Influence of substrate pore structure and nanolime particle size on the effectiveness of nanolime treatments

Nanolime is a promising consolidation treatment for the conservation of historic structures thanks to its high compatibility with carbonate-based substrates. Nanolime products can effectively reduce the porosity and restore the mechanical properties of treated surfaces. Whilst the popularity of nanolime has been growing, its consolidation mechanism still needs to be fully understood when applied to porous substrates. The aim of this paper is to determine the influence of nanolime particle size and substrate pore structure on the effectiveness of nanolime treatments. Results suggest that nanolime products with larger particle size tend to close predominantly large sized pores, while nanolime with smaller particle size tends to fill both large and small pores equally. These results suggest that for a consolidation treatment, the nanolime product must be chosen taking into consideration the substrate pore structure

Formulating mortars for use in restoration practice

The principal uses of Roman cement mortars in the field of restoration are for the production of cast decorative elements and renders. The formulation of these mortars differs in terms of mix proportions, workability and workable life. A typical specification for a “cast” mortar is 1:0.5 to 1:1 by volume, flow of 19.5 cm and a workable life in the range 15 – 30 minutes; a render mortar is typically 1:1.5 to 1:2.5 by volume, flow of 15.5 cm and a workable life of between 1 – 2 hours. Whilst the former workable life can be obtained by the use of chemical retarders the prolonged life required for renders is generally not possible without the excessive use of chemicals which impairs the performance of the hardened mortar and an alternative pre-hydration technique has been developed

Sticky rice - nanolime as a consolidation treatment for lime mortars

For almost 1500 years, many ancient Chinese mortars have remained unaltered despite exposure to atmospheric agents. The main reason for this long-term durability is the addition of sticky rice water to the standard mortar ingredients (lime and sand) following traditional recipes. In recent years, these mortars have been methodically studied leading to the conclusion that amylopectin, a polysaccharide in the sticky rice, plays a crucial role in regulating calcite crystals growth, creating a denser microstructure and providing the mortar with hydrophobic properties which contributed to their survival. In recent decades, nanolime products based on Ca(OH)2 nanoparticles suspended in alcohol or hydro-alcoholic medium, have been extensively used for the consolidation of calcareous substrates mainly due to their chemical affinity and absence of side-effects. Nanolime products have resulted in successful superficial consolidations. However, in-depth consolidation still needs to be achieved, and research needs to focus on ways to attain this objective. This study aimed to test a novel approach consisting of applying a pre-treatment of sticky rice and subsequently the nanolime. The resulting consolidation was evaluated by measuring changes of superficial cohesion, porosity, contact angle, drilling resistance, water absorption by capillarity, drying rate and aesthetic properties. The durability of the treatments was investigated by exposing samples to accelerated weathering. Results showed that the use of sticky rice in combination with nanolime yields a higher degree of consolidation increasing drilling resistance and delivering hydrophobic properties although prolonged exposure to high temperature and moisture can compromise treatment durability

Development of lime based, load-bearing materials for wall construction

Construction of buildings in the UK is traditionally done using building materials such as concrete blocks, bricks and less so, timber. Although timber is a sustainable product, concrete blocks and bricks require a lot of energy input during fabrication, concrete especially being a large producer of CO2 during its manufacture. Reducing energy consumption either domestically or industrially is an important part of achieving the UK Government’s legally binding commitment to reducing greenhouse gas emissions by at least 80% (relative to 1990 levels) by 2050. New, low embodied energy construction materials are urgently required to enable the construction industry to revolutionize and drastically decrease its carbon footprint. The constituents of the materials investigated were selected based on low embodied energy criterion. To achieve this, lime was selected as the base material with hemp (fibers and shives) and PVAc used as additives. Specially selected nanomaterials were used as fillers. The constituents were combined in a manner, which led to different materials being developed, all exhibiting different characteristics. One characteristic was strength (load bearing) to eliminate the use of timber studding during construction. The results show that the highest strengths were achieved by mixing 10 wt. % hemp fiber, 4 wt. % nanozinc oxide and 12 wt. % PVAc at a 0.4 W/L ratio, yielding 17.7 MPa in compression and 7.3 MPa in flexure

Influence of nanomaterials on properties of lime and hemp/lime composites for energy efficient wall design

A mixture of thermal, porosity and compressive strength properties of lime based materials were determined after adding different percentages of nanomaterials to enhance performance (nSiO2, nClay and nZnO). Specimens were formulated for use in the design of a five layer energy efficient wall. Materials consisted of lime nanocomposites (used as ‘Renders’, properties determined were thermal conductivity () and porosity) and lime/hemp shiv nanocomposites for thermal isolation ('Insulators', ). A lime/hemp fibre nanocomposite, with PVAc glue for strength, was developed as a load bearing material ('Core', , strength). A solvent exchange method for drying the specimens was applied as soon as practically possible to investigate if rapid drying could be considered without adverse effects. Results showed that the maximum 28 day decrease in for the Render was by using 4% nZnO, being -18% compared to the control sample. The same render also exhibited the lowest density. For the Insulator, λ was -31% when also using 4% nZnO in comparison to the nanofree specimen. Strength of the Core exceeded 10 MPa, much greater than the minimum load bearing requirement. The paper concludes by comparing the U value of a wall utilising these findings to those from an existing lime/hemp design

Nanolime for the consolidation of lime mortars: a comparison of three available products

Nanolime products are one of the most promising consolidation methods for historic calcareous substrates. Whilst the popularity of nanolime has been growing, its consolidation mechanism still needs to be fully understood when applied to highly porous substrates. The aim of this paper is to compare the three available nanolime products in terms of consolidation efficacy on lime mortar specimens. It is shown that repeated applications of a low concentrated nanolime can increase the superficial cohesion and the mechanical strength of the mortar within 1cm from the surface, while also reducing porosity, number of micro-pores and capillary water absorption coefficient. Nanorestore Plus® yielded the highest short-term consolidation effect. However, L'Aquila nanolime showed a higher durability which was attributed to a better developed crystalline structure

Influence of nanomaterials on properties of lime and hemp/lime composites for energy efficient wall design

A mixture of thermal, porosity and compressive strength properties of lime based materials were determined after adding different percentages of nanomaterials to enhance performance (nSiO2, nClay and nZnO). Specimens were formulated for use in the design of a five layer energy efficient wall. Materials consisted of lime nanocomposites (used as ‘Renders’, properties determined were thermal conductivity () and porosity) and lime/hemp shiv nanocomposites for thermal isolation ('Insulators', ). A lime/hemp fibre nanocomposite, with PVAc glue for strength, was developed as a load bearing material ('Core', , strength). A solvent exchange method for drying the specimens was applied as soon as practically possible to investigate if rapid drying could be considered without adverse effects. Results showed that the maximum 28 day decrease in for the Render was by using 4% nZnO, being -18% compared to the control sample. The same render also exhibited the lowest density. For the Insulator, λ was -31% when also using 4% nZnO in comparison to the nanofree specimen. Strength of the Core exceeded 10 MPa, much greater than the minimum load bearing requirement. The paper concludes by comparing the U value of a wall utilising these findings to those from an existing lime/hemp design

Determination of transfer stress from ruptured pre-load galvanised tendons in tanks and bund walls

Circular concrete tanks and containment bunds constructed by the pre-load method involves pre-stressing the concrete by repeatedly wrapping layers of highly tensioned tendons. Each layer is covered with gunite. Corrosion may lead to rupture and an explosive type failure is avoided if the gunite is able to absorb the transfer stress. Zinc galvanizing is used to increase the tendons resistance to corrosion but its smoothness can influence bond characteristics, as can corrosion if extensive. This paper investigates the pre-stress transfer of ruptured pre-load tendons in gunite, both in the uncorroded and corroded state. Laboratory testing was conducted where tendons were pre-loaded in custom-built stressing moulds (to 1000 MPa) and simulated gunite applied. Different degrees of accelerated corrosion were applied to the tendons (0-10%). The bond stress at transfer was determined by measuring the contraction of the tendon during release of the pre-stress (replicating a broken tendon). The results show that a low bond stress was found either as a result of the smooth zinc coating (uncorroded tendons) or due to higher levels of corrosion. These results were compared to design equations from Eurocode 2 and recommendations are made for reducing the bond coefficient Ƞp1, the coefficient that takes into account the type of tendon and the bond situation. Analysis is subsequently conducted to determine the transfer stress in the gunite by modelling single and double tendon ruptures and establishing the magnitude of compressive stress which, if excessive, may lead to an explosive type failure of the gunite

An overview of nanolime as a consolidation method for calcareous substrates

Ca(OH)2 particles with submicrometric dimensions (nanolimes) represent one of the most promising consolidants for the conservation of calcareous substrates. The nanolime treatment is similar to the limewater technique, traditionally used for its durability and high compatibility with the calcareous matrix but requiring a large number of applications and not always yielding a highly effective consolidation. Since 2001, alcohol-based dispersions of Ca(OH)2 nanoparticles have been synthesised to overcome the limitations of the limewater treatment. Nanolimes present the same high compatibility and durability of the traditional technique but superior properties in terms of higher consolidation, penetration and reactivity, and fewer side effects. Since their discovery, nanolimes have been investigated by several research groups with the aim of refining their synthesis process, properties and applications. This paper presents an overview of the most relevant literature about nanolime as a consolidant for calcareous substrates

European natural cements - their key technical properties under standardised conditions

The first comparative study on 7 commercially available Roman cements has been undertaken. In the absence of a European Standard, the testing procedures have followed a protocol proposed by the EU FP7 funded ROCARE project, which itself is based upon various ENs for cement and building limes. Evaluation has been made of mineralogy, particle size distribution, setting time, strength, water absorption, pore size distribution and mortar microstructure. Five of the cements required retardation and citric acid was used. The use of a pre-hydration technique was also investigated to extend the workable life of mortars to some 2 hours. The results confirm the view that the term Roman cement refers to a broad family of cements with a diverse range of properties which will need to be accounted for in future work to produce an all-encompassing Standard