In situ tests and seismic assessment of a stone-masonry building

The injection of grout into multi-leaf stone masonry walls with a sufficient amount of voids can be an effective technique for the seismic strengthening of such walls. In order to evaluate the effectiveness of different types of commercial grouts that fulfilled the adopted criteria, the stone masonry walls of an actual building were strengthened by means of grout injection, using cement and combined cement–lime grouts. The quality and effectiveness of grout injection technique was assessed by non-destructive tests (sonic and radar tests), minor destructive tests (surface and in-depth probing and coring, and the double flat jack test), and destructive test (shear-compressive test), all in situ. Preliminary laboratory tests were also performed on mortar and stone specimens, on the injection grouts, and on cylinders representing the inner core of the strengthened walls. Finally, the seismic resistance of the building was evaluated in non-strengthened and strengthened variants (i.e. after grout injection of the walls with cement or lime–cement grout) by means of non-linear static analysis, using the pushover method. Obtained results show that shear characteristics of the walls (tensile strength and stiffness) depend significantly on the type and properties of the injected grout, i.e. on the grout’s ability to achieve a solid bond between the stones and the leaves including the properties (strength and stiffness) of the grout itself. In the case of the type of masonry under consideration, an adequate level of seismic resistance can be achieved also by using combined cement–lime grouts, although cement grout can provide higher seismic resistance.     

Design and evaluation of hydraulic lime grouts for the strengthening of stone masonry historic structures

The present paper discusses an experimental procedure realized in order to design hydraulic lime based grouts adequate for the strengthening of stone masonry historic structures. With the aim to minimize incompatibility problems between the original materials and the grouts, several natural hydraulic lime based grouts, as well as a ternary (lime–pozzolan–cement) grout with reduced cement content, have been studied. The selection of the most suitable grouts was performed based on a set of criteria, namely injectability, mechanical and durability characteristics. The selected grouts were subsequently injected into cylindrical specimens that simulate the infill of three-leaf stone masonry. The experimental results obtained from mechanical tests carried out on the injected cylinders demonstrated that all grout mixes studied within this work were efficient in strengthening the infill material; they exhibited, however, differences in terms of durability properties. Finally, an empirical formula was developed to predict the compressive strength of the injected infill, as a function of the mechanical properties of grouts.     

The Bond Mechanism in Stone- or Brick-to-Grout Interfaces

Abstract:  An experimental research on the bond between masonry units and grout has been carried out at the National Technical University of Athens. In this study, tension and shear tests on composite substrate/grout specimens were performed. The composite specimens were consisted of two pieces of substrate connected with one grout joint. The substrate was either stone or brick, whereas hydraulic lime or tripartite (lime–pozzolan cement) or cement grouts were used. The experimental results have demonstrated that the developed tensile and shear bond strength of the studied hydraulic lime and tripartite grouts is comparable with those of cement-based grouts. Moreover, the value of the reached bond strength (tensile or shear) is governed mainly by the substrate characteristics and the binding properties of the grouts. It was also found that interfaces subjected to shear exhibited similar behaviour with interfaces within concrete; thus the beneficial effect of normal compressive stress on the interface was confirmed. Finally, the experimental results are used for the formulation of a Mohr–Coulomb criterion for grout to travertine joints in shear–compression and shear–tension. The results of this project clearly confirm the efficiency of grouts with medium or low mechanical properties (tripartite and hydraulic lime grouts) for retrofitting historic masonries.     

Removal and recovery of metal ions from acid mine drainage using lignite--A low cost sorbent

Acid mine drainage (AMD), has long been a significant environmental problem resulting from the microbial oxidation of iron pyrite in presence of water and air, affording an acidic solution that contains toxic metal ions. The main objective of this study was to remove and recover metal ions from acid mine drainage (AMD) by using lignite, a low cost sorbent. Lignite has been characterized and used for the AMD treatment. Sorption of ferrous, ferric, manganese, zinc and calcium in multi-component aqueous systems was investigated. Studies were performed at different pH to find optimum pH. To simulate industrial conditions for acid mine wastewater treatment, all the studies were performed using single and multi-columns setup in down flow mode. The empty bed contact time (EBCT) model was used for minimizing the sorbent usage. Recovery of the metal ions as well as regeneration of sorbent was achieved successfully using 0.1 M nitric acid without dismantling the columns.     

Sulfide oxidation and acid mine drainage formation within two active tailings impoundments in the Golden Quadrangle of the Apuseni Mountains, Romania

Sulfidic mine tailings have to be classified as one of the major source of hazardous materials leading to water contamination. This study highlights the processes leading to sulfide oxidation and acid mine drainage (AMD) formation in the active stage of two tailings impoundments located in the southern part of the Apuseni Mountains, in Romania, a well-known region for its long-term gold-silver and metal mining activity. Sampling was undertaken when both impoundments were still in operation in order to assess their actual stage of oxidation and long-term behavior in terms of the potential for acid mine drainage generation. Both tailings have high potential for AMD formation (2.5 and 3.7 wt.% of pyrite equivalent, respectively) with lesser amount of carbonates (5.6 and 3.6 wt.% of calcite equivalent) as neutralization potential (ABA=-55.6 and -85.1 tCaCO(3)/1000 t ) and showed clear signs of sulfide oxidation yet during operation. Sequential extraction results indicate a stronger enrichment and mobility of elements in the oxidized tailings: Fe as Fe(III) oxy-hydroxides and oxides (transformation from sulfide minerals, leaching in oxidation zone), Ca mainly in water soluble and exchangeable form where gypsum and calcite are dissolved and higher mobility of Cu for Ribita and Pb for Mialu. Two processes leading to the formation of mine drainage at this stage could be highlighted (1) a neutral Fe(II) plume forming in the impoundment with ferrihydrite precipitation at its outcrop and (2) acid mine drainage seeping in the unsaturated zone of the active dam, leading to the formation of schwertmannite at its outcrop.     

Interventions to historic masonries: Investigation of the bond mechanism between stones or bricks and grouts

Within the present work, the mechanism of bond is studied in composite grout/substrate specimens. Three types of tripartite (lime-pozzolan-cement) grouts are examined, combined with three substrates (two types of limestone and bricks). The interfaces between grout and substrate are characterized by means of mechanical tests in direct tension and shear. The in-time development of the tensile and shear bond strength is also investigated. In order to correlate the characteristics of the substrates and the obtained strengths of the interfaces, their surfaces and porosity are examined. The main conclusions of this study are that the studied tripartite grouts can develop tensile and shear bond strength comparable to Portland cement-based grouts, and that the value of the reached bond strength is governed mainly by the substrate characteristics and the binding properties of the grouts. The results of this project confirm the efficiency of tripartite lime-pozzolan-cement grouts with reduced Portland cement content for repair and strengthening of historic masonries.     

Removal of heavy metals from acid mine drainage (AMD) using coal fly ash, natural clinker and synthetic zeolites

Acid mine drainage (AMD) is a widespread environmental problem associated with both working and abandoned mining operations, resulting from the microbial oxidation of pyrite in presence of water and air, affording an acidic solution that contains toxic metal ions. The generation of AMD and release of dissolved heavy metals is an important concern facing the mining industry. The present study aimed at evaluating the use of low-cost sorbents like coal fly ash, natural clinker and synthetic zeolites to clean-up AMD generated at the Parys Mountain copper-lead-zinc deposit, Anglesey (North Wales), and to remove heavy metals and ammonium from AMD. pH played a very important role in the sorption/removal of the contaminants and a higher adsorbent ratio in the treatment of AMD promoted the increase of the pH, particularly using natural clinker-based faujasite (7.70-9.43) and the reduction of metal concentration. Na-phillipsite showed a lower efficiency as compared to that of faujasite. Selectivity of faujasite for metal removal was, in decreasing order, Fe>As>Pb>Zn>Cu>Ni>Cr. Based on these results, the use of these materials has the potential to provide improved methods for the treatment of AMD.     

Evaluation of cement grouts for embedding anchors under water

Approximately 110 pull-out tests were conducted on grouted anchors cast in the laboratory to investigate the effects of the rheological and mechanical properties of cement grouts, the initial free drop distance of grout, as well as the age of testing on the behavior of anchorages cast in dry and submerged conditions. The anchors consisted of 19-mm, conventional steel bars with an embedment length fixed at five times the bar diameter. Two different casting procedures corresponding to initial free drop of the grout in water of 20 and 200 mm were investigated. The cement grouts used in this investigation incorporated either a Type 10 or a blended silica fume cement and a fixed water-binder ratio of 0.40. The grouts incorporated various concentrations of a high-range water reducer, a rheology-modifying admixture, and silica fume. The rheology-modifying admixture and high-range water reducer were jointly incorporated to enhance both fluidity and washout resistance. The test results indicate that properly designed grouts can be easily cast into place, and yet be cohesive enough to resist the washout of cementitious materials. The spread in load-carrying capacity between anchor bars cast in dry versus submerged conditions can decrease when cement grouts having a greater washout resistance level are used which can be secured by incorporating a rheology-modifying admixture and silica fume. The bond strength is shown to increase when incorporating silica fume regardless of the casting condition.     

Modelling temperature-dependent heat production over decades in High Arctic coal waste rock piles

Subsurface heat production from oxidation of pyrite is an important process that may increase subsurface temperatures within coal waste rock piles and increase the release of acid mine drainage, AMD. Waste rock piles in the Arctic are especially vulnerable to changes in subsurface temperatures as the release of AMD normally is limited by permafrost. Here we show that temperatures within a 20 year old heat-producing waste rock pile in Svalbard (78°N) can be modelled by the one-dimensional heat and water flow model (CoupModel) with a new temperature-dependent heat-production module that includes both biological and chemical oxidation processes and heat source depletion over time. Inputs to the model are meteorological measurements, physical properties of the waste rock material and measured subsurface heat-production rates. Measured mean annual subsurface temperatures within the waste rock pile are up to 10 °C higher than the mean annual air temperature of −5.8 °C. Subsurface temperatures are currently decreasing with 0.5 °C per year due to decreasing heat production, which can be modelled using an exponential decay function corresponding to a half-life period of pyrite oxidation of 7 years. Simulations further suggest that subsurface temperatures two years after construction of the pile may have been up to 34.0 °C higher than in 2009 and that the release of AMD may have been more than 20 times higher. Sensitivity simulations show that maximum temperatures in the pile would have been up to 30.5-32.5 °C lower and that the pile would have been frozen 12-27 years earlier if the pile had been initially saturated with water, constructed with a thickness half of the original or a combination of both. Simulation show that the pile thickness and waste rock pyrite content are important factors controlling the internal build up of heat leading to potential self-incineration. However, site specific measurements of temperature-dependent heat production as well as simulation results show that the heat produced from pyrite oxidation alone cannot cause such a temperature increase and that processes such as heat production from coal oxidation may be equally important.     

Evaluation of engineering properties for the use of leached brown coal ash in soil covers

The need to engineer cover systems for the successful rehabilitation or remediation of a wide variety of solid wastes is increasing. Some common applications include landfills, hazardous waste repositories, or mine tailings dams and waste rock/overburden dumps. The brown coal industry of the Latrobe Valley region of Victoria, Australia, produces significant quantities of coal ash and overburden annually. There are some site-specific acid mine drainage (AMD) issues associated with overburden material. This needs to be addressed both during the operational phase of a project and during rehabilitation. An innovative approach was taken to investigate the potential to use leached brown coal ash in engineered soil covers on this overburden dump. The basis for this is two-fold: first, the ash has favourable physical characteristics for use in cover systems (such as high storage capacity/porosity, moderately low permeability, and an ability to act as a capillary break layer generating minimal leachate or seepage); and second, the leachate from the ash is mildly alkaline (which can help to mitigate and reduce the risk of AMD). This paper will review the engineering issues involved in using leached brown coal ash in designing soil covers for potentially acid-forming overburden dumps. It presents the results of laboratory work investigating the technical feasibility of using leached brown coal ash in engineered solid waste cover systems.     

Recovery and purification of copper sulfide nanoparticles from acid mine drainage by biological sulfate reduction and microfiltration using low-cost ceramic membrane

Clean Technologies and Environmental Policy - Acid mine drainage (AMD) typically has a high amount of copper that can be recovered in pure form for different industrial applications. This 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 (T _limit) 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 T _limit=20 °C and for the grout with NHL5+15 % of FA T _limit=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.     

On the development of unmodified mud grouts for repairing earth constructions: rheology, strength and adhesion

The conservation and rehabilitation of several sites of cultural heritage and of the large housing stock built from earth requires the development of techniques and materials compatible with this kind of construction. Grout injection is one repair solution which has been put forward over the last few years, whereas there is preference for employing grouts that incorporate earth in their composition. However, knowledge of such grouts is still very limited and requires further research. The experimental program discussed in this paper contributes to the comprehension of the influence of the composition of an unmodified mud grout, namely regarding its fresh-state rheology, hardened-state strength and adhesion. In general, the results obtained showed that the rheological behaviour of a mud grout greatly depends on the colloid behaviour of the clay fraction, and that the addition of a deflocculant and modification of the clay content (with a silt size material) is required to obtain grouts with adequate solid fractions.     

Penetrability of hydraulic grouts

Design of hydraulic grouts for strengthening of masonry historical buildings seems to follow rather empirical procedures, with all the related uncertainties, both in terms of economy and efficiency. This paper is part of a broader attempt to establish a rational methodology for the design of such grouts, based on their discrete injectability characteristics, i.e. (i) Penetrability, (ii) Fluidity and (iii) Stability. This paper deals with penetrability and constitutes the first part of this holistic methodology. The second part regarding the fluidity and the third regarding the stability are separately published. Grouting is intended to fill voids, fissures and open joints of the masonry as a system, producing a “dendrite” (a three-dimensional skeleton), directly contributing to the strength of the masonry as a whole. However, to do so, the grout should be able to pass through the “narrowest” possible width of such discontinuities, in order to reach the maximum possible internal volume of masonry and open joints, avoiding most of possible blockages. In the specific case of three-leaf masonries, the most decisive result of the grouting is expected to be the strengthening of the bond along the interfaces between the external layers and the infill; the rather small voids, as well as pre-existing fissures along these interfaces have to be penetrated. In this paper the penetrability of hydraulic grouts is discussed, and relationships between two characteristic diameters of the grains of the solid phase of the grout and the nominal minimum width of fissures and voids of the structure to be injected are proposed. Furthermore the beneficial role of replacing part of the cement or hydraulic lime with ultrafine materials in order to improve penetrability is presented, and related criteria are proposed.     

Environmental footprint study of mortar,render and plaster formulation / Studie über die Umweltauswirkungen von Mörtel

A comparative environmental assessment study focusing on the stages of mortar production and carbonation through hardening has been conducted by the European Lime Association in collaboration with mortar producers from various EU countries on 17 formulations of mortars, renders and plasters. The results of the “cradle‐to‐gate” for mortar and renders indicated that: There are no significant differences between products with low and high lime contents and depending on the lime content in the products, the contribution of the hydrated lime to the different environmental indicators can range between 0 % and about 20 %. However, there are clear differences in the environmental footprints of gypsum or lime based plasters. Based on the plaster composition investigated in this study, it appears that lime based plasters have the lowest environmental footprint for some of the impacts (primary energy consumption, abiotic depletion and water eutrophication), whereas for the remaining indicators the gypsum based plasters have the lowest environmental footprint. Depending on the lime content in the plasters, the contribution of the hydrated lime to the different environmental indicators can vary in a wide range, i. e. between 0 and 40 %. The differences in the environmental impacts of mortars, renders and plasters produced in integrated or non‐integrated mortar plants are generally rather small The lime carbonation process lowers the overall carbon footprint during the first period of the use phase of the mortars in buildings. This impact shall be taken into account in holistic LCA studies. If not, this leads to a wrong interpretation of the environmental impact of the mortars.     

Fluidity of hydraulic grouts for masonry strengthening

Design of hydraulic grouts for strengthening of masonry historical buildings seems to follow a rather empirical procedure, with all the related uncertainties, both in economical and efficiency terms. This paper is part of a broader attempt to establish a rational methodology for the design of such grouts, based on their discrete injectability characteristics, i.e. (i) penetrability, (ii) fluidity and (iii) stability. The first part of this holistic methodology proposing a procedure to be followed in order to make a first selection of suitable grain size distribution of solid materials of the grout to fulfill penetrability requirements was published elsewhere. The second part regarding the fluidity of the grouts is the subject of this paper. A new practical fluidity measurement is proposed (the fluidity factor test [FFT]); and a ??fluidity factor?? is defined. It is proved that the follow-up of this factor as a function of the water-to-solids ratio may reveal fundamental characteristics of the grout-composition under design. The influence of the mixing method and superplasticizer on grout??s fluidity is also examined. The paper concludes with a case study to highlight the practical use of the proposed test. Furthermore, stability of the suspension against segregation or excessive bleeding should also be ensured since, otherwise, blockage may soon appear and the quality of the intervention could be severely affected. This matter is examined by the authors in a separate paper, where specific semi empirical formulae permitting a first selection of water content and percentage of ultrafine materials, useful for the design of a grout composition are proposed.     

Critères d’injectabilité de coulis de ciments ultrafins

This study deals with the specific injection of grouts into granite blocks which present cracks having an opening of less than 100 μm. Two conditions must be met:

injection must not cause the cracks to open due to the use of low pressure (<0.1 MPa), in which case the dimensional stress between the size of the solid elements of the grout and the size of the cracks is increased;

long-lasting impermeability must be attained; the hardened grout must be stable in a potentially aggressive environment.

A possible solution would be to inject grouts of very fine cement appropriate to the setting. The purpose of this paper is to present some criteria to characterise the penetrability of such grouts in a fairly impermeable milieu. The standardised “sand column” test was used for the experiments. The optimal grout fluidity was sought (thirteen super-plastifiers were tested and their optimal dosage determined). The study shows that the criterium of fluidity alone is not sufficient to characterise the penetrability of grouts. The evaluation of their stability, particularly by a filtration test with a low pressure filter press, provides complementary data for the characterisation of their penetrability. The negative effect of the entrained air on penetrability was also noted. Two superplasticisers, one from the condensed sulfonated naphthalene formaldehyde group and the other from the condensed sulfonated melamine formaldehyde group, proved to be the most effective.     

Controlled low-strength material using fly ash and AMD sludge

Controlled low-strength material (CLSM) is a cementitious material with properties similar to stabilized soil. After hardening, CLSM provides adequate strength in bearing capacity and support but can also be easily excavated. To be classified as a CLSM, the material must have a compressive strength between 450 kPa (65 psi) and 8400 kPa (1200 psi). Typical CLSM contains coal-combustion fly ash (FA), cement, water and fine or coarse aggregate. In this paper, physical and strength properties of CLSM formed by combining sludge, a by-product from the treatment of acid mine drainage (AMD), with Class F FA are investigated. The sludge is a lime-based waste product that when combined with FA, exhibits self-hardening characteristics similar to cement. A main focus of this research is to develop a CLSM mix in which by-product material utilization is maximized while satisfying workability and performance requirements. A mixture of 10% AMD sludge, 2.5% Portland cement (PC), 87.5% Class F FA (dry wt.%) with water provided unconfined compressive strength values within the range for classification as CLSM. This mixture satisfies the excavatability and walkability requirements as well as the hardening time and stability criteria.     

Development of an injectable grout for concrete repair and strengthening

This paper deals with the coupled effect of temperature and silica fume addition on rheological, mechanical behaviour and porosity of grouts based on CEMI 42.5R, proportioned with a polycarboxylate-based high range water reducer. Preliminary tests were conducted to focus on the grout best able to fill a fibrous network since the goal of this study was to develop an optimized grout able to be injected in a mat of steel fibers for concrete strengthening.The grout composition was developed based on criteria for fresh state and hardened state properties. For a CEMI 42.5R based grout different high range water reducer dosages (0%, 0.2%, 0.4%, 0.5%, 0.7%) and silica fume (SF) dosages (0%, 2%, 4%) were tested (as replacement of cement by mass). Rheological measurements were used to investigate the effect of polycarboxylates (PCEs) and SF dosage on grout properties, particularly its workability loss, as the mix was to be injected in a matrix of steel fibers for concrete jacketing. The workability behaviour was characterized by the rheological parameters yield stress and plastic viscosity (for different grout temperatures and resting times), as well as the procedures of mini slump cone and funnel flow time. Then, further development focused only on the best grout compositions. The cement substitution by 2% of SF exhibited the best overall behaviour and was considered as the most promising compared to the others compositions tested. Concerning the fresh state analysis, a significant workability loss was detected if grout temperature increased above 35 °C. Below this temperature the grout presented a self-levelling behaviour and a life time equal to 45 min. In the hardened state, silica fumes increased not only the grout’s porosity but also the grout’s compressive strength at later ages, since the pozzolanic contribution to the compressive strength does not occur until 28 d and beyond.     

Reduction of acidity and removal of metal ions from coal mining effluents using chitosan microspheres

Effluents from coal mining operations are not only highly acid but also depict elevated concentrations of metals which may contaminate the environment. Due to the polybasic characteristic of chitosan, this biopolymer is capable of both neutralizing and removing iron, aluminum and copper ions from such effluents. The present study aimed at evaluating the use of chitosan microspheres for their importance in continuous systems. The microspheres were prepared by the phase inversion method. Their average diameter and morphology were determined. Water samples from decantation pool (DP) and acidic mine drainage (AMD) effluents were treated using different amounts of microspheres. The pH and concentration of Fe, Al and Cu ions were evaluated both before and after treatment of effluent samples. The results revealed that the microspheres were capable of increasing the pH of DP and AMD samples from 2.34 and 2.58, respectively, to 6.20, i.e., close to neutrality. The treatment also resulted in full removal of the metals investigated.