EFFECT OF CONCRETE GRADE ENHANCER ADMIXTURE ON STRUCTURAL DESIGN OF HIGH-RISE BUILDING USING REINFORCED CONCRETE AT SEMERA

The thesis deals about the effect of concrete grade enhancer admixture on structural design of high-rise building using reinforced concrete at Semera, Ethiopia. Semera is a highly seismic area with a few apartment blocks, residence, hotels, administrative buildings, stadium and Airport. The research aims to investigate the effect of this admixture in related to structural design cost, concrete performance and other structural design related parameters using laboratory tests and sample structural designs. The laboratory test is done using 32 cubic and 32 prism specimens for compressive and flexural strength tests to determine concrete performance in related concrete workability, ductility, compressive and flexural strength. Among the total 64 concrete samples half of them is prepared using concrete grade enhancer admixture called “MegaFlow SP1, High Range Water Reducing Superplasticiser”. The average value of slump height, compressive and flexural strength of the selected trial mix is 3.76 Cm, 33.35 Mpa and 4.954 Mpa for C-25 concrete (concrete without admixture) and 5.22 Cm, 44.84 Mpa and 7.047 Mpa for C-40 concrete (concrete with admixture) respectively. Moreover, C-40 concrete is more ductile than C-25. The amount of admixture added on mixing proportion of C-25 concrete to get C-40 concrete is 2% by weigh of cement or 1 kg for one bag of cement with water cement ratio of 0.3. Accordingly, the mix ratio for C-40 concrete is 1:1:2:3 by volume with a box size of 50x40x18cm. Sample structural design is done for G+2, G+7 & G+12 multipurpose buildings with typical floor plan placed on 957m2 at Semera using C-25 and C-40 concrete types. The structural design cost using C-40 concrete is reduced by 7.74%, 12.79% and 22.03% for G+2, G+7 & G+12 buildings respectively in compare with C-25 concrete. However, even if the total cost of structural design is reduced, the usage of admixture for slab and staircase is not significant reduced structural design cost. Due to usage of admixture, the floor area which will be occupied by columns is reduced by 23.61% (2m2), 17.84% (2.59m2) and 12.45% (2.39 m2) for G+2, G+7 and G+12 buildings respectively. Furthermore, the floor clear height also increased by 1.79% (5cm), 1.82% (5cm) and 3.70% (10cm) for G+2, G+7 and G+12 buildings respectively due to reduction of beam depth. The percentage of cement saved due to usage of admixture in place of cement is 32.08 % or 170 kg with 44.01 % or 2992.71 birr cost reduction for 1m3 concrete work. Considering the facts, it is highly recommended to use a concrete mix with concrete grade enhancer admixture for structural design of buildings and other reinforced concrete structures.