Importance of water quality in the concrete mix

With water in short supply in many parts of South Africa, concrete producers could face increasing pressure to use water from sources other than municipal tap water in future, says John Roxburgh, senior lecturer at Cement and Concrete SA’s School of Concrete Technology.

Poor quality water could affect the quality of concrete, says CCSA.

“But the quality of concrete may be adversely affected by using poor quality water,” Roxburgh warns.

He says likely consequences could include:

· Alteration of the concrete’s setting times;

· Increase in water demand;

· Entraining of excessive air;

· Change in the concrete’s strength gain characteristics;

· Degradation of the hardened concrete;

· Corrosion of the reinforcement in the concrete;

· Staining and production of efflorescence.

“Mixing water makes up about 8% of the total mass of concrete. So, the proportion of impurities in the mixing water compared to the mass of cement is typically very low. Nevertheless, non-potable water should always be assessed for suitability for use as mixing water in concrete. The limits to the quantities of impurities in the water should be checked against the requirements of the South African National Standards’ SANS 51008 which contains specifications for sampling, testing and assessing the suitability of water for concrete production,” Roxburgh states.

John Roxburgh, senior lecturer at Cement and Concrete SA’s School of Concrete Technology

He says when assessing the suitability of water of unknown quality, both the composition of the water and proposed application of the concrete should be considered. In general, the suitability of water for concrete depends on its origin. The following types could be encountered:

Potable water is suitable for use in concrete and needs no testing.

Water recovered from processes in the concrete industry will normally be suitable but must conform to SANS 51008.

Water from underground sources may be suitable but must also be tested and assessed in accordance with the requirements of SANS 51008.

Natural surface water and industrial waste water may be suitable for use in concrete, but here also needs testing in terms of SANS 51008.

Sea water or brackish water may be used for concrete that will not contain steel reinforcement or other embedded metal. For concrete with steel reinforcement, or embedded metal, the permitted total chloride content in the concrete is the determining factor.

Sewage water is not suitable for use in concrete.

Sea water may be used for concrete – but only when it will not contain steel reinforcement or other embedded metal.

“Some common substances deleterious to concrete and found in water are chlorides, sulphates, acids, alkalis, humic matter, oil, algae, sugar and detergents. There are many more and SANS 51008 should be consulted.

“Water for use in concrete must conform to the requirements for preliminary assessment and for chloride, sulphate and alkali contents. The water must also conform to either the chemical requirements for harmful contamination, or the requirements for setting time and compressive strength,” Roxburgh adds.

“The sulphate content of the water must not exceed 2 000 mg/ℓ. This limit should always be assessed with regards to sulphate content within the aggregate and cement. If alkali-reactive aggregates are to be used in the concrete, the water must be tested for its alkali content. If high, the water may be used only if it can be shown that actions have been taken to prevent deleterious alkali-silica reactions,” Roxburgh explains.

Regarding harmful contamination, firstly qualitative tests for sugars, phosphates, nitrates, lead and zinc must be carried out. If the qualitative tests are not performed or show a positive result, either the quantity of the substance concerned must be determined or tests for setting time and compressive strength be performed.

“The initial setting time obtained on specimens made with the unknown water must not be under an hour and not differ by more than 25% from the initial setting time of specimens made with distilled or de-ionised water. The final setting time must not exceed 12 hours and not differ by more than 25% from the final setting time obtained on specimens made with distilled or de-ionised water.

“The mean compressive strength at seven days of the concrete, or mortar specimens prepared with the water, must be at least 90% of the mean compressive strength of corresponding specimens prepared with distilled or de-ionised water,” he advises.

When sampling water, volumes of at least five litres must be used, taking the possible effects of seasonal fluctuations in consideration. The water must be tested within two weeks of sampling.

“SANS 51008 also provides test methods for the tests required, applicable frequencies for testing and detailed requirements for the use of water recovered from processes in the concrete industry,” Roxburgh concludes.



Latest


18 Jun 2021
Biophilic design colours and textures

Biophilic design has experienced a resurgence in popularity driven largely by the upswing in time-spent-at-home. The design of living areas…

Biophilic design colours and textures

Biophilic design has experienced a resurgence in popularity driven largely by the upswing in time-spent-at-home. The design of living areas is focused on creating healthy spaces for people to gather, in a post-pandemic imagining of what our public and private spaces could be. To this end, the earthbound design draws…

18 Jun 2021
Zutari co-creates innovative structural solutions for iconic 16 on Bree

At 120 m and 36 storeys, 16 on Bree is the tallest residential and second-tallest mixed-use development in Cape Town…

Zutari co-creates innovative structural solutions for iconic 16 on Bree

At 120 m and 36 storeys, 16 on Bree is the tallest residential and second-tallest mixed-use development in Cape Town in the last 20 years. FWJK Developments conceived the project as an iconic high-rise to meet the demand in the market for quality residential apartments. A key requirement for the…

15 Jun 2021
DuPont performance building solutions launches Residentially Speaking podcast series

Podcast series spotlights industry trends with thought leaders of the residential home building industry  DuPont announced Residentially Speaking, a podcast series hosted by…

DuPont performance building solutions launches Residentially Speaking podcast series

Podcast series spotlights industry trends with thought leaders of the residential home building industry  DuPont announced Residentially Speaking, a podcast series hosted by Alan Hubbell, Residential Marketing Leader, DuPont Performance Building Solutions. Each educational podcast features expert guests addressing topics most relevant to building high performance residential and multi-family wood-framed homes. The Residentially Speaking series brings the…

14 Jun 2021
Winners of 2019 & 2020 Corobrik Student Architecture Awards announced

The winners of the 2019 & 2020 Corobrik Student Architecture Awards were announced at a first-ever hybrid event hosted by…

Winners of 2019 & 2020 Corobrik Student Architecture Awards announced

The winners of the 2019 & 2020 Corobrik Student Architecture Awards were announced at a first-ever hybrid event hosted by the company in Johannesburg on Thursday 10 June. The 2019 awards ceremony had to be postponed due to Covid-19, but Corobrik adapted and instead decided to host the 2019 and…


Top stories


05 Mar 2020
First Green Key Boutique Hotel in South Africa

21 Nettleton attains their Green Key Award from WESSA, becoming South Africa’s first boutique hotel to achieve this accolade for…

First Green Key Boutique Hotel in South Africa

21 Nettleton attains their Green Key Award from WESSA, becoming South Africa’s first boutique hotel to achieve this accolade for its efforts in sustainability. An exciting partnership between WESSA and 21 Nettleton has resulted in the private boutique hotel in Clifton, Cape Town being awarded the prestigious Green Key award.…

27 Feb 2020
The Nxuba wind farm Renewable Energy

In its ongoing efforts to showcase the potential that renewables can play in boosting the security of energy supplies in…

The Nxuba wind farm Renewable Energy

In its ongoing efforts to showcase the potential that renewables can play in boosting the security of energy supplies in South Africa, Enel Green Power (EGP) highlights its commitment to the country as it nears the completion of its Nxuba wind farm in the Eastern Cape. The company recently started…

23 Jan 2020
Refurbishment at North West University

As the three established divisions of Norcros SA, TAL, Johnson Tiles and Tile Africa recently played important roles in an…

Refurbishment at North West University

As the three established divisions of Norcros SA, TAL, Johnson Tiles and Tile Africa recently played important roles in an extensive tiling project at North-West University’s Potchefstroom campus in North West Province. The project entailed refurbishing the five-block Sports Village, a guest house facility providing accommodation for the public, athletes…

06 Mar 2020
7 Awe-inspiring marble use cases

Marble, an exceptionally versatile material used for centuries to create awe-inspiring art, majestic staircases, classic kitchens and resplendent flooring. With…

7 Awe-inspiring marble use cases

Marble, an exceptionally versatile material used for centuries to create awe-inspiring art, majestic staircases, classic kitchens and resplendent flooring. With today’s contemporary design trends, the wide selection of marble can be used in more ways than ever before.


Visit the official COVID-19 government website to stay informed: sacoronavirus.co.za