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Most earthen historical buildings have been abandoned for decades, exposed to the weathering and the passage of time. In Mexico, the low status of earthen constructions has increased these deterioration processes, resulting into the risk of disappearance of this significant architectural heritage. Historical adobes from monumental buildings in the State of Michoacan were sampled and collected in the localities of La Huacana (H) and Santa Cruz de Morelos (SC). The specimens were characterized in the materials laboratory, assessing their physical-chemical, mechanical and durability properties. An interdisciplinary methodology was designed through institutional cooperation and the application of different test methods. The adobes showed totally different compositions and proportions, and stabilizers like vegetal fibers, nevertheless, the mechanical performance of both samples was very similar, achieving respectable values in the context of historical adobe structures. Several correlations were found through the analyses: the physical properties like the density, the color or the electrical resistivity were related with the mechanical and durability ones; the non-destructive testing (NDT) allowed to calculate the dynamic elasticity modulus and infer the mechanical behavior; the chemical characterization enabled to obtain the elemental and mineralogical composition; and the Atterberg limits gave the soil classification. The research showed the broad diversity of earthen solutions and demonstrated how the granulometry is not a limitation to the adobe production, since the local soils can achieve similar mechanical and durability behaviors. Furthermore, H presented very different composition than the guidelines for earthen construction; nevertheless, the samples showed better durability performance and lower capillarity absorption rates. It is hoped that the results obtained with this research can help the further development of the earthen materials characterization and t, Authors want to acknowledge the economic support of the research project DBMC 2020 through the 1st International Contest for Cooperation and Development of the XV International Conference on Durability of Building Materials and Components— DBMC 2020; the CIC Projects of the Universidad Michoacana de San Nicolas de Hidalgo (UMSNH); the Consejo Nacional de Ciencia y Tecnología (CONACYT), through the Becas Nacionales program; and the the project “Proyecto TED2021-129705B-C31” funded by MCIN/AEI/10.13039/501100011033 and European Union NextGeneration EU/PRTR. The authors also thank the technical support of the Laboratory “Ing. Luis Silva Ruelas”, in the Faculty of Civil Engineering of UMSNH. The authors from SEMB (UdL) would like to thank Generalitat de Catalunya for the project awarded to their research group (2021 SGR 01370), Peer Reviewed, Preprint

[EN] Several technologies are being put in place to improve the efficiency of spark-ignition engines. Two of these technologies are variable valve actuation and exhaust gas recirculation, both of which can have an impact on combustion according to the literature. However, this impact is due to variations in both the in-cylinder tem-perature and composition, linked to the different characteristics of internal and external residuals, which are difficult to decouple. In this paper, a methodology aimed at improving the understanding of the temperature and composition effects on combustion parameters is developed. Internal residuals are controlled through a variable valve timing actuation, and evaluated thanks to a previously validated one-dimensional engine model, while the externally-circulated exhaust are extracted after the catalyst through a low-pressure system. Combustion is analyzed based on in-cylinder pressure acquisition and emissions measurement at the engine-out, before the aftertreatment module. Different combinations of internal and external residuals are tested with different stra-tegies from the point of view of the spark actuation: first, a constant spark timing for each value of total residuals; then, a spark timing adapted to maintain the same temperature inside the cylinder at the combustion start, and finally an optimized calibration from the point of view of the engine efficiency. Results show a general trend to enhance combustion timings as higher share of internal residuals are introduced for the same amount of total residuals. It can be seen how this trend comes mostly from the temperature effect at low total residuals fraction, while composition effects are more significant as the amount of total residuals increase. Empirical correlations developed in the paper confirm the need to decouple internal and external residuals to have a proper estimation of the combustion timings. Despite the positive impact of internal residuals on the combustion dur

[EN] The current paper presents a flow behaviour analysis of twin-entry radial turbines by means of experimental measurements and computational fluid dynamics (CFD) simulations. The experimental data were measured at partial, unequal and full admission conditions, and was used to globally validate CFD simulations. The experimental results hinted towards considering twin-entry turbines as two separated single-entry turbines working in parallel when used in simplified physics-based models such as in one-dimensional simulations. After analysing the CFD results, a simple flow capacity model was developed, exploiting some of the observed characteristic phenomena to reduce the number of fitting parameters to their minimum while keeping its accuracy and extrapolation capabilities.

[EN] In the present paper, the mid-term performance of two different architectures of a solar-driven jet-ejector refrigeration system is numerically compared: the first one is fitted with a fixed-geometry jet-ejector while the second one is equipped with an adjustable spindle that modifies the jet-ejector area ratio. The jet-ejector behavior has been predicted with a validated computational fluid dynamics approach and the dynamic response of the overall system accounts for transient effects in a small parabolic trough collector and a hot thermal storage tank. The investigation shows that the adjustable jet-ejector allows for continuous and smooth operation in a much wider range of outdoor conditions. Additionally, it enables more efficient management of the thermal level in the hot storage system. As a result, the adjustable refrigeration system improves the performance indicators in all the warm months of the typical meteorological year under evaluation. The maximum improvement potential is found in May; the fixed-geometry system provides an average COPth of 0.34 while the adjustable system reaches an average COPth of 0.48 considering the same boundary conditions in both cases. (c) 2020 Elsevier Ltd and IIR. All rights reserved.

[EN] The present paper evaluates numerically the feasibility of a solar jet-ejector refrigeration system from an efficiency maximization perspective with three low environmental impact refrigerants, namely, R1234yf, R1234ze and R600a. Special emphasis is given to the jet-ejector internal geometry optimization as a mechanism to improve the overall cycle performance. The jet-ejector entrainment ratio in different operating conditions and geometric configurations is determined by using a Computational Fluid Dynamics (CFD) approach experimentally validated which includes real gas models of R1234yf, R1234ze and R600a. R1234yf exhibited the best performance in terms of overall system efficiency closely followed by R600a and R1234ze. This suggests that the influence of the working fluid can be considerably mitigated if a thorough design of the jet-ejector is carried out. Afterwards, the refrigerant R1234yf is selected to carry out sensitivity studies with different collector typologies and solar irradiation scenarios. The Evacuated Tube Collector (ETC) model provided the highest overall system efficiency (eta(ov) = 0.213) for the peak solar irradiation (1000 W/m(2)). Nevertheless, one of the Parabolic Trough Collectors (PTC) models under investigation offered the most robust performance if a wider range of solar irradiation scenarios is considered.

[EN] The mixing of gaseous streams at different humidity and temperature conditions may generate bulk con- densation, which is a particular thermodynamic process that usually implies a great computational effort. A model that provides in-flow condensation predictions without heavily impacting on the simulation time becomes a potential tool for studying situations where the presence of water droplets is a problem. For instance, in a Long- Route Exhaust Gas Recirculation (LR-EGR) system, intake fresh air is mixed with humid and hot exhaust gases, generating water droplets that may impact on the turbo-compressor impeller and produce harmful erosion. Serrano et al. [1] developed a condensation submodel for such purpose. In this work, the 3D CFD methodology is analyzed by means of sensitivity studies on the numerical setup and intake throttle valve angle. Validation of the model is addressed by means of measurements in a fully instrumented continuous flow turbocharger test bench, obtaining quantitative and qualitative agreement. Particularly, a consistent correlation was found between predicted condensation rate and the impeller damage for seven LR-EGR configurations. Moreover, the T-joint geometry is noticed to have a great impact on condensation generation, thus showing the potential of such a 3D model for improving the LR-EGR design.

[EN] The present paper evaluates a jet ejector refrigeration system intended to cool down diesel engine intake below ambient conditions. Performance is assessed by means of 1D thermodynamic model of the cycle fed with ejector maps obtained with CFD code using R134a as working fluid. In the first study, no particular ejector geometry is fixed thus allowing the genetic algorithm to adapt the cycle to different engine conditions. Following this approach engine intake temperatures close to 0 degrees C can be attained in those engine operating points in which exhaust thermal power is sufficient to drive the jet-ejector refrigeration system. In the second evaluation, ejection cycle configuration which provided best results for the most frequent operating point in a standard driving, designated as 2000 rpm and 50% load, is selected. With this particular configuration the rest of engine operating points are reassessed. In this study performance degradation is found away from the design point showing that ejector size is a limiting factor. (C) 2019 Elsevier Ltd and IIR. All rights reserved.

[EN] During the latest years, downsizing in internal combustion engines has moved the operating conditions of the compressor closer the surge limit. Surge onset depends on the geometry of the compressor inlet and is difficult to predict. Unfortunately, the determination of the surge line is essential for engine design and calibration, since surge is an oscillating phenomenon that endangers the turbocharger integrity. This work is addressed to study the impact of placing different geometries, namely a tapered duct, a convergent-divergent nozzle and a divergent nozzle in the compressor inlet on different compressor parameters such as stability, efficiency and noise emission. 3D-CFD simulations are performed using the commercial code STAR-CCM+ at both near-surge conditions and high mass flow rate, focusing on the flow structures generated by each configuration. The results are compared with corresponding experimental tests and show a meaningful sensitivity of geometry to the performance, indicating potential benefits of using some of these geometries in turbocharger configurations.

[EN] State of the art techniques for reducing pollutant emission in internal combustion engines often require local flow assessment, specially in the air management field. This work addresses the interaction between a turbo- charger compressor and the 3-way long-route EGR joint, where exhaust gases of the combustion are mixed with fresh air. A validated methodology for compressor simulation is combined with a validated condensation model for this work. Numerical simulations of two different working points with three flap positions are conducted. The influence of these operating conditions on the flow field is evaluated. Particularly, there is a connection between the mixing of both steams and the generation of water condensates, responsible for the erosion of the impeller and the loss of compressor efficiency. Moreover, neglecting the impact of the compressor presence on the condensation production is shown to be of low magnitude, so that simulations without the compressor are regarded as accurate, thus reducing the computational effort by two orders of magnitude.

[EN] In order to comply with the legislation, car manufacturers are looking for a way to lower the CO2 emission by improving engine efficiency. About one third of the fuel combustion energy is wasted through exhaust gasses. Waste Heat Recovery (WHR) could improve engine efficiency by recovering a part of exhaust gasses energy. In this study, the potential use of an open loop Brayton cycle with a volumetric compression expansion machine for exhaust gas waste heat recovery was investigated. The use of the Brayton cycle system with only two main elements, a heat exchanger and a volumetric machine, could be very interesting due to its compactness and versatility. However, the publications on this subject are scarce. The present paper aims at bridging this knowledge gap by studying the cycle viability for passenger car application characterized by low temperatures, variable working conditions and several restrictions of available space and weight. The simulated vehicle was a Ford Mondeo family car with an Ecoboost 2.0 engine. The main components of the Brayton cycle WHR system model were a heat exchanger and an alternating piston machine that was used both as a compressor and as an expander. Theoretical studies were conducted in the compression-expansion machine model in order to determine the main parameters that influence the cycle and optimize those parameters in order to obtain the maximum recuperated power. The conclusion was that the cycle viability is not clear because cycle losses are in the same order of magnitude as the recuperated power. Considering future improvements of the compression-expansion machine and the heat exchanger, the recuperated power could be positive. Nevertheless, it is hard to expect that recuperated power would be sufficient to justify the application of this WHR system in the vehicle. (C) 2017 Elsevier Ltd. All rights reserved.

[EN] Centrifugal compressor performance at low mass flow rates has become an issue in the latest years due to engine downsizing and the increase of low-end torque request. The principal drawback of this operating region is the appearance of the surge phenomenon, which is strongly affected by the compressor inlet geometry. This work is addressed to study the impact of different inlet geometries on the compressor performance, including compressor efficiency, noise emission and surge margin. An engine test bench is set up with a centrifugal compressor and both steady and transient (tip-out) tests are performed in order to obtain a complete view of the influence of each configuration. The results show a clear sensitivity of the compressor parameters to the variations of the geometry upstream the compressor inlet. (C) 2016 Elsevier Ltd. All rights reserved.

This paper presents a mathematical model of a bottoming Organic Rankine Cycle coupled to a 2 l turbocharged gasoline engine to optimize the cycle from a thermo-economic and sizing point of view. These criteria were optimized with different cycle values. Therefore, a methodology to optimize the ORC coupled to Waste Heat Recovery systems in vehicle applications is presented using a multiobjective optimization algorithm. Multi-objective optimization results show that the optimum solution depend on the importance of each objective to the final solution. Considering thermo-economic criteria as the main objective, greater sizes will be required. Considering sizing criteria as the main objective, higher thermo-economic parameters will be obtained. Therefore, in order to select a single-solution from the Pareto frontier, a multiple attribute decision-making method (TOPSIS) was implemented in order to take into account the preferences of the Decision Maker. Considering the weight factors 0.5 for Specific Investment Cost (SIC), 0.3 for the area of the heat exchangers (Atot) and 0.2 for Volume Coefficient (VC) and the boundaries of this particular application, the result is optimized with values of 0.48 m2 (Atot), 2515 /kW (SIC) and 2.62 MJ/m3 (VC). Moreover, the profitability of the project by means of the Net Present Value and the Payback has been estimated.

This paper deals with the experimental testing of a bottoming Organic Rankine Cycle (ORC) integrate in a 2 l turbocharged gasoline engine using ethanol as working fluid. The main components of the cycle are a boiler, a condenser, a pump and a swash-plate expander. Both steady and transient tests were performed in three engine operating points to understand the behavior and inertia of the system. Pressure-Volume diagram during these transients were presented and analyzed. Operating parameters of the expander, such as expander speed and boiler power, were shifted. The objective of these tests is to understand the inertia of the system and to have a robust control in all the possible transient tests. New European Driving Cycle was tested with and without the expander because it is supposed to represent the typical usage of a car in Europe. It was used to validate the control of the ORC in realistic dynamic conditions of the engine. The importance of each parameter was analyzed by fixing all the parameters, changing each time one specific value. The main result of this paper is that using a slightly simple and robust control based on adaptive PIDs, the two dynamic effects of an ORC could be taken into account, i.e. high inertia effects (boiler and condenser) and low inertia effects (pump and volumetric expander).

This paper deals with the evaluation and analysis of a bottoming ORC cycle coupled to an IC engine by means of conventional and advanced exergy analysis. Using experimental data of an ORC coupled to a 2 l turbocharged engine, both conventional and advanced exergy analysis are carried out. Splitting the exergy in the advanced exergy analysis into unavoidable and avoidable provides a measure of the potential of improving the efficiency of this component. On the other hand, splitting the exergy into endogenous and exogenous provides information between interactions among system components. The result of this study shows that there is a high potential of improvement in this type of cycles. Although, from the conventional analysis, the exergy destruction rate of boiler is greater than the one of the expander, condenser and pump, the advanced exergy analysis suggests that the first priority of improvement should be given to the expander, followed by the pump, the condenser and the boiler. A total amount of 3.75 kW (36.5%) of exergy destruction rate could be lowered, taking account that only the avoidable part of the exergy destruction rate can be reduced.

Centrifugal compressor aeroacoustics are analyzed by means of a three-dimensional CFD model. Three operating points at nominal compressor speed are simulated ranging from best efficiency point to near-surge conditions. Experimental measurements are obtained using a steady flow rig mounted on an anechoic chamber. URANS and DES predictions of compressor global variables and pressure spectra are compared against experimental measurements. Flow-induced noise increases as the operating point moves toward surge line. Stall at the suction side of the blades exists even for high mass flow conditions, causing a high frequency boundary layer oscillation. Low momentum cells rotating at the diffuser are found at points closer to surge, causing the so-called whoosh noise. Inducer rotating stall is also present at these conditions. Point closest to surge shows a rotating tornado-type vortex at the inducer, determining a moving low pressure region that increases low frequency noise content.

Automotive turbocharger turbines usually work under pulsating flow because of the sequential nature of engine breathing. However, existing turbine models are typically based on quasi-steady assumptions. In this paper a model where the volute is calculated in a quasi-2D scheme is presented. The objective of this work is to quantify and analyse the effect of the numerical resolution scheme used in the volute model. The conditions imposed upstream are isentropic pressure pulsations with different amplitude and frequency. The volute is computed using a finite volume approach considering the tangential and radial velocity components. The stator and rotor are assumed to be quasi-steady. In this paper, different integration and spatial reconstruction schemes are explored. The spatial reconstruction is based on the MUSCL method with different slope limiters fulfilling the TVD criterion. The model results are assessed against 3D U-RANS calculations. The results show that under low frequency pressure pulses all the schemes lead to similar solutions. But, for high frequency pulsation the results can be very different depending upon the selected scheme. This may have an impact in noise emission predictions.

This paper deals with the experimental testing of an Organic Rankine Cycle (ORC) integrate in a 2 liter turbocharged gasoline engine using ethanol as working fluid. The main components of the cycle are a boiler, a condenser, a pump and a swash-plate expander. Five engine operating points have been tested, they correspond to a nominal heat input into the boiler of 5, 12, 20, 25 and 30 kW. With the available bill of material based on prototypes, power balances and cycles efficiencies were estimated, obtaining a maximum improvement in the ICE mechanical power and an expander shaft power of 3.7% and 1.83 kW respectively. A total of 28 steady-state operating points were measured to evaluate performance of the swash-plate expander prototype. Operating parameters of the expander, such as expander speed and expansion ratio, were shifted. The objective of the tests is to master the system and understand physical parameters influence. The importance of each parameter was analyzed by fixing all the parameters, changing each time one specific value. In these sensitivity studies, maximum ideal and real Rankine efficiency value of 19% and 6% were obtained respectively.

CFD has become an essential tool for researchers to analyze centrifugal compressors. Tip leakage flow is usually considered one of the main mechanisms that dictate compressor flow field and stability. However, it is a common practice to rely on CAD tip clearance, even though the gap between blades and shroud changes when compressor is running. In this paper, sensitivity of centrifugal compressor flow field and noise prediction to tip clearance ratio is investigated. 3D CFD simulations are performed with three different tip clearance ratios in accordance to expected operating values, extracted from shaft motion measurements and FEM predictions of temperature and rotational deformation. Near-surge operating conditions are simulated with URANS and DES. DES shows superior performance for acoustic predictions. Cases with reduced tip clearance present higher pressure ratio and isentropic efficiency, but no significant changes in compressor acoustic signature are found when varying clearance. In this working point, tip clearance is immersed in a region of strongly swirling backflow. Therefore, tip leakage cannot establish any coherent noise source mechanism.

This paper presents the development and validation of a one-dimensional radial turbine model able to be used in automotive turbocharger simulations. The model has been validated using results from a numerical 3D CFD simulation of stationary and pulsating flow in a variable geometry radial turbine. As the CFD analysis showed, the main non-quasi-steady behavior of the turbine is due to the volute geometry, so special care was taken in order to properly model it while maintaining low computational costs. The flow in the volute has been decomposed in its radial and azimuthal direction. The azimuthal flow corresponds to the flow moving along the volute, while the radial flow is computed by coupling its flow with a stator model. Although the stator caused fewer accumulation effects than the volute, a small accumulation model has been used for it, which also allows to compute the evolution of the flow inside the turbine with lower costs. The flow in the moving rotor can be considered quasi-steady, so a zero-dimensional model for the rotor has been developed. Several losses models where implemented for both the stator and the rotor. The results show good agreement with the CFD computations. 2014 Elsevier Ltd. All rights reserved.

Nowadays, turbocharged internal combustion engines (ICEs) are very common in automotive powerplants, monopolizing the Diesel sector and having a steadily increasing percentage in the gasoline one. In this frame, the interest in modeling the behavior of the turbomachinery components involved, with the ultimate goal of characterizing the performance of the turbocharged ICE, seems clear. A turbomachine can be simulated using 3D-CFD software, but its computational cost does not allow to reproduce the whole turbocharger test rig. Moreover, the existence of long ducts requires a considerable computational time until the pressure reflections at the boundaries dissipate in order to reach a periodic solution. The use of non-reflecting boundary conditions reduces the needed length of ducts without introducing spurious wave reflections. An anechoic boundary condition (BC) based on the Method of Characteristics has been previously developed, considering the case of an inviscid and adiabatic 1D flow of a perfect gas. However, real flows do not behave in such ideal manner. In this paper, the extension of the scope of the previous BC is sought. In this way, a methodology to evaluate the performance of the anechoic BC under these real flow situations is shown. The consideration of ideal gas instead of perfect gas, the flow viscosity and the non-homentropic flow makes it necessary to modify the Method of Characteristics, since the Riemann Invariants are not constant any more. In this frame they are referred to as Riemann Variables. An additional issue that has been considered is the effect of swirl flow, as the one in the turbine outlet, on the anechoic BC. Some improvements to be implemented in the BC are proposed in order to have a better performance in these real flow situations.

This paper presents a numerical study analyzing the effect of pulsating flow in a variable geometry radial inflow turbine. The turbine behavior is analyzed under isentropic pulses, which are similar to those created by a rotating disk in a turbocharger test rig. Three different pulse frequencies (50, 90 and 130 Hz) and two pulse amplitudes (100 and 180 kPa) were considered. Turbine flow was studied throughout the pressure pulsation cycles in a wide range of off-design operating conditions, from low pressure ratio flow detachment to high pressure ratio choked flow. An overall analysis of the phasing of instantaneous mass flow and pressure ratio was first performed and the results show the non-quasi-steady behavior of the turbine as a whole as described in the literature. However, the analysis of the flow in the different turbine components independently gives a different picture. As the turbine volute has greater length and volume than the other components, it is the main source of non-quasi-steadiness of the turbine. The stator nozzles cause fewer accumulation effects than the volute, but present a small degree of hysteretic behavior due to flow separation and reattachment cycle around the vanes. Finally, the flow in the moving rotor behaves as quasi-steady, as far as flow capacity is concerned, although the momentum transfer between exhaust gas and blades (and thus work production and thermal efficiency) is affected by a hysteretic cycle against pressure ratio, but not if blade speed ratio is considered instead. A simple model to simulate the turbine stator and rotor is proposed, based on the results obtained from the CFD computations.

Heat transfer in wall-flow monoliths has gained in interest because of the widespread adoption of these systems by automotive industry to fulfil soot emission regulations and the importance of heat exchange on the regeneration process control to avoid damaging the monolith. This paper presents a heat transfer model for wall-flow diesel particulate filters coupled with an unsteady compressible flow solver. The heat exchange between the gas and the solid phase is based on a bi-dimensional discretisation of the porous medium both in axial and tangential directions. The monolith can be discretised in the radial direction to account for the heat fluxes towards the environment through the monolith and the canister, which is also coupled with the inlet and outlet ducts of the filter. The model is validated against experimental data obtained in a flow test rig. A test campaign under non-reacting conditions has been conducted to show the capability for thermal response prediction. Tests cover clean and soot loaded monolith, continuous flow under steady and transient thermal conditions, and pulsating flow. In this case, the characteristics of the pressure waves in amplitude and frequency are similar to those that the monolith can undergo depending on its location along the exhaust line. © 2012 Elsevier Ltd.

This paper presents a new representation of the turbine performance maps oriented for turbocharger characterization. The aim of this plot is to provide a more compact and suited form to implement in engine simulation models and to interpolate data from turbocharger test bench.The new map is based on the use of conservative parameters as turbocharger power and turbine mass flow to describe the turbine performance in all VGT positions. The curves obtained are accurately fitted with quadratic polynomials and simple interpolation techniques give reliable results.Two turbochargers characterized in an steady flow rig were used for illustrating the representation. After being implemented in a turbocharger submodel, the results obtained with the model have been compared with success against turbine performance evaluated in engine tests cells. A practical application in turbocharger matching is also provided to show how this new map can be directly employed in engine design. © 2010 Elsevier Inc.

An on-engine method for dynamic characterisation of automotive NOx concentration sensors is presented. Steps in start of injection on a diesel engine are employed to achieve step-like NOx concentration variations on exhaust flow. On the basis of the sensor response, delay and dynamic response can be easily identified; the paper shows a simple least squares procedure although other models and identification techniques could be used. Application data is presented for three NOx sensors: a research-grade chemiluminescence exhaust gas analyser, and two different commercial ZrO2-based sensors. © 2010 Elsevier Inc.

180 different mortars made with a dolomitic lime and different aggregates were prepared in order to be used in restoration works. This paper focuses on the effect of technological variables on pore structure and mechanical properties of magnesian lime-based mortars. Compressive and flexural strengths of the specimens were discussed according to curing time, binder : aggregate ratios, attributes of the aggregates and porosity, at long-term tests. A strong increase in the strength of mortars has been found after 365 curing days as compared to 28 curing days. The strength has been mainly attributed to the portlandite carbonation, because no significant changes have been observed in the brucite. However, higher strengths than similar aerial lime-based mortars led us to think of other mechanism which increases the strength: the calcite formation through a reaction of dedolomitization (alkali carbonate reaction, ACR) and the brucite crystallization were discussed. The pore structure has presented a significant influence on the strength. More binder amounts mean more strength due to the higher values of open porosity, which allows the carbonation process. The aggregate characteristics have been correlated with the strength and porosity. Limestone and angle-shaped aggregates, reducing large pores, cause a strength increment.

Lime-mortars to be used in restoration works of Cultural Heritage are being more and more studied. The knowledge on the lime-pastes allows understanding the behaviour of the binder fraction. The aim of this work is to study the influence of the kneading water on two critical aspects of the lime-pastes: pore structure and capillary porosity, because both of them are related to the service life of the material, particularly with the moisture transport. Mercury intrusion porosimetry has been performed to establish the pore size distribution: one pore range has been checked in the different pastes tested, setting linear relationships between the pore diameter and the water/lime ratio. Fractal geometry has been used from the MIP results in order to evaluate the pore surface complexity, as a function of the kneading water. From the results, it can be concluded that kneading water is only responsible for a swelling of the structure, but it does not change the pore surface (keeping constant the surface fractal dimension). DIA analysis has been carried out, confirming the previous results. Finally, the correlation obtained between the capillary coefficient and the water/lime ratio confirms the postulated pore structure for the different amount of kneading water in lime-pastes.

One hundred eighty different mortars made with a natural hydraulic lime (NHL) and different kinds of aggregates were prepared to be used in restoration works. The factors affecting the mechanical behavior have been studied at long-term test. Compressive and flexural strengths of the specimens were discussed according to curing time, binder/aggregate ratios, attributes of the aggregates and porosity. Three phases of hardening have been established as a function of the chemical composition: C3S contributes to the strength at early ages. C2S and the carbonation process give their strengths at long term. Specimens with larger binder amounts have shown higher porosity and strength. The characteristics of the aggregates have been correlated with the strength and porosity. Limestone aggregates contribute to the strength. Rounded-shaped aggregates increasing large pores cause a strength reduction, hence their use is not advisable. Aggregates with small grain size show a good cohesion at the interface improving the strength.