Alkali-Silica Reaction Lab Report

QUESTION 1

(A)

Alkali-silica reaction

• Chemical reactions that take place between the alkali pore solution of concrete and metastable forms of silica.

• The aggregates that react to alkali can be identified by using the petrographic examination or the laboratory test found in SANS 6245.

Hydration reaction

• Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products.

• Heat is given off during the chemical reaction as the cement hydrates.

• Fast reaction (C3S + H => C-S-H + C-H) which increases the rate of the heat being released and the development of strength.

• It is a lime producing reaction.

Pozzolanic reaction

• A chemical reaction that occurs

• Step 2 o In 4 x 10kg containers place 5kg of stone in the first, 5kg of sand in the second, 10kg of stone in the third and 10kg of sand in the last.

• Step 3 o Place the contents of step 1, the 5kg of stone and the 5kg of sand in a mixing container and mix until you get a “sloppy” consistency.

• Step 4 o Add and keep adding handful amounts of the 10kg of stone and the 10kg of sand from step 2 into the mixing container in step 3 until the consistency is wetter than required.

• Step 5 o Measure the slump of the contents in step 4 and if too low restart the “Eye-ball” mix, if too high continue the process of step 4 until the optimum slump is reached.

• Step 6 o When the correct slump is reached check the cohesiveness and the stone content of the mix adjust if necessary. o Weigh out the left-over 10kg of stone and 10kg of sand then calculate the concrete mix proportions.

(B)

• Method 1 o Membrane-forming liquids sprayed onto the surface of concrete to inhibit evaporation of water must be applied as soon as either the bleed water has evaporated from the surface or bleeding has