Question

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Reference for problem 4 Pornland Cemen S handout (uploaded to elearning PCA mannal (5 edition) chaper MCPman p 52-54 Problem 4 . List at least three sources of mixing water. 2What are the two perfoemance requirements listed in ASTM C16 for mixing water? Briefly describe the impact of following impurities on concrete Impurity Chlorides Sulfate Alkali Carbonate and Bicarbonate Inorganic Sabts Iron Salts Alkaline Waters Acid Waters Silt or Suspended Particles

Answer 1

1. Mixing water sources are

1. Batch water which is weighed or metered through the batch plant

2. Ice

3.Free moisture on aggregates

4.Potable water

5. Water introduced in the form of admixtures

2. Two performance requirements for mixing water listed in ASTM C-1602 are

a. Compressive strength of concrete after 7 days made from questionable water supply should be not less than 90 % of strength of concrete made from 100% potable water or distilled water.

b. Deviation of the time of set of concrete (h : min) made from questionable water supply should be within the limits of 1:00 early to 1:30 from the concrete made from 100% potable or distilled water.

3. Chlorides :They tend to cause persistent dampness and efflorescence on the surface of concrete.

Sulphates : They result in the formation of calcium sulphate and calcium sulphoaluminate (ettringite) causing expansion and disruption of concrete.

Alkali Carbonates and Bicarbonates: Effect the setting time of concrete.Sodium carbonate causes quick setting while the bicarbonates either accelerate or retard the setting.

Inorganic Salts : They reduces strength of concrete and also results in corrosion of reinforcement.

Iron Salts: Marked reduction in strength of concrete.

Alkaline water: Effect the Setting time and reduces the strength of concrete.

Acidic water: Leads to the corrosion of reinforcement decreasing the strength and ultimately causing failure of concrete.

Silts and suspended particles: they interfere with setting, hardening and Bond characteristics.