Resilient hemp shiv aggregates with engineered hygroscopic properties for the building industry

This study focuses on the surface treatment of an extremely hydrophilic natural plant material, hemp shiv, using a functionalised silica based coating to provide hydrophobicity while retaining its moisture buffering ability. The chemical composition and physical structure of bio-based materials results in their extremely hydrophilic behaviour. In this work, a simple one step coating process was used to enhance the water-repellence of hemp shiv without compromising its ability to adsorb and release moisture. The coating modified the morphology and surface roughness of hemp shiv providing a hydrophobic surface having a water contact angle of 118° and reduced the bulk water absorption by 250% over 24 h. Mercury intrusion porosimetry (MIP) showed that the treatment refined the pore size distribution of hemp shiv, reducing the size of larger pores but not completely blocking the smaller pores thereby allowing hemp shiv to buffer moisture. Fourier-transform infrared spectroscopy (FTIR) revealed the chemical composition was modified by the coating, reducing the hydroxyl groups. Hemp shiv aggregates treated with functionalised silica based coating show potential for the development of robust lightweight building materials with enhanced hydrophobicity

Modification of hemp shiv properties using water-repellent sol–gel coatings

For the first time, the hydrophilicity of hemp shiv was modified without the compromise of its hygroscopic properties. This research focused on the use of sol–gel method in preparation of coatings on the natural plant material, hemp shiv, that has growing potential in the construction industry as a thermal insulator. The sol–gel coatings were produced by cohydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) using an acidic catalyst. Methyltriethoxysilane (MTES) was added as the hydrophobic precursor to provide water resistance to the bio-based material. Scanning electron microscopy (SEM) and focused ion beam (FIB) have been used to determine the morphological changes on the surface as well as within the hemp shiv. It was found that the sol–gel coatings caused a reduction in water uptake but did not strongly influence the moisture sorption behaviour of hemp shiv. Fourier transformed infrared (FTIR) spectroscopy shows that the coating layer on hemp shiv acts a shield, thereby lowering peak intensity in the wavelength range 1200–1800 cm−1. The sol–gel coating affected pore size distribution and cumulative pore volume of the shiv resulting in tailored porosity. The overall porosity of shiv decreased with a refinement in diameter of the larger pores. Thermal analysis was performed using TGA and stability of coated and uncoated hemp shiv have been evaluated. Hemp shiv modified with sol–gel coating can potentially develop sustainable heat insulating composites with better hygrothermal properties

Resilient hemp shiv aggregates with engineered hygroscopic properties for the building industry

This study focuses on the surface treatment of an extremely hydrophilic natural plant material, hemp shiv, using a functionalised silica based coating to provide hydrophobicity while retaining its moisture buffering ability. The chemical composition and physical structure of bio-based materials results in their extremely hydrophilic behaviour. In this work, a simple one step coating process was used to enhance the water-repellence of hemp shiv without compromising its ability to adsorb and release moisture. The coating modified the morphology and surface roughness of hemp shiv providing a hydrophobic surface having a water contact angle of 118° and reduced the bulk water absorption by 250% over 24 h. Mercury intrusion porosimetry (MIP) showed that the treatment refined the pore size distribution of hemp shiv, reducing the size of larger pores but not completely blocking the smaller pores thereby allowing hemp shiv to buffer moisture. Fourier-transform infrared spectroscopy (FTIR) revealed the chemical composition was modified by the coating, reducing the hydroxyl groups. Hemp shiv aggregates treated with functionalised silica based coating show potential for the development of robust lightweight building materials with enhanced hydrophobicity

The initial reactions of lime-pozzolan pastes for conservation of masonry

Throughout the lifetime of historic buildings the masonry will often undergo at least one conservation intervention. The need for conservation arises from the different elements of the building and to this end mortars have a very important role to play. Historic lime mortars and the various components from which they are made including the type of lime, pozzolan and aggregates have been extensively studied. They have received attention concerning their degree of reactivity and how they interact with the masonry units which are commonly stone or brick. The pozzolan-lime reactions, and the hydration and carbonation processes are important factors that influence the final properties of any lime-pozzolan mortars. In this study lime-pozzolan paste combinations are defined as a combination of calcium lime (CL 90) with a pozzolanic additive. The pozzolanic materials; wood ash, brick dust and Argical M1000 have been investigated in this study. To understand the role of the different pozzolans on the initial hydration reactions of the lime in pozzolan-lime pastes, the rheology and hydration kinetics were evaluated using a TA Hybrid Rheometer DHR – 2 and a Calmetrix I-Cal 4000 calorimeter respectively. In terms of kinetics evolution, Argical M1000, a type of metakaolin exhibited greater pozzolanic activity than wood ash and brick dust. Calorimetry and rheology tests have shown corroborative results regarding the initial hydration reactions of the pozzolan-lime pastes, different effects were observed for each type of pozzolan

Control of carbonation mechanism in Portland Cement paste using synthetic carbon-capture aluminosilicates

In this research, synthetic aluminosilicate nanoparticles in the form of engineered synthetic aluminosilicates (ESA) were added to a cement paste to create a more controlled environment for carbonation and subsequent hydration reactions. To date, early-age CO2 curing of Portland cement pastes has been shown to reduce the later-age performance due to the decalcification of hydration products and starvation of water by early-age carbonation. However, in this study, it was demonstrated that it is possible to control the carbonation and subsequent hydration reactions through the addition of ESA. Two types of synthetic aluminosilicates were synthesised using organosilanes, tetraethoxysilane (TEOS), and functionalised organosilane, 3-aminopropyltriethoxysilane (APTES). The two aluminosilicates behaved slightly differently, confirming the possibility of altering the carbonation and subsequent hydration reactions. The research demonstrates that tailored nanoparticles enhance carbonate formation by preventing decalcification of the hydration product. The ESA took part in pozzolanic reactions which resulted in no starvation of water on carbonation and led to improved performance at a later age when compared to the samples without ESA. Furthermore, decalcification of portlandite was not observed on the addition of ESA. The carbonation reaction mechanisms on the addition of these ESAs were postulated, and the possibility of increase in carbon uptake without affecting the mechanical performance at later ages were shown

Control of carbonation mechanism in Portland Cement paste using synthetic carbon-capture aluminosilicates

In this research, synthetic aluminosilicate nanoparticles in the form of engineered synthetic aluminosilicates (ESA) were added to a cement paste to create a more controlled environment for carbonation and subsequent hydration reactions. To date, early-age CO2 curing of Portland cement pastes has been shown to reduce the later-age performance due to the decalcification of hydration products and starvation of water by early-age carbonation. However, in this study, it was demonstrated that it is possible to control the carbonation and subsequent hydration reactions through the addition of ESA. Two types of synthetic aluminosilicates were synthesised using organosilanes, tetraethoxysilane (TEOS), and functionalised organosilane, 3-aminopropyltriethoxysilane (APTES). The two aluminosilicates behaved slightly differently, confirming the possibility of altering the carbonation and subsequent hydration reactions. The research demonstrates that tailored nanoparticles enhance carbonate formation by preventing decalcification of the hydration product. The ESA took part in pozzolanic reactions which resulted in no starvation of water on carbonation and led to improved performance at a later age when compared to the samples without ESA. Furthermore, decalcification of portlandite was not observed on the addition of ESA. The carbonation reaction mechanisms on the addition of these ESAs were postulated, and the possibility of increase in carbon uptake without affecting the mechanical performance at later ages were shown

Hygrothermal and mechanical characterisation of novel hemp shiv based thermal insulation composites

This study focuses on the development of advanced water resistant bio-based composites with enhanced hygrothermal performance for building applications. The highly porous structure of hemp shiv is responsible for low thermal conductivity and allows the material to adapt to varying humidity conditions providing comfortable indoor environment. However, the pore network and the hydrophilic nature of hemp shiv affects the compatibility and durability of the material in presence of excess moisture conditions. In this work, novel hemp shiv composites were prepared in a starch based or silica based matrix and characterised for their hygroscopic, thermal and mechanical properties. The hemp shiv based composites were resistant to water yet permeable to vapour and showed excellent moisture buffering capacity when compared to conventional hemp-lime composites. The composites prepared were light weight with low thermal conductivity values of 0.051–0.058 W/mK and showed good mechanical performance. Hemp shiv composites with superior hygrothermal characteristics have immense potential as robust thermal insulation building materials

Effect of recycled geopolymer concrete aggregate on strength development and consistence of Portland cement concretes

Numerous studies have shown that production of geopolymer cement concretes can have lower carbon emissions compared to Portland cement concretes. However, for a full lifecycle assessment of environmental impacts, scenarios for the end of structures’ design life of must be considered, including reuse options. The work presented here is part of a wider study investigating the recyclability of fly ash-slag geopolymer cement (GC) concrete as an aggregate in Portland cement (PC) concretes. Three types of GC concretes with varying Na2O % per mass of precursor and SiO2/Na2O molar ratio were produced in the laboratory. All other mix design parameters were kept constant. The concretes were investigated thoroughly through physical and mechanical testing and chemical characterization at various ages and then crushed mechanically to form recycled geopolymer concrete aggregates (RGCA). Two series of PC concretes with 20% aggregate replacement by RGCA were produced – one of S1 consistence class and one of S3 consistence class (design slumps of 10-40mm and 100-150mm). The effect of RGCA on PC concrete fresh properties was investigated. The compressive strength development was assessed by testing at 7, 28 and 90 days. All results were evaluated against concretes with recycled Portland cement concrete aggregates (RCA) and natural limestone aggregates. These results were paired with calorimetric studies of pastes produced with recycled concrete aggregate leachate. Although mix designs were adapted according to water absorption requirements, the consistence of concretes appeared to be largely dependent on the type of aggregate. The results showed that strength trends remained unaltered between the two concrete series and were mostly influenced by the aggregate type. Mixes with RGCA presented overall higher strengths than the RCA and limestone aggregate concretes. Tests at 90 days showed a continuous increase of compressive strength, while the trends between the concretes remained unaltered. Overall, this study has shown that RGCA affect new concretes in a different way to RCA. However, none of the factors investigated here should prevent the use of RGCA in new concretes

Hydrophobicity of hemp shiv treated with sol-gel coatings

This is the first time sol-gel technology is used in the treatment of hemp shiv to develop sustainable thermal insulation building materials. The impact on the hydrophobicity of hemp shiv by depositing functionalised sol-gel coatings using hexadecyltrimethoxysilane (HDTMS) has been investigated. Bio-based materials have tendency to absorb large amounts of water due to their hydrophilic nature and highly porous structure. In this work, the influence of catalysts, solvent dilution and HDTMS loading in the silica sols on the hydrophobicity of hemp shiv surface has been reported. The hydrophobicity of sol-gel coated hemp shiv increased significantly when using acid catalysed sols which provided water contact angles of up to 118° at 1% HDTMS loading. Ethanol diluted sol-gel coatings enhanced the surface roughness of the hemp shiv by 36% as observed under 3D optical profilometer. The XPS results revealed that the surface chemical composition of the hemp shiv was altered by the sol-gel coating, blocking the hydroxyl sites responsible for hydrophilicity