International Concrete Abstracts Portal

Ferrocement is a construction material that (in comparison to traditional reinforced concrete) provides superior crack control, impact resistance, and toughness. However, while extensive literature exists on the deterioration mechanisms and maintenance of reinforced concrete structures, little attention has been given to the durability of ferrocement. In this study, the adoption of ethyl silicate, a newly developed nanomaterial, is investigated to improve durability of ferrocement. Such nanomaterials are expected to penetrate the cementitious matrix without changing the appearance of the surface. Once penetrated, pozzolanic behavior is displayed forming calcium silicate hydrate and consequently increasing durability and mechanical performance. Particular attention is given to the carbonation-induced corrosion of reinforcement, which should be considered a major concern in ferrocement due to the initially small diameter of the mesh wires and the thin mortar cover. Despite its importance, there is a limited amount of literature on carbonation-induced corrosion of ferrocement structural elements.

A noble cause motivated the interest to carry out research work on an inexpensive strengthening technique using ferrocement for reinforced concrete beams applicable in developing countries. Ferrocement as an inexpensive strengthening material is suitable for some developing countries where using such a technique offers an optimum strengthening solution for deteriorated structures. The main experimental component of this research work on strengthening reinforced concrete beams has been already published. This paper primarily presents material characterization and finite element models to study the flexural and interfacial types of behavior of ferrocement-strengthened concrete beams. Twenty-seven (27) ferrocement specimens were tested under direct tension to characterize the behavior of the used ferrocement. Special grip attachments have been designed and manufactured to elude local failure at the specimens’ ends. Based on the direct tension test results, a stress-strain relationship has been developed to describe the uniaxial tensile constitutive relation for ferrocement in the finite element models. The interfacial bond behavior between the ferrocement and the concrete is considered in the models by using interface elements. Moreover, a user-defined subroutine for the microplane constitutive law is integrated into the model for the concrete material. Results of the finite element modeling are presented for the ultimate load-carrying capacities, load-deflection history, and stress distributions at the ferrocement/concrete interface. The finite element modeling results have been validated against the published experimental findings and have shown reasonable agreement.

An experimental program is described to investigate the effect of high axial load on seismic performance of non-seismically designed reinforced concrete beam-column joints with or without strengthening. Four two-thirds-scale interior joints, including two control specimens and two specimens strengthened by ferrocement jackets with embedded diagonal reinforcements, are tested. The specimens are subjected to two levels of axial load representing low and high axial load ratios at 0.2 and 0.6, respectively. Test results indicate that increasing axial load to 0.6fc'Ag is detrimental for the joint with and without strengthening. Joints under low axial load exhibit higher peak strength, higher drift ratio, and better energy dissipation compared to those under high axial load. Despite joints under high axial load having relatively higher initial stiffness, joint stiffness degrades rapidly. The proposed strengthening method is more effective for the joint under high axial load. Furthermore, a modification on softened strut-and-tie model (SSTM) is proposed to account for the influence of high axial load on joint shear strength. The comparison of predicted strength to tested strength indicates that the proposed modification increases the accuracy of SSTM for joints under high axial load.

Ferrocement, a reinforced cementitious composite, may attain its optimal reinforcing capability for soil reinforcement applications owing to its synergetic action from two components of wire mesh and mortar. This paper presents some experimental results on the performance behavior and failure modes of ferrocement elements reinforced with woven square mesh and chicken mesh under pullout tests in two types of backfill materials. It is demonstrated that the failure modes of ferrocement depend on the surface properties of ferrocement, mortar composition, and type of mesh. Tests results reveal that square mesh-reinforced ferrocement with smooth surface shows frictional failure only under normal stresses, whereas with chicken mesh-reinforced ferrocement, there is mortar failure at higher normal stresses. It is also observed that the pullout resistance of ferrocement is improved significantly by using some small parallel channels on the surface of ferrocement elements transversely to the pullout direction. In the case of ferrocement containing two, four, and six channels, only the mortar failure is observed for square mesh-reinforced ferrocement, whereas the mesh failure is apparent for chicken mesh-reinforced ferrocement. A discussion regarding the corrosion of ferrocement elements as embedded in soil and a comparison between this technique and other soil reinforcement methods, such as geogrids or geosynthetics, in terms of cost, strength, and durability, are presented.

An electrochemical-based accelerated corrosion technique has been employed to study the corrosion durability of ferrocement. Variables considered include cover thickness; composition of the matrix in terms of water-cement ratio (w/c), sand-cement ratio (s/c),and contents of mineral and chemical admixtures; and use of stainless steel wire mesh. After suitable exposure, maximum crack width, percentage of steel loss, and reduction in flexural strength served as the bases for assessing the relative performance of various means considered. Test results indicate that the addition of mineral admixtures, application of a suitable surface coating, and the use of deeper concrete cover provide excellent protection against reinforcement corrosion. Employment of stainless steel as reinforcement and the use of so-called corrosion inhibitor or a low w/c in the matrix also slows down the corrosion process, but is not as effective as others. Based on test results, a hybrid protection system combining three lines of defense is suggested for enhanced durability of ferrocement.