Carlos Chastre

Flexural Strengthening of Low-grade Concrete Through the Use of New Cement-based Composite Materials

UNIVERSITY OF THE BASQUE COUNTRY, PhD Supervisor: Dr. José Tomás San José Lombera

Up until the end of the 19th century, masonry and timber were the most widely used construction materials. However, the irruption of Reinforced Concrete revolutionised construction technology. Its tentative application over the last few decades of that same century eventually led to its widespread use, which may be explained by the prodigious properties resulting from the union of two materials: concrete and steel. 
Nowadays, the need to strengthen or upgrade the existing housing stock, largely built out of reinforced concrete, is very apparent. Rehabilitation in certain European countries might also represent an opportunity to counter the crisis in the construction sector. There may be several causes for that need, such as changes in functionality, damage caused by mechanical actions and environmental effects, more stringent design requirements, poor original design, faulty construction and structural ageing.
A considerable number of structures were erected when knowledge of the material was still limited and constructions standards contained no specifications for durability issues. Thus,
these generations of low-grade concrete structures fail to comply wit modern-day standards, in
terms of their mechanical characteristics as much as their durability requirements.
An innovative strengthening system for the rehabilitation of RC structures is investigated, within the framework of this Doctoral Thesis, which provides an alternative to more conventional retrofitting methods such as Fibre Reinforced Polymers. The research aims to widen the knowledge base on the behaviour of this technology, based on fibre textiles embedded in an inorganic (cement-based) matrix known as Textile Reinforced Mortar (TRM), and on its effectiveness as a strengthening system in retrofitted RC beams in flexure.
The main objectives of this thesis are: 
• To conduct a thorough study of the characteristics of low-grade concrete and its
strengthening processes, carefully assessing their mechanical properties, materials, causes of
failure and drawbacks.
• To evaluate the flexural strengthening of low-grade concrete with TRM.
The experimental work was designed to fulfil the second objective. A first stage involved
tests that focused on the strengthening material, especially on the parameters that affect
mechanical behaviour, and its constituent materials. Three different fibres were employed as
the TRM reinforcement core: basalt, carbon and cold-drawn steel wire. In the second stage,
thirty four one-third scale beams and fourteen full-scale beams were manufactured with lowgrade concrete and strengthened with TRM.
Finally, two different numerical analyses validated the data obtained from the experimental campaign. One, developed by the author, is based on the classic assumption for the calculation of RC cross sections in flexure. The other arises from the application of Finite Element Analysis to the same materials. The experimental and analytical results have validated the mechanical effectiveness of TRM for the strengthening of RC beams in flexure.