Effect of Age and Environment on Strength of Old Baked Clay Bricks of Indus Valley Civilization

This paper presents results of experimental investigations conducted on old baked clay bricks of Indus Valley civilization of tenth century. The object of this study is to evaluate the effect of age and environmental conditions on the strength of the baked clay bricks which are about 1000 years old. The brick samples were collected from six different archeological sites at the banks of old route of River Indus in district Sanghar, Sindh, Pakistan. These specimens were tested for apparent density, compressive strength, tensile strength, modulus of rupture and the weathering effects on them during the course of time. ASTM (American Society for Testing and Materials) standard for baked clay bricks, based on compressive strength, suggests that the bricks of four sites can withstand severe weathering while the bricks of two sites are resistant to moderate weathering. These results were compared to the values of the corresponding data of bricks, of same period, obtained from the historical monuments of the world as reported in the literature. The comparison showed that the values of physical properties of old baked clay bricks of Indus valley civilization of tenth century are in agreement with that of old baked clay bricks of contemporary era. The results of this study could also be helpful for preservation of old archeological sites of Indus valley civilization.

Brick masonry is one of the ancient and most reliable methods of construction used by people throughout the ages. It is still commonly used in modern buildings [1].
The study of old baked clay bricks reveals that physical, chemical and mechanical properties of these bricks show scattered values. The values of apparent density, and compressive strength of old baked clay bricks vary from 1500-1800 kg/m 3 and 1.5-50 MPa, respectively [1].
Brick is an artificial metamorphic rock [2] and is prone to weathering and disintegration due to atmospheric and environmental effects with time, and results in less compressive strength if not baked and compacted properly [3][4][5][6][7][8][9]. To preserve masonry historical buildings and monuments [10][11][12][13][14][15][16][17], much care is needed nowadays because of high content of ChloroFlouro Carbon in atmosphere which can deteriorate baked clay bricks in short time [18]. The moisture content and the salts present in the bricks and the surroundings where these bricks are buried is also a governing factor for weathering of these bricks [19][20].
In Pakistan, there are a number of masonry buildings and archeological sites which represent its cultural heritage and national identity. Therefore, it is necessary to save these monuments of brick masonry to preserve them in their original shape and condition against such environmental and weathering effects. Thus, it is important to study the effect of age and environment on the bricks through its service life. In order to get insight of the environmental and weathering effect on old baked clay bricks, such bricks were collected from six ruined sites of Indus valley in District Sanghar, Sindh, Pakistan, on the banks of river Indus. These sites were destroyed by an earthquake that occurred in 975 AD [21]. The object of this study is to determine physical properties of old baked clay bricks such as apparent density, compressive strength, tensile strength, modulus of rupture and effect of weathering on these bricks with time.

MATERIALS AND METHOD
To study structural behaviour and resistance to weathering of historical baked clay bricks of Indus valley, the baked clay bricks were collected from six different ruined sites of district Sanghar, Sindh, Pakistan (Figs. 1-3). These sites are on the banks of old route of river Indus. Of these four were human settlements while other two were grave yards situated near these sites. These sites lie within a circle of 2 km radius. The description and Global Position of these sites is given in Table 1.

Test Specimens
To determine compressive strength, tensile strength, modulus of rupture, apparent density and water absorption ratio, three brick specimens were collected from each site and tests were conducted to determine above structural properties. Each of the following briquettes having neck section equal to 25x25mm (iii) small beam section 50x50x225mm.

Tensile Strength
Tensile strength of old baked clay bricks was determined by cutting one briquette from each baked clay brick. The size of briquettes was 76x44mm and having neck section equal to 25mm (Fig. 4). These briquettes were tested in briquettes testing machine (Fig. 5).

Compressive Strength
Cubes of 50mm size were cut from each baked clay brick and tested for compression in UTM (Universal Testing Machine) (Figs. 6-7).

Modulus of Rupture and Apparent Density
Small beam specimens having size of 50x50x225mm were sawed form each brick to determine modulus of rupture and apparent density. These plain beam specimens were tested in flexure by applying point load at mid-span of the beam.

Water Absorption Ratio
The brick specimens were oven dried at 110 0 C for 24 hours and were immersed in water at room temperature.

RESULTS AND DISCUSSION
These bricks were investigated for apparent density, compressive strength, tensile strength, and modulus of rupture, water absorption and the effect of weathering.
The results are given in Table 2.

CONCLUSION
Old