265-TDK : Testing methods for determination of double-K criterion for crack propagation in concrete

Technical Committee 265-TDK

General Information

Chair: Prof. Shilang XU
Deputy Chair: Yao WU
Activity starting in: 2011
Activity ending in: 2018
Cluster A

Subject matter

The task of the new Technical Committee is to deal with the double-K criterion which describes crack formation in concrete (or other quasi-brittle materials). The double-K criterion has been developed in the nineties of last century. The double-K constitute two material parameters, the first is called Kcini which defines the onset of cracking, and the second is called Kcun which defines the onset of unstable cracking or failure. Both are derived from linear-elastic fracture mechanics principles. The two material parameters characterize the mechanical behaviour of concrete. It has been shown that the double-K does not depend on the size of the specimens. Many comparative tests have been performed with specimen sizes varying in a large range and no size effect could be found. So, the determination of double-K is straight forward. For the determination of double-K, the specimen geometry can be chosen according to the availability in the laboratory. Tests have been performed on three-point bending notched beams, on compact-tension specimens, on uniaxial tension specimens, and on wedge-splitting specimens. The testing of double-K can be done on every universal testing equipment, even without displacement control. One does not need loading-unloading cycles.

The double-K criterion has been used to assess the safety of large concrete structures like dams. The Chinese standard number DL/T 5332-2005 defines testing methods for the determination of double-K. It has been introduced in the People’s Republic of China in 2005.

The aim of the new TC is to make the knowledge of double-K internationally available by preparing a RILEM recommendation.

Terms of reference

It is estimated that the new TC needs about 4 years to finalize the work.

The members will come mainly from universities and research institutes. They will be selected by the chairman and the secretary of the TC. General information will be given on relevant symposia and RILEM members will be called for support.

To validate the testing method of double-K, a round robin champagne will be organized.

Detailed working programme

1 Literature survey

The literature will be screened with respect to fracture-mechanics testing with special emphasis on double-K criterion.

2 Round-robin testing

Double-K criterion testing has been performed in Stuttgart (Germany), Dalian, Hangzhou (China), Jamshedpur and Kharagpur (India), maybe at other places as well which are not yet detected. At the places mentioned, the results show good agreement as the testing method is concerned. However, a draft recommendation should be validated before it is finalized. Therefore, a round-robin campaign is proposed with at least two laboratories.

First option: The specimens are made at one place and shipped to the other testing site(s). Two types of concrete will be used.

Second option: Two types of concrete will be specified. The type of cement and addition, the water-cement ratio, the type of aggregate, the curing condition, the testing age will be prescribed. The testing labs will follow the instructions as punctually as possible and produce the concrete with local materials.

In both cases the testing results will be evaluated and compared with each other.

3 Recommendation

A recommendation will be prepared which defines the testing methods for double-K criterion. There will be several specimen shapes, such as three-point bending, wedge splitting, compact tension, and uniaxial tension. The methods how to analyze the test will be given in formulas. The recommendation will comprise the following paragraphs: background of double-K criterion, dimensions of specimens, fabrication of specimens, testing apparatus, measuring devices, test procedure, test results and calculations, test report, references.

4 Workshop

A workshop is planned for the presentation of the TC’s work and of the draft recommendation. Other experts who deal with fracture mechanics of concrete will be invited. Maybe, the workshop could be a joint workshop of RILEM and ACI. The proceedings of the workshop will help to bring the recommendation into its final shape.

5 Literature

_Bažant, Z.P., Kazemi, M.: Size dependence of concrete fracture energy determined by RILEM work-of-fracture method. Int. J. Fract. 51 (1991), 121-138
_Bažant, Z.P., Kim, J.-K., Pfeiffer, P.A.: Determination of fracture properties from size effect tests. J. Struct. Eng. ASCE 112 (1986), No. 2, 289-307
_Bažant, Z.P.: Concrete fracture models: testing and practice. Eng. Fract. Mech. 69 (2002), 165-205
_Brühwiler, E., Wittmann, F.H.: The wedge splitting test: A method of performing stable fracture mechanics tests. Eng. Fract. Mech. 35 (1990), 117-125
_Carpinteri, A.: Decrease of apparent tensile and bending strength with specimen size: two different explanations based on fracture mechanics. Int. J. Solid Struct. 25 (1989), No. 4, 407-429
_Elices, M., Planas, J.: Fracture mechanics parameters of concrete – an overview. Adv. Cem. Based Mater. 4 (1996), 116-127
_Hillemeier, B., Hilsdorf, H.K.: Fracture mechanics studies on cement compound. Cem. Concr. Res. 7 (1977), 523-536
_Hillerborg, A.: Results of three comparative test series for determining the fracture energy GF of concrete. Mater. Struct. 18 (1985), No. 5, 407-413
_Jenq, Y.S., Shah, S.P.: A fracture toughness criterion for concrete. Eng. Fract. Mech. 21 (1985), 1055-1069
_Jenq, Y.S., Shah, S.P.: Two parameter fracture model for concrete. J. Eng. Mech. ASCE 111 (1985), 1227-1241
_Kumar, S., Barai, S.V.: Determining double-K fracture parameters of concrete for compact tension and wedge splitting tests using weight function. Eng Fract Mech 76 (2009), 935-948
_Kumar, S., Barai, S.V.: Determining the double-K fracture parameters for three-point bending notched concrete beams using weight function. Fatigue Fract Eng Mater Struct (2010), DOI: 10.1111/j.1460-2695.2010.01477.x.
_Kumar, S., Barai, S.V.: Equivalence between stress intensity factor and energy approach based fracture parameters of concrete. Eng Fract Mech 76 (2009), 1357-1372
_Kumar, S., Barai, S.V.: Influence of specimen geometry on determination of double-K fracture parameters of concrete: A comparative study. Int J Fract 149 (2008), 47-66
_Reinhardt, H.-W., Cornelissen, Hans A.W., Hordijk, Dirk A.: Tensile tests and failure analysis of concrete. In: Journal of Structural Engineering 112 (1986), No.11, S. 2462-2477
_Reinhardt, H.-W., Shilang Xu: Crack extension resistance based on the cohesive force in concrete. In: Eng. Fracture Mechanics 64 (1999), S. 563-587
_RILEM Draft Recommendations (TC 89-FMT): Determination of fracture parameters KsIC and CTODc of plain concrete using three-point bend tests, proposed RILEM draft recommendations. Materials and Structures 23 (1990), No. 138, 457-460
_Shah, S.P., Ouyang, C.: Fracture mechanics for failure of concrete. Annu. Rev. Mater. Sci. 24 (1994), 193-320
_Shailendra Kumar and Sudhirkumar V. Barai (Eds.) „Concrete Fracture Models and Applications“, Springer 2011
_Shilang Xu, Reinhardt, H. W.: Determination of double-K criterion for crack propagation in quasi-brittle fracture, Part II: Analytical evaluation and practical measuring methods for three-point bending notched beams. In: Int. J. of Fracture 98 (1999), S. 151-177
_Shilang Xu, Reinhardt, H.-W.: Crack extension resistance and fracture properties of quasi-brittle softening materials like concrete based on the complete process of fracture. In: Int. J. of Fracture 92 (1998), S. 71-99
_Shilang Xu, Reinhardt, H.-W.: Determination of double-K criterion for crack propagation in quasi-brittle fracture, Part I: Experimental investigation of crack propagation. In: Int. J. of Fracture 98 (1999), S. 111-149
_Shilang Xu, Reinhardt, H.-W.: Determination of double-K criterion for crack propagation in quasi-brittle fracture, Part III: Compact tension specimens and wedge splitting specimens. In: Int. J. of Fracture 98 (1999), S. 179-193
_Tada, H., Paris, P.C., Irwin, G.: The stress analysis of cracks Handbook. Hellertown, PA, Del Research Corporation, 1985
_Wittmann, F.H., Rokugo, K., Brühwiler, E., Mihashi, H., Simopnin, P.: Fracture energy and strain softening of concrete as determined by compact tension specimens. Materials and Structures 21 (1988), No. 1, 21-32
_Xu, S., Reinhardt, H. W.: Determination of the double-K fracture parameters in standard three-point bending notched beams. In: _Mihashi, Hirozo, Rokugo, Keitetsu (eds.): Fracture mechanics of concrete structures: Vol. I: Fracture properties and parameters. Freiburg: Aedificatio Publ., 1998. – ISBN 3-931381-22-X, S. 431-440
_Xu, Shilang, Reinhardt, H.W.: Double-K parameters and the cohesive-stress-based KR curve for the negative geometry. In: V.C. Li, C.K.Y. Leung, K.J. Willam, S.L. Billington (Eds.) „Fracture mechanics of concrete structures“, Proc. of 5th Intern. Conf. on Fracture mechanics of concrete structures 2004, Vail, USA, Vol. 1, pp 423-430
_Zhang Xiufang, Xu Shilang. A comparative study on five approaches to evaluate double-K fracture toughness parameters of concrete and size effect analysis. Engineering Fracture Mechanics, 2011, 78 (10): 2115-2138
_Zhao, G., Jiao, H., Xu, S.: Study on fracture behavior with wedge splitting test method. Fracture Processes in Concrete, Rock and Ceramics (Ed. by van Mier et al.), London 1991, E & FN Spon, 789-798
_Zhao, Z., Kwon, S.H., Shah, S.P.: Effect of specimen size on fracture energy and softening curve of concrete. Part 1, Experiments and fracture energy. Cem. Concr. Res. 38 (2008), 1049-1060

Technical environment

The double-K is a new approach of fracture mechanics of concrete. The previous TC 50-FMC worked on the determination of the fracture energy of mortar and concrete, TC 89-FMT dealt with the determination of fracture parameters of the two-parameter fracture model and with the size-effect model for determining fracture energy and process-zone size of concrete. Active TCs are not involved in fracture-mechanics items. So, there is no overlap with other TCs.

The ACI Committee 446 “Fracture Mechanics” is dealing with other subjects.

As RILEM is concerned there was always great interest in mechanical properties and fracture of concrete. The new TC would continue the great tradition. Further on, RILEM recommendations often serve as pre-normative standards for international standardization bodies.

Expected achievements

The TC will produce a recommendation which can be applied by everybody in the world. It is anticipated that the recommendation serves as a model for an international standard.

Towards the end of the work, a workshop will be organized for dissemination of the results. In the meantime, the TC will report during the Technical day of a RILEM week.

Group of users

The users of the recommendation are academics and testing laboratories in research and industry.

Specific use of the results

The recommendation makes it possible for everybody to measure fracture-parameters of concrete in an easy way. Nowadays, fracture parameters are gained in rather sophisticated manner with displacement-controlled testing devices. The new approach is more economic.