Civil Engineering Horizon - effect of water quality on concrete

The properties of concrete are vital factors, which determine to a great extent the strength and serviceability of structures. Concrete is plastic and malleable in green state but strong and durable when hardened. These qualities explained why concrete can be used for constructing skyscrapers, bridges, etc (Portland Cement Association, 2005). There are many factors that determine the quality of concrete and its strength. These include the type of cement used, aggregate quality and grading, the degree of compaction, quality and quantity of water used in concreting, curing method, type of reinforcement embedded including its sizes, arrangement and spacing, etc.

Of important at present is the quality of the mixing water. According to Neville (1996), the quality of water plays a significant role; impurities in water may interfere with the setting of the cement paste; adversely affect the strength of the concrete or cause straining on its surface, corrosion of the reinforcement. Steinour (1960) agreed that some waters which adversely affect hardened concrete may be harmless or beneficial when in mixing. In drawing specifications for many civil engineering projects, the water requirement is covered in a clause saying it must be fitted for drinking.

Water fitted for drinking is generally satisfactory, but there are exceptional cases. For instance, in some arid areas, local drinking water is saline and may contain an excessive amount of chloride, undesirable amount of alkali carbonates and bicarbonates, which could contribute to the alkali-silica reaction (Neville, 1996). However, some waters that are not fit for drinking may be suitable for concrete production (Portland Cement Association, 2005). McCoy (1978) opined that water with pH range of 6.0 to 8.0 is good for concreting. McCoy (1956) suggested the use of water with pH 9.0, which does not taste brackish in concrete work.

Furthermore, mixing water with high content of suspended solids needs to stand in a settling basin before use; a turbidity limit of 2000ppm has been suggested by U.S. Bureau of Reclamation (1975). Natural waters that are slightly acid are harmless, but water containing humic or other organic acids may adversely affect the hardening of concrete (Neville, 1996). Different ions have separate effect on concrete (Steinour, 1960). Doell (1954) investigated the effect of algae on concrete, which resulted to entrainment of air with a consequent loss of concrete strength. Building Research Station (1956) reported the success recorded in the use of water with higher salts contents such as chloride (higher than 500ppm) and trioxosulphate v (higher than 1000ppm).

Thomas and Lisk (1970) suggested that sea water slightly accelerates the setting time of cement. Water containing large quantities of chlorides (sea water) tends to cause dampness and surface efflorescence. Such water should not be used where appearance of concrete is of importance or where a plaster finish is to be applied (Lea, 1956). The presence of chlorides in concrete containing embedded steel can lead to steel corrosion (Neville, 1996). Tests on mixes with ranges of water suitable for use in concrete showed no effect on the structure of the hydrated cement paste (Ghorab et al. 1989). Al-Manaseer et al (1988) showed that water containing very percentages of salts of sodium, potassium, calcium and magnesium used in making concrete containing Portland cement blended with fly ash did not affect the strength of concrete. Chatveera et al (2006) utilised and recycled sludge water as mixing water for concrete production and found that concrete slump and strength reduced drastically.

Compressive strength, mineralogy, chloride ingress, and corrosion of steel bars embedded in concrete made with seawater and tap water were investigated based on the several long-term exposure under tidal environment. Seawater-mixed concrete showed earlier strength gain. After 20 years of exposure, no significant difference in the compressive strength of concrete was observed for concrete mixed with seawater and tap water (Mohammed et al, 2004). Islam and Kaushik (1995) studied the mixing and curing effect of sea water on setting time, compressive strength of cement-sand mortar and corresponding concrete, rebar corrosion, chloride content and variation of alkalinity over a period of 18 months in a laboratory simulated splash/tidal zone of marine environment. The test results indicate that sea water was not suitable for the mixing and curing of both plain and reinforced concrete in marine conditions.

Su et al (2002) described the effect of different types of mixing water on properties of mortar and concrete such as compressive strength, setting times and workability. The compressive strength of concrete mixed with wash water or underground water was as good as that with tap water. Therefore, it was suggested that underground water should be considered as mixing water for concrete and wash water be recycled where tap water resources are scarce. The potential use of groundwater and oily production water in flowable fills was investigated by Al-Harthy et al (2005). Flowable fill blends prepared using brackish groundwater gave higher strength than mixes prepared using oily production water. Kumar (2000) studied the effects of the quality of mixing water and initial curing on the strength of concrete exposed to seawater attack in marine environment for a period of 1year. Results of this study showed that the use of precasting in place of casting-in-situ mitigated the effect of marine environments on concrete specimens considerably.

Even though, the basic requirement for water for concreting is its potability; the question that comes to mind is the availability of potable water for concreting. In developing countries, provision of water to meet domestic demand has not been fulfilled. In urban areas, such as Ibadan, Lagos Kano etc in Nigeria, only few percentages of the populace have access to potable or wholesome water. Ibadan city, the biggest city in West African countries is facing with scarcity of potable water supply. The two water treatment plants are not adequate to produce the water need. The plants are producing below installation capacities due to inadequate power supply and other problems. If the potable water available can not meet the domestic requirement, it will be difficult for an average contractor to comply with the requirement for mixing water in contract document. The contractors would seek for alternative means by using available surface water once it is clean, clear and of little or no odour for concrete work without testing its suitability.

The city of Ibadan has one major stream called Ogunpa that serves as major drain. Occasional flooding of the stream occurred in early 1980s that instigated the need to carry out channelisation of the stream and construction of bridges over the stream. The project started few years ago and later abandoned. Presently the contract has been re-awarded, which involves about a several cubic metre of concrete. The quantity of water required for the concrete works will be enormous and as such temptation may arise on the part of the contractors to use Ogunpa stream water. Consequently, the research was conducted to determine suitability of Ogunpa stream water for concrete work.

Abstract Introduction Methodology Result Discussion Conclusions References

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