Improving Durability of Compressed Earth Blocks in Low ... · Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant 2005 physical

J. Civil Eng. Architect. Res Vol. 4, No. 4, 2017, pp. 2003-2010 Received: May 31, 2017, Published: April 25, 2017

Journal of Civil Engineering

and Architecture Research

Improving Durability of Compressed Earth Blocks in Low-Cost Housing Construction Using Sap from Cactus Plant

Ivan Agaba, Lawrence Muhwezi and Sam Bulolo

Department of Civil and Building Engineering, Kyambogo University, Kampala, Uganda

Corresponding author: Lawrence Muhwezi ([email protected])

Abstract: Adequate shelter is a basic human need and yet about 80% of the urban population in developing countries Uganda inclusive still lives in spontaneous settlements as they cannot afford the high cost of building materials. CSBs (compressed stabilized blocks) have been identified as a low-cost material with the potential to address the problem and reverse the shelter backlog in Uganda. While their other properties are well understood, their durability remains unknown. This research, therefore, investigated the viability in the use of cactus sap to improve the durability of CSB’s, as alternative building materials in Uganda. The sap sample was extracted from prickly pear cactus plant and applied on CSB surfaces obtained from a local producer. Laboratory abrasion test, water absorption and mechanical strength of the earth blocks were conducted. Comparison of the properties of traditional earth blocks (control samples) and other blocks improved by either cactus sap only or a combination of cactus sap with lime was carried out. It was established that the latter exhibited abrasion coefficient and wet compressive strength of 147 mm2/g and 1.53 N/mm2 while the former, 219 mm2/g and 1.90 N/mm2 respectively which were higher than 118 mm2/g and 1.27 N/mm2 for the traditional blocks. It was concluded that cactus could be used as a protective cover material on earth block surfaces hence improving their durability when used as external walling units. The findings of this study will contribute to the widespread use of CSB’s in low cost housing construction since prospective users can now be confident about their durability under wet conditions. Further research is recommended to explore the performance of CBSs when a combination of cactus mucilage with lime when the percentages of lime are varied to obtain the optimum amount of lime needed.

Keywords: Durability, strength, cement-soil stabilized blocks and cactus.

Abbreviations

CSBs Compressed Stabilised Blocks

ILO International Labour Organisation

UNIDO United Nations Industrial Development Organisation

UNCHS United Nations Centre for Human Settlements

WCS Wet Compressive Strength

TWA Total Water Absorption

BBD Block Dry Density

BRE Building Research Establishment

1. Introduction

Adequate shelter is one of the most important basic

human needs, yet 25% of the world’s population does

not have any fixed abode, while 50% of the urban

population lives in slums [1, 2]. Indeed 80% of urban

settlements in developing countries consist of slums

and spontaneous settlements made of temporary

materials [3, 4].

With the population in developing countries

growing at rates of between 2% and 4% per year and

the population in their major cities growing by double

these figures, demand for low cost housing far

outstrips the capacity to supply [5]. No developing

country without strategies for low cost materials is

likely to meet its shelter targets [6, 7].


2004

Developing countries planning to expand their

housing stock for the low-income groups will

inevitably need to identify the lowest feasible unit

housing costs. The main costs of shelter provision are

for building materials (about 60%), machinery,

manpower and loan interest repayments [8-10].

Strategies are therefore urgently needed to develop

low-cost, readily available and durable building

materials. A naturally abundant material such as soil

that is found on most of the surface of the earth should

be a significant resource for building in developing

countries.

1.1 Advantages of Using CSBs

The use of CSBs will continue to grow due to the

several merits and economics associated with its use.

Firstly, as the basic raw material is soil, its source will

remain abundant and this facilitates direct

site-to-service application, thereby lowering costs

normally associated with acquisition, transportation

and production. House construction and ownership

can therefore be achieved at comparatively low costs.

Secondly, the initial performance characteristics of the

material such as the WCS (wet compressive strength),

dimensional stability, TWA (total water absorption),

BDD (block dry density) and durability are technically

acceptable. They are also comparable to those of rival

materials [2, 11, 12]. Thirdly, promoting the use of

CSBs generates more direct and indirect employment

opportunities within the local populace than would be

the case with other materials. Fourthly, use of the

material contributes directly to the social, cultural and

educational advancement of the population [13-15].

Their use also contributes to the training and

re-training of artisans and to the provision of new

skills. Use of the material through the provision of

local infrastructure such as schools, community

centres, health centres and administrative units results

in the promotion of human interactions and social

development. Finally, use of the material is

environmentally friendly, appropriate and correct

since it utilises the otherwise unlimited natural

resource in its natural state.

Moreover, this is achieved with little resultant

depletion of other resources, or pollution and requires

no excessive energy consumption and wastage as is

the case with clamp fired bricks. The elimination of

the need for wood fuel resources is seen as a major

attraction over such bricks. The use of CSBs is thus in

keeping with current sustainable development

strategies [16-20].

1.2 Shortfalls of Using CSBs

Despite the above advantages however, as with

most relatively new materials, shortcomings

associated with their use have recently begun to

emerge, especially in tropical environments. These

regions are characterized by frequent and intense

rainfall, high relative humidity and high diurnal

temperature changes [21-23]. CSBs are produced from

soil as the bulk constituent (over 90%). Soil is known

to have poor resistance to erosion and to disintegration

in water, a low tensile strength, low resistance to

abrasion, high water absorption and retention capacity,

and is dimensionally unstable during cyclic wetting

and drying [24-26]. The vulnerability of soil has in

turn led to blocks showing considerable defects over

short periods under conditions of normal and severe

exposure in the humid tropics [27-31].

Defects in CSB structures are mainly presented as

surface erosion, volume reduction, cracking and

crazing, surface pitting and roughening and

detachment of render. These deterioration phenomena

have been predominantly witnessed in the wet humid

tropical regions of the world. Whereas the initial

building costs might be low, the subsequent high

maintenance costs, or even early rebuilding costs are

not affordable by many. Some promoters have also

done harm to the image of the material by claiming a

high degree of long-term technical performance only

to be contradicted by premature deterioration only a

few years later. The most significant part of the


2005

physical structure is the walling constituents, which is

about 60% [32]. Thus, it makes greater sense to

concentrate work on low-cost walling. Dwelling cost

can be split into a number of separate areas.

Although the problem is more acute in the humid

tropics than in the arid zone, it nevertheless has not

been seriously addressed by research. Interest in

studying the durability of CSBs is therefore likely to

remain a major research concern for the foreseeable

future. It is the long-term durability of the block,

rather than any other factor that will be the key to their

widespread acceptance [33]. It was therefore the aim

of this research to investigate the viability of using

cactus sap as a waterproofing material that can

withstand severe exposure conditions of wetting,

abrasion and drying.

2. Materials and Methods

Soil, cement and cactus sap were the raw materials

that were used for this study (Table 1). Earth or soil,

considered suitable for manufacturing compressed

earth blocks was taken from Kyambogo University

compound in Kampala. HIMA cement, was the

cement used and cactus mucilage required for

stabilisation of the blocks was harvested from cactus

plants near Nabisunsa Secondary school in the

neigbourhood of Kyambogo University. The other

material used to moist the above stated materials was

tap water.

Twenty one blocks in total were delivered at

COMATLAB, a private material testing company and

different tests: abrasion test, water absorption

properties of the blocks and the mechanical strength of

the earth blocks were conducted. The research

examined the interplay between constituent materials

used (cement, soil, water) in production of blocks and

the block surface characteristics with regard to

abrasion resistance and water absorption after

applying prickly pear cactus. Through literature

review, the characteristics of sap, its extraction

process from cactus, and the current methods used to

Table 1 Raw materials for sample preparation

Material Type Effect Process

Prickly

pear cactusCactus

Water

proofing Physical-chemical

Portland

cement Mineral Cementation Chemical

Soil Sandy-clayey

material Compaction Mechanical

select the main constituent materials in CSB’s were

reviewed.

2.1 Cactus Sap Harvesting

All production operations were carried out

manually with simple harvesting tools (Fig. 1): knife,

tongs, basin or bucket and gloves. Cactus pads were

cut into smaller pieces that can be easily cut further by

the grater. The sap sample was collected and stored in

a bucket.

2.2 Soil Preparation

The soil sample that was used to produce CSBs was

obtained from Kyambogo University which was

predominantly clay, sandy soil was then purchased to

be mixed with it in propotions of 75% with 25% of the

sample already had, to form the soil of the desired

design properties.

2.3 Sap Extraction Process (Fig. 2)

The following procedure was followed to extract

the sap:

Cactus pads were harvested and cut into very small

Fig. 1 Harvesting of the cactus pads.


2006

pieces using a grater. The volume of cut cactus pads

filled aquater of the bucket volume. Water was added

in a proportion of 3 times the volume of chopped

cactus. The mix was left in the bucket in a storeroom

for three days, covered to limit evaporation. This mix

was less viscious than the one left after two days.

The blocks were first sprayed with water using a

pipe. Using a painting brush, the cactus sap was

applied on the block surfaces in three layers, applying

each layer a day (Fig. 3). One block was not painted

with the sap and both categories were left in an open

place (humid conditions) for a week. After two weeks

visual evidence showed that the block surface without

cactus was being eroded. A combination of cactus sap

and lime was similarly applied on surfaces of other

sample blocks using the same procedure.

During this research three categories of blocks were

investigated namely:

Earth blocks without anything;

Earth blocks with cactus only;

Earth blocks with cactus mixed with lime.

Fig. 2 Removing the spines from the cactus pad Application of cactus sap on blocks.

Fig. 3 Process of applying cactus sap on the blocks.

3. Laboratory Tests and Findings

3.1 Dry Compressive Strenth Test

The method adopted for this experimented is well

detailed in BS 1881, Part 116: 1983. The dimensions

of each block were first taken using a measuring tape

and afterwards, they were weighed (Fig. 4). Blocks

were then placed under two plates of the crushing

machine. At the point of failure, the machine

automatically calculated the compressive strength and

the value was displayed on its monitor (Fig. 5). The

averages of the three block categories were each

calculated.

3.2 Abrasion Strength Test

The procedure adopted is described in Ref. [34]. A

CSB was subjected to mechanical erosion applied by

brushing with a metal brush at a constant pressure

over a given number of cycles. The brushing was

applied to the sides of the block which are actually

used as facing, i.e. usually the header or the stretcher.

Fig. 4 Taking readings of the block weights.

Fig. 5 Crushing machine.


2007

The abrasion coefficient can then be calculated as the

ratio of the brushed surface area to the quantity of the

material removed by brushing and is proportional to

the abrasive strength. The brushed surface area was

calculated

(1)

where L = length of the brushed face of the block, W =

width of the brush.

The Abrasion Coefficient,

Ca = [S/(Ml - M2)] (2)

where M1 is mass of block before brushing and M2 is

mass of block after brushing.

3.3 Water Absorption Test

The TWA (Total Water Absorption) was calculated

by taking the amount of water absorbed by a dried

sample that had been immersed in water for a

specified period of time (24 hours). Mean values

obtained were taken as the TWA of the sample. The

result was expressed as a percentage of the original

dry mass of the specimen to the nearest 0.1% of the

dry mass. The method adopted for this experimented

is well detailed in Ref. [35].

The dimensions of each block were first taken and

then placed an oven for 24 hours. Blocks were fully

immersed in a water bath, and left there for 24 hours.

Blocks were removed from the water bath after 24

hours and wiped. The water absoption was then

determined using Eq. (3).

Water absorption = [(Mw – Md)/Md *100] % (3)

where Mw (g) is mass of wet blocks, Md (g) is mass of

blocks after drying.

4. Results and Discussion

4.1 Compressive Strength

The results of dry compressive strength of CEBs

from the laboratory are shown in Table 2. These

values fall within the permissible compressive strength

of earth building elements which are between 3 and 5

N/mm2 [36] and Ref. [37] provides results of between

2 and 7 N/mm2. Therefore, the tested blocks can be

used as building units.

The results and findings from the laboratory

experiments which compared the properties of

traditional blocks (control sample) and blocks

improved by either cactus mucilage only or a

combination of cactus mucilage with lime, established

that all the three block categories indicated a dry

compressive strength slightly above 3 N/mm2. The

latter indicated abrasion coefficients of 147 mm2/g,

219 mm2/g and wet compressive strengths of 1.53

N/mm2, 1.90 N/mm2 respectively which are higher

than 118 mm2/g and 1.27 N/mm2 for the traditional

blocks.

4.2 Wet Compressive Strength

It has been recommended in earlier studies that the

ratio of the mean dry and wet compressive strength in

CSB’s should not be greater than 2 [12]. The ratios for

the tested blocks were 0.47, 0.62, 0.39 for earth blocks

with cactus only, cactus with lime and those without

anything added respectively. The results obtained as

indicated in Fig. 6 are therefore within the

recommended limits.

The difference in strength can be explained by the

fact that the blocks without anything added to their

surface absorbed more water and the presence of more

moisture in these blocks lowers the weak van der

Waals bonds between the surfaces of the cement

hydrates and the surface of the sand particles in the

material more than the other two categories.

The moisture state of a block can influence its

strength. Saturated blocks are weaker than dry blocks

[12, 33]. The difference in strength can be explained

in a number of ways. Firstly, the presence of moisture

in a block lowers the weak van der Waals bonds

Table 2 Dry compressive strength of different blocks.

Block identity Dry compressive

strength (N/mm2)

Earth blocks with Cactus only 3.25

Earth blocks with Cactus and lime 3.06

Earth blocks without anything added 3.29

2008

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[38] A.J. Newman, Microclimate and its effects on durability, Paper to SCI/BBA Symposium on Building Deteriology, Garston, England, 1986.

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