Shrinkage Of High-strength Concrete Research Articles

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.

Measurement and modeling of creep property of high-strength concrete considering stress relaxation effect

Measurement of concrete creep under constant sustained stress conditions is usually a long process. The external load applied on the specimen may relax gradually during this long process due to the time-dependent properties of concrete and test set-up, which would lead to an improper assessment of concrete creep without considering the stress relaxation effect. This study developed a theoretical method based on the linear superposition principle to derive the specific creep of concrete from the compressive creep test results where a certain amount of stress has relaxed. Three types of high-strength concretes were cast for the creep tests. In addition, the workability, mechanical properties, and shrinkage of the three concretes were measured. Then the application of the existing models including the ACI model, CEB-FIP model, GL2000 model, and B4 model to predict the creep and shrinkage of high-strength concrete was discussed. The results reveal that the specific creep of concrete used in this study without considering the stress relaxation effect decreases by 4.3%∼11.0% when 6.7%∼13.1% of the applied stresses relax during the creep tests. Both creep and shrinkage of high-strength concrete exposed to drying decrease with increasing curing age. It is found that the CEB-FIP model can predict the shrinkage of high-strength concrete well and the B4 model can give a predicted result relatively close to the measured creep of high-strength concrete.

Mitigation of autogenous shrinkage of high-strength concrete using rice husk ashes with distinct pore structures

The effect of particle size (50% passing size (D50) of 20 μm, 14 μm and 7 μm) and content (8%, 10% and 12% by mass) of rice husk ash (RHA) on the autogenous shrinkage evolution of high-strength concrete was investigated. RHA samples were selected based on differences in their pore structures, which were investigated by means of nitrogen adsorption isotherms, scanning electron microscopy and absorbency tests. Cement–pozzolan hydration development was studied using isothermal calorimetry. The concretes were subjected to mercury intrusion porosimetry and compressive strength tests. Considering a statistical 22 factorial analysis with a central point, the results showed that D50 and the interaction between D50 and RHA content influenced the autogenous shrinkage at 28 and 100 days. The water absorbed internally by the preserved RHA pore structure (D50 ≈ 20 μm) in the high cement replacement (12% RHA) mixes reduced the final autogenous shrinkage of concrete without a decrease in compressive strength. In addition, the RHA with a more preserved pore structure accelerated the hydration kinetics by heterogeneous nucleation. However, this behaviour did not influence the early autogenous shrinkage results.

Influence of Barchip fiber on early-age autogenous shrinkage of high strength concrete

High strength concrete (HSC) is vulnerable to early-age cracking owing to a low water-to-cement (w/c) ratio. Barchip fibers have been utilized to reduce the autogenous shrinkage of concrete. The relationship between autogenous shrinkage and ultrasonic velocity of HSC reinforced with Barchip fibers was studied utilizing the non-contact shrinkage test. Results indicated that the autogenous shrinkage and ultrasonic velocity of concrete decreased with the volume percentage of Barchip fibers increasing. Besides, models for predicting early-age autogenous shrinkage strain were proposed considering the fiber volume percentage and age based on the results of ultrasonic velocity.

Eliminating the Shrinkage of High Strength Concrete by using Super Absorbent Polymer (SAP)

High Strength Concrete (HSC) is one of the most popular types of concrete used in the world. This type of concrete has a low rapid hydration of cementation materials with low w/cm and the external surrounding environment condition exposed the HSC to high autogenous shrinkage. If this shrinkage is not treated well that well led to cracking, in this case HSC need to convenient curing necessary at the earliest time. This study presents the use of Super Absorbent Polymer (SAP) as internal curing agent to eliminate shrinkage. Two types of shrinkage are tested in this study (Autogenous shrinkage and drying shrinkage). Two groups of concrete mixes(A and B) are studied in this study each group have five types of concrete mixes, four mixes with high and ultra-high compressive strength (RPC, MRPC, HSC and SCC) and the last one with normal compressive strength (NSC). Group A represent concrete mixes without SAP addition and group B for concrete mixes with SAP. SAP was added for all mixes at 0.3% by weight of cement and adding 20ml water for each gram of SAP, specimens with dimensions (40*40*160) mm were used for testing shrinkage for each mix with and without SAP, average values for two specimens was taken as a results. It was found that concrete mixes of group B have lower shrinkage than the shrinkage of concrete mixes in group A at 28 days age with reduction of autogenous shrinkage(AS) of (57%, 35%, 37%, 44.5% and 37.5%) respectively and for drying shrinkage the percentage of reduction was (89.5%, 72%, 82%, 70% and 71%) respectively, addition of SAP to concrete mixes proves to have active effect in reducing the shrinkage of concrete.

유지류를 중심으로 한 수축저감제 종류 변화가 고강도 콘크리트의 기초물성 및 자기수축에 미치는 영향

In this research, the fundamental properties and autogenous shrinkage behaviors of high strength concrete of 0.30 water-to-binder ratio was evaluated depending on the various shrinkage compensating admixtures such as soybean oil (BO), wasted cooking oil (WO), and emulsified refined cooking oil (ERCO) comparing to commercial shrinkage reducing admixture (SR), and expanding admixture (EA). According to the experiment results, the workability of the concrete mixture showed decreased when it contained BO, and WO rather than Plain. In the case of ERCO, due to the water dispersing effect caused by emulsification, similar workability was obtained to Plain. For compressive strength, the concrete mixtures with BO, and WO decreased compressive strength rather than Plain concrete mixture, while the concrete mixture with ERCO showed decreased compressive strength at early age and recovered strength at later age. Regarding the autogenous shrinakge reducing performance, the oil-based admixtures of BO, WO, and ERCO showed better performance than SR and EA; it is considered that the saponification, the hydrolyzed reaction of fatty-acid from oils by calcium hydroxide, the hydration product of cement paste, contributes on filling the capillary pores of the concrete matrix, and thus it decreases the shrinkage. eventually, workability, strength, autogenous shrinkage reducing of 30~40 %, and economical aspects, it can be state that using ERCO may be an efficient solution for autogenous shrinkage of high strength concrete.

Fundamental aspects of the interaction between hardened cement paste and water applied to improve prediction of shrinkage and creep of concrete: A Critical Review

In this contribution, selected fundamental properties of concrete are presented and discussed. Basic mechanisms of shrinkage are first described in some detail. With increasing age of concrete different mechanisms of shrinkage become activated. During the first few hours after mixing, dissolution of cement is the main shrinkage mechanism. Depending on the humidity of the surrounding air, capillary pressure in the pore water may cause serious damage in the first few hours. After this initial loss of water, the remaining aqueous solution is retreated in the pores between fine aggregates and first hydration products. At this scale, the role of disjoining pressure is pointed out in detail and it becomes clear that the influence of capillary pressure on shrinkage of hardened concrete can be neglected. Additionally, at relative humidity lower than 50%, the dominating mechanism is the increasing surface energy of the drying gel particles. Shrinkage of high-strength concrete has a totally different time evolution. The moisture distribution n aging high-strength concrete is completely different. If high-strength concrete is exposed to an environment with RH higher than 80%, there will be no shrinkage at all but swelling. These fundamental aspects of shrinkage have to be taken into consideration when long-term shrinkage is to be predicted. Creep of concrete can be described in a realistic way by means of rate theory. Elements of rate theory are briefly described. The influence of temperature and applied stress is outlined. Most important, however, is the influence of humidity content. As the humidity content of high-strength concrete is comparatively low, creep is significantly reduced as compared to normal concrete. Prediction of creep can be significantly improved if these fundamentals are taken into consideration.

Reduction of the Early Autogenous Shrinkage of High Strength Concrete

The results of a laboratory investigation on the early autogenous shrinkage of high strength concrete, and the possibilities of its reduction, are presented. Such concrete demonstrates significant autogenous shrinkage, which should, however, be limited in the early stages of its development in order to prevent the occurrence of cracks and/or drop in the load-carrying capacity of concrete structures. The following possibilities for reducing autogenous shrinkage were investigated: the use of low-heat cement, a shrinkage-reducing admixture, steel fibres, premoistened polypropylene fibres, and presoaked lightweight aggregate. In the case of the use of presoaked natural lightweight aggregate, with a fraction from 2 to 4 mm, the early autogenous shrinkage of one-day-old high strength concrete decreased by about 90%, with no change to the concrete's compressive strength in comparison with that of the reference concrete.

Heterogeneous Shrinkage of High-Strength Concrete by the Volume of Large-Size Structural Elements

The article introduces results of the experimental research of the influence of the scale effect on the shrinkage strain of high-strength concrete of C70/85 class as well as recommendations for accounting in practical calculations of the scale effect influence on the characteristics under research.

Combination Effects of Internal Curing and Permanent Formwork on Shrinkage of High Strength Concrete

In this paper, the influences of internal curing using pre-soaked lightweight aggregate (PSLWA) and pre-fabricated fiber reinforced engineered cementitious composite (ECC) board as permanent formwork on shrinkage and internal relative humidity of high strength concrete were investigated. Three mixture proportions with induced curing water-to-cement ratios (WIC/C) of 0, 0.08 and 0.12 were utilized in the experiments. The test results show that the progress of the internal relative humidity of high strength concrete since casting exhibits first a vapor saturated stage (RH=100%, stage I), followed by a gradually reducing stage (RH<100%, stage II). As PSLWA is added, the reduction rate of internal relative humidity in stage II is greatly decreased. As ECC cover is used, the reduction on internal humidity of high strength concrete is further reduced. Shrinkage of high strength concrete decreases with increase of induced internal curing water. However, internal curing cannot completely eliminate the shrinkage of high strength concrete developed in the stage I. The combined effects of internal curing and ECC cover can reduce the shrinkage not only developed in the stage II, but also the shrinkage developed in stage I.

Effect of pre-soaked superabsorbent polymer on shrinkage of high-strength concrete

Pre-soaked super-absorbent polymer (SAP) was incorporated into high-strength concrete (HSC) as an internal curing agent to study its effects on early-age shrinkage and mechanical properties. On the basis of the capillary stress based model for shrinkage prediction of concrete, together with the experimental results of cement hydration kinetics, evolution of internal temperature and humidity, development of pore structure and mechanical properties, the working mechanism of SAP was discussed. Results indicate that the addition of pre-soaked SAP significantly reduces the autogenous shrinkage as well as the early-age shrinkage of HSC under drying condition. In sealed HSC specimens, the drop of internal humidity caused by the self-desiccation effect is notably postponed by addition of pre-soaked SAP. The addition of pre-soaked SAP slightly reduces the compressive strength of HSCs and this effect is more pronounced in early-age concrete. Furthermore, an insightful comparison of the behaviours of the internal curing water introduced by the pre-soaked SAP and the additional free mixing water in concrete was made. Results indicate that the internal curing water behaves differently from the additional mixing water in influencing the cement hydration kinetics, pore structure of hardened cement pastes and the mechanical strength of concrete, due to the different spatial distribution of the two types of water in the concrete bodies. The shrinkage-reducing effect on HSC due to the addition of extra internal curing water incorporated by pre-soaked SAP is much stronger than that of the additional mixing water. Besides, the internal curing water shows much less strength-reducing effect than the additional mixing water. In virtue of the shrinkage prediction model, the working mechanism of pre-soaked SAP in reducing autogenous shrinkage of HSC is proposed on the basis of the following two aspects. The participation of internal curing water in cement hydration process leads to a total volume gain of the hardening cement pastes. Meanwhile, the release of internal curing water from the pre-soaked SAP postpones the drop of internal humidity. The synergistic effect of these two factors effectively reduces the autogenous shrinkage of HSC.

Effects of hydration heat velocity on autogenous shrinkage of high-strength concrete

The purpose of this study was to quantitatively investigate the effects of a micro encapsulated retarder (MER) on the hydration heat velocity (HHV) and autogenous shrinkage velocity (ASV) of high-strength concrete (HSC). A series of laboratory experiments was designed and conducted with the main variables being the amount of MER (0, 0·4 and 0·8% of total cement weight), specimen size (300 × 300 × 300 mm3 and 100 × 100 × 400 mm3) and two different curing conditions (semi-adiabatic and in air at 20°C). As a result, the MER was demonstrated to be effective for retarding the cement hydration process without reducing the compressive strength of the hardened concrete. Analysis of the results showed that the hydration temperature and the HHV of the HSC decreased as MER amount increased. Increasing the amount of MER also decreased the ASV and ultimate autogenous shrinkage for HSC. Finally, it was found that the HHV is strongly correlated with the ASV, and an approximate formula relating the two parameters is proposed. The findings in this study will be useful for optimum concrete design by controlling early-age shrinkage in HSC.

Research on the Effect of Superfine Powder Micro Bead on the Properties of High-Strength Concrete

A sub-micron spherical powder material-micro bead, which has good water reduction, filling and enhancement effect, could be used as active mineral admixture in high-strength concrete. The affection of micro bead on the hydration temperature rise, mechanical properties, and shrinkage properties of high-strength concrete were studied, and the results showed that: micro bead could reduce the highest temperature peak of concrete, and at the low water-cement ratio, its small dosage could develop the compressive strength of concrete, and after instead of silica fume with suitable dosage, it could reduce the shrinkage of high-strength concrete.

The Experimental Study on Creep and Shrinkage of High Strength Concrete with Fly Ash

Shrinkage and creep characteristics of concrete are significant factors in the design of prestressed concrete structures. With large scale/span concrete structures developed, the fly ash or other blends are added into high strength concrete to improve the mechanical properties and workability. As a result, the existing shrinkage and creep predicting models have certain limitations. The creep and shrinkage behavior of high strength concrete with fly ash are studied in this paper. Proper predicting model for shrinkage and creep of high strength concrete is recommended. The influence factor of fly ash is proposed as well. These conclusions would be of great useful for structures with fly ash concrete.

EFFECT OF ADDITION OF FLY ASH ON SHRINKAGE CHARACTERISTICS IN HIGH STRENGTH CONCRETE

This paper presents the results of an experimental investigation carried out to evaluate the shrinkage of High Strength Concrete. High Strength Concrete is made by partial replacement of cement by fly ash. The shrinkage of High Strength Concrete has been studied using the different mixes from a minimum of 10% to maximum of 70 %. From the test results of the above investigation it can be concluded that the shrinkage strain of High Strength Concrete increases with increase in fly ash content. The rate of increase in shrinkage with time is uniform for low fly ash content, whereas it generally increases after 28 days for high volume of fly ash and the high volume fly ash concrete yields slow strength development at an early age.

Autogenous shrinkage of concrete with design strength 60–120 N/mm2

It is well known that autogenous shrinkage of high strength concrete (HSC) with a low water-to-binder ratio (W/B) is a major contributor to premature shrinkage cracking, which reduces the durability, strength and aesthetics of concrete structures. For concrete containing silica fume and having a low W/B, it is essential to accurately predict the autogenous shrinkage behaviour. In order to investigate the autogenous shrinkage behaviour of HSC, very high strength concrete (VHSC) and ultra high strength concrete (UHSC), five different W/B (0·3, 0·25, 0·2, 0·16 and 0·12) were studied in this work. To estimate the influence of admixtures on UHSC with W/B less than 0·2, fly ash (FA) and granulated blast-furnace slag (BFS) were added (0, 10, 20% and 0, 15, 30% by weight of total binder respectively). The experimental results and published data relevant to autogenous shrinkage were predicted using five different models for various grades of concrete. The test results showed that the largest amount of autogenous shrinkage was observed at W/B = 0·16, and additions of both of FA and BFS reduced autogenous shrinkage. The Eurocode 2 model and the Jonasson and Hedlund model substantially underestimated autogenous shrinkage of UHSC below W/B = 0·2, whereas the JSCE model and Dilger and Wang model overestimated the results for HSC and VHSC.

초기재령 고강도콘크트의 수화발열과 자기수축 특성의 상관관계에 관한 기초적 연구

In this study, to analyze the correlation between hydration heat and autogenous shrinkage of high strength concrete at an early age, hydration heating velocity and autogenous shrinking velocity as quantitative coefficients which represent the main properties of hydration heat and autogenous shrinkage were proposed. Two coefficients were calculated by statistical analysis and were equal with the regression coefficient. The complemented semi-adiabatic temperature rise test as test method to evaluate the hydration heat and autogenous shrinkage of concrete were proposed. In results of proposed test and analysis method, it was possible that early age properties of hydration heat and autogenous shrinkage of concrete were expressed numerically, and autogenous shrinkage was represented by equation with coefficients of hydration heat.

Estimating long-term creep and shrinkage of high-strength concrete

This paper presents the development of formulas to estimate the long-term creep and shrinkage of high-strength concrete. The experimental part of the work focused on concrete mixes having a fixed water/binder ratio of 0.35 and a constant total binder content of 500 kg/m 3 . The percentages of silica fume that replaced cement in this research were: 0%, 6%, 8%, 10% and 15%. According to the experimental results some equations are proposed for predicting the time-dependent behaviour of high-strength concrete. Based upon a survey of published experimental data, the accuracy of the proposed equations compares favorably with that of several common methods, which were developed for estimating the creep and shrinkage of normal strength concrete. Also, according to the experimental work, it is shown that to improve the estimation of long-term deformations of high-strength concrete utilizing the ACI and CEB methods, the results of short-term tests should be substituted into them.

Shrinkage of High Strength Concrete

This paper presents the results of an experimental investigation carried out to evaluate the shrinkage of High Strength Concrete. High Strength Concrete is made by partial replacement of cement by flyash and silica fume. The shrinkage of High Strength Concrete has been studied using the different types of coarse and fine aggregates i.e. Sandstone and Granite of 12.5 mm size and Yamuna and Badarpur Sand. From the test results of the above investigation it can be concluded that the shrinkage strain of High Strength Concrete increases with age. The shrinkage strain of concrete with replacement of cement by 10% of Flyash and Silica fume respectively at various ages are more (6 to 10%) than the shrinkage strain of concrete without Flyash and Silica fume. The shrinkage strain of High Strength Concrete is also compared with that of normal strength concrete. Test results show that the shrinkage strain of high strength concrete is less than that of normal strength concrete.

Autogenous shrinkage of high strength lightweight aggregate concrete

The characteristic of autogenous shrinkage (AS) and its effect on high strength lightweight aggregate concrete (HSIAC) were studied. The experimental results show that the main shrinkage of high strength concrete is AS and the amount of cement can affect the AS of HSLAC remarkably. At the early stage the AS of HSIAC is lower than that of high strength normal concrete, but it has a large growth at the later stage. The AS of high strength normal concrete becomes stable at 90 d age, but HSIAC still has a high AS growth. It is found that adjusting the volume rate of lightweight aggregate, mixing with a proper dosage of fly ash and raising the water saturation degree of lightweight aggregate can markedly reduce the AS rate of HSIAC.