Review and Exploration of River Sand Substitutes for Concrete Production in Asian Countries
Chun-pong Sing & P.E.D Love
Department of Construction Management, Curtin University, Western Australia, Australia
Chi-ming Tam
Department. of Civil and Architectural Engineering, City University, Hong Kong
ABSTRACT: Concrete is a stone like material obtained by carefully proportioned mixture of cement, fine sand, aggregate and water, hardened in the forms of shape and dimensions of the desired structure. High quality concrete mixture can only be produced with a proper choice of fine sand with requisite fineness module. The natural river sand is the cheapest option due to the ease of acquisition and in a well-grade nature. However, excessive excavation of river sand creates a serious environmental problem in Asian countries such as China, Thailand and India. Thus, natural river sand substitutes have to be explored urgently.
Keywords: concrete, natural river sand, substitutes 1 BACKGROUND
Quality of concrete production is highly dependent on the constituents and their optimum ratio. Fine sand and coarse aggregates generally occupy 60% to 75% of the concrete volume and thus strongly influence its hardened properties, mixture proportion and economy. The engineering properties of fine sand are highly related to the relative proportions of different sizes of particles presented. Natural river sand is commonly used as fine sand in concrete production as it is the cheapest natural material. Such sand is well-graded in nature with well-distributed particle sizes under mechanical and chemical weathering. However, worldwide unbridled urbanization is fuelling the growth of the construction sector, which has resulted in excessive mining of river sand. According to Joel (2010), several Asian countries such as India and Singapore are experiencing severe shortage of natural river sand to meet the increasing needs for infrastructure development. In addition, the excessive excavation of river sand has caused serious environmental problems. For example, in India and Thailand, riverbeds are becoming uneven and their landscape is dramatically changing (Khamput, 2004). To deal with this challenge, it is important to consider alternative materials or substitutes.
2 CASE STUDY: HONG KONG
River sand was one of the major constituent materials used in the production of concrete in Hong Kong. According to the CEDD (2009), the natural river sand used in Hong Kong has been mainly imported from mainland China and in 2009, it was reported to be 1,800,000 (tonnes). Figure 1 shows that almost 24% of the river sand imported was used for concrete production.
Figure 1
production in Hong Kong (CEDD, 2009)
River sand consumption for concrete
China is the major supplier of river sand to Hong Kong. The Chinese government has warned the environmental impact of uncontrolled extraction and export of natural sand for some time. For
example, in 2007, the Ministry of Commerce (MOC) in China has announced to ban export of natural sand. Under this policy, only Hong Kong and Macau have been exempted from this forbiddance. A Hong Kong importer should apply for the permit called “Export License of the People’s Republic of China for Natural Sand” from the Mainland Authority for importing natural sand from the Mainland. In addition, Indonesia has banned export of natural river sand to Singapore.
3 REVIEW OF THE MOST WIDELY USED RIVER SAND SUBSTITUTIES
The world consumption of natural river sand as fine aggregate for concrete production is very high and several countries have encountered shortage of natural fine sand. As a result, river sand has become increasingly expensive and also scarce (Raman et al., 2007). Most importantly, good sand may be not readily available in every riverbed (Ilangovan & Nagamani, 2007). The sand available in a riverbed is sometimes very coarse and may contain a high percentage of silt and clay. The presence of clay and silt in sand reduces the strength of concrete as it holds dampness. In addition, the quality and composition of river sand from riverbed can even vary significantly and its quality cannot be guaranteed. Some Australian manufacturers advocate the use of 100% manufactured fine aggregate for concrete to ensure its quality (CCAA 2008).
According to the guidelines published by Cement, Concrete & Aggregate Australia (CCAA) in 2008, Japan has been developing and applying new technology for producing manufactured sand, since their natural sand resources were depleted. In Canada river sand is still abundant, though alternatives are being developed. Alternative sources for river sand are: (a) crushed and screened waste glass, (b) crushed rock sand, in the form of granite dust, (c) crushed rock sand, in the form of quarry rock dust, (d) recycle copper slag and (e) sea sand.
(a) Crushed and screened waste glass
In the United States (US), research has shown that crushed and screened waste glass may be used as a sand-substitute in concrete and cement mortar production (NAHB Research Centre, 2001). Nearly all waste glass can be used in concrete applications, including glass that is unsuitable for recycling. In Australia, field and laboratory tests have demonstrated that crushed and screened waste glass is robust and economical when used as
a sand-substitute in concrete production. In addition, the use of waste glass helps keep material out of landfills.
(b) Crushed rock sand, in the form of granite dust
The dust produced from granite crushers is one of the alterative materials for river sand. In Singapore and New Zealand, for example, crushed rock sand, in the form of granite dust, is often used as fine aggregate to replace natural sand in various proportions (Malagavelli & Rao, 2010). It has been demonstrated by Malagavelli & Rao (2010) in their laboratory tests that it is technically feasible to replace sand with crushed rock to produce concrete.
(c) Crushed rock sand, in the form of quarry rock dust (classified as manufactured sand)
The utilization of quarry rock dust, which can be called “manufactured sand”, has been accepted as an economic alternative to river sand in countries such as Australia, Germany, Japan and the UK (Ilangovan & Nagamani, 2007). Quarry rock dust is defined as a residue, tailing or other non-valuable waste materials after the extraction and processing of rocks to form fine particles less than 4.75mm. Manufactured sand is seen as an appropriate substitute for natural river sand. In Malaysia, as much as 20% quarry waste is being used as a replacement for natural river sand in the production of concrete (Safiuddin et al., 2007). However, to ensure the performance of concrete, strict control should be placed on items such as the surface texture, elongated particle shape and size graduation of the manufacturer sand.
In Australia, O’Flynn (2000) reported that the closure of the Brisbane River to extractive dredging and the exhaustion or limitation of other sand sources have caused the industry shifting to manufactured sand for concrete fine aggregate. It is reported that fine aggregate is produced from 12 of the major hard rock quarries in southeast Queensland. Companies have achieved only partial replacement of natural sand, to around 40% of the fine aggregate component in their concrete mixes. While improved technology and management will further reduce the amount of natural blend sand required, river sand is unlikely to be fully replaced in the foreseeable future. There is still a large room for exploring the possibility to enable 100% manufactured aggregate for substituting natural river sand.
(d) Recycled copper slag
The vast amount of copper slag, a by-product obtained during smelting and refining of copper,
was for many years, treated as a waste with no further use thereafter (Al-Jadri et al., 2009). Asia’s countries like Singapore and Japan have found a novel way of encapsulating copper slag into concrete, reducing the use of natural fine sand in cement production and avoiding land filling, which used to be the common way of disposing this “waste”.
(e) Sea sand
Many countries have begun to utilizing sea sand in place of natural river sand for concrete and cement mortar production (Jayawardena & Dissanayake, 2006). Sea sand is extracted from below around 15m deep of ocean (e.g. beyond the surf zone). However, the saltiness of sea sand (or called chloride level) with respect to the enhancement of corrosion to reinforced steel has been the greatest concern on deterring it to replace river sand.
The above reviews have explored the alternatives that have been significantly applied for substituting natural river sand in concrete production. In addition, key factors listed as following should be critically examined:
(a) Supply of raw material: the availability within the region is a significant economic benefit to the regional construction industry.
(b) Economic consideration: any additional benefit of using alternative materials, for example: using crushed glass waste would lead to (i) reduce the concrete unit cost, (ii) lower the freight cost and (iii) avoid landfill cost.
(c) Accessibility: transportation costs of the raw material should be critical for selecting the river sand substitutes.
(d) Environmental impact: use of any recycled materials as substitutes of river sand would help keep the material out of landfills. Recycling practices can also decrease the environmental impact.
(e) Suitability for local construction works: for example, whether the sand substitutes are suitable for producing a high strength concrete.
4 SPECIFICATION OF RIVER SAND SUBSTITUTES FOR CONCRETE PRODUCTION
Current specifications/ guidelines for the use of the river sand substitutes include:
New Zealand
The New Zealand Standards Association has incorporated a performance-based specification for concrete aggregate, which allows the substitution of river sand in concrete production. There is no specified grading limit imposed. Alternatively, there are some criteria on controlling the flow time and void content of the sand substitutes using flow cone tests in accordance with New Zealand Standard.
Singapore
Singapore Standard (SS) 31: Specification for aggregates from natural sources for concrete permits the use of crushed rock sand to totally replace natural sand for concrete. However, the grading requirements of crushed rock sand must be in accordance with SS31.
Europe
According to European Standard EN12620 (2002), definitions for concrete are given for: fine aggregates, the smaller aggregate sizes with diameter less than or equal to 4mm. Fine aggregate can be produced from natural disintegration of rock or gravel and/ or by the crushing of rock or gravel or processing of manufactured aggregate.
Australia
An amendment was made in 1998 to Standard Australia AS2758.1, which increased the acceptable level of <75 m size to 20% of the crushed fine aggregate, in contrast to natural sand where the limit is 5%.
5 CONCLUSIONS
Natural river sand has played an important role in concrete production. Riverbeds have been over-excavated, which has caused serious environmental impact in many countries such as China and Indonesia. As a result they have begun to cease exporting natural river sand. Asian countries such as as Hong Kong and Singapore face several challenges as a result of shortage of river sand. There are several types of fine sand substitutes such as crushed waste glass. However, several key factors such as supply sources of substitutes and accessibility should be considered for developing the use of substitutes in the region. In addition, the specification of river sand substitutes for concrete production with reference to those currently adopted in local and foreign construction works should be critically examined. A set of well-defined guidelines for the use of river sand substitutes for local industry need to be established.
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Cement Concrete & Aggregates Australia (CCAA). 2008. Guide to the Specification and Use of Manufactured Sand in Concrete, Australia.
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