A Case Study to Understand Rammed Earth Construction

Introduction to Rammed Earth

Soil is the most versatile material to use in the construction industry. It is been used in the construction industry in many various forms. Rammed earth is one of the fields for its application. Just like soil stabilization, it is an ancient and traditional technique that has revived again in this modern era with a different view. The use of rammed earth technique started a long ago but disappeared due to other sound materials and their better performance. Although, having several disadvantages rammed earth has reappeared as an alternate of other construction methods to save the environment. In recent times rammed earth construction industry has evolved dramatically because of its greater aesthetics and other environmental advantages.

Rammed earth is compacted earth having various material homogeneously mixed together with soil/dirt. It is very easy to apply as a normal wooden form-work and a rammer is required with little skills to act ^[1]. It can be applied as a wall by compacting soil in form-work or form of blocks by compacting it in a small mould. The application of rammed earth is evolved as the industry started using waste material in the construction as plastic bottles, waste rubber tyre, etc. construction methods to save the environment. In recent times rammed earth construction industry has evolved dramatically because of it greater aesthetics and other environmental advantages.

There are several reasons why it is popular and why it not widely accepted.

Considering its natural texture after its application is not a match with other materials in terms of aesthetics.
Having a look at its shape of application it is difficult to apply it in other than box patterns due to its necessity of sound compaction and bonding.
Construction rammed earth structure is easy but also a laborious and intensive process. Furthermore, it is very difficult to correct the work once it is completed which is indeed a disadvantage of rammed earth.
Rather than other materials which should be bought from the particular source its main ingredient soil is easily available within the surrounding which reduces the overall cost of the construction. In contrast, the cost may lift at a higher point due to the unavailability of skilled labors of its application or selecting a costly material for its stabilization.
Rammed earth is having low durability when compared to other construction practices like concrete, which makes it inadequate to apply in certain conditions.
As most of the materials used are from nature itself, the application, as well as its sustainability, depends on the surrounding environment and the practices followed.
Numerous documents have been published for the sustainability of the rammed earth construction in terms of its strength characteristics and prove it as a better construction method for certain environmental situations. Whereas, its strength and other engineering properties are depended on the selected soil of surroundings, selected additives for the stabilization and the method adopted for the construction ^[1]^[2]^[3]^[4]^[5]^[6]^[7]^[8]^[9]^[10].
Moreover, the selection of additive materials for the mixing is also a challenging part where the impact of materials on the soil as well as on the environment both has to be considered. The stabilization or mixing of soil with additives is one of the initial stages before the construction in rammed earth. Selecting appropriate additive is essential as their mixing pattern and particle size are also the factors that affect the properties of soil ^[11]^[12]. So it is advisable to select a material wisely as well as use them in finer size to have a complete mixture with soil so that proper compaction can be applied to gain more bonding and higher strength.
Application of reinforcement in the rammed earth construction has also gained its importance in both research and industry. Just like the additive material selection of reinforcement are also plays a vital role in the future sustainability of the structure. Numbers of research have proved that using reinforcement bars in rammed earth construction improves its stability in terms of performance. Although, the application of natural reinforcement and its performance still needs more research on it ^[13].

A Case Study - Application of Rammed Earth & Discussion

For a better understanding of its application, a case study of a small project is presented here. The project was conducted for the construction of rammed earth wall with the application of soil stabilization using locally available soil for a food court boundary at an educational institute. The following data will represent the method of application, the challenges they faced and solutions.

The idea was to build the rammed earth wall as a boundary to create a compound with natural materials. The area to cover by the boundary wall is 9.83 m horizontal to 5.83 m vertical. The wall was constructed in a discontinued pattern over the area having bamboo placed between two consecutive walls. The structure is having 4 foot of overall height where 1 foot is in the ground and 3 foot kept over the ground. The structure was having reinforcement bars at the centre of it up to 3 foot considering from the bottom most of the wall i.e. from beneath the ground. The reinforcement used in the structure was of 8 mm, 10 mm and 12 mm diameter of TMT bars and a normal bamboo as a natural reinforcement. All the reinforcements mentioned are used in different wall i.e. not utilized in a single wall. Each wall has only one bar placed at its centre vertically.

Layout of Area: (Dimensions are in m)

For the stabilization, we have utilized a very common and easily available ingredients cement and lime. The proportions were fixed at 5% of both replaced with the dry weight of soil. A total 14% of the water is decided to make a homogeneous mix of the soil, cement, and lime. The proportions and the water content were decided after the laboratory experiment through the standard proctor test ^[14].

During the process, we utilized two different mould of wood. The first mould was prepared from the different small size wooden planks conjoining them together with multiple clamps to form a complete shape of form-work having 4 foot of total vertical size and 3 foot of total horizontal size in to in. The first wall was constructed using mould one with bamboo as a reinforcement at the centre.

Mould 01:

The mould one was immediately discontinued after the application of the first wall due to its excessive expansion from the multiple joints and poor performance. The joint expansion also affected the wall adversely as we found separation cracks in the wall due to improper compaction resulting due to mould defect. Along with deflections and poor shape of wall, the mentioned separation crack is also observed due to the expansion of bamboo due to moisture addition. The inserted bamboo was completely dry and raw, no other treatment was provided to the reinforcement before application. The following images represent the defect of mould and wall as well.

Expansion of Mould:

Final Product of Mould 01:

To overcome the problem of unnecessary expansion due to multiple joints of mould planks we prepared another mould having continuous single plank at each side. Extra nut bolts and clamps were added to the joints to reduce the expansion due to compacted earth. The product that we had after the application of new a mould was having a very smooth and aesthetic surface with proper edges and greater strength than the old one. The second wall was constructed with a reinforcement bar of a 10 mm diameter at the centre. For the better performance wooden mould of the planks were painted from inside to reduce the effect of moisture on it.

Mould 02:

Mould 02 with Additional Clamps and Supports:

Final Product of Mould 02:

The next consecutive wall was built with the same new mould with a 12 mm diameter reinforcement bar. The same effect as previous one was observed in the wall. No further deflection in the wall or cracks was observed after the removal of form-work.

Similarly, other walls were constructed with the new mould including 10 mm, 8 mm and bamboo as a reinforcement in the walls separately. The uniform drying behavior was observed in walls in the layers horizontally. The drying of layers observed in the wall stating from the top layer to bottom layer.

Drying Behavior of Rammed Earth Wall:

The durability and sustainability of rammed earth against weathering is one of the challenging tasks to perform due to current environmental conditions. It is difficult for the rammed earth wall to withstand in the region of moderate to heavy rain. To minimize the effect of weathering and deterioration we have applied a natural cover on the surface of the wall. The cover we have provided is very popular and widely used in the rural areas to build the walls of a small houses as well as for the plastering purpose of the walls and floors. It is known as mud cover. The mud cover consists of a homogeneous mix of cow/buffalo dung, soil, and water mixed in equal proportions. The mud cover provides better aesthetics and a weatherproof plaster to the rammed earth walls.

Rammed Earth Wall with Mud Cover: