Ring Shrinkage Research Articles

Studies on the Influence of Drying Shrinkage Test Procedure, Specimen Geometry, and Boundary Conditions on Free Shrinkage

Although considerable progress has been made in enhancing the use and interpretation of free ring shrinkage test, little is known about the impact of the test procedure, the specimen geometry, the surface area-to-volume (S/V) ratio exposed to drying, and the boundary conditions (sealing configuration) on the measured shrinkage. This paper highlights recent findings illustrating the influence of the test procedure, the S/V ratio exposed to drying, the geometry of specimen, and the boundary conditions. A series of experimental results are presented from free shrinkage on ring test specimens to illustrate that the test procedure can significantly influence the measured free shrinkage. A second series of experimental results are presented from specimens with different geometries and S/V ratio exposed to drying to illustrate that drying shrinkage is dependent on both the specimen geometry and the surface exposed to drying. Test results further show that, even for the same S/V ratio exposed to drying, shrinkage is strongly dependent on the specimen’s geometry and boundary conditions.

Restrained shrinkage cracking of amorphous metallic fibre-reinforced concrete

In this study, the cracking characteristics of amorphous metallic fibre (AMF)-reinforced concrete, due to restrained drying shrinkage, were experimentally investigated. Three types of test were carried out to investigate the effect of the fibres on the free and drying shrinkage of concrete: free drying shrinkage test, ring shrinkage test and slab shrinkage test. The fibre volume fractions used in the test were 0·2% and 0·4% for ring specimens, and 0·2%, 0·4% and 0·6% for slab specimens. Based on the results of the free drying shrinkage test, it was found that the addition of AMF into concrete could significantly reduce the free drying shrinkage: when using AMF-reinforced concrete, free drying shrinkage was reduced by 24%. In addition, in the test results of the restraint shrinkage tests (ring and slab types), crack development time was delayed from 5 to 7 d, and crack width was reduced to from 36·5% to approximately 74·6%, according to the fibre volume fraction. Thus, AMF can be used to improve the shrinkage cracking performance of concrete.

On concrete restrained eccentric ring and squared eccentric ring shrinkage test methods

In the conventional restrained ring test method (RRTM) for evaluating restrained concrete shrinkage, the specimen geometry is a concentric ring, which causes cracking initiation anywhere in the ring randomly and it is inconvenient to observe. Aiming at improving the identification of cracking location, this article presents two improvements based on RRTM, namely the restrained eccentric ring test method (RERTM) and the restrained squared eccentric ring test method (RSERTM), in which the specimen geometry is a non-concentric ring for the former and a square with a non-concentric hole inside for the latter. In other words, in comparison with RRTM, the specimen geometry in RERTM and RSERTM now is featured with the inner ring being placed eccentrically. Numerical simulation was performed to guide the selection of specimen dimensions and to reveal the stress concentration phenomenon. Experiments were conducted to record cracking time and cracking locations. It is seen that, compared with RRTM, the eccentricity introduced in RERTM and RSERTM will give rise to stress concentration, guide cracking location, and noticeably shorten cracking time.

Evaluation of Shrinkage Resulted Cracking of High Strength Calcium Sulfoaluminate Cement Concrete with Impact of Internal Curing

In this paper, restrained ring test and shrinkage test are carried on three kinds of concrete—high-strength portland cement concrete, high-strength calcium sulfoaluminate cement concrete and high-strength calcium sulfoaluminate cement concrete with internal curing in order to evaluate the shrinkage induced cracking performance of the concretes. The experimental results show that calcium sulfoaluminate cement concrete exhibits lower shrinkage caused by surface drying comparing to portland cement concrete. Internal curing can eliminate most of the autogenous shrinkage of concrete. In the ring test, the latter two concrete did not crack during the whole test history—42 days, while high-strength portland cement concrete cracked at the 13th day after casting. High strength calcium sulfoaluminate cement concrete exhibits better anti-cracking ability than the high strength portland cement concrete with the same strength grade.

Numerical modelling of desiccation cracking in a restrained ring test

Tensile cracking due to desiccation and fracture properties are of great importance in clay liners, earth dam engineering, waste contaminant systems, and mine tailings. This paper presents restrained shrinkage test results and analyses of consolidated desiccating soil, and compares results with numerical analyses using the computer program Universal Distinct Element Code (UDEC). The cohesive crack method was used as it is more appropriate than linear elastic fracture mechanics for soil cracking at high moisture contents with the likely presence of plasticity during fracture. The variation of the radial stresses on the inner ring with water content was used to model mode I cracking and gather fracture properties of the propagating crack. The model was validated on kaolin clay tested under restrained ring shrinkage and was compared with various test results and results from the literature. The test could be a valuable tool in determining fracture properties during desiccation.

Numerical analysis of the thermal active restrained shrinkage ring test to study the early age behavior of massive concrete structures

Several tests, devoted to the study of cracking due to autogenous and drying shrinkage, exist in the literature. They are generally not relevant for the study of massive structures for which thermal strains plays a key role. Therefore, an active ring test has been developed to study cracking due to restrained thermal shrinkage. This test is an evolution of the restrained shrinkage ring test which allows us to take into account both autogenous and thermal shrinkage. With this test, the early age cracking due to thermal restrained shrinkage (effect of the temperature rate), the influence of reinforcement and construction joints have been studied (Briffaut et al. (2011) [1]).Nevertheless, in this test, several phenomena occur simultaneously (hydration, shrinkage, creep…) and their effect cannot be easily decoupled. So, complementary tests have been performed to study each phenomenon separately and the ring test has been numerically simulated in order to identify coupling between creep and damage and to quantify the strength decrease due to construction joints. A good agreement between experimental and numerical results has been obtained for ring with reinforcement and construction joints. With the proposed model and the identified materials parameters validated on the active restrained ring test, numerical simulations of the construction of a real massive structure have been performed, and a parametric study has been achieved to highlight the creep effect.

Quality characteristics of air-dried apple rings: Influence of storage time and fruit maturity measured by time-resolved reflectance spectroscopy

With the aim of studying the influence of maturity and of cold storage time on the quality characteristics of air-dried apple rings, 60 apples (cv Pink Lady®) were measured at harvest by time-resolved reflectance spectroscopy (TRS) at 670nm, ranked on the basis of decreasing absorption coefficient at 670nm (μa670, increasing maturity) and hence classified based on the ranking order as less mature (LeM), medium mature (MeM,) and more mature (MoM). The sixty fruit were, then, randomized into 3 batches corresponding to 3 storage times (0, 3 and 5 months in normal atmosphere at +1°C), and, at each storage time, 3 rings/fruit were air-dried at 80°C up to a constant weight using a pilot air circulated drier. Quality characteristics of fresh fruit and of air-dried rings were analysed by ANOVA and PCA statistical analyses. Stored fruit compared to fruit at 0m were softer, had lower stiffness and energy-to-rupture, and higher soluble solids content (SSC), relative intercellular space volume (RISV) and L*f. LeM class had lower SSC and dry matter, and the MoM class higher a*f and lower b*f than the other two classes. 3m-Apples showed the highest differences with respect to fresh ring in browning index (BI), total colour, chroma and hue, compared to fruit processed at 0m and 5m. Air-dried rings from less mature apples (i.e. those processed at 0m and of LeM class) had higher Fmax, Emod, E and BI than those from more mature fruits (i.e. those processed after storage and of MoM class). PCA underlined the positive relationship between mechanical characteristics of fresh fruit with those of dried rings and ring shrinkage, which were opposite to RISV, SSC and weight loss.

A thermal active restrained shrinkage ring test to study the early age concrete behaviour of massive structures

In massive concrete structures, cracking may occur during hardening, especially if autogenous and thermal strains are restrained. The concrete permeability due to this cracking may rise significantly and thus increase leakage (in tank, nuclear containment…) and reduce the durability. The restrained shrinkage ring test is used to study the early age concrete behaviour (delayed strains evolution and cracking). This test shows, at 20 °C and without drying, for a concrete mix which is representative of a French nuclear power plant containment vessel (w/c ratio equal to 0.57), that the amplitude of autogenous shrinkage (about 40 μm/m for the studied concrete mix) is not high enough to cause cracking. Indeed, in this configuration, thermal shrinkage is not significant, whereas this is a major concern for massive structures. Therefore, an active test has been developed to study cracking due to restrained thermal shrinkage. This test is an evolution of the classical restrained shrinkage ring test. It allows to take into account both autogenous and thermal shrinkages. Its principle is to create the thermal strain effects by increasing the temperature of the brass ring (by a fluid circulation) in order to expand it. With this test, the early age cracking due to restrained shrinkage, the influence of reinforcement and construction joints have been experimentally studied. It shows that, as expected, reinforcement leads to an increase of the number of cracks but a decrease of crack widths. Moreover, cracking occurs preferentially at the construction joint.

Shrinkage Cracking Behavior of Fiber Reinforced Concrete: As Assessed Using the Restrained Ring Test

Abstract The restrained shrinkage ring test has been used to assess the shrinkage cracking potential of concrete mixtures and to assess the influence of mixture proportions, admixtures, and the use of fiber reinforcement on shrinkage cracking. However, further work is still needed to link the shrinkage cracking performance of fiber reinforced concrete as evaluated using the restrained ring test to the behavior of these mixtures in different size concrete elements in the field. This study used finite element analysis to investigate the cracking behavior of restrained rings of different sizes. The results indicated that due to damage localization the crack widths that develop in the restrained rings are greatly dependent on the size of the restrained ring, the degree of restraint, and the softening behavior of the concrete. This size dependence would influence the performance that would be expected in the field.

Implementation of Internal Curing in Transportation Concrete

Internal curing is one method used to improve the mechanical properties and durability of concrete. Internal curing provides additional water to the hydrating cement particles that is not part of the original mixing water. The Ohio Department of Transportation (Ohio DOT) observed significant differences in early-age cracking of high-performance bridge decks in northeast Ohio and attributed it to differences in the absorption of the coarse aggregate. Ohio DOT sponsored a study to investigate the properties and cracking tendencies of several of its classes of concrete, including high-performance concrete, paving concrete, structural concrete, and bonded overlays. A large number of studies have been published documenting the benefits of internal curing; however, work is necessary to implement it. The focus of this study is on the benefits of internal curing for pavement and overlay mixtures and the use of internal curing in the field. Evaluation was done of the fresh and hardened concrete properties of the different Ohio DOT concrete classes, made with different coarse aggregates and with lightweight aggregate replacements. Restrained shrinkage ring tests were used to predict which concrete mixtures were most likely to crack. Field tests were also conducted, and shrinkage ring data from field samples showed a possible improvement in the cracking potential of mixtures that utilized internal curing. The lightweight aggregate substitution improved both early and ultimate strength, and reduced cracking tendency. Since these are key performance measures for concrete pavements and overlays, internal curing offers strong promise for the development of long-life concrete pavements and structures.

Cracking of Fiber-Reinforced Self-Compacting Concrete due to Restrained Shrinkage

Fiber-reinforced self-compacting concrete (FRSCC) is a new type of concrete mix that can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete and cracking resistance in plain SCC concrete. This study focused on early-age cracking of FRSCC due to restrained drying shrinkage, one of the most common causes of cracking. In order to investigate the effect of fiber on shrinkage cracking of FRSCC, ring shrinkage tests were performed for polypropylene and steel fiber-reinforced SCC. In addition, finite element analyses for those specimens were carried out considering drying shrinkage based on moisture diffusion, creep, cracking resistance of concrete, and the effect of fiber. The analysis results were verified via a comparison between the measured and calculated crack width. From the test and analysis results, the effectiveness of fiber with respect to reducing cracking was confirmed and some salient features on the shrinkage cracking of FRSCC were obtained.

Influence of superplasticizers on strength and shrinkage cracking of cement mortar under drying conditions

The effects of polynaphthalene series superplasticizers(PNS) with a low content of sodium sulfate (H-UNF),with a high content of sodium sulfate(C-UNF) and polycarboxylate type superplasticizer (PC) on strength and shrinkage cracking of cement mortar under drying conditions were investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase the initial cracking time of mortars, and decrease the cracking sensitivity of mortars. As for decreasing the cracking sensitivity of mortars, PC>H-UNF>C-UNF. To incorporate superplasticizers is apparently to increase the free shrinkage of mortars when keeping the constant w/b ratio and the content of cement pastes. As for the effect of controlling the volume stability of mortars, PC>C-UNF>H-UNF. Maximum crack width of mortars containing PC is lower, but the development rate of maximum crack width of mortars containing H-UNF is faster in comparison with control mortars. The flexural and compressive strengths of mortars at 28-day increase with increasing superplasticizer dosages under drying conditions. PC was superior to PNS in the aspect of increasing strength.

Study on early-age cracking of cement-based materials with superplasticizers

The addition of superplasticizers is an important approach to prepare high performance cement-based materials. The effect of polynaphthalene series superplasticizer (PNS) and polycarboxylate type superplasticizer (PC) on early-age cracking and volume stability of cement-based materials was investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase initial cracking time of mortars, and decrease cracking sensitivity of mortars. As for decreasing cracking sensitivity of mortars, PC > H-UNF (high-thickness-type PNS) > C-UNF (common-thickness-type PNS). To incorporate superplasticizers is apparently to increases free shrinkage of mortars when keeping the constant W/B ratio and the content of cement pastes. As for the effect of controlling volume stability of mortars, PC > C-UNF > H-UNF. Maximum crack width of mortars with PC is lower, but the development rate of maximum crack width of mortars with H-UNF is faster in comparison with control mortars. Flexural and compressive strength of mortars and concretes at 28 days increased with increasing superplasticizer dosages under drying conditions. C-UNF was approximate to H-UNF, but PC was superior to PNS in the aspect of increasing strength of cement-based materials.

Cast-in-Place Cellulose Fiber-Reinforced Cement Paste, Mortar, and Concrete

Fiber-reinforced concrete is a fast-growing technology. This research considers the use of cellulose fibers as an inexpensive alternative to synthetic fibers. This study characterizes the behavior of cellulose fiber-reinforced paste, mortar, and concrete and investigates rheological, dispersion, and mechanical properties of the materials. The addition of cellulose fibers to a cementitious material stiffens the matrix. This stiffening limits the maximum usable fiber volume. At fiber volumes used, fibers offer little improvement in flexural properties. Optical and scanning electron microscopy are used to inspect fiber dispersion. A technique is developed to locate fibers in hardened specimens. Correlations among fiber dispersion, mechanical performance, and rheology are investigated. Restrained ring shrinkage tests are performed on paste and mortar. Fibers are found to reduce the width of shrinkage cracks in both materials. Fiber dispersion, matrix rheology, and mechanical performance cannot be correlated. Fibers disperse well under normal mixing conditions, regardless of matrix rheological properties.

Shrinkage Cracking Characteristics of Concrete Using Ring Specimens

This paper outlines a testing and analysis procedure to quantify behavior of concrete under restrained shrinkage ring specimens. Cracking resistance is found to depend not only on shrinkage potential and tensile strength, but also on shrinkage rate and tensile creep characteristics of the concrete. The creep strain obtained for the ring specimens can be as high as 50% of the free shrinkage strain, indicating that tensile creep is significant and must be considered in evaluating the risk of cracking under restrained conditions. Shrinkage reducing admixtures greatly enhance the cracking resistance of concrete by reducing both the shrinkage potential and the shrinkage rate. A separate study was conducted on the concrete mixtures to determine the tensile creep characteristics under a constant stress. Results from the 2 studies are compared, and findings are discussed.

Studies on carbon/sulfur cluster anions produced by laser vaporization: Experiment (collision-induced dissociation) and theory (ab initio calculation). II C4Sm− (4⩽m⩽10)

Carbon/sulfur binary cluster anions with various compositions can be produced from laser vaporization of a sample mixed with sulfur and carbon powders in a 20:1 molar ratio. After mass-selection, their molecular formula was determined by collision-induced dissociation. The cluster anions consist of even carbon atoms only and their number of clustering sulfur atoms equals or exceeds that of carbon atoms. In this paper, we focus on mass spectrometry investigation and ab initio calculations on the cluster anions containing four carbon atoms, C4Sm− (4⩽m⩽10). Geometry of various isomeric structures of the clusters was optimized at the ROHF/6-31G* level and their energies were compared to find the most stable isomers. The structures of C4Sm− clusters computed in this paper were designed based on the structural features learned from the previous study on C2Sm− and the results of mass spectrometry experiments. Among the structures, four low-lying forms with two dangling sulfur atoms and two closed rings have the lowest energy. Based on the experimental and theoretical investigations, a ring shrinkage scheme is proposed to account for the dissociation process of the binary cluster anions observed in the experiment.

Ring Shrinkage Test for Expansive Clays: A Suggested Simple Test Method for Determining Vertical, Lateral, and Volumetric Shrinkage Potential

Abstract The ring shrinkage test is proposed as a new soil testing method for expansive clays to describe quantitatively the soil shrinkage potential. The test provides direct measurements of the linear shrinkage in the form of vertical and lateral changes. In addition, the test provides an alternative test method for determining the shrinkage limit and volumetric shrinkage. The method requires undisturbed samples, and it utilizes the standard oedometer ring of consolidation testing equipment. Description of the proposed test method is presented including details of specimen preparation and data measurements.

Polymerization of 2,6,7-trioxabicyclo[2.2.1]heptane with either contraction or expansion

2 ,6 ,7-Trioxabicyclo[2.2.1] heptane (I) polymerizes to poly ortho ester (Poly-I) at −78°C with opening of one ring and volume shrinkage. Heating Poly-I with acid isomerized it to an open chain poly-ether formate (Poly-II); this occurred with a large volume expansion. Direct conversion of I to Poly-II by heating with acid occurred with net moderate increase. Monomer I is the first reported monomer which can be polymerized with either shrinkage or expansion as desired. Saponification of Poly-II gave Poly-III, a new water-soluble copolymer.