Properties and behaviour of GRC composites

The properties of GRC composites are a function of the production process (Table 8.3), fibre content and length. When considering the long-term performance, the environmental conditions and the type of glass fibres (E vs. AR glass fibres) must also be considered. Even for fibres that are classified as AR fibres, differences in the ageing characteristics are observed. In addition, the mechanical behaviour of the GRC composite can be analysed on the basis of some of the concepts discussed in Chapters 3 and 4. However, to be applied to this composite, the special microstructure of the GRC must be considered (see Section 2.3.2 and Chapter 5). 

The composition of the matrix may also affect the nature of hydration products developing and depositing around the strand and within it. The presence of supplementary cementing materials, and in non-Portland cement matrices, the growth into the strand may be reduced and the nature of products deposited there may be much more porous, affecting the mechanical properties of the composite (see Section 8.6.2.2). 

The significance of the strand microstructure and the deposition of hydration products in it led to several studies inwhich indentation and micro-indentation techniques were applied to characterize the strand and the nature of the matrix around individual filaments within the strand [50-52]. Zhuand Bartos [51] applied microindentation techniques to push in individual filaments to determine the resistance to their slip and through that assess the development of the microstructure within the strand. They demonstrated that in young composites the microstructure and interfacial bond of individual filaments was weaker within the fibre bundle than at the bundle-matrix interface. Upon ageing the inner microstructure within the strand became denser and stronger, and the resistance to the push-in force of the internal filaments increased to become similar to that of the external filaments. Purnell etal. [52] resolved by thin section petrographic techniques similar characteristics of strand fi 11 i ng upon ageing, but commented that the deposits of hydration products within the strand were not uniform and monolithic. 

Totai depth v )— / Plastic depth Final depth 

The better preservation of the strength reflects the fact that the composite cannot become weaker than the matrix cracking stress. At this point, as the strength is reduced to its lower limit, the properties of the composite are not much different from those of the matrix, which is characterized by a very low toughness, but with a 

---