Research output: Chapter in Book/Report/Conference proceeding › Meeting abstract (Book)

Up to now, the design of glass fibre reinforced cementitious composites is mainly focussed on strength, or more specifically on the evolution of strength with time. The glass fibres are degraded mainly by the high alkalinity of the cementitious matrix. Modification of glass fibres and introduction of new matrices is currently leading to cementitious composites showing notably increased durability. Since cementitious composites are functional to manufacture lightweight structures in buildings, the main design concern will shift gradually from durability to serviceability limit state (stiffness, ingress of water and chemicals in micro-cracks).

This contribution is dedicated to the non-linear stress-strain behaviour of cementitious composites. Linear elastic stress-strain behaviour can be adapted for the studied cementitious composites in compression. However, due to the low tensile strength of the matrix material, matrix cracks are formed at relatively low stress levels. This matrix crack formation reduces the stiffness of the composite in tension as a function of the applied composite stress. This contribution focuses on the stress-strain behaviour of the glass fibre reinforced cementitious composites under monotonic tensile loading and limited cycling. Typical stress-strain behaviour under limited cyclic loading is shown below.

Figure 1. Typical stress-strain behaviour cementitious composite under limited tensile loading, 2D-random oriented short fibres (50mm), fibre volume fraction 10%

The model used in this contribution to describe the behaviour of glass fibre cementitious composites is based on the well-known ACK theory (Aveston-Cooper-Kelly), used generally for brittle matrix composites. However, the main shortcoming of the ACK theory is found in the assumption that the matrix strength is a deterministic material parameter along the whole brittle matrix composite. The real multiple cracking phenomenon is thus compressed in to one "multiple cracking stress". An applicable model describing the stochastic nature of the matrix tensile strength of inorganic phosphate cement is verified to be the Weibull distribution model. If the basic assumptions of the ACK theory are combined with the Weibull distribution of the matrix tensile strength, a stochastic matrix cracking model can be found, predicting gradual matrix multiple cracking and matrix-fibre debonding as a function of the applied load. This theory can also be used to predict average matrix crack distance and width. Despite the introduction of the stochastic nature of the matrix strength in this model, the stress-strain behaviour of such a composite can be formulated analytically.

This contribution is dedicated to the non-linear stress-strain behaviour of cementitious composites. Linear elastic stress-strain behaviour can be adapted for the studied cementitious composites in compression. However, due to the low tensile strength of the matrix material, matrix cracks are formed at relatively low stress levels. This matrix crack formation reduces the stiffness of the composite in tension as a function of the applied composite stress. This contribution focuses on the stress-strain behaviour of the glass fibre reinforced cementitious composites under monotonic tensile loading and limited cycling. Typical stress-strain behaviour under limited cyclic loading is shown below.

Figure 1. Typical stress-strain behaviour cementitious composite under limited tensile loading, 2D-random oriented short fibres (50mm), fibre volume fraction 10%

The model used in this contribution to describe the behaviour of glass fibre cementitious composites is based on the well-known ACK theory (Aveston-Cooper-Kelly), used generally for brittle matrix composites. However, the main shortcoming of the ACK theory is found in the assumption that the matrix strength is a deterministic material parameter along the whole brittle matrix composite. The real multiple cracking phenomenon is thus compressed in to one "multiple cracking stress". An applicable model describing the stochastic nature of the matrix tensile strength of inorganic phosphate cement is verified to be the Weibull distribution model. If the basic assumptions of the ACK theory are combined with the Weibull distribution of the matrix tensile strength, a stochastic matrix cracking model can be found, predicting gradual matrix multiple cracking and matrix-fibre debonding as a function of the applied load. This theory can also be used to predict average matrix crack distance and width. Despite the introduction of the stochastic nature of the matrix strength in this model, the stress-strain behaviour of such a composite can be formulated analytically.

Original language | English |
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Title of host publication | First International RILEM Symposium on Advances in Concrete Through Science and Engineering, Evanston 21-24 March 2004 |

Number of pages | 2 |

Publication status | Published - 2004 |

Event | Unknown - Duration: 1 Jan 2004 → … |

Conference | Unknown |
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Period | 1/01/04 → … |

- stochastic strength, cementitious composite, textile reinforced cement

ID: 2199872