Shrinkage Strain Values Research Articles

Early age and long‐term properties of mortars containing metakaolin and limestone powder as SCMs

AbstractIn this study we focus on the development of plastic shrinkage and capillary pore pressure on mortars containing metakaolin and limestone powder as cement replacement. Isothermal calorimetry was also used to compliment the early age properties of the investigated mortars. Strength development and phase assemblage using thermal analysis were also investigated. Five different replacement levels of metakaolin and LSP and two different amounts of SP were used. Our data show that the shrinkage strain values increased as the amount of SCMs increased, while capillary pressure showed a mixed trend. The hydration kinetics did not appear to be influenced much from the SCMs used. Strength development improved in general when metakaolin was used while decreasing when LSP was added, as already expected. The TGA data show an increase in the consumption of portlandite as the amount of SCMs was increased.

Shrinkage performance and modelling of concretes incorporating crushed limestone sand with a high content of fillers for pavement slabs

Because of the gradual depletion of gravel and river sand resources and restrictions on quarrying activities to maintain the ecological balance, limestone crushed sand with a high content of limestone fillers is being explored to be used, as an alternative source of supply, in Portland cement concrete (PCC) for rigid pavement. This paper aims to first present mechanical test results carried out on three types of PCC formulated with crushed limestone sand as fine aggregates, devoid of superplasticizers. Since shrinkage cracking is an important problem for rigid pavement, the shrinkage behaviour of these concretes is then experimentally investigated. Furthermore, three existing models (ACI-209, Eurocode2, and triple-sphere models) and a novel-developed model are used to estimate the mixtures’ shrinkage. Results showed that the designed mixtures exhibited normal shrinkage values. The shrinkage modelling revealed that the proposed model well fitted the experimental data. Besides, Eurocode2 and ACI-209 models may be adapted for the case of limestone concretes containing a high content of limestone fillers and then used to accurately estimate their shrinkage strains. However, the triple-sphere model was unsuitable for these concretes and overestimated their ultimate shrinkage since it does not take into account their high filler content. Nevertheless, by adjusting the paste shrinkage expression, the ultimate shrinkage strain values of the tested mixtures were improved.

Shrinkage model for concrete incorporating coal gangue coarse and fine aggregates

Our study aims to formulate a model for predicting the shrinkage behaviour of concrete incorporating coal gangue coarse and fine aggregates (CGCA and CGFA). In order to achieve this, the study conducted an experiment measuring the shrinkage of coal gangue aggregate concrete (CGAC) over a period of 126 days. The experiment involved varying replacement ratios of CGCA and CGFA, including 0%, 50%, and 100% of both types. Test results show that: (1) both CGCA and CGFA significantly increased concrete shrinkage strain, and the shrinkage strain increased by 145% when both CGCA and CGFA were 100% used, (2) the CGCA has a more pronounced influence on the shrinkage compared to CGFA, and (3) the incorporation of CGCA leads to a faster development of shrinkage in the concrete, whereas CGFA has no significant effect on the shrinkage development over time. A novel theoretical model was developed that can accommodates the coal gangue aggregate's effect on the development and ultimate value of shrinkage strain in CGAC. Benchmarking analysis was carried out using the study's test data and data from literature, which showed that the proposed model can well predict the CGAC shrinkage.

Laboratory modeling of thermal and temporal cracking in swelling clays

Crack development in a changing environment is the controlling factor for the stability and strength of expansive soils. Expansive soils exhibit large volumetric changes with changes in their moisture conditions that may occasionally lead to reduced bearing capacity and foundation failures. This study purports to model crack initiation and its spatial progression in relation to the moisture content and drying period, respectively. Volumetric soil shrinkage is determined using high-definition digital camera imaging and Vernier scale methods, while the soil settlement under vertical shrinkage deformation could be captured through a tensile stress model for soils. It was revealed that a small change in suction could trigger crack initiation, which would propagate further under different environmental conditions. Furthermore, it was observed that the crack volume increased rapidly at specific moisture content and could penetrate as deep as 1 m after nearly 1.5 months that is fully consistent with the current model predictions. A comparison between the performance of the model proposed in this study and that of two existing models shows that the former predicts the vertical shrinkage strain values in closer agreement with those observed experimentally and is less conservative than those predicted by both models. Nevertheless, the findings from this study could be used to quantify the detrimental behavior of expansive soil present in pavement subgrades and shallow foundations for lightweight structures.

Effect of preheating on polymerization shrinkage strain of BIS-GMA free and containing resin composite restorative materials (in vitro study)

BackgroundThis study investigated the effect of preheating of bulk-fill BIS-GMA free and containing resin composite on post-gel shrinkage strain. In a split Teflon mold, sixty resin composite specimens were prepared with dimensions 7 mm length × 4 mm width × 4 mm height. Thirty specimens of each tested restorative materials were prepared, ten specimens for each selected temperature used in the study (room temperature 23 °C, 50 °C and 65 °C). The resin composite was monitored for post-gel shrinkage strain for 3 min after light irradiation using strain gauges. For pairwise comparisons, Duncan’s multiple range test was used to analyze the data after two-way ANOVA. The p ≤ 0.05 significance level was chosen.ResultsViscalor thermoviscous bulk-fill composite Bis-GMA containing had the lowest polymerization shrinkage strain values in the three different temperatures. There was a statistically significant difference between groups according to material used at different temperatures. Both tested materials showed the highest shrinkage strain when preheated at 65 °C.ConclusionsWhile the technology of thermoviscous is introduced to deliver the viscosity of a flowable resin composite so reducing the polymerization strain, it actually had adverse effect on it. Preheating of bulk-fill BIS-GMA free resin composite either to 50 °C or 65 °C had no effect on decreasing the polymerization shrinkage strain. Polymerization shrinkage strain of bulk-fill BIS-GMA contains resin composite either without or with preheating far superior to that of BIS-GMA free resin composite.

Shrinkage behavior of concrete containing bottom ash granules as partial replacement of natural sands

This study aims to provide databank and comprehensible design equations for the shrinkage strain curve of concrete using bottom ash granules to replace conventional natural sands. We prepared 27 concrete mixtures with various parameters, including the substitution level of natural sand for fine bottom ash aggregates, unit water content, and fine aggregate-to-total aggregate volume ratios. To derive reliable design models to predict the drying shrinkage of concrete using fine bottom ash aggregates, the time function specified in fib 2010 was modified by introducing the parameter of equivalent porosity of aggregates. Moreover, the shrinkage strain values at an age of 91 days were formulated by conducting a regression analysis using test data as a specified reference to determine the ultimate shrinkage strain. The test results showed that the shrinkage strain of concrete is marginally affected by the bottom ash aggregate content but significantly affected by the volume fraction of aggregates and their equivalent porosity. The proposed models are promising for estimating the shrinkage strain response of concrete using fine bottom ash aggregates by considering the restraining action of aggregates.

Shrinkage test of concrete: Methodology and variation of strain

Evaluation of shrinkage strain in long concrete structures such as prestressed concrete box girder bridges is very important for the design of such structures. A wrong evaluation may contribute to loss of prestressing force, excessive deflections, cambers and cracking of the structure. It may also affect the durability and serviceability of the structure. The value of shrinkage strain is required during design, far before the construction process. However, realistic evaluation is still a difficult problem because shrinkage strain is influenced by the concrete composition and environmental factors such as humidity and temperature. Therefore, to gain the best evaluation, an experimental program was conducted to measure the shrinkage strain of concrete versus concrete age. Several concrete specimens were collected during pouring of several box girder segments of Tauranga Harbour Link, New Zealand. Variation of shrinkage strain versus concrete age for almost two years of data collection was plotted.

Experimental assessment and optimization of mix parameters of fly ash-based lightweight geopolymer mortar with respect to shrinkage and strength

The aim of the study is to determine the impact of various NaOH molarities, sodium silicate-to-sodium hydroxide ratios, binder amounts and the age on the compressive strength and free shrinkage of fly ash based lightweight geopolymer mortars. After experimental evaluation, the data were used to model and optimize mix proportions of lightweight geopolymer mortars through response surface method. NaOH molarities were determined as 6 M, 8 M, and 10 M. sodium silicate-to-sodium hydroxide ratios were chosen as 0.5, 1.5, and 2.5 and binder amounts were used as 600, 700, and 800 kg/m3. For the same variables, except the binder amount, the compressive strengths of geopolymer pastes were also determined. The usage of lightweight aggregate as a replacement of river sand (25%) affected the results due to pore structure and its strength. Thus, it was concluded that strength and shrinkage of the samples reduced in comparison to the geopolymer mortars only including sand. The increase of molarity improved compressive strength of pastes and mortars. However, higher sodium silicate-to-sodium hydroxide ratio resulted in lower strength values. Geopolymer mortars with higher binder amounts and NaOH molarities showed a lower drying shrinkage strains, while resulted in increase of the autogenous shrinkage. The effect of sodium silicate-to-sodium hydroxide ratios were also observed in both shrinkage types. Besides, the optimum variables based on maximum strength and minimum shrinkage strain values were reached in optimisation study conducted with response surface method (RSM). The optimum values for the parameters of NaOH molarity, binder amount and sodium silicate-to-sodium hydroxide ratio were specified as 9.892 M, 600 kg and 0.5, respectively. The corresponding desirability value for this optimisation was obtained as 0.833 within the acceptable range.

Polymerization shrinkage kinetics and degree of conversion of resin composites.

This study compared shrinkage strain, polymerization shrinkage kinetics, and degree of conversion (DC) of a set of resin composites and investigated their influencing factors. Ten commercial resin composites were assessed, and 5 specimens (n = 5) were developed for material and subjected to light curing using light emitting diode light at 650 mW/cm2 for 40 s. The laser triangulation method was adopted to assess the shrinkage strain, and Fourier transform infrared spectroscopy was used to measure DC. The shrinkage strain was monitored for 5 min in real time and its data were subjected to differential calculations to get the shrinkage strain rate curve with respect to time, obtaining the maximum shrinkage strain rate (Rmax) and gel time. The values of shrinkage strain varied from 1.28% to 2.10%. The Rmax values were between 5.17 μm/s and 21.83 μm/s. Gel time values varied from 3.08 s to 4.32 s. The DC yielded values ranging from 53.62% to 87.01%. The values of polymerization shrinkage and DC were dependent on the composition of materials, including the monomer matrix and filler system. Compared to the micro-filler materials, the nano-filler resin composites had higher values of DC. Some resin composites are suitable for clinical applications because of their superior polymerization shrinkage properties and DC.

3D Digital Image Correlation Analysis of the Shrinkage Strain in Four Dual Cure Composite Cements.

The introduction of resin-based cements and an adhesive-bonding system in daily dental practice has given the opportunity to increase the retention of previously conventional cemented restorations and the optimal results in esthetic. This experimental study employed the 3D Digital Image Correlation Method (3D-DIC) for detecting shrinkage strain in four dual cured composite cements. The aim was to visualize measure, analyze, and compare strain fields in four resin-based cements using the 3D-DIC method. A total of 72 samples were divided into 4 groups considering variations in sample types, diameter, and thickness. Four types of composite cements: RelyX U200 (3 M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Multilink Automix (Ivoclar Vivadent, Schaan, Liechtenstein), and SeT PP (SDI, Australia) were used. Each type had diameters of 3 mm, 4 mm, and 5 mm, respectively, combined with two different values of thickness: 1 mm and 2 mm. Thickness had an important role on strain detected in all tested materials showing higher strain in samples with 2 mm thickness compared to 1 mm samples. Shrinkage strain values were the highest in Set PP samples indicated the possibility of undesirable de-bonding.

Discussing Different Approaches for the Time-Zero as Start for Autogenous Shrinkage in Cement Pastes Containing Superabsorbent Polymers.

Many studies have already been published concerning autogenous shrinkage in cementitious materials. Still, no consensus can be found in the literature regarding the determination of the time-zero to initiate the recording of autogenous shrinkage. With internal curing agents, a correct evaluation of their efficiency depends on an appropriate choice of the time-zero. This study investigates different approaches to estimate the time-zero for cement paste mixtures with and without superabsorbent polymers as internal curing agents. The initial and final setting times were determined by an electronic Vicat and ultrasonic pulse velocity measurements (UPV); the transition point between the fluid and solid state was determined from the autogenous strain curve; the development of the capillary pressure was also studied. The choice of time-zero before the transition point led to higher values of shrinkage strain that should not be taken into account for autogenous shrinkage. A negligible difference was found between the strains when the final setting time and the transition point were taken as time-zero. Considering the artefacts and practical issues involving the different methods, the use of the transition point from the autogenous strain curve is the most suitable technique for determining the time-zero.

Shrinkage properties of plain and recycled steel–fibre-reinforced rapid hardening mortars for repairs

This article investigates the time dependent transport properties and shrinkage performance of rapid hardening plain and fibre reinforced mortars for repair applications. Two plain and two SFRC mixes with 45 kg/m3 of recycled clean steel fibres made with rapid hardening cements (CSA – calcium sulfoaluminate cement and RSC – calcium aluminate cement) are studied. It is found that mixes with CSA cement have much lower shrinkage values (around 220 and 365 microstrains) compared to mixes with RSC cement (around 2690 and 2530 microstrains), but most of the shrinkage in these mixes is autogenous. Nonetheless, fibres reduce the drying shrinkage of RSC cement mixes by approximately 12%. Model code 2010 and ACI equations can be used to estimate the shrinkage development with time for these mixes provided suitable parameters for each cement type are adopted. Inverse analysis using finite element method is successfully employed to determine the moisture diffusivity and the hygral contraction coefficient of each mix. A comparison is made between the values of shrinkage strain predicted by the numerical models over time, for different depths, and code equations. A simple analytical procedure is used to assess cracking and/or delamination risks due to restrained shrinkage for these materials in overlay applications.

Time-Dependent Behavior of Shrinkage Strain for Early Age Concrete Affected by Temperature Variation

Shrinkage has been proven to be an important property of early age concrete. The shrinkage strain leads to inherent engineering problems, such as cracking and loss of prestress. Atmospheric temperature is an important factor in shrinkage strain. However, current research does not provide much attention to the effect of atmospheric temperature on shrinkage of early age concrete. In this paper, a laboratory study was undertaken to present the time-dependent shrinkage of early age concrete under temperature variation. A newly developed Material Deformation Tester (MDT), which can simulate consecutive variation of atmospheric temperature, was used to collect the shrinkage strain of specimens and temperature data. A numerical model was established to describe the thermoelastic strain of a specimen. The results show that (1) there are several sharp shrinkages up to 600 μfor early age concrete in the first 3 days; (2) the absolute value of shrinkage strain is larger than thermal strain; and (3) the difference of shrinkage strain under temperature variation or constant temperature is up to 500 μ.

Self-compacting fine-grained concretes with compensated shrinkage

This paper substantiates the efficiency of application of fine-grained concrete for erection of cast-in-place concrete and reinforced concrete structures of different purpose. On the basis of analysis of experimental research results it was established that the introduction of microfillers with expansion effect to composite binder allows not only improving the rheological properties of fine-grained concrete, but also decreasing of value of shrinkage strain and improving of concrete crack resistance and durability. The analysis of the results of industrial use of fine-grained concretes with compensated shrinkage is given.

Evaluation of shrinkage-induced stress in a runway repaired using compliant polymer concrete

The aim of this study is to investigate shrinkage-induced stresses in a part of a runway pavement repaired using compliant polymer concrete. For this purpose, material properties of partially cured polymer concrete at different degrees of cure during the cure process were estimated and used in the stress analysis. To measure the degree of cure and shrinkage strain in the repaired part, a monitoring system comprising dielectrometry and fiber Bragg grating (FBG) optic sensors was installed in an airport (Gimpo airport, Korea). The shrinkage strain values measured at the various degrees of cure of the polymer concrete were used in finite element analysis to estimate shrinkage-induced stresses. To improve accuracy of stress analysis, property change of the polymer concrete during the curing process were also considered. It was concluded that property variations during the curing process should be considered for estimating material failure because the cure shrinkage of the repair material induces tensile stress following the critical loading pattern of concretes.

Effects of residual stresses on the tensile fatigue behavior of concrete

The influence of Eigenstresses due to drying shrinkage on the development of residual deformations characterizing the tensile fatigue behavior of concrete is analyzed. During the loading phase the Eigenstresses are locally released around the cracks inducing a mismatch between the crack surfaces which inhibits a perfect crack re-closure. The analysis is performed by means of a 2D mesoscale implicit finite-element model. The shrinkage strain is first applied determining the development of a diffused micro-damage and then quasi-static loading–unloading tests are simulated. Different microstructures and different values of shrinkage strain are considered. The results show that the presence of residual stresses increases the amount of total dissipated energy and naturally leads to the development of residual deformations. However, the obtained values are only a portion of the residual deformations experimentally measured. The possible concomitant effect of another mechanism, namely the formation of debris at a small scale, is therefore discussed.

Polymerization shrinkage kinetics and shrinkage-stress in dental resin-composites

ObjectivesTo investigate a set of resin-composites and the effect of their composition on polymerization shrinkage strain and strain kinetics, shrinkage stress and the apparent elastic modulus. MethodsEighteen commercially available resin-composites were investigated. Three specimens (n=3) were made per material and light-cured with an LED unit (1200mW/cm2) for 20s. The bonded-disk method was used to measure the shrinkage strain and Bioman shrinkage stress instrument was used to measure shrinkage stress. The shrinkage strain kinetics at 23°C was monitored for 60min. Maximum strain and stress was evaluated at 60min. The shrinkage strain rate was calculated using numerical differentiation. ResultsThe shrinkage strain values ranged from 1.83 (0.09) % for Tetric Evoceram (TEC) to 4.68 (0.04) % for Beautifil flow plus (BFP). The shrinkage strain rate ranged from 0.11 (0.01%s−1) for Gaenial posterior (GA-P) to 0.59 (0.07) %s−1 for BFP. Shrinkage stress values ranged from 3.94 (0.40)MPa for TET to 10.45 (0.41)MPa for BFP. The apparent elastic modulus ranged from 153.56 (18.7)MPa for Ever X posterior (EVX) to 277.34 (25.5) MPa for Grandio SO heavy flow (GSO). SignificanceThe nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress. Higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials. The bulk-fill materials showed comparable result when compared to the traditional resin-composites.

Effect of Restorative Protocol on Cuspal Strain and Residual Stress in Endodontically Treated Molars.

To evaluate the effect of the restorative protocol on cuspal strain, fracture resistance, residual stress, and mechanical properties of restorative materials in endodontically treated molars. Forty-five molars received mesio-occlusal-distal (MOD) Class II preparations and endodontic treatment followed by direct restorations using three restorative protocols: composite resin (CR) only (Filtek Supreme, 3M-ESPE), resin modified glass ionomer cement in combination with CR (Vitremer, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity), conventional glass ionomer cement in combination with composite resin (CGI-CR) (Ketac Fil, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity). Cuspal strain was measured using strain gauges, and fracture resistance was tested with an occlusal load. Elastic modulus (EM) and Vickers hardness (VH) of the restorative materials were determined at different depths using dynamic microhardness indentation. Curing shrinkage was measured using the strain gauge technique. The restorative protocols were also simulated in finite element analysis (FEA). The shrinkage strain, cuspal strain, EM, VH, and fracture resistance data were statistically analyzed using split-plot analysis of variance and Tukey test (p=0.05). Residual shrinkage stresses were expressed in modified von Mises equivalent stresses. Shrinkage strain values (in volume %) were Ketac Fil (0.08±0.01) < Vitremer (0.18±0.01) < Filtek Supreme (0.54±0.03). Cuspal strain was higher and fracture resistance was lower when using CR only compared with the techniques that used glass ionomer. The EM and VH of the materials in the pulp chamber were significantly lower for glass ionomer. The FEA showed that using CR only resulted in higher residual stresses in enamel and root dentin close to the pulp chamber than the combinations with glass ionomers (RMGI-CR and CGI-CR). The choice of restorative protocol significantly affected the biomechanical behavior of endodontically treated molars. Using glass ionomer to fill the pulp chamber is recommended when endodontically treated molars receive direct composite restorations because it reduces cuspal strain and increases fracture resistance.

Evaluation of the influence of shrinkage strain on the fatigue strength of the connection in steel–concrete composite beams

The paper presents the author's proposal for calculation of shear stresses (disintegrating) induced by concrete shrinkage at the interface of steel and concrete. The proposal also presents expressions to calculate the fatigue strength of a connection in steel–concrete composite girders. The expressions to calculate fatigue strength are based on the results of experiments performed by the author. Based on the results of analyses it can be stated that the load bearing capacity of a connection with flexible shear connectors is strongly affected by a concrete slab adhesion to a steel girder. This effect depends on the stiffness ratio of the girder to concrete deck (coefficient δ), concrete strength and diameter of shear studs d, as well as the value of shrinkage strain of concrete. Fatigue strength of a connection with strip connectors is affected by the geometry of the composite girder and its components, concrete strength and concrete shrinkage strain. At low values of δ, low concrete grades and large diameters of shear connectors or holes, the fatigue strength of the composite connection is likely to be exhausted.

Forming composite strength in the presence of lime silica sol

Provides information about the mechanism of hardening lime composite in the presence of silica sol. It is shown that lime composites are characterized by lower values of shrinkage strain when wet.