Sustainable Masonry

Stability and Behavior of Structures

Thierry Ciblac, Jean-Claude Morel

• Editore: Wiley-ISTE
• Anno: 2014
• ISBN:
  9781119003588
• Edizione: 1
• Argomento: Technology & Engineering
• Categoria: Materials Science

This book covers the impact of sustainable masonry on the environment, touting the many benefits of utilizing local and/or low embodied energy materials in the construction of sustainable buildings.

Part 1

Technologies and Construction Process

1

Introduction to Sustainable Masonry

1.1. Definitions of sustainable masonry

This book is particularly focused on masonry structures made of local materials, stone and earth. They are among the first materials to have been used by humans to build shelters thousands years ago and they are called, in this book, Earth Materials. In this context, earth masonry deals with adobe or compressed earth block, or rammed earth if the material is manufactured in successive layers.

This book does not particularly apply to baked clay brick and cement sand blocks, which are within the scope of Eurocode 6.

1.1.1. Sustainable constructions

Here, we consider sustainable development as defined in [BRU 87] as “a development mode that meets the needs of present generations without compromising the ability of future generations to meet their own needs”.

In this book, we will only consider the mechanical stability of masonry. However, in this introductory chapter, we consider some elements of thermal and hydric behavior, socio-economic aspects, and sustainability and environmental impacts of these structures. These elements will include references so that the reader, if he wishes, can further his knowledge of all these key aspects of sustainability.

Local materials are acquired from or near the construction site. Here, ‘near’ means a distance of about 20 km. Local materials used in construction have an impact due to their transportation. When a material is taken from on-site, as was often the case for earth, rubble stone masonry (rubble stone blocks and earth or sand lime mortar) and dry stone constructions, the impact is obviously reduced [HAB 12].

This precision concerning the implied proximity of the word “local” is important since it implies that the production of these materials cannot be completely industrialized. Materials therefore maintain a very variable composition, depending on the soil that is available locally and the geology. Therefore, it is not possible to give a standard composition of these materials. Local materials of interest here are: cut or uncut stone assembled with (rubble stone masonry) or without (dry stone) mortar, adobe and earth mortar and finally rammed earth. These materials are “earth” materials.

1.1.2. Masonry structures

By masonry structures, we refer to an arrangement of blocks hand-stacked by a mason, regularly or irregularly, with or without a mortar, over successive layers. We exclude “Cuzco rampart” type masonry or blocks exceeding one ton, quarry cut and assembled with a crane and Opus Incertum in general.

This masonry is done manually, thus is greatly dependent on the mason’s skill, but following specific rules, which form part of the mason’s skill set. We will also consider rammed earth as a part of masonry as they depend on a mason’s art, even if they do not constitute a stack of small elements but rather layers of compacted earth.

In an industrial context, “sustainable development” can be interpreted as requiring structures to be designed based on criteria, taking all environmental consequences (in the broad sense of the word) induced by these constructions into account. However, the objects discussed here are the result of a systemic approach whereby an optimum is obtained according to environmental and sustainability criteria, amongst others, which revert to being current. Vernacular architecture was erected in a context of limited resources and energy shortages, thus respecting the criteria of minimum impact on the planet. Their age provides an obviously tangible guarantee of durability. However, we must also consider the innovation that characterizes sustainable masonry, as the use of old materials in a modern context can only be achieved through an adjustment that includes innovation.

1.2. Challenges of sustainable development in construction

The use of earth materials in construction allows a technological leap in terms of sustainability. A case study shows that for structural work of this type of construction, transport of materials (expressed in t.km), that is to say the amount of mass transported over a given distance, can be reduced five-fold, and embodied energy [MOR 01] can be reduced three-fold – embodied energy is the energy required to manufacture the “product” from its design to the end of its life. [HAB 10, HAB 12] presents an alternative method for quantifying the impact of construction using earth materials, which offer notable benefits in terms of their low impact. Moreover, another case study shows that work time on the construction site is tripled: this work has a positive impact upon the economy because it requires skills [MAR 09].

1.2.1. Socio-economic aspects

Our context concerns materials and therefore structures for which new constructions are few and far between in 21st Century Europe, as they are transformed and constructed primarily by manual labor. Society’s choice of industrialization is reflected in the price of non-animal energy (electricity, oil, etc.), which is one to two hundred times cheaper than human labor [MAR 02]. Under these conditions, new constructions or restorations are hard to carry out with short term competitive costs, while the need to innovate increases; this also comes at a cost. However, there are hundreds of new structures and many more renovations carried out using masonry with earth materials. These sites provide some figures for numerical analysis. Socioeconomic aspects are the least well-covered to our knowledge, however information on these challenges can be found in [MAR 02, MAR 09, RIG 02].

1.2.2. Environmental impact

Many more studies have been carried out on environmental impact than on socio-economic aspects. General tools currently used for calculating this impact are still being developed, but mature tools already exist for industrial materials and structures. These include lifecycle analysis (LCA). These tools, despite their complexity, are inadequate for technologies and architectures using earth materials [HAB 12]. In addition, the databases necessary for their use are not yet available in the case of earth materials.

The two best-covered areas in the published literature are embodied energy and energy expended during service (mainly for heating buildings). In France, thermal regulations (RT) only apply to the consumption of service energy. With increasing generalization of construction of “passive” buildings that do not consume “external” service energy or energy efficiency, the concept of embodied energy should become more important.

[HAB 12] covers works of art, particularly dry stone retaining walls, and the case study [BAU 12] covers rubble stone masonry bridges. For earth material buildings, see [MOR 01, MAR 02, MAR 09].

1.2.3. Sustainability

Sustainability is an important point in works on earth materials, but it depends on the geology of the site, and as for all structures, the quality of maintenance. It also depends on the design, the quality of implementation and therefore on cultural, economic or political criteria. However, it should be noted that paradoxically, the trend continues to favor conventional industrial approaches and therefore constructions with low durability by, for example, decreasing the thickness of concrete and the quantities of steel used.

Compared to current design criteria, monumental constructions such as Roman bridges appear to be oversized, while more vernacular structures are undersized, for example dry stone retaining walls used in farming. In the first case, the aim was to limit maintenance work in accordance with the available manual labor force; in the other case, it was to save manual labor on rebuilding collapsed parts after a storm, if necessary.

Unsuitable contemporary renovations have a more or less significant effect on reducing the lifecycle of earth materials and can even cause their sudden destruction. These consequences are the result of two main families of errors: coatings that are not sufficiently porous, and mechanical reinforcements that are too rigid to survive earthquakes. This last point is further detailed in [FER 05]. Further details concerning the case of industrial coatings which can not be applied to earthen material walls may be found in [ECO 13].

For sustainability issues concerning physicochemical actions, such as those caused by pollution or salt, readers may wish to consult the thesis [GRO 09] for the particular case of earthen structures. There are also many publications in this field regarding stone constructions. Organizations such as ICCROM [ICC 14] (International Centre for the Study of the Preservation and Restoration of Cultural Property), the Paul Getty Trust [GET 13], have studied this area extensively.

1.2.4. Recycling and reuse

By definition, the non-industrial use of an earth material allows direct reuse (of rubble stone masonry, earth mortar and earth masonry). This practice has been used for thousands of years and is still widespread. Reuse of a material qualifies it as renewable, even if the resource is not infinitely renewable. This reuse of an earth material neither affects biodiversity nor does it tie down agricultural land, unlike intensive forestry, for example. ...