WHO'S WHO IN CONCRETE
Sea water may be used for concrete, but only when it does not contain steel reinforcement or other embedded metal
As current and future water scarcity intensifies, concrete producers could come under increasing pressure to use alternatives sources to potable water. While that’s a practical solution, testing will be required to ensure it meets quality standards, says John Roxburgh, senior lecturer at Cement and Concrete SA (CCSA).
Water quality in the concrete mix
M
ixing water makes up about 8% of the total mass of concrete. So, the propor tion of impurities in the mixing water compared to the mass of cement is typically ver y low. For example, 2 000 mg/ℓ of total
John Roxburgh, senior lecturer, Cement and Concrete SA
dissolved solids in water equates to about 400 g of material per cubic metre of concrete, compared with 300 kg to 400 kg of cement. Most of the time, these impurities have little to no effect on the hardened concrete; however, the limits to the quantities of
TABLE 1 Requirements for preliminary inspection of mixing water
Item Oils/fats Detergents Colour Suspended matter
Odour
Acids Humic matter
10
IMIESA May 2021
Requirement No more than visible traces Any foam should disappear within two minutes Water not recovered from processes in the concrete industry: the colour must be assessed qualitatively as pale yellow or paler Water from processes in the concrete industry (see SANS 51008) Water from other sources: Maximum 4 mℓ sediment Water from processes in the concrete industry: there must be no smell, except the odour allowed for potable water and a slight smell of cement. Where blast furnace slag is present in the water, a slight smell of hydrogen sulfide is acceptable Water from other sources: there must also be no smell, except the odour allowed for potable water. No smell of hydrogen sulfide after addition of hydrochloric acid is acceptable The pH level must be greater than or equal to 4 The colour must be assessed qualitatively as yellowish brown or paler, after addition of NaOH
impurities in the water should always be checked against the requirements of SANS 51008. In general, water suitability depends on its origin. Viable examples include: - potable water, which is suitable for use in concrete and needs no testing - water recovered from processes in the concrete industr y - water from underground sources - n atural sur face water and industrial wastewater - sea water or brackish water where the concrete formed does not contain steel reinforcement or other embedded metal;
