Lightweight Expanded Clay Aggregates for a Multitude of Applications

Ironstone's Clear Hills Project features a significant amount of bentonitic-rich expandable clays that overlie the near-surface iron-vanadium deposit. These clays will be stripped and stockpiled from the surface to expose the flay-lying ironstone using electric draglines during the mining operations. Ironstone has identified a number of applications for these valuable clays, and will be conducting ongoing research and product development initiatives with a focus on addressing the many markets and applications available for these environmentally-friendly aggregate products.

What Are Lightweight Expandable Clay Aggregates?

Lightweight expanded clay aggregates (informally known as LECA) are totally natural products containing non-harmful substances with thermal insulating and water absorption/retention properties. With just 15% of the density of traditional aggregates, they are non-biodegradable, non-combustible and resistant to moisture, frost and chemical attack.

Lightweight aggregates can fill many roles that will make human activity more environmentally responsible. The greenhouse gas emission associated with both the processing of the raw material and from the fuel burned to produce the expansion of the raw material pales in comparison to the environmental rewards derived from its use. In Ironstone's case, waste heat derived from its iron-processing kilns and furnaces will be used for the most part, thereby making enhancing the environmentally benefits even more so.

Lightweight expanded clay aggregates or bloated clays is a light-weight aggregate made by heating clay at high temperature in a rotary kiln. The yielding gases expand the clay by thousands of small bubbles forming during heating producing a honeycomb-like structure. LECA has an roughly round shape due to circular movement in the kiln, and is available in different sizes and densities. Lightweight aggregates can fill many roles that will make human activity more environmentally responsible. The raw material generally being high in silica content releases low amounts of greenhouse gases upon heating unlike the ingredients used to make cement. The emissions from manufacturing cement are about one tonne of CO2 per tonne of cement and for expanding clay is generally about 0.3 tonnes of CO2 per tonne of aggregates produced.

AGGREGATES used in ConstructioN

Structural concrete made with rotary kiln produced lightweight aggregate solves weight and durability problems in buildings and exposed structures. The structural lightweight concrete has strengths comparable to normal weight concrete, yet is typically 25% to 35% lighter. Structural lightweight concrete offers design flexibility and substantial cost savings by providing less dead load, improved seismic structural response, longer spans, better fire ratings, thinner sections, decreased story height, smaller size structural members, less reinforcing steel, and lower foundations costs. Structural lightweight concrete precast elements have reduced trucking and placement costs. The excellent durability performance of structural lightweight concrete made with expanded clay lightweight aggregate is a result of the ceramic nature of the aggregate, and its exceptional bond to and elastic compatibility with the cementitious matrix.

Making lightweight concrete has been the dominant use of lightweight aggregates in the past. It has been shown that the extra energy expended to expand clay in a rotary kiln can easily be recovered in the savings associated with the decrease in density of the concrete made from them. The savings arise not only from reduced footings, columns and beam sizes, but also from the enhanced thermal properties of the concrete. The manufacture of lightweight aggregates results in the release of some CO2 but the savings in CO2 emissions associated with the need for less of the other materials more than compensates for this release.

Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined materials in the world. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement to add strength to the overall composite material. Due to the relatively high hydraulic conductivity value as compared to most soils, aggregates are widely used in drainage applications such as foundation and French drains, septic drain fields, retaining wall drains, and road side edge drains. Aggregates are also used as base material under foundations, roads, and railroads. In other words, aggregates are used as a stable foundation or road/rail base with predictable, uniform properties (e.g. to help prevent differential settling under the road or building), or as a low-cost extender that binds with more expensive cement or asphalt to form concrete.

Aggregates Used in Geotechnical applications

Lightweight aggregate fills are approximately half the weight of common fills.  This advantage, coupled with its predictable high internal friction angle, can also reduce lateral forces by more than one-half.  It has been effectively used to solve numerous geotechnical engineering problems and to convert unstable soft soil into usable land. Lightweight fill also provides permanent non-degradable insulation around water lines and steam lines, and other thermally sensitive elements.  Expanded clay lightweight aggregate is a reliable and economical geotechnical solution when used in waterfront structures, landscape & elevated plaza fills, bulkheads and retaining walls, as fill over poor soil and marshlands and landfill leachate drainage systems, to name but a few.

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More recently lightweight aggregates have found new uses such as for horticultural applications such as a growing medium for creating a lusher environment. Not only do the low density aggregates provide up to a 30% lighter growing medium in order to reduce the weight of plants and landscapes soils, but the pores within the aggregates become a reservoir for irrigating water and fertilizers thereby reducing the cost of maintaining a green roof.

When combined with growing mediums and blended with other growing mediums such as soil and peat to improve drainage, water is retained during periods of drought, roots are insulated during frost and roots are provided with increased oxygen levels promoting very vigorous growth.

Lightweight aggregates are also used in water treatment facilities for the filtration and purification of municipal wastewater and drinking water as well as in other filtering processes, including those for dealing with industrial wastewater and fish farms.

Aggregates used in HORTICULTURE and reducing heat island effects

Expanded clay aggregates plays a valuable role in today's horticulture and landscape design. For innovative, cost-effective, long-term solutions to modern horticulture and landscape design challenges, design professionals have turned to clay aggregates, whether it is creating an ideal planting media for a rooftop garden, designing a soil for an athletic field or improving an existing soil to sustain a plant design. Native soils have silts and clays that may clog the filter materials or drainage layer and reduce effectiveness. Weight reduction and product performance are the primary reason clay aggregates are so versatile and used in so many different applications

n the quest to reduce the “heat island” generated by cities, the easiest and most common approach is to replace impermeable non-reflective surfaces such as tar and gravel roofs with vegetation (i.e. Green Roof). This presents an increased structural load which can easily be reduced by employing expanded aggregates as part of the growing medium and as a drainage layer. Not only does this reduce the load, but it also acts to provide a controlled release of irrigating water and fertilizer. In this instance an aggregate with a high water absorption is desirable. The combination of high water absorption and a relative low particle density in expanded aggregates that makes them ideally suited for this use.

Other Lightweight Aggregate Applications

The superior qualities of structural lightweight aggregate are effective and economical in many other applications.  Examples include wood floor topping, bagged concrete mixture, cement wallboard, artificial stone, concrete roof tile, refractory concrete, phosphorous removal, subsurface flow wetlands, traction grit, grog, insulating fill and many, many more.

Aggregates Made From Steel Furnace Slag

The largest-volume of recycled material used as construction aggregate is steel furnace slag. This type of slag develops strong hydraulic cementitious properties and can partly substitute for portland cement in concrete. Steel furnace slag aggregates can be used in road bases and surfaces, asphaltic concrete, ready-mixed concrete, and other uses. Ironstone will be investigating and testing its steel slag for use in specific construction aggregates.