Micromechanical modeling on autogenous and drying shrinkages of concrete

Han

2016

ACT

Self Cite

In this paper, the effect of internal curing with pre-soaked lightweight aggregate (PSLWA) on shrinkage and interior relative humidity of four series concretes with compressive strength at 28 days around 30MPa, 60MP, 90MPa and 100MPa is investigated. The shrinkage induced cracking performance of concretes is evaluated with concrete-steel composite ring tests. The results show that the development of the internal relative humidity of concrete since casting exhibits first a vapor saturated stage (RH=100%, stage I), followed by gradually reducing stage (RH<100%, stage II). Under sealing, internal relative humidity at the center of the specimen for a given age is obviously decreased with increase of concrete strength. Under drying, similar internal relative humidity value is observed at 28 days for all concretes without internal curing. As PSLWA was added, the reduction rate on interior humidity in stage II is significantly decreased. But the efficiency on internal humidity rising is greatly influenced by concrete strength. The autogenous shrinkage is increased with increase of concrete strength. The drying shrinkage is decreased with increase of concrete strength. The total shrinkage of concrete is increased with increase of concrete strength. As PSLWA was added, the shrinkage reduction in both autogenous and drying shrinkages is obviously in high strength concretes, such as 90MPa and 100MPa concretes. The shrinkage reduction of internal curing on relatively low strength concrete, such 30MPa and 60MPa concrete is not obvious. Internal curing with PSLWA can greatly improve the shrinkage induced cracking performance. All concrete rings without internal curing are cracked under drying. The compressive strain in the steel ring at the concrete ring cracking is about 75 to 101μm/m. By contrast, the stable compressive strain at the inner steel ring for the concretes with internal curing becomes 10 to 40μm/m and no visible cracks were found on the specimens.

Section: Development Of Shrinkage and Internal Relative Humiditymentioning

confidence: 86%

Evaluation of Shrinkage Induced Cracking in Concrete with Impact of Internal Curing and Water to Cement Ratio

Han

2016

ACT

Self Cite

Magazine of Concrete Research

“…Several researchers have attempted to predict the behaviour of autogenous shrinkage in concrete, but only how autogenous shrinkage changes with hydration time, w/cm ratio and the replacement ratio of fly ash (CEB-FIP, 2009;Dilger and Wang, 2000;Jonasson and Hedlund, 2000;Lee et al, 2003Lee et al, , 2006Miyazawa and Tazawa, 2001;Zhang et al, 2012). In fact, as shown by the results of the experimental work presented here, autogenous shrinkage of modern HPCs changes not only with these parameters, but also with air content and aggregate to cementitious materials paste ratio.…”

Section: Prediction Of Autogenous Shrinkage In Hpcmentioning

confidence: 98%

A prediction model for autogenous shrinkage of high-performance concrete in bridge engineering

Wang¹,

Li²

2013

Based on an experimental method of studying the autogenous shrinkage of high-performance concrete (HPC) in a mould of low-density flexible corrugated pipe, this paper presents experimental results and a prediction model for autogenous shrinkage of HPC with respect to water to cementitious materials ratio, replacement ratio of fly ash, air content and aggregate to cementitious materials paste ratio. Reasonably good agreement is observed between the experimental and predicted autogenous shrinkage, thus indicating that the proposed model can be successfully used to estimate the effects of the studied parameters on the development of autogenous shrinkage in HPC.Notation a, b, c, d constants that depend on cementitious material type and air-entraining agent C total weight of cementitious materials G weight of aggregate N aggregate to cementitious materials ratio of fresh concrete m, n constants that depend on cementitious material type and aggregate q, p constants that depend on cement type and fly ash S weight of sand t age of the concrete in days W weight of water in fresh concrete AE coefficient that describes the effect of cement type and fly ash â(t ) coefficient that describes the development rate of autogenous shrinkage strain with time ª coefficient that describes the effect of air content å AS (t ) autogenous shrinkage strain of concrete at t days, in microstrains å 28 (w/cm) autogenous shrinkage strain at 28 days ç coefficient that describes the effect of aggregate to cementitious materials ratio

International Journal of Damage Mechanics

“…The impacts of curing conditions, including environmental humidity and temperature on concrete shrinkage should be reflected in the model by cement hydration degree and interior relative humidity. The shrinkage model is verified by experiments with three kinds of concretes with compressive strength at 28 days of 34.1, 50.0, and 88.7 MPa (Zhang et al, 2012). Concrete mixture proportions and compressive strength at 28 days are listed in Table 1.…”

Section: Modeling On Moisture Variation Induced Strainmentioning

confidence: 99%

“…Parameter k 0 is obtained by comparing the model and experimental results (Zhang et al, 2012). Parameter S in (equation (1)) is called saturation fraction, S ¼ V ew /V p .…”

Section: Modeling On Moisture Variation Induced Strainmentioning

confidence: 99%

Evaluation of shrinkage induced cracking in early age concrete: From ring test to circular column

Jun

Gao

Han

et al. 2015

Self Cite

This article focuses on the modeling of shrinkage stress and evaluation of shrinkage induced cracking in early-age concrete. In the modeling, an integrative model for autogenous and drying shrinkage predictions of concrete at early-age is introduced first. Second, a model taking both cement hydration and moisture diffusion into account is used to calculate the distribution of internal humidity in concrete. Using above two models, the distribution of shrinkage stress in concrete ring and column at early-age from concrete cast are calculated. Meanwhile, the ring test is utilized to identify the time of shrinkage cracking of three kinds of concretes with compressive strength at 28 days around 30, 50, and 80 MPa. Based on model and ring test results, the shrinkage induced cracking tendency of concrete columns made of the three kinds of concretes is evaluated individually. The model results show that before drying, a uniform shrinkage strain along radial direction of a concrete column or ring is expected. After surface drying, shrinkage gradient along the radial direction is significant and the maximum and minimum shrinkage occur at the outer surface and the center of column or interior surface of the ring, respectively. The distribution of shrinkage stress along the radial direction of the ring or column is nonlinear and the nonlinearity is strong close to the drying surface. Due to the difference on restraint condition, lower shrinkage induced cracking tendency is expected in concrete column than that of steel restraint concrete ring, even both of them having the exact same outer diameter.