Effect of total dissolved solids-contaminated water on the properties of concrete

Highlights

• Effect of TDS on the properties of concrete mixtures, with different concentrations of TDS in mixing water, was examined.

• TDS in mixing water showed significant effect on workability, setting time, strength, and durability characteristics.

• A TDS concentration of 1000 ppm may be safely allowed in the mixing water for producing concrete.

Abstract

Total dissolved solids (TDS) is one of the main impurities in the mixing water that can influence the properties of concrete, and therefore, the codes of practice limit the concentration of TDS in water used for producing concrete. The present study investigates the effect of TDS present in the mixing water on the properties of concrete in fresh and hardened states. Concrete mixtures were prepared using water with different selected concentrations of TDS (500, 1000, 5000, and 15000 ppm) keeping the proportions of the main ingredients invariant. Experimental tests including workability, initial setting time, air content, compressive strength, water absorption, water permeability, chloride permeability, and electrical resistivity were conducted. The results showed that the workability and initial setting time were reduced with increase in the TDS concentration, however, these properties remained within the acceptable limits as specified by ASTM C191-18a. At higher concentrations of the TDS, air content and water absorption of concrete deceased by about 31% and 6%, respectively, and compressive strength increased by about 20%, indicating positive effect of the higher concentration of TDS on the quality of concrete. However, the compressive strength was found to be slightly lower at the TDS content of 15000 ppm. Resistance against water penetration and electrical resistivity of concrete decreased slightly at higher TDS concentrations, however, water permeability class and the likelihood of reinforcement corrosion remained unaffected. The chloride permeability increased from moderate to high level when TDS concentration exceeded 1000 ppm. Based on the finding of this study, it may be concluded that the waters having TDS up to 1000 ppm can be recycled for concrete production that would benefit in cost reduction and conservation of water resources.

Introduction

Water is one of the essentially required ingredients for producing paste, mortar and concrete using hydraulic cements. Presence of water in a concrete mixture facilitates proper mixing of the ingredients and most importantly hydration of cement, without which the strength would not be evolved. Water is also used for curing concrete to make sure that the concrete achieves targeted strength and durability without undergoing unacceptable shrinkage. The potable water is ideally suitable for producing concrete, however, this is not always possible to use potable water due to resource and cost constraints [1]. Tay and Tip [2] indicated that the un-drinking water can be still suitable for concrete mixtures provided that the water should satisfy the standard requirements. To avoid the detrimental effects of the impurities in water on the fresh and hardened properties of concrete, maximum permissible limits of chemical substances such as oil, organic, acid, alkali, total dissolved solids (TDS), chlorides, sulfates, etc., are specified by the relevant codes of practice (ASTM C94 [3], ASTM C1602 [4], ACI 318 [5], AASHTO T 26 [6], BS: 3148–1980 [7]).

Up to date, no detailed guidelines are available for specifying the quality of the questionable waters for producing concrete [8]. The specifications pertaining to the permissible limits of the impurities in questionable waters, made by the codes of practice, vary. ASTM C1602 [4] specified the TDS to be less than 50,000 ppm for mixing water for concrete. Other standards restricted TDS limit to be around 2000 ppm [10]. However, some specific recommendations and restrictions are considered in the areas, such as the Middle East countries, where water contains uncommon harmful materials. For example, according to Saudi ARAMCO¹ standards, the concentration of TDS in water for producing concrete should not exceed 5000 ppm.

The study conducted by Su et al. [1] on the usage of different types of water (tap water, underground water and wash water) as a mixing water for producing concrete revealed that the quality of mixing water has a direct effect on the fresh and hardened properties of concrete that included workability, setting time, strength development, and overall durability characteristics. Although the wash water contains residual cement particles, all types of water satisfied the ASTM C94 [3] requirements. The results showed that the underground and wash water (collected from either the top or middle of the mixer with total solids of 1530 ppm) gave the same slump and compressive strength as those of the tap water. Matos et al. [11] investigated the effect of water obtained from truck mixer wash on the fresh and hardened properties of concrete. The wash water has a solid content of 6240 ppm and pH of 11.07. The test results showed that the wash water increased the viscosity of the pastes and yield stress by 11% and 25%, respectively. In addition, the concrete prepared using wash water exhibited a compressive strength comparable with that of the reference concrete made with fresh water.

Asadollahfardi et al. [12] experimentally investigated the feasibility of re-using the concrete wash water (CWW), obtained from washing batching plants and concrete truck mixtures, in producing concrete. The chemical analysis of CWW showed that it contains total solids of about 2500 mg/l compared to 530 mg/l for tap water. Concrete specimens were made using five different water combinations: 50% tap water (TW) plus 50% concrete wash water (CWW), 100% TW, 70%TW + 30%CWW, 30%TW + 70%CWW and 100% CWW. For samples with 50% TW + 50% CWW, the setting time was higher compared to those of 100% tap water. However, in terms of the compressive strength at 7, 14 and 28 days, the 50%TW+50%CWW specimens showed the highest strength. At the later age, at 90 days, specimens produced with 100% TW had an average compressive strength of 45 MPa and those with 100% CWW had 41 MPa. The statistical analysis of the tensile and flexural strength did not indicate any significant difference among the different combinations of water. Asadollahfardi et al. [13] investigated the properties of concrete produced using CWW having 3550 ppm and admixed with 7% micro-silica and 0.5% superplasticizer. The results indicated that adding micro-silica and superplasticizer decreased slightly the compressive strength and tensile strength when compared to mixtures without admixtures.

In another study conducted by Sandrolini and Franzoni [14], the utilization of concrete wash water (CWW) in producing the new concrete was examined. The CWW had a solid content of 40,000 mg/l, which is close to the limits allowable by ASTM C94 [3] (50,000 mg/l). The results revealed that the 28 days compressive strength was 96% compared to the reference specimens made with drinking water. In addition, capillary water absorption and mortar microporosity were improved and these were attributed to the filling action due to the presence of fine materials in the wash water.

Babu and Ramana [8] investigated the possibility of using wastewater collected from treatment plants as mixing water in concrete. The chemical and physical properties of wastewater were analyzed. The compressive and flexural strength of concrete made with this water were below the reference concrete that made with potable water. However, the authors reported that this reduction in strength is within the allowable limits specified by BS: 3148–1980 [7], which selected the maximum acceptable reduction is 20%. In addition, the XRD analysis revealed that new hydration products were formed due to the presence of bicarbonates and chlorides in the mixing water.

Asadollahfardi et al. [15] studied the suitability of using treated wastewater in mixing and curing of concrete. Even though, the results showed an increased setting time, it was within the acceptable limits of ASTM C191 [16]. The 28-day compressive and tensile strengths were in the ranges of 93–96% and 96–100%, respectively, when compared to the control specimens that were made with the tap water. In addition, the water absorption and surface resistivity of concrete were not significantly affected by using the treated wastewater. Asadollahfardi and Mahdavi [17] concluded that treated industrial wastewater with TDS of 1034 ppm can be used in concerete prodcution with satisfactory properties. Their reslts showed that the compressive stremgth and tesnile strength decreased by 8.7% and 11.8%, respectively, while the electrical resistivity increased by 7.7%. Hassani et al. [18] found that the wastewater increased the chloride ion diffusion coefficien, especially in higher water to cement ratios. Furthermore, Kaboosi and Emami [19] explored the possibility of using the treated industrial wastewater in concrete mixtures incorporated zeolite. The treated industrial wastewater had a TDS concentration of 1638 ppm while the reference tap water had a TDS content of 806 ppm. Concrete mixed with treated industrial wastewater showed a compressive strength within the allowable range (i.e., reduction in strength by less than 10% compared to the reference concrete). In addition, the authors reported that the treated industrial wastewater can be used satisfactorily in the construction of plain concrete, however, more precaution should be taken in reinforced concrete where it might raise concerns about reinforcement corrosion.

Chatveera and Lertwattanaruk [20] studied the feasibility of using sludge water, that was collected from a ready-mixed concrete plant, as mixing water in concrete. Their study was aimed to select the optimum total solids content of sludge water for use in the production of concrete with acceptable strength and durability. Thus, they selected sludge water with different levels of total solids content (0.5, 2.5, 5, 7.5, 10, 12.5, and 15%). The results showed that sludge water with total solids content more than 5–6% reduced the compressive strength and shortened the setting time. In addition, the authors reported that it is beneficial to add fly ash or superplasticizer in producing the concrete with sludge water for the purpose of enhancing the mechanical and durability properties. Another study conducted by Chatveera et al. [21] utilized sludge water at different replacement levels of tap water (ranging from 0% to 100% by weight). The used sludge water had TDS of about 63,400 ppm (which exceeding the limit of ASTM C 94 [3]) and the chloride and sulfate contents were 25 ppm and 12.7 ppm, respectively. It was reported that with increasing sludge water the shrinkage and weight loss due to acid attacks had increased and the slump and compressive and flexural strength had decreased.

For the purpose of sustainability effect, seawater was investigated by Younis et al. [22] to be used as a mixing water in concrete. The chemical composition of seawater reported that it contains about 30,300 mg/l of TDS and chloride and sulfate contents of 18,600 mg/l and 2359 mg/l, respectively. The results revealed that seawater had no significant effects on the density and air content; however, the workability and initial setting time were remarkably affected. With regards to the mechanical properties, a reduction in compressive and tensile strength in order of 7–10% was reported.

Al-Jabri et al. [23] investigated the effect of using wastewater on the properties of high strength concrete. Wastewater was collected from different car washing stations and the chemical analysis showed it contains TDS, chloride and maximum sulfate concentration of 254 ppm, 74.2 ppm and 97.7 ppm, respectively. Although, the wastewater had a different chemical composition than that of the freshwater, it was reported that the compressive strength and water absorption were not affected.

Ghrair et al. [24] investigated the suitability of using grey water (with and without treatment) for producing of concrete. The grey water was collected from the treatment plant and the chemical compositions showed that the TDS contents of the raw and trated waters were 980 mg/l and 803 mg/l, respectively. The fresh properties of concrete showed a higher setting time and lower slump. The 28 day compressive strength of the treated grey water was not affected, however, for the raw grey water there was an advese impact on the compressive strength.

The effect of treated wastewater on the properties of concrete was studied by Meena and Luhar [25]. Two types of treated wastewater were used, namely tertiary treated wastewater (TTWW) and secondary treated wastewater (STWW). The results indicated that at the 100% replacement of tap water, the compressive strength of concrete was in the range of 85–94%. With regards to the durability performance, the use of treated wastewater increased the carbonation depth and chloride concentration in concrete.

From the reviews of the studies reported in the literature, as presented above, it is found that almost all researchers have evaluated the basic properties of concrete made using contaminated water. However, according to the authors’ knowledge, no detailed investigation has been conducted on the effect of varying dosage of TDS on the fresh and hardened properties and durability performance of concrete. Therefore, in this study, an experimental test program was carried out to investigate the effect of increasing the TDS content in the mixing water on various properties of concrete including workability, setting time, air content, and compressive strength. In addition, the durability characteristics of concrete in terms of water absorption, water permeability, electrical resistivity, and rapid chloride permeability were also evaluated. Based on the test results, useful conclusions were withdrawn that might be helpful in limiting the TDS dosage at an optimal level.