11
The design, properties and performance of shape optimized masonry blocks
Abstract
The choice for a certain masonry unit depends mainly on its functional performance. The new European Directives regulations require different solutions challenging manufacturers to develop optimized systems. In particular, in south European countries where the mild winter climate justifies the use of high-thermal-performance masonry walls, the search for optimized masonry units and the design of single-leaf masonry external walls is a challenge. In this chapter, the basic requirements for enclosure walls used in the building façades are analysed. A review of innovative masonry blocks developed in recent years is presented. An example of an optimized lightweight concrete masonry unit, for single leaf enclosure walls with no external insulation, developed within a collaborative project with MAXIT group, is illustrated. The iterative problem of finding the optimal geometry and topology, namely position, size and spacing of the holes within the block that minimizes the wall thermal transmittance, is supported by a genetic algorithm constrained by the characteristics and construction practices of masonry materials. Numerical simulations and laboratory tests of two new wall solutions currently under development at the University of Porto are reported. Finally, future trends for the development of masonry systems are also introduced.
Keywords
Enclosure; Energy efficiency; Masonry; Optimization; Units11.1. Introduction
Recent European Directives concerning building energy efficiency are imposing the development or improvement of building envelope systems, since the growing importance of well-being, in conjunction with architectural trends, specifically the widespread increase of the glazed area in buildings, has led to an increase in unacceptable energy consumption levels.
These envelope systems are one of the features that needs improvements, because, despite their economic and functional importance, they present a high tendency to develop noticeable defects (e.g. cracking, water infiltrations). On the other hand, the thermal comfort and energy saving are pressuring the construction industry to comply the technical requirements and to increase performance of their products with acceptable costs, thus presenting a challenge to the development of façade systems.
Traditionally, the opaque part of the façades of buildings was generally made of masonry, usually designated by enclosure walls. The thermal efficiency induced important changes for these types of enclosure walls, in particular in south European countries where traditionally the mild winter climate justifies the use of walls with moderate thermal performance.
Now it makes sense to ask if whether or not the masonry will continue to have such a relevant importance in the construction of buildings, since given the technological evolution and development of new materials, masonry could lose importance to other solutions that have better cost/behavior effectiveness.
In order for masonry to continue to have a distinguishing presence in buildings, it would need to evolve, thus ensuring more functions and always at a competitive cost.
One of the ways by which the masonry can answer to these new challenges is by using thick single leaf walls with distributed insulation, by using thermal shaped optimized units made from lightweight materials with good thermal insulation and sufficient mechanical resistance, usually lightweight clay or concrete.
The primary intention of these wall solutions is to achieve, simultaneously, thermal insulation levels without the use of specific thermal insulation materials, adequate mechanical resistance and economic competitiveness.
These purposes must be obtained not only from the unit cost, but also by productivity gains associated with unit laying, since the dimensional increase of the units highlights one of the main problems of construction using masonry, which is the arduous nature of the workmanship in its laying. Also, this type of task is repetitive and physically exhausting, exposing workers to the risk of serious injury, with severe consequences in terms of productivity.
In order to answer adequately to current needs, it will be necessary to
• Develop solutions which are better adapted to environmental issues and to the needs of workmanship, being easier to handle and with less waste.
• Increase industrialization by concentrating multiple roles in a single element, generalizing the concept of the system with a greater emphasis on prefabrication.
• Design construction projects more oriented towards execution difficulties, and more concerned with site conditions.
These overall objectives require a complex optimization process, integrating various aspects, from numerical simulations and laboratory trials to experimental factory productions.
11.2. Searching for the optimal masonry block
Masonry enclosure walls are elements that are most exposed to environmental conditions (rain, temperature, wind loading, seismic vibrations) and to actions related to the use of the occupants. In order to accomplish these functions, masonry walls must be a multifunctional system able to answer to several demands, such as thermal and acoustic comfort, watertightness, fire resistance, safety in use, stability to loading effects, amongst others.
Most of these functions are performed by masonry walls, or can be partially or exclusively performed by other systems applied to the masonry, such as rendering systems to improve watertightness or thermal insulation. The use of these rendering systems with masonry supports increases the construction complexity and the difficulty of the characterization of the behavior of walls. Research and innovation are strongly needed to assess the vulnerability of existing constructions, to define economical rational design rules, to allow for build, novel shapes and novel applications of masonry and to contribute to masonry innovation.
11.2.1. Modern masonry solutions
A building's enclosure constructed in masonry is a very common solution worldwide and single leaf or cavity walls are both frequent. However, modern masonry walls are usually single leaf, made from large units and finishes with a specific behavior in order to significantly improve some specific aspects, for example thermal insulation or/and watertightness (Figures 11.1 and 11.2).
In Europe, clay units (vertically or horizontally perforated) are commonly used, but other units, like those made from concrete, have also large utilization (Figure 11.3).
Modern masonry systems are made from a set of pieces, i.e. units with different topologies and dimensions, which allow various applications and details to be carried out, thus making the wall as a constructive system for which, in addition to the standard base units, special units are also developed to solve particular situations, such as connections between walls, integrations of windows or reinforcements (Figure 11.4), amongst others.
The units are usually laid in general purpose mortar joints, which can have an improved thermal behavior, but can also be laid in thin layer mortars for both better mechanical and thermal performance.
Also ancillary components (e.g. bed joint reinforcement, wall ties) can be used to improve the behavior of masonry in some situations, such as the connection between walls and other structural elements (Figure 11.5), but in general the use of these elements is not very common in some European countries.
11.2.2. External wall requirements
Construction works, including components and materials, must accomplish the basic requirements established in the European Directives (European Parliament, 2011):
1. Mechanical resistance and stability
2. Safety in case of fire
3. Hygiene, health and the environment
4. Safety and accessibility in use
5. Protection against noise
6. Energy economy and heat retention
7. Sustainable use of natural resources
The accomplishment of these requirements is made through the comparison between reference/minimum characteristics and the confirmed performance of the building components. The reference/minimum characteristics are referred in national regulations and design codes, and the performance of the building components are usually determined from laboratory tests or from established practises of design and construction.
When masonry walls are used in façades of buildings, i.e. used as enclosure masonry walls, they must also help to accomplish the basic requirements, including the units and the mortar joints. These constituent materials are important since they play an important role in the behaviour of the masonry, since they can influence a diversity of behaviours of the wall, such as thermal, acoustical, watertightness and mechanical performance. Therefore, the basic requirements for enclosure walls used in the building façades are important to be analysed.
11.2.2.1. Mechanical resistance and stability
Structural masonry used for enclosure walls should be checked to avoid collapse under loading of the whole or part of the wall, to avoid major deformations or damage to other elements or installed equipment. Design codes for masonry, such as EC6-Eurocode 6 (CEN, 2005) or EC8-Eurocode 8 (CEN, 2004), can be used.
It is important to underline that although this checking is not required for nonstructural enclosure walls, it is important to ensure the stability and mechanical resistance of these walls for wind loading according to EC6 (CEN, 2005), and also to other possible actions induced by their support that can originate cracking (e.g. deformation, thermal actions). Also, a seismic verification of nonstructural walls is referred in EC8 (CEN, 2004), including applied coatings and connections to support the walls.
For the constituent materials, EC6 (CEN, 2005) and EC8 (CEN, 2004), together with a vast set of recent European standards, point to requirements for these materials as well as for structural masonry, many of them also applicable to infill/nonstructural masonry. The main objective of these requirements is to ensure a better mechanical behavior of masonry walls. It concerns geometrical characteristics (e.g. volume of holes, thickness of webs and shells for the units), mechanical characteristics (e.g. minimum compressive strengths of units and joints), and also aspects related to masonry detailing practices (e.g. interlocking of units), use of perpend joints, thickness limits for joints, use of shell bedded laying and use of bed joint reinforcement, amongst others.
11.2.2.2. Safety in case of fire
Masonry walls provide good fire resistance performance for the usual thicknesses (30–35 cm). Moreover, the constituent materials have a good reaction to fire (noncombustible materials, usually low in organic aggregates – class A1).
The determination of the class of fire resistance (REI and EI) can be performed through laboratory tests or estimated from tables of EC6 (CEN, 2005) through the thickness and composition of the wall. The determination of the classes of reaction to fire when necessary (different from class A1), is only measurable through testing.
11.2.2.3. Hygiene, health and the environment
To ensure watertightness of rain and lack of condensation on walls improves the health of the internal building environment and durability of the wall and applied materials.
Watertightness normally is achieved by using higher wall thicknesses and an adequate treatment of joints, or through the masonry wall and rendering systems with low permeability, or just by waterproofing membranes/coatings without a specific contribution from the masonry wall. In general, the watertightness can only be evaluated by testing (e.g. ASTM, 2011). However, there are some design/construction practices established in technical documents for assessing the watertightness of some masonry wall solutions (e.g. CSTB, 2008).
On the other hand, ensuring proper heat transfer coefficients, U value and appropriate thermal bridge technical solutions can greatly reduce the risk of condensation on the walls.
Finally, the most common constituent materials for masonry systems do not constitute danger to the users nor to the environment since there is an absence of noxious materials.
11.2.2.4. Safety in use
The walls must be able to guarantee an adequate impact resistance and the suspension of eccentric moderate loading (200–400 kg). In general, masonry is a heavy and rigid solution, and usually is connected to the building structure. These characteristics usually are enough to ensure all requirements.
On the other hand, the facings of the walls, including applied finishes and installations, must be executed in a way that does not cause injury (contact and safety use).
11.2.2.5. Protection against noise
Since usually masonry is a heavy solution, this aspect is beneficial to airborne sound insulation, easily satisfying the most demanding requirements of sound insulation for exterior walls referred in national regulations. However, these acoustic requirements are more demanding for interior walls (e.g. separation between dwellings). This aspect often requires the use of thicker walls or even double walls with integration of specific acoustic insulation.
11.2.2.6. Energy economy and heat retention
The thermal performance and mitigation of the thermal bridges are one of the most crucial aspects of the façade walls. Thermal comfort requirements demand that the exterior walls contribute towards ensuring comfortable thermal conditions on the inside. To this effect most regulations establish maximum permissible values for the overall heat transfer, U value. These values have become increasingly stricter to ensure higher levels of thermal insulation. An improved performance can be achieved using masonry solutions made with units thermally optimized that can be complemented with specific thermal insulation.
It is important to notice that thermal insulation of building façades depends not only on the masonry (opaque part), but also on other building elements such as glazed elements.
11.2.2.7. Sustainable use of natural resources
The use of masonry systems that integrates pieces/units to solve singular situations (e.g. openings, integrations of reinforced elements, connections between walls) can reduce the amount of construction waste. Moreover, a large part of the waste from the demolition of masonry can be recycled for other uses in the construction industry, since most of the raw materials used are natural.
On the other hand, the use of natural raw materials (e.g. clays, sand, cork, wood powder and rice husk) avoids the use of synthetic materials that are harmful to the environment.
11.3. Enhanced performance of masonry blocks using optimization techniques
The development of new masonry units, possessing properties which match or exceed current existing products, is conventionally performed within a laboratory. The presence of air cells in concrete units and mortar joints affecting the thermal conductivity of a wall was evaluated by Abdou and Murali (1994). Pierzchlewicz (1996) presented a pioneering research work in which 13 kinds of hollow blocks with different hole geometry (aligned and staggered) were developed, and their thermal and strength properties were analyzed. Bastos, Sousa, & Melo (2005) correlated the mix design with different properties of lightweight concrete masonry blocks, including compressive strength and thermal conductivity through tests on three walls. Later Al-Jabri, Hago, Al-Nuaimi, & Al-Saidy (2005) carried out an experimental investigation on the thermal insulation properties of lightweight concrete hollow blocks.
The time-consuming and laborious process often demands for thousands of samples to be produced and tested. Several authors have addressed the problem of utilizing numerical techniques to enhance the efficiency of the experiment-based development of a new product. The development of mathematical models plays an important role in the simulation and optimization of complex systems leading to efficient and economical designs. With the aim of providing improved layouts for a wide class of structural elements, the information generated by finite element analyses was employed to select the best design among a number of alternative constructive possibilities.
Extensive numerical investigations were carried out by del Coz Díaz et al., in particular, heat-insulating lightweight concrete hollow brick walls (del Coz Díaz, García Nieto, Betegón Biempica, & Prendes Gero, 2007) and slabs floors (del Coz Díaz, García Nieto, Domínguez Hernández, & Suárez Sánchez, 2009), taking into account the nonlinearity deriving from radiation effects (del Coz Díaz, García Nieto, Suárez Sierra, & Betegón Biempica, 2008; del Coz Díaz, García Nieto, Suárez Sierra, & Peñuelas Sánchez, 2008). Furthermore, focusing on new numerical methodologies del Coz Díaz and coworkers have been constantly innovating to access the effects of thermal properties of different constituent materials and the dimensions of recesses on the overall thermal performances of several structural components – floors made up of clay, concrete and lightweight concrete hollow blocks (del Coz Díaz et al., 2010, 2014) and multi-holed lightweight concrete blocks (del Coz Díaz, García Nieto, Álvarez Rabanal, & Domínguez Hernández, 2012; del Coz Díaz, García Nieto, Díaz Pérez, & Riesgo Fernández, 2011). The same authors also carried out experiments focusing on the hygrothermal properties of different mixes of lightweight concrete that are commonly employed in the fabrication of blocks making up the building envelope and provided best fitting numerical studies (del Coz Díaz et al., 2013). Interesting applications of innovative hollow concrete masonry blocks in which new layouts are characterized by reduced weight, adequate strength, and enhanced handling possibility have been presented. Javidan, Safarnejad and Shahbeyk (2013) have numerically observed that inserting a horizontal diaphragm in the middle or the bottom of a block can increase its ultimate effective strength (load resistance/weight).
The possibility of utilizing powerful optimization techniques to reduce the amount of experimental data required to develop a new product has been coupled to empirical modeling focusing on challenges to the masonry industry. Sousa, Sousa, et al. (2011) and Sousa, Castro, et al. (2011) have used a genetic algorithm for the definition of the geometry of lightweight concrete blocks that minimizes their transmittance, by determining the optimum values of a finite number of parameters that define the position, the size and the spacing of the holes within the block. The holes are assumed to be of rectangular shape and arranged in a regular mesh, either aligned or staggered. A more general approach has been presented by Bruggi and co-workers (Bruggi & Cinquini, 2011; Bruggi, Cinquini, & Taliercio, 2013; Bruggi & Taliercio, 2013a, 2013b) with no a priori assumption made about the geometry of the holes in the block, so as to fully exploit the potentials of topology optimization; nevertheless, the presented two-dimensional problem of topology optimization should be studied as 3D. The search for new environment-friendly masonry products urges for mixes composed entirely of recycled and waste aggregates. Recently, Vu, Forth, Dao, & Toropov (2013) showed that the use of optimization techniques has a potential to provide economies during future scaling-up and manufacturing processes as compared to experimental optimization alone (Forth, Dao, Toropov, & Vu, 2010).
11.3.1. Optimization methodology using a genetic algorithm
Advantageous computational methods of design optimization do not guarantee to arrive at the true optimum, but offer an efficient method that has a high probability of finding the optimum or of getting close to it. There should be no requirement for any of the functions or constraints to be continuous or for differentials to exist allowing continuous and discrete design variables to coexist concerning geometry, materials and systems of construction. Evolutionary algorithms are optimization procedures that apply the Darwinian principle of survival of the fittest by maintaining a population of solutions of which the poorest are eliminated. Each solution is ranked according to a fitness value closely related to the objective function.
Implemented genetic algorithms supported by elitist strategies are based on operators such as selection, crossover, elimination/substitution and mutation, preserving a core of best individuals to be transferred into the next generation. A suitable and efficient elitist genetic algorithm (GA) has been described in the literature (António, 2002; António, Castro, & Sousa, 2005; Sousa, Castro, et al., 2011). Given a population, its individuals are ranked according to their fitness, and the elite group is defined as the best-fit individuals. Selection is performed by randomly choosing pairs of progenitors with one individual from the best-fit group (elite) and another from the least-fit group. The offspring genetic material is obtained using a modification of the parameterized uniform crossover technique. Solutions with similar genetic properties are eliminated and then substituted with new randomly-generated individuals. Implicit mutation is considered by randomly selecting individuals and then, depending on a given probability, one binary digit will mutate. After mutation, the original size population is recovered, the new population is found and the evolutionary process continues. The stopping criterion used is based on the mean fitness value of the best individuals within the population. If the mean fitness value of the elite group does not vary for a defined number of generations, it is assumed that the iterative process has converged; that is to say, the optimal solution was found.
Computational optimization is employed to define the topology of a masonry block that minimizes its thermal transmittance, with the aim of maximizing the thermal insulation of masonry buildings. Block manufacturing is a business that is strongly dependent on demand where standardized sizes are important with block dimensions being specified by the manufacturer. The specific weight of masonry raw material obviously depends on its components. For lightweight concrete with expanded clay aggregates, the lowest specific weight corresponds to the lowest thermal conductivity and the highest thermal insulation performance. On the other hand, the lowest specific weight corresponds to the worst structural behaviour. A compromise between thermal and structural behaviour should be settled with the manufacturer.
Considering a vector of design parameters, b = {b1,…,bD}, and a function that measures the masonry wall transmittance, Π(b), a single-objective optimization problem can be defined as
(11.1)
subject to state equations of the thermal problem and to additional side constraints related to weight and topology block 
.
.In GA implementation, data codification is very important for further manipulation. Each possible solution is associated with an individual that is to say with a chromosome or string of digits. A mixed code format is adopted for the genotype of each chromosome of the individual or solution. A binary code format using a genotype with five digits will be considered for each design variable taking continuous values on intervals, such as vertical or horizontal shell's and web's thicknesses. An integer coding is considered for each discrete variable assigning a position on its domain. Clearly the dimension of the space design, even for a comparatively small chromosome structure, can be very large. An initial population is obtained by randomly generating different individuals within the solution space. Every individual is evaluated according to its fitness value, which is related to the objective function and defined as
(11.2)
where 
is a predefined constant chosen to ensure a positive fitness value. The GA will seek to increase fitness as it operates. The schematic representation of the optimization algorithm is given in Figure 11.6.
is a predefined constant chosen to ensure a positive fitness value. The GA will seek to increase fitness as it operates. The schematic representation of the optimization algorithm is given in Figure 11.6.11.3.2. Optimal thermal insulation of masonry walls using topology optimization
Using computer-aided simulations, it is possible to compare different building designs and to predict temperature fluctuations with a high degree of accuracy. Search for a new lightweight masonry block that will perform according to today's normative requests and exhibits optimal thermal insulation behavior is an ongoing process (Sousa, Castro, et al., 2011; Sousa et al., 2013; Svoboda & Kubr, 2010). Attention has been focused on the optimal design of masonry blocks in order to minimize their thermal transmittance (i.e. to maximize their thermal resistance).
A general mathematical description of an optimization problem includes objectives and constraints. Single objective formulations are straight-forward and allow detailed exploration. For insulation optimization, the objective function measures the masonry wall transmittance and then normative requests and technological constraints have to be embodied in the optimization procedure (Evins, 2013; Gosselin, Tye-Gingras, & Mathieu-Potvin, 2009). In this section, an example of thermal optimization of a lightweight concrete masonry block, according to thermal normative requests, is presented.
The thermal behaviour of a wall can be characterized by the thermal transmittance of masonry units according to normative requests (CEN, 1993; CEN, 2002; CEN, 2005). This coefficient can be correctly calculated by three-dimensional finite element simulation considering the heat transfer simulation. Pure conduction is found in the concrete, and heat transfer by conduction, radiation and convection must be in the holes of the units. A detailed description of the thermal behavior of the voids is described in a previous work (Sousa, Castro, et al., 2011; Sousa et al., 2013).
The heat transfer due to the existence of air voids and the temperature gradient between the interior and the exterior surfaces of masonry walls is calculated using the first law of thermodynamics and the isotropic Fourier law for heat flux (Kreith & Bohn, 2001). The analysis of radiation exchange among the surfaces of an enclosure is complicated by the fact that when the surfaces are not black, radiation leaving a surface may be reflected back and forth several times among the surfaces with partial absorption occurring at each reflection. A proper analysis of the problem, including the effects of these multiple reflections, is presented in a previous work (Sousa, Castro, et al., 2011). The study of the natural or free convection is made considering empirical correlations between the Nusselt (Nu) number, the Prandtl (Pr) and Rayleigh (Ra) numbers in enclosed spaces to determine free convection heat transfer coefficient in the voids (Kreith & Bohn, 2000).
The accuracy of the nonlinear method to predict clear wall thermal conductivity was validated using normative results for masonry units, EN 1745, where maximal discrepancy between referenced and simulated thermal resistance values was below 1% (Sousa, Castro, et al., 2011; Sousa et al., 2013).
In order to get a thermal optimization of vertically perforated lightweight concrete masonry units, the optimization algorithm described in the previous section has been used. The numerical evolutionary algorithm described iterates over the finite element thermal analysis supported by ABAQUS software.
The goal of the study is to find dimensions and distribution of voids that will minimize the thermal transmittance of masonry blocks with the following dimensions: 350 mm length including 5 mm vertical mortar joints on each side, 200 mm height including 10 mm horizontal mortar joint on the top and on the bottom and 350 mm thickness plus 20 mm mortar at internal and external render finish surfaces; total wall thickness becomes 390 mm. These values were provided by the manufacturer according to standard building procedures.
The 3D steady state heat transfer analysis has been performed considering linear solid elements of eight nodes. The internal and external surface temperatures are considered constant and equal to 293 and 273 K respectively. The heat transfer by convection and radiation is considered on the internal and external faces with associated thermal resistances Rsi = 0.13 m2 K/W and Rse = 0.04 m2 K/W. The concrete presents a specific weight equal to 1100 kg/m3 corresponding to a thermal conductivity, (concrete = 0.38 W/m K), according to Portuguese standard NP EN 1745. The experimental values for mortar thermal conductivity are given:
• Mortar thermal conductivity of interior mortar is equal to λ = 0.80 W/(m K).
• Mortar thermal conductivity of exterior mortar is equal to λ = 1.00 W/(m K).
• Mortar thermal conductivity of joint mortar is equal to λ = 0.54 W/(m K).
The thermal transmittance of the blocks is calculated by the following equation:
(11.3)
where Fl is the summation of the node thermal flux at the internal surface as given by ABAQUS, 
is the temperature difference between internal and external block surfaces, L measures the block length and H the block height.
is the temperature difference between internal and external block surfaces, L measures the block length and H the block height.Searching an improvement of the thermal resistance of masonry units, the optimization algorithm will iterate as the topology of the unit evolves to an optimum. The project considers a design vector b with eight process parameters describing the topology as follows: b1 – number of vertical webs; b2 – number of horizontal webs; b3, b4 – vertical shell's and web's thicknesses, respectively; b5, b6 – horizontal shell's and web's thicknesses; b7 – voids staggered (b7 = 0) or “in line” (b7 = 1); b8 – consideration of strip bed joints – no strip bed joints (b8 = 0), strip bed joint on the central row (b8 = 1) or strip bed joints on alternate rows (b8 = 2). The optimization algorithm has been implemented allowing the parameters to vary according to the side constraints given in Table 11.1.
The optimal topology of the block corresponds to 16.5 kg in weight and a thermal transmittance of the masonry wall U = 0.48 W/(m2 K), which is lower than Portuguese standards requests for the more severe climatic zone. This optimal solution exhibits staggered voids and strip bed joints on alternate rows. With this geometry, elongation of the heat flow path through the wall was attained.
This study was completed with some topology changes in order to get an improvement in construction technology and structural behavior. The topology update was made by
• Introducing two large voids in order to improve handling and laying.
• Introducing tongue and groove vertical joints to speed up the construction improving the alignment.
• Filling vertical strip joints with mortar in order to get a better behavior under horizontal loads.
The optimal topology obtained for a lightweight concrete masonry unit is presented in Figure 11.7.
This unit corresponds to a thermal transmittance of the masonry wall U = 0.50 W/(m2 K), which is a good thermal insulation for a single leaf wall made with lightweight concrete blocks. The open surfaces resulting from strip bed joints need proper technology, already available and used in the building industry, in order to avoid mortar filling the air spaces and consequent performance deterioration.
This type of wall can be an interesting alternative to cavity walls, which are expensive components as a single leaf wall with good thermal insulation properties was obtained, with economic and technical advantages due to quicker and easier construction and less dependence on workmanship quality. The area of total holes as a percentage of the gross area is equal to approximately 30%, which is acceptable for good structural behavior.
11.3.3. Industrial developments
At the moment, these concerns are important and two different industrial projects, both with the same aim, have been concluded with the participation of Oporto University, Portugal. The main objective of these projects was to develop wall solutions that answer adequately to the actual requirements, both with regard to thermal standards, as well as to mechanical behavior, watertightness and acoustic comfort, and aiming to rely on solutions based on a single leaf wall, reinforced, confined or only simple infill. The use of structural masonry is limited to small buildings.
Through these projects two masonry systems were developed: concrete masonry system made from lightweight concrete units and mortar (expanded clay aggregates), which fulfils the value of U ≤ 0.5 W/(m2 C), enough for all Portuguese climate zones, and a ceramic masonry, made from a block whose raw material is a porous ceramic paste, which fulfils the value of U ≤ 0.6 W/(m2 C), corresponding to the two climate zones where most construction work takes place.
The units were developed according to numerical processes referred to in 11.3 and 11.4, i.e. a study of the thermal behavior of both masonry systems was made through FEM, and an optimization of the thermal transmittance of masonry was made through modifications on the geometry of the units (considering different shapes for the holes, number of holes and rows and unit width) and the density of the materials intended to be used on those units.
In this optimization process, the requirements to be applied to masonry walls, units and mortar according to Portuguese regulations, European Standards and other references were considered.
Some of the most important requirements considered in the development of both masonry systems were:
• Portuguese reference values for thermal transmittance of walls, U value (Portugal – Leis, Decretos, 2006).
• Density of the unit materials to control thermal conductivity, which was estimated through EN1745 (CEN, 2002).
• Minimum compressive strength of the units defined in the Portuguese NDP – National Determined Parameters of EC8 (CEN, 2004).
• Maximum weight of the unit to ensure minimum safety and health in manual handling work referred in Portuguese regulations (Portugal – Leis, Decretos, 2006).
• Maximum slenderness of the wall referred in the Portuguese NDP of EC8 (CEN, 2004).
• Minimum thickness of the wall to ensure watertightness defined according to French standard (CSTB, 2008).
Considering these aspects, the result was the development of two masonry systems made from large units with lightweight materials, such as clay and lightweight concrete (clay density lower than 1850 kg/m2, mixed with polystyrene aggregates and concrete density lower than 1200 kg/m2, mixed with lightweight expanded clay aggregates).
The main characteristics of clay and lightweight concrete masonry are:
• The width clay and lightweight concrete units is 300 and 350 mm, respectively.
• Both units have vertical holes and are classified as group two units according to EC6 geometrical requirements (CEN, 2005).
• Both units have two grip holes to help handling the units during construction works.
• The concrete unit has a blind face (5 mm thick) for laying the mortar joints.
• The units are bedded on mortar strips joints with an overlap of half of the length of the unit.
• The thickness of the horizontal joints is 10 mm.
• The vertical joints represent 40% of the width of the unit and are filled with mortar to the full height of the joints.
• The vertical and horizontal joints in the clay masonry are made from general purpose mortar, and in the lightweight concrete masonry, the joints are made from lightweight mortar (factory made mortar).
Considering these characteristics, final numerical simulations of the thermal behavior were made for both masonry systems (Figure 11.8), and no significant changes in the U value were recorded, thus maintaining the main objective for thermal transmittance of the wall (U ≤ 0.5 W/(m2 C) for the concrete masonry and U ≤ 0.6 W/(m2 C) for the clay masonry). Moreover, mechanical simulations were made to estimate the compressive behaviour of masonry through an FEM nonlinear model (Figure 11.8), and details about the numerical model can be found in available literature (Sousa & Sousa, 2012; Sousa et al., 2013).
After these simulations, several experimental productions of these units were made in factory by the manufacturers until the desired values for compressive strength and density of the units were achieved. Examples of clay and lightweight concrete units are presented in Figure 11.9, and examples of masonry details are presented in Figure 11.10 and in Figure 11.11 for both masonry systems.
Laboratory tests were made, according to European and American standards, to determine the main mechanical characteristics of the masonry systems (Figure 11.12), and the results obtained were within the expected values for shell bedded masonry. Details on laboratory set-ups for compressive, shear and diagonal tension tests and results for lightweight concrete and clay masonry are available in Sousa & Sousa (2010, 2011).
11.4. Conclusions and future trends
Sustainability and energy saving are the request of today. The hollow block with advantages of high strength, lightness and high performance should be used.
Economy and productivity improvements suggest the usage of building systems that reduce cost, due to the reduction of labour and to increasing geometric accuracy, such as the use of rectified units and special purpose mortars. Masonry unit mortar systems and mechanical aids have been developed, which ensure a fast, simple and qualitatively better construction of the walls. The new generation of masonry systems should be developed by taking modular coordination into account in order to ensure that the constituent materials can adapt better to the length and height of panels and to the layout of spans, finishes or other building materials; new techniques for reinforced masonry seem to be of relevance.
There is a growing emphasis in terms of quality of interior spaces, which leads to higher demands in the building enclosures, in particular in relation to thermal and acoustic comfort requirements without minimizing the requirements related to security, stability and durability of the buildings.
As masonry blocks can be used without rendering, aesthetics innovation calls for increased cooperation between material scientists, architects and civil engineers, combining efficiency and quality-enhanced constructions technologies.
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