I Explain the difference between a supplementary cementitiou

I. Explain the difference between a supplementary cementitious material and a pozzolan (4 points) 2. State four water m iruuiti nd their effet on conerete duive and strength (4 points). Impurity Effect Give concrete mix design examples of how a water-reducing admixture can be used to: a. b. 3. Reduce the amount of cement (2 points) Increase the workability of concrete (2 points) Sample Reference Part (a) Part (b) Admixture Slump Strength kgm2) Cement Ratio content (ky/m (mm)MPa) Cement content Water- 350 0.6 0 50 28 Part (c)

Solution

Solution :

Ans 1)

Supplementary Cementious Material is wide term. They are added to cement as part of the total cementitios system. They may be used in addition to or as a partial replacement of portland cement in concrete. Their purpose is to improve a particular concrete property. Fly ash, ground granulated blast -furnace slag, calcined clay or metakaolin, are materials that, when used used with cement may contribute to one or more properties of hardened concrete.

Where as Pozzolans are a broad class of siliceous and aluminous materials which in themselves possess little or no cementitious value but will, in presence of water, react with calcium hydroxide to form compunds which possess cementitious properties. They are usually of volcanic origin.

Ans 2)

a) Zinc Chloride : The presence of zinc chloride in water results in the retarding of concrete strength gain

b) Sodium and Potassium Carbonate : They cause extremely large rapid setting in large concentrations. This results in the reduction of concrete strength.

c) Organic substances : Reduction in strength and large variations in setting time.

d) Sugar : Severely retards the setting of cement.