Production and characteristics of stabilised interlocking mud blocks

This paper presents an ideology over physical and mechanical properties of interlocking and non interlocking stabilised mud blocks. These properties are useful to assess the performance and behaviour of load bearing masonry structures. This paper also compares the results of both non interlocking solid stabilised mud blocks (NSMB) of size 230 X 190 X 100 mm and interlocking solid stabilised mud blocks (ISMB) of sizes 230 X 190 X 80 and 230 X 190 X 70 mm. These blocks are tested for block density, Initial rate of water absorption, water absorption, wet compressive strength, flexural strength and Modulus of Elasticity. From the results obtained it has been found that shape and depth of interlocking has significant effect on properties of blocks. Flexural strength of 20mm (ISMB 20) and 30mm (ISMB 30) depth interlocking solid stabilised mud blocks produced are very much comparable with NSMB. Flexural strength of ISMB’s has been tested in both the directions of interlocking effects of blocks which has given satisfactory results. This test shows that Shape considered for interlocking blocks do bond well with filler materials. Mechanical and physical properties of both ISMB and NSMB have exceeded the minimum requirements of blocks as per codal provisions.


Introduction
Energy, Economy and Environment are the major areas to be carefully utilized by any nation.Increase in use of existing available natural materials leads to higher levels of pollution and ultimately results in exhaustion of these materials and also leading to many natural disasters [4].At the same time natural resources need to be safeguarded and reusable materials to be produced at affordable cost to sustain economic growth.Hence it is high time to shift focus on usage of less or no carbon emitting materials for a sustainable growth [1].A simple solution to cater the problems of Energy, Economy and Environment is to depend more on locally available materials to satisfy needs which are being used abundantly [6] [8].Even though bricks used for construction purpose is locally produced energy involved in production and transportation is high.Hence there is a need for sustainable alternative solution.
Human beings have used mud to build structures since the days of Egyptian and Mesopotamian cultures.Earliest examples of Soil-cement housing in India can be seen at Karnal in today's Haryana in year 1948.However there has been a drastic increase in construction of dwellings using soil-cement blocks in Bengaluru since 1988.[2] [4]As compaction of soil improves its strength properties, utilisation of pressed soil block in construction of masonry structures has gained popularity. Development of pressed soil block construction in India advanced rapidly due to the research at CST (Centre for Sustainable Technologies) formerly ASTRA, in Indian Institute of Science [5].A new machine was developed by ASTRA in 1979 called "ASTRAM" which was lighter and more flexible than other presses.Astram has been utilising for producing soil-cement blocks during 1980-  [7]Later an improved machine called "ITGE VOTH" was developed.Later a further improved machine was developed called "MARDINI PRESS '' for better,easier compaction and handling.This machine is now widely used at many places in India.Blocks produced using this technology have performed well during the recent past hence people started experimenting with different sizes and shapes in order to produce the most pleasing effects on dwellings constructed [10].
There are various types of interlocking stabilised mud blocks being produced in different parts of the globe.[12]Interlocking size and shape varies from region to region.These interlocking blocks can be classified into two type's one with circular hollow grooves interlocking effect blocks and the other solid interlocking effect blocks.Solid interlocking block being produced in the market has an interlocking effect between 5 to 10mm in both horizontal and vertical directions [11].This paper presents studies on size of interlocking effect of two different dimensions one with 20mm and another with 30 mm. [9][13] [5] Interlocking effect has been provided only in horizontal direction since blocks can be produced with available existing mould rather than preparing a new mould to produce these blocks.

Objectives of the study
In the present construction scenario there are various structures which are being built by using stabilised mud blocks.It is reported by many researchers that stabilized mud blocks are less energy intensive as they are made from locally available soils and a small portion of stabilizer with a simple machine that operates using manual labour.This aspect of sustainability can be further improved by producing interlocking stabilized mud blocks.However there is very little information about interlocking effects in solid stabilised mud blocks.Thus an attempt is made in this direction to evaluate the mechanical characteristics of solid stabilised mud blocks with and without interlocking effects.

Literature review
Considerable amounts of research have happened in usage of interlocking effect in concrete blocks and burnt clay bricks but there are few articles which are completely dedicated for interlocking in stabilised mud blocks.Further the studies on interlocking in stabilised mud block technology is focussed on having interlocking effects by providing hollow effects in blocks which can also be filled with grout and/or steel rebars.Some of the earlier studies on interlocking effects are discussed below.
[3] have studied factors affecting non uniform properties of interlocking stabilised compressed earth blocks.These interlocking blocks were produced with groves within it ie hollow effect.They have concluded that usage of these interlocking blocks have reduced strength parameters such as compression, density, water absorption, flexural strength, and splitting tensile strength tests.However these blocks have satisfied minimum requirements for load bearing masonry constructions.
[4] have studied on axial compressive behaviour of rubberized interlocking masonry walls with hollow effect type interlocking blocks using crumb rubber.Results have revealed that hollow and grouted specimens, posses' strength which is 15 -20% lower when compared with conventional interlocking masonry walls.However these blocks are more ductile because of utilisation of crumb rubber in its production process.
[5] have worked on understanding the characteristics of hollow effect type dry-stack interlocking compressed earth blocks by conducting compression and indirect tensile strength test on blocks.Produced samples were tested at an age interval of 7days till 28 th day in order to determine the compressive strength characteristics of soil through cylindrical blocks.Results have ranged between 1.20-1.39MPa for 5%, 2.16-2.67MPafor 10% cement stabilised samples.Indirect tensile strength varied between 0.4 to 0.75MPa.[6] studied the flexural strength of different types in compressed stabilized earth -bricks, solid blocks, interlocking solid and hollow blocks and rammed earth.A very low level of pre compression was introduced for determination of flexural strength through masonry wallets.They have concluded by stating that all the types of bricks, blocks and rammed earth can be considered as safe and viable alternative solution for load bearing and internal walls up to 2 storied houses.[7] understood compressive strength, stress-strain relationships, and elastic properties of stabilised masonry blocks.6, 8 & 12% cement by weight of mix was used for block production and various combinations of mortars.They have concluded that masonry modulus increases as the block strength increases.The block strength will be increased with increase in cement content.
It can be observed through these literatures that a considerable amount of research is on-going in production of interlocking SMB.Interlocking stabilised mud blocks with circular hollow grooves have reduced strength carrying capacity when compared with plain stabilised mud blocks.This paper focuses on overcoming this issue and mainly emphasizes on understanding the characteristics of both non interlocking and solid interlocking stabilised mud blocks.

Methodology
Present study has two parts, Initial part as production and second part as characterization of stabilized solid mud blocks with and without interlocking effects.In order to produce blocks, an interlocking effect of 20mm and 30mm has been considered.These blocks have extensions in bottom and openings at top.These extensions and openings produce interlocking effects in masonry walls when placed one above another.120x 190 mm extensions and openings are provided for both types of interlocking blocks produced.Extensions and openings are tapered with 1:1.5 leading to 10mm for 20mm depth and 15mm for 30mm depth interlocking blocks.In order to understand the characteristics of produced solid stabilised mud blocks with and without interlocking effects tests such as dimensionality, density, wet compression, water absorption, Initial rate of water absorption, flexural strength and modulus of Elasticity have been studied.Since modulus of elasticity is a material property it has been conducted only on stabilised mud blocks without interlocking effects.However the remaining tests are conducted on both types of blocks Soil used in this investigation was sourced from soil excavated for hostel building in JSS Science and technology university campus located in Mysuru, Karnataka.Soil mixture had 78% of sand and silt & clay constituted to 22%.Liquid and plastic limits of soil are 36% and 15.25% respectively.Using this soil along with 7% cement as stabiliser blocks have been produced using ITGE VOTH.Blocks were cured for 28 days under wet burlap.Fresh density of 2.05 g/cc, has been maintained throughout production process for all three types of solid stabilised mud blocks.Non interlocking stabilised mud blocks with size 230 X 190 X 100 mm, interlocking stabilised mud blocks with an overall size of 230 X 190 X 80 mm and 230 X 190 X 70mm have been produced.Reduction in size of interlocking blocks is because of extensions and openings which have been introduced for production of special types of blocks.Interlocking effects has been provided by using wooden moulds.Produced blocks are shown in

Dimensionality test:
Dimensionality test has been carried out to determine average dimensions of blocks produced.Twenty blocks are randomly selected and laid on level ground.Blocks were arranged on a surface which is free from any unevenness.Blocks were laid lengthwise, width wise and depth wise.Total length of all the blocks was measured using a steel tape in one stretch and then average measurements were determined.Table 3.1 shows different dimensions of blocks arrangement and average dimensions of blocks.

Block Density:
In order to determine block density, 12 samples were randomly selected out of the produced blocks aggregating to minimum 4 from each type.Blocks were free from loose particles and were oven dried in order to remove moisture.Results of the same are tabulated in Table 3.2.Average block density of all the three types of Stabilized earth blocks produced is found to be 1.86 g/cc which is greater than 1.750 g/cc.

Initial rate of water absorption (IRA):
In order to determine IRA, 12 blocks were selected and were positioned lengthwise (Fig 3 .1)so that immersion of either extensions or opening faces only is avoided for interlocking blocks.The blocks were immersed in water bath of 2.5cm depth for duration of 1 minute.Weight of blocks before and after immersion in water was noted and average IRA was determined.Average IRA value is found to be decreasing as depth of block is reduced as observed in Table 3 12 blocks were randomly selected to determine wet compressive strength of block.The test has been carried out in Compression Testing Machine.Prior testing-void spaces created because of extensions and openings in interlocking blocks and frogs of non interlocking stabilised solid blocks were filled with 1:2 rich cement mortar and were soaked in water for 48 hours.Load was applied axially at constant increasing rate at 14 N/mm 2 /min till failure.Ultimate load at which unit failed was noted.
Readings are tabulated in Table 3.5.Wet compressive strength of the NSMB is 3.10Mpa which clearly shows that blocks belong to grade 2.5.However the strength and grade increases with increase in depth of interlocking for same soil mix proportion and same quantity of stabiliser.This is due to apparent strength increase due to platen friction effects in testing machine.Web splitting, vertical cracking and face spalling were common modes of failures observed during testing.In order to determine flexural strength of non interlocking and interlocking solid stabilised blocks 3 point loading arrangement was applied and tested in CBR apparatus with a rate of loading of 1.25mm/minute.Interlocking solid blocks were tested for both directions ie along direction of interlocking effect and perpendicular to direction of interlocking effects.

Conclusions:
With reference to investigations carried out following broad conclusions can be drawn: Size and shape of blocks: • Blocks were produced by making slight modifications to existing mould.
• With the same mix and machine we were able to produce all the three types of blocks i.e. noninterlocking solid stabilised mud blocks, interlocking stabilised mud blocks with 20 and 30 mm interlocking effects respectively with ease and fine edges.Strength Parameters: • Wet compressive of ISMB 20 and ISMB 30 is around 4 MPa and hence can be considered for load bearing masonry construction.However the NSMB falls to Grade 2.5 which can be considered for G+ 1 storied structure.• Blocks exhibited good flexural strength.Interlocking stabilised mud blocks too exhibited good flexural strength which concludes that the blocks will adjoin with the filling material i.e. mortar in both the directions.
This study has facilitated for further research in this area leading to production and usage of solid stabilised interlocking mud blocks.In non interlocking solid stabilised mud blocks, bond between mortar and block plays a major role in understanding bond strength.However, by providing interlocking effects in blocks this strength can be improved because of presence of interlocking effect along with mortar.Increase in bond strength will increase lateral load carrying capacity of a masonry wall.Enhancement in lateral load carrying capacity of masonry wall reduces the damages to a structure during a natural disaster.This leads to a sustainable infrastructure development as there will be less damages and casualties during a natural disaster.

Fig 2 . 1
Fig 2.1 Blocks produced with and without interlocking effects

Table 3 .
1 Dimensionality test measurements for Stabilized Earth Blocks

Table 3 .
3 Initial rate of water absorption in solid stabilised

Table 3 .
.3.4Water absorption of stabilised solid3.4Waterabsorption12selectedblocks were immersed in curing tank (cold water) for 24 hours.Wet and dry weights were noted down.Average water absorption of all the three types of blocks is tabulated in Table3.4 which is in accordance with IS 3952-1998.

Table 3
Results in both directions 1282 (2023) 012011 provided similar results but change in values can be observed in table 3.7 and table 3.8 because of change in moment of inertia value and not because of increase or decrease in load carrying capacity of interlocking solid stabilised mud blocks.All the blocks failed by bending.NSMB and ISMB30 behaved in similar fashion i.e. blocks failed by inclined shear as shown in Fig 3.6.Whereas ISMB20 were broken into two pieces which shows the brittleness of the blocks as shown in Fig 3.7

Table 3 .
7 Flexural strength test of stabilised solid blocks (perpendicular the direction of interlocking)

Table 3 .
8 Summary of the results obtained.