applied sciences Article Mechanical and Thermal Properties of Insulating Sustainable Mortars with Ampelodesmos mauritanicus and Pennisetum setaceum Plants as Aggregates Dionisio Badagliacco 1 , Carmelo Sanfilippo 1,*, Bartolomeo Megna 1,2 , Tommaso La Mantia 3 and Antonino Valenza 1 1 Department of Engineering, University of Palermo, 90128 Palermo, Italy; [email protected] (D.B.); [email protected] (B.M.); [email protected] (A.V.) 2 INSTM Research Unity of Palermo, 90128 Palermo, Italy 3 Department of Agricultural, Food and Forest Sciences, University of Palermo, 90128 Palermo, Italy; [email protected] * Correspondence: carmelo.sanfi[email protected] Abstract: The use of natural fibers in cement composites is a widening research field as their application can enhance the mechanical and thermal behavior of cement mortars and limit their carbon footprint. In this paper, two different wild grasses, i.e., Ampelodesmos mauritanicus, also called diss, and Pennisetum setaceum, also known as crimson fountaingrass, are used as a source of natural aggregates for cement mortars. The main purpose is to assess the possibility of using the more invasive crimson fountaingrass in place of diss in cement-based vegetable concrete. The two plant fibers have been characterized by means of scanning electron microscopy (SEM), helium Citation: Badagliacco, D.; Sanfilippo, picnometry and thermogravimetric analysis. Moreover, the thermal conductivity of fiber panels has C.; Megna, B.; La Mantia, T.; Valenza, been measured. Mortars samples have been prepared using untreated, boiled and Polyethylene glycol A. Mechanical and Thermal 4000 (PEG) treated fibers. The mechanical characterization has been performed by means of three Properties of Insulating Sustainable point bending and compression tests. Thermal conductivity and porosity have been measured to Mortars with Ampelodesmos characterize physical modification induced by fibers’ treatments. The results showed better thermal mauritanicus and Pennisetum setaceum and mechanical properties of diss fiber composites than fountaingrass one and that fiber treatments Plants as Aggregates. Appl. Sci. 2021, lead to a reduction of the thermal insulation properties. 11, 5910. https://doi.org/10.3390/ app11135910 Keywords: natural fibers; reinforced mortar; thermal conductivity; sustainable mortar; mechanical Academic Editor: Doo-Yeol Yoo characterization; surface treatments; diss; crimson fountaingrass Received: 14 May 2021 Accepted: 22 June 2021 Published: 25 June 2021 1. Introduction In the last decades, a significant amount of relevant research has been carried out Publisher’s Note: MDPI stays neutral concerning the use of lignocellulosic materials in cementititous matrices for building with regard to jurisdictional claims in applications. For their high sustainability and good physical and mechanical properties, published maps and institutional affil- natural fibers find practical applications in composite materials for automotive parts and iations. building construction panels and furniture [1,2]. Residues of sisal, banana tree, common reed and eucalyptus have been used as reinforcement of cement leading to good mechanical performance of the composites [3–7]. The terms Agro-concrete or green concrete are defined as a mix between granulates from lignocellulosic plant (directly or indirectly from agriculture Copyright: © 2021 by the authors. or forestry origin), which represent the bulk of the volume, and a mineral binder [8]. Licensee MDPI, Basel, Switzerland. In this study, the characterization of eco-sustainable composite materials in the This article is an open access article field of green building, for application as insulating plasters has been performed. Diss distributed under the terms and (Ampelodesmos mauritanicus) and Crimson Fountaingrass (Pennisetum setaceum), have been conditions of the Creative Commons used as aggregates for cement mortars. Pennisetum setaceum is an invasive plant that is Attribution (CC BY) license (https:// gradually replacing the Ampelodesmos mauritanicus in Italy [9]. Alien invasive plants creativecommons.org/licenses/by/ represent one of the main threats to biological diversity on a world-wide scale, and 4.0/). Appl. Sci. 2021, 11, 5910. https://doi.org/10.3390/app11135910 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 14 Appl. Sci. 2021, 11, 5910 2 of 13 gradually replacing the Ampelodesmos Mauritanicus in Italy [9]. Alien invasive plants rep- resent one of the main threats to biological diversity on a world-wide scale, and hard effort is required every year to ward off, control and eradicate them [10]. In Sicily, Pennisetum hardSetaceum effort is isone required of the most every aggressive year to ward and off,quick control invaders and of eradicate coastal and them hilly [10 ].areas. In Sicily, Dur- Pennisetuming the 70 years setaceum followingis one ofits the first most introduction, aggressive it and has quickestablished invaders and of spread coastal over and many hilly areas.coastal During areas up the to 70 600 years m.a.s.l. following and especially its first introduction, on south-facing it has slopes established within andthe th spreadermo- overMediterranean many coastal belt areas [11]. up It has to 600 also m.a.s.l. invaded and H. especially hirta thermo on south-facing-xeric grasslands slopes and within even thethe thermo-Mediterraneanmore mesophilous Ampelodesmos belt [11]. ItMauritanicus has also invaded grasslands.H. hirta It thermo-xericis likely to continue grasslands to spread and eveninto many the more other mesophilous favorable localities,Ampelodesmos with significant mauritanicus andgrasslands. long-lastin Itg isenvironmental likely to continue con- tosequences spread into [12]. many On the other basis favorable of these localities,considerations, with significantthis research and was long-lasting aimed to assess environ- the mentalpossibility consequences of using crimson [12]. On fountaingrass the basis of these in place considerations, of diss, which this in research previous was works aimed has to assessalready the been possibility used as ofan usingaggregate crimson for green fountaingrass concrete [ in8,13 place], in oforder diss, to which promote in previousthe erad- worksication has of alreadythis invasive been usedplant as with an aggregatefundamental for greenbenefits concrete for the [8 ,biodiversity13], in order of to the promote terri- thetory. eradication of this invasive plant with fundamental benefits for the biodiversity of the territory. 2. Materials and Methods 2. Materials and Methods 2.1.2.1. RawRaw MaterialsMaterials 2.1.1.2.1.1. DissDiss ((AmpelodesmosAmpelodesmos mauritanicus Mauritanicus)) DissDiss (Figure(Figure1 )1 is) is a largea large grass grass widespread widespread growing growing in thein the Mediterranean Mediterranean North North Africa Af- andrica inand the in dry the regions dry regions of Greece of toGreece Spain, to Balkans, Spain, TurkeyBalkans, and Turkey Asia Minoris. and Asia In France,Minoris. it isIn establishedFrance, it is in established the departments in the ofdepartments Var, Southern of Corsica,Var, Southern and Herault. Corsica, It isand a perpetual Herault. plantIt is a ofper thepetual Poaceae plant family, of the which Poaceae lives family, in arid which and sandy lives soils,in arid often and in sandy neat associations, soils, often typicalin neat ofassociations, the Mediterranean typical of grasslands. the Mediterranean In Sicily, Ampelodesmosgrasslands. In Sicily, grasslands Ampelodesmos are commonly grasslands found fromare commonly 0 to 1200 mfound a.s.l., from chiefly 0 to within 1200 them a.s.l., meso chiefly Mediterranean within the and meso thermo-mediterranean Mediterranean and bioclimaticthermo-mediterranean belts [11]. It bioclimatic is composed belts of [ strong11]. It leaves,is composed up to of 1 mstrong long leaves, and about up to 7 mm1 m wide,long and very about rough, 7 mm with wide, tortuous very edges.rough, Thewith long tortuous andtough edges. leaves The long can and be sharp tough for leaves the skincan be if scrubbedsharp for betweenthe skin if fingers. scrubbed This between plant was fingers. previously This plant used was in thepreviously construction used ofin oldthe dwellingsconstruction because of old ofdwellings its mechanical because and of physicalits mechanical properties and physical [14]. Its fibrousproperties feature, [14]. withIts fibrous a thorny feature surface, with may a conferthorny high surface adhesion may confer to the cementhigh adhesion paste and to hencethe cement promising paste propertiesand hence topromising green concrete properties [15]. to Ingreen the literature,concrete [15 it]. is In reported the literature a Tensile, it is Strength reported of a 3 100Tensile MPa, Strength Density of of 100 850 MPa, g/cm Density, Modulus of 850 of Elasticityg/cm3, Modulus 2.17 GPa of Elasticity and a Water 2.17 Absorption GPa and a CoefficientWater Absorption at saturation Coefficient of 112% at [saturation16,17]. of 112% [16,17]. FigureFigure 1.1. DissDiss ((AmpelodesmosAmpelodesmos mauritanicusMauritanicus)) plant. plant. 2.1.2.2.1.2. CrimsonCrimson FountaingrassFountaingrass ((PennisetumPennisetum setaceum Setaceum)) PennisetumPennisetum setaceumSetaceum (Figure(Figure2 )2) is is a a plant plant of of the the Poaceae Poaceae family. family. The The species species is is native native toto NorthNorth Africa,Africa, thethe MiddleMiddle EastEast andand thethe ArabianArabian peninsula.peninsula. IntroducedIntroduced