Use of foamed glass gravel for sustainable concrete construction
With the introduction of waste legislation, in the form of regulations and directives, in many parts of the world a significant move towards sustainable waste management is becoming a legal requirement. Emphasis is now being placed on increasing recycling and promoting more sustainable practices for waste materials, including glass. The present research, therefore, aimed at examining the feasibility of Foamed Glass Gravel (FGG) as construction material, in particular Geofil Foamed Glass Gravél (GFGG), a manufactured lightweight secondary aggregate, for use as a primary aggregate substitute in concrete production. Comparison is made at all times with other FGG material, namely Hasopor, and other lightweight by-product manufactured material namely Lytag. In the main, research was carried out in three distinct parts; Part 1 examining the key characteristics of GFGG (following relevant BS and BS EN standards), Part 2 assessing its suitability for use in concrete applications, and Part 3 providing practical implications of the findings. The programme of work was designed to establish benchmarking level for coarse and fine GFGG and to provide simple practical guidelines for its use in concrete. The research has identified some of the key practical and application issues for utilising GGFG in concrete. The physical characteristics of GFGG were found to be comparable, and in some cases superior, to those obtained for currently available manufactured lightweight secondary aggregates. The grading of GFGG was found to be almost within the limits of lightweight aggregates with similar voids ratio as that of NA. Typically, GFGG, rough in it's texture, could create better mechanical interlocking with cement paste than smooth aggregates. GFGG had 60- 65% lower bulk density, 40-50% lower apparent particle density and water absorption 3 to 5 times higher than natural Thames Valley Gravel but still performed comparable to other lightweight aggregates. However it was found to have slightly higher density than Hasopor, but also higher heat and crushing resistance. Overall, characterisation test results showed that GFGG has a potential for use as quality lightweight aggregate in concrete production. However, it was noted that the precautions may be necessary to take account of bubble densities and water absorption characteristics to guarantee suitable fresh properties of concrete. In order to determine the practical upper limit of GFGG content for a range of applications and to assess the performance of GFGG concrete, mixes were proportioned using Natural Aggregate (NA) and GFGG bubbles blends with up to 60% coarse or 15% fine bubbles- by volume. The general trends observed indicate comparable workability with inclusion of GFGG in concrete mixes and slump loss with time was not adversely affected. Results of compressive strength testing showed that up to 30% coarse or 15% fine GFGG had negligible effect on the cube and cylinder strength of concrete and using up to 15% fine GFGG caused a slight increase in cube, cylinder and other engineering properties. Moreover, within 3-days 30% coarse GFGG and (5-15%) fíne GFGG concrete mixes achieved on average 73% of 28-day compressive strength. This increased to 85% within 7 days, regardless of GFGG content when compared to NA (Control) concrete mixes. However, results show gradual reduction in strength with an increase in GFGG content beyond 30% coarse in the mix. Indeed, the results showed that such reduction in strength with high GFGG proportions can be compensated for by adjusting the mix water/cement ratio. The results also showed that the original glass source had a negligible effect on fresh and key bulk engineering properties of resulting concrete. The subject of GFGG concrete durability study included initial surface absorption, carbonation rates and alkali-silica reaction testing. In general, GFGG concrete mixes were found to posses near surface absorption properties similar to the corresponding NA concrete mixes, providing GFGG content was restricted to 30% coarse or 15% fme. Carbonation rates for up to 60% GFGG mixes were comparable to NA mixes. Results of accelerated ASR testing of 30-100% fine GFGG mortar prisms indicated that none of the tested samples expanded significantly during the test and that damaging deleterious expansion due to ASR did not occurred during testing. The practical implications of the study to the construction industry are also discussed.