Effect of Sudanese Aggregate on Production of High Strength Concrete

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The purpose of this paper was to study the effect of use of Sudanese aggregate with supplementary cementitious materials silica fume and fly ash in high strength concrete mixes, and study the effect of water- cementitious materials ratio and concrete ingredients in compressive strength, workability and cost of high strength concrete. The concrete specimens were tested at different age levels, 7-days and 28-days for mechanical properties of concrete, namely, cube compressive strength, fresh properties, slump test. This paper presents a part of an ongoing experimental laboratory investigations being carried out for production and characterization of high strength concrete for heightening of an existing concrete dam in the south of Sudan. Brief description of the main features of the dam and concrete works are presented. Hundreds of specimens were performed and tested using local Sudanese aggregates with addition of supplementary cementitious materials (Silica Fume and Fly Ash) and Super plasticizers. Various percentages of silica fume and fly ash were added at different water/cementitious (w/cm) ratios. Thirty three trial mix designs of grade 80 MPa according to ACI 211.4, high strength concrete had been success fully produced and their mechanical properties were measured and documented. The results have offered an important insight for relationship and influence of components mixture in properties of high strength concrete and in cost. The effect of w/cm ratio on strength of high strength concrete was also highlighted. Optimum replacement percentage is not a constant one but depends on the w/cm ratio of the mix. It is concluded that local concrete materials, in combination with supplementary cementitious materials can be utilized in producing high strength concrete in Sudan, water/cementitious ratio (w/cm)is in inverse relationship with compressive strength and its effect is very strong in strength, silica fume had a positive effect in producing high strength concrete and contributed to both short and long-term properties of concrete, fly ash had inverse relationship with28 days compressive strength, fine aggregate had an inverse relationship with compressive strength and local Sudanese coarse aggregate had a strong positive effect in producing high strength concrete. Also the effect of concrete ingredients in slump and cost were studied. Keywords- Compressive strength, Fly ash, High strength concrete, Silica fume, Super- plasticizers