Fine aggregates

Concreteyiggregate. A versatile appHcafion for coarse limestone aggregate is in Pordand cement concrete, either job-mixed or ready-mixed for a wide variety of concrete appHcafions, such as footings, poured foundations, paving, curbs, stmctural products, etc. Limestone sand also provides a satisfactory fine aggregate, but usually it is more cosdy than conventional sand from local pits. 

Railroads also require coarse and fine aggregate of physical strength and durabiHty similar to concrete and roadstone for road beds. Railroads prefer gradation of 19—63.5 mm as coarse aggregate. 

Umestone Sand. A discrete gradation of substantially 2.38—0.225 mm (8—65 mesh) size provides a versatile fine aggregate or sand for road mixtures, concrete, plaster, or any constmcfion use suppHed by siHca sand. The only disadvantage is that in many areas conventional sand is less cosdy. 

China clay waste, Quarrying Mainly tipping and in As fine aggregate in... 

As fill and in manufacture of bricks, cement and lightweight aggregate As fine aggregate in concrete, in manufacture of bricks and blocks and as fill Some resource and energy recovery... 

Concrete is a composite material composed of cement paste with interspersed coarse and fine aggregates. Cement paste is a porous material with pore sizes ranging from nanometers to micrometers in size. The large pores are known as capillary pores and the smaller pores are gel pores (i.e., pores within the hydrated cement gel). These pores contain water and within the water are a wide variety of dissolved ions. The most common pore solution ions are OH", K+ and Na+ with minor amounts of S042" and Ca2+. The microstructure of the cement paste is a controlling factor for durable concrete under set environmental exposure conditions. 

Quartz fine aggregates and normal Portland cement were used to prepare mortar at a w/c of 0.6. Mortar was cast into 30-mm diameter by 30-mm length cylinders and cured for 3 days. At the end of the curing period the specimens were oven dried at 105 °C until a constant mass was reached. Epoxy was then applied to the curved surface and the specimen was placed such that 1-2 mm of its height was immersed in a 20% NaCl solution. 

Quartz fine aggregate and normal Portland cement were used to prepare mortar with a w/c of 0.5. A cylindrical specimen, 43 mm in diameter and 50 mm long, was cast and cured under sealed conditions for 3 days at 23 °C. The specimen was then oven dried at 105 °C for 1 day prior to exposure to lithium nitrate solution. The specimen was then placed such that the bottom of the cylinder was submerged approximately 1-2 mm into a lithium nitrate solution with Teflon tape applied to the curved surface. 

The grain size distribution of spent foundry sand is very uniform, with approximately 85 to 95% of the material between 0.6mm and 0.15mm (No. 30 and No. 100) sieve sizes. Five to twelve percent of foundry sand can be expected to be smaller than 0.075 mm (No. 200 sieve). The particle shape is typically subangular to round. Spent foundry sand gradations are too fine to satisfy the fine aggregate standard specified in specification ASTM C33 Standard Specification for Concrete Aggregates. 

Sand equivalent value of soils and fine aggregate... 

Natural sand is a major component of most flowable fill mixes. Ferrous spent foundry sand can be used as substitute for natural sand (fine aggregate) in flowable fill.48 49 Spent sands from nonferrous foundries and foundry baghouse dust can contain high concentrations of heavy metals that may preclude their use in flowable fill applications. Some of the engineering properties of spent foundry sand that are of particular interest when foundry sand is used in flowable fill applications include particle shape, gradation, strength characteristics, soundness, deleterious substances, and corrosivity. 

For solid wastes to be suitable as a full or partial replacement for components in other applications, it should be free of objectionable material such as wood, garbage, and metal that can be introduced at the foundry. It should be free of foreign material and thick coatings of burnt carbon, binders, and mold additives that could inhibit product manufacture, such as cement hydration. It may be necessary to crush the solid waste to reduce the size of oversized core butts or unclasped molds. Magnetic separation is a good solution to producing a suitable coarse or fine aggregate product. 

Some end-use applications may prefer the characteristics of foundry solid waste. For instance, spent foundry sand is a uniformly graded fine aggregate containing chemically active iron and organics. Spent foundry sand can be superior to other types of granular materials, such as compacted soils or clays, for hydraulic barriers. In this case, spent foundry sand provides better performance at lower cost. 

Ontario Ministry of Transportation, Resistance of Fine Aggregate to Degradation by Abrasion in the MicroDuval Apparatus, LS-619, Ontario Ministry of Transportation, Ontario, Canada, 1996. 

Tennessee Department of Transportation, Test Reports on Samples of Coarse and Fine Aggregates, July, 1995. 

Bhat, S.T. and Lovell, C.W., Design of Flowable Fill Waste Foundry Sand as a Fine Aggregate, Paper 961066, Transportation Research Board, 75th Annual Meeting, Washington, DC, 1996. 

Vassiladou EE (1993) Utilization of fly and bottom ash as a partial fine aggregate replacement in asphalt concrete mixtures. Symposium proceedings Recovery and Effective Reuse of Discarded Materials and By-products for Construction of Highway Facilities. Federal Highway Administration, FHA 101... 

Coarse aggregate was crushed limestone with a maximum size of 19 mm. Fine aggregate was natural sand. Air-entraining admixture was a sulfonated hydrocarbon. 

Concrete which is produced using fine aggregates deficient at the fine end of grading, e.g. sea dredged aggregates, exhibit a tendency to bleed and segregate. The presence of a small amount of entrained air (2-4% by volume) leads to an improvement in cohesion, or mix stability. Alternatively, with mixes which are adequate in this respect, a reduction in sand content can be made when air is entrained without loss of cohesion. The amount that can be removed is approximately equal on a volume basis and leads to a reduction in water-cement ratio to minimize the effect of entrained air on compressive strength. 

There is no evidence to suggest that coarse aggregate shape or geological origin affect the amount of air entrainment obtained. The only exception is where crushed rock aggregates contain an appreciable quantity of dust which could influence the fine aggregate gradings considered below. 

Fig. 3.21 The effect of fine aggregate of 3-600 pm diameter on the air entrainment of concrete (Craven), of air. The effect of fly ash on air entrainment is also dependent on its carbon content (LOl - loss of ignition).

The presence of entrained air clearly makes the concrete more cohesive and allows a reduction in the quantity of fine aggregate, without increasing the tendency to segregate. The quantity of sand that can be removed from a concrete that is satisfactory in terms of cohesion prior to air entrainment is approximately 20 kg m 3 for each 1% of additional air content. 

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