EFFECT OF GYPSUM POWDER AS PARTIAL REPLACEMENT OF EAST CEMENT ON FRESH AND HARDENED PROPERTIES OF SELF-COMPACTING CONCRETE
Creators: name: CHERNET GETANEH TEBABAL
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2019
Subjects: Self-compacting Concrete, Gypsum Powder, East Cement, Compressive Strength

description: Self-compacting concrete (SCC) is among the latest advancements in concrete<br> technology. SCC has got its flow-ability and compact-ability properties by the use of a<br> high amount of cement and fine aggregate as compared to normal concrete. The use of a<br> high amount of cement increases the cost of self-compacting concrete. To reduce the cost<br> of cement and to gain the subsequent improvement of properties, replacing it partially<br> with other cementitious or non- cementitious materials is taken as one solution. Many<br> types of research have been done on the replacement of cement with limestone, silica<br> fume, phosphogypsum, etc. Gypsum is naturally abundant in Ethiopia. Only in Muger<br> and Jema Valleys, more than 57,000,000 tons reserve of gypsum is available. Even<br> though it is not quantified, comparable or more deposit is available in Abay gorge,<br> Mekele outlier, and other locations. Using this abundant material as a replacement of<br> cement will reduce the cost of self-compacting concrete and play a huge role in the<br> reduction of carbon dioxide emissions to the environment. In this study, the potential of<br> gypsum powder as a replacement of cement and its effect on the fresh and hardened<br> properties of SCC with different percentage replacement is investigated. The aim of the<br> study is to determine the optimum amount of gypsum powder replacement for the desired<br> compactability, flowability, viscosity and strength properties in addition to spotting the<br> effect of increment of gypsum powder as 0%, 5%, 10%, 15%, and 20% along with its<br> economic viability. SCC mixes with gypsum powder replacement were prepared with the<br> ACI mix design method for SCC. Cement grade CEM I 42.5N, coarse aggregates less<br> than 12.5mm size, river sand, and Sikament® NN superplasticizer were used. Slump flow,<br> L-box, V-funnel and setting time tests were conducted for fresh SCC properties while<br> compressive tests were done for hardened concrete properties with ASTM testing<br> procedures. A total of 36 cube samples was prepared for tests at 7, 14 and 28 days.<br> Among the replacements, 20% replacement did not satisfy the fresh SCC properties and<br> was not considered for strength comparison. 15% replacement was found as an optimum<br> replacement percentage. Compressive strength at twenty-eight days of 5%, 10% and 15%<br> replacements attained respectively 72.18%, 58.12% and 60.56% strength of the control<br> (0%) 40MPa SCC. Gypsum powder replaced cement showed accelerated setting times.<br> Only 5% of replacement cement maintained the Portland cement setting time limits.<br> Initial setting time is highly improved to more than 5hrs for all replacements with the<br> addition of superplasticizer. Hence, gypsum powder can be used as a cement replacement<br> for the production of SCC with reduced compressive strength.