Early Age Of Concrete Research Articles

Development of mechanical properties of concrete in vacuum tunnel of vacuum-based maglev train

The vacuum-based maglev train is an emerging transportation system currently under development worldwide. While concrete is a technically viable material for constructing vacuum tunnels, its mechanical performance in this unique environment remains unclear. This paper investigates the behavior of concrete in vacuum using a large customized vacuum tube. The results show that concrete undergoes significant water loss in vacuum, resulting in impeded cement hydration and porous hydration products with a foam structure. Vacuum exposure during the early ages of concrete has negative effects on mechanical properties. However, once the cement hydration reaches a high level of maturity, further vacuum exposure has little influence. Compared with atmospheric conditions, the shrinkage of concrete in vacuum is significantly increased. These findings provide a valuable experimental database and new insights for the use of concrete in vacuum-based maglev trains.

Early-age concrete strength development monitoring using piezoelectric self-emission and detection (SED) and coda wave energy (CWE)

The property of concrete is very significant to structural safety, and the early hydration process plays a critical role in the final concrete property. This paper develops a self-emission and detection (SED) principle with a single piezoelectric smart aggregate (SA) transducer, which is used as both an actuator and a sensor, to monitor the concrete early age strength development. The signal analysis is carried out by the coda wave energy (CWE). Experiments of concrete specimens with and without the SAs were conducted. Experimental results show a high correlation between the strength of early-age concrete and the CWE and non-linear fitting is used to establish the relationship between them. The proposed CWE features a simple analysis method, and the SED principle does not require consideration of the matching between the transmitting transducer and the receiving sensor, such as frequency range, sensitivity. Furthermore, the proposed method can be used as a reference for health monitoring of other structures and has good application prospects.

PERFORMANCE OF SUSTAINABLE GREEN CONCRETE INCORPORATED WITH FLY ASH, RICE HUSK ASH, AND STONE DUST

The performance of a sustainable green concrete with fly ash (FA), rice husk ash (RHA), and stone dust (SD) as a partial replacement of cement and sand was experimentally explored. FA and RHA have a high silica content, are highly pozzolanic in nature and have a high surface area without any treatment. These by-products show filler effects, which enhance concrete’s density. Results showed that the FA and RHA materials have good hydration behaviour and effectively develop strength at an early age of concrete. SD acts as a stress transferring medium within concrete, thereby allowing the concrete to be stronger in compression, and bending. Consequently, water absorption capacity of the sustainable concrete was lower than that of the ordinary one. However, a little reduction in strength was observed after the replacement of the binder and aggregate using the FA, RHA and SD, but the reduction was insignificant. The reinforced structure with sustainable concrete containing the FA, RHA, and SD generally fails in concrete crushing tests initiated by flexural cracking followed by shear cracks. The sustainable concrete could be categorized as a perfect material with no significant conciliation in strength properties and can be applied to design under-reinforced elements for a low-to-moderate service load.

3D Printing of Concrete Structures Modelled by FEM

This paper presents the possibility to utilize the 3D printing technology in civil engineering field specifically for concrete structures. Since this technology is booming last years and spreads in different fields of industry, the tools to analyse structures in such a way is important. Many research groups worldwide try to develop cement-based material suitable for 3D printing so that it might be used for civil engineering structures. Moreover, this technology brings necessity to check the safety of the structure at early ages of concrete. Therefore, the modelling and simulation of the digitally printed concrete structure would be of great help for such effort. The software tool that enables simulation of digitally printed concrete structure using a nonlinear FEM analysis is presented. ATENA is well established tool for such analyses of civil engineering structures made of concrete. The new module for digital printing simulation is developed as an additional feature of ATENA software. The 3D extrusion technology is supported. The paper describes the whole procedure how to model and analyse such structures and stress out all the differences compared to analyses of structures produced by traditional manner. The structure itself is modelled as usual in FE software, whereby based on velocity of printing head the time of printing, i.e. production of each element is calculated. It is later used to activate the elements during analysis and it also influence the material behaviour, such as shrinkage, strength etc.

Reinforced Spun Concrete Poles-Case Study of Using Chemical Admixtures.

The current research paper is focused on the experimental investigation of features of chemical admixtures (superplasticizers C-3, ‘Dofen’ and formaldehyde resin ACF-3M) utilizing in reinforced spun concrete structures. For the sake of comparison, the results of studying the effects of chemical admixtures on physical and mechanical properties on vibrated and spun concrete are provided. As a separate part of spun concrete products, the supporting poles of overhead power lines are introduced. The results obtained indicate, that the positive effect of chemical admixtures for spun and vibrated concrete is most pronounced at an early age of concrete. The effective amount of chemical admixtures for spun concrete is 0.15% of cement mass when formaldehyde resin ACF-3M and 1% of cement mass when superplasticizers C-3 and ‘Dofen’ are used. Moreover, the brief review about the reinforced spun concrete members is provided.

A new test method to characterize the pressure-dependent shear behavior of fresh concrete

The development of formwork pressure is essentially affected by the rheological behavior of fresh concrete, while the shear behavior itself might be influenced by the magnitude of normal pressure. A test set-up was developed in which the fresh mortar and concrete can be sheared in a pressure cell by a vane as a part of a concrete rheometer (ICAR). The concrete is directly loaded in the pressure cell by a hydraulic jack. Preliminary shear tests were conducted on concretes with moderate and high flowability at constant water/binder-ratio of 0.4 with the focus on the static yield stress. The additional pressure was applied up to 240 kPa. The consistency class of the concrete F4, F5 and F6 was varied by choosing the paste volume to 300, 315 and 330 l/m3, respectively. The results show the significant influence of applied pressure on the measured yield torque or yield stress in early concrete age especially for concretes with moderate flowability (F4) or with relatively high volume fraction of aggregates respectively. However, a significant increase of yield resistance by applied pressure was identified for all concretes after 90 min concrete age.

EXPERIMENTAL STUDY ON COMPRESSIVE YOUNG’S MODULI AND TENSILE YOUNG’S MODULUS OF FLY ASH CONCRETE

Initial cracks due to volume changes at an early age affect the durability of concrete structures, so numerical simulations are often conducted in order to predict cracks. Such prediction requires some mechanical properties of early age concrete. Tensile Young's modulus is directly dependent on the prediction of tensile stress and is one of the important input data for FEM analysis. However, direct tension test for tensile Young's modulus needs a unique apparatus and specimen, and such test is not suitable for evaluating Young's modulus at early ages of concrete. The present study compared tensile Young's modulus with compressive Young's moduli of Fly ash concrete. Compressive Young's moduli used in this study were secant modulus and initial tangent modulus. In addition, linear modulus taken from a regression line of a compressive stress-strain curve in the range of stresses less than the splitting tensile strength was also evaluated. It is found that the secant modulus, which is generally used as Young's modulus in Japan was clearly smaller than the tensile Young's modulus, which means that, tensile stresses evaluated using a secant modulus might be underestimated. On the other hand, linear modulus and initial tangent modulus were almost equal to the tensile Young's modulus. This result indicates that tensile stresses can be evaluated using Young's modulus obtained from a compression test with general apparatus and specimens.

Characterization of palm oil fuel ash and eggshell powder as partial cement replacement in concrete

The utilization of palm oil fuel ash (POFA) and eggshell powder (ESP) in concrete as a cement replacement is possible as green concrete materials. However, the POFA has original cellulose and physical modification is needed. This paper presents the characterization of POFA; unground POFA (UPOFA) and ground POFA(GPOFA) and ESP under microstructure examination includes x-ray fluorescence (XRF), scanning electron microscopy (SEM), and particle size analyzer (PSA). Then, the POFA-ESP as a cement replacement in concrete was investigated. Optimum mix proportion of POFA-ESP concrete was determined from compression test and GPOFA-ESP and UPOFA-ESP were through further investigation on pozzolanic reaction under x-ray diffraction (XRD) test at 14 days-concrete age. It was found that the combination of GPOFA-ESP as a cement replacement produced a concrete enhanced the compressive strength than normal concrete. ESP in this study seems like a catalyst which acting as mild accelerator or booster to improve the early age of strength development without disturb the later strength development of concrete. In addition, combination of GPOFA-ESP could increase the C-S-H gel at early age of concrete. It can be concluded that the combination of GPOFA-ESP had dual function; ESP and GPOFA took at early and later strength development, respectively.

Dynamic Measurements for Determining Poisson’s Ratio of Young Concrete

Abstract Knowledge of the elastic properties of concrete at early age is often a pre-requisite for numerical calculations. This paper discusses the use of a laboratory technique for determining Poisson’s ratio at early concrete age. A non-destructive test set-up using the impact resonance method has been tested and evaluated. With the method, it has been possible to obtain results already at 7 hours of concrete age. Poisson’s ratio is found to decrease sharply during the first 24 hours to reach a value of 0.08 and then increase to approximately 0.15 after seven days.

Effect of coarse aggregate type on chloride ion penetration in concrete

Long-term durability and sustainability of crucial infrastructure systems such as bridges and pavements are of utmost importance for the economic health of any society. Understanding factors that affect long-term deterioration of reinforced concrete structures can help enhance durability and sustainability of these systems. This paper investigates the effect of the type of coarse aggregate used in concrete on chloride ions penetrability. Twelve coarse aggregate types of different geologic formations (sedimentary, igneous, and metamorphic) were used to prepare fresh concrete in which silica fume and class C fly ash were used. All mix parameters including gradation and volumes of different aggregates were held constant in different mixes with the only variable being the aggregate type. The Rapid Chloride Penetration Tests were conducted on concrete specimens made with various aggregate types at ages of 28, 56, 91 and 365 days. Analysis of test results showed that the aggregate type as well as aggregate absorption rates have significant influence on the electrical charges passed through concrete, especially in early ages of concrete containing aggregates with sedimentary rock origin and relatively high absorption. These specimens exhibited the highest RCPT results indicating higher capacity to allow chloride ion penetration when compared to specimens with igneous and metamorphic rock aggregate of lower absorption values. This influence (discrepancy) diminishes with time for both aggregate type and absorption rates in terms of the magnitude of measured total charge passed.

Early-age performance of lag screw shear connections for glulam-lightweight concrete composite beams

Mechanical behavior of the shear connections has a significant influence on both the load-carrying capacity and the bending stiffness of timber-concrete composite (TCC) beams. All the studies reported so far have concentrated on the performance of TCC connections in mature concrete. The performance of shear connections for TCC beams at early concrete ages, however, has not been investigated yet. This information is essential to evaluate the structural behavior of TCC floors or bridges during construction. In this paper, a total of 18 push-out tests with concrete ages ranging from 12h to 28days are performed, to investigate the early-age performance of lag screw shear connections in the lightweight concrete. Development of concrete strength with time is also analyzed. At the concrete ages shorter than 7days, both the stiffness and strength of the screw connectors increase evidently with time, which follows the same growth trend with the concrete strength. After a 7-day cure, screw shear connections reach almost 100% of both the 28-day serviceability slip modulus and shear strength. Material properties of the glulam and the screw fastener are decisive in the shear performance of connections when the concrete hardens to some degree. Based on the experimental results, the accuracy of the design methods proposed in Eurocode 5 is evaluated. In addition, by non-linear regression of the experiment data, expressions to predict the development of load-carrying capacity and serviceability slip modulus for screw shear connections before 28days are established.

Shrinkage and creep behavior of an alkali‐activated slag concrete

In this paper, experimental results about the shrinkage and creep behavior of an alkali‐activated slag concrete (AAS‐concrete) are presented. The autogenous shrinkage of AAS‐concrete is pronounced at a relatively high water to binder ratio of 0.41. The ultimate value of autogenous shrinkage is determined to be higher than that of high‐strength concrete (HSC). The observed self‐desiccation at a later concrete age can be one of the reasons for the autogenous shrinkage. In a drying environment of 65% relative humidity AAS‐concrete exhibits a significantly higher total shrinkage compared to normal‐strength concrete composed of Portland cement.In the contrary to normal and HSC carbonation shrinkage must not be neglected for AAS‐concrete in the early concrete age. The sum of drying and carbonation shrinkage develops much more rapidly for AAS‐concrete in the first weeks after the beginning of drying. Based on the experimental results the shrinkage behavior of AAS‐concrete cannot be predicted by conventional models. The creep behavior of the AAS‐concrete was investigated under sealed and unsealed conditions. The creep coefficients for both conditions are higher than those calculated when using conventional models.

STAGED NONLINEAR STATIC ANALYSIS OF SHRINKAGE IN REINFORCED CONCRETE ONE-WAY SLABS

The cracking due to restrained shrinkage at early ages of concrete is one of the shortcomings of concrete, which may reduce its sustainability. Staged nonlinear static analysis adopted by SAP2000 software is used to analyze one-way slabs applied to restrained shrinkage. Staged nonlinear static analysis has been improved using the concept of cracked element and the proposed model showed good correlation with test results. Creep strain calculated by CEB-FIP cannot be used correctly with shrinkage at early ages of concrete (first three months), and a modification factor has been suggested in the present research. The modification factor is dependent on the steel ratio. Shrinkage relaxed due to creep has been found slightly affected by the steel ratio, which may be considered constant and equals to 60% approximately. Steel reinforcement will control crack width by reducing the restrained length of shortened concrete due to shrinkage, which is equal to the distance between multiple cracks.

조기강도 개선형 시멘트 및 초기수화 촉진 혼화제를 사용한 콘크리트의 조기압축강도 발현특성 평가

본 연구에서는 콘크리트의 조기강도 확보를 통해 골조공기를 단축하는 것을 목표로 하여 시멘트 종류, 고성능감수제의 감수율, 초기수화 촉진 혼화제의 혼입에 따른 콘크리트의 조기강도 발현성능을 검토하였다. 조기강도 개선형 시멘트와 Sodium persulfate, Potassium hydroxide의 초기수화 촉진물질에 의해 12시간에 5MPa, 18시간에 14MPa의 조기강도를 확보할 수 있는 것으로 나타났다. 이를 통해 건설현장에서 거푸집의 골조공기를 단축시켜 원가절감이 가능할 것으로 기대된다. In this study, revelation performance of concrete at early age according to types of cement, water reducing ratio of high performance superplasticizer and mixing of accelerator for early hydration was examined aiming for reduction of construction period of framework through securing strength at early age of concrete. It was observed that strength at early age, 5MPa in 12hours, 14MPa in 18hours, is secured by early strength improvement type cement and using promotion admixture for early hydration which are Sodium persulfate, Potassium hydroxide. Therefore cost reduction is expected to be possible in construction site by reducing construction period of frame work.

Application Acoustic Emission Method and Impedance Spectroscopy for Monitoring Concrete During Hardening

It is known that concrete is one of the most popular building materials nowadays. There are many traditional, mainly destructive methods for monitoring its properties during its lifetime. It is clear that its properties depend significantly on the composition of concrete mixture. Concrete lifetime depends mainly on curing during the first 7 days after making the mixture. The paper shows the possibilities of applying Acoustic Emission and Impedance Spectroscopy methods during the early age of concrete.

Experimental study on the development of compressive strength of early concrete age using calcium-based hardening accelerator and high early strength cement

Steam curing is necessary to be used in the manufacturing of precast concrete, thus, a large amount of energy is consumed and the turnover of forms is low. This practice leads to reduction in productivity. This paper focuses paper focuses on developing early stage strength for precast concrete of more than 10MPa after 6h of curing at room temperature without steam curing. Various micro-analysis tools such as TG/DTA, Conduction Calorie Meter, XRD, SEM and MIP were conducted on concrete and cement paste with the amount used of calcium-based hardening accelerator (CHA) for tricalcium silicate (C3S). Results show that the reaction effect of the CHA was terminated before reaching 12h, the initial setting of concrete was in 80 min with 3% of CHA. The rate of heat evolution is increased in the mechanism of developing the compressive strength in early age and the yield of Ettringite, Ca(OH)2 and C–S–H is increased at early age due to the fact that the CHA stimulates tricalcium aluminate (C3A) and C3S in high early strength cement when using calcium-based hardening accelerator into high early strength cement. Additionally, the pore volume of range of 20–100nm decreased with the CHA content.

Dilation behavior of seven-wire prestressing strand – The Hoyer effect

In prestressed concrete elements, bond between pretensioned strands and the surrounding concrete is attributed to adhesion, mechanical interlock and the friction and ‘wedge-action’ attributable to radial expansion of the strand following release. The latter effect is referred to as the Hoyer effect and is the subject of this paper. The Hoyer effect contributes primarily to the transfer of the initial prestressing force to the concrete thereby affecting the transfer length. The transfer of large prestressing forces, particularly at an early concrete age, can lead to local cracking associated with bursting stresses or splitting associated with transfer of the strand force through bond. An analysis of embedded strand behavior based on fundamental principles of mechanics clearly demonstrates the importance of strand dilation characteristics in the development of concrete stresses and therefore the transfer of prestressing forces. An experimental program demonstrates that the dilation of seven wire strand is affected by not only the Poisson’s ratio for steel but also the ‘tightening’ of the helical wires and effects of bearing between these wires. The resulting dilation of a seven wire strand is larger than Poisson’s ratio for steel and is found to be a function of strand diameter. A discussion of design code provisions for prestressing strand transfer length is included. North American practice, while conservative, does not explicitly address the mechanics of stress transfer. Improvement in this regard could result in more efficient prestressed concrete structures. European practice, on the other hand, appears to reasonably capture the Hoyer effect.

Experimental Study on the Impact of Admixture for Concrete Heat of Hydration and Early-Age Contractile Properties

During the technology development of modem concrete, concrete structure crack (especially early-age crack) becomes more and more serious and has been one of main research directions of civil engineering. This paper aims at the seriousness of concrete structure crack and presents one of main cause is that concrete early-age (especially autogenous shrinkage) become large through the experimental study. autogenous shrinkage are mainly belongs to temperature cracks and desiccation cracks. Analyses the affection of ash and water reducing agent on the hydration heat, under the optimum proportion experiment which aims at reducing he hydration heat of cement. The best program are obtained that double mix with 20% fly ash and 1.5% water reducing agent .Design mortar’s early anti-crack experiment, and study crack-resistance and other mechanical properties based on different ages & different mix proportion. From the experiment, analyses early cracking under the influence of admixtures. The mix proportion of 20% fly ash, 10% slag and 1.2% water reducing agent can minimize the creation of cracks.

Concrete early age basic creep: Experiments and test of rheological modelling approaches

Early age cracking of massive concrete structures highly depends on creep and especially basic and thermal tensile creep. Direct tensile test are difficult to perform and actually no consensus on phenomenon involve and on tensile creep compliance (with respect to compressive one) is available. This contribution compares creep compliance of a concrete mix which is representative of a French nuclear power plant. The obtained creep compliances are similar in tension and in compression. Since temperature evolution could be important in massive structures, temperature effects are also studied. A significant increase of creep strains is shown for an elevated temperature (60°C) but also for a temperature variation (from 20°C to 60°C). Finally, this paper highlights the ability of rheological models to reproduce creep strains due to complex loading history (thermal and mechanical ones).

One Monitoring Device for Concrete Early Age Shrinkage

With liquid as transmission medium, using ultrasonic precision measurement, an effective device was studied and developed for monitoring early age shrinkage of concrete. With it, shrinkage of concrete in the plastic stage could be accurately monitored. During the measurement, 0.01mm and even higher monitoring accuracy could be achieved.