Masonry Consolidation Research Articles

The Contribution of Glass Microspheres and PP Fibers in the Properties of NHL Grouts

Although, over the last decades, different types of additions have been used in mortars for conservation of heritage buildings, their use in lime-based grouts for stone masonry consolidation is limited. The purpose of this study is to contribute to the increase of knowledge regarding the performance of injection grouts prepared with glass microspheres and polypropylene (PP) fibers. The effects of glass microspheres and PP fibers on the properties of natural hydraulic lime-based grouts were analysed by rheological measurements, mechanical strength tests, water absorption and drying test. The content of glass microspheres (5-20%) and PP fiber (0.1-0.5%) was added by the weight of binder and to reduce the water demand, a polycarboxylate superplasticizer was used. From the assessment of the results, it was asserted that the fresh state behaviour was slightly affected by these additions, as in general the rheological properties worsened compared to the reference grout composition. On the other hand, the PP fibers influenced the hardened grouts’ properties in a positive way, while their mechanical and physical properties were slightly improved or maintained which is a crucial feature for the success of consolidation intervention.

Performance of Silica Fume-Based Geopolymer Grouts for Heritage Masonry Consolidation

Despite the increasing number of studies on geopolymer-based materials, a lack of information still prevails concerning the use of geopolymer materials for the consolidation and conservation of the built heritage. Since the introduction of the term “geopolymer” by Davidovits, several studies have pointed out geopolymers as a potential replacement for traditional binders, mainly due to their advantages associated with mechanical properties and low carbon dioxide emissions. The geopolymers (also known as alkali-activated materials or inorganic polymers) are obtained by a chemical process through which precursors rich in silica and alumina interact with an alkaline medium to result in a material with binding properties. The aim of this study is to exploit the potential of geopolymer-based grouts in the consolidation of stone masonry buildings. Grouting or grout injection is a technique used for the consolidation of heritage masonry buildings; it consists of the introduction of a binding agent to fill the internal voids and cracks. An experimental program was carried out to improve knowledge of geopolymer grouts suitable for consolidation purposes. The experimental findings revealed that the silica-fume-based geopolymer grout has a worse performance from a rheological point of view, whereas it showed promising results in terms of mechanical strength when compared to traditional hydraulic-lime-based grout.

Cement-based grouts for masonry consolidation with high content of limestone filler, metakaolin, glass powder and ceramic waste

This article reports an experimental research on the influence of high-volume mineral additions on the rheological, physical and mechanical properties of cement-based grout for stone masonry structures consolidation. Binary grout mixtures were produced by replacing 50% weight of cement by limestone filler, metakaolin, glass powder and ceramic waste. Grout flow properties, rheological parameters, bleeding water, bulk density and injectability were evaluated. Grout physical and mechanical properties were also tested. New methodology previously used in mortars was applied to interpret flow behaviour. Results showed that a high-volume mineral addition in cement-based grout is compatible with the required fresh and hardened properties.

Rheology of Natural Hydraulic Lime Grouts for Conservation of Stone Masonry—Influence of Compositional and Processing Parameters

This review provides an overview of the recent progress in the field of the rheology of grouts for historic masonry consolidation. During the last two decades, significant research has been devoted on the grouting technique for stone masonry consolidation but most results are scattered by scientific papers, congress communications, and thesis. This paper compiles and briefly demonstrates the effect of several intrinsic and extrinsic parameters, such as admixtures, additions, pressure, temperature, and measuring instrumentation, on the rheological performance of natural hydraulic lime-based grouts.

Hybrid nano-composites for the consolidation of earthen masonry

HypothesisEarth is one of the oldest silicate-based materials in stone heritage, still largely used in architecture worldwide. Earthen materials are highly susceptible to wind and water erosion, leading to loss of cohesion and crumbling. Conventional consolidants (alkoxysilanes, synthetic or natural polymers) lack physico-chemical compatibility or effectiveness, and can promote degradation. We propose for the first time nano-composites for the surface consolidation of adobe, i.e. unbaked earth bricks often containing organic fibers and lime. ExperimentsWe investigated, mimicking the setting of portland cement, the formation of calcium silicate hydrate (CSH) within adobe porosities, owing to the pozzolanic reaction between nanoparticles of silica and calcium hydroxide, to consolidate a powdery substrate. Different formulations were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), dynamic light scattering (DLS), and turbidimetry (UV–Vis spectroscopy). FindingsA ternary composite made of SiO2 nanoparticles, Ca(OH)2 nanoparticles, and hydroxypropyl cellulose, dispersed in a (4:1) ethanol:water blend, was formulated. Each component is compatible with adobe, and plays a role in its consolidation. The treatment of adobe samples with the composite leads to the in situ formation of CSH, providing resistance to peeling, abrasion, and wet-dry cycles, with no aesthetic alteration. This opens new perpectives in the preservation of one of the most widely used construction materials.

Experimental laboratory design of lime based grouts for masonry consolidation

ABSTRACTConservation and strengthening of historic masonry buildings should preserve their significance and ensure their structural stability. The condition of a structure and the extent of the damage determine the type of actions needed. It is important that the selected strategy maintains the existing aesthetic value of the masonry, as well as its structural integrity and the function of components, both during and after any intervention. Grouting is a well-known technique, which can be durable and mechanically efficient, whilst preserving the historic value. The selection of a grout for repair is based on the physical and chemical properties of the existing masonry. Compatibility between the existing and the injection material is a major factor in the success of the intervention. Parameters such as rheology, fluidity, and stability of the mix should be considered to ensure the effectiveness of grout injection. Many commercial ready-mix grouts are available but the use of lime-based grouts formulated in laboratory, with the addition of materials like fly ashes, silica fume, bentonite, hydraulic lime, or metakaolin, have been proposed by different researchers. This article addresses the development of ternary grouts, which show satisfactory mechanical and physical properties, and are viable low-cost alternatives to the commercial grouts.

Grouts with Improved Durability for Masonry Consolidation: An Experimental Study with Non-Standard Specimens

Multi-leaf stone masonry walls are among the most vulnerable elements of historic constructions. Grout injection is a common and efficient technique to consolidate such masonries. It consists of introducing a grout into the masonry inner core in order to upgrading the cohesion of the wall by ensuring the transversal bond between the external leaves and improving its monolithic behaviour. Notwithstanding, the recrystallization of salts due to changes in moisture content causes several damages in these masonries, even after the consolidation intervention. This paper aims to assess the potential use of linseed oil in natural hydraulic lime-based grouts to mitigate the water penetration and therefore the damages from salts crystallization. Linseed oil was used in former times as an additive for mortars in order to grant hydrophobicity. In this study several properties of the grouts were evaluated: rheology, mechanical strength, water absorption, adhesion and durability assessed by testing the resistance to sodium chloride. Moreover, this paper also analyses the correlation between non-standard specimens (with reduced size) and standard specimens (40x40x160 mm3). The experimental results revealed that the grouts durability and water transport are significantly improved with added linseed oil. It was also possible to observe a small reduction in mechanical resistance with the presence of linseed oil; however, acceptable strength values to promote an appropriate consolidation were ensured. Furthermore, the reduced size specimens revealed to be a viable alternative to the standard ones.

Consolidation and Strengthening of Historical Masonry by Means of Mineral Grouts: Grout Development

Abstract:Mass consolidation of stone and brick masonry is considered, with exclusion of pure crack repair. Damage and specific failure mechanisms in multiple leaf masonry are presented. The aims of consolidation are explained, and the inherent advantages and disadvantages of distinct strengthening and consolidation techniques are given. An historical overview of consolidation methods and of development of consolidation grout materials is given, which explains how technology evolved to the actual procedures.

Consolidation and Strengthening of Historical Masonry by Means of Mineral Grouts: Modeling Structural Behavior of Grouted Three-Leaf Masonry

Abstract Development of mineral grouts for consolidation and strengthening of historical masonry was discussed in Ref. [1]. The properties of the injection grout must counteract the elements that initiate the failure mechanism of multiple leaf historical masonry and lead to its collapse. This paper presents a macro-approach to model the structural behavior of three-leaf masonry. A global approach is used, based on the properties and the behavior of the external leafs, in combination with the properties and behavior of the central core of the three-leaf wall. Evaluation of the models is made by comparison with experimental data.

Evaluation of the Effectiveness of Masonry Consolidation Treatments Based on Scratching Tomography

A challenge in the restoration of historical buildings is the correct identification of materials which need to be strengthened in order to guarantee their durability and the evaluation of the results of consolidation treatments which may be applied during their repair. Methods which make such a complex characterization possible are rare. This paper presents an investigation carried out at the University of Mons (Belgium) in collaboration with the technical support and control unit, restoration directorate, of the Walloon region, aiming to evaluate the effectiveness of consolidants used to strengthen stone masonry. The characterization of the materials is based on a novel semi-destructive scratching method which allows tomographic representation of the strength of the damaged and treated areas. This paper describes the experimental methodology and presents results from laboratory experiments as well as a case study.

Rheological behaviour of hydraulic lime-based grouts. Shear-time and temperature dependence

This paper deals with the coupled effect of temperature and fly ash (FA) addition on rheological behaviour of natural hydraulic lime (NHL5) based grouts, currently used in masonry consolidation. The use of a grout injection technique for masonry consolidation may lead to an increase of hydrostatic pressure and lead to structural damage. This means that the thixotropic effects become self-evident in grout design. It was shown that there is a relation between the structuration rate of each grout and the pressure that occurs inside masonry during its consolidation. According to the results, it seems also that there is a grout threshold temperature (Tlimit) that separates a domain where the grout build-up structure area is almost constant, from another where flocculation area starts to increase significantly. We believe that in the first region the thixotropic effects are almost isolated from the irreversible effects (due to hydration). For the NHL5 based grout Tlimit = 20 °C and for the grout with NHL5 + 15 % of FA Tlimit = 15 °C. Grouts' characterization based on maximum resisting time, structuration rate and on the analysis of the hydraulic lime grout behaviour tested at different shear rates was performed using a shear thinning model and assuming that the structure is shear- and time-dependent. The goal is to use this methodology during mix proportioning and design for masonry injection purpose. The tested grout compositions were optimized compositions obtained in previous research using the design of experiments method.

Optimisation of flow behaviour and stability of superplasticized fresh hydraulic lime grouts through design of experiments

One of the techniques of old masonry consolidation is the injection of grouts. For a successful injection it is necessary to ensure an adequate flow of the grout inside the porous media, for which it becomes essential to control the grout rheological behaviour and stability. This paper analyses the influence of grout mixing procedures on rheological behaviour, water retention and stability of hydraulic lime grouts with superplasticizer. This research has particular relevance due to lack of information about the use of superplasticizers in hydraulic lime grouts, compared to the amount of information that exists in the case of Portland cement based mixtures. The research showed that fresh grout behaviour can be improved using an appropriate mixing procedure, optimised with the Taguchi method.

Natural hydraulic lime based grouts – The selection of grout injection parameters for masonry consolidation

The goal of this research was to develop a methodology for grout composition optimization concerning specific applications. It could be developed for masonry consolidation or bonded prestressed tendon grout, pre-placed aggregate grout, among others. The grout development does not only depend on its intrinsic properties but also on the nature and features of the support. The purpose of a grout injection technique applied in a multiple leaf wall is to increase the compactness and create links between the internal and external leaves, which improve not only shear and flexural resistance but also the compressive strength. In practice, the variability of voids within masonries requires an ability to fine tune the rheological properties of the grout in order to optimally fill the voids. The methodology proposed here for testing grout injectability in a porous media like masonry is a logical tool to use in grout optimization. It shows that several grout parameters should be controlled for a successful injection. Concerning the support and its typology, the mortar between stones plays a fundamental role in the effectiveness of the intervention, due to its reduced porosity and composition. Besides that, earth and mortar, for example, can be present in the interior of masonry and make difficult, with their absorption, the injection. Thus, the water retention capacity of grout should be controlled to prevent that problem, as it was made in this work, using the optimized mixing procedure that takes into account that and other fresh grout properties. This study analyses some relevant grout properties such as yield stress, plastic viscosity, flowability and injectability for natural hydraulic lime based grouts in different porous media. The research shows that there are differences in the grout behaviour, especially in rheological properties, when different mixing procedures and/or grout composition (different water/binder or fly ash/binder ratios) are used and that fresh grout properties may be optimized for injection purpose.

Effect of environmental temperature and fly ash addition in hydraulic lime grout behaviour

The purpose of grout injection is to increase the compactness of the masonry and its injection optimization is a task of major importance for masonry consolidation. Fresh grout properties seem to be as important as the ones in the hardened state since grout consistency is an essential characteristic to allow the filling of voids. Since the grout rheological behaviour is associated with its fresh properties, they should be well understood and controlled so that the fluid may be pumped and flow correctly inside the porous media. This paper analyses some relevant rheological properties for natural hydraulic lime grouts, such as yield stress, plastic viscosity, consistency and power-law index. The study envisage to increase the understanding of the influence of environmental temperature and of the addition of fly ash in fresh grouts behaviour. An attempt was made to achieve an optimal grout composition by using the Taguchi method. The paper shows that fly ash is capable of substantially changing the grout rheological parameters, while the effect of temperature is negligible for the parameters tested.

Evaluation of masonry consolidation by geo-electrical relative difference resistivity mapping

Evaluation of masonry consolidation by geo-electrical relative difference resistivity mapping

Experimental study of cement grout: Rheological behavior and sedimentation

Three basic elements (cement, water and admixture) usually make up injectable cement grouts used for prestressed cable coating, repair and consolidation of masonry, soil grouting, etc. The present study was divided into two parts. First, in order to characterize rheologically fresh cement paste with water/cement ratios (W/C) varying between 0.35 and 1, an experimental study was carried out and has revealed that the cement past behaves like a shear-thinning material, whatever is the W/C ratio. Second, to study the time evolution of their density, a γ-densitometer bench was used. Relying on the water content and the density measured, we demonstrate that the computation of the degree of hydration of cement is possible. The cement/geotechnics interdisciplinary approach proposed here has made it possible to obtain a large range of original results useful to improve our understanding of the sedimentation processes for cement pastes with different W/C ratios.

Evaluation of masonry consolidation by geo-electrical relative difference resistivity mapping

A methodology was developed to clean geo-electrical measurements on masonry structures from geometrical and other disturbing factors such as moisture and salts.

Excavation at Auchindoun Castle, Moray District, in 1984

A clearance excavation in an L-shaped tower-house prior to masonry consolidation was undertaken to attempt to examine and interpret the entrance into the tower. Extensive stone-robbing frustrated this aim, but a stone-lined chamber cut into the bedrock beneath the floor of the main cellar was found. The function of this chamber remains uncertain. MH

Recent Excavations at Carn Liath Broch, Golspie, Sutherland

Summary Following the late J X W P Corcoran's rescue work in 1972 within the broch, recent excavations at this state care monument, prior to masonry consolidation, examined outworks to the NE of the broch and re-opened its entrance passage and guard cell. Despite thorough Victorian disturbance, a tentative chronology was established for the site. The Bronze Age was represented by a Beaker fragment and later putative cist with Food Vessel and shale washer necklace. Settlement, shown by post-holes, hearth and a severely-truncated structure of slot construction, predated the building of the broch and attendant ring-wall, while later Iron Age activity included the division into outbuildings of the area between the broch and outer wall by the addition of cross-walls. Previously unrecorded circuit walls and midden were identified downslope of the main outworks, and the site produced evidence of shale and iron working.