Description
The recent earthquakes in the Mediterranean area provoked serious damages and collapses to the existing buildings, including masonry ones, that represent the highest percentage of current structures. The need of preserving the existing structures to prevent economic and human losses is always accompanied by the compelling necessity of also conserving the environment due to the increasing attention to the sustainability issues. In this framework, retrofit solutions, that are already widespread and considered effective in the construction sector, can be improved from an environmental point of view. One of the most applied techniques in the past years for masonry structures is the Fiber Reinforced Cementitious Matrix (FRCM), that is usually made of artificial fibers such as steel, carbon, and glass. The sustainability of this kind or reinforcement can be improved by replacing artificial fibers with natural ones, such as hemp, that claims good mechanical properties and is carbon negative. The research means to experiment a retrofitting system, called Hemp-FRCM, that is made of a hemp mesh drowned in a lime matrix. In a first phase, the system is investigated by applying the reinforcement on masonry samples made of solid bricks and carrying out compressive tests. In a second phase, the adhesion capacity to the substrate, by performing delamination tests on two different supports, namely solid bricks and yellow Neapolitan tuff blocks, is performed. The test results show premising results on the possibility of using hemp meshes, instead of artificial ones, for the structural retrofit of existing masonry buildings.
The need of experimenting sustainable components for building products is underlined by the prominent energy and raw material consumptions and carbon dioxide emissions, which see the construction industry as main responsible. Natural fibers, in particular hemp ones, are very worthwhile thanks to their adequate mechanical properties and environmental advantages. The research aims to experiment two types of lime-based plasters reinforced with hemp braids with different diameters, added in the mixture in different percentages, as seismic retrofit systems of existing buildings. In particular, two premixed NHL mortars, namely M5 and M15, and three diameters of hemp braids (0.4 mm, 1 mm and 2.2 mm) in percentages by weight of lime from 0.25% to 3%, are examined. The amount of water absorbed by hemp braids is assessed by performing imbibition test and allows to define the quantity of water to add in the mixture. All the mix designs are tested on a shaking table to evaluate the effect of hemp braids on the workability of the mortar and, finally, compressive and bending tests are performed on the mixtures considered as acceptable doughs after the preliminary test phase. The results of the laboratory tests show that hemp braids produce a decrease in the workability of the plasters that remains acceptable for low percentages of fibers. The braids also allow an increase in the flexural strength and a decrease in compressive strength, which is however not detrimental for application in seismic zones. In both mechanical tests it is evident the sewing and confinement effect of the fibers, that allow a more ductile behavior of the inspected mortar.
