Relaxation of Structural Concrete due to its Shrinkage in Terms of Age-Adjusted Effective Modulus Method

2017 ◽  
Vol 737 ◽  
pp. 471-476
Author(s):  
Lukáš Zvolánek ◽  
Ivailo Terzijski
Keyword(s):  
Residual Stresses ◽  
High Performance ◽  
High Performance Concrete ◽  
Relaxation Mechanism ◽  
Effective Modulus ◽  
Tensile Creep ◽  
Ring Test ◽  
Polypropylene Fibres ◽  
Creep Effect ◽  
Modulus Method

This paper focuses on the calculation of residual stresses due to shrinkage with a tensile creep effect. Whereas the shrinkage of concrete causes stresses in the material, the tensile creep counteracts the shrinkage as a stress relaxation mechanism. The main objective of this paper is to evaluate the ageing coefficient c (referred to as Trost-Bazant Coefficient) reflecting the load history. The coefficient is used for the residual stress analysis by means of a simplified method called Age-adjusted Effective Modulus Method. The tensile creep effect was evaluated according to the rheological model provided by Eurocode 2. Although the Eurocode predicts the creep for the structural members subjected to compressive stresses, this study proves that it can be used for the tensile creep prediction as well. We tested three types of concrete: reference concrete, high-performance concrete with reduced shrinkage magnitude by means of special admixtures, and fibre concrete with the content of polypropylene fibres. From the obtained results, it can be stated, that the ageing coefficient can be considered to be the value of 0.45 for any shrinkage development. It was also proved, that the tensile creep value essentially affects the magnitude of residual stresses, even in the “early age” concrete. The correctness of the calculated residual stresses was verified by means of a Ring-test.

Age-Adjusted Effective Modulus Method for Creep of High-Performance Concrete

2006 ◽  
Vol 302-303 ◽  
pp. 693-699
Author(s):  
Bing Han ◽  
Yuan Feng Wang
Keyword(s):  
Experimental Data ◽  
Plastic Flow ◽  
High Performance ◽  
High Performance Concrete ◽  
Effective Modulus ◽  
Relaxation Coefficient ◽  
Modulus Method ◽  
Set Up

This paper discusses the suitability of using several creep theories of common concrete for creep of high-performance concrete (HPC). Based on the Age-Adjusted Effective Modulus method (AEMM) for creep of concrete, Improved Dischinger (ID) method and the Elastic Continuation and Plastic Flow (ECPF) theory for calculating relaxation coefficient and considering characteristics of HPC, a method is set up for calculating the creep of HPC under changing stresses, and comparing results gotten by the method with some experimental data, it can be considered that the above methods are suit for the calculation of creep of HPC.

An Evaluation on the Restrained Shrinkage of Ultra-High Performance Concrete

2012 ◽  
Vol 525-526 ◽  
pp. 449-452 ◽  
Author(s):  
Jung Jun Park ◽  
Doo Yeol Yoo ◽  
Sung Wook Kim ◽  
Young Soo Yoon
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Tensile Creep ◽  
Ring Test ◽  
Early Age ◽  
Restrained Shrinkage ◽  
Reinforcing Bars ◽  
Ultra High Performance Concrete ◽  
Shrinkage Cracking ◽  
Coarse Aggregates

Since ultra-high performance concrete (UHPC) is subject to large occurrence of shrinkage at early age due to its low water-to-cement ratio, the mixing of large quantities of powdered admixtures and the absence of coarse aggregates, UHPC presents large risks of shrinkage cracking caused by the restraints provided by the form and reinforcing bars. Accordingly, this study intends to evaluate the shrinkage behavior of UHPC under restrained state by performing restrained shrinkage test using ring-test. The test results reveal that increasing thickness of the inner ring increases the tensile creep at early age leading to the reduction of the average strain and residual stress of the inner ring.

Methods Considering the Concrete Creep due to Shrinkage

2017 ◽  
Vol 259 ◽  
pp. 3-8
Author(s):  
Lukáš Zvolánek ◽  
Ivailo Terzijski
Keyword(s):  
Effective Modulus ◽  
Tensile Creep ◽  
Ring Test ◽  
Concrete Creep ◽  
Young Concrete ◽  
Modulus Method

Creep of concrete is a phenomenon that is not only significant in the long term, but also at young concrete. The paper deals with methods considering the tensile creep of concrete due to shrinkage. It was proved, that the tensile creep can be taken into account by simplified methods called Age-adjusted Effective Modulus Method with the ageing coefficient χvalue falling between 0.4 and 0.45. Calculated values were experimentally verified by means of Ring-test.

Usage of Heat Pretreatment for Reduction of Explosive Spalling of High Performance Concrete

2014 ◽  
Vol 1054 ◽  
pp. 37-42
Author(s):  
Iveta Nováková ◽  
Ulrich Diederichs ◽  
Lenka Bodnárová
Keyword(s):  
Compressive Strength ◽  
Water Vapour ◽  
High Performance ◽  
High Performance Concrete ◽  
Mercury Porosimetry ◽  
Concrete Structures ◽  
Explosive Spalling ◽  
Polypropylene Fibres ◽  
Rapid Reduction ◽  
Micro Cracks

Fire resistance of concrete structures could be improved by add of polypropylene fibres in to the concrete mixture in butch from 1 to 2 kg per 1 m3 of fresh concrete. This method is effective, but it is not possible to use it for existing concrete and existing reinforced concrete structures. The new method which has good potential for fire protection of existing structures is based on creation of capillary pore and micro cracks system, which allowed water vapour evaporate from concrete. This study deals with determination of appropriate temperature in which is created adequate network of capillary pores and micro cracks which has no influence on strength and durability of the concrete. The formation of macro cracks and bigger pores could cause rapid reduction of compressive and tensile strength, decrease of resistance to aggressive substances and decrease of the frost resistance. The high performance concrete (HPC) has very low porosity, which can cause explosive spalling while the water vapour tries to evaporate from concrete structure during the fire. The HPC concrete has high compressive strength and high density. The HPC samples were exposed to temperatures 150, 250, 350 a 450°C, and after cooling down to normal ambient were carried out tests to define changes in porosity by mercury porosimetry, mass looses and compressive strength changes. The heated HPC concrete is regaining humidity into its structure from surrounding atmosphere, which can cause rehydratation of some chemical compounds. [1] For verification of these hypotheses the HPC samples were kept in water storage for 4 weeks and then tested.

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