Laterite stone blocks have been used for masonry purposes in many tropical regions where they are readily available. In the western coastal regions of India, the abundance of the laterite had been utilised for the construction of permanent structures, which includes monuments like forts, temples, churches, and residential buildings. Laterite being locally available, cost effective, energy efficient and environment friendly building material in the Malabar region of Kerala and Dakshin Kannada and other parts of Karnataka makes, it is a material of choice for the present day constructions (Riza et al.,2010). The use of mobile rotary saw machine for laterite quarrying, since 1993, resulted in the large-scale production and use of laterite ashlars, in the construction industry. In spite of the advent of many new materials, laterite continued to be the predominant masonry material in the Malabar region of Kerala and coastal Karnataka (Ramaji, 2012). The provision of good quality housing is recognized as an important responsibility for the welfare of people in any country. For this, building materials based on natural resources are often used (Jagadish, 2008). The commercial exploitation of these resources often leads to various environmental problems (Veena et al., 2014). Therefore, the development of much alternative walling material made using different cementetious and pozzolonic materials will be of immense benefit to minimize the impact on the environment (Kabiraj & Mandal, 2012). Earth can be used for the construction of walls in many ways. However, there are few undesirable properties such as loss of strength when saturated with water, erosion due to wind or rain and poor dimensional stability (Modak et al., 2012). These drawbacks can be eliminated significantly by stabilizing the soil either with cement or lime. But for the production of cement, very high amount of energy is needed. The carbon dioxide emission was found to be nearly 1 ton for every 1ton production of cement. This harmful effect on environment can be reduced by the effective usage of resources (Amin, 2013). Hence, the new technology focuses on stabilized compressed earth block development incorporating an industrial by-product material, which is vital for the future construction (Riza et al., 2010). The added environmental advantage of utilizing industrial by-products available in the country will further improve the sustainability of masonry brick production (Nagaraj et al., 2014).

The main objective of this experimental work was to study the properties of fabricated bricks for the various percentage proportionate like combination of 92% laterite soil + 3% cement + 5% fly ash, 90% laterite soil + 5% cement + 5% fly ash, 88% laterite soil + 7% cement + 5% fly ash.

1.1 Materials Used

1.1.1 Laterite Soil

The disturbed laterite soil was collected from the laterite quarries of Hosanagar, Chandragutti, Thyagarti and Anandapura of Shimoga district, Karnataka. The residue (disturbed) laterite soil available after dressing of natural laterite building blocks was used, which is reddish brown in nature classified as A-2-7(0) using the American Association of State Highway and Transportation Officials (AASHTO) soil classification system and GP by the United soil classification system, and is shown in Figures 1 and 2. The physical and chemical properties of testing laterite soil are given in Tables 1 and 2, respectively.

Figure 1. Surface Texture of Laterite Blocks before Dressing and After Dressing

Figure 2. Residue Laterite Soil Available After Dressing and Passed through 4.75 mm is Sieve for Production

Table 1. Physical Properties of Laterite Soil

Table 2. Chemical Properties of Laterite Soil

Fly ash used was obtained from Grasim Industries, Harihar, Karnataka, india.

1.1.3 Cement

Cement used in this investigation was Ordinary Portland Cement (OPC-43 grade), which satisfies the requirements of IS: 8112-1989 specifications.

1.1.4 Water

Ordinary potable water free from organic content, turbidity and salts was used for the mixing and for curing throughout the investigation.

1.2 Experimental Procedure

For the production of pressure moulded laterite brick, the 4 kg of laterite soil was taken for each brick, based on the size of mould, soil was spread on clean and flat hard surface, to this known percentage of stabilizer (cement + fly ash) was added on weight basis followed by thorough hand mixing to the get uniform mix, finally potable water (calculated as per optimum moisture content) was added to the dry mix by sprinkling, soil was mixed with water gently but quickly, and care was taken to avoid formation of lumps in it during mixing. Entire mixing was carried out in an enclosed area and nearer to the compressing device, to avoid the evaporations of moisture content in the mix and to maintain the workability of wet mix. As soon as the wet mixture was prepared, the homogeneous mix was transported to compacting machine for pressing. The wet mix was placed on known size of the mould and compacted through hydraulic pressure. After compaction, the mould was taken out from the machine in ejection process. Further, brick was lifted carefully from the mould base plate and placed in an open dry place. Since the bricks are not burnt and less initial handling strength, extra care was taken while lifting, placing and stacking of the bricks.

The Hydraulic press paver block and brick making machine was used for the production of bricks. The bricks produced having uniform dimension of 230 x 100 x 75 mm. A net load of 10 tonne was applied a over cross-sectional area of 23000 mm² of the brick. Since there was a constant compaction effort on all the bricks, there was less variation in strength characters of bricks that are produced and expected advantage of this research work. Due to heavy compaction, the difficulty of brick ejection from the mould may occur due to generation of suction pressure at the corners of mould.

The curing method used in this investigation was “Hay curing”. The paddy straw was spread over bricks, such that it completely covers them. The bricks were cured in sprinkling water gently on straws, thrice a day as shown in Figure 3. The curing was continued for 7, 14, 21, and 28 days based on the testing.

The following tests were conducted for stabilized laterite soil bricks.

Figure 3. Production of Laterite Stablized Soil Bricks, Curing, and Testing

1.2.1 Dry Compression Test and Wet Compression Test

The bricks were dried in sunshine for 2 to 3 days to remove moisture content inside the bricks completely for dry compression test. To conduct wet compression test, completely dried bricks were immersed in water for a duration of 24 hours. The bricks were than removed from water and the wetted surface was wiped out cleanly for test. For each average result five bricks per set were taken and the bricks were tested for compression as per IS: 3495- Part (1)-1992 specification on each specimen. The test results were tabulated in Tables 3 - 8.

Table 3. Test Results of Stabilized Laterite Soil Bricks (C3) Produced from Combination of 92% Laterite Soil + 5% Fly Ash + 3% OPC

Table 4. Test Results of Stabilized Laterite Soil Bricks (C5) Produced from Combination of 90% Laterite Soil + 5% Fly Ash + 5% OPC

Table 5. Test Results of Stabilized Laterite Soil Bricks (C7) Produced from Combination of 88% Laterite Soil + 5% Fly Ash + 7% OPC

Table 6. Average Dry Compressive Strength and Strength Ratios Test Results of Stabilized Laterite Soil Bricks

Table 7. Average Wet Compressive Strength and Strength Ratios Test Results of Stabilized Laterite Soil Bricks

Table 8. Comparitive Test Results of Burnt Bricks and Stabilized Laterite Soil Bricks

1.2.2 Absorption Test

The dry weight (W_dry) of the bricks was taken and then it was dry immersed completely in clean potable water for 24 hours. After 24 hours, the bricks were removed from water and the wet surface was wiped out with a clean cloth and the weight was taken (W_wet) as per IS: 3495-Part (2)-1992 wet specification. The absorption was given by the relation,

(1)

Five bricks per set were taken and the average of five results was considered as 'Water absorption' of the bricks. The results were tabulated in Tables 3 - 8.

1.3 Experimental Results

Tables 3 to 8 give the test results of stabilized laterite soil bricks produced from various combinations of the laterite soil + fly ash + OPC.

• From the results mentioned in Table 3, it was observed that 5% fly ash + 3% OPC stabilizer is sufficient in order to get the minimum required strength within 7 days of water curing and less water absorption satisfies IS specification.
• From the results mentioned in Table 4, it was observed that addition of 5% fly ash + 5% OPC stabilizer gives more than the required strength within 7 days of water curing and further reduces water absorption as the stabilizer percentage increases from 3 to 5%.
• From the results mentioned in Table 5, it was observed that addition of 5% fly ash + 7% OPC stabilizer gives more than the required strength within 7 days of water curing and water absorption also within the limitation, but not appreciable increase in results compared to as mentioned in Tables 3 and 4.
• From the average dry compressive strength results mentioned in Table 6, it was observed that C3 bricks give the required strength within 7 days of water curing and strength ratio is not much appreciable as the percentage of stabilizer increases further.
• From the average wet compressive strength results mentioned in Table 7, it was observed that C3 bricks give more than the required strength in wet condition also that is within 7 days of water curing and strength ratio is not much appreciable as the percentage of stabilizer increases further.
• From the ratio of dry and wet compressive strength results mentioned in Table 8, it was observed that C3 bricks give twice the required strength in both dry and wet conditions that is within 7 days of water curing and three times the required water absorption.

Based on the experimental results, the following observations and discussion were made.

2.1 Observations

• It has been observed that at increasing in the OPC content along with fly ash and use of hydraulic press paver block and brick making machine for brick making process, density of stabilized laterite soil bricks increases, in turn it increases the compressive strength and reduces water absorption. Maximum dry (11.47 N/mm²) and wet compressive strength (9 N/mm²) can be obtained at the age of 7 days of curing period; further strength can be obtained at the age of 28 days of curing period.
• It has been observed that from the test results of stabilized laterite soil bricks, the minimum of 3% and maximum of 7% OPC content along with 5% fly ash is sufficient in the order to obtain required dry (9.93 N/mm² to 14.04 N/mm²) and wet compressive strength (5.17 N/mm² to 9.56 N/mm²) and resistance to water absorption values (5.56% to 1.85%).

2.2 Discussion

• Stabilized laterite soil bricks prepared in this experimental investigation were more stable than the traditional burnt red clay bricks to resist higher compressive loads and absorb very less water. Thus higher the compressive strength of the brick, higher will be the serviceability of the wall, thus increasing serviceability/durability of the structure in case of load bearing walls too. Further, laterite soil, being more acidic in nature, not suitable for the process of traditional brick making, stabilisation of such a soil with stabilizers like cement, lime, pozzolana will enable in preparing stabilized laterite soil bricks. Production of laterite soil bricks do not require any heat treatment process to gain required compressive strength. Finally, stabilized laterite soil bricks are more economical and environmental friendly construction building material compared to conventional red clay bricks and it decreases threat to the environment by deforestation and by Global warming.

Based on the experimental results, the following conclusions were drawn,

• It can be concluded that the compressive strength shown in stabilized laterite soil bricks are nearly twice and in some cases, more than twice the strength of red clay bricks, which satisfies requirements of IS: 3495-Part (1) - 1992 specification.
• It can be concluded that the percentage of water absorption shown by stabilized and laterite soil bricks are less than 20%, which satisfies requirements of IS: 3495-Part (2) - 1992 specification.
• It can be concluded that stabilized laterite soil bricks fall under class 7.50 to class 12.50 of bricks category according to IS:1077-1992 specification.
• It can be concluded that strength and durability properties of the stabilized laterite soil bricks can be increased with the addition of stabilizer further, but not economical.
• It can be concluded that stabilized laterite soil bricks can be used as a substitute to tradational burnt red clay bricks for construction purposes.