It is possible to use up to 100% recycled coarse aggregate in concrete under controlled conditions. There is no noticeable difference in workability and strength, although a structural engineer should always specify the final mix. A common approach is to use 30% recycled aggregate for typical structural concrete. Such replacement decreases the amount of material going to landfill, reduces embodied energy, and can lower costs. Using recycled aggregateĬoarse aggregate and sand can be replaced by recycled materials such as crushed concrete from demolition, slag aggregates and recycled sand. In some smaller plants it may not be feasible to have 2 cement silos, or an additional silo for fly ash or slag. Most batch plants can provide blended cements. New technologies include the use of reactive magnesia in combination with Portland cement. Extenders include fly ash, ground blast furnace slag and silica fume which are waste materials from other manufacturing processes. Various blended cements are available, some with high proportions of extenders (up to 85%) replacing Portland cement. These extenders (also known as ‘supplementary cementitious materials’) are commonly available from most concrete batching plants. Replacing a proportion of the Portland cement with waste products called ‘extenders’ can significantly reduce embodied energy and greenhouse gas emissions. Portland cement is the most common type of cement used in concrete. Concrete’s main environmental impacts are greenhouse gas emissions from cement production, and the mining of raw materials. Photo: Austral Precast Environmental impact of concrete slab floorsĬonventional concrete has high embodied energy and embodied carbon, but there are ways to reduce the environmental impact of concrete.Ĭoncrete has 3 main components: coarse aggregate (stone), fine aggregate (sand) and cement, with water added to the mix to catalyse the reaction that causes it to solidify. Precast concrete floor panels installed and ready for light top reinforcement and pouring of a thin covering slab They can be made from conventional or post-tensioned reinforced concrete, or from autoclaved aerated concrete (AAC). Precast slabs are manufactured off site and craned into place, either in finished form or with an additional thin pour of concrete over the top. Suspended slabs are formed and poured in situ, with either removable or ‘lost’ nonloadbearing formwork, or permanent formwork that forms part of the reinforcement. Both may benefit from slab edge insulation. Conventional slabs can be insulated beneath the broad floor panels waffle pods are insulated beneath. There are 2 types: conventional slabs with deep excavated beams and waffle pod slabs, which sit near ground level and have a grid of expanded polystyrene foam pods as void formers creating a maze of beams in between. Slab-on-ground is the most common type of slab. Some types of concrete slabs may be more suitable to a particular site and climate zone than others. If reinforcement is correctly designed and placed, and if the concrete is placed and compacted well so there are no voids or porous areas, concrete slabs can have an almost unlimited lifespan. Thermal mass needs to be combined with other passive design principles to be effective.Ĭoncrete has high embodied energy, but this can be offset by its permanence. Concrete slab floors provide good thermal mass, which works particularly well in cool climates and climates with a high day–night temperature range. Care should be taken during construction to prevent cracking and termite incursion.Ĭoncrete slab floors come in many forms and can be used to provide thermal comfort and lifestyle advantages.Conventional concrete has high levels of embodied energy, but this can be reduced by the use of cement extenders, geopolymer or magnesium cements, recycled aggregates or hempcrete.To act effectively as thermal mass, slabs should be internally exposed (that is, not covered with carpet, rugs or other flooring).Slabs should be insulated underneath in cold climates, and can be insulated on the edge in all climates. They can be insulated both underneath and on the edges. Concrete slabs need to be appropriately insulated to suit the climate.Concrete slabs can be onground, suspended, or a mix of both.A concrete slab floor provides a simple way to add thermal mass to a design. Thermal mass is useful in most climates, particularly cool climates and those with a high day-night temperature difference. Concrete slabs offer high thermal mass.Concrete slab floors suit many home designs and, when combined with appropriate passive design, can provide thermal comfort and reduce energy use.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |