Experimental Investigation on Environmentally Sustainable Cement Composites Based on Wheat Straw and Perlite.

Andrea Petrella,Michele Notarnicola,Magdalena Dobiszewska,Francesco Todaro,Sabino De Gisi,Milvia Elena Di Clemente,Stefania Liuzzi,Ubaldo Ayr

doi:10.3390/ma15020453

Andrea Petrella, Michele Notarnicola + Show 6 more

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https://doi.org/10.3390/ma15020453

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Abstract

Environmentally sustainable cement mortars containing wheat straw (Southern Italy, Apulia region) of different length and dosage and perlite beads as aggregates were prepared and characterised by rheological, thermal, acoustic, mechanical, optical and microstructural tests. A complete replacement of the conventional sand was carried out. Composites with bare straw (S), perlite (P), and with a mixture of inorganic and organic aggregates (P/S), were characterised and compared with the properties of conventional sand mortar. It was observed that the straw fresh composites showed a decrease in workability with fibre length decrease and with increase in straw volume, while the conglomerates with bare perlite, and with the aggregate mixture, showed similar consistency to the control. The thermal insulation of the straw mortars was extremely high compared to the sand reference (85–90%), as was the acoustic absorption, especially in the 500–1000 Hz range. These results were attributed to the high porosity of these composites and showed enhancement of these properties with decrease in straw length and increase in straw volume. The bare perlite sample showed the lowest thermal insulation and acoustic absorption, being less porous than the former composites, while intermediate values were obtained with the P/S samples. The mechanical performance of the straw composites increased with length of the fibres and decreased with fibre dosage. The addition of expanded perlite to the mixture produced mortars with an improvement in mechanical strength and negligible modification of thermal properties. Straw mortars showed discrete cracks after failure, without separation of the two parts of the specimens, due to the aggregate tensile strength which influenced the impact compression tests. Preliminary observations of the stability of the mortars showed that, more than one year from preparation, the conglomerates did not show detectable signs of degradation.

Highlights

Cement mortars were prepared with CEM II A-LL 42.5 R [39] from Buzzi Unicem (Rc (2 days) > 25.0 MPa, Rc (28 days) > 47.0 MPa) which is characterised by 80–94% clinker, 6–20% limestone LL (
Expanded perlite (P) (3–4 mm size range) is an inorganic material derived from volcanic rock with the following chemical composition: SiO2 74.5%, Al2 O3 12.3%, K2 O 4.2%, Na2 O 4%, Fe2 O3 1%, CaO 1.4%
It was observed that the fresh composites showed a sensible decrease in the flow with increase in straw volume due to the increasing water absorption which determined the manufacture of the dry materials, as in the case of the S3B and S3C samples (−60% and −100%, respectively)

Summary

Introduction

Concern for environmental protection is growing, especially in the agro-food industry which generates wastes from direct consumption of primary products. Most of these by-products are non-hazardous and are currently underutilised or wasted. For this reason, the concept of bioeconomy is spreading as a new approach to production that gives new life to materials which would otherwise be destined for destruction [1,2,3,4,5,6,7,8]. A large amount of waste needs to be disposed of

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