混凝土断裂韧性评价方法 PCER方法

Evaluating plain concrete flexural toughness using PCER method

Jianguo Han 1, a , Peiyu Yan 2,b and Gangling Li 3,c

1 Department of Civil Engineering, Tsinghua University, Beijing, 100084, China

2 Department of Civil Engineering, Tsinghua University, Beijing, 100084, China 3

Department of Civil Engineering, Tsinghua University, Beijing, 100084, China a

hanjg@, b yanpy@, c ligangling120@

Keywords: Concrete, Flexural Toughness, PCER Method, Strength, Curing Age.

Abstract. Using PCER (post-crack energy ratio) method, the influence of strength grade and curing age on flexural toughness of plain concrete were analyzed. Results show that along with the increase of strength grade and curing age, the flexural toughness of plain concrete decrease; and along with the increase of the K value used in the calculating equation, the flexural toughness of plain concrete decrease too. Meanwhile, the changing tendency of PCER value along with the K value manifests that when evaluating the flexural toughness of different quality concrete, the same K value should be used. Introduction

Usually, plain concrete is a quasibrittle material, and along with the increase of strength, its brittleness increase too. The so-called brittleness is a material property; it is relative to toughness. When the external force reaches certain limit, the property of sudden rupture without apparent plastic deformation is defined as brittleness; and the property of manifesting apparent plastic deformation but without sudden rupture is called toughness.

For plain concrete, along with the decrease of water to binder ratio and the introduce of mineral admixture, the quality of transition zone increases, thus during the concrete fracture process under external force, the crack propagation mode transfers form following the transition zone to penetrating the coarse aggregate, resulted the increasing brittleness [1]. Adding fiber to concrete can increase its toughness, but up to now there is not universal specification worldwide on how to evaluating the flexural toughness of fiber reinforced concrete. The common used specifications such as ASTM C1018 [2], JSCE SF4 [3], RILEM TC162 [4] and PCS [5] method have its advantages and disadvantages and using scope. For example, the identify of initial crack point according to ASTM C1018 method is somewhat subjective, the contribution of fiber to toughness is not explicitly distinguished in JSCE SF4 method, RILEM TC162 method can not be used to plain or poorly reinforced concrete, and the information before the peak load is not fully used in PCS method. Based on the aforementioned flexural toughness evaluating methods, the author proposed a new flexural toughness evaluating method named PCER (post-crack energy ratio) method [6]. Comparing with the aforementioned flexural toughness evaluating methods, the PCER method has the properties of accuracy, simplicity and wide applicable scope. PCER Method

Base on bilinear model, the ascendant branch of PCER method is from the beginning point to peak load, and the descending branch is from peak load to the set deflection point define by the value of K. PCER method evaluates concrete toughness by the area ratio of area under the descending branch of bilinear model to area under the real load-deflection curve after the peak load, as illustrated in Fig. 1 and Eq. 1. Since the area under the load-deflection curve is the energy dissipated during crack propagation, the area ratio is energy ratio in actually. The higher the PCER value calculated by Eq. 1, the higher the flexural toughness of the tested concrete possesses.

Advanced Materials Research Vols. 287-290 (2011) pp 1184-1188Online available since 2011/Jul/04 at © (2011) Trans Tech Publications, Switzerland

doi:10.4028//AMR.287-290.1184