Design and evaluation of hydraulic lime grouts for the reattachment of lime plasters on earthen walls

Abstract

A laboratory and field testing programme for the formulation and evaluation of hydraulic grouts was developed for the reattachment of lime plasters on earthen (adobe) walls. Formulations utilizing kaolin, hydraulic lime, ceramic microspheres, and fine silica sand, with and without the addition of an acrylic emulsion, were prepared and evaluated in a three-stage testing programme. Standard tests were employed to measure injectability, viscosity, set time, shrinkage, weight, splitting/tensile strength, water vapour transmission rate, and adhesive bond strength. Grout microstructure was comparatively examined using scanning electron microscopy. Of the 18 grout formulations tested, only one mixture composed of (parts by weight) 1 part microspheres, 1 part sand, 2 parts hydraulic lime, 10% part acrylic emulsion was found to meet all the essential performance criteria established.     

Predictive Tri-Linear Benchmark Curve for In-Plane Behavior of Adobe Walls

In the present study, numerical simulations are conducted to estimate the in-plane response of adobe walls subjected to pseudo-static cyclic loading based on the finite element code ABAQUS. The simplified micro-modeling approach is adopted and an interface model reported in ABAQUS material library is applied as material model for zero-thickness interface elements. The comparison between obtained results and field test data results in good agreement. Parametric studies are carried out to evaluate the effectiveness of independent parameters changes on response of adobe walls. It is noted that mechanical properties of joints and adobe units play an active role on in-plane behavior of walls. A tri-linear benchmark curve is proposed to predict the response of aforementioned walls. In this regard, a statistical study is performed to derive the predictive tri-linear benchmark curve. The regressive analysis on 59 numerical models resulted in proposing predictive models. Finally, by comparing tri-linear curves obtained from the regressive analysis, numerical analysis, and experimental study, appropriate accuracy of theoretical model can be found.     

Seismic Retrofitting Techniques for Historic Adobe Buildings

This article presents a comprehensive overview of the techniques available for the seismic retrofitting of adobe buildings. It analyzes these techniques’ viability from a structural engineering standpoint and evaluates their suitability in the context of historic preservation. Analysis was based on an exhaustive review of studies addressing retrofitting techniques of earthen structures, as well as consultation with field experts. The guiding principles of conservation relating to the structural reinforcement of monuments were taken into account. Traditional techniques that enhance the stability of the building, such as wooden ring beams, wooden ties interconnecting parallel walls, corner keys, and the addition of buttresses were found to be effective solutions since they employ compatible and low-cost materials such as earth and wood. When these techniques prove insufficient, minimally invasive measures such as introducing a plywood diaphragm, horizontal steel rods, a geomesh covered with mud rendering or a strapping system can be appropriate.     

Reburial research: preliminary field experiments at Fort Selden

Abstract

Preservation through reburial is an effective strategy for cultural sites, and information exists that identifies broad categories of fill type, materials and the below-ground physico-chemical and biological conditions that favour survival of cultural artefacts. This apart, relatively little systematic research and testing has been undertaken on the reburial of archaeological materials under alternating wet—dry conditions, which pertain in many areas of the world where rich archaeological resources exist that are also a focus of excavation. Preliminary field research and testing was undertaken at the site of Port Selden, New Mexico, over an approximate eighteen-month period in 1995–1996 as a precursor to intended longer-term experiments. The ultimate objective was to determine optimal conditions for designed reburial interventions of archaeological materials. Testing was done in pits and on the ground and utilized a standard artefact comprised of adobe and lime as well as several indicator materials (wood, textile, brass). The problems associated with the design of the experiment, instruments and monitoring are discussed, as well as findings relevant to current practice and future testing. The eighteen-month preliminary testing itself followed an earlier (1988) reburial test at Fort Selden in which adobe walls were buried. The results of this test wall experiment are also included here, as they are pertinent to an understanding of the behaviour of earthen architectural materials in the reburial environment.     

Effectiveness of FRCM Reinforcement Applied to Masonry Walls Subject to Axial Force and Out-Of-Plane Loads Evaluated by Experimental and Numerical Studies

ABSTRACT

An experimental campaign and a numerical analysis devoted to the investigation of the out-of-plane behavior of masonry walls reinforced with Fiber Reinforced Cementitious Matrix (FRCM) are presented here. The main goal of this study is to analyze and evaluate the effectiveness of the strengthening system, by discussing failure modes and capacity of strengthened masonry walls, in order to assess their behavior under out-of-plane horizontal actions, such as, for example, seismic actions. A purposely designed experimental set-up, able to separately and independently apply an axial force and out-of-plane horizontal actions on masonry walls, was used. Experimental results are discussed and compared with the outcomes of nonlinear analyses performed on simplified finite element models of the walls. A proper evaluation of the flexural capacity of FRCM strengthened walls is the first step of the ongoing process of drawing reliable code guidelines leading to a safe design of strengthened masonry structures.     

A programme for the conservation of architectural plasters in earthen ruins in the American Southwest: Fort Union National Monument,New Mexico,USA

Abstract

Plasters constitute an important component of many ruined architectural and archaeological sites. Methods for their in situ conservation have lagged far behind the field treatment of other materials due to their ephemeral nature and the lack of programmatic laboratory and field research. A preservation strategy involving documentation, stabilization, interpretation and maintenance offers a methodological approach adaptable to most contexts. A pilot conservation programme is described for the stabilization and interpretation of the lime plasters within the nineteenth-century adobe ruins of Fort Union National Monument in New Mexico. Methods of documentation, emergency stabilization, injection hydraulic lime grouting and mortar repairs are described.     

Temporary site protection for earthen walls and murals at Çata1höyük,Turkey

Abstract

The exposure of earthen architecture at archaeological sites presents tremendous difficulties both during and after excavation. While it is the intent of most reburial programmes to stabilize exposed structures against the long-term effects of loss of pressure and fluctuations in moisture, relative humidity and temperature, reburial does not easily afford practical protection against immediate damage caused during excavation. At the Neolithic site of Çata1höyük in Anatolia, Turkey, a phased programme to integrate the excavation and conservation of the site was developed. This included emergency stabilization and protection of the mud brick walls, plasters, mural paintings and relief sculpture, both during and between excavation seasons. One component of this programme included the development of a temporary perlite-vermiculite protection system.     

Aztec period houses and terraces at Calixtlahuaca: The changing morphology of a Mesoamerican hilltop urban center

Abstract

Calixtlahuaca, a Middle–Late Postclassic site in the Toluca Valley of central Mexico, was occupied ca. a.d. 1100–1530. Our excavations reveal some of the processes involved in the creation, functions, and decay of a large hilltop urban center. At its height, the majority of the site’s surface (264 ha) was covered with residential-agricultural terraces supported by a complex water management system. House construction techniques included the use of adobe brick, wattle-and-daub, and stone pavements. Our fieldwork contributes to a growing body of research on hilltop political capitals in Mesoamerica. Using a refined chronology, we illuminate the processes by which people constructed the residential zones of this ancient hilltop city.     

Synthesizing Broadband Time-Histories at Near Source Sites; Case Study, 2003 Bam Mw6.5 Earthquake

The main objective of this article is to synthesize the 2003 Bam earthquake. A hybrid method is proposed for synthesizing the near-fault broadband timehistories; a theoretical green's function method and a stochastic finite-fault approach for generating time histories at low and high frequencies, respectively. A genetic algorithm is developed to optimize the differences between synthesized and recorded ground motions.

The proposed technique can be used for dynamic nonlinear analysis of structures and site specific hazard analysis of the regions with lack of sufficient data and also for retrofitting the damaged structures during Bam earthquake, particularly the well-known adobe buildings of Arg-e-Bam.     

Analytical methods for the conservation of the Buddhist temple II of Krasnaya Rechka,Kyrgyzstan

Abstract

The methods employed for selecting the repair material for the Buddhist temple II of Krasnaya Rechka, a site located in the upper Chuy Valley, Kyrgyzstan, are described in this article. The temple is built of mud brick and was excavated during several campaigns between 1938 and 1998 with no provision being made for conservation. The first emergency protective measures were initiated in 2003 during a UNESCO project that included other sites located in the Chuy valley. Most of the eroded walls of the temple were given a temporary shelter coat of mud bricks, a method that has proved effective. The main problem after proving the shelter coat was how to assess the repair material for future conservation work (it is planned to repeat the application of the shelter coat, but with materials with improved performance). Assessment was carried out after extensive laboratory analysis of both historic and repair materials, but also after test wall construction and monitoring. The methods explained here could be of use to conservators working in similar projects in the Middle East or Asia.     

Degradation of mud brick houses in an arid environment: a geoarchaeological model

A common assumption in Near Eastern tell archaeology is that the majority of sediments originate from degraded mud bricks. Little is known about the mechanism of mud brick wall degradation. Here we present a detailed macro- and microscopic ethnoarchaeological study of the degradation of a mud brick house and propose a comprehensive mechanism for tell formation processes in arid environments. The study took place in southern Israel by trenching a ca. 60 year old abandoned mud brick house, followed by extensive sediment sampling. Macroscopic observations showed that mud brick walls degrade by collapse of single bricks and/or collapse of intact wall parts, either inwards or outwards. In addition, infill sediments within the house and outside it, in close proximity to its walls, form alternating sedimentary layers of various colors and textures. The degraded mud brick material lost its distinctive macroscopic structure, which makes it impossible to accurately identify this material by field observations alone. Mineralogical and elemental analyses established the sources of the house infill sediments, namely mud bricks and wind blown sediments. Alternating layers mostly originate from mixing between degraded mud brick material and wind blown sediments. Micromorphological observations revealed microscopic mechanisms of mud brick degradation and include processes of mud slurry gravity flows, sediment coatings and infillings, wind abrasion of walls, small-scale puddling, and bioturbation. This study provides a working scheme for site formation of abandoned mud brick structures in arid environments. It provides a set of criteria by which it is possible to differentiate floors from post-abandonment sedimentary features and thus improves the reliability of activity area research.     

The devolution of mudbrick: ethnoarchaeology of abandoned earthen dwellings in the Bolivian Andes

This ethno-geoarchaeological study considers the formation of archaeological deposits through a study of abandoned contemporary mudbrick structures on the Taraco Peninsula, Bolivia. The study site was a domestic compound with rooms for different functions that had been abandoned for over 50 years. Structures were in variable states of decay in terms of roof cover, walling integrity and abandonment fills. Geoarchaeological samples were collected from intact and weathered adobes, earthen hearths, mud plaster, and flooring. Adobes and mud plaster were locally derived from topsoil containing archaeological sediments with added gravel and plant temper. This study found a relatively light anthropogenic signature for decayed earthen houses.Rising damp exfoliated mud plaster despite un-mortared cobble wall foundations. Organic matter from roof fall attracted thriving soil faunal populations, which furthered site destruction through bioturbation, particularly packed earth floors. Sediments derived from weathered mudbrick retained little evidence of prior use as construction materials unless exposed to heat. Sediments exposed to high-temperatures produced the most distinctive rubified features but were structurally compromised. Isolated thermal features from decomposed adobe would not be distinguishable from other hearth types. Adobes exposed to low or moderate heat had few distinctive features in thin section. Intact adobes and floors that were not exposed to heat have fewer pores than natural sediments and distinctive grass inclusions. These adobes disarticulated into loose sediments when exposed to weathering. Adobe fall outside the crumbling structures blended into topsoil.This study sheds light on functional attributes of pre-Columbian construction practices. Thick, fine-textured sterile flooring is commonly encountered in the study region. This would control bioturbation from roof fall in a previous occupation enabling reconstruction in abandoned dwellings. In contrast to the contemporary dwelling, prehistoric mortared cobble foundations would resist rising damp. Cobbles without mortar may relate more to design and construction than durability. These contrasts between contemporary and prehistory construction practices reflect differences in the design, construction costs and functional use-life of adobe structures.     

A Reinterpretation of the Occupational History of the Pendleton Ruin,New Mexico

Abstract

The Pendleton Ruin, an adobe pueblo of approximately 125 rooms in the “boot heel” of sw New Mexico, was excavated by Alfred V Kidder, C. Burton Cosgrove, and Harriet S. Cosgrove in 1933. It defined the Animas phase, dated between A.D. 1150 and 1450. In this paper, the occupational history of the Pendleton Ruin is reexamined, beginning with the excavators' assumption that the lack of trash accumulation indicated a brief occupation. Based on the published report, field notebooks, and collections, it is concluded that the site was occupied longer than thought. Evidence for at least one hiatus in occupation may explain how a long occupation is compatible with low artifact yields. Evidence also points to the construction of a platform mound along the northern side of a plaza. A reinterpretation of regional settlement and social organization, focused on the role and scale of settlement instability, is presented. Finally, the results present a case study of how reanalysis of excavated materials can be a useful archaeological practice.     

Wood deterioration in Chacoan great houses of the southwestern United States

Abstract

‘Great houses’ built by the Ancestral Puebloans (Anasazi) (900–1200AD) still contain thousands of pieces of wood used as beams, secondary roof supports and lintels. The wood is an integral part of the surviving Chacoan architecture and has served as a valuable resource for determining the exact age of the structures and for obtaining information about raw material production, procurement and harvesting methods. An assessment of wood deterioration at the great houses in Aztec Ruins National Monument and Pueblo Bonito, Pueblo del Arroyo and Chetro Ked located in Chaco Culture National Historic Park in New Mexico have revealed that both microbial and non-biological deterioration was taking place. The major type of decay found throughout the structures was caused by soft-rot fungi. Cavity formation in secondary walls of conifer woods and an erosion of cell walls in aspen woods was prevalent. A brown-rot type of wood degradation was also found, primarily associated with areas of subterranean termite damage. Another form of deterioration present in some of the woods was a chemical de fibration of wood. This corrosive attack, caused by high concentrations of salts, destroyed the middle lamella between cells, resulting in a stringy mass of loosely attached fibres. Reburial of great house structures as an effective conservation strategy will require an environment that is not conducive to decay, since active wood-destroying fungi are present in the prehistoric woods. If moisture and other conditions suitable for decay exist, the wood will be destroyed and this important historical resource lost.     

Experimental Study on Postponing the Deboning of FRP Sheets in Masonry Walls

ABSTRACT

A large number of buildings all around the world are constructed of unreinforced masonry. These structures do not act well during earthquakes because of their vulnerable behavior. In last two decades, fiber-reinforced polymers (FRPs) has been used widely in seismic rehabilitation and strengthening unreinforced concrete and masonry structures. One important issue in using FRP composites for strengthening masonry walls is the inopportune debonding of composites from the wall surface; thus, in this article new methods are proposed to further delay the mentioned debonding issue. For this purpose, 13 masonry panels with 100x870x870 mm dimension are strengthened by using carbon and glass FRPs (CFRPs and GFRPs). A variety of strengthening methods such as surface preparation, boring, grooving, nailing, and plaster are used to mount FRP composites to the walls. For each specimen subjected to diagonal compression test, the loading level along with tensile and compressive diagonal displacements are evaluated. In order to assess the effect of FRP composites, four unreinforced masonry walls are tested as well. The results show 110% increase in ductility index of reinforced specimens compared to the unreinforced ones.     

Establishment of conservation,design and construction criteria for protective shelters at Fort Selden State Monument,New Mexico

Abstract

Foit Selden State Monument, located in southern New Mexico, consists of the exposed adobe ruins of a military post that was occupied from 1865 to 1981. A management plan for the site is currently being developed in which an option being considered for preservation is the construction of a protective shelter.

The process of establishing conservation, design and construction criteria for a potential shelter at Fort Selden involves the assessment of technical issues and the evaluation of public support for the criteria and purpose of the monument. The conservation concerns are based upon accepted standards for conservation and construction criteria while the design and construction standards involve a higher degree of Public concern, particularly the public expectations exerted on a historic site in the United States.

The criteria for Fort Selden are currently being codified. This paper outlines the preliminary criteria as well as the process by which these criteria will be established and meshed with the public expectations of the site. The planning process is presented and the underlying philosophies of deciding to shelter, designing the shelter and constructing the shelter. Future evaluations of the shelter's success can be gauged against these original criteria and mindset.     

The Use of Adobe in the Mormon Cultural Region

The distinctiveness of the Mormon culture region has been described by several authors. One of the items which contributes to this distinctiveness was the widespread use of adobe (sun-dried brick) in relic buildings in the region. The process of adobe making was diffused from Spanish settlements in the American Southwest, and highly modifed by the Mormon builders in the Great Basin. Adobe was initially used in almost all forms of construction because of limited timber for construction and fuel to kiln-dry bricks. Advent of the railroad prompted construction of lines to open coal mines providing a cheap fuel for brickmaking. With low-cost kiln-dried brick, adobe was rapidly replaced as a building material. Thousands of the original adobe structures still remain, however, and constitute an important element in the landscape of the region. Existing adobe structures are normally plastered over, but the distinctive architectural styles associated with the period when most were constructed make them easily recognizable.