Wheat is the most common type of cereal used worldwide and the production of wheat husk waste from the refinement process is estimated to ca. 10 million tons in 2020 only in the EU. Since now, no well-defined recycling strategy exists and natural decomposition with the consequent production of polluting greenhouse gases is often the final destination of these materials. Recycling of agricultural by-products, in particular in the building sector, have recently been in focus through many EU-funded project. However, wheat husk has not yet been investigated. Although current thermal insulation materials have excellent performances, they are generally based on petroleum-derived raw materials (e.g. extruded polystyrene, expanded polystyrene, polyurethane foam, etc.). So-called bio based building material are more environmental-friendly alternatives, the most common one available on the market being lime hemp concrete. This material contains hemp hurds as filler and hydrated and/or hydraulic lime as binder. The material has good thermal insulation properties (0.05-0.12 W/m*K) and excellent moisture buffering and acoustic properties. An alternative to lime-based binders, having the same or even better green value, are magnesia-based ones. The present work was aimed to the design of wheat husk insulating material as potential alternative to hemp lime concrete. The idea was to combine the necessity of finding valid recycling alternative for wheat husk with the need of the building sector for environmental-friendly insulation materials. The results from initial physical characterizations of wheat husk showed a low dry thermal conductivity (ca. 0.05 W/(m.K)), comparable to hemp hurd, as well as good hygric regulation performances (MBV equal to 2.06 g/(m2.%RH)). Hence, the material was considered a viable alternative as filler in biocomposites. In subsequent investigations, lime wheat husk concrete was prepared and compared to a lime hemp concrete. Despite the higher dry apparent density of the former, the total porosity (around 80%) and dry thermal conductivity (ca. 0.09 W/(m.K)) were similar for both types of concrete. The somewhat lower mechanical performance of lime wheat concrete (~0.20 MPa) with respect to lime hemp concrete (0.24 MPa), although in line with those expected for infilling walls without load bearing requirements, was found to be due to lower adherence of wheat husk to the lime-based binder. In order to obtain a material with improved mechanical performance, subsequent work was dedicated to investigated an alternative binder with better compatibility with the novel vegetal filler. In particular, a magnesia-based cementitious materials was investigated. Setting and hardening of the investigated system relied on hydration of reactive MgO in the presence of MgSO4 and a vegetal flour leading to a complex porous microstructure composed of needle-shaped magnesium oxy sulfate cement phases as well as magnesium hydroxide with carbon uptake potential. Wheat husk magnesia concrete and hemp hurd magnesia concrete were prepared and compared to the corresponding lime-based materials previously investigated. Mechanically stronger composites were obtained with magnesia-based binder. In addition, the best mechanical performance was observed for composites containing wheat husk as filler. Microstructural investigations showed that both lower porosity and stronger adhesion of wheat husk aggregate with the binder phase are responsible for the improved mechanical performance. Concluding, the results obtained during this PhD research showed that direct utilization, i.e. without any energy-consuming pre-treatments, of wheat husk for the production of bio based building materials intended for thermal insulation purposes is a viable recycling option and a valid alternative/substitute for less environmental-friendly traditional insulation materials.

Il grano è il più comune cereale impiegato in tutto il mondo. In Unione Europea, la quantità di scarto ottenuto dalla sua lavorazione è stimata a circa 10 milioni di tonnellate nel 2020. Attualmente non esiste una precisa strategia che preveda il recupero di questo sottoprodotto, il cui smaltimento, spesso incontrollato, provoca forti problemi ambientali. Recentemente, numerosi progetti finanziati dalla UE hanno evidenziato le possibilità di impiegare scarti agricoli nel settore edilizio, senza tuttavia prendere in considerazione uno dei principali sottoprodotti dalla lavorazione del grano: la lolla. Sebbene i materiali attualmente impiegati per l'isolamento termico dell'involucro edilizio abbiano prestazioni eccellenti, essi sono sintetici (polistirene estruso, polistirene espanso, schiuma di poliuretano, ecc.). Al contrario, i cosiddetti biocompositi sono eco-sostenibili. Tra questi, il più comune sul mercato è il calce-canapulo, ottenuto dalla combinazione della parte legnosa dello stelo di canapa e un legante a base di calce idrata e/o idraulica. Tale materiale ha buone proprietà di isolamento termico (0,05-0,12 W/(m*K)), eccellenti valori di Moisture Buffer e proprietà acustiche. Un'alternativa, ai leganti a base di calce calcica, sono i cementi magnesiaci. Il presente lavoro è finalizzato all'impiego della lolla di grano per lo sviluppo di un materiale isolante in alternativa al calce-canapulo. In tale contesto, sono state combinate le esigenze di due settori produttivi trasformando un materiale di scarto agro-industraiale in risorsa per l’edilizia. I risultati delle caratterizzazioni iniziali degli scarti di grano hanno mostrato valori di conducibilità termica (0,05 W / (mK)) e Moisture Buffer Value (2,06 g / (m2.% RH )) paragonabili al canapulo. Dunque, tale scarto è stato considerato una valida alternativa come riempitivo leggero per realizzare biocompositi. In successive indagini, il biocomposito a base di lolla e calce è stato preparato e confrontato con il canapulo-calce. Nonostante la maggiore densità apparente del primo, la porosità totale (circa 80%) e la conducibilità termica (0,09 W /(m.K)) sono simili per entrambi i biocompositi. Prestazioni meccaniche leggermente inferiori sono state riscontrate per il composito contente la lolla (~ 0,20 MPa) rispetto all’equivalente con canapulo (0,24 MPa), ciò è stato attribuito alla minore adesione riempitivo-legante. Al fine di ottenere un materiale con migliori prestazioni meccaniche, il lavoro successivo è stato dedicato allo studio di un legante alternativo caratterizzato da una migliore compatibilità con il nuovo riempitivo vegetale. In particolare, è stato studiato un cemento magnesiaco, la cui presa e indurimento si basa sull'idratazione del MgO reattivo in presenza di MgSO4 e una farina vegetale. Il risultato è una microstruttura porosa complessa composta da fasi di magnesio ossisolfato a forma di ago e idrossido di magnesio. I biocompositi lolla-matrice magnesiaca e canapulo-matrice magnesiaca sono stati preparati e confrontati con i corrispondenti biocompositi a base di calce precedentemente studiati. Migliori prestazioni meccaniche sono state riscontrate per i compositi preparati con legante magnesiaco. Nel particolare, sono state osservate le più alte resistenze a compressione per i compositi preparati con la lolla. Indagini microstrutturali hanno dimostrato che sia la minore porosità che la maggiore adesione dello riempitivo con la fase legante sono responsabili delle migliori prestazioni meccaniche. Concludendo, questa ricerca di dottorato ha evidenziato la possibilità di utilizzare scarti di lavorazione del grano, senza pretrattamenti energivori, per lo sviluppo di materiali destinati all’isolamento termico in alternativa ai materiali isolanti tradizionali più inquinanti.

Scarti cerealicoli: una risorsa rinnovabile e sostenibile per il settore edilizio / Virginia Barbieri , 2020 Mar 10. 32. ciclo, Anno Accademico 2018/2019.

Scarti cerealicoli: una risorsa rinnovabile e sostenibile per il settore edilizio

BARBIERI, VIRGINIA
2020

Abstract

Wheat is the most common type of cereal used worldwide and the production of wheat husk waste from the refinement process is estimated to ca. 10 million tons in 2020 only in the EU. Since now, no well-defined recycling strategy exists and natural decomposition with the consequent production of polluting greenhouse gases is often the final destination of these materials. Recycling of agricultural by-products, in particular in the building sector, have recently been in focus through many EU-funded project. However, wheat husk has not yet been investigated. Although current thermal insulation materials have excellent performances, they are generally based on petroleum-derived raw materials (e.g. extruded polystyrene, expanded polystyrene, polyurethane foam, etc.). So-called bio based building material are more environmental-friendly alternatives, the most common one available on the market being lime hemp concrete. This material contains hemp hurds as filler and hydrated and/or hydraulic lime as binder. The material has good thermal insulation properties (0.05-0.12 W/m*K) and excellent moisture buffering and acoustic properties. An alternative to lime-based binders, having the same or even better green value, are magnesia-based ones. The present work was aimed to the design of wheat husk insulating material as potential alternative to hemp lime concrete. The idea was to combine the necessity of finding valid recycling alternative for wheat husk with the need of the building sector for environmental-friendly insulation materials. The results from initial physical characterizations of wheat husk showed a low dry thermal conductivity (ca. 0.05 W/(m.K)), comparable to hemp hurd, as well as good hygric regulation performances (MBV equal to 2.06 g/(m2.%RH)). Hence, the material was considered a viable alternative as filler in biocomposites. In subsequent investigations, lime wheat husk concrete was prepared and compared to a lime hemp concrete. Despite the higher dry apparent density of the former, the total porosity (around 80%) and dry thermal conductivity (ca. 0.09 W/(m.K)) were similar for both types of concrete. The somewhat lower mechanical performance of lime wheat concrete (~0.20 MPa) with respect to lime hemp concrete (0.24 MPa), although in line with those expected for infilling walls without load bearing requirements, was found to be due to lower adherence of wheat husk to the lime-based binder. In order to obtain a material with improved mechanical performance, subsequent work was dedicated to investigated an alternative binder with better compatibility with the novel vegetal filler. In particular, a magnesia-based cementitious materials was investigated. Setting and hardening of the investigated system relied on hydration of reactive MgO in the presence of MgSO4 and a vegetal flour leading to a complex porous microstructure composed of needle-shaped magnesium oxy sulfate cement phases as well as magnesium hydroxide with carbon uptake potential. Wheat husk magnesia concrete and hemp hurd magnesia concrete were prepared and compared to the corresponding lime-based materials previously investigated. Mechanically stronger composites were obtained with magnesia-based binder. In addition, the best mechanical performance was observed for composites containing wheat husk as filler. Microstructural investigations showed that both lower porosity and stronger adhesion of wheat husk aggregate with the binder phase are responsible for the improved mechanical performance. Concluding, the results obtained during this PhD research showed that direct utilization, i.e. without any energy-consuming pre-treatments, of wheat husk for the production of bio based building materials intended for thermal insulation purposes is a viable recycling option and a valid alternative/substitute for less environmental-friendly traditional insulation materials.
Cereal by-products: a renewable and sustainable resource for bio-based building materials
10-mar-2020
MANFREDINI, Tiziano
SILIGARDI, Cristina
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