Financial and Technical Feasibility of
production of sand by washing soils
T.A.S. De Silva
Supervisor: Prof. Asoka Perera
Abstract: Natural sand is a
major material in concrete production and due to exponential rise in
construction industry the demand for natural sand is huge. The conventional
natural source for fine aggregate which is river sand present many
environmental problems when it is extracted. As a remedy to that alternatives
like quarry dust, ocean sand and other sources can be used. One of them is
production of sand by soil washing. Soil contains more than 50% of sand and different soils contain
different types of sands. From researches conducted it was found that soil can
replace river sand as an alternative to fine aggregate. In the world there
are large scale soil washing which implement soil separation in to fractions of
different particle size. Most of them are done to clean contaminated soils.
Different soil washing methods implement in many sites around the world for
this purpose and many researches are conduct which utilize soil washing in the
soil remediation process. It is worthwhile to examine the technical and
financial feasibility of production of sand by soil washing.
Washing; Sand; Soil Separation; Sand from Soil
Sand is one of the most consumed
natural resource in the world. It is used in many industries, but intensively
used in the construction industry. As the source of sand, river sand is used
due to its desirable characteristics. Due to the exponential rise of the
construction industry in the recent years an extensive amount of sand is
required. So many countries import sand to meet the demand. China which is the world’s ninth largest sand importer
used more cement between 2011 and 2013 than the U.S. used in the entire 20th
century (Swanson, 2015). Other than in construction industry sand is used in
territorial expansion (“Such quantities of
sand,” 2015) in countries like Singapore.
sand mining which is the conventional way of getting required sand pose many
problems. According to a study done on the Poyang Lake which is the largest
fresh water body in China it was found out that the water level of the lake
during dry period has gotten low. One of the main reasons for this is excessive
sand mining (Lai et al., 2014). According to this
study it was found out that the discharge from the Poyang Lake to the Yangtze River at low
water levels has increased up to 1.5-2 times the values after the beginning of
excessive sand mining. Due to the sand mining, lake’s discharge channel width
and depth was increased which increased discharge ability of the lake resulting
lower lake levels during dry season.
problems due to sand mining occurs when the rate of extraction of sand from
rivers exceeds the rate that natural process generates them. In 2010 Malaysia
consumed sand and gravel, with a value of $5.7 billion. By a
case study from Bestari Jaya, Selangor, Peninsular Malaysia it was found that
the main reason for impacts from in-stream sand mining is due to removal of more
bedload than the system can replenish or shortening of the stream channel (Ashraf, Maah, Yusoff,
Wajid, & Mahmood, 2011).
How the slop stability of the
levees are affected due to extensive sand mining and formation of sand pits is
examined by Wang (Wang, Ding, &
Yang, 2012). It was indicated that the probability of instability
risk nearly doubled after commencing of sand mining.
Case study details examining
river sand mining issues about Amaravathi River, Tamil Nadu, India and Pampa
River, Kerala, India were presented by Podila Sankara Pitchaiah (Sankara Pitchaiah,
those various negative impacts the need of alternatives to river sand is required.
Many different alternatives were introduced for this purpose each of them
having their own advantages and disadvantages. This study is about such an
alternative. It will be examined the technical and financial feasibility of
producing sand from soil washing.
2. Alternatives to River Sand
of the main alternatives to the river sand is the use of coastal/ocean sand. In
many countries sea-sand is used as fine aggregates in many major projects. Lots
of researches were conducted on this front to check the suitability of ocean sand
in concrete industry. From the research conducted by Xiao (Xiao, Qiang, Nanni,
& Zhang, 2017) the workability,
mechanical properties and durability of concrete made using sea sand was
examined. Sea-sand is needed to be properly processed before use as fine
aggregates as the chloride it contains can cause steel corrosion in reinforced
concrete and affect the hydration process of the Portland cement. So it is needed
to be washed using fresh water to get the desired quality. That may raise
durability and safety issues. The surface texture and particle size
distribution is bit different from river sand. So sometimes it may need
processing before utilization. Percentage of sea shells in sea-sand also
affects the use of sea-sand.
From the research results by Ratnayake (Ratnayake, PUSWEWALA, Chaminda, & EKANAYAKA AND
M.N. JAYAWARDENE, 2014) to evaluate the potential of sea sand as an
alternative to river sand shows that it can be a competitive alternative to
replace river sand. Comparison of compressive strength, textural properties and
salt contents with respect to grade 30 concrete produced by quarry dust and
river sand was done to get the results. Use of sea- sand in the context of Sri
Lanka could be done with one to two years of natural washing by monsoon to
remove chloride according to this research.
or ocean sand mining also present environmental problems. In Southern Monterey Bay in USA between 1940 and 1984
128,000 m3 sand per year was mined causing massive shoreline erosions (Thornton et al.,
mining was ceased after 1990 but other than some locations the coastal erosions
has not reduced.
mining can also cause problems like affecting the marine lives in negative ways
(Jonah, Agbo, Agbeti,
Adjei-Boateng, & Shimba, 2015) and some
impacts on sea bed due to excessive sand mining. There are various management
policies for marine sand mining (Trop, 2017).
alternative used in the construction industry as fine aggregate is manufactured
sand. The micro fines in the manufactured sand fills the pores thoroughly
compared to the river sand. And due to being free from silt increases the
strength characteristics of concrete made from manufactured sand is higher than
concrete made from river sand. It concluded form researches (Elavenil & Vijaya,
2013) that concrete from manufactured
sand has higher flexural strength, abrasion resistance, higher unit weight and
rock sand or quarry dust are manufactured sand. Various researches also have
been conducted on using quarry dust for concrete works. Compressive strength
tests and beam flexure tests were conducted on various mix designs for
different grade of concrete made by river sand and crushed rock sand and a
comparison between them were done by Mundra (Mundra, Sindhi,
Chandwani, Nagar, & Agrawal, 2016). Quarry dust is defined by
crushing quarry stone up to it passing through 4.75 mm sieve. The compressive
strength, split tensile strength and the durability properties of concrete made
of quarry rock dust are nearly 14% more than the conventional concrete. A higher
blend ratio of crushed stone to natural sand will decrease workability. The
surface texture is not as good as the rive sand. Even the best shaped
manufactured sands are usually more poorly shaped than the river sand. Therefore
for mix with 70?100% crushed rock sand replacement it is desired to mix washed
crushed rock sand along with proper screening at crushing stages so that one
gets compressive strength higher than the designed strength.
Use of desert sand for
concrete production was also considered. From the tests conducted on performance
of mortar and concrete made with fine aggregate of desert sand by Zhang (Zhang, Song, Yang,
& Liu, 2006) shows that it can be
used. The desert sand belongs to superfine sand. They were not suitable to be
used as masonry mortar due to poor workability. To get a good workability admixtures
are need to be used.
Study on Iron slag
(I-sand) (Noufal E. &
Manju, 2016) which is a by-product
of iron and steel industry was conducted to see whether it can be used as an
alternative to river sand. With comparison and experiment on mechanical,
chemical and physical properties of I-Sand with river sand shows that it can be
used for concrete production.
Soil as fine aggregate
Soil contains more than
50% of sand and different soils contain different types of sands. It is
necessary to evaluate the feasibility of these sand for technical and financial
Using soil texture triangle
different type of soil can be labelled according to the percentage of sand,
clay and silt (Eagle, 2016).
Soil texture triangle
Coarse Sand = diameter 2-0.2 mm
Fine Sand = diameter 0.2-0.02 mm
Silt = diameter 0.02-0.002 mm
Clay = diameter less than 0.002
all sand is suitable to concrete production. The fine aggregates should be
within the required parameters according to the standards used. The fine
aggregates grading required according to the ASTM Standards are given in table
Standard C33 – Specification for Concrete Aggregates,” 2003).
Table 1: specified
the requirements for grading fine aggregate according to ASTM C 33 – 03
Sieve (Specification E 11)
95 to 100
80 to 100
50 to 85
25 to 60
5 to 30
0 to 10
Researches were conducted on
using soil as a replacement for fine aggregates in concrete. In an experimental
investigation (Thumati, 2015) the durability properties of
soil and sand concretes such as acid attack, alkaline attack, thermal resistance,
porosity characteristics, abrasion resistance and impact resistance were compared.
Resistance against acid attack for soil concrete was higher than sand concrete
and resistance against alkaline attack was same for both of them. Porosity and
water absorption was higher in soil concrete. Characteristics of soil concrete
is within the allowable parameters for sand concrete. Hence soil was suitable
to produce concrete according to this research.
Results from another study by Thumati on strength properities of
soil concrete is given in table 2 (Thumati, 2014). Sieve analysis
was done to separate sand from soil. To prepare test samples mix proportion of
1:1:2 with w/c ratio of 0.45 was used. The characteristics of soil concrete was
within the permissible range.
Comparison of test results of soil concrete and sand concrete
rapture (by testing 100 mm x 100 mm x 500 mm)
can be done to increase the quality of sand of the alternatives used for river
sand. A study for comparison between washed quarry sand and unwashed quarry
sand of corresponding concrete mixes shows workability of washed sand is
higher. The industrial case study was conducted on a large scale sand washing
plant and 500 tons of sand materials were used (Cepuritis &
Mørtsell, 2016). It was shown that
washing quarry sand greatly improve the performance of quarry sand in concrete.
the world there are large scale soil washing which implement soil separation in
to fractions of different particle size. Most of them are done to clean
contaminated soils. In the process of soil remediation, soil washing was used
as a volume reduction method.
the soil washing hazardous materials are removed and they were concentrated
into a small volume. The contaminants mostly contains in silt and clay of
soils. So To remedy contaminated soils first it is need to separate silt and
clay from sand and gravel (A Citizen’s Guide
to Soil Washing, 1992). It can be done by
soil washing. After that the reduced volume with highly contaminated soil
fraction can be disposed by an appropriate method according to the regulations.
In a soil the more there are silt and clay, the more difficult it will be to
separate particles into fractions according to size. Soil washing can be used
as a volume reduction technique to reduce the final volume up to 10% of the
initial volume. So the volume need further treatment can be greatly reduced. The
hazardous contaminated soils can be treated on site. A wide variety of
contaminants can be removed using soil washing method.
washing was used in superfund sites. Superfund sites are sites which contains
hazardous contaminated soil that may pose a threat to public health in USA.
These are identified by USA’s Environmental Protection Agency (EPA) and placed
on National Priorities List (NPL). The first Full-scale Soil Washing Project in
the USA. was the King of Prussia (KOP) Technical Corporation Superfund
site, located in Camden County, New Jersey (Mann &
Groenendijk, 1996). The site was
consisted with six lagoons for the purpose of industrial waste processing.
After it was abundant it was found that lagoons sludge and surrounding soil was
metal contaminated. After a feasibility study was conducted to find the most
appropriate way for remediation, soil washing was chosen. Soil washing was done
in 1993. It was implemented by the Alternative Remedial Technologies, Inc.
(ART). This project was able to treat 25 tons of soil per hour using
washing techniques. At there, it was capable of treating soils which were
contaminated with metals, polynuclear aromatics, pesticides and radioactive contamination.
remediation process consist with screening, separation, froth
sampling and analyse methods need to be carry out before utilizing the soil washing
process on field. The technology details for soil washing change from site to
site. So, proper commercially available machines from vendors are need to be
site specific. Engineering Bulletin (“Engineering
Bulletin – Soil Washing Treatment,” 1990) describe individual treatment
technology used on hazardous waste sites and in the performance data tables in
the bulletin gives details about Proprietary vendor, scale of operation, year
range of particle size treated, contaminants extracted from soil, Extraction
agent, by product wastes generated, extraction equipment and efficiency of
of sand, silt and clay fractions from has been described by Genrich (Genrich, 1972). This was done by sieving and
sedimentation procedure. To separate soil particles from each other the bond
between individual soil particles are needed to be disrupted. The agents
responsible for the bonds are known as “”cementing agents”. Baver (Baver, 1956) lists organic matter, colloidal
clay, and dehydrated colloidal oxides of iron and aluminium as cementing agents
commonly found in most soils. According to the soil type the difficulty to
disrupt the bonds depends. Different types of chemical and mechanical methods
are used to separate these bonds.
researches were conducted on Remediation of soil
contaminated with various materials which implement soil washing (Kumpiene,
Nordmark, Carabante, Sužiedelyt?-Visockien?, & Aksamitauskas, 2017; Li,
Guo, & Hu, 2016; Muñoz-Morales, Braojos, Sáez, Cañizares, & Rodrigo,
2017; Voglar & Lestan, 2013, 2014).
Due to the increasing demand for
river sand, the need for alternatives which are not harmful to environmental
and economical is imminent. Researches and studies were conducted on using soil
as fine aggregate in concrete. There exist methods to separate soil in to
fractions according to particle size. These methods are used as part of soil
remediation process. But a research on soil washing to produce industrial grade
sand was not done. In this research the technical and financial feasibility of
production of sand from soil washing will examined.
The support received from University of Moratuwa to carry out literature
review is highly appreciated.
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