Drying Shrinkage Strain Research Articles

Mechanical, Durability, and Time-Dependent Properties of Recycled Aggregate Concrete with Fly Ash

This paper presents the results of tests on mechanical properties, durability, short-term testing for creep, and drying shrinkage of recycled aggregate concrete (RAC). A natural aggregate concrete (NAC) mixture was designed for a characteristic compressive strength of 40 MPa (5.8 ksi) and the natural coarse aggregate (NA) was replaced by coarse recycled concrete aggregate (RCA) at 50, 75, and 100%. The existing concrete mixture design method was slightly modified to design the RAC mixtures, taking into account the lower specific gravity of the RCA. Fly ash was used as mineral admixture. The test results were compared with those of NAC and the NAC containing fly ash (NAF). The RAC exhibited comparable slump and strength to, and lower elastic modulus than, that of NAC. The resistivity was higher and chloride permeability was lower for RAC when compared to NAC; however, the same were inferior to NAF. The drying shrinkage strain of RAC mixture with 100% RCA was observed to be 1.24, 1.37, and 1.41 and creep strain was 1.15, 1.10, and 0.98 times that of NAC at 30 days, 60 days, and 90 days, respectively.

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.

Contribution of acrylic fibre addition and ground granulated blast furnace slag on the properties of lightweight concrete

The experimental investigation concerning the mechanical performance, drying shrinkage and residual strength upon heat exposure of acrylic fibre reinforced lightweight oil palm shell concrete (OPSC) containing ground granulated blast furnace slag (GGBS) is reported. The addition of 0.1% acrylic fibres in OPSC containing 20% GGBS was found to be the most effective in enhancing the tensile strength. The addition of acrylic fibres in OPSC was also found to reduce the 60-day drying shrinkage strains by up to 10% and improve the relative residual strength by up to 23%. Generally, the OPSC containing 20% GGBS had superior performance among the investigated hardened OPSC properties, except for the residual strength upon heat exposure, in which mixes with 70% GGBS achieved lower strength loss.

Influence of mineral composition of siliceous rock on its volume change

A method for predicting volume changes of aggregate during variations in humidity and temperature was studied. Siliceous rock aggregates commercially available in Japan were sampled from various regions and subjected to XRD (X-ray diffraction) analysis, thermal analysis, and volume change experiments. Drying shrinkage strain and the thermal expansion coefficient of the aggregates were found to be related to their mineral composition and bound water content. Experiments confirmed that drying shrinkage was correlated with the chlorite and bound water content of the aggregate, and that thermal expansion coefficients were correlated with the aggregate’s quartz content.

Drying shrinkage and microstructure characteristics of mortar incorporating ground granulated blast furnace slag and shrinkage reducing admixture

This paper presents an experimental study of the effects of cement type, ground granulated blast furnace slag (GGBFS) fineness, curing age, and use of shrinkage reducing admixture (SRA) on the drying shrinkage property and microstructure in mortar. The relationship between drying shrinkage and the microstructure characteristics is determined, and an equation that can reasonably predict the drying shrinkage behavior is also proposed according to the dependent variables. The test results revealed that the drying shrinkage evolution can be significantly affected by the GGBFS powder fineness, the cement type – ordinary Portland cement (N), moderate heat Portland cement (M), and low heat Portland cement (L), and the SRA dosage and pore volume of the mortar, but not the curing age (7 and 28days). For mortar samples without GGBFS, the N and L mortar samples exhibited greater shrinkage strain evolution compared to the M sample. For the case of mortar samples incorporating GGBFS, the L mortar sample exhibited the greatest drying shrinkage strain among the investigated mortar mixes. In addition, the drying shrinkage increased significantly with the increase in the GGBFS fineness for the M and L Portland cement mortars. Moreover, the addition of SRA could effectively reduce the drying shrinkage, which is mainly controlled by the pore size distribution and mass loss. In the case of mortar without and with SRA, the drying shrinkage was found to have a high correlation with the pore size ranges of 6–30nm and 0–20nm in diameter, respectively. As a result of the high correlation of pore volume and mass loss observed in this study, the prediction equation for the drying shrinkage of GGBFS mortar is proposed, which verifies good accuracy compared to the test results.

Shrinkage cracking of amorphous metallic fibre-reinforced concrete

Free and dry shrinkage tests are performed to investigate the dry shrinkage characteristics of fibre-reinforced concrete. Based on the test results, tensile stress and strength curves according to concrete ages are developed for predicting the cracking time of concrete ring test specimens. In a proposed model, the cracking time is defined at the intersection point of tensile stress and strength curves. The tensile stress of concrete is defined by using the elastic modulus of concrete and dry shrinkage strain acquired from compressive and shrinkage tests performed at different concrete ages. The tensile strength of concrete is defined by using the CEB–FIP strength model and the flexural tensile strength acquired from flexural tensile tests performed at different concrete ages. In the comparison with the test results, it is found that the proposed model can accurately predict the cracking time of concrete ring test specimens.

Creep and drying shrinkage of a blended slag and low calcium fly ash geopolymer Concrete

Abstract The main purpose of this research is to study the time dependent behaviour of a geopolymer concrete. The geopolymer binder is composed of 85.2 % of low calcium fly ash and only 14.8 % of ground granulated blast furnace slag. Both drying shrinkage and creep are studied. In addition, different curing conditions at elevated temperature were used. All experimental results were compared to predictions made using the Eurocode 2. The curing regime plays an important role in the magnitude and development of both creep and drying shrinkage of class F fly ash based geopolymer concrete. A minimum of 3 days at 40 °C or 1 day at 80 °C is required to obtain final drying shrinkage strains similar to or less than those adopted by Eurocode 2 for ordinary Portland cement (OPC) concrete. Creep strains were similar or less than those predicted by Eurocode 2 for OPC concrete when the geopolymer concrete was cured for 3 days at 40 °C. After 7 days at 80 °C, creep strains became negligible.

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.

Influence of 3D spacer fabric on drying shrinkage of concrete canvas

Concrete canvas has taken attention for their rapidly deployable hardened characteristic property in civil engineering. However, the drying shrinkage of concrete canvas has not been addressed yet in the literatures. In this study, a theoretical model was presented for studying influences of 3D spacer fabric on drying shrinkage of concrete canvas. The model was based on assumption that drying shrinkage restraint provided by 3D spacer fabric is joint action of each component of 3D spacer fabric separately. To calibrate this model, the drying shrinkage of two concrete canvases reinforced by PET-based 3D spacer fabric with one solid outer textile substrate was experimented. Moreover, a simplified expression of maximum tensile stress generated in the matrix of both concrete canvases was obtained for evaluating their risk of drying shrinkage-induced cracking. The results showed that drying shrinkage strain of concrete canvas samples became lower due to the restraint provided by 3D spacer fabric and a satisfactory correlation between model predictions and experimental results was found at later age. For both concrete canvases, a greater restraint was found in warp direction, thereby resulting in a larger tensile stress generated in the matrix. Furthermore, the restraint on the drying shrinkage of concrete canvas was provided mostly by spacer yarns and thereby it contributed to the most of maximum tensile stress generated in the matrix of concrete canvas.

Evaluation of models for estimating concrete strains due to drying shrinkage

AbstractThe present contribution focuses on a comparative study of shrinkage prediction models according to the European Standard Eurocode 2 (EC2), the recommendation by ACI committee 209 and fib Model Code for Concrete Structures 2010. The estimated ultimate drying shrinkage strains and the predicted evolution of drying shrinkage strains are compared with respective shrinkage strains measured on normal‐strength concrete specimens of different sizes. For all prediction models, the estimated ultimate values are found to agree quite well with the ultimate drying shrinkage strains measured on thin concrete slices. Whereas the evolution of drying shrinkage strains measured on small concrete prisms agree quite well with the predicted values, substantial differences between code values and experimental data are encountered for larger specimen sizes.

Palm Oil Fuel Ash as a Partial Cement Replacement for Producing Durable Self-consolidating High-Strength Concrete

Palm oil fuel ash (POFA) has been used as a partial cement replacement to produce self-consolidating high-strength concrete (SCHSC). The fresh and hardened properties of SCHSC containing POFA have been extensively investigated by researchers. However, research is needed to study the effect of this supplementary cementitious material on the durability properties of SCHSC. For this purpose, the ordinary Portland cement was substituted with 0, 10, 15, and 20 % POFA in a self-consolidating high-strength concrete. Durability characteristics, such as drying shrinkage strain, rapid chloride permeability, initial surface absorption, acid resistance, and water absorption, have been investigated. The test results showed that by incorporating of POFA in SCHSC, the durability characteristics of the concrete significantly improved.

Laboratory evaluation of cement treated aggregate containing crushed clay brick

Abstract: The waste clay bricks from debris of buildings were evaluated through lab tests as environmental friendly materials for pavement sub-base in the research. Five sets of coarse aggregates which contained 0, 25%, 50%, 75% and 100% crushed bricks, respectively, were blended with sand and treated by 5% cement. The test results indicated that cement treated aggregate which contains crushed clay brick aggregate had a lower maximum dry density (MDD) and a higher optimum moisture content (OMC). Moreover, the unconfined compressive strength (UCS), resilience modulus, splitting strength, and frost resistance performance of the specimens decreased with increase of the amount of crushed clay brick aggregate. On the other hand, it can be observed that the use of crushed clay brick in the mixture decreased the dry shrinkage strain of the specimens. Compared with the asphalt pavement design specifications of China, the results imply that the substitution rate of natural aggregate with crushed clay brick aggregate in the cement treated aggregate sub-base material should be less than 50% (5% cement content in the mixture). Furthermore, it needs to be noted that the cement treated aggregate which contains crushed clay bricks should be cautiously used in the cold region due to its insufficient frost resistance performance.

TIME-DEPENDENT BEHAVIOUR OF A CLASS F FLY ASH-BASED GEOPOLYMER CONCRETE

The main purpose of this research is to study the time dependent behaviour of a geopolymer concrete. The geopolymer binder is composed of 85.2% of low calcium fly ash and only 14.8% of GGBFS (Ground Granulated Blast Furnace Slag). Both drying shrinkage and creep are studied. Tests were performed on small size specimens according to Australian Standard AS1012.13 for shrinkage and AS1012.16 for creep. Different curing regimes at elevated temperature were used. All experimental results were compared to Australian Standard AS3600 predictions. Curing regime plays an important role on both creep and drying shrinkage of class F fly ash based geopolymer concrete. A minimum of three days at 40 0 C or one day at 80 0 C is required to obtain final drying shrinkage strains similar or less than the one predicted by AS3600 for OPC concrete. Creep strains are reduced of about 70% compared to predicted OPC concrete values when the geopolymer concrete was cured for three days at 40 0 C. After 7 days at 80 0 C, creep strains were very low.

The Effect of Palm Oil Fuel Ash as a Cementreplacement Material on Self-Compacting Concrete

In this study ground palm oil fuel ash (POFA) has been used as cement replacement in percentages of 0%, 10%, and 20% in a self-compacting concrete (SCC). Fresh properties such as slump flow, T50, V-funnel, J-ring, L-box and segregation index; concrete properties such as drying shrinkage strain, initial surface absorption test (ISAT) as well as compressive strength were investigated. Test results showed that substitution of cement with POFA up to 20%, the fresh properties of the concrete fulfilled the requirements of a self-compacting concrete. The results revealed that concrete has higher compressive strength, lower drying shrinkage, and lower initial surface absorption than control mix. The results indicated that POFA can be used up to 20% as a cement replacement material for producing self-compacting concrete.

Drying Shrinkage of Fly Ash-Based Self-Compacting Geopolymer Concrete

–The drying shrinkage behaviour of fly-ash-based self-compacting geopolymer concrete (SCGC) was studied for a period of one year. Two SCGC and One OPC-based conventional mixture were used in the present investigation. Drying shrinkage test commenced on the 7th day after casting the test specimens. Once the appropriate curing regime was completed, the specimens from each mix were placed in the laboratory room where the temperature was maintained at 23°C, however, the relative humidity of the room varied between 56 and 64 percent. Strain readings taken at specific intervals were analyzed to determine the time-dependent deformations of each mixture. Test results indicated that the heat-cured fly ash-based SCGC experienced very low drying shrinkage than that of water-cured OPC based concrete. After one year of exposure, in comparison to 466 με, the value experienced by OPC concrete, the drying shrinkage strains of SCGC mix specimens ranged between 141 and 159 με. These values were about 65-70% lower than that of OPC concrete. It is anticipated that the findings of this investigation would help in predicting the behaviour of SCGC. Keywords-Fly ash, Geopolymer concrete, Self-compacting Geopolymer concrete, Drying shrinkage

Study of Ultra High Performance Fiber Reinforced Concrete with Expansive and Shrinkage Reducing Agents

UltraHigh Performance Fiber Reinforced Concrete (UHPFRC) exhibits remarkable mechanical performance, which can allow to reduce the cross-section of structural members. However,a problem involving UHPFRC isthe likely tendency to crack at early age, due to autogenous and plastic shrinkages, caused by the very low water-to-binder ratio adopted. Therefore, this experimental work intends to detect the effectiveness of a possible solution for reducing the risk of shrinkage cracks in UHPFRC, by adding to the mixture a suitable combination of expansive and shrinkage reducing agents.Compressionand bending testswere carried out up to28 days of curing. Free drying shrinkage strains were evaluated up to 56 days of exposure to 50% relative humidity. The experimental results obtained by using expansive and shrinkage reducing agents were extremely encouraging in termsof free dryingshrinkage reduction, and even surprising in terms of flexural behaviour.

Structural lightweight aggregate concrete using two types of waste from the palm oil industry as aggregate

Abstract Huge quantities of raw materials are used in making concrete. Due to the limitations of natural materials the use of waste and by-product materials in concrete can eliminate the negative impact of concrete on the environment. To produce a cleaner and greener concrete two waste materials from the palm oil industry were used as coarse and fine aggregates. For this purpose normal sand was replaced with oil-palm-boiler clinker (OPBC) sand from 0 to 50% in oil palm shell (OPS) lightweight aggregate concrete. Properties, including workability, different types of density, compressive strength in different curing regimes, splitting tensile and flexural strengths, stress–strain curve, modulus of elasticity, water absorption and drying shrinkage strain of green lightweight concretes, were measured and discussed. The results showed that it is possible to produce environmentally-friendly structural lightweight concrete by incorporating high volume waste lightweight aggregates from the palm oil industry.

Computational Model for Internal Relative Humidity Distributions in Concrete

A computational model is developed for predicting nonuniform internal relative humidity distribution in concrete. Internal relative humidity distribution is known to have a direct effect on the nonuniform drying shrinkage strains. These nonuniform drying shrinkage strains result in the buildup of internal stresses, which may lead to cracking of concrete. This may be particularly true at early ages of concrete since the concrete is relatively weak while the difference in internal relative humidity is probably high. The results obtained from this model can be used by structural and construction engineers to predict critical drying shrinkage stresses induced due to differential internal humidity distribution. The model uses finite elment-finite difference numerical methods. The finite element is used to space discretization while the finite difference is used to obtain transient solutions of the model. The numerical formulations are then programmed in Matlab. The numerical results were compared with experimental results found in the literature and demonstrated very good agreement.

Microstructural and bulk property changes in hardened cement paste during the first drying process

This paper reports the microstructural changes and resultant bulk physical property changes in hardened cement paste (hcp) during the first desorption process. The microstructural changes and solid-phase changes were evaluated by water vapor sorption, nitrogen sorption, ultrasonic velocity, and 29Si and 27Al nuclear magnetic resonance. Strength, Young's modulus, and drying shrinkage were also examined. The first drying process increased the volume of macropores and decreased the volume of mesopores and interlayer spaces. Furthermore, in the first drying process globule clusters were interconnected. During the first desorption, the strength increased for samples cured at 100% to 90% RH, decreased for 90% to 40% RH, and increased again for 40% to 11% RH. This behavior is explained by both microstructural changes in hcp and C–S–H globule densification. The drying shrinkage strains during rapid drying and slow drying were compared and the effects of the microstructural changes and evaporation were separated.