By Eng.Dr. R.O. Onchiri, Mrs. B. Sabuni, Kiprotich James

Abstract

Sugarcane bagasse ash (SCBA) is a by-product generated by burning bagasse in boilers of sugar and ethanol plants and consists mainly of silica (SiO2); a characteristic that indicates the ash’s potential for use as a supplementary cementitious material in ordinary cement-based mixes for the production of low-cost building earth blocks.

This study presents the potential use of sugarcane bagasse ash as a partial replacement for cement to stabilize self-interlocking compressed earth blocks (SSIEBs) using various bagasse ash contents (0.0%, 1.6%, 3.2%, 4.8%, 6.4% and 8.0% by weight of total mix).

Rationale for study

The poor housing conditions and its quick deterioration in developing countries necessitates finding appropriate low-cost cost and stronger building materials from local materials. When cement is used to stabilize soil, the cost of construction is high and soil’s shrinkage increases with the increase in cement content. (Adam, 2001).Building materials such as fired clay bricks, lime and Portland cement are energy based and hence prove to be expensive.

Objectives

To establish the potential of sugarcane bagasse ash as a partial replacement for cement to stabilize self-interlocking earth blocks

Materials

  1. Documented Materials
  2. Sugarcane Bagasse Ash:
  3. Ordinary Portland Cement
  4. Soil
  5. Water

Methods of obtaining Data

a) Linear shrinkage Box test (ASTM C356):

b) Mechanical Analysis of Soil (BS 1377:2)

c) Compaction Proctor Test (BS 1377:4)

d) Atterberg Limits (BS 1377:2)

e)Compressive Strength Test (ASTM C109)

Methods of analyzing data

After obtaining the required data, a number of calculations were carried out.  Calculations of averages, percentages, soil mix proportions among others required thorough and accurate calculations.

The data obtained were effectively presented in tables where, by a glance, one can easily understand the data. In design, there are standard sheets in form of tables that will be used in data publication.

Sieve Analysis Test Results

Linear shrinkage Box Test Results

Atterberg Limits Test Results (before stabilization)

Atterberg Limit Value (%)
Liquid Limit 33.1
Plastic Limit 16.7
Plasticity Index 16.4

 

Atterberg Limits Test Results For Stabilized Soil:

SCBA Percentage 0.0% 1.6% 3.2% 4.8% 6.4% 8.0%
OPC Percentage 8.0% 6.4% 4.8% 3.2% 1.6% 0.0%
Liquid Limit 44.0 44.9 45.9 45.5 49.9 47.2
Plastic Limit 33.4 35.9 34.4 34.4 36.1 31.1
Plasticity Index 10.6 9.0 11.5 13.4 13.8 16.1

 

In  the  experiments  conducted  it  was  decided  that  of  these  several  variables,  only the stabilizer content be varied while all the other parameters would remain fixed. The reason for  this  decision  and  approach  was  based  on  the  fact  that  it  was  the  stabilizer  content, which,  according  to  the  literature  on  stabilized  soils,  was  significantly  responsible  for  the improvement in compressive strength.

From the for 7-day strength curve, the maxima is at (3.2%, 2.12MPa). From the for 28-day strength curve, the maxima is at (3.2%, 3.03MPa). However, these co-odinates might not represent the optimum replacement of OPC with SCBA. The optimum replacements are close to 3.2% as indicated by green arrows.

When the OPC is replaced with SCBA in the ratio SCBA: OPC ≈ 1:1.5 (3.2%: 4.8%), then the pozzolana produced (from SCBA) reacts completely with Ca(OH)2 (from OPC) and hence it will be the optimum replacement. This replacement ratio however, may be only for use the soil tested and NOT with other types of soil. The strength obtained was an acceptable one since blocks with strength of 2.2MPa are suitable for construction after receiving further treatment.

Conclusions

The addition of SCBA and reduction of OPC to the soil generally increases its plasticity Index.

The compressive strength obtained at the age of 28 days for SCBA:OPC ratio of 1:1.5 was the optimum as it produced the highest strength greater than that specified in the British Standard (BS 5628 Part 1) of 2.2N/mm2. Stabilized soil bricks have more advantage when compared to burnt bricks because they are environmentally friendly, low energy requirement and require very little mortar for joining.

Recommendations

Further research should be carried out to investigate the water absorption behavior of the Stabilized Self-Interlocking Blocks.These compressed stabilized earth blocks can be used for partitioning and other unexposed works since the water absorption characteristics had not been ascertained.Further research on use of stabilized soil bricks for low-rise buildings is required. In this case a study on the strength of walls against lateral and dynamic loading.

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