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Application in concrete – Design of concrete mixes

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Application in concrete – Design of concrete mixes

July 11, 2023 nflg 0 Comments

The difference in surface texture, shape properties and particle surface texture indicates that natural and manufactured sands are two different types of material and must be treated accordingly. These facts require development of new concrete mix designs, and knowledge for the application of this material. Experiences of traditional concrete mixed design based on natural sand should not be automatically transferred into this new material.

The R&D and tradition of using manufactured sand in concrete has been driven by need in different countries. This implicates that the practice differs in various parts of the world. Japan is an example of a country that early started developing and applying new technologies, since their natural sand resources got depleted many years ago.

On the opposite side, North American – especially Canadian – resource conditions have been (and still are) of an order that do not call for alternatives to glaciofluvial sand/gravel as aggregate. In other countries, such as Australia, manufactured sand is seen as an appropriate substitute for natural sand, but it is claimed that it appears difficult to only depend on 100% manufactured sand. In Norway manufactured sand has both been applied in blends with natural sand and as 100% fine aggregate.

It must be our ambitions for the future to enable 100% use of manufactured aggregate in concrete, producing high quality concrete, both in the fresh and hardened state.

Principal objectives and scope

The main aims of this report are to present state-of-the-art knowledge regarding production and utilisation of manufactured sand. The overall objective is to develop a technology platform for the shift from natural to manufactured aggregates based on hard rock. This includes knowledge of resource management, cost effective production, use of manufactured aggregates in concrete and mix design concepts for concrete.

Background – Why Manufactured Sand

The motivation for this project is the increasing miss balance between the need for aggregates in the society and the availability of traditionally suitable geologic sources. A strong need is realised for developing and implementing technology that can enable the use of alternative resources, reduce the need for transport and present zero waste concepts for the aggregate and concrete industry.

Aggregate producers are faced with constant demands for higher quality aggregates and, at the same time, have to take environmental issues into account. The most pressing issues being the excess amounts of fines (< 4 mm) following the crushing process for manufactured aggregates and the depletion of natural aggregate resources.

Excess fines were, and in many countries still are, considered waste and were disposed of accordingly, at great costs and contamination. Producers recognised an unused opportunity and experimented with manufactured sand from gravel and crushed rock. Of advantage is that such sand has rough surface texture and the Particle Size Distribution (PSD) curve can be adjusted when the material is manufactured.

In addition specific properties can be selected by selecting the source rock material. Extensive research programmes have been carried out, where properties of manufactured sand and usability in concrete have been the main focus. The results have in general been in favour of using manufactured sand, given the right conditions concerning rock type and production process. However, design parameters are different compared to natural sand.

A development has been realised, from trying to duplicate the properties of natural sand, to production of a new product with new and improved properties. Another advantage when sand and aggregates are manufactured is that quarries can be kept in the near vicinity to its place of end-use, thereby shortening transport distances, followed by less pollution and increased employment opportunities for the locals.

It is anticipated that in the future aggregate production from crushed rock will increase and production from natural sand and gravel deposits will decrease.

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