Long Term Existence of Cement Stabilized Rammed Earth Walls

It is known that researchers have valued the properties of rammed earth walls in terms of natural comfort, durability, affordability and ecofriendliness. Variety of developments has been introduced continually by them for adoption in building construction. As a result, cement stabilized rammed earth (CSRE) and cement stabilized earth bricks (CSEB) are being used today for constructing load bearing walls of houses in many parts of the world. CSRE has been practiced in Sri Lanka from 2004 and a few housing projects have been successfully completed with minimal cost. CSRE walls in randomly selected housing units in a project were investigated after a period of 13 years and found that these walls are in good condition with the protection of surface coating and little maintenance. CSEB wall junctions, soil erosion near the base of walls especially at the external gable walls are identified as defects of CSRE walls. Defects at CSEB wall junctions have been solved in recent research. Good cooling effect in these houses is highly recognized by the users. High level of supervision is required when constructing CSRE to keep its durability, strength, and especially to gain acceptability from the users.


Introduction
Rammed earth is one of the developing walling materials for wall construction in buildings in almost all parts of the world due to its features of natural comfort, Eco friendliness, low cost and durability. Over one third of the world's population live in homes built with earth, and over 70% of the earth's landmass is either pure clay or laterite [1]. Because of the shortage of building materials after World War I, use of rammed earth has comeback during 1920s [2] and new developments have been introduced for the application of rammed earth during the last few years to encourage house builders to select this technology as one of the cost effective housing options. Cement stabilized rammed earth (CSRE) was introduced to the building industry and it is presently used for constructing load bearing walls by following structural design according to New Zealand NZS 4297:1998 or any other earth building code [3].

CSRE Walling
Originally rammed earth walls were made with pure earth by ramming manually using timber and rammed earth construction was first recorded by the Babylonians in 5000 BC [4], [5] & [6]. Major centres of rammed earth construction include North Africa, Australasia, regions of North and South America, China and Europe, including France, Germany and Spain [7]. A great variety of rammed earth techniques has been used in different parts of the world by using local soils. New Zealand research has indicated that monolithic earth walls perform better under earthquake conditions than walls made of separate bricks or blocks [7]. Many rammed earth houses are still standing and it has been further developed by stabilizing earth using cement to increase its strength and durability. Cement was investigated as a good stabilizer for earth building technique due to its good binding property and high strength [8]. Cement stabilized rammed earth is a mixture of soil, Portland cement and water compacted mechanically or manually in a mould to make a dense mass. A detailed study has proven that cement stabilized rammed earth has comparable performance as a walling material [5]. Laterite soil has been recommended for cement stabilized rammed earth construction [8]. The experimental programme on durability properties of earth buildings indicated that cement content above 5% may be able to almost eliminate durability related problems. It further revealed that laterite soil available in Sri Lanka could give durable and strong walls with at least 5% cement for stabilization [9]. The basic control factors for satisfactory achievement in cement stabilization are selection of good soil, adequate cement content, proper moisture content and adequate compaction. Selection of soil for CSRE technology is taken for granted and maintained less than 30% clay content while performing the research activities on load bearing walls. On site soil has been selected through jar test as jar test has proved accurate results in previous experimental works. The composition of 5-20% gravel, 45-60% sand, 20-35% silt and clay has been recommended for better performance of wall construction. Composition can be checked by performing a jar test [9]. Careful selection of the earthen materials for a CSRE wall is required consistently to maintain the required minimum strength and each soil mix must be analyzed and tested to determine the appropriate amount of cement required to meet the minimum strength specified [10].
Cement stabilized earth compressed bricks (CSEB) have also been introduced as a new alternative walling material and it has been widely spread in the housing sector due to its affordability and suitability to the environment. According to the experimental programmes carried out, it is found that CSEB can provide stronger walls which may be used even as load bearing walls of two storey houses with different types of bond patterns [11]. CSEB has been selected for building junctions of CSRE walls in load bearing walls as vertical guides for casting CSRE walls using steel slip-form [12,13]. CSRE walls along with CSEB wall junctions have been applied in several housing projects in Sri Lanka at the initial stages of the development of CSRE technology. Instead of making CSEB wall junctions, CSRE wall junctions have been introduced later to avoid the separation cracks at CSEB wall junctions. This method was successfully applied in a house construction at Akkuressa, Sri Lanka as a cost effective technology for housing [14]. Soil can be found almost everywhere in the country at low cost. Steel or plywood timber sheet can be used for moulds when making walls so that surfaces of the wall can be finished without additional cement plaster. Hence cost can be further reduced. Use of sand can be limited in this technology as sand is not necessary for wall making. This is cost effective technology as it reduces both material cost and labour cost.
Affordable housing does not mean lack of standards. Structural design and guidelines for building rammed earth walls have been described for one or two storey buildings based on limiting geometry and axial compressive stress [6]. CSRE load bearing walls have been designed according to Masonry code of practice BS 5628: Part 1-2005 [15] and constructed in two storey houses in Sri Lanka using steel-slip form moulds for the purpose of disseminating the technology as an affordable housing method [13]. Same technology has been used for building load bearing walls of two storey houses with timber moulds and CSRE wall junctions by designing the walls structurally using New Zealand code of practiceNZS 4297:1998 [3].

2.2
Durability of CSRE Durability is a parameter which is a concern when selecting any material or method of production. Governing factor of durability is the life span of the structure, the way of treating repairs and maintenance. This is a very critical issue for an earthen structure as it is liable to attack by the environment. Earthen buildings in Spain are usually in a terrible state of decay and owners prefer to demolish them instead of repairing [16]. Many historic examples from around the world are a clear demonstration of the durability of natural earth as a material in a wide variety of building types, techniques, climates and cultures. Key factors in this success are good design and detailing followed by regular maintenance and repair when necessary [7]. With attention to construction details and with a reasonable amount of routine maintenance, simple beachfront construction can last a very long time [17]. History of earth buildings around the world provides good evidence for durability. Even earthen homes in Sri Lanka have lasted more than 100 years and it is understood that sufficient external coats for walls and width of eaves are the main requirements of protecting walls from the effect of water. Due to being constructed using soil, the structures are particularly vulnerable to decay caused by environmental factors such as rain, wind and water flow [4]. Rammed earth possesses a generally high durability but all types of rammed earth walls are porous by nature and need protection from driving rain and long term exposure to moisture [10]. Defects in rammed earth that arise after construction include shrinkage and separation cracking at wall junctions. They may be due to the deficiencies of surface coatings, poor construction methods or structural defects.
Though there are some possible defects in earthen buildings and adverse effects on durability, earth has been identified as the alternative material for building walls of houses. Shrinkage cracks can be limited if drying out of the wall is carefully controlled, the clay content of the soil reduced and movement joints introduced [7]. Despite having a long and acceptable history in architecture, many associate earth use with poverty and under-development [18]. Rammed earth technology has developed through recent research and presently CSRE has been used in most parts of the world as a modern earthen building technology. Rammed earth popularity surged again during the 1970s when resources were once again limited and there was more of an emphasis on how humans impacted the environment. Rammed earth, as one of the oldest building methods, was seen as a good alternative to the usual building materials for its abundance and its low impact on nature [2].

Objectives
This study was based on a housing project at Madampagama, Hikkaduwa in order to; i. Examine existing conditions of CSRE walls in single storey houses after 13 years. ii. Identify possible defects of CSRE walls when using for a 13 years period. iii. Find the level of maintenance required for CSRE walls. iv. Assess the user's perceptions on CSRE walls.

Methodology
Data collection was done in this study under following two procedures. a) Visit and observe the CSRE walls in houses at Madampagama housing project to cover following information of CSRE walls of randomly selected housing units. i. Wall cracks. ii. Erosion of earth walls. iii. Changes in wall finishes. iv. Repairs. v. Modifications. b) Questionnaire was filled by author to collect following information of CSRE walls through discussions with users of randomly selected houses. i. Durability. ii. Living conditions. iii. Maintenance. iv. Cooling effect.
The combination of the above two procedures will help to reveal a broader view of existence of CSRE walls after a 13 years period and to find users' perceptions on CSRE walls for housing.

Data Collection
Houses were randomly inspected (

6.
Analysis of Data 6.1 Surface Coating It was found that in all inspected housing units occupants had applied either lime wash or emulsion painton the surface of the walls, especially inside the houses. Users said that when they touch walls, earth marks remained in their hands, sometimes on their body or cloth. Donor has taken action at initial stages to plaster walls in a few houses because of the requests from users.   Table 2) in house inspections. Summary of the information collected are presented against the defects identified.

Users' Comments on CSRE Walls
Data collected from the users were tabulated in Table 3 to evaluate their comments on CSRE walls.

Conditions
Housing   Since No. 15 and 16 houses have wall separation cracks they are not satisfied with CSRE walls. They think that these walls have low durability than other walling materials. They have experience in its deterioration and highly criticized quality of construction. They mentioned that these walls may have high strength but the failure is due to poor method of construction. Users in houses No. 33, 34 and 35 happily said that they received sample houses and there are no defects.

Figure 5 -Sample Houses
CSRE walls are new technology for these users; hence they are not in position to recommend durability or strength of CSRE walls. However 11 families (84%) are living in these houses without fear. Users have experience in living in cement block work houses and they believe cement blockwork is the best method for wall construction. According to their 13 years of experience all users said that there is a good cooling effect than cement block work.

6.5
Maintenance CSRE wall existence or conditions are analyzed with respect to the method of maintaining these houses by the users during the past 13 year period. Housing units are categorized into four as follows. Cleaning is a constitute part of building maintenance activities [19]. Category A -Well maintained house where no deterioration of CSRE walls were observed. Category B -Well maintained house where surface coating has been applied on CSRE walls and painted. Wall cracks have been repaired. Category C -Poorly maintained house where surface coating has been applied on CSRE walls and painted. Wall cracks have not been repaired. Category D -Modified house House modified by the users by adding one or more compartments using cement block masonry walls, applying surface coatings, plastering walls, painting, fixing ceilings and laying floor tiles and wall tiles in kitchen and bath areas.

Figure 6 -Modified Houses
It is found that about 61% of users have taken good attempts to maintain these houses satisfactorily but 31% of users have poorly maintained due to their economic condition. All elements of building deteriorate at a faster or slower rate depending on materials and methods of construction, environmental conditions and the use of the building [19]. These families occupied these houses as a donation due to tsunami disaster in December 2004. They are not rich enough to maintain these houses as required. It is noted that some have taken to repair walls but it has failed. At the discussions with these users, the author realized that they are afraid to make changes on walls and attend modification or repairing walls as this technology is new to them.

Results and Discussion
Defects of earth buildings can assume two main forms: deficiencies of surface coatings; and, structural defects [7]. In this study it is found that most of the walls are protected by lime wash and in some walls decorated with coloured paint applied on lime wash. Therefore, CSRE walls require surface coating which should be based on soil or lime. After applying lime wash, colour painting can be applied on walls to keep a good appearance [3].  [20]. From the analysis based on defects of CSRE walls, it is found that 60% of houses are in good condition, 27% are in moderate condition and only 13% are in poor condition. When comparing the existing condition and the level of maintenance, good condition houses have been well maintained and moderate and poor condition houses have been poorly maintained during this 13 year of period. Maintaining a house, including cleaning, is necessary to fulfil its function and present a good appearance. It is highly desirable but hardly feasible to produce buildings that are maintenance free [19]. Soil erosion cases that have been noted at the base of gable side of external walls in most of the houses may be due to rain water gathered at the base of these walls. Water is a major agent of decay for earth buildings. Therefore, any routine maintenance work should primarily include measures to prevent deterioration from the effects of water [7].
It is highly recognized by the users that CSRE walls have good cooling effect in this housing project but most of the users did not make a good comment of the durability and the strength of the walls. This community needs a program on CSRE walling method and its maintenance to keep them aware on the acceptability of this technology. Since the author is continuingly carrying out development of CSRE walls in Sri Lanka, it is realized that cause of deterioration is not only due to the effect of water but also poor quality in construction in few of the houses at the later part of the this housing project. Though CSRE is one of the cost effective methods of wall construction it needs high supervision on quality control when constructing on site.

Conclusion
i. It is revealed that CSRE wall needs surface coating based on lime or earth to protect wall erosion and maintain good living conditions in the house. Colour paint can be applied to make the wall to be of good appearance. ii. Wall cracks at CSEB wall junctions, peeling of plaster and soil erosion at base of walls are the defects identified in CSRE walls after a 13 year period. Majority of users (87%) maintained CSRE walls are in a satisfactory condition while living there without fear during the last 13 years. Economical wall repairing method is to be introduced to these users with an awareness program on CSRE wall construction as they are the people now living in these houses. iii. CSRE wall junctions can be included along with proper supervision for the construction of CSRE walls to avoid separation cracks at wall junctions in future constructions. iv. It is identified by the users of this housing project that CSRE walls have good cooling effect and most of CSRE walls are still in good condition with low level maintenance. v. Three sample houses constructed under proper supervision are in good condition without any defects for 13 year and the occupants are still satisfied about the construction. Therefore CSRE wall technology needs high supervision at construction stage to keep its durability, strength, and especially to be acceptable to the users.

Further study
It is necessary to find suitable cost effective repairing methods of cracks for 13 year old CSRE walls and apply them in one house (No 15 or 16). An awareness program should be conducted for all users of this housing project regarding CSRE walling methods and demonstrate the repairing methods to enable them to attend to them when necessary.