Abstract

The volume changes of cement-based composites are significantly exhibited during the hardening process. Initial phases of the hardening are complemented by the expansion due to the heat evolution that is subsequently alternated by the shrinkage. Both could cause the crack initiation causing significant loss of the durability and service-life shortage. The present paper focuses on the experimental investigation of the surface treatment of fresh concrete, which is applied to prevent sudden loss of the moisture during a hardening process, especially during the concrete highway construction. The technology of concrete highway production is extremely costs demanding, but its efficiency is determined by the longer lifespan in comparison with the asphalt pavement. However, negative impacts of the drying shrinkage could significantly reduce the durability. The efficiency of used treatment was investigated in terms of restrained shrinkage tests, water adsorption and mechanical testing. In addition, there were studied two types of conventional Portland cement. Performed program confirmed great sense of the curing on the concrete durability; in addition, there was well illustrated the efficiency of the utilization of blended binder systems in the paper.

Abstract

Reinforcement/matrix interaction is recognized as a key issue in polymeric composite materials. From the mechanical point of view, being the link between the fibres and the polymer, a proper load transfer is ensured only if a good enough interphase exists. This is particularly critical in carbon fibre (CF) composites since, due to the non-polar characteristics and chemical inertness of carbon, sometimes they exhibit weak interfacial adhesion. In this sense, various surface treatments for CFs are currently being investigated, in order to improve their interaction with the polymeric matrices: wet chemical or electrochemical methods, chemically or physically activated oxidation procedures, application of thin coatings and plasma treatments. This is precisely one of the challenges addressed in the MODCOMP project.

This paper describes part of the work carried out within the mentioned project in order to estimate the improvement of properties that can be achieved through enhancements of the CF/epoxy interphases. The study covers both elastic engineering constants and strengths predictions, and it has been performed using finite element models of RVEs of UD fibres and introducing cohesive elements to take into account the interfacial failure mode. The results obtained allow identifying which range of CF/epoxy interphase properties enhancement should be achieved in order to get significant effects in the composites mechanical response.

Abstract

The automotive, aerospace and renewable energy generation industries have replaced significantly the use of traditional materials, such as steel and aluminum, by reinforced fiber composites. It has recognized that joints drilling and screwing joints damage the fibers introducing a higher concentration of stresses. That is why the application of structural adhesives, as a method of joining in reinforced composites, has increased in recent years. Delamination is the most critical failure mode of composite materials resulting in stiffness and structural strength losses.

This works studies the behavior against delamination under mode I and mode II interlaminar fracture of adhesive bonded joints in carbon-epoxy composite materials, using structural adhesives of epoxy and acrylic bases. For the execution of the joints, different surface treatments have been employed: sanding, grit blasting and peel ply technique, allowing to make a fracture resistance comparision study. The double cantilever beam (DCB) and end notched flexure (ENF) tests configuration were used to determine stress-strain behavior and fracture toughness for mode I (GIC) and mode II (GIIC), respectively. Surface modifications have been evaluated by  contact angle measurements and scanning electron microscopy (SEM). The experimental results are shown in the same situation. The experimental results obtained show that, even if not showing the same delamination tendency for both fracture modes, the strain energy release rate are higher for an improved of wetting properties and an increase of surface roughness.