Drying Shrinkage Cracking Research Articles

버블시트 피복양생법에 의한 소성 및 건조수축 균열저감

버블시트 피복양생법에 의한 소성 및 건조수축 균열저감

Effectiveness of Fiber Reinforcement on the Mechanical Properties and Shrinkage Cracking of Recycled Fine Aggregate Concrete.

This paper presents an experimental study conducted to investigate the effect of fiber reinforcement on the mechanical properties and shrinkage cracking of recycled fine aggregate concrete (RFAC) with two types of fiber—polyvinyl alcohol (PVA) and nylon. A small fiber volume fraction, such as 0.05% or 0.1%, in RFAC with polyvinyl alcohol or nylon fibers was used for optimum efficiency in minimum quantity. Additionally, to make a comparative evaluation of the mechanical properties and shrinkage cracking, we examined natural fine aggregate concrete as well. The test results revealed that the addition of fibers and fine aggregates plays an important role in improving the mechanical performance of the investigated concrete specimens as well as controlling their cracking behavior. The mechanical properties such as compressive strength, splitting tensile strength, and flexural strength of fiber-reinforced RFAC were slightly better than those of non-fiber-reinforced RFAC. The shrinkage cracking behavior was examined using plat-ring-type and slab-type tests. The fiber-reinforced RFAC showed a greater reduction in the surface cracks than non-fiber-reinforced concrete. The addition of fibers at a small volume fraction in RFAC is more effective for drying shrinkage cracks than for improving mechanical performance.

Early age performance and mechanical characteristics of recycled PET fibre reinforced concrete

In this study the performance of concrete reinforced with fibres produced from waste non-biodegradable plastic, polyethylene terephthalate (PET), has been thoroughly investigated. The novelty of the study, to the authors’ knowledge, consists in the fact that fibres have been employed as directly shredded from collected waste plastic bottles, with no processing through, e.g., plastic melting and fibre spinning. Moreover, a comprehensive investigation has been herein undertaken, which ranges from the identification of the mechanical behaviour of the fibres to the assessment of their bond with the matrix and of the early age and hardened state properties of the recycled PET fibre reinforced concrete.Different types of shredded recycled PET fibres, straight and deformed, together with different fibre lengths, 30mm and 50mm, have been assessed, for varying percentage addition in concrete. The tensile properties and pull out characteristics of the fibres have been determined. The effects of fibres in mitigating plastic and restrained drying shrinkage cracking were then assessed and, finally, the compressive strength and the flexural performance of the fibre concrete were determined. The cracking potential of fibre-reinforced mortar thin slabs was also assessed.The use of shredded recycled PET fibres in concrete has been shown to lead to interesting improvements in performance for various fibre concrete characteristics and offers a potential alternative for this material.

전력구 콘크리트 구조물의 건조수축 균열특성에 관한 연구

The purpose of this study is to predict the cracking behavior and suggest the method of controlling the cracking in concrete box culvert for power transmission due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis cor responding to drying shrinkage on concrete box culvert are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of box culvert shows the different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

Paste backfill of high-sulphide mill tailings using alkali-activated blast furnace slag: Effect of activator nature, concentration and slag properties

The effect of activator type, concentration and slag composition on the strength and stability properties of paste backfill (CPB) of high-sulphide tailings using alkali-activated slag (AAS) as binder (7wt.%) were investigated in this study. Acidic and neutral (AS–NS) slags were activated with liquid sodium silicate (LSS) and sodium hydroxide (SH) at 6–10wt.% concentrations. Ordinary Portland cement (OPC) results were used for comparison. The strength development was found to remarkably improve with increasing the concentration from 6 to 8wt.%. Further increase in concentration did not enhance the strength. SH was determined to produce higher early-age strength whilst LSS produced higher long-term strengths as an indication of slag selectivity for activators. More extensive gypsum formation was observed at lower concentrations in SEM/EDS studies. An increase in Na2O concentration raised the activator consumption. High concentrations also led to poorly crystallized C–S–H gel, loose structure and drying shrinkage cracks especially in NS–SH samples. A reduction in total porosity up to 20% was obtained in AAS samples compared to OPC. Amorphous structure, chemical modulus ratio and/or basicity index (BI) values were seen to control the pozzolanic reactivity, and therefore, the alkali-activation and hardening process.

Prediction of restrained shrinkage crack widths of slag mortar composites by Takagi and Sugeno ANFIS models

Shrinkage is an important parameter affecting crack development of mortars and concrete. With the occurrence of shrinkage cracks, the concrete starts to be exposed to the corrosion which significantly decreases the durability of concrete or mortars. In this study, the results of free shrinkage tests determining the length changes and ring test determination of the restrained drying shrinkage cracks are used for predicting the crack widths of granulated blast furnace slag fine aggregate mortars using adaptive-network-based fuzzy inference system (ANFIS). Subsequently, replacement ratios, drying time and free shrinkage length changes are used as inputs and crack width as output in order to predict the shrinkage cracking of these mortar types. The experimental test and the prediction results from the ANFIS model are compared with each other. It is clear that ANFIS can be employed directly in the prediction or discussion of the drying shrinkage cracks.

EFFECT OF CERAMIC POWDER (CP) ON COMPRESSIVE STRENGTH AND DRYING SHRINKAGE CRACKS OF CEMENT MORTAR

This investigation is conducted to study the effect of addition of ceramic powder (CP) on drying shrinkage cracks and compressive strength of cement mortar. Steel molds having a trapezoidal section, and the end restrained at square shape used to study restrained drying shrinkage of cement mortar. Specimens of compressive strength, density, were cast. The admixture (CP) was used as addition with three levels of (2%, 4% and 8%) by weight of dry cement. All specimens were cured for (14 days). Average of six results was taken for any test of compressive strength and density. The experimental results showed that the adding of this admixture cause a delay in a formation of cracks predicted from a drying shrinkage, increase compressive strength at levels of (4%) of admixture and cause the decreasing in the density of cement mortar Specimens. The increment in compressive strength at level (4%) was (6.11%), but at level of (8%) it was decreased by (3.9%). The admixture has the visible effect in delay of the information of shrinkage cracks and decrease of its number.

Prediction of Drying Shrinkage Cracking of Eco-efficient Steel Chip Reinforced Cementitious Composite Considering Tensile Creep

This paper reports on the characteristics of drying shrinkage and creep of steel chip reinforced cementitious composite (SCRCC). In this study, first, four restrained wall specimens made of normal mortar and SCRCC with various numbers of steel reinforcing bars (4 or 10) were prepared to compare drying shrinkage characteristics. The specimens were re-strained on the rigid laboratory floor so that shrinkage cracks were induced. The drying shrinkage strains were measured by the contact gauge method and compared with unrestrained small specimens. The number of cracks was simultane-ously observed. Second, bond tests were prepared to evaluate the bond characteristics between the SCRCC and the steel bar. Third, creep tests were performed to improve the accuracy of the analysis of the drying shrinkage behavior. Twelve block specimens were made and a constant flexural load was applied for 7, 14, and 28 days. The observed shrinkage strains and creep strains of SCRCC were modeled according to CEB-FIP Model Code 1990. These models were incor-porated with bond computation between the SCRCC and the steel bar to predict the number of drying shrinkage cracks. The computed equivalent number of cracks based on the shrinkage strain model, the creep model, and the bond model derived from a pull-out test generally agreed with the test results.

최적화 프로니 급수를 이용한 콘크리트 건조수축 균열해석

If the concrete members are restrained, drying shrinkage strain develops tensile stress and consequently develops cracks. Creep which is another long term characteristic of concrete relaxes the tensile stress due to shrinkage. Creep is represented in the form of creep function or relaxation function and the relaxation effect of creep can be considered by numerical integration. Creep function or relaxation function depend on two time variables representing creep effect and aging effect, respectively. In general purpose finite element program like Abaqus, Prony series are used in creep analysis to evade the complexity of numerical integration of creep function. However, Prony series in Abaqus has critical deficiency that it can represent only creep effect excluding aging effect. In this paper, optimized Prony series was proposed to complement the weakness of Prony series in Abaqus. The optimized Prony series can include not only creep effect but also aging effect. Drying shrinkage crack analysis was performed using XFEM features in Abaqus to demonstrate the efficiency of the optimized Prony series. Analysis model representing the drying shrinkage crack test specimen specified in KS F 2595 was used to compare with the shrinkage crack development measured in experiment. Analysis results with the optimized Prony series were quite similar to the experiment results and show the effectiveness of the proposed method in long term analysis of concrete structures.

Load Transfer Behavior of Cracking for Cement Concrete Pavement

In order to reduce the temperature and drying shrinkage cracking in cement concrete pavement, setting up cracks which becomes the weakest part of the cement concrete pavement. Load transfer behavior of cracking has a great influence on road performance and used lifetime in cement concrete pavement. The improvement of load transfer behavior of cracking is conducive to maintain effective load transfer between the pavement and to enhanced bearing capacity of pavement structure, also to reduce the damage of the structure, which is an important technical approach to extend the used lifetime of pavement. This paper describes the mechanism of load transfer and research status of crack, and points out the problems existing in the crack load transfer ability of research and development trend.

미립 잔골재 혼입이 콘크리트의 배합 및 건조수축 균열 특성에 미치는 영향

In the middle east and the north africa, very fine sand such as dune sand (or desert sand) is used in concrete production as concrete fine aggregate. The particle size and grading of dune sand are very small and the properties of concrete could be greatly affected when very fine sand is used as concrete fine aggregate. In this study, the effects of very fine sand on the properties of concrete mixture and drying shrinkage cracking were investigated. Under condition of same amount of superplasticizer of plain mixture, to meet the target slump range, water content increased as the replacement of very fine sand increased. Compressive strength of concrete used very fine sand were 7.6~15.3% higher than that of plain concrete. Also, tensile strength were increased 24.0~28.4% when very fine sand used in concrete. Time-to-cracking were 16.8~25.7% shortened and stress rate was increased maximum 32.7% when very fine sand was used in concrete. It indicated that the risk of drying shrinkage cracking of concrete used very fine sand was higher than plain concrete. However, the higher use of very fine sand did not lead the higher risk of drying shrinkage cracking.

Modeling the Drying Shrinkage Cracking of Untreated Soils and Cementitiously Stabilized Soils

Shrinkage cracking is a major concern that greatly limits the use of local soils and their cementitious stabilization in geosystems. Few studies have addressed the fundamental mechanisms of shrinkage and the related cracking in soils and cementitiously stabilized soils. This study characterizes two untreated soils and two soils treated with cement. On the basis of the matric suction and free-shrinkage measurements, a relationship was established between moisture loss and the drying shrinkage potential of untreated and cementitiously stabilized soils. Thus, on the basis of moisture loss, the shrinkage potential of the soils could be predicted. In addition, stress–strain relationships of soils that were affected by matric suction and cement hydration were developed on the basis of indirect tensile testing. Models were input into finite element analysis to characterize the moisture loss, drying shrinkage potential, shrinkage stress under given restraint condition, and shrinkage cracking of untreated and cementitiously stabilized soils. A drying shrinkage cracking test was designed to verify the models and procedure in terms of cracking time, tensile strength, and tensile load due to shrinkage. This study provides an approach to predicting the shrinkage cracking to properly design a pavement.

スチールチップ補強セメント系複合材料の引張クリープを考慮した乾燥収縮ひび割れの予測

This study investigates characteristics of drying shrinkage and creep of “Steel Chip Reinforced Cementitious Composite (SCRCC)”. Firstly, four restrained wall specimens made of normal mortar and the SCRCC with varied amount of steel reinforcing bars (4 or 10) are prepared to compare the drying shrinkage characteristics. The specimens are restrained on rigid laboratory floor so that shrinkage cracks are induced. The drying shrinkage strains are measured by contact gauge method and compared with unrestrained small specimens. Number of cracks are simultaneously observed. Secondly, creep test is carried out to improve accuracy of analysis of the drying shrinkage behaviors. Twelve block specimens are made and constant flexural load is applied for 7, 14, and 28 days. The shrinkage strains and creep strains of SCRCC are modeled by modifying CEB-FIP Model Code 1990. These models are incorporated with bond computation between SCRCC and steel bar to predict the number of drying shrinkage cracks.

팽창재와 수축저감제를 사용한 HPFRCC의 수축 저감 성능

HPFRCC는 물-결합재비 (W/B)가 20%로 상당히 낮고 굵은 골재를 사용하지 않으며, 고분말 혼화재료를 혼입하기 때문에 자기수축이 상당히 크게 발생하여 구조물 적용 시 균열저감대책이 필요하다. 따라서 이 연구에서는 HPFRCC의 수축을 효율적으로 저감시키기 위한 방법으로 수축저감제와 팽창재의 사용을 검토하기 위하여 이들의 단독 또는 병행 혼입률에 따른 역학적 특성과 구속 수축특성을 평가하였다. 구속수축 실험 중에서 링-테스트 (Ring-test)를 통하여 HPFRCC에 사용되는 시멘트에 대하여 중량비로 수축저감제 1%와 팽창재를 7.5%를 병행 사용하였을 경우 압축강도와 인장강도가 크게 저하되지 않으면서도 수축을 가장 효율적으로 저감시킬 수 있는 최적 배합임을 도출하였고 수정된 건조수축 균열실험을 통하여 이를 검증하였다. High-performance fiber-reinforced cement composite (HPFRCC) shows very high autogenous shrinkage, because it contains a low water-to-binder ratio (W/B) of 0.2 and high fineness admixture without coarse aggregate. Thus, it needs a method to decrease the cracking potential. Accordingly, in this study, to effectively reduce the shrinkage of HPFRCC, a total of five different ratios of SRA (1% and 2%), EA (5% and 7.5%), and a combination of SRA and EA (1% and 7.5%) were considered. According to the test results of ring-test, a combination of SRA and EA (1% and 7.5%) showed best performance regarding restrained shrinkage behavior without significant deterioration of compressive and tensile strengths. This was also verified by performing modified drying shrinkage crack test.

Performance of waste glass powder (WGP) supplementary cementitious material (SCM) – Drying shrinkage and early age shrinkage cracking

Performance of waste glass powder (WGP) supplementary cementitious material (SCM) – Drying shrinkage and early age shrinkage cracking

고분말도 혼화재를 첨가한 삼성분계 시멘트 콘크리트의 내구성 평가

PURPOSES : The purpose of this study is to evaluate the durability of ternary blended concrete mixtures adding ultra fine admixture. METHODS : From the literature review, crack was considered as the main distress failure criterion on concrete bridge deck pavement. To reduce the initial crack development due to drying shrinkage, CSA expansion agent and shrink reduction agent were used to ternary blended concrete mixtures as a admixture. Laboratory tests including chloride ion penetration test, surface scaling test, rapid freeze & thaw resistance test, non restrained drying shrinkage and restrained drying shrinkage test were conducted to verify the durability of ternary blended concrete mixtures. RESULTS : Based on the test results, proposed mixtures were verified as high qualified durable materials. Expecially initial drying shrinkage crack was not occurred in ternary blended concrete mixtures with CSA expansion agent. CONCLUSIONS : It is concluded that the durability of proposed ternary blend concrete mixture was acceptable to apply for the concrete bridge deck pavement.

Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus.

Curing cement concrete by using shrinkage reducing admixture and curing compound

The performance of near surface concrete plays an important role in improving durability of concrete structures. The early-age drying shrinkage cracking of near surface concrete due to the moisture loss or poor curing is a main cause of durability deterioration. To minimize the drying shrinkage and moisture loss of concrete, a double-coating curing method was proposed in this study, which was coating the concrete with a shrinkage reducing admixture (SRA) and then a curing compound successively on the concrete surface after demolding. The effects of the curing method on drying shrinkage, moisture loss, strength, chloride-penetration resistance and water absorption of cement mortar and concrete were investigated. The results indicated that the curing method can obviously minimize the drying shrinkage and moisture loss of cement mortar. And the water absorption rate and chloride penetration of concrete cured under this method are significantly reduced.

Potential use of fibrous grass silage press-cake to minimise shrinkage cracking in low-strength building materials

The fibre-rich press-cake fraction produced by ‘green biorefineries’ may provide a sustainable solution for the control of restrained drying shrinkage cracking in stabilised soil blocks and cementitious mortars. Following determination of the tensile strength of selected grass species at different harvest dates, the effect of press-cake inclusion was assessed in controlling the shrinkage of clay and mortar specimens. The press-cake was found to be effective in controlling the onset of early-restrained drying shrinkage cracking in both clay and cementitious specimens. The addition of press-cake fraction to terracotta pottery clay had a pronounced beneficial effect on early-restrained shrinkage, increasing the time to first crack by over 5 h and reducing the crack width by 4.9 mm relative to the control. Inclusion of the press-cake fraction in mortar specimens (at a rate of 2.2 kg m −3 ) eliminated crack formation completely, compared with the unreinforced mortar specimens which cracked after 3 h. This positive influence on the consequences of restrained shrinkage occurred despite the fact that early-age free shrinkage rates were found to increase in proportion to press-cake inclusion rate. Furthermore, in cementitious specimens the performance of the press-cake compared well with polypropylene fibres in respect of mitigating the risk of cracking due to early-age restrained shrinkage in cementitious specimens.

Study on Anti-Cracking of Mortar and Concrete Pavement in Dry Areas of North China

It always is a technical problem about the drying shrinkage cracking of mortar plastering layer and concrete surface layer of building wall in construction field. The influencing factors of cracking have regional climate characteristics, building structures, raw materials, construction standards etc. Analyzed the cracking principle of mortar and concrete pavement in dry areas of North China, and developed the complex additives having five kinds of performances: efficient water conservation, compensated shrinkage, fiber reinforcement, self-repair cracks in the matrix and polymers toughening, which is used to mortar and concrete to alleviate drying shrinkage cracking. The series of processes and product performances of the complex additives has been introduced in this paper.