Porous structure and water vapour sorption of hemp-based materials

Lanas²,

Cement and Concrete Research

2010

Lime-based mortars modified with admixtures were prepared and subjected to different environments such as outdoor and indoor exposures, climatic chamber, SO 2 -chamber, and freezing-thawing cycles. The influence that the different admixtures (water repellents, water retainers, polypropylene fibre and a viscosity modifier) had on the pore size distribution of the hardened specimens was assessed and related to the water absorption capacity, and hence to the durability. Ageing resistance and mechanical strengths improved when additives reduced the water intake and increased the aircontent. High dosages of water repellents were necessary to enhance the durability, sodium oleate being the most effective additive to endure freezing processes. Also the low tested dosage of fibre, a water retainer (guar gum derivative), and a starch proved to be useful. SO 2 deposition caused the formation of calcium sulphite hemihydrate as the main degradation product. A very small amount of calcium sulphate dihydrate was observed. A crystal habit composed of acicular agglomerates of calcium sulphite hemihydrate was detected in SO 2 deposition on calcareous materials.3

Section: Mortars With Water-repelling Agentssupporting

confidence: 78%

Ageing of lime mortars with admixtures: Durability and strength assessment

Lanas²,

Cement and Concrete Research

2010

“…All of them showed a main peak -almost unimodal distribution -corresponding to1 μm diameter pores, which was in accordance with previous work on lime-based mortars [9,48,49]. The addition of SO and CS led to a reduction in the percentage of the small peaks related to larger pores (diameters from 100 μm to 10 μm) and to an increase in the volume of intruded mercury at the main peak.…”

Section: Pore Structure and Microstructuresupporting

confidence: 77%

Effect of water-repellent admixtures on the behaviour of aerial lime-based mortars

Lanas²,

Cement and Concrete Research

2009

120

Two different anionic surfactants, sodium oleate and calcium stearate, commercialized as water repellents for cement-based mortars, were added to lime-based mortars in order to check whether they were improved by these admixtures. Different properties of limebased mortars were evaluated: fresh state behaviour through water retention, air content and setting time, hardened state properties such as density, water absorption through capillarity, water vapour permeability, long-term compressive strengths, pore structure through mercury intrusion porosimetry, and durability assessed by means of freezingthawing cycles. A clear improvement in lime-based mortars was achieved when sodium oleate was added: strong capillarity reduction and excellent durability in the face of freezing-thawing processes, without any compressive strength drop. The mechanism for this improvement was related to air void formation due to the air entraining ability of these surfactants. Insolubility of calcium stearate turned out to be responsible for fewer air bubbles -as SEM examination revealed -and showed lower effectiveness.3

“…Figure 5 shows the obtained results for the hardened mortars. The reference mortar and F-1 sample showed a main peak -almost unimodal distribution -corresponding to1 μm diameter pores, which was in accordance with previous work on lime-based mortars [9,27,42]. The addition of a low dosage of polypropylene fibre led to a reduction in the percentage of the small peaks related to larger pores (diameters from 100 μm to 10 μm) and to an increase in the volume of intruded mercury at the main peak.…”

Section: Water Vapour Permeability -Pore Structuresupporting

confidence: 76%

Effect of a polypropylene fibre on the behaviour of aerial lime-based mortars

Lanas²,

Construction and Building Materials

2011

A polypropylene fibre was added to lime-based mortars in order to check whether they were improved by this admixture. Different properties of lime-based mortars were evaluated: fresh state behaviour through water retention, air content and setting time;hardened state properties such as density, shrinkage, water absorption through capillarity, water vapour permeability, long-term flexural and compressive strengths, pore structure through mercury intrusion porosimetry, and durability assessed by means of freezing-thawing cycles. An improvement in some properties of aerial lime-based mortars -such as permeability, mechanical strengths, reduction in macroscopic cracks or durability in the face of freezing-thawing cycles -was achieved when fibre was added at a low dosage. When a larger amount of additive was used, only the reduction in cracks and the durability of the material were improved.