Partial replacement of river sand with volcanic pyroclastics as fine aggregates in concrete production

The most commonly used fine aggregate in concrete production is river sand.Its extensive mining has led to massive environmental degradation.Volcanic activity in most parts of the world has deposited enormous amounts of pyroclastics especially volcanic tuff and lapilli which can be used to reduce overdependence on river sand.The effects of sand-pyroclastics mixture on workability of fresh concrete, absorption and compressive strength of cured concrete were investigated.Factorial experiments were done with 0%, 25%, 50%, 75%, and 100% sand replacement by weight of sand.Concrete test cubes were casted in 150 mm x 150 mm x 150 mm cube steel molds with a water-cement ratio of 0.445, and cured for 28 days.Workability decreased with increase in sand replacement.Water absorption for 150 x 150 x 150 mm concrete test cubes after 28 days curing period increased with increase in the amount of sand replaced.This followed the trend of individual aggregates.Compressive strength increased from 25.6 kNm -2 (0% sand replacement) to an optimum of 27.8 kNm -2 and 27.2 kNm -2 at 25% sand replacement for volcanic tuff and lapilli respectively at 28 days curing period due to the pozzolanic activity of volcanic tuff and lapilli material.The results have shown that replacing sand with up to 50% volcanic tuff or lapilli can produce lightweight concrete of class 25.This would reduce the amount of sand used in concrete manufacture with subsequent decrease in environmental degradation associated with mining of river sand.