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Use of Coloured Glass Fragments for the Manufacture of Concrete, Tiles, and for Road Construction

Summary

This report summarises the results of three separate pilot studies on the use of coloured glass fragments for the manufacturing of concrete, tiles, and materials for road construction.

Concrete
The possibility of using glass filler in concrete was surveyed. The used glass filler is ground to the same blaine as cement. Based on the results the following conclusions can be drawn:

From a concrete technological point of view the results do not indicate that there are any obstacles to using glass filler in the manufacturing of concrete. It turned out that it is possible to manufacture concrete with glass filler that offers good workability, sufficient frost resistance, and resistance against chloride, and an ability to tolerate damaging alkalikisel damages as is the case with fly ashes. Small strength reductions were, however observed, which will influence the amount of glass filler that can be added to the concrete and the fractions of the materials that can be substituted. Finally, when using glass filler in white concrete a change of the colour of the concrete appeared, which can hardly be distinguished by the naked eye, and therefore a possible alternative to white silica, which is a quite expensive material.

The possibility of using glass filler in concrete depends on the concrete technological conditions as well as on current legislation on concrete. According to the present regulations (the standard DS 481), it is allowed to use glass filler in large quantities in concrete used for passive environment (corresponding to approx. 70% of all concrete). In this environmental class, it is only necessary to DoCument that the glass filler does not damage the properties of the concrete, which the present pilot studies do not show any indication of.

EN 206-1 and a national supplementary DoCument DS 2426 to the European standard will within a very short time frame replace DS 481. According to the standard it is allowed to use puzzolan additions beside fly ashes and silica fume in all environmental classes, provided it is specified in the project specification or a national standard is prepared within the area. It may imply a tightening as well as a relaxation of the use of glass filler. Relaxation is given when there are no obstacles to the use of glass filler in all environmental classes. However, in practice it may easily seem a tightening that the use of glass filler has to be specified in every single project specification, because at present there is no national standard for using glass filler in concrete. It will be difficult for the concrete manufacturer to incorporate glass filler in his standard formulas right away, as each project specification will presumably imply different specifications.

Bricks
The use of glass sand and glass powder as addition agents in clay mixtures for red soft mud bricks from two different brick works Hammershøj and Sønderskov was surveyed.

The results primarily show that the effect of using glass sand and glass powder respectively, vary considerably:

Glass sand bloats up. The effect can be traced as dark irregularities at the visible parts of the tiles when exposed to 975^oC. At 1000^oC the bloating can be seen with the naked eye.

The same effect cannot be traced when using glass powder, not even in a microscope.

The results of weight loss during incineration indicate an increasing development of gases at increasing temperatures. It may explain the bloating of the glass particles.

Likewise, differences in how the two types of clay are affected by the use of glass can be detected, even though they are both red burning. The effect on clay from Hammershøj is, at best, neutral. The effect from glass sand on the clay from Sønderskov is close to neutral, while the effect is generally positive when using glass powder.

The possibility of using glass in the manufacturing of tiles can be estimated as follows:

Glass sand can be used at temperatures below 975^oC without any bloating. Therefore, it might be possible to use glass sand in the manufacturing of bricks for inner walls, which are typically burnt at temperatures below 800^oC.

The bloating, which appears at high temperatures, may be used for production of a more porous and absorbing material, assuming that a reduction in the strength of the tile can be accepted.

Glass sand can probably be handled as ordinary sand is handled today If there is a risk of biological activity due to nutrients in the glass material it may, however, be necessary to wash the glass or alternatively to keep it totally dry as long as possible.

The testing of the glass indicates that it is possible to obtain sufficient properties at low burning temperatures when using glass powder. It will therefore be possible to lower the burning temperatures by up till 50^oC. A low temperature will normally give a more pink material. Even though the testing implies that the addition of glass powder gives a darker colour compared to the reference colour, it is, however, possible to manufacture a pink tile material, which is more dense than normal for pink tiles.

It is also possible to use glass powder for manufacturing bricks for inner walls.

Special handling of glass powder will require special handling at the brick works. The material should be kept dry as long as possible if there is any risk of biological activity due to nutrients in the glass material that may not be totally clean. Transport will probably have to take place in a tanker and storage in a silo.

Road construction

The possible unbound uses of crushed glass in Denmark could be as fill material as sub-base sand or filter gravel.

The use as non-load-bearing fill material it estimated not to cause any technical problems. If the glass is sufficiently crushed it can be placed and compacted satisfactorily, even as a 100 % glass aggregate. For fill purposes demanding a certain bearing capacity, the low CBR value of the glass may be a problem. Mixing with natural aggregate can probably improve the quality.

Based on the laboratory tests carried out it appears that broken glass can meet the Danish requirements for sub-base materials. Among others the amount passing the 0.075 mm sieve must be less than 9 %, which can meet the requirements with a good margin. Besides the sand equivalent has to be larger than or equal to 30 %. The test has not been carried out with crushed glass, as it has not been estimated to be relevant due to the low content of fines.

The poor stability of the broken glass may end up being the largest obstacles for using the glass in its pure form. Using broken glass as the lower layer in a two-layer sub-base or a mixture with natural aggregate can be possible solutions to the problem.

It has not been possible to find any foreign references on the use of a 100 % glass aggregate for applications, corresponding to the Danish sub-base. the normal pr^oCedure is only to use up to 20-30 % glass aggregate. However, it cannot be excluded that a 100 % use of glass aggregate is technically possible, but evidently it has not been tested.

It might be possible to use broken glass as filter gravel, which is used around drains etc. Due to its uniform grain size structure almost without fines, the glass should be very suitable as a drain material. In the literature it is even mentioned quite often that broken glass has a good drainage capacity.

However, studies indicate that the grain size distributions of the two glass fractions are not included in the Danish Road Standards curve limits for filter gravel I. The grain size distributions are generally too coarse-grained and uniform materials. The explanation to this apparent paradox is that a good filter material does not only have to have the ability to drain, but also be able to preserve it, and therefore prevent fines from the surroundings to penetrate and fill up the voids.

Generally speaking it should be noted that the study does not consider the environmental aspects when using broken recoverable glass, which therefore has to be dealt with separately. If the material is estimated to be potentially contaminated it might not be possible to use it for road construction purposes where the material is exposed to water flow, i.e. as filter material, sub-base and non-uncovered fill.

Perspectives of using coloured glass fragments

Pilot studies indicate that it is possible technically to use glass in the manufacture of concrete, tiles, and road constructions. However, to ensure that glass becomes a popular alternative in line with other constituents, which are used in the mentioned building materials, the economic conditions are of vital importance, among others, if the use of broken glass is to succeed

Two possible methods are available: Either the pre-treatment of the glass is reduced to a minimum (e.g. only crush the glass) to allow it to compete with the rather cheap materials such as e.g. natural materials for road filling. Or the glass can be worked up into a more refined product such as glass filler, which implies cleaning and grinding. However, it can then compete with products of a high quality standard. Table 0.1 shows an estimate on the prices of the products, which can be replaced by glass if ^oCcasion should arise.

The market value of glass for free purposes in connection with road construction is compared with the natural materials it can replace in the area of DKK 0-50/ton.

When using glass filler in concrete the glass filler market value will very much depend on whether it is to be used in a manufacturing of white or grey concrete. There are not many suitable filler materials that do not effect the colour of the white concrete. In white concrete the glass filler will compete with e.g. white slag, which costs DKK 600-700/ton. Therefore similar expenses can be accepted for pr^oCessing the glass. At the moment the quantity of white concrete for construction purposes is rather limited. The concrete manufacturers are also interested in alternative filler materials, which e.g. totally or partly can substitute fly ashes in grey concrete. But the price of fly ashes is rather low compared with the price of white slag. This fact has a large impact when deciding whether it is profitably to manufacture glass filler for the production of grey concrete. Besides, it must be included in the considerations that there are also costs involved for the concrete manufacturer when handling an extra filler material, e.g. extra silo capacity is necessary.

It is difficult to predict the market price for glass sand or glass filler for brick manufacturing, as it does not depend on the price as much as on the materials it will replace. E.g. the price of sand for addition is approx. DKK 45/ton, which is based on the fact that an improved pr^oCess at the brick works must be obtained. In general, it is difficult to estimate the value of such a pr^oCess improvement (saving of energy at low burning temperatures etc.), as it very much depends on l^oCal conditions at each brick work, incl. the raw materials at their disposal.

Table 0.1 Price estimates FOR the products that broken glass may be able to replace

1. PRESUPPOSING that manufacturing of chamotte is based on the broken bricks from the brick work, I.E. that the price includes breaking and transport.

2. Sintering additive is not used in Danish tile manufacturing but commercial products are sold e.g. in Germany.

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Version 1.0 Januar 2004, © Miljøstyrelsen.