Creep Of High-strength Concrete Research Articles

Experimental Study on Shrinkage and Creep of High-Strength Concrete Used in a Coastal Complex Environment Bridge under a Cyclic Load

Tang, Y.; Feng, J.; Fu, Y., and Xue, S., 2020. Experimental study on shrinkage and creep of high-strength concrete used in a coastal complex environment bridge under a cyclic load. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 63–69. Coconut Creek (Florida), ISSN 0749-0208.In recent years, the construction of expressway road networks in China's coastal areas has been accelerating. Numerous coastal, offshore, and cross-sea bridges have appeared. Under the complex environment of marine erosion, typhoons, waves, etc., most bridges use high-strength concrete as a building material. Shrinkage and creep, two of the basic characteristics of high-strength concrete, can cause abnormal growth of structural deformation and even concrete cracking, which affects the safety of bridge structures. Numerous studies have focused on the shrinkage and creep characteristics of high-strength concrete under a constant load, but there are few reports on the shrinkage and creep of high-strength concrete under a cyclic load. Using standard concrete creep specimens and prestressed reinforced concrete beam members as the test objects, the authors carried out a creep test of high-strength concrete under a cyclic load and obtained the elastic modulus and creep coefficient. Comparative analysis of the creep coefficient and an existing shrinkage and creep model shows that the creep of high-strength concrete under a cyclic load is significantly greater than that creep a constant load. In addition, the creep development of high-strength concrete under a cyclic load shows a uniform increasing characteristic, suggesting that a coupling relationship between the prestress loss and the creep process of high-strength concrete.

Effect of limestone powder on creep of high-strength concrete

Effect of limestone powder on creep characteristics and internal relative humidity of high-strength concrete has been investigated. The results indicate that limestone powder can reduce creep of concrete, with a greater reduction in creep at higher replacement levels. Limestone powder delays the variation of internal relative humidity of concrete, and there exists a good linear relationship between creep and internal relative humidity of concrete, so creep can be predicted according to internal relative humidity. The creep prediction data of CEB-FIP 90 model obviously overestimate the test data of high-strength concrete with limestone powder always.

The Experimental Study on Creep and Shrinkage of High Strength Concrete with Fly Ash

Shrinkage and creep characteristics of concrete are significant factors in the design of prestressed concrete structures. With large scale/span concrete structures developed, the fly ash or other blends are added into high strength concrete to improve the mechanical properties and workability. As a result, the existing shrinkage and creep predicting models have certain limitations. The creep and shrinkage behavior of high strength concrete with fly ash are studied in this paper. Proper predicting model for shrinkage and creep of high strength concrete is recommended. The influence factor of fly ash is proposed as well. These conclusions would be of great useful for structures with fly ash concrete.

Modelling creep of high strength concrete

Recent developments in concrete mixing made possible the production of concretes with high compressive strength showing, simultaneously, high workability. These concretes also present high strengths at young ages, allowing the application of loads sooner. It is of fundamental importance to verify if creep models developed for current concrete still apply to these new concretes. First, a FEM-based software was adopted to test available creep models, most used for normal strength concrete, considering examples with known analytical results. Several limitations were registered, resulting in an incorrect simulation of three-dimensional creep. Afterwards, it was implemented a Kelvin-chain algorithm allowing the use of a chosen number of elements, which adequately simulated the adopted examples. From the comparison between numerical and experimental results, it was concluded that the adopted algorithm can be used to model creep of high strength concrete, if the material properties are previously experimentally assessed.

Elasticity modulus, shrinkage, and creep of high-strength concrete as adopted by AASHTO

This paper covers the experimental and theoretical components of National Cooperative Highway Research Program (NCHRP) research project Number 18-07, which is discussed in NCHRP Report 496. The components are related to modulus of elasticity, shrinkage, and creep of concrete. An experimental program was conducted at various bridge sites and at the University of Nebraska-Lincoln for specimens produced from raw materials and mixture proportions provided by 4 participating states: Nebraska, New Hampshire, Texas, and Washington. Previously reported measurements of material properties are also included. The experimental program was used to extend the pre-2005 AASHTO-LRFD specification prediction formulas to concrete with compressive strengths up to 15 ksi (104 MPa). For each material property, a summary of the experimental values is presented followed by a comparison with the values obtained from the pre-2005 AASHTO-LRFD specifications and the American Concrete Institute 209 committee report. The proposed formulas provide designers of prestressed concrete girders with more realistic estimates of long-term material properties, including effects of aggregate type and other significant factors. The use of these formulas with high-strength concrete (HSC) should result in more realistic camber predictions and lower prestress loss estimates. The background and recommendations for prediction of the modulus of elasticity, shrinkage, and creep of HSC are provided. To help with clarity, the notation and units employed in the pre-2005 AASHTO-LRFD specifications are adopted as much as possible. Stresses are expressed in units of ksi (MPa) rather than psi.

Effects of manufactured-sand on dry shrinkage and creep of high-strength concrete

The influences of natural sand, manufactured-sand (MS) and stone-dust (SD) in the manufactured-sand on workability, compressive strength, elastic modulus, drying shrinkage and creep properties of high-strength concrete (HSC) were tested and compared. The results show that the reasonable content (7%–10.5%) of SD in MS will not deteriorate the workability of MS-HSC. It could even improve the workability. Moreover, the compressive strength increases gradually with the increasing SD content,and the MSHSC with low SD content (smaller than 7%) has the elastic modulus which approaches that of the natural sand HSC, but the elastic modulus reduces when the SD content is high. The influence of the SD content on drying shrinkage performance of MS-HSC is closely related to the hydration age. The shrinkage rate of MS-HSC in the former 7 d age is higher than that of the natural sand HSC, but the difference of the shrinkage rate in the late age is not marked. Meanwhile the shrinkage rate reduces as the fly ash is added; the specific creep and creep coefficient of MS-HSC with 7% SD are close to those of the natural sand HSC.

Composite model for basic creep of high-strength concrete

Most of the reported work on creep of high-strength concrete (HSC) covers measurements of total creep on standard specimens kept in a standard environment of 50% relative humidity and 23 °C. The results of these studies are used to establish the basic creep factor of high-strength concrete, assuming that the environmental effect on creep of HSC is similar to that for normal-strength concrete (NSC). However, some recent work has shown that the effect of the environment on creep of HSC is different from that observed for NSC, which indicates that a realistic creep model for HSC needs to be developed based on more fundamental material behaviour. This paper reports a theoretical study of a composite model for predicting basic creep of concrete, considering it as a composite material of coarse aggregate, fine aggregate and cement paste. The model is based on the age-adjusted effective modulus method proposed by Bazant, and can take into account the composition of the concrete, the degree of compaction and the hydration of cement paste. The model is shown to predict basic creep measurements reported in the literature with reasonable accuracy.

Tensile creep behavior of high strength concretes at early ages

Early age tensile creep of high strength concrete loaded during the first day after casting was studied. The effect of silica fume was evaluated, using two types of loading scheme: (i) creep which occurs in a restrained autogenous shrinkage test and (ii) creep measured in a conventional test under constant load. The two methods showed that the addition of silica fume increased the early age tensile creep of high strength concrete, when compared to concrete without silica fume but with similar water/binder ratio. This enhanced creep is of practical significance as it provides a mechanism to relieve some of the restraining stress that develops due to autogenous shrinkage.

Shrinkage and Creep of High Strength Concrete

Shrinkage and Creep of High Strength Concrete

1042 高強度コンクリートのクリープに関する研究(材料・施工)

1042 高強度コンクリートのクリープに関する研究(材料・施工)