TESTS ON WATER FOR CONCRETE
A simple way of determining the suitability of water for mixing is to compare the setting time of cement and the strength of mortar cubes using the water in question with the corresponding results obtained using de-ionized or distilled water. The initial setting time should not be less than 1 hour and to be within 25% of the result with distilled water. Final setting time shall not exceed 12 hours and also be within 25% with the distilled water. The mean strength should be atleast 90 per cent of that obtained with distilled water. Those requirements may be compared with BS 3146: 1980, which suggests a tolerance of 30 min in the initial setting time and recommends a tolerance of 10 per cent for strength. The ASTM C 1602 – 06 requirement for setting time is from 1 hour early to 1 hour 30min later, while strength has to be at least 90 per cent.
Whether or not staining will occur due to impurities in the curing water cannot be determined on the basis of chemical analysis and should be checked by a performance test involving simulated wetting and evaporation.