The structural exploitation of fibrous-cement composites in reinforced concrete T-beams
The thesis expounds the logic behind a new concept of composite construction which exploits fibre reinforced cement composites in the form of channels, placed in the tensile zone of reinforced concrete T-beams. The fibre reinforced cement composites, which act as 'surface reinforcement', incorporate high modulus, asbestos fibres in a predominantly two-dimensional random distribution in a cement matrix. Compared with concrete, these units have a high tensile strength and greater extensibility. The first stage of this investigation is primarily concerned with the design of the fibre reinforced cement composites of suitable mechanical properties for use as surface reinforcement in large structural components. The mechanical properties are affected both by the thickness and the composition of these composites. In the second stage the structural utilisation of the compositesis examined in relation to strength, cracking and deflection characteristics; static, fatigue and sustained loading tests are carried out on reinforced concrete T-beams cast in conjunction with asbestos-cement composites. Altogether twenty-four beams are tested, the cross-sections of which,the type and the amount of tensile steel remain constant, whereas the variables investigated are the effect of the upstand length, thickness and composition of the surface reinforcement. It is shown that this type of construction considerably enhances the structural performance of reinforced concrete beams; the degree of improvement being a function of the composition and the upstand length of the surface reinforcement. At the design working load, for example, the deflection is reduced by up to 33% whilst cracks can be completely eliminated. Furthermore, the resulting composite could, in using surface reinforcement that extends a full depth of the web of a T-beam, ameliorate shuttering and consequently reduce the cost of the product.
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