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.

Effect of Internal Curing with Superabsorbent Polymers on Bond Behavior of High-Strength Concrete

High-strength concrete (HSC) is widely used in engineering due to its high strength and durability. However, because of its low water-to-cement ratio, external curing water hardly enters the dense internal structure of HSC so that high self-desiccation shrinkage often takes place. As a result, superabsorbent polymers (SAP) are added as an internal curing material to effectively reduce the shrinkage of high-performance concrete. Meanwhile, the bond performance between reinforcing steel and SAP HSC concrete remains unknown. In this paper, the bond performance of HSC mixed with SAP is studied by pull-out tests, and the results were obtained as follows: (1) the bond strength of HSC mixed with SAP increased first and then decreased with the increase of SAP content; (2) the slip at ultimate bond strength of HSC with SAP decreased with the increase of compressive strength; (3) a prediction model of the stress-slip relationship between steel rebars and HSC was established.

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.

A mechanistic model for the time-dependent autogenous shrinkage of high performance concrete

An accurate prediction of time-dependent autogenous shrinkage behaviors of concrete, especially for high performance concrete (HPC) at an early age, is of great significance to assess and control the cracking risks of restrained structural elements. In this study, based on the capillary tension theory, a mechanistic model for evaluating the time-dependent autogenous shrinkage behaviors of high performance concrete is proposed. A total of 416 data points including the concrete composition, curing condition, age of concrete, water-to-cement (binder) ratio, internal relative humidity, elastic modulus, and measured autogenous shrinkage are selectively collected for the model establishment. The effects of silica fume on the development of autogenous shrinkage are also considered. Upon the sound physical basis, the model requires only a few parameter inputs related to the mixture proportion and physicochemical properties of constituents. The reasonable agreements between the analytical predictions and independent experimental results, as well as common used formulas from different codes (i.e., ACI 209, Eurocode 2, and Model Code 2010), demonstrate that the time-dependent evolution of autogenous shrinkage of HPC can be reasonably predicted by the model proposed in this study.

Studying the effect of low reactivity metakaolin on free and restrained shrinkage of high performance concrete

Producing high performance concrete with a low reactivity pozzolan such as metakaolin is challenging. On the other hand, high performance concretes could be more prone to shrinkage cracking due to their higher cement content. No consensus exists in the literature on how metakaolin affects concrete's shrinkage. In this study, the possibility of making high performance concrete with a low reactivity metakaolin was assessed. Moreover, the effect of using a low reactivity metakaolin on the mechanical properties, durability, and free and restrained shrinkage of high performance concrete was evaluated. The results showed that increase in the percentage of metakaolin replacement led to reduction in the mechanical properties and durability of high performance concrete. The effect of metakaolin on shrinkage of high performance concrete was observed to be dependent on the water to cement ratio. Overall, it is possible to produce high performance concrete with a low reactivity metakaolin (up to 20% replacement level) only at low water to cement ratios.

Prediction of autogenous shrinkage of cement pastes as poro-visco-elastic deformation

Precise and robust predictions of autogenous shrinkage of high performance concrete are essential to limit self-induced stresses and cracking in modern concrete structures. This paper presents predictions of autogenous shrinkage for three cement pastes of different compositions by considering first only the poro-elastic deformation and then including also the poro-visco-elastic response. This study used experimentally-determined parameters for the material properties of both the elastic and the visco-elastic components, which ensured the reliability of the calculations. The prediction of the poro-visco-elastic response of the material to the internal stress was performed using a generalized Kelvin-Voigt model that also considered aging. It is found that, while the poro-elastic calculations systematically underestimates the measured shrinkage, predictions with the inclusion of the viscous response overestimates the shrinkage.

Pozzolanic Reactivity and the Influence of Rice Husk Ash on Early-Age Autogenous Shrinkage of Concrete

In this study, the role of a locally available rice husk ash (RHA) in reducing early-age shrinkage of high performance concrete (HPC) after evaluating its pozzolanic reactivity was evaluated. The X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analyses were performed after burning rice husk to 700 and 950 oC. Presence of relatively high deposits of amorphous siliceous phases in RHA at 700 oC indicated its pozzolanic potential. Subsequently, this RHA was ground to desired fineness, followed by sieving through sieve No. 200. Eventually, the fine RHA was used as a substitute of cement in different percentages (10, 15 and 20%) to evaluate its influence in mitigating autogenous shrinkage in concrete. Prismatic concrete beams (100 mm x 100 mm x 800 mm) were cast to measure autogenous shrinkage along with cylinders (150 mm dia. x 300 mm height) to test compressive strength of concrete. The results indicated a slight increase in compression strength with addition of 10% RHA, which however, reversed and slightly reduced in concretes containing 15 and 20% RHA. Unlike strength results, the trend of autogenous shrinkage was rather uniform as the rate as well as the amount of early-age autogenous shrinkage continued to decrease with increasing percentage of RHA. Moreover, despite of reduced rate during first 24 hours, thereafter, the effect of 20% RHA on further reduction of autogenous shrinkage was insignificant and ended up only slightly lesser than the 15% RHA concrete at 7 days. Finally, the control cement sand mortar and mortar containing 15% RHA were cast to further validate the pozzolanic reactivity of RHA through scanning electron microscopy (SEM), EDX and thermogravimetric analysis (TGA) tests. An observation of reduced amount of calcium hydroxide (Ca(OH)2) in RHA mortar samples indicating its excellent pozzolanic potential when used as a partial substitute of cement in HPC.

Drying Shrinkage and Suppression Technology of HPC in Extremely Arid Area

Supplementary materials Such As Slag (SG), Fly Ash (FA) and Silica Fume (SF) are necessary for reducing the drying shrinkage of High-performance Concrete (HPC) in arid environments and extremely arid area. This paper investigates the drying shrinkage of HPC with the composites of 10% Silica Fume (SF) and 20% Fly Ash (FA) additions and another HPC incorporated with 10% SF?20% FA and 20% slag (SG), which were exposed to the conditions of 30% Relative Humidity (RH) and 50% RH. The inhibitive mechanism of Aluminate Expansion Agent (AEA) on the drying shrinkage of HPC reveals that the dry shrinkage can be inhibited by the expansion agent as long as the high density of concrete structure and the internal “surplus water” can be ensured. Furthermore, the additions of the composites of SF, FA and SG, super-plasticizer, high modulus fiber (PF) and AEA, can reduce the drying shrinkage and improve the moisture sensitivity of shrinkage of the concrete. The drying shrinkage rate of HPC in extremely harsh environment decreased to about 300 × 10−6 and no shrinkage cracks appeared on the surface of the HPC incorporated with SF, FA and SG. The perfect combination of high volume stability and high durability of HPC was realized.

Influence of initial water content of aggregates on the compressive strength and the shrinkage of High Performance Concretes

The time-dependent deformations of concretes, particularly in the case of high performance concrete (HPC) must be taken into account precisely when measurement of civil engineering works. theses deformations is essential for predicting the deflections, the stress distribution in statically indeterminate structures and the loss of pre-stressing force in elements of pre-stressed concrete. However, the experience shows a certain dispersion of values of instantaneous and delayed deformations measured and some significant differences with the values calculated using the building codes. The objective of the present paper focuses on the parameter which is not taken into account in building codes, which could causes the inaccuracies of their predictions: the initial water content of aggregates. The experimental program includes a comparative study of the mechanical behaviours (instantaneous deformations and shrinkage) of HPC with the same basic formulation (water cement ratio, volume of paste), differing principally in the initial water content of aggregates. The experimental results show that HPC made with wet aggregates has a higher resistance than others (dry aggregates). The pre-saturated aggregates would be a water reservoir in which the dough could slow the self-drying due to hydration in the capillary pores at the level of the Interfacial Transition Zone (ITZ). This would increase the amount of hydrates and improve the mechanical behaviour of this interface through better adhesion and less porosity. If the evolution of shrinkage of HPC with wet or dry aggregates can be distinct during the first months, the effect of this formulation parameter is not clear since it differs according to the type of aggregate. Moreover, in the long term, convergent shrinkage shows that this influence becomes insignificant. The comparisons with estimations of Eurocode 2 model were also performed and showed significant differences with the experimental values.

Influence of initial water content of aggregates on the compressive strength and the shrinkage of High Performance Concretes

Influence of initial water content of aggregates on the compressive strength and the shrinkage of High Performance Concretes

Comparison of calculation models’ estimates with actual measured autogenous shrinkage in High-Performance Cement Composites

There are several calculation models for estimation of shrinkage in concrete. The most popular ones are: ACI-209R-92 method, Bažant-Baweja model (B3), Gardner’a-Lockman’a model (GL 2000), CEB-FIP (CEB MC90-99), Spanish model (EHE), EuroCode method (EC-2) from 2004 and Tazawa–Miyazawa model (JSCE). Majority of aforementioned models do not include the deformation caused by the autogenous shrinkage. The methods assume the total deformation as a result of drying shrinkage action. Additionally, a non-standard method was proposed by Jonasson and Hedlund. However it only is used to determine the autogenous shrinkage of High-Performance Concretes (HPC). Tazawa-Miyazawa model and Jonasson-Hedlund method are based on the proportions and material properties such as water/cement ratio, water/binder ratio, type of the cement, or start of setting time. In contrary, the CEB MC90-99 and EC-2 models correlate the autogenous shrinkage with the overall compressive strength of concrete. The article presents the analysis of various calculation models in comparison to actual measurements. The autogenous shrinkage was measured in four cement composites starting at casting up till 28 days of curing.

Experimental study on shrinkage of HPC containing fly ash and ground granulated blast-furnace slag

The present study investigated experimentally total shrinkage and autogenous shrinkage of high performance concrete (HPC) containing fly ash (FA) and ground granulated blast-furnace slag (GGBS) simultaneously, where the effects of total amount of mixtures and mixture proportion were addressed. To allow for the effects of FA and GGBS, a prediction model for shrinkage was developed where the ratio and total percentage of FA and GGBS were included. Regression analysis was implemented to verify the proposed model. The experimental results show that the inclusion of FA and GGBS in HPC can lead to a great decrease in total shrinkage but an increase in autogenous shrinkage, and the role of FA and GGBS differs in the shrinkage evolution. The fitted equations for total shrinkage and autogenous shrinkage give acceptable predictions.

Prediction of internal relative humidity in concrete modified with super absorbent polymers at early age

Shrinkage of high-performance concrete (HPC) mixtures may ultimately lead to early-age cracking and a reduction of service life of concrete structures. Autogenous and drying shrinkage are direct consequences of the decrease of internal relative humidity (IRH) due to self-desiccation and external drying. Therefore prediction of shrinkage of HPC requires the knowledge of IRH variations. Internal curing (IC) with super absorbent polymers (SAPs) is utilized to mitigate the shrinkage of HPC. Although investigations on IRH in concrete have been conducted, the prediction model for IRH in early-age concrete internally cured with SAPs in consideration of both water-to-cement (w/c) ratio and critical time is still lacking. Therefore investigations on predicting the IRH in early-age concrete internally cured with SAPs were conducted in present study and results showed that: (1) a prediction model for the working w/c ratio in early-age concrete internally cured with SAPs was proposed in consideration of age, effective and IC w/c ratios of concrete; (2) a prediction model for the critical time of IRH was proposed in consideration of both effective and IC w/c ratios; (3) a prediction model for the IRH in early-age concrete internally cured with SAPs was proposed in consideration of working w/c ratio, critical time, and age. These models showed the good accuracy of the test results.

Autogenous Shrinkage in High Performance Concrete with Chemical Admixtures

Durability in High Performance Concrete have resulted in the development of admixtures to mitigate several concrete deterioration mechanisms. Due to the low water/binder, HPC enables autogenous shrinkage that could lead to cracks at early ages. Superabsorbent polymers, shrinkage reducing admixtures and corrosion inhibitor based on calcium nitrite were used in HPC with silica fume to evaluate autogenous shrinkage. SAP was added with an amount of intenal curing water determined by the modification proposed by Jensen to the Power’s Model. Results showed that admixtures could improve or aggravate autogenous shrinkage.

Effect of SAP on the tensile creep of early-age concrete using ring specimens

Internal curing with super-absorbent polymer (SAP) has been developed to improve autogenous shrinkage of high performance concrete (HPC) in recent years. However, studies about effect of SAP on the tensile creep of HPC seem insufficient. In this paper, a series of concrete ring tests were conducted to investigate effect of SAP on the tensile creep of early-age HPC. Meanwhile, shrinkage and mechanical properties of concrete with SAP were also investigated. Results show that tensile creep coefficient of concrete with SAP was similar to that of reference concrete with same basic w/c, but lower compared with that of reference concrete with same total w/c.

Evaluation of FLWA and SRAs on autogenous deformation and long-term drying shrinkage of high performance concrete

The use of pre-wetted fine lightweight aggregate (FLWA) as partial replacement of normal weight fine aggregate has been shown to effectively reduce the deleterious effects of autogenous shrinkage in high performance concrete (HPC). In this study, autogenous deformation of mortar, free drying shrinkage of concrete prisms, and mechanical property development with various shrinkage mitigation methods were examined. HPC drying shrinkage specimens were externally wet cured for 14days or less to commensurate with field curing. Three different methods were evaluated to provide a potential reduction in drying and autogenous shrinkage; pre-wetted FLWA, shrinkage-reducing admixtures (SRAs) or the combination of pre-wetted FLWA and SRA. It was observed that the combination of shale FLWA and SRA was the most effective at reducing autogenous deformation, and was 84% less than the control. HPC mixtures with SRA reduced the drying shrinkage by 17% at 1095days of drying. Furthermore, extending the external wet cure beyond three days had little effect on the magnitude of drying shrinkage for all mixtures when compared to a control mixture cured for 14days.

Effects of using recycled concrete aggregates on the shrinkage of high performance concrete

Over the past twenty years the use of Recycled Concrete Aggregate (RCA) has been mostly limited to normal-strength concretes. However, satisfactory properties have been found in previous studies dealing with the use of RCA sourced from medium to high strength concrete in the production of High Performance Concrete (HPC). In this study the effects of RCA were investigated in the plastic, autogenous and drying shrinkage of HPC. The quality of the RCA (sourced from concretes of 100, 60 and 40MPa) and the replacement ratio (20, 50 and 100%) were assessed. The results revealed that the plastic and drying shrinkage became higher as the quality of the RCA decreased and the replacement ratio increased. However, a reduction in the autogenous shrinkage was proved to be possible by the employment of a higher content of lower quality RCA, as this, in fact, acted as internal curing agent. The effects of the internal curing explained the similar or higher compressive strength results of concretes containing RCA when compared to those obtained from the reference concrete.

Effect of internal curing with super absorbent polymers on the relative humidity of early-age concrete

High-performance concrete is used extensively in practice. However, the water-to-cement ratio of this concrete is low and causes self-desiccation. Due to moisture diffusion and this self-desiccation, internal relative humidity (IRH) decreases in concrete structures that are exposed to ambient air and induces autogenous shrinkage. Internal curing with super absorbent polymer (SAP) is used to mitigate this shrinkage in high-performance concrete; nonetheless, IRH variation influences changes in the autogenous shrinkage of concrete with SAPs. Although tests have been performed to mitigate the autogenous shrinkage of concrete that was internally cured through SAPs, experimental study on IRH variation in such concrete remains lacking. Thus, such a study was conducted to determine the effect of internal curing with SAPs on the IRH of early-age concrete under sealed and unsealed conditions, as detailed in this paper. Test results showed that: (1) the IRH of concrete that was internally cured with SAPs increased with an increase in the content of internal curing water 28days after casting under sealed and unsealed conditions. (2) The degree of decrease in the IRH of internally cured concrete was lower under sealed conditions than under unsealed conditions 28days after casting. (3) The critical time of the IRH of internally cured concrete increased with increases in the content of internal curing water under both sealed and unsealed conditions. (4) The decrease rate of the IRH in early-age concrete that was internally cured with SAPs dropped with an increase in the content of internal curing water under sealed and unsealed conditions. (5) A formula was proposed to calculate the IRH of early-age concrete that was internally cured with SAPs in consideration of the content of internal curing water under unsealed conditions. This formula indicates the good accuracy of the experimental results.

Restrained Shrinkage Test of High Performance Concrete Ring Specimen

The aim of this study was to quantify the restrained shrinkage of high performance concrete (HPC). Ring test was used for the measurement of restrained shrinkage. Mechanical properties of the HPC as well as free shrinkage were determined for assessment of theoretical stress in shrinkage restrained material. The results from the ring test showed a lot of information about material such as development of actual residual stress, cracking potential, microcracks and relaxation.

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.