Feasibility of Using Ready Mix Concrete Plants Wash Water as Mixing Water in Concrete

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Feasibility of Using Ready Mix Concrete Plants Wash Water as Mixing Water in Concrete

https://doi.org/10.21203/rs.3.rs-4898109/v1

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Egypt relies heavily on the Nile River as its main source of drinking water. With Ethiopia's new dam and Egypt's increasing population, researchers anticipate a major water shortage. In response, the Egyptian government has launched several initiatives, such as canal linings and seawater desalination plants, to prevent potential water loss. This research aims to offer a solution by reducing the use of potable water in concrete production, which currently accounts for over 16% of the country's fresh water consumption. The proposed approach involves using recycled wash water from ready-mix plants instead of potable water. At present, these plants use potable water for washing. Each cubic meter of concrete produced requires 70 litres of wash water for the truck mixer and pump. By replacing potable water with recycled wash water, potable water usage could decrease by 30%. Given Egypt's concrete production levels, this could save around 11 million cubic meters of water annually. This saved water could irrigate 70,000 feddans using traditional methods or 420,000 feddans with advanced irrigation techniques. This research explores the feasibility of using wash water in concrete by examining four replacement ratios: 25%, 50%, 75%, and 100%. The findings suggest that while wash water can be used in concrete with an optimal replacement ratio with potable water.

Concrete is a crucial component of infrastructure and is among the most widely used construction materials globally. However, producing concrete in ready-mix plants requires substantial natural resources, including fresh water, and generates significant amounts of wastewater used to clean the mixing trucks and batching plants. This wash water contains cement particles, aggregates, and admixtures, creating an environmental challenge for ready-mix plants. Traditional treatment methods are costly, and improper disposal can pollute waterways and soil. Recent research, however, is investigating the potential of using wash water as a sustainable alternative for producing fresh concrete. Klus et al. [1] found that recycling wash water from concrete plants to partially replace mixing water in mortar production, at ratios of 20% and 50%, is feasible without negatively impacting the concrete's mechanical properties. The study revealed that using wash water in fresh concrete mixes reduced the setting time by 15 minutes and increased both flexural and compressive strength at 28 days. Tsimas and Zerkavi et al. [2] conducted research on recycling wash water from ready-mix concrete plants, finding that all collected water samples had a pH above 11.5, classifying them as hazardous waste unsuitable for direct environmental disposal. However, they observed that all samples complied with ASTM [3], and EN 1008 [4] standard specifications for mixing water in concrete production regarding the chemical properties of the mix.

Xuan et al. [5] reviewed waste processing in cement plants and its potential for reuse. Washing-out systems are widely used in ready-mix concrete plants, and sometimes reclaiming systems are employed to produce recycled aggregates and concrete slurry waste. Despite significant interest in finding alternative uses for these wastes, published methods and principles are sporadic and lack conclusive results or comprehensive explanations of the treatment process. The review highlighted challenges faced by management, including poor product performance, low reutilization rates, high costs, and stringent regulatory requirements, all of which hinder sustainability.AM Ghrair et al. [6] recently conducted a study in Jordan, a country with similar arid conditions to Egypt, and found that raw wash water from mixer vehicles did not meet the maximum concentration limits required by EN 1008 [4], or ASTM [3] standards. The study showed that using raw wash water significantly reduced the compressive strength and slump value of concrete, leading to poor workability, even after dilution. Additionally, raw wash water was deemed hazardous, even after the removal of large undissolved particles. However, when raw wash water replaced 75% of potable water in the mixing process, there was no reduction in concrete strength or significant impact on workability. The filtered wash water also did not show any significant decrease in strength or workability. Al-Joulani et al. [7] examined the impact of using treated wash water from a wastewater treatment facility. They found that replacing 30–40% of fresh water with treated wash water did not significantly affect the strength or efficiency levels in their samples, and the results met the required standards. The literature review indicates that numerous studies have shown the potential for using wash water from ready-mix concrete plants as a replacement for fresh water in concrete mixes after appropriate treatment. However, there remains uncertainty about the impact of wash water on the mechanical properties and workability of fresh concrete. Therefore, additional experimental work is necessary, particularly in arid regions like Egypt, to develop sustainable solutions for reducing water consumption in the construction industry.

In this study, an experimental investigation has been conducted on concrete specimens using different replacement ratios of wash water collected from a ready-mix plant in Cairo, Egypt. The replacement ratios examined were 25%, 50%, 75%, and 100% wash water to potable water. The study investigates the impact of these replacement ratios on the properties of the produced concrete.

An experimental program was designed to investigate the effect of using wash water from ready-mix concrete plants in concrete production. The program consists of five mixes: a control mix using 100% potable water and four mixes with varying replacement ratios of wash water. The replacement ratios considered were 25%, 50%, 75%, and 100% wash water to potable water. A chemical analysis test was performed on the treated wash water. Additionally, slump, compressive strength, tensile, and electric resistivity tests were conducted on the various mixes.

2.1. Materials

In this study, cement type CEM I 42.5 N locally produced in Egypt which conforms to the BS EN 197-1 [8] standard was used. Crushed limestone coarse aggregate with a nominal maximum size of 20 mm was utilized. In addition, silicious natural sand was used as fine aggregate. The grading and properties of the used aggregates are conforming to BS 12620 [9]. The raw materials of the concrete mixes were mixed using a tilting drum. Table 1 illustrates the concrete mixture design used in this study. The concrete samples were labelled as follows, C for the control mix and M (percentage of wash water replacement) for the other mixes. For example, M50 indicates that 50% of the water used in the sample was wash water.

The water used in the control concrete mix was potable. For the other concrete mixes, a combination of wash water and potable water with different replacement ratios was used. The wash water was collected from a ready-mix concrete truck in the New Administrative Capital in Cairo, Egypt. The mix ratios per cubic meter of the collected wash water were as follows: cement 450 kg/m³, sand 650 kg/m³, coarse aggregate 1150 kg/m³and admixture 6.75 L/m³. The used admixture was commercially available and it was retarding admixtures and high-range water reducers which conform to type G of ASTM standards [10]. The commercial name of the admixture was X-Calibur X500.

Table 1

Concrete mix proportions per m³
Concrete Sample	Wash water replacement ratio %	Water cement ratio (W/C)	Cement (Kg/m³)	Fine Aggregate (Kg/m³)
C	0	0.51	350	850	1100	180
M25	25	0.51	350	850	1100	180
M50	50	0.51	350	850	1100	180
M75	75	0.51	350	850	1100	180
M100	100	0.51	350	850	1100	180

2.2. Wash Water Treatment

After collecting the wash water from the concrete mixing transport truck, a simple treatment process was applied. The water was passed through a standard aggregate sieve with an opening size of 0.075 mm. The colour of the wash water changed from brownish before treatment to light yellow after treatment. Figures 1 and 2 show the wash water before and after treatment with respectively.

2.3. Specimen preparation

The concrete mixes were prepared by using a laboratory-grade mixer with a capacity of 1/7 cubic meter. The concrete mixture was blended for a duration of 2 minutes. For every mix, a total of six cubes, each measuring 150 x 150 x 150 mm, and three cylinders with a diameter of 150 mm and a height of 300 mm were prepared and cast in accordance with the specifications outlined in BS EN 12390 [11].

2.4. Tests

A chemical analysis test was carried out on the wash water according to ASTM D512 [12] and ASTM D516 [13]. The compressive strength test was carried out on the previously casted cubes after curing in potable water for 7 and 28 days according to BS EN 12390 [11]. Also, a splitting tensile (Brazilian) test was carried out on the cylinder specimens after curing for 28 days according to BS EN 12390 [11]. Furthermore, slump tests were carried out just after the mixing had finished according to BS EN 12350-2 [14]. Finally, an electric resistivity test was carried out.

In this study, an advanced electric resistivity test on concrete mixes was introduced. The test was conducted on concrete cube specimens under both dry and fully saturated conditions at the age of 28 days. The electric resistivity device was fabricated using an additive manufacturing technique (3D printing). Copper rods with a diameter of 1 mm were inserted into pre-existing holes in the device frame. The experiment was conducted using a power supply providing direct current (DC) at 30 volts. Multimeters were used to measure the current and potential differences across the rods. Figure 3 depicts the electric resistivity apparatus.

3.1. Chemical Analysis

A chemical analysis test has been conducted on the wash water collected from the ready-mix concrete plant to evaluate the impact of the wash water on the properties of the fresh and hardened concrete. Table 2 illustrates the chemical analysis of the wash water. The results of the chemical analysis were compared to the Egyptian Code Requirements [15]. It was found that the results were accepted to the Egyptian code values. However, the requirements of the Egyptian code are stricter when compared to other codes such as ASTM C1602 [3] or BS EN1008 [4] as shown in Table 2. It is worth mentioning that the concentration of the salts in the wash water may be changed to lower values when mixed with potable water.

Table 2

Results of the chemical analysis for wash water
Properties/ Unit	pH^*	Cl^{− 1 **} (gm/l)	So3^−*** (gm/l)	TDS^**** (g/ml)
Measured Values	9.1	0.0888	0.30	0.66
Egyptian Code Requirements [15]	More than 7	Less than or equal to 0.5	Less than or equal to 0.3	Less than or equal to 2.0
ASTM C1602 [3]	----	Less than or equal to 1.0	Less than or equal to 2.5	Less than or equal to 50
BS EN 1008 [4]	----	Less than or equal to 1.0	Less than or equal to 1.6	----

pH^* is the potential of hydrogen.

Cl^{− 1 ** is} Chlorine (gm/l).

SO3^{− 2 ***} is Sulphate (gm/l).

TDS**** is Total Dissolved Solids (gm/l).

3.2. Slump Test

The slump test results showed a decrease in slump after the addition of wash water. For all mixes containing wash water, the slump decreased to 6 cm, compared to 12 cm for the control mix. This reduction may be attributed to the presence of admixtures and fine cement particles in the wash water. Figure 4 illustrates the slump test results for the control mix.

3.3. Compressive Strength Test

The compressive strength test was conducted on the cubes at 7 and 28 days for the different mixes. Figure 4 presents the compressive strength at 7 days, while Fig. 5 shows the results at 28 days. According to the Egyptian code, a maximum reduction of 10% in compressive strength is permissible when using non-potable water. The test results are summarized in Table 3. Applying this limit to the 7-day compressive strength, It can be observed that the mixes with 25% and 50% wash water ratios meet the criterion. However, for mixes with 75% and 100% wash water ratios, this limit was exceeded. For the results at the age of 28 days, it was observed that the average percentage of reduction for all mixes was 17%. However, The higher reductions observed at 28 days are within the normal variation range for concrete which may be varied from batch to batch or within test variations which may be considered acceptable. In addition, this reduction can be addressed by designing concrete mixes to target higher initial compressive strength, ensuring that after the reduction, the mixes still meet the required compressive strength for concrete.

Figures 7 and 8 illustrate the relationship between the compressive strength using wash water at 7 days (F_cw) and 28 days (F_cuw) compared to the compressive strength using potable water at the same ages (F_cp, Fc_up) with respectively. An equation was proposed based on average values to estimate the reduction in compressive strength due to the use of wash water. This equation was validated using the experimental results and demonstrated good agreement. Table 4 illustrates the validation results. However, it is limited and requires further experimental validation. The uncertainty in compressive strength was calculated using type A uncertainty, as indicated by equation [1]. The resulted uncertainty was then multiplied by 2 for a 95% level of confidence. The maximum uncertainty found was 1.3% for the compressive strength of concrete cubes.

\(\:{U}_{A}=\frac{standard\:deviation}{\sqrt{n}}\) [1]

Where: n is the number of specimens.

Table 3

compressive strength test results according to BS EN 12390 [11] ^*Percentage of the sample compressive strength to the control sample
Concrete Sample	Compressive Strength (MPa)
	7 days		28 days
	f_cu measured	% f_cu ^*	f_cu measured	% f_cu ^*
C	16.6	100	25.5	100
M25	15.0	90	21.5	84
M50	14.9	90	25.5	100
M75	13.1	79	21.1	83
M100	12.5	75	20.9	82

Table 4

validation of proposed equations
Concrete Sample	Compressive Strength (MPa)
	7 days			28 days
	Experimental	Predicted	%^*	Experimental	Predicted	%^*
C	17.8	16.4	1.08	26	25.05	1.04
	15.9		0.97	24.3		0.97
	16		0.97	26.4		1.05
M25	15.3	15.4	0.99	21	22.45	0.94
	14.8		0.96	21.4		0.95
	15.1		0.98	22.1		0.98
M50	14.2	14.4	0.99	25.4	25.05	1.01
	14.9		1.03	25.3		1.01
	15.7		1.09	25.2		1.01
M75	13.7	13.4	1.02	20.8	20.54	1.01
	13.2		0.99	20.2		0.98
	12.3		0.92	22.4		1.09
M100	13	12.4	1.05	21.1	21.23	0.99
	11.4		0.92	20.9		0.98
	13		1.05	20.8		0.98

* Percentage of the experimental result to the predicted value.

3.4. Splitting Tensile Test results

The splitting tensile test was performed on three cylinders each was l50 x 300 mm to estimate the tensile strength of each concrete mix. The results are shown in Table 5. The uncertainty for the test was calculated based on Eq. (1) and the result was 0.54%. Figure 9 shows the results of the tensile strength test for the investigated concrete samples. The tensile strength was noticed to be increased after using the wash water in the concrete mix. When the wash water replacement was 25% and 50%, the tensile strength of the samples increased by 57% and 76% respectively, compared to the control sample that did not include wash water. However, it was observed that the rate of increase in tensile strength decreased when the samples had more than 50% of wash water replacement. The tensile strength only increased by 12% and 8% for the samples with 75% and 100% wash water replacement, respectively. This concludes that wash water can enhance the tensile strength of the concrete mix. Moreover, This may be attributed to enhancement in the bond in concrete after using the wash water. The ratio of tensile strength to compressive strength was calculated for all the mixes. It was found that the ratio was 0.06, 0.12, 0.11, 0.09, and 0.08 for C, M25, M50, M75, and M100 respectively.

Table 5: Splitting tensile test results

Concrete Sample	Tensile strength (MPa)
Concrete Sample	Test 1	Test 1	Test 3	Average	%*
C	1.6	1.5	1.8	1.63	100
M25	2.6	2.6	2.5	2.57	157
M50	2.4	3.2	3	2.87	176
M75	1.7	1.5	2.3	1.83	112
M100	2.3	1.6	1.4	1.77	108

* Percentage of the sample average tensile strength to the tensile strength of the control sample

3.5. Electric resistivity test

The electric resistivity test on concrete can help to provide insight into the long-term characteristics. Additionally, it aids in forecasting the likelihood of future corrosion. The electric resistivity test described in this study is significantly simpler compared to traditional tests like chloride penetration or half-cell potential test. The test duration lasts approximately 60 seconds. Moreover, the device is easily transportable, allowing for the test to be conducted directly on construction sites. The test was conducted on two different conditions. The initial condition is a state of saturated surface dryness, while the second condition is achieved by drying the concrete specimens in an oven at 80 C. The test results are shown in Table 5. The electric resistivity test results exhibited a positive correlation with the increased percentage of wash water, indicating improved durability and decreased vulnerability to corrosion when compared to the control specimens. Conversely, a different behaviour was observed during the examination of dehydrated samples. The recommended condition for the test is the saturated condition.

Table 6

Results of the electrical resistivity test
Concrete Sample	Wet test condition		Dry test condition
Concrete Sample	Potential difference (mV)	Resistivity kΩ.cm	Potential difference (mV)	Resistivity kΩ.cm
C	5	25	90	456
M50	8	40	57	288
M75	15.5	78.5	43	217
M100	35	178	23	116

In this research, an experimental study has been conducted to investigate the impact of utilizing wash water from ready-mix concrete plants as a replacement for fresh water in concrete mixes. The investigated samples included concrete mixes with varying replacement ratios of wash water The replacement ratios considered in this study were 25%, 50%, 75%, and 100% wash water to potable water. After presenting and discussing the test results in the previous sections, the following conclusions can be deducted:

The PH of the treated wash water increased by 30% compared to potable water. This may result in the enhancement of alkalinity of concrete which provides more protection for steel reinforcement from corrosion.

The treated wash water up to a replacement ratio of 50% fulfils the requirements of Egyptian, American, and British standards with respect to compressive strength reduction limit. Therefore, this type of water can be used as a sustainable replacement for potable water.

A significant enhancement in the tensile strength of concrete was found, as the wash water resulted in an increase in the tensile strength reached up to 76% for the 50% replacement mix.

A 50% reduction in workability, measured by slump, was observed in mixes containing treated wash water. This reduction may be attributed to the increased fines percentage in the mix. However, this issue can be mitigated using chemical admixtures.

An increase in the electric resistivity of concrete was observed by increasing the ratio of treated wash water. This may lead to a reduction in the probability of corrosion in concrete elements for future life. Therefore, the wash water is recommended to be used in coastal areas in which the structures are subjected to severe corrosion.

The electric resistivity test is a promising test to evaluate the durability of concrete elements. However, a correlation between the relative humidity and the test results shall be made to make sure the test can be carried out on construction sites.

8.1 Funding

The authors didn’t receive any fund from any authority

8.2 Conflict of Interest

The authors declare that no competing interest in this manuscript and no fund have been received for this manuscript.

8.3 Availability of Data and Materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

8.4 Code Availability

Not applicable

8.5 Authors contribution

Dr. Ayman Shamseldein participated in research topic idea origination, writing the first draft and supervision. Mr. Mohamed Amr participated in carrying out the tests. Dr .Fatma Attia participated in reviewing the manuscript and supervision.

14.Acknowledgements

The authors would like to express their gratitude to Prof. Hany Elshafie and Engineer Mohamed Fahmey for their invaluable assistance in collecting the wash water samples.

15. Authors' information

Ayman Shamseldein, Assistant professor of Structural Engineering Department, Faculty of Engineering, Ain Shams University, Egypt.

Assistant professor at Civil Engineering Programme, School of Engineering and Computer Science, University of Hertfordshire Hosted by GAF

Mohamed Amr, Student at Civil Engineering Programme, School of Engineering and Computer

Fatma Attia, Assistant professor at Civil Engineering Programme, School of Engineering and Computer Science, University of Hertfordshire Hosted by GAF

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No competing interests reported.

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You are reading this latest preprint version

Feasibility of Using Ready Mix Concrete Plants Wash Water as Mixing Water in Concrete

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Version 1

Abstract

Figures

1. Introduction

2. Experimental program

2.1. Materials

2.2. Wash Water Treatment

2.3. Specimen preparation

2.4. Tests

3. Test Results and Discussion

3.1. Chemical Analysis

3.2. Slump Test

3.3. Compressive Strength Test

3.4. Splitting Tensile Test results

3.5. Electric resistivity test

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

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