EPOKA UNIVERSITY Tirana, ALBANIA 2011 Faculty of Engineering and Architecture Department of Architecture Arch 322 Historical Environment and Conservation Lida MIRAJ Lesson 6. Historic Building Survey, Inspection and Recording. Design, relief, environment. Diagnosis of Building Failures.
EPOKA UNIVERSITYTirana, ALBANIA2011Faculty of Engineering and ArchitectureDepartment of ArchitectureArch 322Historical Environment and ConservationLida MIRAJLesson 6
History of Architectural Techniques. The informative and methodological aspect, the traditional architectural cultures, their language system and the technique-constructive aspects. Architectural relief and the critical reading of specific examples.
Vitruvius, writing around 25 BC in his Ten Books on Architecture, distinguished types of aggregate appropriate for the preparation of lime mortars. For structural mortars, he recommended pozzolana, which were volcanic sands from the sandlike beds of Puteoli brownish-yellow-gray in color near Naples and reddish-brown at Rome. Vitruvius specifies a ratio of 1 part lime to 3 parts pozzolana for cements used in buildings and a 1:2 ratio of lime to pulvisPuteolanus for underwater work, essentially the same ratio mixed today for concrete used at sea
In most usage, the raw concrete surface was considered unsightly and some sort of facing was applied. Different techniques were characteristic of different periods and included:
Roman concrete (also called Opus caementicium) was a material used in construction during the late Roman Republic through the whole history of the Roman Empire. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern Portland cement. By the middle of the 1st century, the material was used frequently as brick-faced concrete, although variations in aggregate allowed different arrangements of materials. Further innovative developments in the material, coined the Concrete Revolution, contributed to structurally complicated forms, such as the Pantheon dome.
Concrete, and in particular, the hydraulic mortar responsible for its cohesion, was a type of structural ceramic whose utility derived largely from its rheological plasticity in the paste state. The setting and hardening of hydraulic cements derived from hydration of materials and the subsequent chemical and physical interaction of these hydration products. This differed from the setting of slaked lime mortars, the most common cements of the pre-Roman world. Once set, Roman concrete exhibited little plasticity, although it retained some resistance to tensile stresses.
The setting of pozzolanic cements has much in common with setting of their modern counterpart, Portland cement. The high silica composition of Roman pozzolana cements is very close to that of modern cement to which blast furnace slag, fly ash, or silica fume have been added.
Italy, Rome, via Appiaantica, tomb. The remains show the internal core of the building, made in roman concrete (cementizio: opus caementicium).
Opus Caementiciumwas the core of every Roman wall after the 2nd century BC. Mostly walls made in opus caementicium were covered with other materials to make a more robust and workable surface. Opus caementicium is a construction technique using an aggregate, water and a binding agent. The aggragate functioned as a filler like gravel, chunks of bricks or stones and rubble. The binding agent is usually called mortar like lime, gypsum or pozzolana (nowadays (Portland) cement is used).
Most Roman buildings are made up of opus caementicium, a sort of concrete which was laid into timber structures until it hardened. The resulting walls were very solid, but not nice to see, so very often some sort of facing was applied.
The Romans developed a very effective kind of mortar by mixing pozzolana, a volcanic ash of the region around Naples, with lime; they obtained a cement which was resistant to water. In his work De Architectura (a treatise on architecture dedicated to Emperor Augustus) Vitruvius so described pozzolana: There is a species of sand which, naturally, possesses extraordinary qualities. It is found about Baiæ and the territory in the neighbourhood of Mount Vesuvius; if mixed with lime and rubble, it hardens as well under water as in ordinary buildings. This seems to arise from the hotness of the earth under these mountains, and the abundance of springs under their bases, which are heated either with sulphur, bitumen, or alum, and indicate very intense fire. The inward fire and heat of the flame which escapes and burns through the chinks, makes this earth light; the sand-stone (tophus), therefore, which is gathered in the neighbourhood, is dry and free from moisture. Since, then, three circumstances of a similar nature, arising from the intensity of the fire, combine in one mixture, as soon as moisture supervenes, they cohere and quickly harden through dampness; so that neither the waves nor the force of the water can disunite them.
Terracina (provinciadi Latina, Lazio, Italia), tempiodiGioveAnxur,
fiancodellaterrazzasu cui sorgevailtempio, in Opus incertum.
Opus incertumUsing irregualar shaped and random placed uncut stones or fist-sized tufa blocks inserted in a core of opus caementicium, used from the beginning of the 2nd century BC, later superceded by opus (quasi) reticulatum
Opus (quasi) reticulatumSmall square tufa blocks placed diagonally to form a diamond-shaped mesh pattern, often supllemented by other materials at frames of windows and doors or at reinforments at corners of buildings with oblong tufa blocks
In early usage (often called the "Etruscan way"), the joints between the blocks introduce discontinuities, making the blocks uneven. Examples of such construction can be found in reservoirs, basements, terrace walls, and temple podiums in Etruscan cities and Rome.
Subsequently (the "Greek way"), the blocks would be placed in one of two rotations. "Stretchers" would be placed so the longer side was on the face of the wall, and "headers" would be placed so the shorter side was on the face of the wall, and would thus extend further back into the wall thickness. Various patterns could be produced by changing how the blocks were placed, and it was common to strengthen the wall by ensuring that the joints between blocks were centered over the blocks in the row below.
The earliest walls built in Europe were constructed placing stones one upon the other without any mortar to bind them together (dry-stone walls). Near Rome examples of such walls can be seen at Alatri, Segni and at other locations south of the city: they are called cyclopean, because archaeologists felt that only the mythical Cyclopes could have moved the enormous boulders which made up these walls.Improvements in the tecnique used for cutting stones led to the construction of walls with stones having the same size (Isodomum - Vitruvius - De Architectura). In order to strengthen the wall, blocks were placed alternately with the longer side (stretchers) or the shorter side (headers) on the face of the wall (opus quadratum).Romans were so fond of the texture effect of opus quadratum that they continued to use this technique even after having developed more effective kinds of masonry. The wall built at Forodi Augusto with the blocks projecting from the surface inspired Renaissance
Opus vittatum was a ancient Roman construction technique, sometimes square with tuff blocks intersected by one or more brick-bands at regular or irregular distances, and Opus caementicium.
This technique was mostly used to erect high walls, as in the Baths of Caracalla and the Aurelian Walls in Rome.
With the introduction of Roman concrete, continuous outer walls were often constructed, with some blocks laid as headers in order to attach to the inner wall. Tile or marble can be found cemented to such walls, but this was less common for those structures that were particularly load-bearing, such as arches and pillars used for bridges and aqueducts.
Oblong or occasionally square tufa blocks intersected by one or more brick bands, at regular or irregular distances. Square blocks (re-used reticulate blocks) appear mainly in third century masonry. After that they disappear as building material. Opus vittatummixtum has two subgroups: A and B. The distinction is made purely for chronological reasons.
From the Severan period throughout late antiquity.
Opus vittatummixtum A(wall facing) Alternating oblong tufa courses and brick bands, 1:1. Tufa blocks usually rather well cut. From the early third century throughout late antiquity. Main appearance in the third and fourth century.
Opus vittatummixtum B (wall facing) Alternating oblong tufa courses and brick bands, in all other combinations than 1:1. Oblong, often rather egg-shaped tufa blocks appearing in an irregular number of courses, and alternated at irregular distances with one or more courses of brick. Main appearance in later fourth century. Continuing until the Mediaeval period.
Opus vittatum simplex(wall facing) Oblong tufa blocks without any other interference. Blocks very well cut during the Republic and early Principate. From the last decades of the Republic mostly found in combination with opus reticulatum. In late antiquity an increasing tendency to egg-shaped blocks, which appear in the fourth century. From the Republic until Nero. Re-appears in the third century.
Masonry of reticulate (small tufa blocks placed diagonally) reinforced and/or intersected by brick bands (normally five to six courses). The reticulate and the bricks are sometimes interlocking. The reticulate fields are rather large.
Opus craticiumTerm both used for wattlework and walls of half-timer construction, filled in with stones and/or staw and plastered with mortar
Opus signinum(floors and walls) Waterproof floor- and wall-revetment consisting of mortar mixed with terracotta sherds and crushed tiles or bricks.
The Romans learned from the Etruscans the use of arches to make large openings in a wall; the gates of the Etruscan towns (see for example Arco Etrusco at Perugia) show the first examples of arch. The laws of Physics explaining the conditions required for an arch not to collapse were not fully understood until the XIXth century; yet the Etruscans, and after them the Romans, developed empirical methods for designing arches which still stand more than 2,000 years later.
An important aspect the Romans paid attention to was the choice of materials: travertine proved to resist stress with limited strain and was widely employed to build arches. Roman architects found also a way to link the arch to the wall which was both effective from a structural viewpoint and decorative from an aesthetic one.