Assessment of Mechanical Properties of Concrete When Groundwater With Different Ferric Iron (Fe 3+ ) Concentration is Used for Mixing and Curing: a Case Study in Sylhet, Bangladesh

doi:10.21203/rs.3.rs-3618220/v1

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Assessment of Mechanical Properties of Concrete When Groundwater With Different Ferric Iron (Fe 3+ ) Concentration is Used for Mixing and Curing: a Case Study in Sylhet, Bangladesh

https://doi.org/10.21203/rs.3.rs-3618220/v1

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Concrete's strength largely depends on the level of quality of the components used in its formation. One of the components required is mixing and curing water which has to be compatible with making concrete. The state of the water is of the utmost importance because unwanted substances can weaken the strength of concrete and trigger reinforcement inside to corrode. In Bangladesh, groundwater serves as a major source of clean water for most of the population living in the countryside. The aforementioned water has been reported to contain substantial amounts of iron in the form of Ferric Iron (Fe³⁺) in various regions of the country, especially in Sylhet. The impact of this exposure to iron (Fe) in water on the mechanical strength of concrete is unknown. In the current study, it was investigated the effects of varying iron (Fe) concentrations in groundwater sources when these were used for concrete mixing and curing. Experimental testing was done on the cement setting time, workability, compressive strength, and split tensile strength of concrete. Portland limestone cement of grade 42.5N was used to create a total of 270 nos. of M20 grade concrete cylinder samples, each with a measurement of 300 mm height and 150 mm diameter. Water was sourced from 05 different locations of Sylhet district with iron (Fe) concentration of 0.2 mgl^− 1, 2.2 mgl^− 1, 3.1 mgl^− 1, 3.9 mgl^− 1and 4.9 mgl^− 1. Mechanical strength tests were performed on curing day- 07, 14 and 28. Initial setting time of cement was increased by 17% and final setting time increased by 7.5% when iron (Fe) concentration was increased from 0.2 mgl^− 1 to 4.9 mgl^− 1 in water. For 55% water/cement ratio, 29% slump was decreased. When iron (Fe) concentration was increased from 0.2 mgl^− 1 to 4.9 mgl^− 1 in both mixing and curing water, compressive strength of concrete reduced by 33% and splitting tensile strength reduced by 42%. From this study, groundwater source with iron (Fe) concentration within 2-2.5 mgl^− 1 was observed as safe for concrete mixing and curing work.

Cement setting time

concrete’s mechanical strength

groundwater quality

ferric iron (Fe 3+ )

Portland Limestone Cement

Concrete is a substance that resembles stone that is made by allowing a carefully measured mixture of cement, sand, gravel or other coarse aggregate and water to set in forms that have the intended structure's shape and proportions [01]. Concrete is by far the most durable, sturdy, and reliable construction material. It is frequently utilized because of its availability, affordability and flexibility to take on necessary shape. It requires substantially less trained workers and is both fire and corrosion resistant [02]. To produce high caliber concrete, care must be given in selecting the ingredients, combining them in the right ratios and then curing it as directed [03]. There must be caution when producing concrete of high quality in order to meet the demands for both longevity and strength. The components must adhere to the required guidelines.

A critical feature of concrete preparation is water. The chemical process known as hydration causes concrete to set and harden when it is mixed with water. While some of the mixing water is used to hydrate the cement, additional water is required to make the concrete workable [04]. Concrete manufacturing is significantly influenced by the quality of water. Water impurities may have a negative impact on the longevity of concrete as well as the cement's ability to set. The chemical components often found in water can actively participate in chemical reactions influencing the setting time of concrete and development of strength [05]. Therefore, precaution should be taken while choosing the source of water. Depending on the geographic location and season, water quality might differ dramatically from one source to another [06]. In order to prevent structural flaws water used in construction sites for mixing and curing of concrete should be analyzed especially where large-scale works are being done [07].

More than half of the world's population currently relies on groundwater for survival according to an estimate [08]. Both shallow and deep tube wells are used to extract groundwater at construction sites where potable water supply is not available. When groundwater is used for a specific purpose, such as for mixing and curing of concrete on a construction site, its quality is crucial. When ground water is discharged from tube well and exposed in the atmosphere, it undergoes through numerous processes and reactions affecting the quality of water [09]. Iron (Fe^+ 2, Fe^+ 3), manganese (Mn^− 2), silica (SiO²), chloride (Cl⁻), fluoride (F⁻), nitrate (NO³⁻), sulphate (SO4^− 2), dissolved gases, dissolved oxygen, hydrogen sulphide (H₂S), carbon dioxide (CO₂), radio nuclides, miner constituents, calcium (Ca²⁺) and magnesium (Mg²⁺) are the common substances found naturally in some groundwater [10]. It is highly likely that, these typical substances of water may affect the setting time and strength of concrete, promote corrosion of the reinforcing bars hence making the structure of the building vulnerable to degradation or failure [11].

The main cause of contractor’s inability to use the required potable water for mixing and curing of concrete in Bangladesh is the lack of inadequacy of its delivery at the project sites; as a result, groundwater is mostly used for concrete mixing and curing. In many areas of the country this groundwater is known to have elevated levels of iron (Fe), as high as 41.7 mgl^− 1 which was found in the year 1998 at 11 m. depth (shallow tube well) in the Islampur union, Companiganj upozila, Sylhet district [12]. When drawn straight from a well, anaerobic groundwater may have ferrous iron (Fe^+ 2) concentrations of up to several milligrams per liter without the water becoming cloudy or discolored. However, when exposed to air, ferrous iron (Fe^+ 2) oxidizes to ferric iron (Fe^+ 3) which is the insoluble form of iron (Fe) and gives the water a distasteful reddish-brown color [13]. In Bangladesh, where potable water is not easily accessible to reduce its consumption groundwater sources are widely used as an alternative option which sometimes becomes the primary option for works like concrete mixing and curing. Accordingly, it is crucial to investigate if the groundwater source contains high concentration of iron (Fe) in the form of ferric iron (Fe³⁺) how it may affect the mechanical strength of concrete and its setting period. This kind of research has not been yet done in Bangladesh.

In the present study, laboratory tests are carried out on concrete samples prepared using groundwater from five distinct sources each having different level of iron (Fe) concentrations to determine how ferric iron (Fe³⁺) affect the cement setting time, workability, compressive strength and splitting tensile strength. All the five sources of groundwater are taken from Sylhet district which is located in the north-eastern region of Bangladesh (Fig. 1).

Source of water

The primary source of water supply in Sylhet district is groundwater from deep or shallow tube well. The majority of the residents in this district rely heavily on groundwater to meet their daily requirements. The Sylhet municipality also distributes a significant amount of ground water everyday throughout the urban area. Though, greater Sylhet's hydrogeological conditions are less conducive to groundwater extraction than those in most other Bangladeshi regions [14]. Groundwater test results of 23 different locations in Sylhet district was collected from Senior Chemist Zonal Lab of Department of Public Health Engineering [15] where iron (Fe) concentration was listed which is shown here in Table 1. From the table highest concentration of iron (Fe) is observed as 4.9 mgl^-1 in two locations, Laki of Gowainghat upazila and Changakhai of Companigonj upazila and the lowest iron (Fe) concentration is observed as 0.2 mgl^-1 at Bahubol of Sadar upazila. According to World Health Organization [13] at Iron (Fe) level below 0.3 mgl^-1, there is typically no discernible taste, nevertheless turbidity as well as color may appear. In Bangladesh, for the purpose of irrigation, health, domestic and environment the EQS (Environmental Quality Standard) of iron (Fe) in groundwater set by the Department of Environment is 0.3-01 mgl^-1[16].

Purpose of the current study is to examine the mechanical strength of concrete mixed and cured with groundwater of different concentration of ferric iron (Fe⁺³) in Sylhet. So, water is sourced from the five locations mentioned as sample 01, 02, 03, 04 and 05 in Table 1. Sample wise concentration of iron (Fe) in the form ferric iron (Fe⁺³) is: sample 01: 0.2 mgl^-1, sample 02: 2.2 mgl^-1, sample 03: 3.1 mgl^-1, sample 04: 3.9 mgl^-1 and sample 05: 4.9 mgl^-1. These five samples of water were used separately for the preparation and curing of concrete samples.

Cement

The cement employed in this study was Portland Limestone Cement (PLC) of grade 42.5N, which complies under Bangladesh Standard (BS) EN 197-1: 2003, CEM II/ B-L [17] and is manufactured by a well-known global industry. In accordance with BDS EN 197-1: 2003, Table 2 outlines the ingredients and the mechanical, physical, and chemical parameters for this particular kind of cement.

Coarse and fine aggregate

For coarse aggregate, specification as per BDS EN 12620:2011 [18] was followed having maximum size of 20 mm. or 0.75” (three- fourth of the minimum clear spacing between individual reinforcing bars) down grade. As per standard, the boulders to be used for coarse aggregate in concrete should be composed of limestone, sandstone, granite, trap rock or rock of similar nature, is uniform light color, free of thin laminations, adherent coatings, deleterious substances and has the properties mentioned in Table 3. Shari river sand from the Sylhet region of Bangladesh composed of clean, hard, durable uncoated particles resulting from the disintegration of siliceous and/or calcareous rocks was used and had the properties listed in Table 3 as per BDS EN 12620:2011 [18].

Table 1. Test result of iron (Fe) concentration in groundwater at the different locations in Sylhet [15]

Sample No.	Upazila	Location	Fe (mgl^-1)
	Sadar	Tultikor	0.6
Sample 01	Sadar	Bahubol	0.2
Sample 02	Sadar	Noapara	2.2
	Sadar	Sheikhghat	3.5
Sample 03	Sadar	Borkapon	3.1
	Sadar	Mirapara	1.4
	Sadar	Shamimabad	3
	Kanaighat	Baiampur	1.1
	Kanaighat	Chatranar	0.9
	Kanaighat	Uporbari	1.9
	Kanaighat	Ratanpur	3.8
	Kanaighat	Haratoil	3.1
	Kanaighat	Shatpari	3.7
	Gowainghat	Laki	4.9
	Gowainghat	Mitrimohol	1.2
Sample 04	Companigonj	Talikhal	3.9
	Companigonj	Roypur	3.7
Sample 05	Companigonj	Changakhai	4.9
	Companigonj	Chilardohor	1.2
	Beanibazar	Nadanpur	1.8
	Beanibazar	Sadarpur	1.6
	Golapgonj	Chowdhury bazar	1.2

Mix design

Cement, sand, and coarse aggregate were prepared as construction ingredients for concrete specimens. The proportions ratio for M20 concrete grade was maintained at 1:1.5:3. For all mixes, the water to cement ratio remained constant at 0.55. Concrete was prepared using mechanical mixture machine and slump was maintained 25-50 mm. for M20 as per ACI 211.1-91 [19] and BNBC 2020 [20] mix design.

Table 2. Physical properties of cement [17]

Composition (% by mass)				Mechanical strength (MPa)		Initial setting time (min)	Soundness (expansion, mm.)	Chemical requirements (%)
Clinker (K)	Limestone (L)		Minor additional constituents	Early strength	Standard strength	≥60	≤10	Sulfate as SO₃
65-79		21-35	0-5	2 days	28 days			≤3.5
				>10	≥ 42.5

Table 3. Physical properties of aggregates [18]

Coarse aggregate		Fine aggregate
Properties	Value	Properties	Value
Compressive strength	35 Mpa	Clay lumps and friable particles – maximum	3%
Specific gravity	2.2-2.6	Coal and lignite	0.25%
Unit weight	22-25.1 kg/cum	Material passing the 0.075mm (No. 200) sieve	1%
Porosity	2.10%	Shale, coal, soft or flaky fragments	1%
Water absorption (max.)	2.5% by weight	Sulfur compounds	0.30%
Wear loss	≤ 35%	Organic material content	0%
		Fineness modulus	2-2.5%

Table 4. Experimental setup, sample distribution

Water sample as per Table 1	Iron (Fe) concentration in water (mgl^-1)	Curing period	Test Category 01		Test Category 02		Test Category 03
			SRH & UTM	UTM	SRH & UTM	UTM	SRH & UTM	UTM
			Compressive	Tensile	Compressive	Tensile	Compressive	Tensile
Sample 01	0.2	07 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		14 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		28 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
Sample 02	2.2	07 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		14 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		28 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
Sample 03	3.1	07 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		14 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		28 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
Sample 04	3.9	07 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		14 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		28 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
Sample 05	4.9	07 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		14 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples
		28 day	3 samples	3 samples	3 samples	3 samples	3 samples	3 samples

Sample preparation

The concrete samples used for experimental tests were determined by the kinds of test criteria and standards that were available. A total number of 270 concrete cylinder sample of 300 mm. height and 150 mm. diameter were prepared, cured, and evaluated for compressive strength and splitting tensile strength at the age of 7, 14 and 28 days using sample water from 05 different sources as mentioned in Table 1. Compressive strength test was performed by both nondestructive test (NDT) using the Schmidt Rebound Hammer (SRH, Figure 1b) and destructive test (DT) using Universal Testing Machine (UTM, Figure 1a). As mentioned in the Table 4 the experiments were distributed in 03 categories:

Category 01: Both compressive strength and splitting tensile strength tests were performed. 90 cylinders were prepared using 05 different sample water (Table 1) for mixing but for curing only water Sample 01 (0.2 mgl^-1) was used.

Category 02: Both compressive strength and splitting tensile strength test were performed. 90 cylinders were prepared using water Sample 01 (0.2 mgl^-1) for mixing only but for curing 05 different sample water (Table 1) were used.

Category 03: Both compressive strength and splitting tensile strength test were performed. 90 cylinders were prepared using the 05 different sample water (Table 1) for both mixing and curing purpose.

The findings on cement setting time, and mechanical characteristics of fresh and hardened concrete are presented and discussed in this section.

Setting time and workability

The initial and final setting times of concrete were recorded by preparing cement paste using the five different water sources and tested using Vicat Apparatus (Picture 1b) and the results are summarized in Table 5 and shown in Figure 3. The result shows the consistency value for the five-sample water are within 30%-33%. Test results also indicate that, setting time of cement is lengthening with the increment of iron (Fe) concentration in water. Initial setting time increases from 107 min. for the water sample 01 to 129 min. for the water sample 05 which are more than the minimum reference value of 60 minutes for PLC cement grade 42.5N (Table 2). As for final setting time, the value increases from 228 min. for the water sample 01 to 247 min. for the water sample 05. The results of the slump test demonstrate the workability of fresh concrete. Here for this research, water cement ratio is maintained as 0.55 as mentioned previously. Keeping the ratio constant, the slump values for the five different water samples were recorded in Table 06 which indicates that, slump value decreases from 38 mm. to 27 mm. with the increment of iron (Fe) concentration in water from 0.2 mgl^-1 (sample 01) to 4.9 mgl^-1(sample 05).

Table 5. Workability and setting time of cement

	Fe concentration (mgl^-1)	Consistency (%)	Initial setting time (min)	Final setting time (min)	Slump (mm.) for W/C ratio 0.55
Sample 01	0.2	33	107	228	38
Sample 02	2.2	32	110	235	35
Sample 03	3.1	32	112	235	31
Sample 04	3.9	31	117	241	29
Sample 05	4.9	30	129	247	27

Visual Inspection

Significant color changes on sample’s surface were observed for test category 02 and 03 when iron (Fe) concentration was increased. To show the differences, water sample 01 with 0.2 mgl^-1 and sample 05 with 4.9 mgl^-1 iron (Fe) concentration were compared and shown in Table 6. When the concentration increased in mixing water only the color of cylinder’s surface changed but not significantly. But when the concentration increased for curing water and both for mixing and curing water the cylinder’s surface color changed significantly from grayish to a combination of orangish and yellowish.

Compressive strength

Test result and discussion for Category 01

Total 45 concrete cylinder samples prepared using water of different iron (Fe) concentration (sample 01-05 of Table 5) underwent both NDT using SRH and DT using UTM at curing ages of 7, 14 and 28 days.

Water used for curing of all these 45 cylinders was sample 01 (Table 04) where iron (Fe) concentration was minimum 0.2 mgl^-1 (drinkable, odorless and color change is minor when Fe⁺² is converted to Fe⁺³). All the test results are listed in the Table 7. Average nondestructive (SRH) test result showed that, slightly more than 65% (standard value) strength was achieved on day-07 of curing when the concentration of iron (Fe) was within 3.1 mgl^-1 (sample 03) which decreased to 58% when the concentration was high in water, 4.9 mgl^-1(sample 05). On day-14 of curing nondestructive (SRH) test result shows that, 84% to 92% strength was achieved for the different concentration of iron (Fe) in mixing water where the reference value was 90% on day-14. Strength percentage was summarized in Figure 3. The final average result of compressive strength of concrete samples for the increased concentration of iron (Fe) in water shows decremental pattern in the nondestructive test. The final average strength of concrete decreased from 23 Mpa to 19.1 Mpa when iron (Fe) concentration increased from 0.2 mgl^-1 to 4.9 mgl^-1 in mixing water (Figure 4).

These 45 samples, which were tested by SRH were again tested by destructive method using UTM. Almost similar pattern was observed as found from nondestructive test results. On day-07 of curing, 66% strength was achieved when the iron (Fe) concentration was lowest 0.2 mgl^-1 but when the concentration was highest 4.9 mgl^-1, 58% strength was achieved. On the day-14 the strength percentage reduced from 91% to 84% when the concertation of iron (Fe) increased from 0.2 mgl^-1 to 4.9 mgl^-1 (Figure 3). The final average strength of concrete decreased from 24.5 Mpa to 19.1 Mpa when iron (Fe) concentration increased from 0.2 mgl^-1 to 4.9 mgl^-1 in mixing water (Figure 4).

Test result and discussion for Category 02

The test result recorded in Table 7 shows deviated compressive strength value for the curing age of 7 and 14 days (also shown in Figure 4). The average nondestructive (SRH) compressive strength test result showed that, around 60% to 58% strength achieved at the curing age of day-7 when curing water source contain different concentration of iron (Fe). While on the day-14 the strength was 91% when iron (Fe) concentration was low, 0.2 mgl^-1 but reduced to 85% when the concentration of iron (Fe) increased to 4.9 mgl^-1. Same pattern can be seen in the destructive test result (UTM) where on day 07 the rate of gaining strength reduced from 66% to 58% when the concentration increased from 0.2 mgl^-1 to 4.9 mgl^-1. And for the same type of curing water, strength gaining rate reduced 91% to 84% on the day 14 (Figure 4). On day 28, final compressive strength of concrete as per SRH, reduced from 22.8 Mpa to 18.9 Mpa and as per UTM, reduced from 24.3 to 19.1 when iron (Fe) concentration increased in curing water from 0.2 mgl^-1 to 4.9 mgl^-1 (Figure 5).

Table 7. All tests result of compressive strength

Water sample as per Table 1	Iron (Fe) concentration in water (mgl^-1)	Curing period (day)	Test Category 01		Test Category 02		Test Category 03
Water sample as per Table 1	Iron (Fe) concentration in water (mgl^-1)	Curing period (day)	SRH (Mpa)	UTM (Mpa)	SRH (Mpa)	UTM (Mpa)	SRH (Mpa)	UTM (Mpa)
Sample 01	0.2	07	16	16.21	13.8	16.15	14	16
		14	21.1	22.3	20.83	22.11	20.44	22.15
		28	23	24.5	22.8	24.3	22.8	24.3
Sample 02	2.2	07	15	14.6	13.3	14.23	12.6	14.5
		14	20.05	20.45	20	20.1	19.1	20.33
		28	22.05	22.9	22.01	23	21.68	22.5
Sample 03	3.1	07	13.5	13.2	12	12.6	11.1	12.97
		14	18	17.9	17.77	17.77	16.8	17.5
		28	20.2	21	19.96	20.9	19.1	20.6
Sample 04	3.9	07	12.8	12.33	11.6	12	10.2	12
		14	17.1	17.88	17.1	17	16	16
		28	20.2	20.9	19.5	20.1	18.3	19.5
Sample 05	4.9	07	11	11.1	11	11.1	8.5	8.9
		14	16.1	16.55	16.1	16	13.1	13
		28	19.1	19.1	18.9	19.1	16	16.4

When different concentration of iron (Fe) in water was used for both mixing and curing purpose, significant changes were observed in both rate of gaining strength and final compressive strength (Table 7, Figure 4 and Figure 5). Nondestructive (SRH) test result showed that, the rate of strength gaining reduced to 58% on day 7 and 85% on day 14 when the water contained 4.9 mgl^-1 iron (Fe) concentration. As per SRH, the final strength reduced from 22.8 Mpa to 16 Mpa when the concertation increased from 0.2 mgl^-1 to 4.9 mgl^-1. The same samples on destructive test result (UTM) showed that, the rate of strength gaining reduced to 58% on day 7 and to 84% on day 14 when iron (Fe) concentration was high in water, 4.9 mgl^-1. The final strength was reduced from 24.3 Mpa to 16.4 Mpa when the concertation increased from 0.2 mgl^-1 to 4.9 mgl^-1.

Split tensile strength

Test result and discussion for Category 01

As shown in Table 08, splitting tensile strength test result of the samples mixed with water of different iron (Fe) concentration revealed variation on strength on the day- 7, 14 and 28. As it can be seen in Figure 6, 66% strength was achieved on day 07 for the water Sample 01 (0.2 mgl^-1) but this rate reduced to 58% for water sample 05 (4.9 mgl^-1). For the same condition of iron (Fe) in water, rate of strength gain is reduced from 91% to 84% on day 14 (Figure 9). The final splitting tensile strength is reduced from 3.22 Mpa to 2.45 Mpa when iron concentration in water is increased from 0.2 mgl^-1to 4.9 mgl^-1.

Table 8. All test results of splitting tensile strength

Water sample as per Table 1	Iron (Fe) concentration in water (mgl^-1)	Curing period (day)	Test Category 01	Test Category 02	Test Category 03
Water sample as per Table 1	Iron (Fe) concentration in water (mgl^-1)	Curing period (day)	UTM (Mpa)	UTM (Mpa)	UTM (Mpa)
Sample 01	0.2	07	2.13	2.21	2.03
		14	2.61	2.71	2.50
		28	3.22	3.30	3.13
Sample 02	2.2	07	1.93	1.91	1.60
		14	1.93	1.91	1.60
		28	3.01	2.99	2.67
Sample 03	3.1	07	1.87	1.68	1.32
		14	2.10	1.95	1.62
		28	2.87	2.67	2.28
Sample 04	3.9	07	1.54	1.43	1.07
		14	1.89	1.73	1.33
		28	2.66	2.50	2.01
Sample 05	4.9	07	1.35	1.27	0.88
		14	1.69	1.52	1.10
		28	2.45	2.30	1.80

Test result and discussion for Category 02

In this test category, as shown in Table 8 and Figure 6, 66% strength was achieved on day 7 for water sample 01 (0.2 mgl^-1) which reduced to 55% for water sample 05 (4.9 mgl^-1). For the same condition of iron (Fe) in water, rate of strength gain was reduced from 91% to 84% on day 14 (Table 8 & Figure 6). Final strength reduced from 3.3 Mpa to 2.3 Mpa when iron (Fe) concentration in water was increased from 0.2 mgl^-1to 4.9 mgl^-1 (Figure 7).

Test result and discussion for Category 03

Significant changes were observed in both rate of gaining strength and final tensile strength when different water sample with different iron (Fe) concentration in water was used for both mixing and curing purpose. Test results listed in Table 8 showed that, the rate of strength gaining reduced to 58% from 66% on day 7 test and to 84% from 91% on day 14 when the iron (Fe) concentration was high in water (4.9 mgl^-1). The final tensile strength reduced from 3.13 Mpa to 1.8 Mpa when the concertation of iron (Fe) increased from 0.2 mgl^-1 to 4.9 mgl^-1(Table 8 and Figure 7).

This study is conducted to determine the effect of groundwater with high ferric iron (Fe³⁺) concentration in the mechanical properties of concrete. As iron (Fe) concentration of ground water is high in most of the location of Sylhet, this district is taken as study area and samples are collected from 05 different locations. The tests were divided into 03 categories and 02 types and the key findings are:

For the category-01 tests, when iron (Fe) concentration is increased from 0.2 mgl^-1 to 4.9 mgl^-1 in mixing water only and keeping the level to 0.2 mgl^-1 for curing water, 28-day compressive strength of concrete reduces by 22% and splitting tensile strength is reduced by 24%. The color change of sample surface is not significant.

For the category 02 tests, when iron (Fe) concentration is increased from 0.2 mgl^-1 to 4.9 mgl^-1 in curing water only and keeping the level to 0.2 mgl^-1 for mixing water, compressive strength of concrete reduces by 21% and splitting tensile strength is reduced by 30%. The color change of sample surface is significant from grayish to lite orangish.

For the category 03 tests, when iron (Fe) concentration is increased from 0.2 mgl^-1 to 4.9 mgl^-1 in both mixing and curing water, compressive strength of concrete reduces by 33% and splitting tensile strength is reduced by 42%. The color change of sample surface is significant from grayish to deep orangish.

It has been also observed that the initial setting time of cement is increased by 17% and final setting time increased by 7.5% when iron (Fe) concentration is increased from 0.2 mgl^-1 to 4.9 mgl^-1 in water. For a constant water/cement ratio, 29% slump is decreased.

So, from this study it can be summarized that, high concentration of iron (Fe) in the form of ferric iron (Fe³⁺) in water has significant influence on the mechanical properties of concrete. From the graph plotted in Figs. 3, 4, 5 and 6 it can be roughly suggested that, groundwater source with iron (Fe) concentration within 2-2.5 mgl^− 1 may be the safe choice for concrete mixing and curing work.

Author Contribution

All authors contributed similarly in the manuscript research.

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No competing interests reported.

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Assessment of Mechanical Properties of Concrete When Groundwater With Different Ferric Iron (Fe 3+ ) Concentration is Used for Mixing and Curing: a Case Study in Sylhet, Bangladesh

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