). Cracks were shown on REF wall after one day, while the SAP wall was crack-free. Water flow tests performed on the main crack of the REF wall confirmed that the flow rate is related to the third power of the crack width. All tests showed that SAPs could highly reduce AS in HPC and avoid cracking.

Effect of superabsorbent polymer admixtures on hygric and thermal properties of cement mortar

Materials known as superabsorbent polymers (SAP) or hydrogels are currently used in quite a few applications, ranging from diapers or napkins to nutrient carriers and soil conditioners. The great ability of SAPs to absorb and hold a significant amount of water can be utilized well also in the construction sector. For instance, SAPs can serve as effective admixtures for mitigation of autogenous shrinkage of high-performance concrete, frost protection, or cracks sealing. In this paper, basic physical, hygric and thermal properties of cement mortars containing superabsorbent polymer admixtures are analyzed. Basic physical characteristics are measured using the water vacuum saturation method and helium pycnometry. Moisture diffusivity is determined by utilizing the results of water sorptivity measurements, water vapor diffusion permeability is measured by the cup method. Sorption isotherms are determined by the desiccator method in the range of relative humidity of 11% – 96%. Thermal conductivity and specific heat capacity are measured by pulse method. Experimental results show a very significant dependence of all hygric and thermal parameters on the SAP dosage in the mix.

高强混凝土内养护的研究进展

高强高性能混凝土在各类建筑工程中被广泛地应用。但由于高性能混凝土水胶比较低、胶凝材料用量较大，其早期的自收缩较为严重，从而产生微裂纹进而开裂，严重影响其力学性能和耐久性。而内养护技术依靠预吸水材料释放水分维持混凝土内部充分湿润，可以有效地减少自收缩，保障混凝土的力学性能和耐久性。本文从内养护剂的作用机理、内养护剂的种类、不同内养护剂的作用效果对比以及内养护剂的工程应用等方面总结了近年来高强混凝土内养护的研究进展。 High-performance concrete is widely applied to all kinds of building and construction projects. Due to the low water to binder ratio and large amount of cenmentitious materials, the autogenous shrinkage of high-performance concrete is significantly severe, thus resulting in microcracks and even cracking. So the mechanical properties and durability of concrete are seriously impacted. The internal curing technology relies on the pre-absorbent materials to release moisture to maintain sufficient internal wetting of the concrete, which can effectively reduce the autogenous shrinkage and ensure the mechanical properties and durability of the concrete. This paper has summarized the research progress in internal-curing of high strength concrete in recent years from the aspects of the working mechanism of the internal curing reagents, the types of the internal curing reagents, comparison of the effect of different internal curing reagents and the engineering application of the internal curing reagents.

Early-age autogenous shrinkage and stress characteristics of high-performance concrete at the mesoscopic level

This paper presents a mesoscopic numerical model of high-performance concrete (HPC) based on industrial computed tomography scanning and image reconstruction technology. The paper also presents mesoscopic simulation results obtained for the autogenous shrinkage (AS) of HPC using a finite-element explicit algorithm by assuming that the concrete is an inhomogeneous composite material composed of mortar, aggregate and voids. The accuracy of this mesoscopic simulation method for the AS of HPC is demonstrated by comparison with experimental results. Additionally, the effect of the distribution and particle size of the aggregate and the AS of the mortar on the early-age AS of HPC was analysed. The distribution of the internal stress in the HPC and the effect of the distribution and particle size of the aggregate were determined, which can provide a basis for early-age cracking control in concrete.

Assessment of early-age autogenous shrinkage strains in concrete using bentonite clay as internal curing technique

This research paper addresses the controlling methodology of autogenous deformation, which occurs as an essential attribute of high-performance concrete. The amount of cement present in concrete mix is the main cause of triggering the autogenous shrinkage in high-performance concrete. To reduce this shrinkage, the replacement of cement with bentonite clay was studied. Bentonite clay was used as 5%, 10%, 15% and 20% replacement of cement and the linear shrinkage strain in plain cement concrete beams, of selected dimensions, was monitored. The relative humidity was constantly monitored while the specimens were sealed. The beams prepared in 10% replacement of cement with bentonite showed the most encouraging results among all other mixes. Differential Thermal Analysis (DTA) and Thermo-Gravimetric Analysis (TGA) ensured that bentonite clay possesses stability to withstand high temperature gradients and the Scanning Electron Microscope (SEM)/Energy Dispersive X-ray tests (ED-XRF) showed that bentonite clay imparts certain amount of siliceous and aluminous compounds to the mixes.

A prediction model for autogenous shrinkage of high-performance concrete in bridge engineering

Based on an experimental method of studying the autogenous shrinkage of high-performance concrete (HPC) in a mould of low-density flexible corrugated pipe, this paper presents experimental results and a prediction model for autogenous shrinkage of HPC with respect to water to cementitious materials ratio, replacement ratio of fly ash, air content and aggregate to cementitious materials paste ratio. Reasonably good agreement is observed between the experimental and predicted autogenous shrinkage, thus indicating that the proposed model can be successfully used to estimate the effects of the studied parameters on the development of autogenous shrinkage in HPC.

Influence of Mineral Admixtures on Early-Age Autogenous Shrinkage of High-Performance Concrete

The influence rules of the mineral admixtures containing fly ash, ground slag and silica fume on the early-age autogenous shrinkage of high-performance concrete have been discussed in this paper. According to the research results, fly ash mixture can substantially decrease the early-age autogenous shrinkage of high-performance concrete, while the silica fume will increase the autogenous shrinkage. Meanwhile the influence of ground slag on autogenous shrinkage is related to its fineness and admixture amount. Generally, it is believed that when the fineness of the fly ash is higher than 4000cm2/g, the autogenous shrinkage will increase with the increasing admixture amount. The double admixture or multi-admixture of fly ash or ground slag is better for reducing the early-age autogenous shrinkage of concrete than the single-admixture. The early-age autogenous shrinkage of concrete occurs in distinctive linear dependence with the three types of mineral admixtures.

Effect of hybrid curing on cracking potential of high-performance concrete

Internal curing technology has been developed to counteract autogenous shrinkage of high-performance concrete. However, the total shrinkage of internally cured concrete is reported to be almost unchanged after exposure to drying. On the other hand, shrinkage reducing admixtures have been successfully used to reduce drying shrinkage. A hybrid curing technique that combines internal curing with shrinkage reducing admixture seems to be a promising approach for reduction of total shrinkage and cracking potential of high-performance concrete. Ring test of concrete made at water to cement ratio of 0.33 and internally cured by water-saturated lightweight aggregate and super-absorbent polymer and their combination with shrinkage reducing agent was studied. In parallel, compressive and splitting strength, drying shrinkage and mass loss of the same concrete mixes were measured. The results demonstrate the synergy between internal curing and shrinkage reducing admixture resulting in a marked reduction of cracking potential.

Analysis technique for autogenous shrinkage in high performance concrete with mineral and chemical admixtures

This paper presents an analysis technique for AGS (autogenous shrinkage) in high performance concrete (HPC) with mineral and chemical admixtures. In this paper, comprehensive tests are performed to evaluate the behavior of AGS in HPC. Six mix proportions for evaluating the effect of FA (fly ash), SF (silica fume), and their combinations are prepared. Additional six mix proportions are also prepared for evaluation of the effect of SRA (shrinkage reducing agent), EA (expansive agent), and their combinations. Considering initial setting time and amount of admixture, analysis technique is proposed for prediction of AGS in HPC with mineral and chemical admixture, which can handle the compressive strain due to SRA and EA addition. The results from the proposed technique are compared with test results and they showed a reasonable agreement with test results for verification.

Effect of Curing Methods on Autogenous Shrinkage and Self-Induced Stress of High-Performance Concrete

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Cracking in cement paste induced by autogenous shrinkage

Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is a difficult task. Available techniques either lack the required resolution or may produce additional cracks that are indistinguishable from the original ones. A recently developed technique allows identification of microcracks while avoiding artefacts induced by unwanted restraint, drying, or temperature variations during sample preparation. Small cylindrical samples of cement paste are cast with steel rods of different diameters in their centre. The rods restrain the autogenous shrinkage of the paste and may cause crack formation. The crack pattern is identified by impregnation with gallium and analyzed by optical and scanning electron microscopy. In this study, a non-linear numerical analysis of the samples was performed. Autogenous strain, elastic modulus, fracture energy, and creep as a function of hydration time were used as inputs in the analysis. The experimental results and the numerical analysis showed that samples with larger steel rods had the highest probability of developing microcracks. In addition, the pattern and the width of the observed microcracks showed good agreement with the simulation results.

Effect of Saturated Lightweight Sand Substitution on Shrinkage in 0.35 w/b Concrete

This paper evaluates the effectiveness of internal curing as a method to mitigate autogenous shrinkage in high-performance concrete (HPC) having a low water binder ratio (w/b). To achieve this, the author substitutes 20% of normalweight (NW) sand by an equal mass of lightweight sand (LW) in HPC having a w/b of 0.35. Shrinkage is monitored using vibrating wire gauges cast at the center of 100 x 100 x 400 mm (4 x 4 x 16 in.) concrete samples. Results show that a 20% substitution of NW by a LW sand efficiently reduces autogenous and drying shrinkage. Moreover, the incorporation of 20% LW sand does not have a significant effect on 28-day compressive strength. Results also show low chloride ion permeability in the cementitious matrix. The author concludes that internal curing using partial replacement of NW sand by LW sand presents an efficient way to reduce autogenous and drying shrinkage in low w/b concretes, especially in cases where external water curing disallows in-depth curing of concrete.

Autogenous shrinkage of high-performance concrete containing fly ash

This paper focuses on the effect of fly ash on autogenous shrinkage of high-performance concrete (HPC). The stresses induced by autogenous shrinkage were calculated using finite element method and a model for predicting autogenous shrinkage including the effect of fly ash was proposed. Test results show that autogenous shrinkage of HPC with water-to-cementitious materials ratio (w/cm) of equal to or less than 0·35 developed more rapidly than that of normal-strength concrete (NSC) with a w/cm of 0·50. For HPC with the same w/cm but containing fly ash, autogenous shrinkage decreased – the higher the fly ash replacement percentage, the lower the level of autogenous shrinkage. Numerical analysis results show that the tensile stress induced by autogenous shrinkage may cause early-age cracking in HPC. In conclusion, although partial replacement of cement by fly ash could effectively reduce autogenous shrinkage of HPC, incorporating fly ash only might not prevent early-age cracking.

Autogenous shrinkage of high-performance concrete containing fly ash

This paper focuses on the effect of fly ash on autogenous shrinkage of high-performance concrete (HPC). The stresses induced by autogenous shrinkage were calculated using finite element method and a model for predicting autogenous shrinkage including the effect of fly ash was proposed. Test results show that autogenous shrinkage of HPC with water-to-cementitious materials ratio (w/cm) of equal to or less than 0·35 developed more rapidly than that of normal-strength concrete (NSC) with a w/cm of 0·50. For HPC with the same w/cm but containing fly ash, autogenous shrinkage decreased – the higher the fly ash replacement percentage, the lower the level of autogenous shrinkage. Numerical analysis results show that the tensile stress induced by autogenous shrinkage may cause early-age cracking in HPC. In conclusion, although partial replacement of cement by fly ash could effectively reduce autogenous shrinkage of HPC, incorporating fly ash only might not prevent early-age cracking.