Experimental Study on Partial Replacement of Coarse Aggregate with Crushed Clay Brick to Produce C-25 Concrete

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Addis Ababa University


Concrete is a material that is composed of 60-80% of aggregates by volume. Natural crushed basaltic rock is extensively used in Addis Ababa as a coarse aggregate in concrete production. Studies have shown that extensive production of coarse aggregate from natural resources has negative impact on the landscape, water and atmosphere. To alleviate this negative impact, the experimental research aims to partially replace the basaltic coarse aggregate with waste crushed clay brick obtained from brick factories located in and around Addis Ababa, in concrete production. The research studied the effect of replacing a C-25 grade concrete coarse aggregate with crushed clay brick by 10%, 20%, 30%, 40% and 100% by volume. The effect on workability, hardened density, compressive strength, flexural strength and water penetration depth were investigated. The clay bricks used as replacements were collected from four different brick factories that are found in and around Addis Ababa. A total of twenty one concrete mixes were made that include the control and the replacement mixes. A water/cement ratio of 0.49 was used for all the mixes. In all the mixes the crushed clay bricks were used in a saturated surface dry condition. The findings of the experimental study showed that all the crushed clay bricks obtained from representative four different brick factories can be used as partial replacement of coarse aggregate up to 30% with a water/cement ratio of 0.49. Full replacement of coarse aggregate with crushed clay brick was made possible with a water/cement ratio of 0.40 though that particular concrete mixture was found to be uneconomical compared with the unit cost of the control mix. It was found that the slump and flexural strength of the replacement mix decreased when the crushed clay aggregate replacement percentage increased. The hardened density of the concrete produced with 30% replacement amount decreased by 3% from the control mix. Based on the water penetration test, it was found that the water penetration depth of the concrete increased when the CCB aggregate replacement increased. The amount of cost reduced when using 30% of CCB aggregates in replacement of crushed basalt stone is very insignificant only by 0.98% per one meter cube of concrete.



Coarse aggregate, crushed clay brick, partial replacement