IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Research article
erdEngineering Properties of Adobe Brick for EarthStructures
NAPAT SRIWATTANAPRAYOON*
Faculty of Architecture, Rajamangala, University of Technology Thanyaburi, Thailand
Email: Napat_sr@rmutt.ac.th
Received 16 January 2014

Accepted 1 April 2014(*Corresponding Author)

Abstract The aim of this research is to investigate basic engineering properties of soil
mixture materials and adobe bricks for earth structures. The soil mixture materials consistof soil, sand and rice husks. Samples of soil mixture materials and adobe bricks werecollected from three villages (i.e. sources) in northeastern Thailand with adobe brick earth
structures. The raw materials obtained from the three sources are: (1) soil, sand and ricehusks from Baan Sikha Thai village of Nakhon Ratchasima province, (2) soil and ricehusks from Baan Sai Rung village of Chaiyaphum province, and (3) soil and rice husks
from Baan Thep Pana village of the province of Chaiyaphum. The physical properties ofsoil mixture materials and the mechanical characteristics in terms of adobe bricks and wall
bearing strength (prism strength) were carried out. According to ASTM D-2487 of theUnified Soil Classification System, the soils from the three sources are of sand-poorly
graded (SP) type. PI of soils and the horizontal compressive strength (c) of adobe bricks
from the first, second and third sources were 7.93, 6.02 and 2.88%; and 21.76, 15.76 and13.48 kg/cm2 (ksc), respectively. The findings indicate a positive relationship between
plasticity index (PI) from Atterberg’s limits test and horizontal c. A comparison wasmade between the horizontal c of adobe bricks of three sources and those specified in theUniform Building Code (UBC) Standard 21-1. The horizontal c of the first, second andthird sources relative to the UBC standard (17.6 ksc) were 21.76, 15.76 and 13.48 ksc,
equivalent to 123.65%, 89.57% and 76.57% of the standard, respectively. The horizontal
flexural strengths (fb) of adobe bricks from the three sources were 5.86, 3.24 and 4.27 ksc.
Thus, no indefinite relationship exists between fb and PI as well as horizontal c. Inaddition, a comparison between the horizontal c of adobe bricks from three sources andthe wall bearing strength (prism strength) of walls made from the identical three sources
was performed. The wall bearing strength values of the first, second and third sourceswere 9.44, 6.39 and 3.63 ksc, respectively. The results show a positive relationship ofprism strength to PI and to horizontal c. The performance of adobe bricks in terms ofgreater strength and lower shrinkage could be enhanced by inclusion of appropriatequantities of sand and rice husks in the mixture.
Keywords earth structure, adobe brick, engineering properties

INTRODUCTION
A form of architectural work, earth structures harmoniously coexist with the environment and are
perfectly suitable for the tropics. In addition, most earth structures have been designed andconstructed in line with the livelihoods of local inhabitants. Raw materials of adobe bricks which
are subsequently used to construct earth structures are mostly natural materials, e.g. clay, sand andplant fibers, and can be acquired locally and inexpensively. Besides, several reused items, e.g. glass
bottles, wooden windows and frames, are used in the construction of earth structures. Thus, earthstructures are a viable alternative to meet the housing demand of low-income earners and in linewith the concept of self-sufficiency economy, which in turn promotes the community sustainability.
The current practices of adobe brick-making are nevertheless varied by which local residents
make adobe bricks relying on their past experience and rough estimation. This leads to substandardⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2014) 5-2

adobe bricks in terms of horizontal compressive strength, horizontal flexural strength and wall
bearing strength.
Although previous research studies on improvement of adobe brick-making exist, the local
villagers prefer the traditional local brick-making methods to the improved ones. Therefore, thisresearch paper attempts to examine the engineering properties of raw materials and adobe bricks.
The findings could be adopted as a guideline in building of earth structures to guarantee thestability and safety of the final constructions.

METHODOLOGY
Determination of variables: Types of raw materials and mixing ratios are factors that affect thestrength of adobe bricks. To obtain the results that adequately represent actual outcomes, the raw
materials and their respective quantity in this research work are: 10 kg each of soil and sand fromthree sources (30 kg of soil and 30 kg of sand in total); and 35 finished adobe bricks each fromthree sources (105 ready-to-use bricks in total). The dimensions of adobe brick are 20x40x10cm(WxLxH). Figure 1 illustrates a photograph image of an adobe brick and a drawing of its
dimensions.
L=40 cm
W=20 cm
H= 10 cm

Fig. 1 Image of an adobe brick and a drawing of its dimensions
Selection criteria of sources for collection of raw materials and bricks: The selection criteria oflocations for collection of raw materials and adobe bricks are that: (1) there are a number of adobe
brick earth structures in the area; and (2) local residents are economically self-reliant. The areasfrom which the sample collection were carried out are: (a) Baan Shikha Thai village, Nhong Bua
Sala sub-district, Muaeng Nakhon Ratchasima district of Nakhon Ratchasima province; (b) Baan
Sai Rung village, Tha Mafai sub-district, Khang Kroa district of Chaiyaphum province; and (c)Baan Thep Pana village, Baan Rai sub-district, Theb Satit district of Chaiyaphum province.
Test methods: Tests were carried out on the raw materials and on adobe bricks. The raw materials,i.e. soil, sand and rice husks, were examined according to ASTM standards of the Unified Soil
Classification System. The soil grain size was classified by sieving according to the ASTM D422
standard. Atterburg’s limits of soils were performed according to ASTM D4318, while Atterburg’s
limits of soils mixed with sand were conducted according to ASTM D4318. The soils mixed withsand were obtained by crushing adobe bricks from the three sources. Soil specific gravity values
were determined according to ASTM D854. In addition, the ASTM C128 standard was used todetermine sand specific gravity and absorption values, while the sand grain size was classified bysieving as per ASTM C136. The separation of sand and rice husks from adobe bricks was carriedout using the wet sieve method.
Table 1 Physical requirement of adobe brick
Minimum compressivestrength (ksc)
21.13
17.60
(Average)(Minimum)

Water absorption(%)
2.5

Source: Table 24-B: Uniform Building Code, 1994

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Mowasture content(%)
4.0

Minimum modulus ofrupture (ksc)
3.52
2.46
(Average) (Minimum)IJERD – International Journal of Environmental and Rural Development (2014) 5-2

The strength of finished adobe bricks was tested according to the American Standard for
Testing Material (ASTM) and referenced to the UBC Standard 21-9 (Table 1). The horizontal cand horizontal flexural strengths (fb) of adobe bricks were determined according to ASTM C67-13a.
The wall bearing wall strength was tested according to the Standard Test Methods for Compressive
Strength of Masonry Prisms (ASTM E447 – 74).
RESULTS AND DISCUSSION
Engineering Properties of Soils
Based on the ASTM D2487 standard of the Unified Soil Classification System, soils from the threesources are of coarse grain, poorly-graded soil and sand. Their coefficients of uniformity (CU) andof concavity (CC) are presented in Table 2.
Table 3 summarizes Atterberg’s limits of soil and soil mixed with sand according to theASTM D4318 standard.
The specific gravity of soils from the three sources belongs to the SP group. In addition, thecomposition of soils from the province of Chaiyaphum (i.e. 2nd and 3rd sources) is 50% sand, acondition that enables adobe brick-making without additional sand required. However, soils fromNakhon Ratchasima province (i.e. first source) contain much less sand, thereby necessitating anaddition of sand to the mixture for brick-making. Thus, the specific gravity of sand of the firstsource (i.e. Nakhon Ratchasima province) was determined.
The findings also show that types and ratios of raw materials contained in adobe bricks
influence the brick strength. For example, if the bricks were made of purely or mostly soil, theywould easily disintegrate under the horizontal compressive strength and flexural strength. To
improve the brick performance, sand and rice husks should be added to the mixture because theadditional raw materials (i.e. sand and rice husks) increase the cohesiveness and strength resistance.
Table 4 presents the specific gravity values and material proportions by weight of the raw materials.
Table 2 Characteristics of soil and sand of three sources under study
SourceBaan Sikha Thai
Baan Sai Rung
Baan Thep Pana

Avg. passing
No.4# (%)
93.78490.71599.327

Avg. passing No.200#(%)
2.06<55<6.396<12
5<7.435<12Avg. Cu

Avg. Cc

2.852
6.621
3.333

0.772
0.641
1.071

Group
symbolSSS

Table 3 Atterberg’s limits of soil and soil mixed sand as per ASTM D4318
Properties
Liquid Limit, LL (%)
Plastic Limit, PL (%)
Plasticity Index, PI (%)
Shrinkage Limit, SL (%)
Unified Soil Classification, U.S.C.

Baan Sikha
Thai
21.1718.84
2.32
9.93
SP

Baan Sikha Thai
(Soil+Sand)
30.84
22.91
7.93
9.37
SP

Baan SaiRung
28.47
22.45
6.02
9.39
SP

Baan ThepPana
20.68
17.80
2.88
7.77
SP

Table 4 Specific gravity and material proportions by weight of the raw materials
SourceBaan Sikha Thai
Baan Sai Rung
Baan Thep Pana

Specific gravity
SoilSand
2.681
2.53
2.513
2.542
-Material proportion by weight (%)
SoilSandRice husk
74.75418.8006.346
90.4059.595
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IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Engineering Properties of Adobe Bricks
With respect to the effects of rice husks and sand proportions on the horizontal c, the horizontal
compressive strength values of adobe bricks for different proportions of sand and rice husks areillustrated in Table 5 and Fig. 2.
Based on Fig. 2, the relationship between the proportion of rice husks and the adobe brickhorizontal c; and that between the proportion sand retained with No.4 sieve and the horizontal cof adobe bricks can be expressed by equations (1) and (2), respectively.
Horizontal compressive strength rice husks=-1.7737(% of rice husks) + 32.96(1)

Horizontal compressive strength sand=0.2154(% of sand) + 7.3919(2)

The relationship of PI and the horizontal c is depicted in Figure 3. The figure indicates a
positive correlation between PI and the horizontal c.
Table 5 Effects of rice husks and sand proportions on the horizontal compressive strength
Propertion of mixeture materials
by weight (%)
Percent of sand retained sieve No.4#
Percent of Rice husk
Horizontal c (ksc)

Baan Sikhathai

Baan Sairung

Baan Theppana

56.096.35
21.76

51.44
9.60
15.76

26.30
11.05
13.48

Fig. 2 Horizontal compressive strength of bricks for different sand and rice husk proportions

Fig. 3 Plasticity Index (PI) and horizontal c of samples from the three sources
The relationships of PI of soils to the horizontal c of adobe bricks from the three sources canbe determined by equations 3, respectively.
Horizontal c=where PI denotes plasticity index.
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441.5492PI + 8.3092(3)

IJERD – International Journal of Environmental and Rural Development (2014) 5-2

The horizontal c, fb and minimum strength according to the UBC 21-9 standard of adobe
bricks are depicted in Figure 4. The horizontal c of adobe bricks from the first, second and thirdsources and the minimum standard strength are 21.76, 15.76, 13.48 and 17.6ksc, respectively. Thisvalidates the positive relationship between the horizontal c and PI.
Although adobe bricks from the three sources outperform the minimum standard strength withregard to fb, the bricks performed less satisfactorily relative to the horizontal c. fb of the first,second and third sources and the minimum standard strength are 7.40, 3.36, 4.27 and 2.46ksc,respectively. The low fb are normal since no additives, e.g. cement or rubber milk, were included inthe mixture.
The relationship between the horizontal c and the wall bearing strength (prism strength) isillustrated in Figure 5. The figure shows a strong correlation between the prism strength and thehorizontal c, which is similar to that of PI and the horizontal c. The prism strength of adobe
bricks of the first source is highest. The relationship between the horizontal the horizontal c andthe prism strength can be written as:
Prirm strength= 1.4346c + 7.6943(4)

Prism strength (ksc)Fig. 4 Horizontal compressive and flexural strengths of adobe bricks from three sources andthe minimum standard strengths

Horizontal compressive strength,c(ksc)Fig. 5 Relationship between horizontal compressive strength and Prism strength ofadobe bricks from three sources
CONCLUSION
The experimental results show that prism strength is subject to PI of soil and the horizontal c ofadobe bricks. The proportion of sand in the brick mixture affects the horizontal c, while anaddition of rice husks into the mixture reduces the brick shrinkage.

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IJERD – International Journal of Environmental and Rural Development (2014) 5-2

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Bunjongsiri, J. and Tiyawongsuwan, C. 2005. Study of the properties of adobe in constructing cob buildings.
B.Eng. Dissertation, Department of Civil Engineering, South-East Asia University, Bangkok.
Noonchoo, J. and Rungsimuntuchat, N. 2004. Study of the properties of adobe in constructing cob buildings.
B.Eng. Dissertation, Department of Civil Engineering, Srinakharinwirot University, Bangkok.
Khamput, P. 2008. Using rice hush ash for development strength of adobe. Department of Civil Engineering,Rajamangala University of Technology Thanyaburi, PathumThani, Thailand.
Promchote, W. 2008. Effect of clay types on strength of unburned brick a sample method for strength test.
B.Eng. Dissertation, Department of Civil Engineering, College of Engineering, Rungsit University,Bangkok.
International Council of Building Officials. 1994. Uniform building code volume 3 materials, testing andinstallation standards. New Jersey, USA.
Das, B.M. 2008. Soil mechanics laboratory manual 7th ed. Oxford University Press, USA.

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