1 Introduction

Recycled water which is also known as reclaimed water is treating wastewater through eliminating all solids and suspended particles. Reclaimed water can be implemented in multiple applications including ground water recharging, irrigation, concrete manufacturing, and landscape applications (Angelakis & Snyder, 2015). A byproduct of water reclamation is a sludge that when mixed with biowaste, results in a compost that is extensively used by farmers (Maroušek et al., 2022). However, some plants can be cultivated directly on wastewater such as spirulina (Maroušek & Maroušková, 2021). In this research focus is on the implementation of recycled water in concrete manufacturing and curing. The suitability of treated wastewater in concrete manufacturing can be of additional economic value. For any investor in the field of treated wastewater, adding another customers’ sector such as the field of construction industry, which is an ever growing economic activity in any society, would encourage investment in this field (Akbari et al., 2021; Pavolová et al., 2021).

According to the American Society for Testing Materials (ASTM C1602-06, 2006), the suitability of non-potable water for concrete production is governed by two factors. Firstly, the difference between the setting time, which is the time required for cement paste to lose its plasticity and withstand some loads, of the cement paste using the non-potable water and the paste made with potable water should be from one hour early to one hour and half later. Secondly, the average compressive strength of concrete made using the unknown quality water should not be less than 90% of the average strength of the control cubes (Vaishali & Prashant, 2023).

Different researchers investigated the effect of using treated wastewater on the properties of cement paste, mortar and concrete (Tonetti et al., 2019).

Al-Joulani (2019) investigated the effect of replacing potable water with tertiary treated wastewater (TTWW) by different percentages. He reported that for water/cement (w/c) ratio of 0.5 to 0.6, an increase in the 14 and 28 days compressive strength with a range of 10–39% takes place. For higher w/c ratio of 0.7, the compressive strength decreased by 16% when the potable water was replaced by TTWW.

Several authors reported that there is no significant impact on concrete strength when secondary treated wastewater (STWW) or TTWW are used; either as partial replacement of potable water or as 100% of mixing water (Al-Jabri et al., 2011).

Others conducted compressive strength investigation while using STWW in mixing either with full replacement of potable water or partial, and reported enhancement in the results among those researchers are; Hegazy and Farouk (2020) and Reddy Babu et al. (2018).

For concrete consistency measured in terms of the slump test results, most authors reported that no significant effect was observed when the results were compared with results of concrete mixed with 100% potable water (Shaikh & Inamdar, 2016).

The impact on setting time attracted the interest of the researcher. This is attributed to the fact that the treated wastewater usually contains organic matter which might retard the cement hydration and affects the formation of Calcium Silicate Hydrate (CSH) (Mohe et al., 2022). The researchers reported an increase in the initial setting with different values. Among them Micheal et al. (2022). The impact is more pronounced for the final setting time (Ghrair & Al-Mashaqbeh, 2016).

Grey water is another source for mixing and curing water for concrete manufacturing. Grey water is defined as the wastewater of kitchens, baths, cleaning activities. Different researchers studied the gray water; either raw or treated, as an alternative to potable water. Among them (Ghrair et al., 2018) and Abushanab and Alnahhal (2021). Moreover, other researchers studied the effect of using industrial waste water in concrete manufacturing (Ahmed & Afifi, 2019). According to (Nasseralshariati et al., 2021), the industrial waste water affects the concrete durability and strength nonlinearly. It is worth mentioning that the implementation of wastewater in concrete manufacturing is not limited to mixing and curing. It can be extended to implementing the phosphorus in the wastewater treatment plants to produce a novel and eco-friendly char cement that can be activated using waste metals (Maroušek & Gavurová, 2022). This novel concrete possesses higher strength and less weight (Maroušek & Maroušková, 2021).

This research is concerned with investigation into the suitability of secondary treated wastewater (STWW) and tertiary treated wastewater (TTWS) for concrete mixing and curing. The investigation covers the effect on cement paste properties, the fresh concrete consistency and the hardened concrete strength and durability. All results will be compared with control case where potable water is used for mixing and curing.

2 Material

The materials used in the experimental work are obtained from the local market. The cement is Ordinary Portland Cement designated as CEM I with strength not less than 42.5 MPa after 28 days designated as grade 42.5. The cement bags are purchased from the local market in 50 kg bags and stored in a dry place for not more than 3 months. The fine aggregate is ordinary desert sand with specific gravity of 2.52 and bulk density of 1345 kg/m3. The coarse aggregate is crushed limestone with maximum nominal size of 10 mm. The mixing water is obtained from a local wastewater treatment plant whose capacity is 60,000 m3/day. Figure 1 shows the treatment procedure adopted in the plant. Eventually, the treatment scheme shown in Fig. 1 is the widely spread scheme for treatment plants of medium scale. However, it is not the only scheme. Other cheaper methods can be found around the world such as the method that incorporate biochar (Maroušek et al., 2019) and extracting water from fermentation residues (Maroušek & Gavurová, 2022).

Fig. 1
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Typical wastewater treatment processes: primary, secondary and tertairy

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The chemical composition of the STWW and TTWW are given in Tables 1 and 2 on the days when the treated wastewater is collected.

Table 1 Chemical Composition for the used STWW
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Table 2 Chemical Composition for the used TTWW
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Where:

  • BOD: Biological oxygen demand

  • COD: Chemical oxygen demand

  • TSS: Total suspended solids in mg/l

  • TDS: Total dissolved salts in mg/l

  • D.O.: Dissolved oxygen in mg/l

  • R-Cl2: Residual Clorine in mg/l

It can be concluded that dissolved salts content in the STWW are higher than the those in the TTWW. This may reflect on the behavior of concrete in its fresh state as will be discussed later. Similarly, the BOD5 content in the STWW is more than the BOD5 in the TTWW. This, in turn, may affect the cement setting time.

To investigate the type of salts encountered in the treated water and to assess its suitability to concrete mixing and curing, chemical analysis is performed on both the STWW and TTWW. The results are shown in Table 3 compared with the ASTM C1602.

Table 3 Chemical Constituents of the used STTW and TTWW compared with ASTM C1602 and
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Despite that both the STWW and TTWW are conformable with the ASTM C1602 limits for mixing and curing water qualities, the behavior of the concrete made with both waters shows a significant different behavior compared with concrete made with potable water when exposed to sulfates as will be discussed in the results section. According to the codes of practice of different countries, the following aspects should be taken into consideration when using a non-potable water in concrete mixing.

  • The initial setting time for cement samples equipped with this water should not be less than 45 min, provided that the initial setting time does not differ by more than 25% of the initial setting time for samples of the same cement prepared with distilled water.

  • The final setting time for the cement samples equipped with this water does not exceed 12 h, provided that the final setting time does not differ by more than 25% of the final setting time for samples of the same cement prepared with distilled water.

  • The compressive strength of the standard mortar after 7 days in which this water was used is not less than 90% of the average compressive strength of similar samples prepared with distilled water at the same age.

3 Methodology

Different tests are conducted on cement paste and concrete in both fresh and hardened state. For cement paste, the initial and final setting time are determined for pastes that contain 100% potable water and other pastes where 25%, 50%, and 100% of the mixing water is replaced by either STWW or TTWW.

3.1 Concrete mix ingredients

For concrete mix design, the absolute volume method is used to determine the concrete mix proportions. The concrete ingredients ratios for cement: sand: coarse aggregate are 1:2:4. The water/cement ratio is kept at 0.45. For mixing water, four different combinations are used. The control mix contains 100% potable water and other three mixes are used where 25%, 50%, and 100% either STWW or TTWW replaces potable water. It is worth mentioning that the type of water used for mixing is the same water used for curing. The ingredients for all mixes are shown in Table 4. The mixing process is done using a rotary mixer for 2 min.

Table 4 Concrete mixes ingredients
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3.2 Concrete consistency tests

The concrete consistency test adopted in this research is the slump test performed immediately after mixing concert according to ASTM C143 (2020).

3.3 Hardened concrete testing

For hardened concrete, the investigation includes compressive strength and flexural strength at the ages of 7, 28, and 90 days. The hardened concrete durability testing includes permeability and sulfate resisting. Moreover, XRD investigation is conducted for the cement paste including 100% potable water, 100% STWW, and 100% TTWW. Details of all tests are presented in the following sections.

For compressive strength determination cube specimens of 15.8 cm side are used. The specimens are put in compressive machine model ELE 1886B0033 and at a loading rate of 14 MPa/min. For the modulus of rapture determination four points bending test is performed. The test setup is shown in Fig. 2. The beam dimensions are 100 × 100 × 600 mm and the span is 500 mm.

Fig. 2
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Hardened concrete flexural strength set up

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4 Concrete durability investigation

Concrete durability is an important property that signifies a concrete that can withstand the environmental conditions while maintaining same performance in the context of strength and serviceability. Different aspects define the concrete durability such as abrasion, permeability, chemical attacks resistance, and weathering conditions resistance.

4.1 Permeability testing

Permeability is an important property of concrete that largely affects its durability as permeable concrete is prone to deteriorate faster due to chemical attacks. The test is conducted at age of 28 days according to BS EN 12390-8 (2003). The specimens are concrete cubes with dimensions 15.8 cm × 15.8 cm × 15.8 cm with roughened surface placed in the apparatus and subjected to water pressure of about (500 ± 50) kPa for (72 ± 2) h.

The concrete cubes are removed after exposure to the water pressure and split to measure the water penetration depth as shown in Fig. 3.

Fig. 3
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Concrete cube after permeability test

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4.2 Sulfate attack testing

The other aspect that characterizes the concrete durability is the chemical attack resistance. Usually, the chemical attack results in either dissolution of concrete components or chemical reaction resulting in expansion and subsequent deterioration. One of the most harmful attacks on concrete is sulfate. Sulfates usually react with the free Calcium Hydroxide Ca (OH)2 to form Calcium Sulfate (Gypsum) as follows:

$${\text{Ca}}\left( {{\text{OH}}} \right)_{{2}} + {\text{Na}}_{{2}} {\text{SO}}_{{4}} .{\text{10H}}_{{2}} {\text{O}} \to {\text{CaSO}}_{{4}} .{\text{2H}}_{{2}} {\text{O}} + {\text{2NaOH}}.{\text{8H}}_{{2}} {\text{O}}$$

The Calcium Sulfate in its turn reacts with Calcium Aluminate to form Calcium Sulfoaluminate according to the equation:

$$\begin{gathered} {\text{4CaO}}.{\text{Al}}_{{2}} {\text{O}}_{{3}} .{\text{19H}}_{{2}} {\text{O}} + {3 }\left( {{\text{CaSO}}_{{4}} .{\text{2H}}_{{2}} {\text{O}}} \right) + {\text{16H}}_{{2}} {\text{O}} \to \hfill \\ \quad \quad \quad \quad \quad \quad {\text{3CaO}}.{\text{Al}}_{{2}} {\text{O}}_{{3}} .{\text{3CaSO}}_{{4}} .{\text{32H}}_{{2}} {\text{O}}\left( {{\text{Ettringite}}} \right) + {\text{Ca}}\left( {{\text{OH}}} \right)_{{2}} \hfill \\ \end{gathered}$$

The resulting chemical component occupied a greater volume than that of the compounds it replaces so disruption of hardened concrete takes place.

The test is performed according to ASTM-C452 (ASTM C452-21, 2021). The specimens’ dimensions are 25 × 25 × 285 mm. The percentage of gypsum to cement is determined such that the mixture contains 7.0% mass of SO3, the ratio of cement to gypsum can be determined using the following equation:

$${\text{Cement}}\;\% = \left[ {{{\left( {{\text{g - 7}}.0} \right)} \mathord{\left/ {\vphantom {{\left( {{\text{g - 7}}.0} \right)} {\left( {\text{g - c}} \right)}}} \right. \kern-0pt} {\left( {\text{g - c}} \right)}}} \right] \times {1}00$$
(1)
$${\text{Gypsum}}\;\% = \left[ {{{\left( {{7}.0{\text{ - c}}} \right)} \mathord{\left/ {\vphantom {{\left( {{7}.0{\text{ - c}}} \right)} {\left( {\text{g − c}} \right)}}} \right. \kern-0pt} {\left( {\text{g - c}} \right)}}} \right] \times {1}00$$
(2)

where:

  • c = percentage of SO3 content of the Portland cement,

  • g = percentage of SO3 content of the gypsum

To determine the percentage of SO3 in both cement and gypsum, the X-ray fluorescence (XRF) test is performed.

The results of the XRF of both cement and gypsum are shown in Tables 5 and 6 respectively.

Table 5 XRF results for cement
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Table 6 XRF results for gypsum
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Substituting in Eqs. 1 and 2, the percentages of cement and gypsum in the mixture should be 90.17% and 9.83% respectively.

Nine test specimens of cement and gypsum mortar with dimensions 25 × 25 × 285 m are prepared. Three specimens for the percentages 100% Potable Water, three with 100% STTW and three with 100% TTWW.

According to ASTM –C452 (ASTM C452-21, 2021), The specimens are cured in the moist closet at 23°C for 22–23 h. The specimens are then removed from the molds, properly identified, and placed in water at 23 °C for at least 30 min. prior to making the initial length measurement. After initial length measurement, the specimens are stored in water which is replenished with fresh water every 7 days for the first 28 days and every 28 days thereafter. The mold and the specimens are shown in Fig. 4.

Fig. 4
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Cement molds and prisms for sulfate attack testing

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4.3 XRD analysis

X-Ray diffraction analysis (XRD) is a nondestructive technique that provides detailed information about the crystallographic structure, chemical composition, and physical properties of a material. XRD works by irradiating a material with incident X-rays and then the intensities and scattering angles of the X-rays that leave the material are measured. This technology is used by many researchers to investigate the chemical compounds encountered in concrete with different additives. Among those researchers are Silva et al (2020), Reddy and Naqash (2019), Kontoleontos et al. (2013), and Singh et al. (2021). For this research, the XRD analysis test is conducted on three specimens: control specimen, 100% STWW, and 100% TTWW.

5 Results

5.1 Initial and final setting results

The initial and setting time result for both STWW and TTWW are shown in Figs. 5 and 6. It can be concluded that all specimens lie in the specification of limit of more than 45 min. However, when compared with the control specimen which records 120 min. for initial setting, it can be concluded that all specimens record an increase in the setting time with about 1%. Nevertheless, this increase is acceptable by all specifications.

Fig. 5
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Initial setting time for mixes with treated wastewater compared with control mix showing the increase in the setting time

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Fig. 6
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Final setting time for mixes with treated wastewater compared with control mix showing the increase in the setting time

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For final setting time, the same behavior is encountered. The final setting time for all specimens with STWW and TTWW is more than the final setting time of the control specimen. The increase is around 1%.

This increase can be attributed to the existence of more organic matters in the treated wastewater other than potable water.

5.2 Slump test results

The slump test results are shown in Fig. 7. The control specimen is a dry mix with slump 30 mm. The slump increases with the increase of the replacement percentage of treated wastewater. This can be attributed to the fine suspended solids encountered in the wastewater which work as lubricants. This phenomenon is also reported by other researchers (Asadollahfardi et al., 2016; Hegazy & Farouk, 2020).

Fig. 7
figure 7

Slump test results for mixes with treated wastewater compared with control mix showing the increase in the slump

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5.3 Compressive strength results

The results of compressive strength at ages of 7, 28 and 90 days are shown in Figs. 8, 9, and 10. It can be concluded that all mixes strength fulfills the specification limit with strength not less than 90% of the strength of the control specimen. The best results are obtained for the mix with 25% STWW. For this mix, the strength is enhanced by around 10% of the control mix. This observation can be found in the work of Ooi et al. (2012).

Fig. 8
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7 days compressive strength for mixes with treated wastewater compared with control mix showing the slight difference in the compressive strength

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Fig. 9
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28 days compressive strength for mixes with treated wastewater compared with control mix showing the slight difference in the compressive strength

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Fig. 10
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90 days compressive strength for mixes with treated wastewater compared with control mix showing the slight difference in the compressive strength

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5.4 Flexural strength result

The flexural strength results for all mixes are shown in Figs. 11, 12 and 13. It can be concluded that the flexural strength at an early age for mixes containing any percentage of treated wastewater is around 83% of the control mix. However, at late ages all mixes prove to be satisfying.

Fig. 11
figure 11

Flexural modulus at age of 7 days for mixes with treated wastewater compared with control mix showing the reduction in the flexural strength

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Fig. 12
figure 12

Flexural modulus at age of 28 days for mixes with treated wastewater compared with control mix showing almost the same flexural strength

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Fig. 13
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Flexural modulus at age of 90 days for mixes with treated wastewater compared with control mix showing the slight difference in the flexural strength

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5.5 Permeability test results

The permeability test results are shown in Table 7. The results show that the penetration depth for all specimens containing treated wastewater is less than the penetration of the control specimen which indicates a good concrete quality.

Table 7 Water penetration depths for the permeability test for concrete cubes with different mixtures
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5.6 Sulfate resisting test results

The average linear expansion of the three mixes; control, 100% STWW, and TTWW are shown in Table 8. It can be observed that the linear expansion of specimens containing any percentage of treated wastewater exhibits more expansion than the control specimen. This phenomenon is more pronounced in the TTWW specimens. Comparing the chemical composition of the STWW and TTWW, Table 3, it can be attributed to the sulfate content in the TTWW which is more than the STWW.

Table 8 Results of linear expansion for all mixes showing the increase in expansion for mixes using STWW and TTWW
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5.7 XRD analysis results

The XRD results for the three specimens; control, 100% STWW, and 100% TTWW are shown in Figs. 14, 15 and 16 respectively. The XRD analysis illustrates that there are four matched chemical compounds in the control, secondary and tertiary examined specimens. These chemical compounds are Ca2SiO4H2O, Ca (OH)2, SiO2 and CaCo3.

Fig. 14
figure 14

Results of XRD for Control Specimens showing the intensity of each component

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Fig. 15
figure 15

Results of XRD for 100% STWW Specimens showing the intensity of each component

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Fig. 16
figure 16

Results of XRD for 100% TTWW Specimens showing the intensity of each component

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For control specimens, it is noticed that there are different peaks with different intensities at 2θ = 27°, 35°, 50° and 56° for SiO2, Ca (OH)2, CaCo3 and Ca2 (SiO4) (H2O) respectively, as shown in Fig. 14.

For 100% STWW specimen, Fig. 15, it is noticed that there are obvious differences in the position and the intensity for the four chemical compounds. Firstly, SiO2 peak is in the same position as the control specimens but with smaller intensity. But CaCo3 peak changes its position to be at 2θ = 30° with a little difference in the intensity. While the peak of Ca (OH)2 changes its position to be at 2θ = 40° with a little difference in the intensity. Also, Ca2 (SiO4) (H2O) changes its position to be at 2θ = 70° with a little decrease in the intensity.

Same differences in the intensity and position can be observed for 100% TTWW specimen as shown in Fig. 16. Firstly, SiO2 peaks have more positions with various intensities than the control specimens. But CaCo3 peak changes its position to be at 2θ = 30° and 40° respectively, with variable differences in the intensities. While the peak of Ca (OH)2 changes its position to be at 2θ = 34° and 47° respectively, with variable differences in the intensities. Also, Ca2 (SiO4) (H2O) changes its position to be at 2θ = 27°, 40° and 50° respectively, with variable differences in the intensities.

6 Discussion

Several experiments are conducted on concrete mixed and cured using treated wastewater with different contents. It can be observed that the chemical compounds encountered in all mixes are the same, however, with different intensities. The results show that this change in the intensities has an impact on the produced concrete in terms of compressive and flexural strength yet within specification. It also delays cement setting, yet such an effect can be override using chemical admixture. The effect is more pronounced for the volumetric changes due to sulfate attack. This is attributed to the different chemical components encountered in the treated water. For fresh concrete properties, no significant impact is observed. The results obtained from all the above-mentioned experiments can be used in conjunction with artificial intelligence to predict the behavior of concrete mixed with different water qualities and compounds in terms of strength, consistency, and durability (Zvarikova et al. 2021). From the financial point of view, and for arid countries that depend on desalination of sea water for all purposes, the cost to desalinate 1 m3 of sea water is around 6$ while the cost of treatment of 1 m3 of wastewater is around 3 $ (Alkhudhiri et al., 2019). For ingredients to produce 1 m3 of concrete as shown in Table 4, and taking into account the prices of concrete materials in an arid country like the Saudi Arabia (https://www.ceicdata.com/en/saudi-arabia/average-construction-materials-price), the cost of 1 m3 of concrete will cost 39.05$ for the use of desalinated water. For the use of treated wastewater, the cost will be around 38$. Thus, the reduction on concrete materials cost is around 1.3% not including the cost of curing water. The main advantages to use treated wastewater in concrete manufacturing and curing is to save the energy required to produce desalinated water and to use a byproduct of the essential industry of water reclamation.

7 Conclusion

A study on the reliability of using treated wastewater in concrete mixing and curing is conducted. Focusing on concrete consistency and strength, the results prove that the treated wastewater can be safely used. The setting time increases in the case of using treated wastewater when compared with concrete mixed with potable water. The maximum increase in initial setting time occurs in the specimens mixed with purely secondary treated wastewater. The increase is 40 min. This increase can be taken into consideration when transporting concrete and controlled using chemical admixtures. The same phenomenon can be observed for the final setting time. For compressive strength and flexural strength, both treated water regimens satisfy the specification limits as all specimens do not deviate from the control specimens by not more than 10%. The concrete mixed and cured using wastewater show less permeability. The concrete durability in terms of sulfate attack resistance shows considerable increase in the linear expansion for mixes where treated wastewater is implemented compared with potable water. The XRD analysis shows different chemical compounds’ position and intensities due to the various chemical compounds found in the treated wastewater. It can be concluded that treated wastewater can be safely used for concrete mixing and curing. Special care should be given to concrete in sulfate containing medium. This conclusion can be of benefit for many countries that suffer scarcity in water and need to reuse water from different sources. However, further research is needed for deeper investigation on the durability of concrete mixed with treated wastewater in harsh environments, specially by using sulfate resisting cements. Other durability parameters also need more investigation such as abrasion and freeze and thaw behavior. Moreover, investigation on the crystallization level is suggested to correlate with the concrete properties.