Hydraulic Lime-based Grouts Research Articles

Valorization of Cappadocia waste earth in the production of sustainable lime-based grouts

Historical structures and natural landscapes in Turkey's Cappadocia Region, a popular tourist spot, have been designated mixed heritage sites on the World Heritage List since 1985. The region's old rock-cut and masonry constructions have been damaged for various reasons. Furthermore, the waste volcanic tuff excavated during the construction of rock-cut structures in the region totals around 10 million tons of waste material per year. It creates severe visual concerns since it cannot be used effectively in the area. Because repairing ancient buildings needs precision, the restoration method and material should be selected based on the structures' structural system and material attributes. Grouting is one of the most common ways of repairing and strengthening masonry buildings or fissured architectural pieces with adequate connected voids. This technique aims to restore damaged structures' continuity, cohesiveness, and strength while keeping their morphology and load-bearing system intact. This research explores the potential use of waste earth from rock-cut structures in the Cappadocia Region in hydraulic lime-based grouts. Thus, an injection material that can be used to repair fairy chimneys and historical rock-cut and masonry structures in this region will be produced. Various lime-based grout types containing Cappadocia waste earth (CWE) were produced in this scope. The evaluation of grout performance encompassed assessments in the fresh state (Fluidity, Penetrability, and Volume Stability) and the hardened state (Flexural and Compressive strength). Furthermore, this research delved into how Cappadocia waste earth (CWE) influences the physical and microstructural characteristics of lime-based grouts. Thanks to this study, both environmental pollution will be reduced, and sustainability will be contributed.

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.

Preliminary Investigation of the Mechanical and Physical Properties of Natural Hydraulic Lime Grouts with Nano-Silica

Natural hydraulic lime-based grouts are often used in the structural consolidation of old stone masonry walls, mainly to re-establish the monolithic behaviour of masonry constructions. To ensure an adequate grouting operation, it is essential to have good fresh and hardened grout properties. The motivation of the present study was to examine the fresh and hardened properties of natural hydraulic lime grouts with nano-silica (NS) and silica fume (SF). The contribution of these materials and the dosage of a high range water reducer admixture (HRWR) were investigated on the rheological properties, water capillarity, open porosity and mechanical strength of injection grouts. The effects on rheology were analysed through plastic viscosity and yield stress. The results indicated that, even for reduced NS content, an increase in plastic viscosity and yield stress occurred, which required a higher HRWR content in order to not compromise the grout’s rheological performance. The results also showed that, when NS and SF were combined, a beneficial joint effect occurred, resulting in a substantial and positive change on the mechanical strength and microstructure of the hardened injection grouts. Taguchi’s method was used to optimize the grout’s formulation and to fulfil the required performance concerning the fresh and hardened state.

Effect of temperature, resting time and brick dust (Horasan) on the rheological properties of hydraulic lime-based grouts

This paper aims to analyze the effect of different ambient temperatures on the time-dependent rheological properties of brick dust blended hydraulic lime-based grouts. Since there are limited studies about the rheological properties of lime-based grouts produced with brick dust (Horasan), the presence of this material (pozzolanic or non-pozzolanic) in the hydraulic lime-based grouts was investigated in terms of rheological parameters. Fluidity, volume stability, penetrability, water retention capacity and setting time of the grouts were determined. Moreover, the rheological measurements were performed with a rotational rheometer and yield stress and plastic viscosity of grouts were calculated from shear stress-shear rate curves. The common result of the methods reveals that the rheological properties of lime-based grouts were dramatically affected by temperature and resting time. Although the yield stress, plastic viscosity, and water retention capacity of lime-based grouts increased with the presence of brick dust, stable and homogenous grouts were obtained for a sufficient injectability. Finally, the temperatures between 20 °C to 30 °C were designated as threshold temperatures to apply the grout without the loss of fresh properties.

Effects of Polypropylene Fibers and Measurement Methods on the Yield Stress of Grouts for the Consolidation of Heritage Masonry Walls

The injection of grouts is a consolidation technique suitable for overcoming the structural deterioration of old stone masonry walls. Grouting operations involve introducing a suspension (grout) into a masonry core with the aim of improving the load capacity of the wall, as well as reducing its brittle mechanisms. The yield stress of injection grouts will affect the injection pressure and their flow inside the masonry. However, the determination of some rheological properties such as yield stress in hydraulic grout is challenging, due to the combined effects of hydration reactions and interactions between the particles present in the suspension. In this study, the determination of the yield stress of natural hydraulic lime-based grouts with polypropylene fibers was carried out. The changes in yield stress with time, fibers content and hydration were evaluated by two measurement methods using a rotational rheometer. Additionally, the static and dynamic yield stress as well as the critical shear–strain rate were determined, which provided useful information on the grout design in order to achieve successful grouting operations.

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.

Comparison of the performance of hydraulic lime- and clay-based grouts in the repair of rammed earth

Earth constructions constitute an important part of the built heritage and are spread worldwide. Rammed earth is among the most used earth construction techniques, though it exhibits a high seismic vulnerability. Nevertheless, the structural behaviour of rammed earth structures is still insufficiently comprehended. Thus, the preservation of this built heritage requires exhaustive characterisation of its mechanical and structural behaviours, as well as the development and validation of adequate intervention solutions. In this context, this paper presents an experimental program aimed at evaluating the effectiveness of grout injection to repair cracks and at further characterising the in-plane shear behaviour of rammed earth walls. The experimental program included the testing of rammed earth wallets under diagonal compression, which were subsequently repaired with injection of a clay-based or a hydraulic lime-based grout, and retested. Furthermore, sonic tests were conducted on the wallets before the destructive tests. The obtained results allowed to highlight that both grouts led to similar repairing performances, though the interlocking contribution promoted by the coarse particles of the rammed earth to the shear behaviour was found to be irrecoverable.

Grouting performance improvement for natural hydraulic lime-based grout via incorporating silica fume and silicon-acrylic latex

Natural hydraulic lime (NHL) based grout has been widely used in construction project related to ancient architecture in recent decades. In order to improve grouting performance of NHL based grout, silica fume (SF) and silicon-acrylic latex (SAL) were incorporated in the preparation of grout. For the grout in fresh state, compared with control grout, bleeding rate of modified grout with SF and SAL incorporation decreased. Wettability, interfacial bond and simulated grouting properties of grout were improved. For the grout in hardened state, water absorption of grout decreased. Compactness, mechanical strength and salt resistance were improved. SAL played a more important role in improving both grout’s flexural strength and interfacial bond property between grout and consolidated matrix. Generally, combined use of SF and SAL made the grout with the most beneficial grouting performance.

The influence of metakaolin on the properties of natural hydraulic lime-based grouts for historic masonry repair

This paper investigates the properties of injection grouts with different amounts of natural hydraulic lime (NHL) replacement by metakaolin MK1 or MK2. The focus is dedicated to the fresh properties of the NHL-based grouts, as well as to a parallel study of the evolution of compressive strength and phase composition of hardened grouts, through tests at 28, 56, 90 and 900 days. Additionally, at 90 days, the influence of the MK1 and MK2 incorporation on the porosity characteristics of hardened grouts was determined. Tensile bond strength, being one of the key hardened properties of the injection grouts, was for the time being determined only at an early age of 28 days. The results showed that by adding metakaolin at constant fluidity, the water demand of the fresh mixture increases with the increase of the metakaolin content. At the same time the water retention capacity of the grout is enhanced. In a hardened state the addition of metakaolin increases early age and long term compressive strength of the grout. Also, its bond strength can be considerably increased, by applying MK1. Mixtures with metakaolin resulted in the formation of hydration products such as ettringite, hemicarboaluminate and monocarboaluminate, whereas stellerite was present only in the case of higher proportions of metakaolin with a higher BET surface area and Al2O3 content.

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.

Out-of-plane shake-table tests of strengthened multi-leaf stone masonry walls

Existing unreinforced multi-leaf stone masonry (URM) buildings are one of the most earthquake prone types of construction. Failure typically occurs even at low levels of earthquake-induced loads, with the out-of-plane delamination of masonry leaves and consequent collapse of the whole facade. Although this issue has been tackled by several researchers, dynamic tests reproducing the earthquake behaviour of as-built and strengthened multi-leaf stone URM walls are very limited in the literature. In response to this lack, shake-table testing of eight full-scale multi-leaf stone masonry walls followed by dynamic modal identification was performed. The application of steel tie-rods in the wall cross-section, the injection of the inner-core using hydraulic lime-based grout, and a combination of the two techniques are presented herein as suitable interventions to enhance the monolithic behaviour of multi-leaf stone URM walls. Tying the outer masonry leaves together increased the seismic capacity by a factor of 1.8 compared to unreinforced condition, while injecting grout into the inner-core of the wall provided resistance to peak ground acceleration (PGA) that were 2.3–3.6 times the PGA resisted by as-built walls, depending on the quality in the execution of the intervention. The results obtained in the walls strengthened with both techniques were significantly related to the grout injection only.

Experimental assessment of in-plane behaviour of three-leaf stone masonry walls

This paper presents an experimental campaign on multi-leaf stone masonry panels, scales 1:1 and 2:3, in both original conditions and strengthened with grout injections. The panels were subjected to horizontal in-plane cyclic loading combined with vertical loading for different pre-compression levels, and provided important information on failure mechanisms, maximum displacement capacity, shear strength and other mechanical parameters, such as shear modulus and tensile strength. Further analysis provided results on other parameters which mainly characterise the behaviour of three-leaf masonry under seismic loads, i.e., stiffness degradation, energy dissipation, and viscous damping.The main aim of this study was to gather information on the static and dynamic behaviour of three-leaf stone masonry structures in non-injected and injected conditions, in order to accurately characterise their mechanical behaviour. In particular, the effectiveness of injections of hydraulic lime-based grout as a reinforcement technique was assessed and validated.

Combined effect of superplasticizer, silica fume and temperature in the performance of natural hydraulic lime grouts

Grouting is a current repair technique for consolidating and strengthening old masonry buildings. Grouts can be seen as mixtures of binder with water, admixtures and/or additives, which should present low viscosity and high penetrability. The grout specification involves the knowledge of the flow capacity within the masonry inner core and physic-chemical compatibility with the original materials. Nevertheless, the grout properties are affected by a large number of parameters, including binder type and composition, mixing procedure, type and dosage of admixture, environmental conditions such as temperature that may lead to different grout injection capacities, as reported by several authors.This paper deals with the effect of environmental temperature over superplasticized hydraulic lime-based grouts with partial replacement of lime by silica fume. Grout performance was analysed in fresh and hardened state by testing its rheological behaviour, injectability as well as its hydration reactions kinetics. In spite of the considerable amount of information that exists for cement based mixtures with superplasticizers, there is little information about the effects of superplasticizers when used in natural hydraulic lime mixtures proportioned with silica fume. This study aims to contribute to a better understanding of the behaviour that superplasticized hydraulic lime grouts present under different temperatures. The results showed that hydraulic lime grouts performance could be improved, regarding rheological parameters and strength capacity if they are properly design and a suitable processing temperature were ensured.

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.

Three-Leaf Masonry in Compression, Before and After Grouting: A Review of Literature

This article summarizes the available experimental results related to the behavior of three-leaf masonry: The behavior and the failure mechanism of this type of masonry under compression is studied. The effect of the mechanical properties of ternary and hydraulic lime-based grout on the mechanical properties of masonry in compression is investigated. Simple formulae are proposed for the estimation of the compressive strength of three-leaf masonry after grouting.

Shaking Table Tests on Multi-Leaf Stone Masonry Structures: Analysis of Stiffness Decay

The influence of the natural hydraulic lime-based grout on the dynamic behaviour of injected multi-leaf stone masonry elements is discussed in the paper. Shaking table experiments on two stone masonry buildings, tested before and after grout injection, have been performed. The paper focuses on the analysis of both the recorded accelerations and related displacements, at the bottom and at each further storey. This leads to evaluate the stiffness of the unstrengthened and injected structures. The input at increasing PGA allowed the stiffness decay to be studied, simulating a gradual damaging of the structures. These results were also interpreted in the light of both computed frequencies and mode shapes. Finally, the comparison among these results, obtained from all the models, allows to deepen the knowledge concerning the effects induced by the lime-based grout injection and on its capability to modify the dynamic behaviour, when intervening on a damaged (repairing) or on an undamaged (strengthening) structure.

Lime-based injection grouts for the conservation of architectural surfaces

This paper reviews the literature on injection grouts used in the conservation of architectural surfaces including wall paintings, plasters, and mosaics. It presents the materials and techniques of grouting, and methods of evaluation, focusing on lime- and hydraulic lime-based grouts. This review indicates that a variety of materials have been investigated for use as injection grouts, and numerous commercial and custom-mixed grouts are available to conservators today. However, there are few standard or well-established methods to assess them, which have led to a wide range of test methods for their preparation, characterization, and evaluation. It is clear that a systematic study of the working and performance properties, test methods, and preparation and curing conditions is needed, as is an evaluation of products being used in the field.

Mechanical properties of three-leaf stone masonry grouted with ternary or hydraulic lime-based grouts

Masonry made up of two exterior leaves of stone masonry with the space between them filled with poor quality mortar and large size aggregates is quite common in structures belonging to the built cultural heritage. Grouting of this type of vulnerable masonry with cement-based grouts (cement content: 50–75%wt.) was proven mechanically efficient. However, the need to protect frescoes, mosaics and decorative elements, as well as the need to avoid problems of durability encountered due to the high content of cement, led to the development of grouts with reduced cement content, as well as to hydraulic lime-based grouts. In this paper, the effect of ternary grouts (mixes of cement [∼30%], pozzolan and hydrated lime) and hydraulic lime-based grouts on the compressive and on the shear strength of three-leaf stone masonry is experimentally investigated. Although the mechanical properties of the applied grouts are substantially lower than those of grouts with higher cement content, homogenization of masonry is achieved leading to a substantial improvement of the mechanical properties of masonry.